COMPARATIVE PATHOGENESIS OF AUTOGRAPHA-CALIFORNICA M NUCLEAR POLYHEDROSIS-VIRUS IN LARVAE OF TRICHOPLUSIA-NI AND HELIOTHIS-VIRESCENS

We compared early viral pathogenesis and dose-mortality relationships for larvae of two highly susceptible hosts, Trichoplusia ni and Heliot his virescens, using a construct of AcMNPV containing the lacZ reporte r gene. Larvae were inoculated either as newly molted fourth instars ( 4(0)) or 15 hr after the molt (4(15)). In 4(0)-inoculated larvae, firs t lacZ expression was detected in the midgut epithelium of T. ni at 4 hr postinoculation (hpi) compared to 18 hpi in H. virescens, and syste mic infections were initiated from tracheole cells servicing the midgu t epithelia beginning at 12 and 20 hpi, respectively The longer viral tenure within the midgut and the slower progression of systemic infect ions within H. virescens ultimately contributed to its longer time to death. For 4(0)-inoculaled H. virescens, proportions of lacZ-expressin g larvae increased from 18 hpi until the onset of the molt to the fift h instar at 36 hpi; at this time point, the proportion of signaling in sects equaled the final larval mortality. Viral infections within the midgut epithelium of H. virescens were lost during the molt to the fif th instar. Dose-mortality relationships suggested that the peritrophic membrane provided little protection from AcMNPV infections for either species. (C) 1995 Academic Press, Inc.