Determination of the optimal parasitoid‐to‐host ratio for efficient mass‐rearing of the parasitoid, Sclerodermus pupariae (Hymenoptera: Bethylidae)

Abstract

Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae) is used as a potential biocontrol agent for several buprestid and cerambycid larvae. This study aimed to enhance the efficiency of mass-rearing of this parasitoid by investigating the fitness gain of this bethylid wasp, including the proportion of successful parasitism and development, brood size, sex ratio, proportion of winged female offspring, body size and longevity of female offspring, under eight different maternal parasitoid density treatments using Thyestilla gebleri Faldermann as host in the laboratory. The results indicated that the foundress densities did not affect the parasitism or emergence rate of this parasitoid. Brood size of the parasitoids increased significantly when the number of maternal wasps ranged from one to four. However, further increases in foundress number did not affect the parasitoid brood size. The sex ratios of S. pupariae were always femalebiased. The proportions of male in the progeny colonies were <10% throughout all experimental treatments. The percentage of winged female progeny was not significantly influenced by the density of adult maternal parasitoids. Body sizes of parasitoids significantly declined with increasing maternal parasitoid densities. Although the parasitoid body size reduced when maternal wasp number was higher, it could be compromised by the relatively higher number of female offspring produced. Further, more than 70% of the parasitoids remained alive when they were stored at 12°C for four months throughout the experiments. These findings suggest that exposure of four female wasps to a single host larva would result in the highest fitness of S. pupariae. Our findings might provide a new approach to enhance the efficiency of mass-rearing of this bethylid wasp.

Relationships between Body Size and Parasitic Fitness and Offspring Performance of Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae)

“…In our study, small female wasps (< 2.4 mm) were found when parasitoid–host ( T . gebleri larvae weighted 200.0–240.0 mg) ratios were more than 4:1 [ 40 ]. An optimal inoculation proportion depends on host species, body size, stage, mobility, behavior, and nutritional quality of the substitute host [ 41 ].…”

Bethylids attacking stored‐product pests: an overview

“…The literature on bethylids that attack stored‐product pests also contains little information on practical aspects, such as collection methods and laboratory rearing. A first step will be to study the production of bethylids in mass rearing, defining the optimal parasitoid:host ratio (Wei et al., ). Current information is insufficient for making best use of these species as biocontrol agents, especially compared to other parasitoid taxa, such as Trichogramma spp., Braconidae, and Pteromalidae.…”

Parasitoid wasps as effective biological control agents

“…Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae) is a newly discovered native gregarious idiobiont ectoparasitoid of the emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), and an excellent parasitoid of larval and pupal Buprestidae and Cerambycidae (Yang et al 2012;Gao S et al 2016). The control efficiency of the bethylid parasitoids in suppression of wood-borers has been investigated in several wasp-host systems, especially S. pupariae (Gao S et al 2016;Gao S K et al 2016;Wang et al 2016;Wei et al 2016Wei et al , 2017. Parasitism and emergence rate in laboratory can be as high as 100% when the ratio of parasitoid-to-host is 1:1 while the rate in the field was 13% (Wei et al 2016).…”