Everglades Station Mimeo Report EES69-1 I.F.A.S. Univ. of Florida May, 1969
CONTROL OF HORN FLIES AND GRUBS 1
B. W. Hayes, M. J. Janes and D. W. Beardsley 2
The horn fly (Haematobia irritans) and cattle grub (Hypoderma lineatum)
have become serious pests to the cattle industry in Florida and especially in
southern Florida. In considering these insect pests it might be of'interest to,
first of all, take a look at their life cycles.
Horn Fly: Horn flies spend the winter as larvae or pupae in droppings of
cattle. In the spring they emerge and begin to appear on cattle. The horn fly
numbers increase quite rapidly as their entire life cycle is completed in ten
days to two weeks. Their eggs are laid on fresh manure. Maggots hatch in a
day or two and become full grown in three to five days. Then they form pupae,
and about a week later, adult flies emerge ready to attack cattle. This cycle
of ten to fourteen days continues until the flies are killed by frost. At this
time the immature stages in manure go into hibernation for the winter. However,
in south Florida where winters are relatively mild, adult flies are active
throughout the year.
Cattle Grub: The grub has a somewhat different life cycle. The adult
insects are commonly called heel flies and are about the size of honeybees.
They lay their eggs on hairs of the heels, legs and belly of cattle. The eggs
hatch into larvae in three to four days; the larvae burrow into the skin and
migrate slowly through the animal's body until they reach the gullet. Here the
larvae remain for several months until winter, at which time they migrate
further to the muscles of the animal's back. They settle beneath the hide and
cut holes through the hide for breathing. The larvae or grubs remain encysted
in the animal's back for about six weeks. During this time they enlarge the
breathing holes. When full grown they drop to the ground where they change to
pupae. The adult heel fly emerges from the pupal case from three to ten weeks
later depending upon the temperature. Then the cycle is begun once again.
The entire life cycle is completed in about a year. The grubs spend eight to
eleven months of this cycle in the animal's body.
I/ Presented at the Eighteenth Annual Beef Cattle Short Course, University of
Florida, Gainesville, Florida, May 2, 1969.
2/ Assistant Animal Nutritionist, Assistant Entomologist, and Animal Nutri-
tionist and Head, Everglades Experiment Station, Belle Glade, Florida.
Horn Fly: In the case of the horn fly, it is quite difficult to estimate
accurately the economic loss caused by this insect's attack on cattle. Bruce
(1964. North Carolina Agr. Exp. Sta. Tech. Bull. No. 157) of the North Carolina
Station has suggested that economic injury begins when the horn fly population
reaches 400 flies per animal. In south Florida horn flies are active throughout
the year, and numbers often exceed 400 flies per animal. In numbers of this
magnitude horn flies would cause considerable annoyance to animals. The horn
fly has specialized mouth parts which enable him to pierce the skin and remove
blood from the host. This probably causes some pain and interferes with the
animal's feeding and resting. Therefore, the animal's weight gain may be
reduced. In addition, the horn fly has been suspected to be a transmitter of
Cattle Grub: The cattle grub probably causes a greater economic loss than
the horn fly. At the Everglades Station grubs have been observed in the backs
of animals every month of .the year except June. Consequently, the cattle grub,
also, is potentially a year round pest in south Florida. Although any one heel
fly probably lives only a few days and eats ho food, his buzzing excites cattle
so that they run wildly with their tails in the air. In addition to this annoy-
ance, the most important economic consideration occurs when grub infested cattle
are shipped to slaughter. Some meat must be trimmed away from the area where
each grub is located and this is in expensive cuts of the carcass. Besides this
loss of expensive meat, the carcass may be downgraded and may sell for a lower
price. Also, the value of grubby, perforated hides for leather is reduced
greatly. In a recent USDA publication (1968. U. S. Dept. of Agr. Leaflet 527)
trim loss on a heavily infested carcass has been estimated to range from five to
seven dollars. More recent experience at the Everglades Station confirms this
estimate. Of 20 experimental steers that were shipped to slaughter, eight were
discounted one dollar per hundred weight of carcass because of grub infestation.
Unfortunately the exact number of grubs on individual steers were not determined.
However, records show that the loss on these eight steers amounted to $53.16, or
$6.64 per steer. This represented an average loss of $2.68 for each of the 20
There are many insecticides used to control horn flies and cattle grubs,
however, the discussion here will be limited to those materials that have been
tested at the Everglades Station. These tests fall into three categories--
(1) those for horn fly control only, (2) those for both horn fly and grub con-
trol, and (3) those for grub control only.
Horn Fly: Some of the early horn fly control work (Haines. 1965. Unpub-
lished-data) involved feeding a salt mixture containing 6% Ronnel (a product of
the Dow Chemical Company) to yearling steers. Three forms of the salt were
used--loose salt, 25-pound blocks of salt made under 50 tons pressure and 25-
pound blocks of salt made under 75 tons pressure. Observations at two and
three weeks after the steers were placed on treatment indicated that the horn
fly population was reduced. Steers consuming the mediated salt had less than
five flies per animal compared to 40 to 60 flies on untreated steers near by.
Daily consumption rates per steer were 0.079 pound for the loose salt, 0.065
pound for the 50-ton pressure blocks and 0.071 pound for the 75-ton pressure
In another experiment (Haines and Beardsley. 1966. Unpublished data),
mature cows were sprayed at two-week intervals with a 0.05% Tiguvon solution or
allowed continuous access to dust bags containing 5% Co-Ral. (Tiguvon and Co-Ral
are products of the Chemagro Corporation, Kansas City, Missouri.) The Tiguvon
solution was sprayed on the cattle at 250 pounds per square inch of pressure
with approximately one-half to one gallon being applied to each cow. Initially,
each dust bag contained five pounds of 5% Co-Ral dust, and make-up dust was
added as needed. On the average each dust bag furnished dust for 28 cows. Fly
counts were taken at weekly intervals over a five-month period beginning May 4,
1966. The average number of flies per cow was 81 for the spray treatment and
42 for the dust bag treatment compared to 209 for the check. The average of 81
flies per cow for the spray treatment bears further explanation. One day fol-
lowing each spray treatment the average number of flies per cow was four whereas
eight days after each treatment there were 151 flies per cow. This suggests that
more frequent sprayings might have reduced the horn fly populations further.
Two concentrations of Co-Ral in dust bags have been compared in a more
recent study (Janes et al. 1968. J. Econ. Entomol. 61:1176). Nine herds of
approximately 40 cows-each were used during a six-month test period beginning
May 22, 1967. Each herd was maintained on 30 acres of pasture. Three herds
were exposed to 10-pound dust bags containing 1% Co-Ral, three herds were
exposed to 10-pound dust bags containing 5% Co-Ral and three herds were main-
tained as an untreated check. In addition to these treatments, approximately
400 yearling steers and heifers were given Co-Ral in a complete mineral mixture.
Co-Ral 50% premix was incorporated into the mineral mixture at the rate of
three pounds per 100 pounds of mineral. This provided a concentration of 1.5%
active Co-Ral in the mineral mixture.
Fly counts were taken at two-week intervals. Seasonal fluctuations caused
some variation; however, fly counts averaged about 12 flies per cow for either
of the dust bag treatments, 60 flies per animal for the mineral treatment and
200 flies per cow in the check herds. The 1% dust was equal to the 5% dust in
controlling horn flies, and the dust bags treatments were superior to Co-Ral in
the mineral. Occasional fly counts, taken from untreated herds outside the
test area, averaged about 500 flies per animal. The fact that fly populations
on the check herds were below those for herds away from the test area points
out the significance of area control.
For the six-month test period a total of 40 to 60 pounds of Co-Ral dust
was used for each herd, which calculated to be one and one-half pound per cow.
Probably half of this was used the first month. Consumption of the mineral
mixture containing Co-Ral averaged 0.07 pound per head per day.
The treatment using 1% Co-Ral dust bags was repeated using greater numbers
of animals in larger pastures (Janes et al. 1968. Unpublished data). For
this 14-week experiment beginning August 6, 1968, 80-acre pastures with 105
steers per pasture were used. Four dust bags were placed in each pasture. Also
10-pound dust bags were compared with 25-pound dust bags. Again, excellent horn
fly control was observed for these treatments. The 10-pound dust bags were
equal to the 25-pound dust bags, and in each case the horn fly population was
kept down to an average of ten flies per steer. On a check herd approximately
one-third mile away from the dust bags, there was an average of about 350 flies
per steer, and an untreated herd located one mile away averaged about 600 flies
For the 14-week period average dust usage per steer was 0.5 pound for the
10-pound dust bag treatment and 0.8 pound for the 25-pound dust bag treatment
The heavier bags were more susceptible to abuse by the animals than the lighter
bags. On occasions the heavier bags were torn which allowed dust to spill to
the ground. This partially explains the greater dust usage from the 25-pound
bags and suggests that this size bag may be a little too heavy.
A limited study (Greer et al.. 1968. Unpublished data) using Ciodrin (a
product of the Shell Chemical-CoT) has been conducted recently. For this test
30 yearling steers were used during an eleven-week test period. Ten steers
were self-treated with a dust bag containing 10 pounds of 3% Ciodrin dust, 10
were sprayed at weekly intervals with two quarts per head of 0.5% Ciodrin
spray and ten served as untreated check animals. Average horn fly populations
(counted twice per week) were 156 per steer for the dust bag treatment, 26 per
steer for the spray treatment and 278 per steer for the check. In this case
the dust bag was much less effective than the spray in controlling horn flies.
These results may have been different had some method of horn fly control been
used in nearby pastures. Excellent results from Co-Ral in dust bags were
obtained previously with area wide treatment.
Horn Fly and Cattle Grub: Some experiments have been conducted to test the
effectiveness of various products in controlling both horn flies and cattle
grubs. One such experiment (Haines and Beardsley. 1967. Unpublished data)
compared feeding a mineral mixture containing 1% Co-Ral with 5% Tiguvon in a
dust bag. Each treatment as well as the check included 38 yearling heifers
on 20 acres of pasture. Fly counts taken once a week during the three-month
test period beginning April 28, 1966, indicated an average of 42 flies per
heifer on the Co-Ral mineral treatment, 32 flies per heifer on the Tiguvon dust
bag treatment and 128 flies per heifer in the check.
Fortunately for the ranchers but unfortunately for this test, the grub
infestation was light--heifers that were not treated had only an average of 1.6
grubs per animal (counts were made in January). Heifers consuming the mineral
mixture with Co-Ral averaged 1.3 grubs per animal, and heifers exposed to the
Tiguvon dust bag averaged only 0.08 grubs per animal. Apparently Co-Ral in the
mineral had no effect, whereas, 5% Tiguvon dust reduced the grub count con-
siderably. Only three grubs were found among 38 heifers on this treatment.
During this three-month test, consumption of the Co-Ral mineral mixture
averaged 0.07 pound per head per day and Tiguvon dust usage averaged 0.006
pound per head per day. Tiguvon dust usage was much less than Co-Ral dust
usage in later studies; however, only one bag was used for the 38 heifers.
Later experience suggests that two bags should have been used for this number
of animals. Although one bag gave fair horn fly control, two bags probably
would have given excellent control.
Another experiment (Haines and Beardsley. 1967. Unpublished data), con-
ducted in conjunction with the one just mentioned, compared two concentrations
of Tiguvon in back oilers when used to control horn flies and grubs on steers.
Two groups of 15 yearling steers each on ten-acre pastures were provided with
one back oiler per group. One oiler was charged with a 0.5% concentration of
Tiguvon in diesel fuel and the other with a 1% Tiguvon solution. During the
three-month test period, fly counts were taken at weekly intervals. These
averaged 33 flies per steer for the 0.5% Tiguvon solution treatment, and 30
flies per steer for the 1% Tiguvon solution treatment. Both were equally
effective in controlling horn flies. The horn fly population on untreated
heifers averaged 128 per animal.
Grub counts taken in January averaged 2.2 grubs per steer for 0.5%
Tiguvon, 1.2 grubs per steer for 1% Tiguvon and 1.5 grubs per steer for the
check. Compared to the untreated steers, neither treatment was particularly
effective in controlling grubs, but this may have been due to the low infesta-
Cattle Grubs: Cattle grub research at the Everglades Station dates back
to 1957, when Harris et al (1959. J. Econ. Entomol. 52:425) compared Co-Ral
and Ronnel (products of the Chemagro Corporation and the Dow Chemical Company,
respectively). A 2.5% solution of Co-Ral was sprayed along the backs of
individual animals at the rate of one pint per head; a 17% solution of Ronnel
was administered at the rate of one ounce per each 100 pounds of body weight.
This resulted in a dosage of five grams of Ronnel per 100 pounds of body weight.
On each of five application dates ten animals were treated with Co-Ral and
another ten with Ronnel so that 50 animals were treated with each insecticide.
The treatment dates were May 6, June 5, July 8, August 22 and September 16.
An untreated group of 25 animals served as a check. Beginning in October,
grub counts were taken at two-week intervals for a total of 14 observations.
The peak of grub infestation among the untreated animals occurred in the middle
of January when there was an average of 18 grubs per animal. The peak of
infestation for animals treated with Ronnel occurred a month later with slightly
less than one grub per animal. With Co-Ral there was no true peak and there was
never more than 0.11 grub per animal. The results indicated that the best time
to treat with Ronnel was September, whereas Co-Ral gave excellent grub control
when used on any of the treatment dates during May through September. However,
Ronnel was more effective than Co-Ral when each was applied in September.
These results prompted another study (Harris et al. 1959. The Florida
Entomol. 42:155) comparing two applications of 0.5-"Co-Ral spray on the same
animals, one application in June and one in September, with single applications
on different animals in June or September. The average number of grubs per
animal was 0.3 for the combination treatment, 1.2 for the June treatment and 4.8
for the September treatment. The difference between the combination treatment
and the June treatment was not significant, and both of these treatments were
significantly more effective than the September treatment. Results of.this
experiment would indicate a June application if 0.5% Co-Ral spray were applied
only once during the season.
Haines (1963. Unpublished data) studied the effectiveness of a material
called Famophos (a product of the American Cyanamid Company) in controlling
the cattle grub. This material, in tablet form, was administered orally to 25
weanling calves in July. In the following February, Famophos treated animals
averaged 0.29 grub per animal compared to an average of 19 grubs for untreated
animals. In this experiment Famophos controlled cattle grubs quite effectively.
Haines (1965. Unpublished data) also compared two rates of Ruelene (a
product of the Dow Chemical Company) application for cattle grub control. Rue-
lene was poured on the backs of 100 calves in August. Fifty calves were treated
with one-half ounce of Ruelene per hundred pounds of body weight, and 50 calves
were treated with one ounce of Ruelene per hundred pounds of body weight. Grub
counts taken the following winter indicated five grubs among the 50 calves on
.the one-half ounce treatment and three grubs among the 50 calves on the one
ounce treatment. The author concluded that both levels of Ruelene application
were satisfactory for cattle grub control. However, no indication of the grub
population on untreated animals was given.
A more recent study (Haines and Beardsley. 1967. Unpublished data)
involved pour-on applications of Tiguvon, Neguvon or Co-Ral (products of the
Chemagro Corporation). In one experiment 3% Tiguvon or 8% Neguvon was poured
oh the backs of heifer calves in August at the rate of one-half ounce per
hundred pounds of body weight. In a second experiment 2% Tiguvon or Co-Ral
was poured on the backs of steer calves in September at the rate of one-half
ounce per hundred pounds of body weight. Grub counts were taken in January.
Excellent control was obtained with both Neguvon and Tiguvon. No grubs
were found in 48 heifers treated with Neguvon, and only one grub was found in
46 heifers treated with Tiguvon. A total of 176 grubs were found in 48 untreated
Excellent control also was obtained with Co-Ral and Tiguvon. No grubs were
found in 40 steer calves treated with Co-Ral, and only three grubs were found in
38 steer calves treated with 2% Tiguvon. A total of 167 grubs were counted in
38 untreated steer calves.
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Since 1957, several materials have been tested for control of horn flies
and cattle grubs. Materials which have given satisfactory control of horn
flies include the following:
1) Ronnel -- 6% in mineral.
2) Tiguvon -- 0.05% spray applied at 2-week intervals; 5% dust in dust
bags; 0.5% in diesel fuel for back oilers.
3) Co-Ral -- 1% dust in dust bags; 1% in mineral.
4) Ciodrin -- 3% dust in dust bags; 0.5% spray at weekly intervals.
Materials which have given satisfactory grub control include the
1) Co-Ral -- 0.5% spray applied in June; pour-on at rate of 0.5 ounce
per 100 pounds body weight in September.
2) Tiguvon -- 0.5% in diesel fuel for back oilers; 2% pour-on at rate of
0.5 ounce per 100 pounds of body weight in August.
3) Neguvon -- 8% pour-on at rate of 0.5 ounce per 100 pounds body weight
4) Ronnel -- 17% drench at rate of 1 ounce per 100 pounds body weight in
5) Ruelene -- pour-on at rate of 0.5 ounce per 100 pounds body weight in
6) Famophos -- tablets administered orally in July.