Abstract
Wing phenotype polymorphism is commonly observed in insects, yet little is known about the influence of environmental cues on the development or expression of the alternative phenotypes. Here, we report how both biotic and abiotic factors affect the wing morph differentiation of a bethylid parasitoid Sclerodermus pupariae. The percentage of winged female parasitoid progeny increased exponentially with temperature between 20 °C to 30 °C. Low intensity light and short-day photoperiod conditions also significantly induced the development of winged morphs. Interestingly, wingless maternal parasitoids produced more winged progeny. Furthermore, the degree of wing dimorphism was significantly influenced by the interactions between light intensity and maternal wing morphs. The percentage of winged female progeny was not significantly influenced by foundress densities, but increased significantly with parasitoid brood sizes. However, the percentage of male progeny increased significantly with the densities of maternal parasitoids. Our findings highlight the phenotypic partitioning of wing morphology and development in the parasitoid S. pupariae under varied environmental cues, and reveal the most favourable conditions for the production of winged females in this bethylid wasp. It is thus possible to increase winged female parasitoid production for the purposes of biological control by manipulation of biotic and abiotic conditions.
Highlights
A paucity of investigations has focused on parasitic insects; merely, studies on the ectoparasitoid Melittobia digitata Dahms indicates that clutch sizes and the nutrient quality are the most important factors influencing its wing dimorphism[7]
Sex allocation is the provision of resources to male versus female offspring[27], and it has been subject to extensive study in parasitoid wasps[27,28,29,30]
This female bias can directly reduce the competition for mates among male individuals[33], the female-biased sex ratios in parasitoid wasps would become less biased with increasing numbers of unrelated individuals[35]
Summary
Studies on the biology of S. pupariae indicate that adult females prefer dark conditions[38]; long-day photoperiods and high intensity light conditions are considered more apt to induce the development of winged progeny for the dispersal of parasitoids from a deteriorating environment. The specific objectives of this study were to (i) examine the effects of both biotic (maternal wing morph variation, parasitoid population density, and brood sizes) and abiotic (temperature, photoperiod, and light intensity) factors on wing morph determination in S. pupariae; (ii) assess the interactions among maternal wing morph, photoperiod, and light intensity on female progeny wing morph determination; (iii) determine how sex ratio and developmental duration of parasitoid progeny vary under different conditions; and (iv) analyse the relationship between female parasitoid wing morph and fecundity
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