Evaluation of Remediation Methods for <I>Nosema</I> Disease in <I>Muscidifurax raptor</I> (Hymenoptera: Pteromalidae)

Abstract

Several methods were investigated for managing Nosema disease in the parasitoid Muscidifurax raptor Girault and Sanders. Treatment of parasitoid eggs or pupae within host puparia with gamma radiation from a cesium-137 source were either lethal to the parasitoids at all dosages tested (eggs) or failed to reduce infection rates (pupae). Exposure of parasitoid eggs within host puparia to heat was effective at several temperatures and exposure times. Optimal results for disease reduction were achieved with a 5-h exposure to 45°C, which resulted in no infection in the resulting adult parasitoids. Continuous rearing at elevated temperatures (30 and 32°C) for three generations resulted in decreased spore loads in infected parasitoids but did not reduce infection rates. Incorporation of the drugs albendazole and rifampicin into rearing media of the parasitoid’s host (house fly immatures) resulted in pupae that were of poor quality and did not reduce infection rates in parasitoids that developed in flies reared on drug-treated media. Treatment of adult parasitoids with 3% albendazole and/or rifampicin resulted in decreased rates of transovarial transmission of the disease. Transmission blockage required 3–7 d of exposure to the drug before substantial treatment effects were manifest. Parasitoids that fed for 7 d on rifampicin-treated honey transmitted the disease to 57.7% of their progeny compared with a 99.1% transmission rate among untreated parasitoids. An uninfected colony of M. raptor was established by pooling cured parasitoids from heat shock and drug treatment experiments. Parasitoids from the uninfected colony lived longer and produced over twice as many female progeny (201.2) as infected parasitoids (85.2).