Predator‐parasitoid‐host interaction: biological control of Rhyzopertha dominica and Sitophilus oryzae by a combination of Xylocoris flavipes and Theocolax elegans in stored cereals

Abstract Post‐harvest management constraints are economically significant in Africa for a broad range of commodities, resulting in a substantial negative impact on food security and livelihoods. Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) coexists with Sitophilus oryzae (L.) (Coleoptera: Dryophthoridae) – they infest stored cereal grains, especially in sub‐Saharan Africa, and cause significant losses in storage. Laboratory studies were carried out to determine the efficacy of Xylocoris flavipes (Reuter) (Hemiptera: Anthocoridae) and Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae), alone or in combination, in suppressing populations of R. dominica and S. oryzae in stored rice and wheat grains. The weight loss and moisture of the infested grains were assessed, for the various combinations of the two pest insects and the two natural enemies. In rice there was a synergistic effect of the combined release of T . elegans and X . flavipes against both R. dominica and S. oryzae compared to the effect of one natural enemy alone. With the combined release, only 2% F 1 progeny of the pest beetles emerged compared to the untreated control (100%), whereas 3.5 and 6% emerged when X . flavipes and T . elegans , respectively, were released alone. When the two natural enemies were released in combination, 0.4% R. dominica F 1 progeny emerged, compared to 1.6% with X . flavipes or T . elegans alone. In the combined release only 0.3% S. oryzae F 1 progeny emerged, whereas 65% emerged with X . flavipes alone and 41% with T . elegans alone. No synergistic effect of the combined release of the two natural enemies was detected in wheat. In stored rice, the lowest percentage of weight loss (44%) was found when both natural enemies and both beetle species were present. We conclude that the combination of the predator and the parasitoid should be recommended when R. domininca and S. oryzae coexist and feed on stored cereals, especially rice.