Number Of Horn Flies Research Articles

Development and validation of a neural network for the automated detection of horn flies on cattle

When the number of horn flies that blood feed on cattle exceeds the economic threshold, they can adversely affect the health and wellbeing of their hosts. Excessive horn fly burdens also lead to reduced weight gain and, consequently, diminished profits for livestock producers. Effective management and treatment require reliable surveillance methods for estimating the degree of horn fly burden (i.e., counting the number of flies on cattle). Traditionally, these estimates are obtained through human visual estimation, either in-person or by counting images on a photo; however, these methods are costly both in terms of time and labor and are prone to subjectivity and bias. In contrast, automated methods can expedite the counting process and remove subjectivity and bias. To this end, a 2-stage method is presented here that uses computer vision and deep learning to identify the location of flies in digital images. The first stage segments the salient cow from all other parts of the image to remove flies on neighboring cattle from consideration. The second stage processes full-resolution patches of the original image and produces a heat map at the location of flies in the images. The method was trained on a set of 375 human-annotated images and tested on 120 images, where significant variation was observed amongst the human scorers. Counting results are compared to four separate human scorers and demonstrate that the neural network produces consistent results and that the method is reliable. Thus, the developed method can be used for monitoring changes in horn fly populations over time by anyone and allows for increased rigor and repeatability. An examination of individual images where the method was closest to and farthest from the human counts provides valuable insights regarding photographic processes that lead to success and failure.

Short communication: Effects of mesh leggings on fly pressure and fly avoidance behaviors of pastured dairy cows

Ectoparasitic stable flies (Stomoxys calcitrans [L.]), horn flies (Haematobia irritans [L.]), and face flies (Musca autumnalis De Geer) negatively affect dry matter intake, milk production, and health of pastured dairy cows. These flies cause fly avoidance behaviors and are a major welfare concern for dairy producers. The objective of this study was to evaluate the effects of mesh Shoofly Leggins (Stone Manufacturing & Supply, Kansas City, MO) on fly avoidance behaviors and numbers of flies attacking pastured dairy cows. In a crossover design, lactating dairy cows (n = 80) were randomly assigned to groups with and without leggings (Shoofly Leggins worn on all legs). All cows were managed in one group. Cows were observed for 2-wk periods, and then treatments were reversed in the next 2-wk interval. Counts of stable flies, horn flies, and face flies on all cows were recorded twice daily (once in morning per cow: 0930 to 1230 h; and once in the afternoon per cow: 1330 to 1630 h), 3 times per wk on Tuesday, Wednesday, and Thursday of each week during the study period. The total number of flies per cow was greater on cows with leggings than cows without leggings. The number of horn flies per cow was greater on cows in with leggings (26.4 flies/side) compared with cows without leggings (24.1 flies/side). Stable fly numbers were similar for cows with and without leggings (12.8 flies/leg). A random subset of 20 focal cows per group was observed during 5-min intervals to record frequencies of 4 behaviors: leg stomps, head tosses, skin twitches, and tail swishes. Counts of head tosses (2.6 vs. 3.1), skin twitches (20.9 vs. 19.6), and tail swishes (21.3 vs. 19.3) were similar for cows without leggings versus cows with leggings, respectively. However, foot stomps were 39% lower for cows with leggings compared with cows without leggings, and leg stomps were 26% higher in the afternoon than in the morning (2.9 vs. 2.4, respectively). A positive correlation was observed between stable and horn flies and all insect avoidance behaviors. Numbers of stable flies were 1.5 times greater in the afternoon than in the morning. The results of this study indicated that flies were associated with cow fly avoidance behaviors regardless of the use of leggings, but leggings effectively reduced foot stomps by 39%, so their use may provide some relief from stable fly injury to pastured dairy cows.

Haematobia irritans parasitism of F1 yak × beef cattle (Bos grunniens× Bos taurus) hybrids.

The horn fly Haematobia irritans (Diptera: Muscidae) is a blood obligate ectoparasite of bovids that causes annual losses to the U.S. beef cattle industry of over US$1.75billion. Climate warming, the anthropogenic dispersion of bovids and the cross-breeding of beef cattle with other bovid species may facilitate novel horn fly-host interactions. In particular, hybridizing yaks [Bos grunniens (Artiodactyla: Bovidae)] with beef cows (Bos taurus) for heterosis and carcass improvements may increase the exposure of yak × beef hybrids to horn flies. The present paper reports on the collection of digital images of commingled beef heifers (n=12) and F1 yak × beef hybrid bovids (heifers, n=7; steers, n=5) near Laramie, Wyoming (∼ 2200 m a.s.l.) in 2018. The total numbers of horn flies on beef heifers and F1 yak × beef heifers [mean ± standard error (SE): 88 ± 13 and 70 ± 17, respectively] did not differ significantly; however, F1 yak × beef steers had greater total horn fly abundance (mean ± SE: 159 ± 39) than female bovids. The present report of this experiment is the first such report in the literature and suggests that F1 yak × beef bovids are as susceptible as cattle to horn fly parasitism. Therefore, similar monitoring and treatment practices should be adopted by veterinarians, entomologists and producers.

Influence of selective treatment of bulls on the infestation of Haematobia irritans on untreated cows

The distribution of Hematobia irritans is not homogeneous in cattle populations. Generally, between 15% and 30% of bovines carry more than 50% of the flies, and higher infestations occur in bulls. In this study, the effect of treating the bulls with ear tags containing 40% diazinon on the infestation of flies on the herd during the breeding season was evaluated. Four groups of cattle were made, each containing one bull and 35 Braford cows. Groups 1 and 2 were on pastures in highlands. Groups 3 and 4 were on pastures in lowlands. At the beginning of the trial, each bull from Groups 1 and 3 was treated with an ear tag. Bulls from Groups 2 and 4 remained untreated. Weekly, for 10 weeks, horn flies were counted from each bull and 15 cows from each group. A repeated measures linear mixed model was used with cows as random effects. The number of horn flies in the treated groups was lower than that in the untreated group, suggesting that selective treatment of bulls could be an effective strategy to control horn flies on the herd. The number of flies was higher in the lowland than that in the highland groups, suggesting an effect of the environment on horn fly infestations. In addition, we estimated the cow level predictions from the model to estimate the cow effect on fly counts, and we compared those values with the observed weekly quartiles for each group. Fly-susceptible cows were defined as those for which the infestation of flies appeared in the upper quartile more than 50% of the weeks and in the lower quartile less than 20% of the weeks. In contrast, a fly-resistant cow was defined as one for which the fly counts appeared in the lower quartile more than 50% of the weeks and in the upper quartile less than 20% of the weeks. In all, 8.3% of the cows were susceptible and 15% were resistant. These results may be used to selectively treat bulls or to treat the bulls and the most susceptible cows during the breeding season.

Evaluation of a commercial vacuum fly trap for controlling flies on organic dairy farms

The objective of this study was to evaluate the efficacy of a commercial vacuum fly trap (CowVac, Spalding Laboratories, Reno, NV) in on-farm organic dairy production systems to control horn flies, stable flies, and face flies. As cows walk through the trap, flies are brushed off the face, flank, and back with hanging flaps and blown off the belly, udder, and legs from one side, and then vacuumed from the air into a chamber from vacuum inlets opposite the blower and above the cow. The study included 8 organic dairy farms during the summer of 2015 in Minnesota, and herds ranged from 30 to 350 cows in size. The farms were divided into pairs by location; during the first period of the summer (June to July), the trap was set up on 1 farm, whereas during the second period of the summer (August to September) the trap was sent to its paired farm. Farms were visited once per week to collect and count flies from the trap as well as count and record flies on cows. Bulk tank milk, fat, and protein production and somatic cell count were collected on farms during the entire study period. Data were analyzed using the GLM procedure of SAS (version 9.3, SAS Institute Inc., Cary, NC). Independent variables for analyses were the fixed effects of farm, trap presence, housing scenario, and summer period. Horn fly numbers on cows were lower by 44% on farm in the presence of a trap (11.4 vs. 20.5 flies/cow-side) compared with the absence of a trap. Stable fly (5.4 vs. 7.1 flies/leg) and face fly (1.0 vs. 1.0 flies/cow) numbers were similar on farm whether the trap was present or absent on farms, respectively. Milk production was similar for farms with the trap (15.5 kg/d) compared to without (15.3 kg/d) the trap. Bulk tank milk, milk components, and somatic cell count were statistically similar in the presence and absence of the trap, so potential benefits of the trap for those measures were not evident at low fly populations observed during the study. The presence of a trap on farm reduced horn fly population growth rates (-1.01 vs. 1.00 flies/d) compared with the absence of a trap. Cows on farms with no housing (100% pasture) tended to have reduced horn fly numbers (11.7 vs. 28.3 flies/cow-side) in the presence of a trap compared with the absence of a trap on farm. Cows on farms with housing had similar horn fly numbers (11.2 vs. 14.8 flies/cow-side) in the presence of a trap compared with the absence of a trap on farm. In summary, these results indicate the trap was effective in reducing horn fly numbers on cows and reduced horn fly growth rates during the pasture season in organic dairy production systems, but benefits in improved milk production were not evident likely because of relatively low fly populations.

Selected Insecticide Delivery Devices for Management of Horn Flies (Haematobia irritans) (Diptera: Muscidae) on Beef Cattle.

The horn fly, Haematobia irritans (L.) (Diptera: Muscidae), is one of the most important pests of the beef cattle industry. Horn fly adults are blood feeders that remain in constant contact with cattle, providing management opportunities via insecticide-impregnated ear tags. Controlling horn flies in the United States is time consuming and costly, but failure to implement management can lead to weight loss and decreased weight gain of calves and yearlings. In the past decade, new chemical combinations have been impregnated into ear tags for pest management. The objectives of this project were to 1) evaluate the efficacy of ear tags against horn fly populations and 2) determine if reduced fly density results in economic return. During 2013, data were compiled by insecticide class; treated cows averaged fly reductions of 198 (s = 38.91; n = 3) for macrocyclic lactone treatments, 175 (s = 62.74; n = 4) for pyrethroid treatments, and 174 (s = 35.28; n = 8) for organophosphate treatments compared with untreated animals (214; s = 50.38; n = 9). During 2014, mean fly reductions were 187 (s = 14.15; n = 4) for macrocyclic lactone, 147 (s = 61.41; n = 13) for pyrethroid, and 143 (s = 77.16; n = 8) for organophosphate treatments relative to the untreated (200; s = 99.83; n = 14). A novel technology, the VetGun application system, tested in 2014, resulted in fly reductions (121 ±, n = 4), but means were not statistically significant from the control (200; s = 99.83; n = 14). Treatment of cattle with ear tags significantly reduced horn fly numbers compared with untreated cattle.

Development of a novel walk-through fly trap for the control of horn flies and other pests on pastured dairy cows

A prototype walk-through fly vacuum system, designed to remove horn flies Haematobia irritans (L.) (Diptera: Muscidae) from cattle, was developed and tested for efficacy. The study was conducted during 4 fly seasons over 17 consecutive weeks each year within the months of May through September at 1 dairy research herd in the coastal plain of North Carolina. Additional data on horn flies, as well as face flies (Musca autumnalis) and stable flies (Stomoxys calcitrans), were collected during 1yr from 7 commercial pasture-based and organic dairy farms in the piedmont region of North Carolina. The number of flies observed on animals in the pasture was compared with the number of flies collected in the trap. Studies were initiated after horn fly densities had met or exceeded a threshold of 200 flies per animal. The vacuum trap removed between 1.3 and 2.5 million flies annually from the research station cattle. Most fly removal occurred during the first few weeks of operation and maintained densities below threshold thereafter. Cattle using the fly trap at the research farm had only about 28% the number of horn flies as untreated cattle, and reductions ranged from 67.5 to 74.5% across the 4-yr study. In addition to large numbers of horn flies, traps placed on commercial dairies during 1yr collected stable flies, face flies, and house flies, all species with differing behavior and larger in size than horn flies. The estimated cost of running the trap is $72 per season at commercial rates of $0.12 per hour and an expected 4h of daily operation during the time of milking. Use of a vacuum system as described herein has potential as a cost-effective method in reducing populations of parasitic flies in pasture-based dairy production systems without the use of insecticides.

Pyric-Herbivory to Manage Horn Flies (Diptera: Muscidae) on Cattle

Pyric-herbivory, defined as fire-driven grazing, was applied as patch-burn grazing management and compared to traditional management (grazing without fire) for the potential to mitigate horn flies, Haematobia irritans (L.), on cattle in Iowa and Oklahoma. Stocking rate was conservative at both locations, and all cattle were black angus, Bos taurus (L.). Study design was two treatments replicated three times for a total of six pastures at each location. Average pasture sizes were 27 ha in Iowa and 55 ha in Oklahoma. The primary objective was to assess response of the Eurasian origin horn fly to fire and grazing disturbances. Numbers of horn flies were assessed at both locations and analyzed for location, treatment, and interaction (location × treatment). Numbers of horn flies differed only between treatments. Patch-burn grazing management resulted in 41% reduction of horn flies, less than in the traditional management system regardless of location (P < 0.0001). Cattle in pastures managed with patch-burn grazing were near the universally accepted economic threshold for treatment (200 flies per cow) compared to double the economic threshold on cattle under traditional management. Cattle in pastures managed with patch-burn grazing were below the behavioral threshold of 300 flies per cow and were expected to have increased grazing time associated with a reduction in stress annoyance behaviors. These results demonstrated that grazing management that includes fire can reduce horn flies on cattle in rangeland systems.

Horn Fly Haematobia irritans irritans (Linnaeus) (Insecta: Diptera: Muscidae)

The horn fly is one of the most economically important pests of cattle worldwide. Just in the United States, hundreds of millions of dollars in losses are attributed to the horn fly annually, while additional millions are spent annually on insecticides to reduce horn fly numbers. Learn more about this pernicious obligate blood-feeding ectoparasite in this 7-page fact sheet, written by Dan Fitzpatrick and Phillip E. Kaufman, and published by the UF Department of Entomology and Nematology, April 2011. EENY490/IN885: Horn Fly Haematobia irritans irritans (Linnaeus) (Insecta: Diptera: Muscidae) (ufl.edu)

Efficacy of Several Insecticide Ear Tags for Control of Horn Flies (Diptera:Muscidae) on Nebraska Beef Cattle

Abstract In 1999, three experimental 20% diazinon + 20% coumaphos impregnated ear tags and a 40% diazinon ear tag reduced horn fly numbers by 70% at the University of Nebraska Research Ranch near Whitman, Nebraska for 16 weeks. Two other insecticide ear tags, 8% beta cyfluthrin + 20% piperonyl butoxide (PBO) and 10% lambdacyfluthrin + 13% PBO reduced horn fly numbers by 95% and 86% respectively at a University of Nebraska pasture site near Ithaca, Nebraska for eight weeks. In 2003 some of the same insecticidal ear tags were reevaluated. Ear tags containing 10% zeta-cypermethrin + 20% PBO, 20% diazinon + 20% coumaphos, 10% lambdacyfluthrin + 13% PBO, 8% beta-cyfluthrin + 20% PBO and 40% diazinon provided a reduction in horn fly numbers ranging from 81.89% to 88.3% at the University Research Ranch for 12 weeks.

Evaluation of Alternative Tactics for Management of Insecticide-Resistant Horn Flies (Diptera: Muscidae)

A 3-yr study was conducted to determine the efficacy of tactics that could be used to manage populations of insecticide-resistant horn flies, Hematobia irritans irritans (L.). Insecticide spray, spot-on or pour-on formulations and two IGRs in bolus formulation, 1.3- and 3.2-ha pasture rotations on different rotation schedules, 0–50% Brahman breeding, selected fly-resistant cows, and a mechanical trap were evaluated singly and in combination. Concentration-mortality tests indicated that horn flies collected from cows used in the current study were significantly less susceptible to diazinon, coumaphos, and methoxychlor than horn flies from cows at the same locations previously used to determine baseline susceptibility. During the 3-yr study at the Southeast Research and Extension Center (SEREC), the IGR-bolus significantly reduced (P < 0.05) horn fly numbers on both the continuous and rotational graze regimens, resulting in significantly (P < 0.05) greater calf weaning weights (average of 24 kg). Horn fly numbers were significantly greater on untreated cows during the 3-yr study at the Southwest Research and Extension Center (SWREC) compared with the mean fly numbers on cows that received fly-management treatments. All tactics and tactic-combinations used at SWREC on cattle having no Brahman breeding failed to significantly reduce insecticide-resistant horn fly numbers. However, the combination of Brahman breeding with the IGR-Bolus and mechanical trap significantly reduced horn fly numbers and resulted in significant increases in calf weaning weight. In addition, mean horn fly numbers decreased significantly as the percentage Brahman breeding increased with 50% Brahman breeding reducing horn fly numbers by 140 flies per cow. No significant difference was found between the mean fly numbers on the fly-resistant purebred group and the cows that had no Brahman breeding but received the IGR-Bolus or used the mechanical trap. The use of synergized zeta-cypermethrin pour-on treatment successfully complimented the use of IGR-bolus and mechanical traps in reducing insecticide-resistant horn fly numbers. Neither 1.3- nor 3.2-ha size paddocks and stocking rates used in the rotation graze regimens at SEREC and SWREC, respectively, significantly reduced horn fly numbers when compared with continuously grazed paddocks. Data indicated the importance of using tactics that reduce horn fly numbers to ≈150 horn flies per cow. These data demonstrated the efficacy of using tactic combinations to manage insecticide-resistant horn fly populations.

Dynamics of Haematobia irritans irritans (Diptera: Muscidae) infestation on Nelore cattle in the Pantanal, Brazil.

From June 1993 to May 1995, horn fly counts were conducted twice a month on untreated Nelore cattle raised extensively in the Pantanal. Horn fly population showed a bimodal fluctuation and peaks were observed every year after the beginning (November/December) and at the end (May/June) of the rainy season, which coincided with mid-late spring and mid-late fall, respectively. Horn flies were present on cattle throughout the year in at least 64% of the animals. Mean horn fly numbers on animals did not exceed 85 flies/cow during peaks and were under 35 flies/cow in most of the remaining periods. The highest infestations (population peaks) were short and dropped suddenly within two weeks. Less than 15% of the animals in both herds could be considered as "fly-susceptible" - showing consistently higher infestations, or "fly-resistant" - showing consistently lower infestations.

Evaluation of insecticide ear tags containing ethion for control of pyrethroid resistant Haematobia irritans (L.) on dairy cattle

A field study was conducted in central Argentina to evaluate the efficacy of ear tags containing 36% ethion against pyrethroid resistant populations of Haematobia irritans on grazing dairy cattle. The treated group consisted of 45 milking Holstein cows which received two tags per head and the control consisted of 22 dry cows from the same cohort. Treated and control groups were grazed on similar lucerne pastures separated for a minimum distance of 800 m but they were not isolated from other cattle herds on the same or contiguous properties. In both groups, horn fly estimation were made weekly by examining cattle in the pastures with the aid of binoculars. The percentage reduction of fly numbers on treated cows was considered as efficacy of control provided by the tags. The ethion ear tags provided a range of 85–99% reduction in horn fly numbers for 16 weeks. During this period, the weekly mean number of H. irritans on the tagged cows ranged between 0.44 and 28.26 compared with 143.5 and 239.1 in control animals. The ethion ear tags could be a useful tool for the control of H. irritans mainly in areas where populations of this insect have developed resistance to pyrethroid insecticides.

Mortalidad de la mosca del cuerno Haematobia irritans (L.) causada por el pigmento Floxin B

Loera GJ, Moreno DS, Waldon M, Mendez RA. Tec Pecu Mex 2000,38(3)211-217. The efficacy of phloxine B against the horn fly Haematobia irritans L. was evaluated. Laboratory reared horn flies were utilized. Treatments were composed by phloxine B added to fresh cow blood in proportions of: 500, 1000, 1500, 2000, 2500 ppm, and fresh cow blood alone as a check. Horn flies were maintained in 30x30x30 cm cages, and treatments were applied three times by using cotton sanitary towels positioned at the outside top level of the cages. To retard treatments dessication, cotton sanitary towels were covered with 12 cm in diameter foam dishes. Each treatment was replicated four times. The day after treatments were applied, cages were moved outside of the laboratory to expose horn flies to sunlight from 0700 to 1100. Total numbers of dead horn flies were registered 24 hours after exposed to sunlight, and data were subjected to Probit analysis. Phloxine B, LC50 and LC90 were 1210 and 2042 ppm, respectively. The effectiveness of this dye in the field will be based upon the development of a practical method of application to facilitate its ingestion by the flies.

Emergência de Haematobia Irritans nas massas fecais de bovinos das raças Nelore e Pantaneira no pantanal mato-grossense

Este trabalho foi realizado na Fazenda Nhumirim de propriedade da Embrapa-Centro de Pesquisa Agropecuária do Pantanal, em Corumbá, MS, no período de 11/93 a 05/94, com coletas mensais de massas fecais de bovinos das raças Nelore e Pantaneira, com o objetivo de comparar o número de moscas-do-chifre nas duas raças e determinar qual das duas exerce maior atração sobre a mosca-do-chifre (Haematobia irritans). De 112 fezes bovinas recolhidas de cada raça, observou-se que em Nelore, 107 (95,5%) massas fecais apresentavam pupas de dípteros, e apenas 72 (64,3%) tinham pupas de H. irritans; na raça Pantaneira, das 105 (94,0%) massas fecais com pupas de dípteros apenas 60 (53,6%) apresentavam H. irritans. Os resultados das medições comparativas dos parâmetros comprimento, largura, diâmetro, altura e volume entre as massas fecais demonstraram que não houve diferença significativa (P&gt;0,05). O número de pupas de dípteros coletadas nas massas fecais de bovinos da raça Pantaneira (n=2892) foi maior do que em Nelore (n=1715) (P&lt;0,05). Em relação à H. irritans, observou-se maior número de pupas nas massas fecais de bovinos da raça Pantaneira (n=399) (P&lt;0,05) do que em Nelore (n=237). As massas fecais dos Pantaneiros apresentavam também maior (P&lt;0,05) número total de pupas por volume de fezes. Os resultados indicam que os bovinos da raça Pantaneira exercem maior atração sobre a mosca-do-chifre.

Comportamento da Haematobia irritans em fazendas com diferentes manejos de bovinos

A dinâmica parasitária da Haematobia irritans foi estudada em três fazendas com diferentes tipos de manejo de bovinos mestiços na região de São Carlos, SP, as quais não utilizavam nenhum tratamento específico à mosca. O experimento consistuiu na contagem de mosca na região dorso-lombar a cada 14 dias no período de outubro de 1992 a outubro de 1994. Cada fazenda adotava um tratamento: T1 (Fazenda Ribeirão Bonito, verminose tratada com levamizole-Ripercol L injetável, carrapato com piretróide - Ectoplus "pouron" e berne com trichlorphon-Neguvon + óleo queimado, usotópico); T2(Fazenda São Carlos, verminose tratada com levamizole - Ripercol injetável, carrapato tratado com banho de imersão com formamidina - Triatox e berne com fenthion -Tiguvon "pour on") e T3 (Fazenda Santa Eudóxia - sem tratamento). Os dados de contagem da mosca-do-chifre (MC), na escala √(MC + 0,5), foram analisados em um modelo que incluiu além da média, os efeitos de tratamentos, ano, mês, período e as interações duplas, sendo que todos os efeitos diferiram entre si (P&lt;0,01). Na escala original observou-se que a contagem nos meses de temperaturas mais elevadas (outubro a março), houve uma carga de 15,7 ± 36,4 moscas/animal, enquanto que nos meses de temperaturas mais baixas (abril a setembro) foi de 6,8 ± 23,6 moscas/animal. A média de infestação de moscas/animal diferiu (P&lt; 0,01) entre os anos (92 = 4,8 ± 7,8; 93 = 8,8 ± 20,0; 94 = 16,6 ± 43,8) e entre fazendas (T1= 3,1 ± 9,7 ; T2 = 2,2 ± 13,7 e T3 = 26,0 ± 44,5), mostrando que o comportamento da mosca-do-chifre é irregular e acíclico. Observou-se ainda, uma eficiência (P&lt;0,05) de 81,1% e 86,3% nos tratamentos T1 e T2, respectivamente, quando comparado com o tratamento T3.

Effect of the Red Imported Fire Ant (Hymenoptera: Formicidae) on Dung-Inhabiting Arthropods in Florida

The effect of the red imported fire ant, Solenopsis invicta Buren, on the horn fly, Haematobia irritans L., and other arthropods associated with cowdung was evaluated in northcentral Florida pastures from August to November 1992 and 1993. Workers of S. invicta were found to infest fresh cowpats heavily and prey on horn fly larvae, pupae, and newly emerged adults. After the fire ant populations were controlled with a bait, Amdro (hydramethylnon), the numbers of horn flies and other muscid and sarcophagid flies emerged from cowpats were significantly greater than those from the untreated area. S. invicta caused 94.3 and 62.9% mortality of horn flies for 1992 and 1993, respectively. It also reduced the populations of staphylinid, hydrophilid, and carabid beetles that are predators of horn flies. Despite this negative effect, S. invicta was evaluated as an effective natural enemy of the horn fly.

Effect of the Arthropod Community on Survivorship of Immature Haematobia irritans (Diptera: Muscidae) in North Central Florida

Field mortality of horn flies caused by the arthropod community was tested by seeding colony-reared horn fly (Haematobia irritans L.) eggs underneath artificial cattle pats placed in the field and collecting the emerging flies using cone traps. Mean numbers of horn flies that emerged from pats exposed to the whole arthropod community during the developmental period of the immature stages were significantly lower than those from pats isolated from all members of the community except Solenopsis invicta Buren. The community-caused mortalities of horn flies were 75.9% and 66.7% in July and August 1992, respectively, with an overall average of 71.3%. Predation by S. invicta raised mortality to at least 93.9%. These results suggest that the other arthropods in cattle dung played an important role in reducing horn fly populations in north-central Florida.

Duration of Efficacy of Diazinon Ear Tags and Ivermectin Pour-On for Control of Horn Fly (Diptera: Muscidae)

A 2-yr field study was conducted to develop a model to predict the duration of horn fly, Haematobia irritans irritans (L.), control measures in nonisolated cattle herds. Piecewise regression was used to model the duration of diazinon-impregnated ear tags and it indicated that these provided >90% reduction in horn fly numbers for 50 d. Control rapidly declined thereafter. A logistic model was used to estimate the duration of efficacy of pour-on ivermectin. Ivermectin reduced adult numbers >90% for 8-16 d and >50% for 18-26 d. Ivermectin treatment reduced larval survival in dung >90% for 5-15 d and >50% for 19-24 d. Ivermectin treatment of animals already bearing diazinon-impregnated ear tags did not increase the level of control, but additively increased the duration of control. Average daily gains were not affected by treatment, possibly because horn fly populations were relatively low during the study.

The effects of selection for size in cattle on horn fly population density.

Statistically significant differences were observed in the population density of the horn fly, Haematobia irritans irritans L., on Angus cows having significantly different frame sizes. Angus cows, averaging < 112.5 cm in height at the hip, had significantly lower numbers of horn flies than Angus cows that measured 112.5-117.5 cm, 117.5-120 cm, 120-126 cm and > 126 cm in height at the hip. The Angus I cows ( < 112.5 cm in height at the hip) were significantly shorter in length (mean distance from the withers to the hip bone) and were smaller in girth than the Angus II (112.5-126 cm) and Booneville Angus cows ( > 126 cm). The estimated heritability (h2) of horn fly resistance was 0.43 +/- 0.07 and 0.95 +/- 0.31 for 1989 and 1990, respectively. Horn fly counts on the Angus I herd ( < 112.5 cm in height) was 118.1 (probable breeding value, PBV = -20.69) to 165 horn flies per cow (PBV = 26.9 flies per cow in 1989) and from 75.9 (PBV = -29.1) to 134.5 (PBV = 29.5) flies per cow in 1990. Angus I bulls had PBV = -23.7 to 13.4 and from -26.5 to 14.75 in 1989 and 1990, respectively. The Angus II cows had horn fly counts that ranged from 159.6 (PBV of -23.5) to 208.1 (PBV of 25) per cow in 1989 and from 232.3 (PBV of -56.2) to 378.7 (PBV of 90) per cow in 1990. Angus II bulls had PBVs that ranged from -17.1 to 18.9 in 1989 and from -28.1 to 48.8 in 1990. The Angus I cows had significantly (P < 0.0001) lower numbers of horn flies (mean of 63.8 horn flies per m2) than the small, medium or large Angus II cows (mean of 129.4, 149.6 and 145.5 horn flies per m2, respectively). The data indicated that some specific factor(s) associated with cow size contribute(s) to innate resistance of cattle to the horn fly.