Studies on the feeding patterns of the sheep headfly Hydrotaea irritans (Diptera, Muscidae) in Great Britain

Serum-precipitin tests carried out on the stomach contents of laboratory maintained and field-caught Hydrotaea irritans showed that a positive result could be obtained for at least seven to 10 days after feeding. Eye, nasal and salivary secretions, even if undiluted, did not give a precipitin response in these tests. Field results from over 3000 flies thus indicate that 20 to 55% of the active fly population had taken a blood meal within the previous 10 days: 75 to 100% of these had fed on cattle blood and 15% or less on sheep blood. Significantly lower feeding levels were obtained from flies collected within plantations, indicating a protracted resting phase in woodland. From "fly feeding areas" high blood-feeding levels were shown from early July, as ovarian development begins. Early feeding rates were similar in both sexes.     

Acetylcholinesterase mutation in diazinon-resistant Haematobia irritans (L.) (Diptera: Muscidae)

Acetylcholinesterase (AChE) cDNA from individual field-collected diazinon-resistant horn flies was amplified by RT-PCR. Sequencing of the amplification products revealed that 8/12 of the diazinon-resistant horn flies contained a point mutation previously associated with resistance to organophosphates in house flies and Drosophila, strongly suggesting that this cDNA encodes the AChE that is the target site for organophosphate (OP) pesticide. The point mutation (G262A) resulted in a shift from glycine to alanine in the mature HiAChE amino acid sequence at position 262. Allele-specific PCR and RLFP assays were developed to diagnose the presence or absence of the G262A mutation in individual flies. Use of the allele-specific assays each demonstrated the presence of the G262A mutation in 10 of 12 individual field-collected flies, demonstrating higher sensitivity than direct sequencing of RT-PCR amplification products. The G262A mutation was found in additional fly populations previously characterized as OP-resistant, further supporting that this AChE is the target site for OP pesticide. The allele-specific assay is a useful tool for quantitative assay of the resistance allele in horn fly populations.     

The role of Hydrotaea irritans in the transmission of summer mastitis

A series of experiments to investigate the possible role of the sheep head fly, Hydrotaea irritans, in the transmission of summer mastitis is reported. These showed that the pathogens Actinomyces pyogenes and Peptococcus indolicus may be harboured in the gut of the fly for up to 96 h following a contaminated meal; A. pyogenes survived on the surface of the fly for a similar period. H. irritans fed on the pathogens can contaminate a subsequent meal by regurgitation. However, no infections resulted from repeated exposure of the teats of heifers or cows to H. irritans fed on blood containing A. pyogenes and P. indolicus or on pus from a case of summer mastitis. In these experiments the frequency of feeding of the flies on the teat was high but subsequent bacterial contamination of the teat skin was low. Artificial contamination of the teat skin with greater than 10(6) cfu A. pyogenes led to a low incidence of mastitis even in the absence of cutaneous damage. Repeated applications of lower doses (less than 10(4) cfu) did not produce infection.     

Population dynamics of horn fly, Haematobia irritans irritans (L.) (Diptera: Muscidae), on Hereford cattle in Uruguay

Abundance of adult horn flies, Haematobia irritans irritans (L.), was monitored on 25 untreated Hereford cows in Tacuarembó Department, Uruguay, during three consecutive grazing seasons, from October 1999 to May 2002. The population showed a variable pattern of abundance during three years, with peaks in late summer-early fall of each year. Adult flies were continuously present, although in very low numbers in intervening winters. Numbers of flies per cow rarely exceeded a reference level of 200 flies per animal during the grazing season. Degree-day calculations indicated that approximately 12 generations were possible each year. Time series analysis of mean densities among consecutive generations indicated that population growth was governed by simple, direct density-dependence, with additional effects of seasonally varying weather. Response surface regressions confirmed that intergenerational growth was inversely related to mean density, and directly related to temperature. Stochastic simulations with the response surface model suggested that within the range of temperatures observed in our study, horn fly populations on Hereford cattle will tend toward densities of approximately 150 flies per animal in summer, and exceed a nominal level of 200 flies per cow one or more times in about 65 of every 100 grazing seasons.     

Variation in population density of horn flies (Haematobia irritans irritans) (L.) (Diptera: Muscidae) in Nellore cattle (Bos indicus)

The population density of horn flies was evaluated in the year 1998 in the municipality of Ara?atuba, S?o Paulo Brazil, in relation to temperature and rainfall conditions. Two lots of 30 Nellore steers (Bos indicus) were used which had no insecticidal treatment and were naturally infested with horn flies. The infestations were assessed by two counting methods, i.e., the traditional estimate method and the filming method. The highest fly frequencies were recorded in spring, summer, autumn and the lowest frequencies were recorded in winter. The increase in fly number was positively correlated (P<0.05) with rainfall.     

Validation of a subjective counting method for a horn flies (Haematobia irritans irritans) (Diptera: Muscidae) population in a cattle herd

A trained observer direct count method to measure horn fly population was evaluated to determine the reliability (inter-observer agreement) and its validity when compared with a "gold standard" method (video film). All the counts were performed with the animals restrained in a chute in a single herd. A direct count of horn flies by each of two observers on opposite sides of the animal was made. In addition a videotape recording of the counting surface on each animal was made. Horn flies were counted on 80 cows in the morning twice monthly from 22 October 1999 to 24 March 2000. The correlation between observer counts was high as was the correlation between observer counts and counts made from a videotape recording. Direct counts by trained observers were highly reliable and had good validity. However, videotape recording can be useful when the horn fly population is high, because it is faster in the field than the direct count method. The results of this study suggest that the direct count method can be used with confidence under field conditions.     

Chlorfenapyr ear tags to control Haematobia irritans (L.) (Diptera: Muscidae) on cattle

The efficacy of ear tags containing 30% chlorfenapyr (total tag weight=13g) to control natural Haematobia irritans (L.) infestations was evaluated for Holstein heifers in Rafaela, province of Santa Fe, Argentina. A group of heifers (TG) was treated with two ear tags (one tag per ear). A control group (ACG) was maintained in a paddock adjacent to the TG paddock and, a distant control group (DCG) was maintained 700m apart from the other groups. From day 4 to day 98 after treatment, H. irritans infestations of ACG were significantly higher (P<0.05, test of Kruskal-Wallis) than the corresponding infestation of TG, but significantly lower than infestation in DCG, probably due to the proximity of TG. The chlorfenapyr control period, with an efficacy higher than 90% to reduce horn fly populations, lasted for 9 weeks when TG infestation was compared to fly numbers in ACG, but increased to 12 weeks in comparison to DCG. The results of this study show that ear tags impregnated with chlorfenapyr are a useful alternative to pyrethroids and organo-phosphate compounds for horn fly control.     

Toxicity of cypermethrin and diazinon to Haematobia irritans (Diptera: Muscidae) in its American southern range

Synthetic pyrethroids are considered currently less effective than organophosphate insecticides for controlling Haematobia irritans on cattle in its American southern range. To test the validity of this hypothesis, horn fly populations from 95 cattle herds in central-northern Argentina and southern Brazil were evaluated to determine 50% lethal concentrations (LC(50)) to cypermethrin and diazinon, respectively. Horn flies were exposed to filter papers and glass vials treated with cypermethrin and diazinon, respectively, and LC(50) values were determined using probit analysis. Two and 78 fly populations showed LC(50) values indicating susceptibility and resistance to cypermethrin, respectively, in comparison to historical LC(50) values obtained when the horn fly populations were susceptible to cypermethrin. Five fly populations had an undetermined resistance status to cypermethrin. The diazinon tests showed no obvious indications of H. irritans resistance. Thirty nine percent of farmers still rely on pyrethroids to control horn fly populations on cattle which represents a decreasing proportion from a few years ago when horn fly control was carried out using pyrethroids almost exclusively. Organophosphates could provide control for horn flies resistant to pyrethroids; however, the reliance on chemicals alone to control H. irritans is not considered a proper approach for the future.     

骆驼斯氏副柔线虫病传播媒介西方角蝇和截脉角蝇各虫态的系统形态学研究

本研究旨在完善西方角蝇和截脉角蝇各虫态的系统形态学资料,为野外采集两种角蝇各虫态样本的分类鉴定提供理论依据,进而为研究斯氏副柔线虫在角蝇体内发育过程,以及制定防控骆驼斯氏副柔线虫病的有效措施等奠定基础。通过实验室人工饲养角蝇,收集西方角蝇和截脉角蝇的卵、各龄幼虫、蛹和成蝇,详细观察并描述两种角蝇各虫态的形态结构,以明确两种角蝇各虫态之间的形态学差异。除西方角蝇和截脉角蝇1龄幼虫外,两种角蝇的卵、2龄幼虫、3龄幼虫、蛹和成蝇都存在可识别的形态学差异。本研究详细描述了西方角蝇和截脉角蝇各虫态的形态特征,并确定了多处可用于区分两种角蝇卵、2龄幼虫、3龄幼虫、蛹和成蝇的形态特征差异。     

Cypermethrin pour-on synergized with piperonyl butoxide: effects on Haematobia irritans (Diptera: Muscidae) natural populations resistant to cypermethrin.

Development of pyrethroid resistance in Haematobia irritans in Santa Fe province, Argentina, resulted in an increased use of pyrethroid insecticides, probably due to lack of suitable alternative treatments. We explored the efficacy of mixtures of cypermethrin and piperonyl butoxide (PBO) against pyrethroid-resistant H. irritans. Groups of 25 Holstein cows each, naturally infested with cypermethrin resistant H. irritans were assigned to treated or control groups in April, September, October and December 1997. Cattle in treated groups were medicated with pour-on oil formulations of 5% cypermethrin (dose = 4 mg per kg of body weight) with 5% or 10% PBO in April, and with a mixture containing 5% of both components thereafter. Efficacy was tested for 21 days after treatment. A treatment of 5% cypermethrin pour-on without PBO was evaluated in October 1997. Samples of horn flies were obtained before September, October and December treatments and exposed for 2 h to filter papers impregnated with different cypermethrin concentrations to determine the 50% lethal concentration (LC50). No difference in efficacy was found between cypermethrin pour-on formulations with 5% or 10% of PBO (more than 94% efficacy on day 21 after treatment). Efficacy of 5 % cypermethrin-5% PBO mixture decreased rapidly in the successive treatments (less than 40% efficacy was observed on day 21 after the December treatment), and the period after treatment with an efficacy higher than 95% was 14 days for the treatment carried out in April, 10 days in September; 7 days for the treatment performed in October and 4 days for the December treatment. The LC50 of cypermethrin was 36.6 microg per cm2 in September and increased to 116.6 and 226.1 microg per cm2 in October and December, respectively. It is concluded that the addition of PBO to cypermethrin did not provide a treatment that would give a long term control of pyrethroid resistant-horn flies.     

A study of relative horn fly,Haematobia irritans (Diptera: Muscidae), abundance on Holstein steers and steers of two Holstein crosses

A study was performed to determine if the number of horn fly (Haematobia irritans) adults differ significantly on Holstein (black and white coat color), Holstein x Holstein Friesian (black and white coat color) and Holstein x Jersey (black coat color) steers, 10-12 months old at the onset of the study. All steers were run together on lucerne paddocks and the number of flies counted at 30-day intervals from September 2000 to August 2001. No significant differences (P > 0.05, test of Kruskal-Wallis) were found in fly numbers, even in the period April-May 2001 when the infestation reached its peak. We were unable to demonstrate that coat color influenced horn fly abundance in the present study. It appears that none of the biotypes evaluated had any advantage for natural control of H. irritans.     

Carriage of Corynebacterium pyogenes by the cattle nuisance flies Hydrotaea irritans (Fallén) and Musca autumnalis (De Geer)

Two species of cattle-visiting Muscidae were experimentally contaminated with C. pyogenes, a pathogen involved in the aetiology of summer mastitis. Surface contamination persisted for at least 4 days. Since M. autumnalis would not feed on media containing C. pyogenes the bacterium did not persist internally. All C. pyogenes were eliminated from the gut of H. irritans in 4 days. H. irritans is thus more likely to transmit C. pyogenes than is M. autumnalis but only by mechanical transfer, and is not a true vector.     

Horn fly (Diptera: Muscidae) resistance to organophosphate insecticides

Insecticidal ear tags impregnated with organophosphate (OP) insecticides were used each year from 1989 to 1998 at Rosepine, LA. Weekly fly counts were conducted to evaluate control efficacy of the treatments, and bioassays were conducted at least twice per year to measure fly susceptibility to OP and pyrethroid insecticides. Between 1989 and 1992, the efficacy of 20% diazinon-impregnated ear tags was reduced from >20 to just 1 week of control. A high risk of control failure was observed when a resistance frequency of approximately 5% was measured in pre-season bioassays. Resistance to diazinon, fenthion, ethion, pirimiphos-methyl, and tetrachlorvinphos was observed. Esterase activity toward alpha-naphthyl acetate was significantly higher in flies collected at Rosepine in 1997 than in flies from a laboratory colony and from a susceptible field population.     

Distribution, seasonality and relative abundance of Stomoxys calcitrans (stablefly) (Diptera: Muscidae) in New Zealand

AIMS: To determine the current distribution, seasonality and relative abundance of Stomoxys calcitrans in New Zealand in order to provide information that could be used to assess risks of transmission of equine infectious anaemia (EIA). METHODS: Adhesive yellow traps were distributed to schools throughout New Zealand and used to detect the presence of S. calcitrans between November 1999 and April 2000 at sites considered likely to be a focus for S. calcitrans breeding and activity. In addition, researchers undertook monthly trapping at six other sites between August 1999 and June 2000 to measure the duration and seasonal periodicity of S. calcitrans flight activity. Veterinary practices and farmers were also surveyed to provide anecdotal evidence of the presence or absence of S. calcitrans, particularly in areas where no flies were trapped by schools. RESULTS: Stomoxys calcitrans was found to occur in both North and South Islands, but principally in locations where dairy farming occurred. The fly was active during most months of the year, except perhaps during July and August, and was particularly active in warmer North Island districts such as the Waikato. Peak activity was recorded from January to May. The fly was more abundant in Northland, Auckland, Waikato, the Marlborough Sounds and Nelson than in other districts, as determined by the number of occasions flies were caught relative to the number of traps set. There are only a few areas, such as around Taupo, the Otago Lakes, Central Otago and the Mackenzie Basin, where S. calcitrans was not trapped or, on the basis of anecdotal evidence, thought not to occur. CONCLUSIONS: Given that other potential vectors of EIA are absent from New Zealand, Taupo, the Otago Lakes, Central Otago and the Mackenzie Basin districts could be considered areas of low risk for EIA transmission to horses. In addition, teachers and school children were capable, in most instances, of supporting a nationwide survey providing the methods were simple and the aims few.     

Populational dynamics of Stomoxys calcitrans (Linneaus) (Diptera: Muscidae) in three biocenosis, Minas Gerais, Brazil

Populational flux of the adult phase of Stomoxys calcitrans was observed in the municipal district of Pedro Leopoldo, Minas Gerais, Brazil. Three biocenoses were selected for the study: stable agrobiocenosis, pastural agrobiocenosis and eubiocenosis. The occurrence and the populational flux of the insects, using the Magoon trap for their capture, were established. For each trap located in different biocenoses, a crossbred calf (Bos taurus × Bos indicus) approximately 6-month-old was used as “live bait,” exposed weekly for 48 h in the traps. Of the three agrobiocenoses studied, the stable agrobiocenosis contributed the greatest number of specimens of. S. calcitrans captured, corresponding to 96.9% of the total flies of this species collected. S. calcitrans shows seasonal behavior for approximately 6 months (spring and summer being the rainiest months of the year). The population peaked during the months of November and December. During the months of July and August, there was no capture of flies.     

Development of treated targets for controlling stable flies (Diptera: Muscidae)

Electrocution techniques were used to determine if treated targets similar to those used for tsetse control could be developed for stable fly control. In a series of two experiments, a half blue and half black (UK) 1 m2 target constructed of trigger cotton poplin was determined to be acceptable for development studies. In the first experiment, an average of 350 stable flies per hour (maximum 794 flies in 1 h) was collected using the UK target. A time-delayed circuit trial using untreated UK targets demonstrated that stable flies remained on or around the targets for at least 30 s. Two experiments were conducted with time-delayed circuits and UK targets treated with 0.1% lambda-cyhalothrin. In the first experiment, the number of flies collected using the 30 s on/off treated target treatment was not different from the number of flies collected using the other treatments. In the second experiment, the number of flies collected using the 30 s on/off treated target treatment was not different than the untreated target continuous or 30 s on/off treatments, but was significantly lower than the treated target continuous treatment. The number of flies collected with UK trigger targets was significantly higher than that for alsynite cylinder traps in two experiments. The mean number of flies collected during 22 1h assays using targets was 6.1-fold higher than that for alsynite traps, and the mean number of flies collected during 40 3 h using the targets also was 6.1-fold higher than that for alsynite traps. The results of this study indicate that treated cloth targets may be a viable addition for stable fly control programs.     

Seasonal dynamics of synbovine flies (Diptera: Muscidae) during the grazing period in Jarov

Synbovine flies and the seasonal pattern of their occurrence were studied throughout the grazing period in the cattle pastures of the Strakonice district. Skufin's traps were used for catching the flies. The total number of dipterous insects caught during the series of trappings in two- to three-week intervals was 2096. The family Muscidae (23 species) was represented most amply in the sample catches (Musca autumnalis 65.9%, Hydrotaea Meteorica 20.4%, Hydrotaea irritans 4.2%, Haematobosca stimulans 2.6%). The maximum occurrence of haematophagous species was recorded at the beginning and at the end of the grazing season. The maximum occurrence of secretophagous species was recorded in June.     

Acetylcholinesterase of Stomoxys calcitrans (L.) (Diptera: Muscidae): cDNA sequence, baculovirus expression, and biochemical properties

A 2193-nucleotide cDNA encoding acetylcholinesterase (AChE) of the stable fly, Stomoxys calcitrans (L.) was sequenced and expressed in the baculovirus system. The open reading frame encoded a 91 amino acid secretion signal peptide and a 613 amino acid mature protein with 96% and 94% identity to the AChEs of Haematobia irritans (L.) and Musca domestica (L.), respectively. Structural characteristics of M. domestica, H. irritans, and Drosophila melanogaster AChEs were conserved in the S. calcitrans AChE. The recombinant enzyme was inhibited by eserine, coroxon, and paraoxon and exhibited K_m values of 63.9 μM for acetylthiocholine and 96.7 μM for butyrylthiocholine, confirming its biochemical identity as an acetylcholinesterase (EC 3.1.1.7). These data will enable rapid identification and assay for mutations that reduce AChE sensitivity to organophosphate (OP) pesticides, potentially aiding resistance management efforts to prevent fixation of the mutations in pest populations.     

Some effects of temperature on the adults, eggs and pupae of Stomoxys calcitrans Linnaeus (Diptera: Muscidae)

Adults could only live and reproduce to their full capacity at temperatures between 20 degrees C and 30 degrees C. At 15 degrees C the females laid no eggs, the adult life span was relatively short and the reproductive capacity of females kept at 35 degrees C was low. The thermal histories of the flies had no apparent effect on their later reactions to temperature in any of the parameters tested. The viability rates of S. calcitrans eggs exposed to temperatures between 10 degrees C and 40 degrees C exceeded 84%, but 45 degrees C was lethal. The optimum temperatures for incubation of the eggs was 30 degrees C. Pupae of S. calcitrans seemed to tolerate temperatures between 20 degrees C and 30 degrees C, but their mortalities increased markedly outside this temperature range. Tests showed that pupal mortalities increased linearly with increasing periods of exposure to a temperature of 15 degrees C.