Interaction between Podisus maculiventris and Harmonia axyridis, two predators used in augmentative biological control in greenhouse crops

Intraguild predation (IGP) between the pentatomid Podisus maculiventris (Say) and the coccinellid Harmonia axyridis (Pallas) in the absence or presence of the extraguild prey Spodoptera littoralis (Boisduval) and Myzus persicae (Sulzer) was studied in the laboratory. Interactions were asymmetric in favor of the pentatomid. Podisus maculiventris readily fed upon eggs and larvae of H. axyridis, but adult beetles were rarely attacked. Success of attacks by P. maculiventris was stage dependent, fourth instars and adults being more successful in killing ladybeetle larvae than second instars. Attacks by H. axyridis on the pentatomid were rare and none of them were successful. The effect of introducing extraguild prey on the level of IGP was tested both in petri dishes and on caged sweet pepper plants. When sufficient numbers of S. littoralis larvae were present to satiate the pentatomid, predation on H. axyridis larvae decreased significantly, indicating that the coccinellid is a less preferred or less vulnerable prey. When the aphid M. persicae was presented as extraguild prey, levels of IGP were not altered. Nymphs of P. maculiventris successfully completed development when exclusively fed on larvae of H. axyridis, but developmental time was longer than on lepidopteran prey. No pentatomid nymphs reached adulthood on aphids alone. IGP by P. maculiventris on H. axyridis may be of some importance in greenhouse crops, where both predators are being used increasingly in augmentative biological control programs. Nonetheless, it is expected that in practice larger larvae and adults of H. axyridis will escape most attacks by the pentatomid.