Juvenile hormone analogs greatly increase the production of a nucleopolyhedrovirus

The commercial production of baculovirus insecticides is limited by the need to produce the virus in living insects. The influence of juvenile hormone analogs (JHA) on the growth and survival of Spodoptera exigua larvae placed on treated diet in the fifth instar was examined. Weight increases observed in methoprene- and fenoxycarb-treated larvae were over three-fold greater than that of control insects, whereas other compounds resulted in lower weight gains (pyriproxyfen) or highly variable responses (hydroprene). Approximately 90% and 70% of fenoxycarb and methoprene-treated larvae, respectively, molted to a supernumerary sixth instar and attained a final weight at 8–10 days post-treatment that was approximately double the maximum weight observed in control larvae. Inoculation of fenoxycarb and methoprene-treated sixth instars with a nucleopolyhedrovirus (SeMNPV) resulted in 2.4- or 2.9-fold increases in final weights, compared to control larvae inoculated in the fifth instar. The total yield of SeMNPV occlusion bodies (OBs) per larva was 2.7- and 2.9-fold greater in fenoxycarb- and methoprene-treated larvae, respectively, compared to fifth instar controls. A significant but small increase in the yield of OBs/mg larval weight was observed in fenoxycarb-treated insects but not in the methoprene treatment. The LC₅₀ value of OBs harvested from fenoxycarb-treated insects was slightly higher than that of OBs from control insects, whereas no such difference was observed in OBs from methoprene-treated insects. We conclude that appropriate use of JHA technology is likely to provide considerable benefits for the mass production of baculoviruses.