The effect of resource provisioning and sugar composition of foods on longevity of three Gonatocerus spp., egg parasitoids of Homalodisca vitripennis

The effect of dietary supplements on the longevity of male and female Gonatocerus ashmeadi, G. triguttatus and G. fasciatus (Hymenoptera: Mymaridae), was determined in the laboratory. Treatments included: water only, 3:1 honey–water solution, floral and extra-floral nectars from five different plants (excised stems from Fagopyrum esculentum, Lobularia maritima, Phacelia tanacetifolia, Anethum graveolens and Vicia faba), honeydew from Coccus hesperidum and Homalodisca vitripennis (formally H. coagulata), a commercially available food supplement (Eliminade) and citrus foliage. Additionally, the sugar composition of each food resource was determined using HPLC and whole flower extracts. Honey–water and F. esculentum nectar significantly increased longevity of male and female G. ashmeadi, G. triguttatus, and G. fasciatus up to 1860%, 1323% and 1459%, respectively, when compared with water. For both sexes and all three parasitoid species, survival on citrus foliage, H. vitripennis excrement, and P. tanacetifolia flowers was equivalent to that on water only. The longevity of G. ashmeadi and G. triguttatus was up to 539% higher on Eliminade compared with water only, however there was no significant effect of Eliminade on survival of G. fasciatus. Coccus hesperidum honeydew increased survival times up to 665% for all mymarid species compared with citrus foliage alone. HPLC analysis indicated that food resources most beneficial to Gonatocerus parasitoids possessed a high proportion of glucose (up to 44%) and fructose (up to 53%), suggesting that sucrose may not be as important for parasitoid survival. Citrus and P. tanacetifolia flowers contained favorable proportions of glucose and fructose, but the inability of Gonatocerus spp. to benefit from this may be related to flower morphology which could prevent access to nectar.