Location: Mosquito and Fly Research Unit
Title: Procedures to ensure the quality of mass-reared filth fly parasitoids Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: November 8, 2013
Publication Date: N/A
Technical Abstract: Nearly all of the commercially produced parasitoids for management of filth flies are in the genera Muscidifurax and Spalangia. Successful production of these species requires close attention to detail and an understanding of the life history characteristics of each species. High host quality is the first element in parasitoid production. Many recipes are available for economical production of house fly pupae, which can be produced for less than $1 per 10,000 pupae. Fly larval densities need to be managed to ensure colony efficiency without sacrificing host quality. Good quality parasitoids can be produced on pupae weighing at least 15 mg each. Even larger pupae (>20 mg) are superior hosts but seldom worth the extra expense required to achieve body sizes above 18 mg. Similarly, host:parasitoid ratios need to be chosen that ensure high rates of parasitism without causing excessive mortality and male production because of superparasitism. The use of killed hosts for mass-production provides a practical method for stockpiling hosts in preparation for colony expansion. Irradiated pupae have the longest shelf life, followed by heat-killed hosts. Freeze-killed pupae are of lower quality, especially for Spalangia spp., but can be used in emergencies. Superparasitism strategies vary with the species being reared. Solitary Muscidifurax (M. raptor & M. zaraptor) have aggressive first stage larvae that help ensure production of a single healthy adult per host. Spalangia spp. show ovipositional restraint to minimize supernumerary oviposition which results in undersized adult parasitoids. Gregarious species such as M. raptorellus respond to changes in host availability by adjusting the number of eggs deposited per host. Rearing and release of species mixtures can improve efficacy but require strict operational control to avoid contamination of stock colonies. Spalangia spp compete poorly with Muscidifurax spp, and solitary Muscidifurax spp. outcompete M. raptorellus. Nasonia vitripennis is a constant threat that can eliminate any other species within a few generations. Every cohort of reared parasitoids should be given a spot inspection for the presence of contaminants. Colonies should be restarted from field material as often as is practical, as laboratory adaptation can occur rapidly. These effects are not always easy to detect. For example, colonized Spalangia cameroni appears to suffer little loss of fecundity or longevity but its ability to find concealed hosts degrades quickly. Nosema disease is common in colonies of filth fly parasitoids, especially M. raptor and M. zaraptor. Infection rates in field populations are low but disease is rapidly amplified under colonization conditions. Maternal transmission is nearly 100% efficient and mass-rearing conditions exacerbate the risks of horizontal transmission. Disease mitigation protocols are available but careful selection of founding stock to cull infected individuals provides the best assurance of colony health.