Effectiveness of the parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae) in the control of Sitophilus zeamais and Rhyzopertha dominica in paddy rice

Rice is an important cereal crop in Spain that is frequently attacked by pests that cause significant quantitative and qualitative losses. Among them, the maize weevil, Sitophilus zeamais, is the key pest, and the lesser grain borer, Rhyzopertha dominica, is a serious pest found later in the season. The cosmopolitan ectoparasitoid, Anisopteromalus calandrae, which attacks late-instar larvae of coleopterans that develop inside grain kernels, has been reported as an efficient natural enemy. In this study, we evaluated whether the control efficacy of this parasitoid on S. zeamais was affected by the presence of the alternative host, R. dominica. Our laboratory experiment demonstrated the parasitoid preference for S. zeamais larvae when mixed with R. dominica larvae at different proportions. This preference for the maize weevil larvae allowed us to maintain a similar control efficacy of S. zeamais when it was offered alone than when it was offered together with R. dominica larvae. In our second experiment, done in 500 kg bags of paddy rice, similar results were obtained, since the presence of R. dominica larvae did not alter the control efficacy of A. calandrae on S. zeamais larvae. Therefore, our results confirmed a good perspective for implementing the use of this natural enemy as a control tool in big bags of paddy rice.