The longevity effects of trehalulose feeding by parasitoids

Insects, particularly phloem-feeding Sternorrhyncha, are known to produce sugars in their honeydew (excreta) that are not found in their host plants. Of these, Bemisia tabaci, the sweet potato whitefly, is the only insect known to produce trehalulose [alpha-D-glucose (1,1) D-fructose] as a major component of its honeydew. The present study aims to determine whether trehalulose is comparable to sucrose as a nutrient source for three whitefly parasitoids (Encarsia formosa, Encarsia pergandiella and Eretmocerus eremicus). In addition, the study also examines trehalulose feeding effects on longevity for a parasitoid of muscoid Diptera, Nasonia vitripennis. Parasitoids are provided diets of either sucrose or trehalulose in varying concentrations (from 0.1% to 70%) or a water control. Sucrose and trehalulose are not significantly different in affecting survival when compared at the same concentration. This was true for all Bemisia parasitoids and N. vitripennis. Certain specific diets are significantly different in pairwise combination tests. There is a significant effect of species, diet type and the interaction of these two factors on the longevity of the three different Bemisia parasitoid species; however, within species, there is no significant increase in longevity observed for either carbohydrate diet. This result contrasts with expectations for the effects of host-modified carbohydrates on longevity. The implications are that, although carbohydrate feeding is essential for these parasitoids, these host-provided sources of carbohydrates are equally capable of extending longevity.