Control of sheep flystrike: what's been tried in the past and where to from here

Abstract

Flystrike remains a serious financial and animal welfare issue for the sheep industry in Australia despite many years of research into control methods. The present paper provides an extensive review of past research on flystrike, and highlights areas that hold promise for providing long-term control options. We describe areas where the application of modern scientific advances may provide increased impetus to some novel, as well as some previously explored, control methods. We provide recommendations for research activities: insecticide resistance management, novel delivery methods for therapeutics, improved breeding indices for flystrike-related traits, mechanism of nematode-induced scouring in mature animals. We also identify areas where advances can be made in flystrike control through the greater adoption of well-recognised existing management approaches: optimal insecticide-use patterns, increased use of flystrike-related Australian Sheep Breeding Values, and management practices to prevent scouring in young sheep. We indicate that breeding efforts should be primarily focussed on the adoption and improvement of currently available breeding tools and towards the future integration of genomic selection methods. We describe factors that will impact on the ongoing availability of insecticides for flystrike control and on the feasibility of vaccination. We also describe areas where the blowfly genome may be useful in providing impetus to some flystrike control strategies, such as area-wide approaches that seek to directly suppress or eradicate sheep blowfly populations. However, we also highlight the fact that commercial and feasibility considerations will act to temper the potential for the genome to act as the basis for providing some control options.

Resistance to dicyclanil and imidacloprid in the sheep blowfly, Lucilia cuprina, in Australia

“…Determining whether the P450‐mediated resistance to both dicyclanil and imidacloprid demonstrated in the present study represents cross‐resistance due to common P450 enzymes(s) will be important for designing drug rotation strategies to minimize the rate at which resistance develops. As described by Kotze and James, 2 a component of this capacity to manage resistance will be increased surveillance, thereby allowing chemical‐use decisions to be based on knowledge of what resistances exist in localized blowfly populations in order to prevent further selection pressure on specific chemicals once resistance is detected. The present study highlights the possibility of utilizing molecular diagnostics for dicyclanil and imidacloprid resistance based on the observed increase in transcription of the cyp12d1 gene in the Walgett strain.…”

“…5 Given the dominant position of dicyclanil for flystrike control, resistance to this compound would have a significant impact on the sheep industry. 2 The ongoing usefulness of the alternative chemicals available presently for flystrike control will depend to some extent on whether cross-resistance between dicyclanil and the alternative compounds is present in field blowfly populations. As the structures of dicyclanil and cyromazine are very similar, it is not surprising that cross-resistance between these two chemicals has been reported previously, 9,10 however no other cross-resistances have been reported for the sheep blowfly among the other chemicals currently used for flystrike control.…”

“…Given the dominant position of dicyclanil for flystrike control, resistance to this compound would have a significant impact on the sheep industry 2 . The ongoing usefulness of the alternative chemicals available presently for flystrike control will depend to some extent on whether cross‐resistance between dicyclanil and the alternative compounds is present in field blowfly populations.…”

“…reduced wool growth and bodyweight gain, and animal death) and costs associated with treatment and prevention 1 . Flystrike control relies largely on the use of insecticides 2 . These chemicals are generally applied as prophylactic treatments given in advance of fly waves, although some also are used as dressing treatments on existing strikes.…”

“…1 Flystrike control relies largely on the use of insecticides. 2 These chemicals are generally applied as prophylactic treatments given in advance of fly waves, although some also are used as dressing treatments on existing strikes. The insecticides currently used for flystrike control belong to various chemical classes: pyrimidine (dicyclanil), triazine (cyromazine), macrocyclic lactone (ivermectin), neonicotinoid (imidacloprid), synthetic pyrethroid (alpha-cypermethrin), spinosyn (spinosad) and organophosphates (diazinon, chlorfenvinphos).…”