Evaluation of a baculovirus bioinsecticide for small-scale maize growers in Latin America

Near identical trials conducted concurrently in maize plots in Honduras and Mexico produced similar results in the pattern of larval mortality of Spod optera frugiperda following application of a baculovirus or a conventional synthetic insecticide. The highest application rates of virus resulted in a pproximately 40% mortality of S. frugiperda larvae. Virus-induced mortality decreased with time. Parasitism by wasps and tachinids also contributed up to 40% mortality in field-collected larvae, The application of chlorpyrifo s resulted in a resurgence of S. frugiperda. Chlorpyrifos also reduced a nu mber of important predators in the maize crop which is likely to have been influential in the observed resurgence of this pest. The use of granulated sugar in the viral formulation caused an increase in the population density of several maize-associated insect species, and in Mexico a transient incr ease in parasitism was observed in sugar-treated plots. Sugar did not appea r to increase the probability of infection by acting as a feeding stimulant in either trial, A preliminary analysis of the cost of viral production an d application indicates that virus was considerably more costly than conven tional control. To be commercially viable, economies of scale both in the c ost of raw material for the insect diet and in the efficiency of manpower-r elated activities are needed to substantially reduce the costs of the viral product. Despite high levels of infestation by S. frugiperda, grain weight /cob was not significantly improved by the application of the biological or synthetic insecticide. Natural mortality factors both biotic and abiotic a ppear to have a large impact on larval S. frugiperda populations. For impro vements in yield, the impact of control measures against S, frugiperda may be dependent on plant growth stage. Trials on timing and frequency of virus application are in progress to test this idea. (C) 1999 Academic Press.