Oviposition, flight and walking capacity at low temperatures of four aphid parasitoid species (Hymenoptera : Aphidiinae)

Precocious activity of parasitoids is a key factor for cereal aphid control. We investigated the oviposition, flight and walking capacities at low temperature of four aphid parasitoids (Aphidius rhopalosiphi, A. ervi, Praon volucre, P. gallicum) on one of their aphid hosts (Sitobion avenae). Oviposition behaviour was tested at 2, 4, 6, 8, 10, 15 and 20degreesC, under a photoperiod of 12 h light. Some females of A. rhopalosiphi oviposited at 6degreesC while the percentage of parasitization below 10degreesC remained low for the other species. The proportion of mates decreased with temperature for A. ervi, P. volucre and P. gallicum but not for A. rhopalosiphi. For all species, flight and walking activities increased with temperature, Aphidius species being active at lower temperature than Praon species. Field captures showed that the activity threshold for A. rhopalosiphi is 12degreesC, 15degreesC for A. ervi and P. volucre, and 19.5degreesC for P. gallicum. These results are discussed regarding the potential of these four species for aphid control.