Oviposition strategy of <i>Aphidius ervi</i> (Hymenoptera Aphidiidae) in response to host density

Abstract

The reproductive response of Aphidius ervi Haliday to the density of pea aphid Acyrthosiphon pisum (Harris) was investigated in plastic cylinders (105 cm high x 85 cm diameter) Mean number of aphids parasitised and eggs laid by a single A ervi significantly increased with an increase of host density Numbers of eggs laid per parasitoid reached a plateau at host densities of 75 aphids/cylinder and above However the number of eggs laid in each parasitised aphid significantly decreased (from 29 to 13 eggs) with the increase of host density from 15 to 75 aphids/cylinder after which no further decrease occurred These results suggest that the parasitoid adjusts oviposition strategy in response to increasing host density through increasing parasitism and decreasing superparasitism The proportion of female progeny developed from fertilised eggs increased (up to 70) with the increase of host density from 15 to 50 or 75 aphids/cylinder after which it gradually declined suggesting that the sperm limit occurs when host density reaches 50 to 75 aphids/cylinder