Hymenopteran pupal parasitoids attacking filth flies in Florida

Livestock producers often use pupal parasitoids to aid in control of filth fly populations. However, many studies present conflicting results regarding the success of parasitoid release programs. Several factors responsible for these disparities may include differences in season, temperature, substrate moisture, host density and depth, and manure-substrate types utilized by filth flies. Other factors, such as parasitoid species competition or dispersal patterns may also affect the outcome of a parasitoid release program. Because differences in habitat type, suitable breeding substrate, and facility size exist between livestock installations, the abundance and species composition of resident parasitoids may also differ. Therefore, it is important to consider all factors that may contribute to the efficacy of a parasitoid-based, fly control program before one is initiated. To accomplish this, parasitoid populations may be sampled using sentinel or field collected pupae prior to the release program. This preliminary survey may elucidate species already adapted to the area, which may result in greater success when released. Filth fly pupae were collected from four farms to determine the parasitoid species composition and naturally-occurring parasitism rates at Florida equine facilities. Because Spalangia spp. were most often recovered from field sites, the ability of Spalangia cameroni, Spalangia endius, as well as Muscidifurax raptorellus to locate stable fly hosts was evaluated under laboratory conditions. No significant differences were detected between parasitoid species when pupae were freely accessible. However, significantly more pupae were attacked by both Spalangia spp. than by M. raptorellus when forced to search for hosts within a substrate.