Control of Rhyzopertha dominica and Sitophilus zeamais in stored rice with different release rates of the larval parasitoid Anisopteromalus calandrae

Abstract

The presence of weevils is a concerning problem surrounding stored rice that is not well controlled with available pesticides, and alternative solutions are demanded nowadays by industry. The introduction of natural enemies can be very effective in closed environments where the grain is stored. In this study, we evaluated the effectiveness of the larval parasitoid, Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae), in reducing the populations of two problematic internal feeders of rice, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae). Three parasitoid:host ratios (1:1, 2:1, 4:1) were tested in small containers with 2Kg of brown rice at 23 and 28ºC during two host generations. Afterwards, host and parasitoid emergence, and rice damage was evaluated. The parasitoid drastically reduced both pest numbers (up to 99% reduction compared with the control treatment without the parasitoid) and their associated damage to rice grains (insect-damaged kernels, frass production and mould presence). The parasitoid was very effective at 23 and 28ºC over S. zeamais and at 28ºC over R. dominica at all parasitoid:host ratios tested. In conclusion, the introduction of A. calandrae could avoid the development of abundant populations of R. dominica and S. zeamais, representing a good control alternative to be further developed for the containment of the two pests in stored rice