Trichogramma parasitoids can distinguish between fertilized and unfertilized host eggs

Host quality varies with size, age, and species, and influences the parasitism preference of parasitoids and the fitness of their offspring. However, it is still unclear whether parasitoids have the ability to recognize fertilized and unfertilized host eggs. We studied the performance of three Trichogramma species, T. japonicum, T. chilonis, and T. leucaniae, on both fertilized and unfertilized eggs of their host Corcyra cephalonica at different host ages. In no-choice tests, three Trichogramma species parasitized significantly more fertilized than unfertilized eggs when host age was 0 days old. In choice tests, all parasitoids parasitized significantly more fertilized than unfertilized eggs at all host ages. Furthermore, the frequency of fertilized eggs visited by Trichogramma parasitoids were significantly higher than those of unfertilized eggs. The number of unfertilized eggs visited by parasitoids without ovipositing was approximately 3.7 times greater than those of fertilized eggs. In addition, all Trichogramma parasitoids developed significantly faster on fertilized than unfertilized eggs at all host ages. In summary, we find that Trichogramma were able to recognize fertilized and unfertilized host eggs in parasitism, which is conducive to biological control programs, since unfertilized eggs enlarge the host reservoir for parasitoid augmentation.