Intraguild predation between macrolophus pygmaeus and Aphidius ervi

This work investigates the intraguild predation (IGP) between the predator Macrolophus pygmaeus Rambur (Hemiptera Miridae) and the aphid parasitoid Aphidius ervi Haliday (Hymenoptera Braconidae). In particular, predation on parasitized Acyrthosiphon pisum (Harris) (Hemiptera Aphididae) aphids was studied at two different stages of parasitism. It is known that A. pisum parasitized by A. ervi exhibits a „suicidal‟ behaviour in presence of a coccinellid. This behaviour may be linked to an increased risk of being preyed, since it has been observed that parasitized A. pisum suffers greater predation rate by Harmonia axyridis (Pallas). The escape response in A. pisum is affected by predator species and hemipterans cause a small disturbance of aphid colony. We hypothesize that parasitized A. pisum at an early stage of parasitization would suffer higher predation risk also if the predator is a hemipteran. We used the generalist predator M. pygmaeus to test this hypothesis. Predation on newly parasitized aphids was tested by offering groups of twenty 2nd instar aphids composed of parasitized and unparasitized individuals in different proportions to the predator. The relative proportion of the healthy and parasitized aphids did not change the total prey consumption. Increased susceptibility to predation for parasitized aphids at an early stage of parasitism was observed. This result is discussed on the basis of the kin selection theory. Predation on pre-mummified and mummified A. pisum aphids was also studied. Our results show that M. pygmaeus preys, on average, about two A. pisum mummies in 24 h, which is fully in line with the consumption of fourth instar aphids. Pre-mummies killed by M. pygmaeus always showed visible damage while mummies did not always show visible signs of the predator feeding activity. The possible consequences of the mass release of generalist predators on parasitoid natural populations are briefly discussed.