Can heteronomous hyperparasitoids recognize host abundance and adjust offspring ratio?

Sex ratio is crucial in the reproductive dynamics of bisexual insects. In the Aphelinidae family, heteronomous hyperparasitoids like Encarsia sophia show distinct behaviors where females (from fertilized eggs) target primary hosts, and males (from unfertilized eggs) parasitize secondary hosts. This sex determination pattern means that host resource abundance significantly impacts sex ratio, affecting population dynamics. However, the sex distribution of these parasitoids remains a topic of debate. This study examined E. sophia targeting Bemisia tabaci, adjusting host densities (30, 50, 70 hosts/9.6 cm²) and secondary host ratios (0.2, 0.5, 0.8). Females were observed for recognition of varying host conditions and adjustments in offspring sex ratio and behavior. When ratio of secondary hosts surpassed that of primary hosts or in cases of low host density (host limitation), E. sophia’s offspring sex ratio adapted according to the relative abundance of primary and secondary hosts. Conversely, with low secondary host ratios (< 0.5) and higher host density, the sex ratio approached 1:1. Observations showed that females quickly perceived host density, increasing oviposition on secondary hosts with higher density, resulting in more males, and increasing feeding on primary hosts, reducing female offspring. Importantly, by examining oviposition and feeding under different host resource conditions, we identified the optimal rearing strategy: a secondary host ratio of 0.2 and a host density of 30 hosts/9.6 cm². This study not only introduces the sex ratio theory for heteronomous hyperparasitoids but also provides a framework for more accurately assessing their environmental adaptability and for large-scale production.