BEHAVIOR AND SURVIVAL IN CORN PLANTS IN OSTRINIA-NUBILALIS (LEPIDOPTERA, PYRALIDAE) LARVAE WHEN INFECTED WITH NOSEMA-PYRAUSTA (MICROSPORA, NOSEMATIDAE) AND PARASITIZED BY MACROCENTRUS-GRANDII (HYMENOPTERA, BRACONIDAE)

To clarify the interaction among the European corn borer, Ostrinia nub ilalis, the parasitic wasp, Macrocentrus grandii, and the entomopathog en Nosema pyrausta, we examined behavior and survival in corn stems of O. nubilalis larvae infected with N. pyrausta and parasitized by M. g randii. Fifty-four percent of heavily infected, parasitize O. nubilali s larvae emigrated from their tunnels before emergence of parasitoid l arvae and did not reestablish on corn plants. One-third as many heavil y infected host larvae as noninfected larvae remained in tunnels until parasitoid larval emergence. The tunnels bored by infected, parasitiz ed O. nubilalis larvae did not differ in length from those of noninfec ted parasitized larvae, suggesting that emigration behavioral changes occur after feeding. Parasitoid larval and pupal mortalities were grea ter in infected O. nubilalis hosts than in noninfected hosts. Greater than 46% of heavily infected M. grandii broods wandered instead of rem aining clustered around host carcasses and pupating. This behavior acc ounted for almost almost-equal-to 40% of the observed mortality in inf ected parasitoids. Wandering was attributed to decreased production of cocoons by hosts, causing parasitoid larvae to search for suitable su bstrates on which to spin their own cocoons. Percentage emergence of M . grandii adults from com stalks was significantly lower in N. pyraust a-infected treatments, but the sex ratio of the parasitoid was unaffec ted by the level of host infection. The mean number of M. grandii adul ts per brood was reduced from 39.8 in the noninfected treatment to 10. 5 in heavily infected larvae.