Releases of the parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae) can control Sitophilus zeamais (Coleoptera: Curculionidae) in big bags of paddy rice

Abstract

Sitophilus zeamais is a key pest in stored rice in Spain and other Mediterranean countries. Today, it is mostly controlled with a few pesticides, such as pyrethroids or phosphine. Apart from the problem of pesticide resistance, this can lead to the accumulation of toxic residues in the stored rice. Therefore, alternative control methods are needed. Biological control with the parasitoid Anisopteromalus calandrae is a feasible and sustainable alternative since it is very effective at limiting the growth of the weevil population. In this study, we evaluated the dispersal capacity and effectiveness of this parasitoid in controlling S. zeamais larvae located deep in 500 kg bags of paddy rice during two seasons, summer and autumn. The parasitoid was easily able to reach the bottom of the bags (1 m) in both seasons. At the released parasitoid-to-host ratio, the parasitoid was also able to limit weevil population growth by around 60% compared to the control treatment, based on the released parasitoid-to-host ratio, indicating that it offers an effective alternative control method.