Biology and management of nosema disease in Muscidifurax raptor (Hymenoptera: Pteromalidae), a pupal parasitoid of muscoid flies

Muscidifurax raptor is a pupal parasitoid of house flies and other filth flies. They are important natural enemies in integrated fly management programs against muscoid flies associated with poultry and livestock production. This parasitoid has been found to be infected with microsporidia in laboratory cultures, in commercial rearing facilities and also in the field where it causes a chronic disease, that reduces fitness and hampers its use as a biological control agent. Studies designed to manage this disease in insect cultures showed that heat shock treatment of infected parasitoid eggs within host puparia at 50°C for 45 minutes resulted in 100% cure and a relative survival of 18%. Heat shock treatment of infected eggs within puparia at 40°C for 1, 3, 5 and 7 hours did not result in significant reduction in the infection level. Continuous rearing of freshly parasitized house fly pupae with infected and uninfected M. raptor at temperatures of 15, 20, 25, 30 and 32°C showed that infected M. raptor had a significantly longer development time than uninfected ones. The differences in development time provided windows for collecting uninfected M. raptor. Also, continuous rearing of freshly parasitized house fly pupae with infected M. raptor at elevated temperatures of 30°C and 32°C did not cause any significant reduction in infection levels although it resulted in significant reduction in the spore concentration of the emerging adults. A 3% solution of albendazole, rifampicin and a mixture of the two when fed to infected adult M. raptor resulted in 20, 40, and 20% reduction respectively, in the infection level of the emerging progeny of host puparia that were exposed to the parasitoids on day 7 post treatment. Host range tests on non-target organisms showed that the spores of N. muscidifuracis readily germinate in a wide range of hosts without causing infection. However they caused infection in Mucidifurax raptorellus, Spalangia gemina, S. cameroni, S. endius, S. nigroaenea and S. cameroni. The infection in all the Spalangia spp. were light and the parasite was transmitted vertically only in M. raptorellus and S. gemina.