Juvenile hormone analogs greatly increase the production of a nucleopolyhedrovirus Rodrigo Lasa, Primitivo Caballero, Trevor Williams * Departamento de Produccio ´ n Agraria, Universidad Pu ´ blica de Navarra, Pamplona 31006, Spain Received 13 December 2006; accepted 21 February 2007 Available online 2 March 2007 Abstract 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). Approxi- mately 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 LC 50 value of OBs harvested from fenoxycarb-treated insects was slightly higher than that of OBs from control insects, whereas no such dif- ference 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. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Baculovirus production; Fenoxycarb; Insect weight gain; Methoprene; Spodoptera exigua; Supernumerary instar 1. Introduction The commercial production of baculovirus insecticides is limited by the need to produce the virus in living insects. This necessitates a large and productive insect colony as a source of healthy larvae that can be inoculated with lethal amounts of virus occlusion bodies (OBs) and later har- vested as moribund or dead infected insects. Previous attempts to improve the efficiency of virus production pro- cesses have focused on the development of suitable insect rearing containers (Hughes, 1994; Ignoffo and Boening, 1970; Vail et al., 1973), reducing the handing times required for certain aspects of the process (Bell et al., 1981), optimization of the quantity of inoculum (Cherry et al., 1997), the rearing temperature (Ignoffo, 1966; Shapiro et al., 1981c), and the timing of harvesting of infected insects (Cherry et al., 1997; Shapiro, 1986). Similar efforts to reduce the direct costs of virus produc- tion have examined the benefits of modifying the ingredi- ents and their relative abundance in artificial diets for rearing infected larvae (Bell et al., 1981; Hunter-Fujita et al., 1998; Shapiro et al., 1981a), and the use of alterna- tive host species that are easy to rear or that produce large larvae (Kelly and Entwistle, 1988; Tompkins et al., 1981). The key parameters of OB production per larva and OB production per milligram of host weight are sensitive to OB dose, duration of infection, growth rate, total weight gain during the infection period, and final weight at death (Orlovskaya, 1980; Shapiro, 1986; Sherman, 1985). There 1049-9644/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.biocontrol.2007.02.012 * Corresponding author. Fax: +52 962 628 98 06. E-mail address: trevw@tap-ecosur.edu.mx (T. Williams). www.elsevier.com/locate/ybcon Biological Control 41 (2007) 389–396