Age makes a difference: Suitability of Bagrada hilaris eggs on life-history parameters of the parasitoid Gryon aetherium

Egg parasitoid fitness is affected by several aspects of the parasitoid-host interaction, where host age plays an important role in host suitability. We hypothesize that host quality for parasitoids progeny often decreases as host embryonic development progresses, leading to a decreased parasitism rate and low offspring fitness. To answer this hypothesis, we use the painted bug Bagrada hilaris, invasive insect recently recorded in Chile and its parasitoid Gryon aetherium which is currently being evaluated as a biocontrol agent, as a study model. The effect of the egg-age of B. hilaris on the parasitism of G. aetherium was evaluated under laboratory conditions. Moreover, developmental time, emergence and sex ratio were also evaluated. Emerged females (< 24 h-old) were exposed to males for 24 h for mating. Then, each female was transferred in a Petri dish (9cm diameter) containing 10 eggs of one of the four following age-classes: 1, 2, 3, and 4 days old. Eggs cluster were exposed to females for one hour in a climatic chamber (25°C, 16:8 Light: Dark) for parasitism. Then, eggs were kept under the same conditions until parasitoid emergence. G. aetherium parasitized eggs of all age-classes. However, their progeny did not develop successfully in all host-ages. Developmental time was longer as egg age increased. In contrast, the offspring emergence was higher ( >85%) in young eggs (1-2 days), and progeny was strongly female-biased ( >70%) in all age-classes. These results suggest that G. aetherium may maximize the period of availability of food sources in young hosts.