Effects of the Spodoptera littoralis granulovirus on the development and reproduction of cotton leafworm S. littoralis

Abstract Laboratory studies were performed to determine the insecticidal activity of granulovirus against cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae). The S. littoralis granulovirus (SpliGV) was tested against first (L1), third (L3), and fifth (L5) instar larvae fed on alfalfa leaf disks treated with aqueous suspensions of occlusion bodies (OBs). LD 50 values were 3.74 × 10 4 , 6.86 × 10 5 , and 1.1 × 10 7  OB/larva, for L1, L3, and L5, respectively. Median lethal times (LT 50 s) to similar response levels (mortality rates between 60% and 70%) decreased with increasing larval age (from 27.98 to 15.93 days). Sublethal effects were studied for the treatment of third instar larvae at a concentration equivalent to the LC 50 (previously determined by bioassay on artificial diet). Larval development time and pupation period were not affected by SpliGV. Significant differences were found in the oviposition period and number of days in which the female laid viable eggs when both sexes derived from treated larvae. Fecundity, spermatophore number and egg viability percentage were not statistically affected, while female longevity increased only when both adults derived from treated larvae. The SpliGV treatment caused morphological alterations in some areas of male reproductive system: width of vas deferens and length of the aedeagus . Histological sections of testes from SpliGV-treated larvae revealed impaired in follicle development and spermatocyte depletion. In 1- and 5-day-old male pupae from larvae treated with SpliGV, there was not visible change in spermatogenesis, but in 9-day-old pupae a reduction was noted in the number of primary and secondary spermatocytes. Treatment increased the number of oocytes in virgin females, but egg production was unaffected in both virgin and mated females. In conclusion, SpliGV treatment failed to cause high mortality rates in S. littoralis larvae, but did prompt deleterious effects on survivors development and reproductive capacity.