Influence of carbohydrate foods and mating on longevity of the parasitoid Bathyplectes curculionis (Hymenoptera: Ichneumonidae)

Abstract

By promoting adult longevity, carbohydrate food sources can influence the effectiveness of parasitoids in biological control of insect pests. Adults of Bathyplectes curculionis (Thomson), a parasitoid of the alfalfa weevil (Gyllenhal) (Coleoptera: Curculionidae), benefit greatly from continual nourishment: field-collected adults lived significantly longer when provided sugar-water than those provided water only. Access to one potential source of adult nutrition in the field, dandelion flowers, enabled laboratory-reared wasps to live only slightly but nevertheless significantly longer than those that had access to water only, foliage of alfalfa, or flowers of Phacelia tanacetifolia Bentham. The wasps were observed foraging readily on dandelion but could not insert their heads into and did not pierce florets to obtain nectar. For each of the foods provided (dandelion, phacelia, alfalfa, or water alone), virgin females lived significantly longer than mated females. This was not the case, however, when wasps were provided a honey-water solution; both virgin and mated females lived more than 20 d on average. These results suggest that even in the absence of oviposition, female longevity is reduced by the simple act of mating when inferior but not superior foods are available. The striking contrast in longevity of wasps provided honey versus other carbohydrate foods raises the question of how much female wasps in nature realize their potential lifespan and fecundity. Dandelions and pea aphid honeydew appear to be the most likely sources of carbohydrates for the wasp in alfalfa fields. Supplemental foods such as floral plantings may promote realization of such potential longevity, but the quality and accessibility of floral foods for the wasp will need to be evaluated carefully.