Food utilization values of gypsy moth Lymantria dispar (Lepidoptera : lymantriidae) larvae infected with the Microsporidium Vairimorpha sp (Microsporidia : burenellidae)

Infection of the gypsy moth, Lymantria dispar, with the microsporidium Vair imorpha sp, strongly influences the development of the host in ways typical of many species of terrestrial entomopathogenic Microsporidia; growth is r educed while development time is extended in infected insects. The appearan ce of the different stages of the parasite in the host relative to the elap sed time after oral infection, as well as the influence of the parasite pro liferation on food utilization of the host, were examined. At 3 days postin fection, midgut muscle cells were infected with primary spores, and the fat body tissues contained meronts, sporonts, and primary spores. Many more fa t body cells contained vegetative stages and primary spores at 4 and 5 days postinfection, and diplokaryotic spores and immature octospores were also present. Approximate digestibility of infected larvae increased during this time period, whereas the conversion of ingested and digested food to body substance decreased. The relative growth rate of infected and uninfected gr oups did not differ significantly between 4 and 5 days postinfection, altho ugh the relative consumption rate in infected L. dispar larvae was higher. Between 8 and 10 days postinfection, the relative growth rate of uninfected larvae increased. The infected group did not demonstrate this increase at a time period characterized by maturation of diplokaryotic spores and octos pores in larval fat body tissues. Total body weight of uninfected larvae re mained higher than that of infected larvae after 8 days postinfection. (C) 2000 Academic Press.