Fitness‐related offspring sex allocation of Anastatus disparis, a gypsy moth egg parasitoid, on different‐sized host species

Abstract

Anastatus disparis (Ruschka) (Hymenoptera: Eupelmidae) is an egg parasitoid and considered a potential biological control agent of the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae). Only male offspring of A. disparis emerge from single eggs of L. dispar in the laboratory, and A. disparis exhibits low parasitism on L. dispar in the field. We therefore selected several lepidopteran species with various body sizes to evaluate the optimal egg size for hosting A. disparis. In addition, we explored whether the nutritional content of a single L. dispar egg influences the sex of A. disparis offspring and why female offspring can be reared from L. dispar eggs in the field. The results indicated that host egg size decisively influenced the body size and sex ratio of the parasitoid offspring. Therefore, larger hosts, especially the largest eggs of Antheraea pernyi Gu erin-M eneville (Saturniidae), might increase the fitness of A. disparis females. Lymantria dispar eggs concealed in the larger egg shell of A. pernyi produced female A. disparis, suggesting that adult A. disparis should prefer hosts with larger bodies and that the nutritional content of L. dispar eggs did not play a decisive role in the sex allocation of A. disparis. The results also indicated that the egg mass and the fur cover of L. dispar egg masses might be the key factors inducing female A. disparis to lay female offspring in L. dispar eggs.

Influence of natal host and oviposition experience on sex allocation in a solitary egg parasitoid, Anastatus disparis (Hymenoptera, Eupelmidae)

“…It can develop three to four generations on L. dispar eggs annually in Northern China (Yao and Yan 1994). In our previous research, we found that the offspring of A. disparis reared on egg masses of gypsy moth were male-biased and small-bodied (Liu et al 2017). However, when they were reared on a larger host, Antheraea pernyi Guerin-Meneville (Lepidoptera: Saturnidae), the offspring were female-biased and had a larger body size compared with those reared from gypsy moth (Liu et al 2017).…”

“…Anastatus disparis Ruschka (Hymenoptera: Eupelmidae) is a solitary egg parasitoid of several noxious lepidopteran forest pests, including the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae) (Crossman 1925, Kurir 1944, Yan et al 1989, Li and Lou 1992, Alalouni et al 2013, Liu et al, 2017. It can develop three to four generations on L. dispar eggs annually in Northern China (Yao and Yan 1994).…”

“…Trivers and Wilard (1973) suggest that females should adjust the sex of their offspring in response to environmental conditions, and there is considerable empirical evidence for such adjustments and deviations from optimal sex allocation strategies (West andSheldon 2002, Lewis et al 2010). As a parasitoid, A. disparis can parasitize small body-sized hosts through to large body-sized hosts, with females seeming to prefer larger hosts which produce more female offspring (Liu et al 2017). However, we do not know whether natal host or oviposition experience influence the offspring sex allocation of adults.…”

Sexual dimorphism and sex-biased gene expression in an egg parasitoid species, Anastatus disparis

“…Sexual dimorphisms related to behaviour, physiology, and morphology in A. disparis have been extensively described. First, although wasp body size is correlated with host quality [44] [46], the body size of females is typically significantly larger than males. Females can live more than one month in the field and lay hundreds of eggs over their lifetime, while males live for only approximately 5-7 days and exhibit frequent and extreme fighting behaviour to acquire mating opportunities [43][46] [47].…”

Sexual dimorphism and sex-biased gene expression in an egg parasitoid species, Anastatus disparis

“…Sexual dimorphisms related to behaviour, physiology, and morphology in A. disparis have been extensively described. First, although wasp body size is correlated with host quality [41] [43], the body size of females is always significantly larger than that of males. Second, females can live more than one month in the field and lay hundreds of eggs over their lifetime, while males live for only approximately 5-7 days and exhibit frequent and extreme fighting behaviour to acquire mating opportunities [40][43] [44].…”