Interactive response of the horn fly (Diptera: Muscidae) and selected breeds of beef cattle

Statistically significant differences were observed in the population density of the horn fly, Haematobia irritans irritans (L.), on different breeds of beef cattle. The European breed Chianina had a population density of horn flies generally less than or equal to 50% than that of the British cattle breeds (Angus, Hereford, Polled Hereford, and Red Poll) and another European breed (Charolais). Generally, no significant difference existed among numbers of horn flies on Hereford, Polled Hereford, and Red Poll cows in 1988 or among Angus, Hereford, Polled Hereford, and Red Poll cows in 1989. Factors other than color appeared to be involved in the selective process between the horn fly and its host. Population densities on two white European breeds (Charolais and Chianina) were significantly different on all weekly intervals except for 4 wk in both 1988 and 1989. No significant difference existed among Charolais and British breeds except during 4 wk in 1988 and 3 wk in 1989. When weaning weights of all calves were adjusted for the effects of age to 205 d, sex of calf, and age of dam, the indirect effect of the horn fly on weaning weight showed a significant linear regression. Each 100 flies per cow caused a reduction of 8.1 kg in calf weaning weight. Cows within each breed with low numbers of horn flies weaned significantly heavier calves than cows with higher numbers of horn flies.     

The effects of hair density of beef cattle on Haematobia irritans horn fly populations

Abstract We show the relationships that exist between the amount of hair and quantity of sebum on cattle skin and the population density of the horn fly, Haematobia irritans. Brahman and Chianina steers had means of 2390 and 1587 hairs per cm², respectively, significantly more than the mean number of hairs on Angus, Brahman x Angus Crossbred, Charolais, and Red Poll steers. The Chianina steers had > 30% more sebum present on their skin and hair (0.58g/929cm²) than the Angus, Charolais, and Red Poll steers at the Beef Cattle Research Station Savoy, Arkansas. The Brahman steers had a significantly greater amount of sebum present on the skin (1.51 g/ 929 cm²) than the Crossbred and purebred Angus steers (0.55 and 0.25g/929cm², respectively) at the South Central Family Farms Research Centre Booneville, Arkansas. The Brahman and Chianina steers had means of 61.9 and 17.0 horn flies per steer, respectively, during the fly season, whereas the Angus, Crossbred, Charolais and Red Poll steers had fly season means that ranged from 76.9 to 265.8 flies per steer. Regression analysis showed that an increase of 100 hairs per cm², was associated with a reduction of 11 horn flies in the Angus II, 5 in Angus I, 20 in Charolais, 37 in Red Poll, and 0.4 in Chianina steers at the Savoy Station and a reduction of 6.6 horn flies for the Angus, Brahman, and Crossbred steers at the Booneville Centre. Regardless of cattle breed, an increase of 1.0 g of sebum per 929 cm² output by the steer was associated with 478.5 additional hairs per cm² on the animal. Each increase of 0.25 g of sebum per 929 cm² resulted in a decrease of 9.2 horn flies per steer. We conclude that some of the factors responsible for fly-resistance in cattle are hair density and the corresponding amount of sebum present on cattle skin and hair.     

Estimation of the effects of buffalo fly (Haematobia irritans exigua) on the milk production of dairy cattle based on a meta-analysis of literature data

Published reports on the effect of buffalo fly Haematobia irritans exigua De Meijere (Diptera: Muscidae) and the closely related horn fly (H. irritans) were examined and analysed using non-linear weighted regression techniques in an attempt to establish the relationship between daily production loss (D), average number of parasites (n) and the average damage per parasite per day (d), and to provide estimates of expected losses in milk yield (MYD) and live-weight gain (LWG) in dairy cattle. A Mitscherlich three-parameter model was used to explain the relationship between the total loss of production attributable to buffalo flies and the average number of flies associated with cattle. This model was significant (P<0.01), with R2 = 20.2% and predicted a threshold number of flies (n = 30) below which no adverse effects would be noted. At a moderate level of infestation (n = 200) dMYD was 2.6 ml/fly/day and dLWG was 0.14 g/fly/day, resulting in estimated daily losses in milk yield (D(MYD)) and live-weight gain (D(LWG)) of 520 ml and 28 g, respectively.     

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 approximately 150 horn flies per cow. These data demonstrated the efficacy of using tactic combinations to manage insecticide-resistant horn fly populations.     

High levels of pyrethroid resistance in horn flies (Diptera: Muscidae) selected with cyhalothrin.

Lambdacyhalothrin cattle ear tags controlled horn fly, Haematobia irritans (L.), for 14 wks or longer during 1986-1988 in Georgia, USA. In 1989 and 1990, control of < 50 horn flies per side of cow was achieved for < or = 4 wk because of high levels of pyrethroid resistance in horn flies selected with lambdacyhalothrin. The highest resistance ratios (RRs) were seen in 1989. These were 498 for lambdacyhalothrin; 92,000 for fenvalerate; and 54 for permethrin. RRs for cypermethrin as high as 8,800 were estimated in 1990 when the RR for fenvalerate was only 1,060. No cross-resistance to diazinon was detected. These high levels of pyrethroid resistance seem to have a large component of metabolic resistance. Synergistic coefficients as high as 3,600 were determined by addition of nonlethal amounts of piperonyl butoxide. Resistance development in a no-pyrethroid-use area indicates movements of > or = 3km by sufficient numbers of horn flies can significantly change the RR.     

Skin lesions and cattle hide damage from Haematobia irritans infestations

The horn fly Haematobia irritans L. (Diptera: Muscidae) has recently spread to Argentina and Uruguay and is believed to cause damage to cattle hides. Four groups of ten Holstein steers each were maintained for 58 weeks under different infestation levels with H. irritans to determine if it was the cause of this problem. Hides (chrome tanned) from steers maintained under minimum infestation level had 4.7 +/- 3.8% of the area damaged. Maintaining the steers under low H. irritans level for the last 44 days of the trial using insecticidal ear-tags, resulted in 29.5 +/- 15.8% of hide area being damaged. Steers that were treated with 5% cypermethrin pour-on, when the H. irritans population was close to 50 flies, showed that 31.3 +/- 16.6% of hide area was injured, and 46.6 +/- 12.8% of damaged hide area was found in hides from non-treated steers. Significant differences were found between mean hide damage from steers maintained continuously under low H. irritans infestation levels and all other groups. Hyperaemia was significantly lower in the skin of steers under low H. irritans infestation level than in the skins of non-treated steers and steers maintained under low-level infestations for the final 44 days. Eosinophil and mononuclear cell infiltration was significantly lower when the population of H. irritans was less than six per steer than when the population was more than 100 flies per steer. Low numbers of Stomoxys calcitrans were found in all groups, but most hide damage was presumed due to H. irritans.     

Dynamics of cypermethrin resistance in the field in the horn fly,Haematobia irritans

The toxicity of cypermethrin to the horn fly Haematobia irritans (L.) (Diptera: Muscidae) was determined for samples collected from untreated herds at a farm in central Argentina from October 1997 to May 2001. Field tests of the efficacy of cypermethrin against horn flies were first carried out at this farm in 1993, when the fly was shown to be susceptible to pyrethroids. Subsequently the horn fly populations on this farm were shown to have become resistant and, since 1997, the use of cypermethrin has been restricted to experimental purposes. In this study, fly samples collected in 1999, 2000 and 2001 were subjected to a polymerase chain reaction (PCR) to detect the presence of a specific nucleotide substitution in the sodium channel gene sequence, which has been associated with target site insensitivity to pyrethroids. This analysis showed that the level of cypermethrin resistance had diminished between 1997 and 2001. However, this was not sufficient to restore the efficacy of this pyrethroid to the level found prior to the onset of resistance. Heterozygous and homozygous resistant flies were detected in all samples of flies subjected to PCR diagnosis of alleles conferring target site resistance.     

Survival, ovarian development and bloodmeal size for the horn fly Haematobia irritans irritans reared in vitro

Horn flies, Haematobia irritans irritans (Linneaus) (Diptera: Muscidae) were reared in vitro using cattle, pig, horse, rabbit, sheep, goat or chicken blood. The highest survival, bloodmeal size and rate of ovarian development were recorded for both female and male flies fed cattle blood. Flies fed pig, rabbit, sheep and goat blood showed intermediate survival. Flies fed chicken blood showed the lowest survival rates, ingested the smallest bloodmeals and did not develop ovaries. The relationship between dietary factors and host specificity of the horn fly, and the efficiency of vertebrate blood source of several animals for laboratory colonization of horn fly are discussed.     

Variation in the load of the horn fly, Haematobia irritans, in cattle herds is determined by the presence or absence of individual heifers

The distribution of horn flies, Haematobia irritans (L.) (Diptera: Muscidae), in herds of Danish Holstein-Friesian cattle was investigated in two studies conducted during two field seasons. In the first study, highly significant differences in fly distribution between the most and the least fly-susceptible heifers were observed. In one herd, the mean difference between the most fly-susceptible and the most fly-resistant heifers was 268 Ha. irritans specimens. The highest ratio between upper and lower mean fly number was 64.1:1, whereas the lowest was 3.1:1. In the second year, it was demonstrated that the heifers kept their rank in fly attraction over time. The trial clearly demonstrated that some heifers were attracting flies, whereas others, even in the same herd, only carried a few. In the second study, heifers were moved in and out of herds in an attempt to manipulate fly loads in the herds. In year 1, one herd (herd A) received four fly-resistant heifers from another herd (herd B), resulting in a drop in the mean number of flies, whereas herd B received four fly-susceptible heifers from herd A, resulting in an elevation of the mean number of flies. In year 2, a similar pattern emerged using herds C and D, and when the cattle were later returned to their original herds, the fly loads returned to their original distribution. The data presented here show unequivocally that, for horn flies, there can be considerable differences in fly loads for individual heifers within the Holstein-Friesian breed. Furthermore, the overall fly load within herds can be manipulated, and can be reversed. Thus, the distribution in the number of flies within a herd appears to depend on the number of fly-resistant or fly-susceptible heifers. The possible role of chemical factors emitted by heifers, i.e. volatile semiochemicals, in determining differences in fly loads is discussed, whereby attractants are emitted by fly-susceptible heifers and enable flies to locate their host, and repellents are emitted by fly-resistant heifers such that the flies are actively repelled from the herd.     

Effects of citrate, heparin and cation supplementation on mortality and egg production of laboratory-reared horn flies

Abstract. The effects of the blood anticoagulants sodium citrate and sodium heparin on horn fly, Haematobia irritans L., egg production were tested. Sodium citrate was added to freshly collected bovine blood to give final concentrations of 5-100mM while sodium heparin was used in concentrations of 10–70 USP units/ml blood. Small cages containing five male and ten female newly emerged laboratory-reared horn flies were maintained for 8–10 days on these blood samples, and mortality and egg production recorded daily. Results showed that as blood citrate concentration was increased, egg production decreased logarithmically. At sodium citrate concentrations of 50 mM and above, severe impacts on egg production and adult horn fly survival occurred. Although no dose-related response of egg production to increasing heparin concentrations was noted, the 25 USP units heparin/ml blood treatments gave the largest egg production, yielding approximately 28% more eggs than any other treatment. Since citrate is a known chelator of divalent metal cations, the effects of supplemental cation additions to citrated blood were tested for their ability to reverse the egg production decrease seen at 50 mM sodium citrate. Blood samples containing 50mM sodium citrate were supplemented with CaCl₂, calcium lactate, CuCl₂, cupric acetate, FeCl₃, ferric citrate, MgCl₂, magnesium acetate, MnCl₂, ZnSO₄, EGTA or EGTA plus calcium lactate, each at 1 mM except EGTA which was used at 2.5 mM. The magnesium acetate supplement and the combination of calcium lactate plus EGTA resulted in a statistically significant increase in egg production ( P < 0.05).     

Behavioural responses of dairy cattle to the stable fly, Stomoxys calcitrans, in an open field environment

Individual cows (25 in each of four herds) were monitored 8-10 times weekly for 12 weeks (stable fly season) on a southern California dairy, with 100 observations per cow. The numbers of biting stable flies, Stomoxys calcitrans (L.) (Diptera: Muscidae) on the front legs and the frequencies of four fly-repelling behaviours per 2-min observation period [head throws, front leg stamps, skin twitches (panniculus reflex) and tail flicks] were recorded. Fly numbers varied, peaking at 3.0-3.5 flies per leg in week 9 (late May). Weekly herd mean frequencies of fly-repelling behaviours were highly dependent on fly numbers, with a linear regression r(2) > 0.8. Head throws and stamps were less frequent than skin twitches and tail flicks. Individual cows differed in numbers of stable flies and behaviours. Behaviours were correlated with flies for individual cows, but at a lower level than were herd means (r = 0.3-0.7). Cows that stamped more within a herd tended to have lower fly counts; other fly-repelling behaviours were less effective. Cows maintained ranks within a herd with regard to fly numbers (r = 0.47), head throws (0.48), leg stamps (0.64), skin twitches (0.69) and tail flicks (0.64). Older cows tended to harbour higher fly numbers and to stamp less relative to younger adult cows. Ratios of leg stamps and head throws to fly numbers dropped significantly through time, suggesting habituation to pain associated with fly biting. Tail flicks were not effective for repelling Stomoxys, but were easiest to quantify and may help in monitoring pest intensity. At this low-moderate fly pressure, no consistent impacts on milk yield were detected, but methods incorporating cow behaviour are recommended for future studies of economic impact.     

Abundance of stable flies on heifers treated for control of horn flies with organophosphate impregnated ear tags

Ear tags containing 40% organophosphate insecticides (diazinon or diazinon plus chlorpyrifos-ethyl) were applied to control Haematobia irritans (L.) (Diptera: Muscidae) in treated (TG01 and TG02) and untreated (UG01 and UG02) groups of Holstein heifers born in 2001 and 2002, respectively. Control and treated groups were assessed for the abundance of Stomoxys calcitrans (L.) (Diptera: Muscidae) from August 2001 to April 2002 and again from August 2002 to April 2003. The treatment had a high efficacy for control of horn flies (maximum median number per heifer of TG01 and TG02 = 5) but a low effect on the abundance of stable flies. The total numbers of S. calcitrans were 1251 (42.9% of the total) and 1668 (57.1%) for TG01 and UG01, and 1423 (48.8%) and 1494 (51.2%) in TG02 and UG02, respectively. No significant difference in stable fly burden was found in 55 of the 76 weeks evaluated. A unimodal peak of abundance in the spring was found during the first fly season, and a bimodal abundance, with peaks in the spring and autumn, during the second season. No strong associations between horn fly and stable fly burdens was found in individuals of the CG01 (correlation coefficient = 0.13, P > 0.05) or CG02 (correlation coefficient = 0.538, P < 0.05, determination coefficient = 0.289).     

Insecticide resistance in the horn fly: alternative control strategies

Abstract.  The horn fly, Haematobia irritans (Linnaeus 1758) (Diptera: Muscidae) is one of the most widespread and economically important pests of cattle. Although insecticides have been used for fly control, success has been limited because of the development of insecticide resistance in all countries where the horn fly is found. This problem, along with public pressure for insecticide-free food and the prohibitive cost of developing new classes of compounds, has driven the investigation of alternative control methods that minimize or avoid the use of insecticides. This review provides details of the economic impact of horn flies, existing insecticides used for horn fly control and resistance mechanisms. Current research on new methods of horn fly control based on resistant cattle selection, semiochemicals, biological control and vaccines is also discussed.     

Azadirachtin as a larvicide against the horn fly, stable fly, and house fly (Diptera: Muscidae)

Effects of azadirachtin, a triterpenoid extracted from neem seed, Azadirachta indica A. Juss., were similar to those of insect growth regulators against the immature stages of the born fly, Haematobia irritans (L.), the stable fly, Stomoxys calcitrans (L.), and the house fly, Musca domestica L. When an ethanolic extract of ground seed was blended into cow manure, LC50 and LC90's for larval horn flies were 0.096 and 0.133 ppm azadirachtin, respectively. An emulsifiable concentrate (EC) had an LC50 for larval horn flies of 0.151 ppm and an LC90 of 0.268 ppm. For larval stable flies, the EC formulation had an LC50 of 7.7 ppm and an LC90 of 18.7 ppm azadirachtin in manure. Against larval house flies, the LC50 and LC90 were 10.5 and 20.2 ppm, respectively. When the EC formulation was administered orally to cattle at a rate of greater than or equal to 0.03 mg azadirachtin per kg of body weight per day or when ground neem seed was given as a daily supplement of greater than or equal to 10 mg seed per kg body weight, horn fly development in the manure was almost completely inhibited. In contrast, ground seed mixed in cattle feed at the rate of 100-400 mg seed per kg of body weight per day caused less than 50% inhibition of stable flies in the manure.     

The prevalence of Stephanofilaria sp. in buffalo fly, Haematobia irritans exigua, in Central Queensland

Abstract  Buffalo fly ( Haematobia irritans exigua ) infestations of cattle are associated with characteristic lesions, the initial cause of which has been attributed to a filarial nematode of the genus Stephanofilaria , for which the fly acts as a vector. Survey work in the 1980s estimated the prevalence of microfilaria in female buffalo fly in Queensland at 2.91%. Since then no information has been published and the current prevalence of microfilarial infection in buffalo fly is not known. Buffalo fly were collected from four geographically distinct sites in Central Queensland in mid-summer 2004 and were dissected to estimate Stephanofilaria sp. infection rates . Larval stages of the nematodes were recovered from female flies from all four sites and the percentage of female flies from which nematodes were recovered ranged from 29% to 57%. The average number of larvae recovered from infected female flies ranged from 1.25 to 1.75. Whereas no infected male flies were found from Sites 2–4, larvae were recovered from 43% of male flies collected at Site 1. This high prevalence of filarial infection in buffalo flies implies a correspondingly high level of transmission to cattle in Central Queensland.     

Effects of horn fly and house fly (Diptera: Muscidae) larvae on the development of parasitic nematodes in bovine dung

Laboratory studies were conducted to determine the effects of horn fly, Haematobia irritans (L.), and house fly, Musca domestica L., larvae on the development of a mixed population of parasitic nematodes in compressed and crumbled bovine dung. Fresh dung (100 g per sample) from a single calf passing trichostrongyle type eggs was infested with 150 horn fly or 150 house fly eggs. After 14-15 d, more horn flies and house flies had emerged from the compressed dung than from the crumbled dung, but more third stage parasitic nematode larvae were recovered from the crumbled dung containing either fly species than from dung containing no flies.     

Managing the horn fly (Diptera: Muscidae) using an electric walk-through fly trap

An electric walk-through fly trap was evaluated for the management of the horn fly, Hematobia irritans (L.), on dairy cattle in North Carolina over 2 yr. The trap relies on black lights and electrocution grids to attract and kill flies that are brushed from the cattle passing through. During the first season, horn fly densities were reduced from >1,400 to <200 flies per animal. Horn fly density averaged 269.2 +/- 25.8 on cattle using the walk-through fly trap twice daily, and 400.2 +/- 43.5 on the control group during the first year. The second year, seasonal mean horn fly density was 177.3 +/- 10.8 on cattle using the walk-through fly trap compared with 321.1 +/- 15.8 on the control group. No insecticides were used to control horn flies during this 2-yr study.     

Accessibility of blood affects the attractiveness of cattle to horn flies

The burden of infestation of the horn fly, Haematobia irritans (Linnaeus) (Diptera: Muscidae), differs among bovines within the same herd. We hypothesized that these differences might be related to the epidermal thickness of the cattle and the blood intake capacity of the fly. Results showed that dark animals carried more flies and had a thinner epidermis than light‐coloured animals, which was consistent with the greater haemoglobin content found in flies caught on darker cattle. Similarly, epidermal thickness increased with body weight, whereas haemoglobin content decreased. Overall, we suggest that accessibility of blood is a factor that partially explains cattle attractiveness to flies.     

The Morgan Recharger: a new horn fly (Diptera: Muscidae) control device for beef cattle

A 20% diazinon formulation was evaluated for control efficacy against the horn fly, Haematobia irritans (L.), in the Morgan Recharger (Morgan International Products, College Grove, Tenn.). The Morgan Recharger releases insecticide with a wicking system from an insecticide reservoir and can be attached to an animal's ear or tail. This device was most effective against the horn fly when used as an ear tag with two per head; horn fly counts did not exceed five flies per side through 8 wk. The diazinon formulation tested was released from the Morgan Recharger at a decreasing rate. The problems and potential of the Morgan Recharger as an effective horn fly control device are discussed.     

Effect of temperature on toxicity of three pyrethroids to horn flies

Predictive models describing best-fit regression equations for per cent mortality of horn flies as a function of temperature were determined for each of three pyrethroid insecticides (fenvalerate, flucythrinate and permethrin) over the temperature range 20-35 degrees C. Susceptible horn flies, Haematobia irritans (L.), were exposed to c. an LC70 dose of each pyrethroid using a residue-on-glass method. This technique used confined exposure in chambers with temperatures of 20, 25, 30 and 35 degrees C. Within this range, mortality was greatest at 25 degrees C with all three insecticides. Estimated temperature-mortality equations for each pyrethroid revealed different responses of horn flies to each of these insecticides. Horn flies exposed to flucythrinate demonstrated a linear mortality response that varied inversely with temperature. The response to permethrin was described by a quadratic equation, while the response to fenvalerate was best fitted by a cubic equation.