Effect of aggregation of horn fly populations within cattle herds and consequences for sampling to obtain unbiased estimates of abundance

Sheep breed and shearing influences attraction and blood-feeding behaviour of Culicoides (Diptera: Ceratopogonidae) on a UK farm

Background

Culicoides biting midges (Diptera: Ceratopogonidae) are responsible for the biological transmission of arboviruses of international importance between ruminant livestock. These arboviruses include bluetongue virus (BTV) and Schmallenberg virus (SBV), which have emerged in unprecedented outbreaks in northern Europe. The impact of breed and shearing of sheep on Culicoides: host contact rates has not been investigated in detail and has the potential to influence arbovirus transmission and control measures employed to limit spread.

Methods

Attraction of Culicoides to Hartline and Hartline/Suffolk cross-breed sheep was compared using 224 drop trap collections over 22 nights and 181 catches from sheared or unsheared Hartline/Suffolk ewes were made over 17 nights to compare Culicoides activity and rates of blood engorgement.

Results

A total of 31,314 Culicoides was collected in the two trials and females of the subgenus Avaritia represented over 96.9% of individuals collected. Attraction to breed was dependent upon species of Culicoides and physiological status, with a significantly greater number of individuals collected on the cross-breed sheep. Shearing of sheep did not significantly increase or decrease the number of Culicoides attracted but increased the rate of successful engorgement.

Conclusions

Both breed and shearing were shown to influence Culicoides biting rate on sheep. These data are useful in a direct context in understanding the likely impact of control measures against arboviruses including BTV and SBV and additionally in providing data from field-based studies to enable modelling exercises of arbovirus transmission and spread.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3003-5) contains supplementary material, which is available to authorized users.

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.

Salivary gland thrombostasin isoforms differentially regulate blood uptake of horn flies fed on New Zealand White rabbits

Thrombostasin (TS) is a previously characterized anticlotting protein with multiple isoforms found in the saliva of horn flies. In this report, the effect of TS isoforms on blood feeding was assessed using individual flies that carried corresponding ts allelles. Laboratory studies of horn fly blood feeding were conducted using colony-reared flies fed on New Zealand White (NZW) rabbits. After timed 20-min feeding periods, each fly was characterized for gender, blood volume uptake, and ts genotype. The results showed that mean blood volumes obtained by individual flies were not related to fly gender but were correlated to the ts genotype(s) carried by each fly. A fly having one or both ts alleles coding for the TS9 isoform took less blood than those possessing one or both ts alleles coding for the TS10 isoform. These results confirm the significant role that TS plays in horn fly feeding and highlight the differential impact of TS protein isoforms that vary by as few as three amino acids.

World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) guidelines for evaluating the efficacy of ectoparasiticides against biting and nuisance flies on ruminants

These guidelines have been prepared to assist in the planning, conduct and interpretation of studies for the assessment of the efficacy of ectoparasiticides (excluding repellents) against the biting and nuisance dipteran flies of ruminants. Information is provided on the selection of animals, dose determination and dose confirmation studies, field studies, record keeping and result interpretation. These guidelines advocate the use of pen facilities for dose determination and dose confirmation studies. These guidelines also are intended to assist investigators on how to conduct specific studies, to provide specific information for registration authorities involved in the decision-making process, to assist in the approval and registration of new ectoparasiticides, and to facilitate the worldwide adoption of standard procedures.