Parasitic Hymenoptera as biocontrol agents against Calliphoridae causing ovine myiasis (flystrike) in New Zealand

Abstract

Braconid and encyrtid species of Hymenoptera that parasitise larval Diptera have been identified as having potential for use as biocontrol agents in pest management systems that control flystrike in New Zealand.

Four parasitoid species were recorded from numerous dipteran hosts occurring in a variety of habitats including active flystrike lesions, dung and carrion. Aphaereta aotea and Tachinaephagus zealandicus were confirmed in flystrike lesions parasitising Calliphora stygia and Lucilia spp. Samples of dung collected from a large geographic range showed that Hybopygia varia was the most common fly species hosting two parasitoid species while Alysia manducator was reared from L. sericata in a sample of sheep dung. This negates an earlier report that it did not attack dung-inhabiting larvae. A study using laboratory reared mice as carrion exposed in three habitats not only provided the most diverse range of dipteran hosts but all four parasitoid species of interest in this investigation were recorded. A preference for carrion fauna was noted with both Aph. aotea and T. zealandicus preferring carcasses in open pasture, while A. manducator and Phaenocarpa antipoda both showed a preference for a more sheltered bush habitat. There were no new host records from larvae in flystrike lesions, although Takaka was reported as a new locality for Aph. aotea. Seven new host records were obtained from the carrion study where A. Manducator was reared from Lucilia spp., C. hilli and Xenocalliphora hortona. The latter two flies were also new host records both for T. zealandicus and P. antipoda, as was C. vicina for the latter.

In the flystrike lesion habitat, parasitoids are likely to encounter insecticides that have been used as flystrike preventatives. The levels of two of these, diazinon and cyromazine, tolerated by Aph. aotea and T. zealandicus were determined in the laboratory. The effect of anthelminitic residues on parasitoids were ascertained from daily collections of H. varia larvae from untreated and Eprinomectin-treated dung. There were fewer parasitised pupae in faeces from treated cattle.

A number of methods were employed to provide information on the distribution and seasonality of the parasitoids. Both A. manducator and Aph. aotea were recorded in fly traps at a number of South Island sites, providing new locality records for both wasps.

To fully utilise parasitoids in the field a method to detect them in situ in hosts would provide valuable information on the species composition within a region or a habitat. This would be important if a field release of a new parasitoid was contemplated or for augmentation of another species. To ensure the continued successful breeding or interbreeding of new or augmented parasitoids they must be compatible with those already present and with the hosts within that environment. Electrophoresis was shown to provide a method for in situ detection of parasitoids within dipteran larvae and was also used to determine strain differences related to geographic distribution and host origin. Other methods of detection and strain differentiation are discussed. It is concluded that parasitoids might be better used for the control of nuisance flies in 'closed' systems, especially poultry houses. This is because the ability to quantify the effect of parasitoids in an uncontrolled field situation such as flystrike, which is at best an episodic seasonal problem, can pose considerable problems. Nevertheless parasitoids do still have a role to play in flystrike management and may be of considerable importance in reducing the populations of flies emerging from carrion both of livestock, feral and wild animals.