The combined foraging of a parasitoid and a predatory bug enhances mortality of Plutella xylostella larvae

Abstract

Interactions between biocontrol agents of crop pests can lead to neutral, detrimental, or improved outcomes for pest control. We investigated the existence and the nature of the additive interactions between a parasitoid, Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae), and two hemipteran predators, Oechalia schellenbergii Guerin-Meneville (Pentatomidae) and Nabis kinbergii Reuter (Nabidae), of the diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), under laboratory conditions. In the presence of the parasitoid, both O. schellenbergii and N. kinbergii increased predation by 56 and 66%, respectively. The escape response of the prey to avoid being parasitized (moving backwards and sometimes spinning down from the leaf on a silk thread, becoming less cryptic to the predators), may be at the basis of the enhanced predation by these predatory bugs; however, further studies are necessary to test this hypothesis. As the predators did not preferentially consume either parasitised or unparasitised larvae, coincidental intraguild predation should not affect this positive outcome in relation to DBM suppression. The findings highlight the potential utility of combining these natural enemies and may have important implications for the management of DBM in brassica crops in Australia and other multi-species systems.