Following the survivorship of Musca autumnalis DeGeer larvae post parasitization by Paraiotonchium autumnale (Nickle)

The nematode Paraiotonchium autumnale (Nickle) (TYLENCHIDA:SPHAERULARIIDAE), parasitically sterilizes female face flies, Musca autumnalis DeGeer (DIPTERA: MUSCIDAE). The prevalence of parasitism among adult flies has traditionally been used to assess the biological control potential of this nematode species. But, the impact of P. autumnale on M. autumnalis populations in the field cannot be assessed accurately by prevalence of parasitism in adult flies alone. We hypothesize that premature, unrecorded deaths of M. autumnalis parasitized by P. autumnale represent hidden mortality. To detect pre-adult mortality of parasitized flies, laboratory reared M. autumnalis larvae of all instars were exposed to nematodes extracted from flies caught in Browns Valley, California. After 5 hours of exposure, larvae were removed and observed with reflected incident light for nematode movement in their hemocoel to ascertain infection. Exposed, infected larvae were individually reared to adulthood and successful parasitism was reconfirmed by dissection after eclosion. Using a standard life table analysis, we compared survivorship of infected versus non-infected M. autumnalis larvae. Pre-adult mortality of M. autumnalis due to parasitism may change the perception of the value of this parasite in biological control programs.