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Everglades Station Himeo Report EES70-4 April, 1970
Horn Flies and Cattle Grubs on Beef Cattle in
the Everglades and Results of Insecticide Testing
H. J. Janes, B. W. Hayes, and D. W. Beardsley 1/
Horn flies and cattle grubs are the most conspicuous and most damaging
insects that occur on beef cattle in the Everglades. Horn flies, Haematobia
irritans (Linnaeus), are present on cattle throughout the year. The numbers
range from an average of less than 100 per animal during the winter months to
500-600 May through November. For many months the numbers exceed the figure of
400 suggested by North Carolina researchers as the threshold of economic damage.
The horn fly pierces the skin to suck blood, causing pain and annoyance and
interfering with the feeding and resting of the animals. In addition the flies
are suspected of transmitting anthrax.
The common cattle grub, Hypoderma lineatum (deVillers), has been found in
the backs of cattle almost every month of the year, reaching by far the greatest
numbers during the winter months. The quality of the meat is lowered where the
maggots tunnel through the flesh of the back, and the value of the hides for
leather is greatly depreciated. Prices paid for "grubby" cattle are lower than
for clean animals, amounting to a loss of one dollar per hundred weight on the
infested steers in a lot marketed from the Experiment Station.
Horn Flies
Horn flies are small, about half as big as houseflies. The name horn fly is
derived from the habit of the flies at certain times, when not sucking blood, of
congregating on the head at the base of the horns. The flies of course do no harm
to the horn and are more often present on the trunks and legs of the animals. The
flies lay their eggs in droppings of cattle. The maggots hatch from these eggs
in a day or two, feed in the dung and become full grown in 3 to 5 days. They then
form pupae inside brown puparia and emerge as flies about a week later.
Tests conducted at the Everglades Experiment Station and surrounding areas
have shown that self-application dust bags can be used by cattle in improved pas-
tures to control the horn fly. Where cattle are obliged to come to a localized
area to obtain water and supplemental feed they will dust themselves on insecti-
cide filled bags hanging nearby.
1/ Assistant Professor (Assistant Entomologist), Assistant Professor (Assistant
Animal Nutritionist), Professor (Animal Nutritionist) and Head of Station,
respectively, Everglades Experiment Station, Belle Glade, Florida 33430.
- 2 -
Structure and placement of dust bags. The dust bags have been constructed of
double thickness of burlap and contained a plastic lining. The lining extended
from the top about 3/4 the length of the bag and was open across the bottom. Dust
bags have been provided at the rate of 2-3 per 40-acre pasture and 4 per 80-acre
pasture. As each bag became emptied from use, it usually had been badly worn by
the cattle buffeting it about. It was replaced by a new bag containing a new sup-
ply of dust. Each bag was suspended from the arm of a separate inverted L support
by 3 ropes tied through eyelets at the top of the bag. The supports were portable,
constructed of pipe, and had weighted bases. The ends of the two supports were
connected by an insert pipe. Other supports which have proved satisfactory have
consisted of 2" x 6" wooden frames with posts set in the ground.
In a test comparing 1% coumaphos -- in 10 and 25 pound bags, no difference
was found in the effectiveness of these two sizes. However, the heavier bags were
more susceptible to abuse by the animals than the lighter bags. On occasion the
heavier bags were torn which allowed the dust to spill on the ground. This sug-
gested that a 25-pound dust bag may be a little too heavy. Over a 14-week period
the use of dust by the cattle from the 10 pound bag was 102 pounds for 210 steers
(0.5 lb. average) and for the 25-pound bag 165 pounds per 210 steers (0.8 lb.
average).
In this test the dust bag contained in addition to an inner plastic lining an
outer plastic shield. The cattle rather quickly tore the outer shield from the bag,
but the bags functioned well without it. The test was conducted in 80-acre pas-
tures, each stocked with 105 head of cattle.
Results of insecticide evaluations. Two seasons' tests have shown that the
use of 1% coumaphos in dust bags, supplied on a continuous basis, May through
November, will keep numbers of flies no higher than 10 per animal through the
season when horn flies are most abundant. The average use of dust was 1-1 lbs/
animal for a 6-month period.
Phosmet -, an experimental product not as yet on the market for livestock,
used in dust bags at 5% and 10% concentrations not only controlled the horn fly,
but in early results has shown promise of also controlling the cattle grub. If
further experiments show that the two types of insects can be controlled by a sin-
gle application method, this would be of great importance. A goal of future
research would be to determine the types of insecticides and the minimum concentra-
tions that would be effective in this application. Coumaphos at 1% was not
effective against the grubs. Higher concentrations should be checked.
2/
- Supplied as Co-Ral by Chemagro Corporation, Kansas City, Missouri.
SSupplied as Prolate by Stauffer Chemical Company, Richmond, California.
- 3 -
Cattle Grubs
The grubs appear in the backs in appreciable numbers in November, the counts
building up to the highest levels in January to early March. There is a sharp
decline in late Tarch and April. The highest numbers of grubs counted on one
animal was 46, on January 19, 1968. On February 19, 1970, 84% of an untreated
control herd of 98 mixed crossbred steers was infested with grubs. The range in
number of grubs per animal was 0-28, and the overall average 5.76.
During spring and early summer, flies about as big as honeybees, chase the
animals in pastures, while laying their eggs on them. The cattle usually run
wildly, and often injure themselves in their attempts to get away. The eggs are
laid mostly about the legs and lower part of the belly. The small maggots from
these eggs tunnel into the skin and migrate through the body for about 6 months
before they lodge in the back. Any one larvae spends about two months under the
skin. The grubs mature and leave the animals during winter and early spring. They
drop to the ground where they transform to pupae from which the adult emerges about
3-5 weeks later.
Results of insecticide testing. One percent coumaphos applied in self-treat-
ment dust bags during the summer months (although effective against horn flies)
was not effective against the grubs. Coumaphos fed in mineral mixture eaten on a
free-choice basis, averaging 1.39 mg/kg of body weight per day, was only partially
effective against the grubs.
In a test using phosmet, 5% and 10% concentrations used in dust bags control-
led both the horn fly and the cattle grub. Results from the dust bag treatment
were equally as effective as a phosmet pour-on application. Numbers of cattle
treated and results are shown in the accompanying table. The dust bags were
installed, 3 per 40-acre pasture, on May 15, 1969. They were replaced periodically
as needed and were completely removed September 8. During this time the average
amount used per steer of the 5% phosmet was 1.8 lb. and of the 10% phosmet, 1.3
pound. The application of phosmet (Prolate 4-OS) pour-on (1 oz/100 Ibs. body wt.)
was made July 30 on steers not receiving the dust treatment.
In addition to the experiment a commercial ranch application of crufomate
(Ruelene) pour-on (1 oz/100 Ibs. body wt.) was made October 9. The results are
included in the table and are approximately the same as those obtained from the use
of phosmet.
EES70-4
700 copies
Cattle Grub Counts taken February 19-20, 1970. a/
Treatment
5% phosmet in dust bags
10% phosmet in dust bags
phosmet pour-on
(1 oz/100 lb body wt)
Untreated check
No. steers % steers No. grubs per steer
No. steers
examined
83
93
69
98
% steers
with grubs
5
6
7
84
No. grubs per
Average
0.24
0.16
0.08
5.76
Commercial ranch application (additional check)
crufomate pour-on
(1 oz/100 lb body wt) 60
Untreated check 60
a/ Experiment conducted at U. S. Sugar Corporation Eastern Division Ranch, Bryant.
steer
Range
0-15
0-4
0-2
0-28
0.10
2.20
0-2
0-16
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