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Florida Entomologist
Official Organ of the Florida Entomological Society
JUNE, 1951
Vol. XXXIV
CONTENTS
Page
MULRENNAN, J. A.-A Half Century of Progress in the Field
of Medical Entomology in the State of Florida -------- 43
PROVOST, MAURICE W.-The Occurrence of Salt Marsh Mos-
quitoes in the Interior of Florida -------------------- 48
WOLFENBARGER, D. O.-Dictyospermum Scale Control on
Avocados - ---------- ------ -54
HUNT, BURTON P.-Reproduction of the Burrowing
Hexagenia limbata (Serville), in Michigan .......---
VAN HORN, M. C.-Entomological Opportunities
Mayfly,
Published quarterly by the FLORIDA ENTOMOLOGICAL SOCIETY
Box 2425, University Station, University of Florida, Gainesville
Mailing Date: May 16, 1951
No. 2
THE FLORIDA ENTOMOLOGIST
UAhe
FLORIDA ENTOMOLOGIST
VOL. XXXIV JUNE, 1951 No. 2
THE FLORIDA ENTOMOLOGICAL SOCIETY
OFFICERS FOR 1950-1951
President ..- --- ----...............-- ---W. G. BRUCE
Vice President ... ...... ~ -------..--...... ......JOHN WILSON
Secretary................................... MILLEDGE MURPHEY, JR.
Treasurer ......... .. ......... ................. ...L. C. KUITERT
Executive Committee ......... ......... J. P. TOFFALETTI
) J. J. DIEM
EDITORIAL BOARD
LEWIS BERNER ---.....-------- ... ......-..-- Editor
A. N. TISSOT ...............................Associate Editor
L. C. KUITERT ....----------- ...........- Business Manager
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VoL. XXXIV-No. 2
A HALF CENTURY OF PROGRESS IN THE FIELD OF
MEDICAL ENTOMOLOGY IN THE STATE OF FLORIDA 1
J. A. MULRENNAN
Florida State Board of Health. Jacksonville
Florida could be classed as the Crown Jewel of the North
American Continent, in that it stands out as a shining light by
the brilliance of its sunshine and by the pointed fact that it
is a peninsular, giving life to a luxurious flora and to an abundant
and unique fauna.
It would seem natural that the Great Creator should have
guided the first explorers to the land of sunshine and flowers
with all of its splendor and beauty which became a mecca for
the naturalists in the early days following her discovery.
The cradle of American democracy with its pearly white
beaches bathed by the blue-green waters of the briny deep
surrounding the great paradise now known as Florida was also
to experience the bitter with the sweet.
The early settlers were to suffer crippling losses from the
stings of mosquitoes which caused the people to stagger and
fall under the yoke of malaria; to have their bones seemingly
break from the scourge of dengue fever and to go into panic
at the mention of yellow fever, all known today to be trans-
mitted by mosquitoes.
Malaria, under a variety of names, has been a terrible scourge
to the people of Florida. Until very recent times it was, in fact,
the pestilence of Florida. By coincidence, or otherwise, the
early settlements were almost entirely within what was later
defined as the "Malaria belt" of the State. Tallahassee, the
capitol, was in the midst of this region. The following state-
ment from an early work ("Views and Recollections of North
America" by the Count of Castlenau, 1842) reveals what malaria
meant to the Tallahassee of a hundred years ago. "But un-
fortunately in opposition to these numerous advantages there
are the greatest plagues that can afflict a new settlement; and
unhealthful climate; every year bilious fevers of a most danger-
ous nature spread consternation in the whole region. Then
all the shops are closed, the fear of the epidemic and the stifling
heat caused the planters of the neighborhood to leave the city,
and all the inhabitants who can afford the expense of this kind
Presidential address given at the 33rd Annual Meeting of the Florida
Entomological Society, December, 1950.
THE FLORIDA ENTOMOLOGIST
go to the northern part of the United States to seek a more
salubrious climate; the merchants take advantage of this season
to go to New York or Philadelphia to place their orders, and the
planter goes to Niagara or Saratoga Springs to display his
luxury and spend in three months his year's revenue.
"However, although the climate is dangerous for strangers
at all times, the most insalubrious months are August, Septem-
ber, October, and November; then no one can be sure of escaping
the plague, neither the planter who has been settled in the
country for years, nor the negro born in the midst of the miasma
of Carolina or under the burning sun of Georgia. The com-
parative extent of the huge cemeteries is a sad warning for one
who, charmed by the beauty of the sight, would want to estab-
lish himself in this region."
The insalubrious situation prevailed in a vast number of
Florida towns and rural areas until as recently as twenty years
ago. Malaria, the greatest of debilitating diseases, caused
misery, poverty, and general economic distress on a scale hardly
to be appreciated by the people of today's Florida.
The story of yellow fever in the State is one of fright and
panic which gave birth to the present State Board of Health.
The epidemic of yellow fever in Fernandina and Jacksonville
in 1877 is inscribed in the archives of the rich history of this
State as the greatest holocaust to ever strike the State. Time
does not permit to review in detail this great catastrophe but
it can be said that a census of Fernandina, taken on September
20, had shown a population of 1632, with 1146 cases of fever
reported. There are 24 deaths, a mortality rate of about 51/2
percent of the total population. Among the white people the
mortality rate was about 16 percent while among the colored
it was less than one percent.
The direction of approach to the control of malaria was
recognized in Florida as early as 1900 by Dr. Porter, the State
Health Officer, when he stated, "It was observed that the at-
tacks (of malaria) were more than usually fatal along the
river bottoms, marsh lands, and in the flat woods country.-It
now is seen that it is not the germ itself which rises from the
soil or water but the carrier of the germ."
However, despite this early recognition of the means at
hand for controlling malaria, no concerted effort was made in
the direction until World War I period. At this time, drainage
and larvicidal measures were introduced at Camp Johnston in
VOL. XXXIV-No. 2
a joint effort of Army, U. S. Public Health Service, and State
Health Department as a part of the general sanitation program
around military establishments.
After this initial start, the State Health Department under-
took its first malaria control project, in the City of Perry, a
typical malarious community in Florida. At that time it was
one of the largest projects of the kind in the country and in-
volved the removal of 47,000 cu. yds. of earth for drainage
canals and ditches at an expenditure of $28,000. The cost of
the project was borne by the City of Perry, the county of Taylor
and the Burton Swartz Cypress Company with the State Board
of Health supplying the technical supervision. A subsequent
letter from the lumbering plant stated that they had been more
than repaid for their share of the cost by increased output
resulting from the better health of their employees.
The first great forward step in the control of mosquitoes
in this State was the organization of the Florida Anti-Mosquito
Association in 1922. This organization has performed a mo-
mentous duty in the promotion and coordinating of the mosquito
control activities in the State.
Another milestone was reached in 1931 when the Rocke-
feller Foundation established a Malaria Control Research Sta-
tion at Tallahassee, Florida, to work in conjunction with the
Florida State Hospital at Chattahoochee and the Florida State
Board of Health. This station from 1931 until its termination
in 1947 performed work in the malaria field of inestimable value
not only to the State of Florida, but to the world as a whole.
Florida received further recognition in the mosquito con-
trol research field when the United States Department of Agri-
culture, Bureau of Entomology and Plant Quarantine estab-
lished in 1932 a mosquito research station at Orlando which is
still functioning today and has received world-wide recognition.
This recognition was quite evident during World War II when
practically all of the research work pertaining to insects of
medical importance was carried out in the Orlando laboratory.
The work of this station has been of great value to the mosquito
control districts and also the citizens of Florida. Their counsel
and advice, as well as the investigations which they have carried
on in the field of mosquito control has assisted greatly in alle-
viating diseases transmitted by mosquitoes in Florida as well
as helping those in charge of mosquito control work to carry
THE FLORIDA ENTOMOLOGIST
out more effective and economical control procedures in the
State.
In 1941 a Bureau of Malaria Control was established in the
State Board of Health to study and make recommendations for
controlling malaria in the State. The Bureau of Malaria Con-
trol gave way in 1946 to the present Division of Entomology
whose scope of activity was to cover all activities pertaining
to all arthropods transmitting human diseases, or annoying
man by their bites.
Next to the mosquito, the rat flea has brought about a con-
siderable blight on the State in recent years. In 1920, 10 cases
of plague were reported in Pensacola. During this outbreak,
seven deaths were reported. No cases have been reported in the
State since this outbreak. Endemic typhus fever began to
appear in 1918 and by 1944, 483 cases were reported with 32
deaths. In some of the larger cities, 83 percent of the rat
population was found infected with typhus.
It can be said that great strides have been made in the
eradication of human diseases transmitted by mosquitoes. It
has been over fifty years since a case of yellow fever was trans-
mitted in the State. The last big epidemic of dengue fever
occurred in the early thirties. The City of Miami and Tampa
both had epidemics in 1932. The last evidence of transmission
of malaria occurred in Naples, Florida, in 1948.
It would seem safe to say that the disease malaria has been
eradicated from the State. It must be remembered, however,
that as long as malaria is alive in other southern states and
also in the world, the disease could spring up in a localized area
in the State.
The eradication of malaria from the State, in my opinion,
is one of the classic accomplishments which has occurred in
the State in the past 50 years. When we look back as recently
as 1929 and find that 470 individuals died from the malady
and for every death there is an estimated 400 cases, it can be
seen that the disease malaria cost this State a tremendous sum.
The disease endemic typhus is being brought under control
in Florida and in a few more years it may be completely eradi-
cated from the State. This year up to the present time there
have been only 34 cases reported. The main tool that has been
so effective in eradicating malaria and bringing typhus under
control is DDT.
VOL. XXXIV-No. 2
The one great problem which still confronts the State is
the mosquito and human-biting fly problem. This is a gigantic
problem and one that affects the economy of the State, not only
from the standpoint of transmission of diseases to animals,
but also by annoying and destroying animals by their bites.
The greatest economic loss, however, brought about by mosqui-
toes is their annoyance to humans and most especially to sum-
mer tourists who come to the State to enjoy our wonderful
beaches and the many other great attractions found in the State.
It is true that great strides have been made in organizing
mosquito control districts. At the present time there are 19
mosquito control districts in the State. The counties and State
are spending approximately one million dollars a year on mos-
quito abatement.
There is a tremendous amount of investigational work which
must be performed if we are to find a solution to this mammoth
problem. We do not have the tools at our command today which
would enable us to even consider eradication of some of the
pest species of mosquitoes. In fact, we do not have tools which
are sharp enough at times to give us satisfactory control and
until we find ways and means of economically controlling pest
mosquitoes, the State will continue to lose thousands of dollars
each year in driving people from the State, most especially
during the summer months.
The citizens as well as the visitors who come to the State
will continue to be annoyed by the bites of mosquitoes and
other arthropods, but there should be some consolation to the
individual to know that their chances of contracting an ar-
thropod-borne disease in Florida is considerably less than any
other southern state or any other state having similar climatic
conditions.
The State, which was at one time considered a teeming
jungle full of mosquito-borne disease, is now becoming the
haven for old folks as well as a winter and summer play grounds
for many people from all over the United States as well as
from the countries to the south of us. Yes, I think we can say
that it is becoming the nation's choice.
We must never relax our efforts in the field of medical
entomology, but should continue to try and develop more ef-
fective means of controlling arthropods of medical importance
so that Florida may become not only disease free, but pest
free as well.
THE FLORIDA ENTOMOLOGIST
THE OCCURRENCE OF SALT MARSH MOSQUITOES
IN THE INTERIOR OF FLORIDA
MAURICE W. PROVOST
Florida State Board of Health, Jacksonville
The salt marsh mosquitoes of Florida referred to in this
paper are Aedes taeniorhynchus primarily and Aedes sollicitans
incidentally. To the best of our knowledge these mosquitoes
deposit their eggs on moist ground in low areas which are likely
to be flooded at a later date by either tide or rain water. They
do not oviposit and develop only in salt marshes. Although the
soil where the eggs are laid is usually saline, the water which
hatches them is generally fresh rain water. If the greatest
producers of these mosquitoes are salt marshes and mangrove
swamps, it could justifiably be argued that it is because these
are the most available temporary-water habitats in coastal areas
and not necessarily because of preferability to the mosquitoes.
The same grassy swales, grassy ditches, and other like depres-
sions commonly referred to as rain pools which produce salt
marsh mosquitoes in coastal areas produce glades mosquitoes,
Psorophora confinnis, away from the coast. Without elaborat-
ing any further on a complex problem, we might say that the
salt marsh mosquitoes appear to be restricted to the coastal
strip because of adult requirements rather than of larval eco-
logical limitations. What it is that the adults require which
restricts them to the coast we can only surmise, and it is highly
probable that a knowledge of these requirements would give
us the answer to the riddle of their remarkable flights.
Before discussing exceptional occurrences of salt marsh
Aedes in the interior of Florida, let us review briefly their
normal distribution with respect to coast line. An examination
of our data reveals that the presence of adult salt marsh mos-
quitoes in Florida in annoying numbers beyond four miles from
tidewater is exceptional. Arbitrarily, we consider annoying
numbers a landing rate greater than one per man per minute
or a light trap rate greater than 24 females per night. And
by exceptional we mean occurring less than three days out of
a year, or 1 % of the time. As an example of the close restric-
tion of these mosquitoes to tidewater areas, we have data from
1 Presented at the 33rd Annual Meeting of the Florida Entomological
Society, December, 1950.
VOL. XXXIV-No. 2
Broward County in 1948. Twice a week during July and Au-
gust, landing rates were taken at 22 stations distributed evenly
over the populated portion of the county. One row of stations
was within two miles of salt water, a second row was parallel
to the coast and from three to five miles from tidewater, and
a third row was at right angles to the other two rows and
ended well within the Everglades 25 miles due west of Ft.
Lauderdale. Not a single specimen of salt marsh mosquito
was either seen, counted, or collected at any of the stations
in row two or row three although they occurred regularly in
August at stations in row one. On the Gulf coast, a light trap
operated semi-weekly and without interruption for four years
at Alva, 10 miles east of tidewater in the Caloosahatchee River,
has caught over 24 female Aedes taeniorhynchus three times
in 1947, not once in either 1948 or 1949, and three times in
1950. The largest collections were 53 females on June 27,
1947, and 43 females on September 8, 1950. We have a similar
record for three years at Myakka River State Park, roughly
10 miles from tidewater in the Myakka River. In 1948, the
greatest collection of female Aedes taeniorhynchus was nine.
In 1949, there was a collection of 128 on June 28 and one of
40 on July 15. The only collection exceeding 24 in 1950 was
one of 40 on July 15. Numerous other trap records verify the
general assertion made that more than four miles from tide-
water in Florida, Aedes taeniorhynchus in significant numbers
is exceptional.
Now we may consider some of the exceptional occurrences
of this salt marsh mosquito in the interior of Florida with
attempts at explanation. Considering first a locality fairly
close to the coast, we have light traps operating semi-weekly
at Princeton and Modello just north of Homestead in Dade
County. These towns are roughly five or six miles west of
the Biscayne Bay coast, which in this area is fairly straight
and narrowly fringed with mangrove. In 1948 and 1949, these
traps had Aedes taeniorhynchus records almost identical to
the ones for Alva and Myakka, across the peninsula. In 1950,
both traps swung to salt marsh mosquitoes in quantities typical
of tidewater areas. The Princeton trap exceeded 100 female
Aedes taeniorhynchus per night 15 times and reached a high
of 688 on August 29 and October 3. The Modello trap exceeded
100 per night seven times and reached a maximum of 1800 on
August 22. The male of the species never reached 50 per night
THE FLORIDA ENTOMOLOGIST
at either station. With salt marsh mosquito experience of
many years and basing his judgment on the bone-dry condition
of known breeding areas and on the failure of his inspectors
to locate breeding anywhere near the affected areas, Mr. Fred
Stutz, Director of the Dade County Anti-Mosquito District,
believes that the Miami area in 1950 was invaded by Aedes
originating in the Cape Sable and southern Everglades wilder-
ness region, where breeding of salt marsh mosquitoes over
tremendous areas is a distinct possibility. If this assumption
is correct, these mosquito swarms reached the Miami area,
40 to 80 miles away, by advancing at right angles to the prevail-
ing southeasterly trade winds. In this connection, it is notable
that the numbers of salt marsh mosquitoes in the Alva trap
mentioned above were synchronized over a four year period
with numbers in the great breeding areas of San Carlos Bay,
30 miles to the west. It, therefore, appears that the occurrence
of salt marsh mosquitoes in the interior of the southern tip
of Florida is best explained as the result of long-distance, swarm-
ing flights.
Farther inland, but still in south Florida, we will consider
the record for Belle Glade, on the southeast shore of Lake Okee-
chobee, some 30 miles from the nearest tidewater. A light
trap has been operated here by the Agricultural Experiment
Station for six years at semi-weekly intervals. For four years,
1945 through 1948, the trap collected only occasional Aedes
taeniorhynchus. Only two collections exceeded 24 females; 36
on July 23, 1945, and 48 on August 10, 1948. There were
only seven collections (largest, nine) in 1946; in 1947 there
were only four collections (largest, two). From this scarcity,
the same trap in 1949 showed a huge increase in Aedes taenior-
hynchus. All, however, came within the brief period-June 22
to July 3. Several collections in this period were over 100
females, the largest being 232; the largest male collection was
20. It had all the appearance of being one big brood that had
blown in. Previous to June 22 and after July 3, the record was
very much as it had been in the four previous years.
We can now discuss the most outstanding occurrence of salt
marsh mosquitoes in the interior of Florida. During the years
1942 to 1945, the Army operated light traps at their installa-
tions in Sebring and Avon Park. The Aedes taeniorhynchus
record for these traps is astounding. The nearest tidewater
is the head of Charlotte Harbor, 30 miles to the southwest; the
VOL. XXXIV-No. 2
east coast at its nearest (Vero Beach) is 45 miles away. The
prevailing summer winds here are southeasterly trade winds.
A foretaste of things to come was obtained when traps were
first set up in the fall of 1942. Throughout October the traps
at Sebring gathered in large numbers of Aedes taeniorhynchus,
the peak being reached on October 12 when one trap picked
up 134 males and 73 females. The identical pattern, though
of much smaller numbers, occurred at Dorr Field, halfway
between Sebring and Charlotte Harbor. In 1943, two large
broods occurred in Sebring. The first and largest lasted from
May 31 to June 12 with a maximum of 914 females in one light
trap collection. The second brood lasted from June 25 to July
11 with a maximum collection of 145 females. Smaller broods
occurred in each month from April to November. Again we
find these same two large broods recorded at Dorr Field, the
early June one reaching a maximum collection of 271 and the
early July brood reaching a maximum of 89 females. During
these infestations, there were never as many as ten males in a
collection at Sebring. At Dorr Field the males rose to 103 in
the early June brood. On the entire Atlantic seaboard there
were no Aedes taeniorhynchus to match the May 31 to June 12
brood at Sebring and Dorr Fields. On the Gulf coast, there
was a big brood culminating on the 1st of May in the Tampa
Bay area, but that was a whole month prior to their appearance
at Sebring. The only region receiving sufficient rainfall be-
tween May 17 and 24 to have produced the mosquito brood was
neighboring Polk County, where no salt water occurs. At Se-
bring and Avon Park, 1944 was a repetition of 1943 except
that there was but one large brood lasting from June 2 to June
26. The largest single night's trap collections of female Aedes
taeniorhynchus were 348 at Sebring and 1144 at Avon Park.
Males were scarce in these collections, the largest numbers
being 19 and 3 respectively. As in 1943, this brood had no
counterpart on either coast, to our knowledge; and also as in
1943, the only rainfall area properly timed to produce such
a brood was in neighboring Polk County. In 1945, there was
a large brood in July at Avon Park and Sebring, but this time
contemporary broods occurred throughout peninsular Florida
including the interior where local record collections of Aedes
taeniorhynchus were made at such widely separated points as
Clewiston (365) and Leesburg (37). At the proper time previ-
ous to this big brood, there had been torrential rains all over
THE FLORIDA ENTOMOLOGIST
Florida, although again Polk County led with a record of 12.52
inches of rain at Lake Wales on June 24.
Northward in the interior of Florida, collections of Aedes
taeniorhynchus become less frequent and smaller. Traps oper-
ated at such points as Bartow, Lake Wales, Kissimmee, and
Orlando usually bring in a dribble of salt marsh mosquitoes,
but never as much as 24 per night or even near that. At Lees-
burg a large number of traps were operated daily in 1948 and
1949. The largest single collection of female Aedes taenior-
hynchus in one night was eight on July 19, 1948. Back in 1945,
as mentioned earlier, one trap did collect a record of 37. By
adding up the totals for all Leesburg traps operating daily in
1948, we arrive at a considerable sample. This readily demon-
strates two broods in June and July. It seems more than
coincidental that these mosquitoes showed up in Leesburg in
both cases within three days of demonstrated huge emergences
in the salt marshes of Brevard County, 60 miles away to wind-
ward. A third big brood emerged there on August 22 to 24
and was followed by a sharp rise in Leesburg traps on August
31 and September 1.
Proceeding northward from Leesburg, records of salt marsh
mosquitoes in Florida's interior soon become exceedingly rare.
Intensive trapping in the Orange Lake area in 1950 yielded a
maximum night's collection of eight females at McIntosh, and
three traps operating almost daily in Gainesville during the
summer of 1948 failed to yield a single Aedes taeniorhynchus
or Aedes sollicitans. A very large number of traps operated
continuously in the Tallahassee area in 1943 and 1944 yielded
only occasional Aedes taeniorhynchus and Aedes sollicitans, al-
though the extensive salt marshes of Wakulla County are but
20 miles away and the prevailing summer winds are from
their direction. The only salt marsh mosquito collection to
exceed four in one night was 80 females on July 25, 1944, which
was obviously a flight. Orange Lake, Gainesville, and Talla-
hassee are referred to because they represent intensive trap-
ping. North Florida was fairly peppered with light traps
between 1942 and 1945, and evidence of salt marsh mosquitoes
at interior points was consistently negligible.
Summarizing the data reviewed, the following tentative
conclusions can be drawn concerning the occurrence of salt
marsh mosquitoes in Florida: (1) Aedes taeniorhynchus and
Aedes sollicitans are normally restricted to within four miles
VOL. XXXIV-No. 2
of tidewater. (2) Although Aedes sollicitans adults have been
collected throughout the interior, only Aedes taeniorhynchus
has occurred here in annoying numbers. (3) With one excep-
tion (Avon Park Sebring), Aedes taeniorhynchus, both in fre-
quency and size of collections, decreases in the interior in a
perfect gradient from south to north. Avon Park is the farthest
north where they have been recorded in nuisance numbers, and
north of Leesburg there are very few light trap collections
exceeding five per night for the interior. (4) Again with *he
exception of Avon Park Sebring, interior occurrence of salt
marsh mosquitoes are explainable as flights from the coasts
and do not necessarily indicate breeding in the interior. (5)
The remarkable numbers of Aedes taeniorhynchus in the Avon
Park Sebring area in 1943 and 1944 are virtually impossible
to explain as invasions from either coast, and most likely
originated somewhere in the interior of Polk County, if not
right there in Highlands County.
As a postscript, we might add that, to our knowledge, there
has been but one proven case of breeding of Aedes taenior-
hynchus in interior Florida. That was in Orlando some years
back and was discovered by workers of the Bureau of Ento-
mology and Plant Quarantine.
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THE FLORIDA ENTOMOLOGIST
DICTYOSPERMUM SCALE CONTROL ON AVOCADOS
D. O. WOLFENBARGER
Sub-Tropical Experiment Station, Homestead, Florida
The dictyospermum scale, Chrysomphalus dictyospermi
(Morgan), was reported by Moznette (1922) to be the most
important scale insect pest on avocado in Florida. It was
reported by Wolfe, et al (1934) as the most destructive insect
attacking the avocado in both nursery and grove. It was first
reported from California, and is occasionally found there on
lemons and avocados, but it has never become abundant nor
widespread, according to Ebling (1949).
The dictyospermum scale is generally distributed in Florida
where it is occasionally serious in some avocado groves. Young
trees seem to be more seriously attacked than old trees. Some
varieties, the Trapp and the Lula for example, are more seri-
ously infested than others. Trees sprayed with bordeaux mix-
ture 6-6-100 were found more heavily infested than where a
neutral copper spray was used, according to Ruehle (1938).
Grove caretakers make little or no effort to control this
insect, for several reasons. They now regard the dictyo-
spermum scale as a minor insect pest in avocado production.
Oil emulsion sprays occasionally used for scale control have
frequently caused heavy leaf fall. High spray pressures and
thorough coverage are necessary for most effective control.
Grove caretakers, furthermore, report that the oil emulsion
spray treatments have been but partially effective. These con-
siderations have made attempts at scale control unpopular and
illustrates the need for an improved insecticide.
Oil emulsions of 1.0 and 1.3 percent oil were reported by
Cressman (1933) to have given practically perfect control of
the dictyospermum scale. Two spray applications, each of 1.4
percent oil, separated by a three-week interval during the
dormant season were recommended by Moznette (1922) to
control the scale. This recommendation has been repeated
since with only slight modifications.
EXPERIMENTAL
Experiments were conducted on trees where the dictyo-
spermum scale populations were variable, from few insects
on some trees to more numerous infestations on others. Con-
VOL. XXXIV-No. 2
ventional power spray machines were used for spraying the
trees in all experiments. The dictyospermum scale ordinarily
infests the bark of branches and twigs. Samples of these were
taken from different parts of treated trees for examination to
determine treatment effects. Bark areas of from one to eight
square centimeters each were cut from infested portions of
the trees. Each section of bark was measured, then examined
under low power (9x) of a binocular for any living scale. By
means of the bark area measurements and the number of liv-
ing scales on the bark the data were reduced to average number
of live scales per square centimeter for each tree. There was
considerable variation, however, in the data obtained.
An experiment was started in January, 1948, by spraying
seven-year old trees of the Booth-7 variety. The bark samples
were taken two weeks after the spray treatments. A summary
of the data is given in Table 1.
TABLE 1.-RESULTS OF SPRAY TREATMENTS FOR DICTYOSPERMUM
SCALE CONTROL.
I Bark area Avg. No. Control,
Treatment examined, live scales percent-
sq. cm. per sq. cm. age
Parathion, 25% w. p.
2 lbs. per 100 gals. water ............ 126 0.072 69
Oil emulsion, 2% oil content -....... 123 0.065 71
Check ..................... .. ................. 123 0.228 -
The parathion and oil emulsion sprays were practically
equal in effectiveness. Less than one-third as many living
scales were found on the sprayed as on the unsprayed bark
samples. Although the concentrations of spray were more than
are ordinarily used no apparent plant injury was observed
following the spray treatments.
Part of the Sub-tropical Experiment Station 17 year old
trees of the Lula variety was found infested with the dictyo-
spermum scale. The infested trees of the planting were divided
into plots for an experiment and were sprayed in December,
1949. Samples of bark were removed and examined at three
and at six weeks after the spraying. The results are sum-
marized in Table 2.
THE FLORIDA ENTOMOLOGIST
TABLE 2.-RESULTS OF SPRAY TREATMENTS FOR DICTYOSPERMUM
SCALE CONTROL.
Treatment (amount of parathion Bark area Avg. No. Control,
is given in lbs. | examined, live scales percent-
15% w.p./100 gals. water) [ sq. cm. per sq. cm. age
Three weeks count
Parathion, 1 lb .................................... 136 0.023 66
Parathion, 2 Ibs .................................. -101 0.022 67
Parathion, 4 lbs. -- ..... 136 0.025 63
Oil emulsion, 11/2% oil ...................... 115 0.023 66
Check .................................... .. 193 0.067 -
Six weeks count
Parathion, 1 lb. .-..--.-..--.......-- ..- ....... 122 0.014 78
Parathion, 2 lbs. .......---......... ........... 157 0.004 94
Parathion, 4 lbs. -----............ ........... --182 0.019 71
Oil emulsion, 11/2 oil .--..---..........--207 0.083 -33
Check ..........--.....-------- ---- 202 0.063
The data taken after three weeks show that all spray treat-
ments were nearly equal in effectiveness, and that all had ap-
proximately one-third as many living scales per square centi-
meter as the samples from the unsprayed treatment. The data
from the six weeks count show that the parathion sprays were
more effective than the other treatments. The data on the six
weeks count were statistically significant at the five percent
level, with a least mean difference of 0.057 live scale per sq. cm.
The data obtained in Table 2 came from trees that were
the largest of any in the experimental groups. Samples were
taken in these trees at heights of from about 10 to 18 feet
from the ground. No attempt, however, was made to determine
control effects at the different heights.
Eight-year old trees of the Booth-7 variety were also used
for a dosage experiment with parathion, applied in January,
1949. The results of counts made three weeks after spraying
are summarized in Table 3.
Parathion was more effective at two and four pounds than
at the one pound dosage.
Two-year old avocado trees of different varieties were
sprayed to evaluate oil emulsion, parathion, and oil and para-
thion combined for dictyospermum scale control. This was a
VOL. XXXIV-No. 2 57
TABLE 3.-RESULTS OF PARATHION SPRAY TREATMENTS FOR DICTYOSPERMUM
SCALE CONTROL.
Treatment (amount of parathion Bark area Avg. No. Control,
is given in lbs. examined, live scales percent-
15'% w.p./100 gals. water) sq. cm. per sq. cm. age
Parathion, 1 lb. ....-............................... 71 0.032 65
Parathion, 2 lbs. -............................... 112 0.003 97
Parathion, 4 lbs. .................................. 25 0.007 91
Check ..-.....-........-- ..-- ....---....-... -- ..--91 0.092 -
cooperative experiment and replications of treatments were
obtained by taking samples from different trees in each treat-
ment strip. The trees were sprayed in December, 1948. Three
weeks later bark samples were examined from infested portions
of from eight to 13 infested trees of each treatment. A sum-
mary of the data is given in Table 4.
TABLE 4.-RESULTS OF SPRAY TREATMENTS FOR DICTYOSPERMUM
SCALE CONTROL.
Treatment (amount of parathion Bark area | Avg. No. 1 Control,
is given in lbs. examined, live scales percent-
15%' w.p./100 gals. water) sq. cm. per sq. cm. age
Parathion, 1 lb. .................. .....----- ...... 117 0.014 84
Oil emulsion, 11/2% oil ........................ 121 0.037 58
Parathion, 1 lb. plus oil emulsion,
1% oil ................. .............. .......... 68 0.070 20
Check .......................................-........ 56 0.088 -
It will be noted from Table 4 that the fewest scales were
found on the parathion and the most on the check treatments.
The oil emulsion ranked second, and the oil emulsion-parathion
combination ranked third in having the lowest average number
of living scales per square centimeter.
SUMMARY
The percentages of control from the treatments in the above
tables were averaged to give figures on the over-all control
obtained from all tests, and are given as follows:
Parathion, lbs. 15% w.p./100 gals. water Oil emulsions
1 2 4
70 86 74 41
The data show that two pounds of 15 percent wettable powder
was the most effective, and that oil emulsion was the least ef-
fective. Although more work is needed on dictyospermum scale
THE FLORIDA ENTOMOLOGIST
control on avocados the results indicate that parathion is fully
as effective as the oil emulsions previously recommended. The
results, furthermore, confirm grove caretakers reports that oil
emulsion is but partially effective on the dictyospermum scale.
LITERATURE CITED
Cressman, A. W. Biology and control of Chrysomphalus dictyospermi
(Morg.). Jour. Econ. Ent. 26: 696-705. 1933.
Ebling, Walter. Subtropical entomology. Pp. 469-471. Lithotype Process
Co. San Francisco. 1949.
Moznette, G. F. The avocado: Its insect enemies and how to combat
them. U. S. Dept. Agric. Farmers Bul. 1261: 1-31, illus. 1922.
Ruehle, G. D. A study of diseases of the avocado and mango and develop-
ment of control measures. Fla. Agric. Expt. Sta. Ann. Rept. for 1938:
191-192. 1938.
Wolfe, H. S., L. R. Toy and Arthur L. Stahl. Avocado production in
Florida. Fla. Agric. Expt. Sta. Bul. 272: 1-96, illus. 1934.
FICOR IECT3B
VOL. XXXIV-No. 2
REPRODUCTION OF THE BURROWING MAYFLY,
HEXAGENIA LIMBATA (SERVILLE), IN MICHIGAN1
BURTON P. HUNT
University of Miami, Coral Gables, Florida
Burrowing mayflies of the genus Hexagenia are abundant
in many lakes and streams throughout Michigan and constitute
an important part of the bottom fauna in these waters. Be-
cause of the importance of the nymphs and winged stages as
fish food and fishing bait,2 a study of the biology and economic
importance of various species which occur in the state was
undertaken by the writer under a fellowship sponsored by the
Institute for Fisheries Research, Michigan Department of Con-
servation. Pertinent information concerning the reproduction
of Hexagenia limbata (Serville) is presented in this report.
Data were obtained during the years 1947-1949 at Pine and
Gun Lakes, Barry County; Big Silver Lake, Washtenaw County;
and portions of the Au Sable River in Crawford and Oscoda
Counties.
The present taxonomic status of some forms of Hexagenia
is neither entirely settled nor completely satisfactory. Hexa-
genids encountered in this investigation which have been de-
scribed as species by earlier workers are H. limbata (Serville),
H. viridescens (Walker), H. occulta (Walker), and H. venusta
Eaton. Since these forms were originally described they have
been considered by various authors as valid species, subspecies
or varieties (Eaton, 1871, 1883; Ulmer, 1921; McDunnough,
1924, 1927; Ide, 1930; Neave, 1932; Needham, Traver and Hsu,
1935; Spieth, 1941; Lyman (MS); and others). In a survey of
the genus, Spieth (1941) concluded that all forms in which
the male imago has strongly hooked penes, marginated cross
veins and uneven coloration of the membrane in the costal mar-
gin of the mesothoracic wing, should be placed in a single species,
Hexagenia limbata (Serville). He recognized as subspecies cali-
fornica, limbata, occulta, venusta and viridescens, and stated
that all of them except californica occur in Michigan. Although
male imagoes collected from the waters investigated show great
diversity in size, intensity of color, coloration and color pattern,
all have the strongly hooked penis and uneven coloration of
1Contribution from the Michigan Institute for Fisheries Research.
Large Hexagenia nymphs are used extensively as fish bait in winter
angling for yellow perch, bluegills, and other pan fish in Michigan.
THE FLORIDA ENTOMOLOGIST
the costal margin of the forewing. Imagoes collected from the
forenamed lakes show that the coloration and color patterns
described for the forms occult, viridescens and venusta and
intergrades between the three, are present at the same time
and in a single mating flight. Imagoes from the Au Sable River
show color phases which agree with descriptions for occult
and viridescens, and intergrades between the two. Since the
populations appear to be completely heterogeneous in their color
characteristics and without discernible differences in ecology,
it has been concluded that although the various described forms
can be recognized they do not merit subspecific rank and should
be considered as color phases or varieties of a single variable
species. Therefore the author chooses to regard the species con-
sidered in this study as Hexagenia limbata (Serville).
The color pattern of limbata in the lakes studied generally
tends toward that of H. occulta as described by Needham, Traver
and Hsu (1935), and of H. limbata occulta listed by Spieth
(1941). In the Au Sable River the color of most imagoes is
somewhat darker and dorsal and ventral abdominal color pat-
terns more pronounced and extensive than in most lake speci-
mens. It is possible that the stream form may eventually prove
to be separable from the ordinary lake form on a physiological
if not on an anatomical basis. It is worthy of note that many
bait dealers who handle thousands of Hexagenia nymphs each
winter fishing season profess to be able to recognize readily
nymphs which come from streams and those which come from
lakes. They maintain that the stream nymphs are darker in
color, are much hardier and are better fish bait than the lake
nymphs.
The variability of H. limbata is very marked when com-
pared to other hexagenids often encountered in Michigan. H.
atrocaudata McD., H. rigida McD., and H. recurvata Morgan
are distinct species which appear to be quite stable and show
little variation in coloration or in color pattern.
EGG PRODUCTION
Eggs of H. limbata are ellipsoid and measure 0.16-0.19 by
0.28-0.32 millimeters. All have a reticular chorionic pattern,
the strands of which run nearly straight. The number of eggs
produced by individual females is of considerable importance
in evaluating the probable success of reproduction of the species.
VOL. XXXIV-No. 2 61
Only two literature references pertaining to the number of eggs
produced by Hexagenia are known to the writer. Needham
(1920) estimated the number of eggs to be upwards of 8,000.
Neave (1932) counted the eggs of two H. 1. occulta imagoes;
one contained 3,631 eggs, the other 3,388. Size of these females
was not recorded. In order to ascertain more exactly the num-
ber produced, actual counts were made of eggs carried by 24
female imagoes. Preserved specimens were used and examined
under a binocular dissecting microscope. Total body length
was carefully measured, the abdomen opened, and eggs counted
when removed from the ovaries. In most cases it was possible
to count the eggs from each ovary separately. Data secured
are presented in Table 1. Total number of eggs varied between
2,260 and 7,684. The greatest difference between the number
in each ovary of any individual was 213. It was at once obvious
that a significant relationship existed between number of eggs
and body length. Plotting length and number of eggs of each
individual showed a positive correlation between body length
and egg production (Fig. 1). A curve drawn by inspection
TABLE 1.-NUMBER OF EGGS PRODUCED BY H. limbata FEMALE IMAGOES.
SEgg count
Body Wing
Locality length length Right Left
in mm. in mm. ovary ovary Total
Pine Lake .......................... 25.5 22.0 --4,356
Pine Lake .......-.....- 24.3 21.6 -3,452
Pine Lake ..... ............ .. 21.9 18.0 1,580 1,684 3,264
Pine Lake ................. 22.4 19.7 2,731
Pine Lake ..-............ 21.9 20.8 -- 2,575
Pine Lake ........................ 22.8 20.3 1,808 1,720 3,528
Pine Lake ......................... 19.9 18.2 1,111 1,243 2,354
Pine Lake .........-- ..-..-.... 21.2 18.3 -- 2,841
Pine Lake ....................... 20.0 19.4 -- 2,695
Pine Lake .......................... 20.3 17.8 1,142 1,118 2,260
Gun Lake ............................ 30.3 28.2 -- 7,684
Gun Lake ........................ 30.2 27.6 3,653 3,440 7,093
Gun Lake -.....--................ 24.7 23.6 2,207 2,333 4,540
Gun Lake _............. ........ 27.1 25.6 3,393 3,198 6,591
Gun Lake .......................... 24.8 23.1 2,039 2,005 4,044
Gun Lake ............................ 28.4 27.0 3,299 3,230 6,529
Gun Lake ......................... 23.1 23.0 2,123 1,942 4,065
Gun Lake .........................- 24.1 22.3 1,773 1,734 3,507
Gun Lake .......................... 24.8 22.7 2,669 2,758 5,427
Gun Lake ............................ 24.7 23.3 2,406 2,417 4,823
Big Silver Lake ......-........ 23.6 21.5 1,844 1,987 3,831
Big Silver Lake ................ 27.3 24.7 2,851 2,763 5,614
Big Silver Lake .............. 26.0 24.0 2,204 2,210 4,414
Big Silver Lake ............. 23.8 22.2 1,938 2,140 4,078
THE FLORIDA ENTOMOLOGIST
00ooo
7000-
000-
2 4000
3000-
1000-
Jooo
19.5 20 21 22 23 24 25 2 27 28 29 30 31
LENGTH OF BODY IN MILLIMETERS
Fig. 1.-Correlation between length of body and number of eggs produced
by H. limbata female imagoes.
indicates clearly that the relationship approaches that of a
straight line. Examination of the figure shows that an average
size female will produce about 4,000 eggs. Although no egg
counts were obtained from females collected on the Au Sable
River, there is no reason to believe the results would vary from
the above.
EGG DEPOSITION
Mating activities of Hexagenia and many other species of
mayflies have been adequately described by Morgan (1913),
Needham (1927), Neave (1932), Needham, Traver and Hsu
(1935), Spieth (1940), and others. However, the deposition
of eggs, the number laid, percentage fertilized, and place and
time of incubation have received little attention. Mating and
ovipositing flights of H. limbata, which take place in May, June
and July in Michigan, ordinarily occur at dusk or shortly after
dark. Extensive night observations by means of a powerful
spotlight supported published statements that females lay their
eggs on the surface of open water in both lakes and streams.
Eggs were deposited in the water in three different ways. The
method employed most frequently was as follows: Once the
females had copulated in the mating dance, which invariably
VOL. XXXIV-No. 2
occurred in the air along the margin of a lake and above a
stream, they left the swarm and flew out over the water. After
flying rapidly back and forth 10-20 feet above it for a few
seconds to several minutes, the females simply plummeted
erratically to the water surface. As they lay fluttering on
the surface, the last two abdominal segments were raised sharply
upward and the two egg packets quickly extruded by rhythmical
contractions of the abdomen. Females picked up within 10-15
seconds after striking the surface had invariably discharged
most of their eggs. Those which had thus "crash landed" usually
drowned, for seldom were they able to right themselves and
fly from the water. The second method, used by comparatively
few individuals, was to light upright upon the surface, remain
quiet for a few seconds, discharge a few eggs, then fly up again
to repeat the performance. Some females which came to col-
lecting lights during ovipositing flights were only partially
spent. Since they easily discharged the remaining eggs when
placed in contact with water, it is obvious they had been merely
dipping to the surface. In the third method, observed only a
few times, the female extruded the eggs while flying above the
water and dropped the packets from a height of 10-15 feet. On
several occasions females were seen carrying partially extruded
egg packets as they plunged to the water surface. Upon con-
tact with water the eggs separated and began to sink immedi-
ately.
Examination of various objects and material from the lake
bottom showed that eggs found lodgment on aquatic vegeta-
tion, pieces of wood and small stones. Surface mud samples,
obtained by utilizing a plastic tube 1/2 inch in diameter and
5 feet long, also contained numerous eggs, indicating that they
were spread over the entire shoal area. Examination of sand
from the water's edge during the height of the ovipositing season
resulted in finding only 2 eggs, and suggests that few of them
are washed ashore and lost. No attempt was made to obtain
eggs at depths greater than 5 feet and nothing is known of
the fate of those which sank into deep water. The fate of eggs
released by ovipositing females in the Au Sable River was not
determined.
Collection of eggs, deposited in Big Silver Lake, by means
of submerged glass plates revealed that distribution of eggs
on the lake bottom was very patchy. Four glass plates (total
area 370 square inches), mounted individually in wooden frames
THE FLORIDA ENTOMOLOGIST
with a stabilizing weight underneath, were placed at random
on the bottom in an area about 100 feet square covered with
water about 3 feet deep. Eggs which settled on the glass soon
became firmly attached and the plates could be raised and
handled without losing them. These plates were in operation
from June 20-27, 1947, during the period of limbata emergence
and mating activities. Each day they were raised and all adher-
ing eggs deposited the previous night removed with a small
brush. The residue was examined under a microscope and the
eggs counted. Average number secured was 336 per square
foot of surface for the 8-night period. Quantity of eggs reach-
ing the plates each night varied greatly, the smallest number
during any night being 25 and the largest 310. Great variation
was also noted in the number of eggs adhering to individual
plates on any night. The indication was that eggs tended to
reach bottom in clumps and were not distributed evenly over
the bottom even in a comparatively small area.
TABLE 2.-TIME REQUIRED FOR EGGS OF H. limbata TO SINK TO BOTTOM
OF A COLUMN OF STILL WATER 25 INCHES DEEP. WATER TEMPERATURE 760F.
S Approximate Time of sinking in seconds
Trial number
of eggs First egg Last egg Median egg
1 9 152 164 160
2 20-30 150 192 155
3 50-70 150 180 160
4 20 170 190 177
5 60 175 192 180
6 100 165 194 176
7 40 160 177 165
8 50 162 177 166
9 50 150 187 178
10 75 160 197 176
11 50 152 177 157
12 50 150 175 160
13 50 153 177 157
14 200 155 192 160
15 100 157 184 174
Avg. time to sink 1 in. 6.3 7.4 6.7
Avg. time to sink 1 ft. 76.1 88.6 80.0
To determine the rate of sinking, a 1,000 cc. graduated cylin-
der was filled with lake water to a depth of 25 inches and allowed
to stand for 2 hours. A black background and a strong light
were so arranged that sinking eggs were clearly visible. Using
a spatula, small lots of eggs, taken from the body of a newly-
VOL. XXXIV-No. 2
emerged imago, were placed on the water with a minimum
amount of agitation. It was noticed that the surface disturb-
ance influenced the start of sinking of individual eggs, but after
sinking began it proceeded at a uniform rate. Time required
for each lot of eggs to reach bottom was recorded (Table 2).
Since eggs of each lot were scattered somewhat when placed on
the water, they sank in a rather scattered group. Time required
for approximately one-half the eggs to reach bottom is recorded
in the table under the heading "Median egg." It was found
that individual eggs sank at an average rate of 1 foot in 80
seconds, but small clumps of eggs settled at a faster rate, ap-
proximately 1 foot in 60 seconds. Four to 6 minutes were re-
quired for eggs to settle to the bottom after the water was
stirred vigorously.
RATE OF FERTILIZATION
Eggs obtained from a number of female imagoes captured
during ovipositing flights were incubated in aerated jars to
determine the efficiency of natural fertilization. Eggs in vari-
ous stages are readily recognized. Those which have hatched
appear as empty shells; live embryos are translucent and the
embryo is visible; dead embryos are usually brown or reddish
in color; and eggs which apparently were not fertilized are
dark or black. A count made after hatching had been completed
(Table 3) showed that in all cases more than 91 per cent of
the eggs hatched (avg. 96.3 per cent). Since some embryos
died during incubation, the initial fertilization rate was slightly
higher. The high fertility and the large number of eggs pro-
duced by individual females point to a high reproductive po-
tential. In nature, however, the loss of eggs and very young
nymphs must be enormous.
Unfertilized eggs obtained from 7 reared virgin female
imagoes were incubated for a long period. Some embryonic
development occurred in a few eggs but no nymphs hatched,
implying that parthenogenesis does not take place.
Artificial insemination of eggs is easily accomplished by
applying macerated sexual elements of a male to the exposed
egg mass of a female (Neave, 1932; Needham, Traver, Hsu,
1935). The author resorted to artificial insemination 27 dif-
ferent times to secure fertilized eggs for various purposes.
In some cases the female could be induced to discharge her
eggs by gently stroking the ventral side of the abdomen with
66 THE FLORIDA ENTOMOLOGIST
TABLE 3.-EFFICIENCY OF NATURAL FERTILIZATION OF H. limbata EGGS AS
SHOWN BY HATCHING EXPERIMENTS.
Number Total Number Per cent
Origin of Lot females eggs eggs eggs
females number stripped examined hatched hatched
Pine Lake .......... 1 1 209 200 95.7
Pine Lake ....-.... 2 1 389 379 97.4
Pine Lake -...... 3 1 517 510 98.6
Pine Lake .......... 4 1 421 419 99.5
Pine Lake .......... 5 12 761 742 97.5
Pine Lake ......... 6 1 851 842 98.9
Pine Lake ......... 7 1 926 905 97.7
Gun Lake ........ 8 1 248 238 96.0
Gun Lake ......... 9 1 686 626 91.2
Gun Lake ........... 10 1 234 226 96.6
Gun Lake ............ 11 50 1,621 1,511 93.2
Au Sable River .. 12 1 351 338 96.3
Au Sable River.. 13 15 436 427 97.9
Au Sable River 14 22 457 442 96.7
Au Sable River.. 15 1 269 265 98.5
Total .....-.- .. 110 8,376 8,070 96.3
a dissecting needle. In most instances, however, it was neces-
sary to dissect the ovaries. The macerated sexual organs of
the male were then mixed with the eggs and allowed to stand
for 1-2 minutes, after which the eggs were placed in water in
glass containers of various kinds. About 45 seconds after com-
ing in contact with water, they became sticky and began to
adhere to the glass. At the end of 3 minutes all were firmly
attached and remained so during incubation and hatching. This
adhesive property made it very convenient to handle them since
they remained in place at all times.
Results of artificial insemination and incubation varied
greatly, for the percentage of eggs which hatched ranged be-
tween 2.7 and 88.6. Poor fertilization resulted when adults
used were old and dying. Imagoes and subimagoes proved to
be equally fertile, showing that ova and spermatozoa are fully
mature when the winged fly first emerges. One attempt to
fertilize eggs from a female subimago with the sexual elements
of a last instar male nymph whose wing pads were quite dark
was unsuccessful.
INCUBATION
Published accounts of the incubation period of Hexagenia
vary greatly. No temperature records were given by Clemens
(1913, 1915, 1922) when he stated that in two instances eggs
VOL. XXXIV-No. 2
of "H. bilineata" hatched in 36 days and in a third from 29-40
days. Eggs of H. 1. occulta from Lake Winnipeg hatched in
17-19 days at temperatures ranging from 18-23 C. (Neave,
1932). Spieth (1938) succeeded in hatching eggs of H. occulta
in the laboratory in 14 days and in a nearby stream in 20 days.
Length of incubation is important since a short one means
a longer growth period for newly-hatched nymphs during the
remainder of the summer. Temperature is an important factor
influencing rate of embryonic development. In the laboratory
at temperatures ranging from 750-950 F., hatching began in
11-14 days. Eggs incubated under temperatures ranging be-
tween 67 and 81' F. began hatching at the end of 18-22 days.
Where eggs were scattered on the bottom of containers, hatch-
ing of all eggs was virtually completed within 4 days after it
started. In other instances, to be discussed later, where masses
of eggs had clumped together, newly-hatched nymphs con-
tinued to appear for many weeks. Eggs placed in 2-quart jars
and submerged in the East Branch of the Au Sable River began
hatching after 20-26 days at temperatures ranging from 62-
730 F.
Effect of temperature was determined more specifically in
the following experiment. A portion of the eggs obtained from
naturally fertilized females (Lots 2, 5, 10, Table 3) was placed
in quart jars in a refrigerator (360-400 F.) 8 days after in-
cubation began. Jars were removed from the refrigerator 70
days later and the eggs allowed to incubate at room temperature
(68-800 F.). Hatching began 16 days later and was completed
in about 4 days, total elapsed time since fertilization being 94
days. The total 26-day incubation period at room temperature
was slightly greater than that for the controls (20 days) and
the percentage of successful hatching was nearly the same. It
can be concluded that embryonic development was extremely
slow or that a state of dormancy existed while the eggs re-
mained at 360-40 F., and that no ill effect resulted from
exposure to low temperatures. It is quite possible that eggs
deposited in late summer in natural waters may remain alive
over winter and hatch successfully when water temperatures
rise in the spring. It is also probable that eggs which settle
in deep water below the thermocline, providing sufficient oxy-
gen is present, may require several months for embryos to
mature.
A greatly prolonged incubation period of H. limbata eggs
THE FLORIDA ENTOMOLOGIST
occurred in several instances under similar circumstances. Eggs
stripped from 50 females captured at Gun Lake, July 1, 1947,
were all placed in a 2-quart jar and incubated in the laboratory
(Lot No. 11, Table 3). Hatching first began July 19, after 18
days of incubation. Within a week more than half of the eggs
had hatched but a diminishing number of nymphs continued
to appear until November 6, 1947, 98 days after the start of
incubation. Circumstances surrounding the position of eggs
in the incubation jar, later duplicated with similar results,
seemed to influence drastically the rate of embryonic develop-
ment. Examination revealed that in some areas on the bottom
of the container, eggs were piled on top of each other 10-20
layers deep and solidly attached together by the naturally ad-
hesive material around them. Those on the periphery of these
masses, and those located singly or in layers no more than 3
eggs deep, hatched within 3 weeks. Embryos within these
masses, however, developed very slowly, those nearest the center
hatching last of all. Reasons for this delayed development
are not known, but the conclusion must be reached that some
condition resulting from the crowding or smothering of these
eggs retarded their development. Even though these embryos
developed slowly, most of them eventually hatched (Lot No. 11,
Table 3). Similar results were obtained by covering eggs firmly
attached to the bottom of jars with 2-3 inches of stream silt.
In these cases development of embryos was greatly retarded
so that hatching did not occur until 2-3 weeks after uncovered
eggs in jars in the same stream had produced nymphs. These
experiments suggest that eggs covered by silt in natural waters
take much longer to hatch than those exposed, and that em-
bryos may be killed from being buried. Prolonged hatching
has been observed among eggs of other mayflies but details
of the conditions of incubation were not given. Ide (1935)
found that eggs of Stenonema canadense, incubated in a glass
container, hatched over a period of 6 weeks and that there
was evidence to indicate that eggs of Iron pleuralis remain
in an unhatched condition in the stream for at least 4 months.
Effect of desiccation on fertilized eggs was determined in
9 cases by dividing eggs both artificially and naturally fertilized
into two groups. One group, serving as a control, was placed
in water immediately and the other dried at air temperature
for periods ranging from 4-72 hours before being placed in
water and incubated. In all cases, nymphs hatched from the
VOL. XXXIV-No. 2
control eggs but none were produced from, nor did any em-
bryonic development occur in, the desiccated eggs.
SUMMARY
1. Examination of the ovaries of 24 female imagoes re-
vealed that the number of eggs produced ranged from 2,260
to 7,684. A positive correlation exists between body length
and number of eggs produced. An average size female pro-
duces about 4,000 eggs.
2. Eggs were deposited on the water surface in three ways.
In most instances ovipositing females plunged erratically to
the water surface, then discharged their eggs within a few
seconds and drowned. Occasionally females alighted upright
on the water, discharged a few eggs, took wing and repeated
the procedure. In a few cases females extruded their eggs in
mid-air and dropped the egg packets from a height of 10 to 20
feet.
3. Eggs deposited in lakes either become attached to aquatic
vegetation and other solid objects or come to rest on the mud
surface. Eggs sink in still lake water at a rate of 1 foot in
80 seconds.
4. Eggs obtained from 110 naturally mated females were
incubated in the laboratory. The percentage of eggs which
hatched ranged from 91.2 to 99.5 (average 96.3).
5. The incubation period is greatly influenced by water
temperature. Eggs hatched within 11 to 14 days when water
temperatures ranged from 75' to 950 F., and within 20-26 days
at a temperature range of 620 to 730 F. Eggs kept at 360 to
400 F. for 70 days apparently lay dormant while refrigerated,
but later hatched when returned to room temperature.
6. Eggs which were air dried for 4 hours or longer before
incubation began failed to hatch.
LITERATURE CITED
Clemens, W. A.
1913. New species and life histories of Ephemeridae or mayflies. Canad.
Ent., 45: 246-262.
1915. Rearing experiments and ecology of Georgian Bay Ephemeridae.
Contr. Canad. Biol., 139: 114-143.
1922. A parthenogenetic mayfly (Ameletus ludens Needham). Canad.
Ent., 54: 77-78.
70 THE FLORIDA ENTOMOLOGIST
Eaton, A. E.
1871. A monograph on the Ephemeridae. Trans. Entom. Soc. London,
1: 1-164.
1883. A revisional monograph of recent Ephemeridae, Part 1. Trans.
Linn. Soc. London, Zoology, 2nd Ser., 3: 1-77.
Ide, F. P.
1930. Contribution to the biology of Ontario mayflies with descriptions
of new species. Canad. Ent., 62: 204-213.
1935. The effect of temperature on the distribution of the mayfly fauna
of a stream. Univ. Toronto Studies, Biol. 39, Publ. Ont. Fish.
Res. Lab., 50: 3-76.
Lyman, F. Earle
1940. Limnological investigation of the Ephemeroptera in Douglas
Lake, Cheboygan County, Michigan, with special reference to
the distribution of immature stages. Unpublished thesis, Univ.
of Mich. Library.
McDunnough, J.
1924. New Canadian Ephemeridae with notes, II. Canad. Ent., 56:
90-98.
1927. Notes on the species of the genus Hexagenia with description
of a new species (Ephemeroptera). Canad. Ent., 59: 116-120.
Morgan, Ann H.
1913. A contribution to the biology of mayflies. Ann. Ent. Soc. Amer.,
6: 371-413.
Neave, Ferris
1932. A study of the may flies (Hexagenia) of Lake Winnipeg. Contrib.
Canad. Biol. Fish., N. S., 7: 179-201.
Needham, James G.
1920. Burrowing mayflies of our larger lakes and streams. Bull. U. S.
Bur. Fish., 36: 267-292.
1927. The life history and habits of a mayfly from Utah. Canad. Ent.,
59: 133-136.
Needham, James G., Jay R. Traver and Yin-Chi Hsu
1935. The biology of mayflies. Comstock Pub. Co., N. Y., 759 pp.
Spieth, Herman T.
1938. A method of rearing Hexagenia nymphs (Ephemerida). Ent.
News, 49: 29-32.
1940. Studies on the biology of the Ephemeroptera. II. The nuptial
flight. Jour. N. Y. Ent. Soc., 48: 379-390.
1941. Taxonomic studies on the Ephemeroptera. II. The genus Hexa-
genia. Amer. Midi. Nat., 26: 233-280.
Ulmer, George
1921. Uber einige Ephemeropteren-Typen alterer Autoren. Arch. f.
Naturg. Abt. A., 87: 229-267.
VOL. XXXIV-No. 2
ENTOMOLOGICAL OPPORTUNITIES1
M. C. VAN HORN
Florida Agricultural Supply Company, Jacksonville
It's a pleasure and an honor to be here today among this
group of distinguished gentlemen who have such a vitally im-
portant role in America's multi-billion dollar economy.
Entomology, the branch of zoology that treats of insects,
has grown to become a profession that affects the lives of vir-
tually every living person on this earth today.
Only the other day, a friend of mine introduced me to a group
of people. He said, "I want you to meet M. C. Van Horn, an
entomologist."
One of the persons in this group shook my hand and said,
"Oh, a 'bug-man'. Isn't that right?"
I nodded. "I suppose that's what you might call it," I told
him.
"In that event," he said, "I guess you know some of the
answers about bugs."
"We try to keep up with current entomological problems,"
I replied.
"Then tell me, Mr. Van Horn," he said, "if ants are such
busy insects, how do they find time to go to so many picnics?"
Seriously though, it hasn't been many years since people
looked upon entomologists as weird and curious creatures. They
were characterized as having long hair, wearing unusual cos-
tumes and flitting around the country with nets chasing butter-
flies.
Today, the public has been educated to a better under-
standing of the entomologist and his contributions to a more
gracious living. The average person knows that the entomol-
ogist is, indeed, an expert in his field.
And by the way, speaking of experts, there are all kinds of
definitions for an expert, too. One of the best I've heard, though,
is "An expert is a fellow with a Phi Beta Kappa key on a gold
chain, but no watch on the other end of the chain."
Anyhow, you know, and I know, that the economic ento-
mologist has little time for chasing butterflies in this day and
age. The pesticide industry, according to recent estimates, has
developed into a 150 million dollar a year business. Pesticides
1A talk given by Past-President M. C. Van Horn (1948-1949) at the
33rd Annual Meeting of the Florida Entomological Society, December, 1950.
THE FLORIDA ENTOMOLOGIST
manufactured to day are used to combat insects, fungi, bacteria,
rodents, weeds and all kinds of parasites.
The importance of pesticides can better be appreciated when
we are told that insects cause an annual damage to American
crops, livestock and property of more than two billion dollars.
This yearly two billion dollar loss does not include the damage
from plant diseases, which, according to recent estimates, an-
nually costs agriculturists and horticulturists another two billion
dollars.
We may find it hard to believe these staggering figures, but
not so hard, perhaps, when we consider that there are in ex-
istence today a horde of insects and more than 50,000 different
plant diseases. For example, corn is susceptible to some 114
diseases. There are 200 diseases that attack apples and 127
with which potatoes are afflicted.
Many of these control problems have us baffled. Nature, we
have discovered, has a way of building up immunity in some
pests to certain pesticides. We have learned, for example, that
mosquitoes and flies have developed a certain amount of im-
munity to DDT.
Thus there is a tremendous challenge in the field of ento-
mology. Where challenge exists, opportunity is nearby. History
has proven this.
Speaking of mosquitoes, I wish nature would provide man
with some kind of immunity against these pests. You have
probably heard one of the definitions of a mosquito-a small
insect designed by the good Lord to make us think better of
the fly. Most mosquitoes, incidentally, are pretty smart. They
all seem to pass the screen tests.
In this world of ours today, there is virtually nothing that
man or animal eats, inhabits or wears, with the exception of
metallic objects, which is not subject to pest problems at some
stage of its development or use. It is up to the entomologist
and his associates, directly or indirectly, to solve these pest
problems.
The problems of the economic entomologist, therefore, in-
volve food, fiber, health, structure, soil, animals, forest, grass,
ornamentals, stored products-the list seems almost endless.
The entomologist is concerned not only with the destruction
of pests and the protection of products, he deals also with con-
structive insects such as the honey bee. The entomologist is
highly concerned, too, with the health problem that arises in the
VOL. XXXIV-No. 2
production, processing, handling and use of toxicants in com-
bating pests.
Although the term pesticide is comparatively new, the science
itself goes far back in history. The findings of archeologists
indicate that certain chemicals were used to combat pests a
thousand years before Christ. Many of the new discoveries and
improvements we are making and developing today have been
made possible only by the detailed scientific work accomplished
by pioneering entomologists-our forefathers. The more I delve
into the history of the development of pesticides, the greater
becomes my respect and admiration for the painstaking work,
study, records and accomplishments of these pioneer entomol-
ogists. Without their early basic scientific studies to rely upon,
our progress today would be greatly impeded.
Today, the opportunities for well qualified entomologists are
arising at a greater rate than at any time since the profession
was known. Throughout the entire world, for reasons of health,
for reasons of security and for reasons of economy, people are
realizing the vital importance of knowing the answer to this
question "who are my friends and who are my enemies?" You
know and I know that in a rapidly moving, quickly progressing
business world it is highly important to know our enemies from
our friends. But we cannot stop there. It is important that
we know our enemies from our friends in the lower animal king-
dom-and specifically, the so-called pests.
The entomologist can pride himself on the fact that the prob-
lems on which he is working are not merely local, state-wide or
even continental in scope. These problems are world-wide. In
solving them, he is contributing to the welfare of the world.2
The measures employed by the entomologist in dealing with
these problems are complex. They involve law, psychology,
physiology, chemistry, physics, ecology, transportation, process-
ing, engineering, salesmanship and diplomacy, not to mention
some mechanical knowledge.
2 Records indicate that as a citizen of the U. S. A., we now enjoy the
largest life expectancy in our history. We believe at least a part of this
accomplishment can be attributed to the advancements made in science,
of which the entomologist, through public health, abundant and quality
food production can claim a part.
One hundred years ago it took 4 people to produce food for themselves
and 1 person in town. Today 2 people on the farm produce enough food
for themselves and 8 people in the town plus 1 person in other nations.
This tremendous increase in production would not have been possible with-
out the services of the entomologist and the pesticides in use today. In
fact, without them it is probable that the world today would go hungry.
THE FLORIDA ENTOMOLOGIST
An entomologist-that is, a good one-needs far more than
a working knowledge of entomology. He should have a basic
understanding and some training in such subjects as chemistry,
pathology, botany, horticulture, toxicology, agronomy, agricul-
ture, public speaking, English composition, journalism, statis-
tics, salesmanship, public relations, advertising and business
administration. He should know how to make friends and in-
fluence people-how to use a camera. On top of all this, modern
society demands that he play a reasonably good game of golf,
know how to hook a sailfish, be an understanding partner at
bridge and a genius at canasta. Confidentially, where that
canasta part is concerned, I am working on a pesticide to com-
bat that problem. It may take a lot of time. Mrs. Van Horn
is not cooperating.
The formal education of an inexperienced entomologist might
be likened to the development of an embryo. The seed has been
sown, it is assumed they have fallen on fertile ground and that
normal development will take place to form the sprouting or
graduation. This formal phase of education basically prepares
the student for his future work. In other words, it places a tool
in his hand with which to work and develop. This training
should give him an advantage over those who are not so pre-
pared; however, this in itself does not assure success.
The knowledge gained must be diligently and intelligently
applied. Usually there is a practical application learning period
which might be likened to an internship. This may continue
for several years before the candidate reaches his entomological
majority.
There is little question that the need for well qualified ento-
mologists has never been greater than it is today and the oppor-
tunities were never brighter. The requirements are broad, the
road to success is not easy but to those who have what it takes
the way is open.
The very fact that you are here today is an indication that
you have what it takes. The very fact that you are interested
enough in our problems to come here and thrash them out means
that you are interested, not merely in your personal and local
entomological problems, but in the science and profession of
entomology as it affects the welfare of the world.
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