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Insect parasitoids and herbivores must balance the risk of egg limitation and time limitation in order to maximize reproductive success. Egg and time limitation are mediated by oviposition and egg maturation rates as well as by starvation risk and other determinants of adult lifespan. Here, we assessed egg load and nutritional state in the soybean aphid parasitoid Binodoxys communis under field conditions to estimate its risk of becoming either egg- or time-limited. The majority of female B. communis showed no signs of egg limitation. Experimental field manipulations of B. communis females suggested that an average of 4–8 eggs were matured per hour over the course of a day. Regardless, egg loads remained constant over the course of the day at approximately 80 eggs, suggesting that egg maturation compensates for oviposition. This is the first case of such “egg load buffering” documented for a parasitoid in the field. Despite this buffering, egg loads dropped slightly with increasing host (aphid) density. This suggests that egg limitation could occur at very high host densities as experienced in outbreak years in some locations in the Midwestern USA. Biochemical analyses of sugar profiles showed that parasitoids fed upon sugar in the field at a remarkably high rate. Time limitation through starvation thus seems to be very low and aphid honeydew is most likely a source of dietary sugar for these parasitoids. This latter supposition is supported by the fact that body sugar levels increase with host (aphid) density. Together, these results suggest that fecundity of B. communis benefits from both dynamic egg maturation strategies and sugar-feeding.

Parasitoids commonly forage in agricultural settings where the predominant sugar source is homopteran honeydew. The aphidiine braconid, Binodoxys communis, is an Asian parasitoid currently being released against the soybean aphid, Aphis glycines, in North American soybean fields. We conducted a number of laboratory experiments evaluating the quality of A. glycines honeydew as a sugar source for this parasitoid. Wasps readily fed on droplets of A. glycines honeydew, honey and 50% sucrose solution, but the length of feeding bouts on honey was significantly longer than on the other foods. Parasitoids lived significantly longer when fed honey or sucrose than honeydew, while starved wasps had the shortest lifespan. At 21±1 °C and 25±5% R.H., male B. communis that were fed honey lived for a maximum of 14 days, while females lived up to 20 days. Honeydew-fed wasps of both sexes lived approximately 3 days on average, which was 2–3 times longer than when they were only allowed access to water. Anthrone tests of whole insects showed that total sugar and glycogen levels of honey or sucrose-fed individuals were consistently higher than those fed honeydew or water. The glycogen levels of honeydew-fed wasps increased significantly after one day of feeding. HPLC analyses revealed that B. communis readily assimilates A. glycines honeydew oligosaccharides such as erlose, while others (e.g., raffinose) did not degenerate. Raffinose was present in much higher amounts in honeydew-fed wasps than in wasps fed other diets, so this sugar could be used as a ‘signature’ sugar for this species. Honeydew-fed wasps also had significantly lower fructose/(fructose+glucose) ratios than those from other diet treatments. Although A. glycines honeydew might be the main carbohydrate source within a soybean field, other sugar sources such as floral nectar appear to be more optimal foods for B. communis from a physiological standpoint. We discuss the results from the perspective of classical biological

The majority of predators and parasitoids require non-prey food as part of their diet. The availability of suitable non-prey food can impact predator–prey and parasitoid–host dynamics and may be critical to the efficacy of biological pest control. A growing body of work addresses the role of floral nectar in conservation biological control programs. In comparison, we know relatively little about the role of honeydew as a sugar source for predators and parasitoids, in spite of the fact that honeydew is often the predominant sugar source in agroecosystems. Here we test the hypothesis that honeydew is a less suitable food source when compared with other sugar sources, using data from parasitoid literature. We also explore whether parasitoids of honeydew-producing insects show particular adaptations allowing them to optimize the exploitation of this suboptimal food source. A review of available literature supports the general hypothesis that honeydew is inferior to other sugar sources, although there is considerable variation in the quality of honeydew depending on the honeydew producer and its host plant. The accrued dataset is not consistent with our second hypothesis that parasitoids of honeydew-producing hosts fare better on this nutritionally inferior food source as compared with parasitoid species which exploit hosts that do not produce honeydew. Finally we review evidence on the use of honeydew by predators and parasitoids under field conditions and explore implications for biological pest control programs.