Combined activity of Maruca vitrata multi-nucleopolyhedrovirus, MaviMNPV, and oil from neem, Azadirachta indica Juss and Jatropha curcas L., for the control of cowpea pests

The insecticidal activity of Maruca vitrata (F.) multi-nucleopolyhedrovirus (MaviMNPV) combined with oil from neem, Azadirachta indica Juss and Jatropha curcas L. (Euphorbiaceae) was studied under laboratory and field conditions against three key insect pests of cowpea, Vigna unguiculata (L.) Walp. Second-instar Aphis craccivora Koch and Megalurothirps sjostedti Trybom nymphs, and third-instar M.vitrata larvae, all from laboratory colonies, were treated with various concentrations of one of the control agents separately or combined. Daily mortality was recorded for five days (A.craccivora and M.sjostedti nymphs) or fourteen days (M.vitrata) and the larval and pupal development as well as adult emergence were assessed. Combination of MaviMNPV resulted in a significantly higher larval mortality in M.vitrata than treatment with either virus or botanical insecticide alone at the corresponding concentrations. Larvae of M.vitrata infected with MaviMNPV and treated with botanical oils died sooner than those infected with only one control agent. Combinations of MaviMNPV and botanical oils produced additive or synergistic effects. No evidence of antagonistic effects was noted. In field experiments, the application of botanical insecticide and MaviMNPV either alone or in combination was effective in reducing insect abundance over the four weeks, and preventing yield loss. In the first field season, where the M.vitrata population was higher, the combination of the virus and either of the botanical pesticides induced significantly higher yields than spraying chemical insecticide. Application of MaviMNPV in combination with J.curcas and A.indica oil has proven to induce consistent MaviMNPV infection in M.vitrata populations. The combined application of MaviMNPV and botanical oils is discussed in the context of integrated pest management.