Sub-lethal effects of indigenous isolate of Spodoptera frugiperda nucleopolyhedrovirus on fall armyworm growth and reproduction in India

Background Baculoviruses are specific pathogens which can lethally infect several lepidopteran pests. However, the sub-lethal effects of baculoviruses are also highly debilitating for the host. The objective of the study was to demonstrate the sub-lethal effects of an indigenous strain of Spodoptera frugiperda nucleopolyhedrovirus (SpfrNPV) infecting fall armyworm in India. Results As a result of larval infection, the larval developmental time was significantly prolonged as compared to the untreated insects. The percentage of pupal mortality ranged from 40.74 to 72.73 at varying doses of SpfrNPV and recorded low pupal weight in all the treatments than control. The fertility and fecundity of infected adult moths was significantly reduced when compared to the untreated insects in a concentration dependent fashion. Sub-lethal effects of baculoviral infection on different biological parameters were studied. Mean developmental period of infected 3rd and 4th larval instars was significantly higher (F = 2.945; F = 18.414; df = 5, 20; P < 0.05) in SpfrNPV infected larvae than the control at all tested viral concentrations. The percentage of pupal mortality ranged from 40.74 to 72.73 in the lowest and highest concentrations of SpfrNPV, respectively. Developmental period of male pupae was found to be significantly longer in infected groups than the uninfected ones. The infected adults had significantly reduced longevity in both males ranged from 3.5 to 5.75 (F = 6.273; P = 0.002) and females ranged from 3.5 to7.00 (F = 13.652; P = 0.001). Further, the mates of virus-treated adults showed a highly reduced egg production (F = 31.255; P < 0.05) ranged from 150.03 to 338.33 and the larval emerging ranged from 71.11 to 227.89 (F = 74.52; P < 0.05), which was again significantly lower than the control. The percentage of egg hatching ranged from 47.40 to 86.41%. Conclusions The sub-lethal effect of SpfrNPV has observed on the growth and development and also reduced percentage of egg hatching in the subsequent generation. Hence, this indigenous SpfrNPV strain can be used in the sustainable and resilience IPM program. Further studies under open field conditions are still needed.