Host preference and oviposition behaviour of Trichogramma aurosum Sugonjaev & Sorokina (Hymenoptera: Trichogrammatidae).

Abstract

Oviposition behaviour and host selection of different German strains of the egg parasitoid Trichogramma aurosum were examined on eggs of five Lepidopteran hosts (Cydia pomonella (L.), Spodoptera littoralis (Boisd.), Helicoverpa armigera (Hübner), Agrotis segetum (Schiff.), Lobesia botrana (Den. & Schiff.)). The parasitization behaviour of individual female wasps was examined in choice and non choice tests. Results from the choice test revealed that 75 – 90 % of C. pomonella eggs attacked by T. aurosum strains were successfully parasitized. Values for L. botrana and for A. segetum ranged between 40 – 80 % and 40 – 70 %, respectively. Time needed by the female wasps to drill on eggs of L. botrana was shorter than the time needed for drilling on C. pomonella eggs. This could be due to differences in egg chorion thickness, which may offer more resistance to penetration of the ovipositor. The female wasps showed no significant preference between the host eggs offered. During direct observation of the parasitism behaviour it was noticed that all strains spent about 20% of the observation time on drilling either C. pomonella or L. botrana eggs, 30 – 60 % on resting, 4 – 15 % on cleaning, > 4% on walking and > 1 % on feeding. Results from the non choice test showed that a significantly higher number of C. pomonella and L. botrana eggs were parasitized in comparison to the other hosts offered. The presence of thick hairs deposited on eggs of S. littoralis and a thick egg chorion in H. armigera seems to represent a physical barrier that impedes successful parasitization.