IN-VIVO PRODUCTION, STABILIZATION, AND INFECTIVITY OF BACULOVIRUS PREOCCLUDED VIRIONS

Wild-type and polyhedrin-negative isolates of Autographa californica n uclear polyhedrosis virus were replicated in fifth-instar Trichoplusia ni larvae. Insect tissues infected with wild-type virus contained two types of virions that are highly infectious when ingested, those occl uded in polyhedra and preoccluded virions, Tissue infected with the po lyhedrin-negative virus contained only preoccluded virions, The relati ve potencies of the two types of infected tissue were determined by do se-mortality bioassays by using the neonate droplet feeding procedure, On a fresh weight basis, preparations of tissues infected with the po lyhedrin-negative virus were approximately four times more potent than equivalent preparations of tissue infected with wild-type virus. Appr oximately half of the observed potency of the wild-type-virus preparat ions was due to polyhedra, and the remaining activity was due to preoc cluded virions present in the tissue. The potency of the polyhedrin-ne gative preparations was not reduced significantly by lyophilization, T he polyhedrin-negative isolate produced about 60% more infectious viru s per unit of larval weight than did the wild-type isolate, The abilit y to produce large amounts of high-potency viral preparations in larva e and the convenience of being able to lyophilize the preparations for long-term storage shows promise for the use of preoccluded virus prep arations as biopesticides.