Spodoptera frugiperda larvae stung by Microplitis demolitor undergo ph
ysiological alterations characteristic of parasitism. However, despite
these physiological modifications, parasitized S. frugiperda larvae n
ever yield adult wasps. Our original hypothesis that unsuccessful para
sitism was due to a transcriptionally inactive polydnavirus proved unt
rue. Microplitis demolitor polydnavirus (MdPDV) successfully infected
and expressed, albeit transiently, in S. frugiperda hemocytes. MdPDV e
xpression was most abundant in the first three days of parasitism, the
n sharply declined on Day 4 post-parasitization and continued to decli
ne for the remainder of the study. During the period of MdPDV expressi
on, S. frugiperda hemocytes were non-adherent, incapable of spreading
in vitro and did not encapsulate M. demolitor eggs in vivo. Concurrent
with diminishing viral expresssion, S. frugiperda hemocytes regained
their ability to adhere and spread in vitro and encapsulated M. demoli
tor eggs in vivo. Although MdPDV disrupted S. frugiperda S encapsulati
on response for the first three days post-parasitization, M. demolitor
was unable to develop in this noctuid species. Failure to develop was
independant of viral activity, all M. demolitor eggs oviposited in S.
frugiperda larvae failed to complete embryogenesis and died within 24
hour of oviposition. S. frugiperda larvae infected with MdPDV exhibit
ed alterations in development very similar to other lepidopterans that
are permissive hosts for M. demolitor. In addition, MdPDV DNA persist
ed in Spodoptera frugiperda hemocytes in the absence of viral expressi
on. (C) 1998 Elsevier Science Ltd. All rights reserved.