Within-host interactions of Metarhizium rileyi strains and nucleopolyhedroviruses in Spodoptera frugiperda and Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Members of the family Baculoviridae have been quite successfully used as biocontrol agents against some lepidopterans. Likewise, a number of fungi are important natural enemies of these pests. An interesting approach to increase control efficacy could be the combination of a given nucleopolyhedrovirus (NPV) and a fungus, since they possess distinct modes of action. As a first step towards this goal, we assessed the interaction between NPV (either AgMNPV-79 or SfMNPV-6nd) and the entomopathogenic fungus Metarhizium rileyi (either CG1153 or CG381), using Anticarsia gemmatalis and Spodoptera frugiperda as hosts. In sequential applications of these pathogens, per os inoculation of an NPV (leaf discs with 2.5 x 10(4) occlusion bodies) either two days before or two days post-spraying of its counterpart fungal strain (5 x 10(3) conidia.cm(-2) sprays) usually resulted in an antagonistic effect. When both pathogens were simultaneously applied at different combined dosages, usually an additive effect was seen. Interestingly, a number of dead larvae showing signs of co-infections (partially with soft integument and partially mummified) were recorded. However, mixes with lower dosages of both pathogens did not cause significantly higher insect mortalities compared to low dosages of the fungus applied alone. The advantages and disadvantages of the simultaneous applications of NPV and M. rileyi aiming at the management of either A. gemmatalis or S. frugiperda were discussed.