Impact of host suitability on oviposition preference toward fertilized and unfertilized host eggs in two Trichogramma parasitoid species

The preference of Trichogramma parasitoids is known to be modulated by the fertilization status of host eggs encountered. However whether the actual suitability of host eggs is at play for modulating the preference of Trichogramma when choosing fertilized vs. unfertilized host eggs has not been well documented yet. In the present study, fertilized and unfertilized eggs of Ostriniafurnacalis (Guenee) (Lepidoptera: Crambidae), of which the eggs are suitable for Trichogramma ostriniae (Pang & Chen) (Hymenoptera: Trichogrammatidae) but are suboptimal for T. dendrolimi Matsumura, were used to investigate host preference, host acceptance, and offspring performance of the two Trichogramma species. The results showed that, in a no-choice test, T. dendrolimi parasitized significantly more unfertilized O. furnacalis eggs than fertilized ones. In contrast, the number of fertilized eggs parasitized by T. ostriniae was significantly higher than for unfertilized eggs. The sex ratio (female proportion), developmental time and fitness of offspring wasps were similar between fertilized and unfertilized host eggs for both Trichogramma species. In a choice test, T. dendrolimi preferred unfertilized host eggs over fertilized ones, whereas T. ostriniae did not show a preference. The higher rate of eggs laying by T. dendrolimi on unfertilized eggs than on fertilized ones may explain the different parasitism performances reported for the two Trichogramma species.