Food deprivation alters reproductive performance of biocontrol agent Hadronotus pennsylvanicus

Impact of Nutritional Supplements on the Fitness of the Parasitoid Binodoxys communis (Gahan)

Alterative nutritional foods consumed by adult parasitoids play an important role in their fitness and ability to control pests because of food scarcity in many crops. While adult parasitoids feed on various sugars, they vary in their nutritional value for parasitoids. We assessed the effects of seven sugars (fructose, glucose, sucrose, trehalose, maltose, melezitose, and sorbitol) on the longevity, parasitism ability, parasitism behavior, and flight ability of B. communis, an important parasitoid of cotton aphids. We found that access to glucose, sucrose, or fructose, increased B. communis adult longevity more than the other sugars offered. All sugars except trehalose increased the parasitism rate to more than 50% compared to the starved control (only provided with water). We then compared parasitoid behaviors of wasps fed glucose, sucrose, or fructose to that of the starved control (with access only to water) and found that those fed B. communis spent more time either examining or attacking aphids than parasitoids in the control group, which spent more time walking or resting. Also, consumption of glucose, sucrose, or fructose also significantly improved the flight ability (the total flight distance, flight time, and average flight speed) of B. communis.

Flourishing with sugars - following the fate of parasitoids in the field

When flowers, plants bearing extrafloral nectaries, or sugar sprays are added to agroecosystems, parasitoids are expected to feed, thereby improving biological control. This paper reviews studies where sugar-feeding of field-collected parasitoids were monitored via biochemical assays. When examined, trends in parasitoid abundance, energetic reserves, longevity, and per capita fecundity are also followed. Starved parasitoids readily feed on sugar sources in the field, and more individuals collected near sugar sources are categorized as 'fed' when sugar is otherwise limited in the agroecosystem. When sugar is not limited (i.e. honeydew prevalent), trends are not as clear. Some studies show improved fecundity and parasitism, while other studies show inconsistent trends between parasitoid feeding, abundance, longevity, and parasitism, with some responses improved but not others. Future research could address the dispersal or resting behavior of wasps following feeding since it can influence eventual biological control, and consider whether field sampling methods might over-/underestimate feeding.

Diet quality influences nutrient retention and reproductive fitness of the biocontrol agent Hadronotus pennsylvanicus (Hymenoptera: Scelionidae)

Diet can have a direct influence on the reproductive success of parasitoid wasps. For synovigenic parasitoids, the nutrients obtained from floral resources, such as nectar and pollen, play a vital role in fueling bodily functions and physiological energy expenditure incurred from reproduction. Insufficient access to nutrient-rich diets can lead to lower rates of reproductive fitness, therefore reducing the efficacy of biocontrol. Here, a study was conducted to evaluate the influence of diet quality on nutrient retention and reproductive fitness of the egg parasitoid Hadronotus pennsylvanicus (Hymenoptera: Scelionidae), a prospective biocontrol agent for the leaffooted bug Leptoglossus zonatus (Heteroptera: Coreidae), a primary pest of almonds and pistachios. Newly emerged parasitoid females were provided host eggs every other day accompanied by diets of varying sucrose concentrations (source of carbohydrates) and pollen (source of lipid and proteins). The sucrose concentration in the diet, regardless of pollen content, significantly increased the survival and lifetime fecundity of female H. pennsylvanicus. While wasps fed high sucrose diets depleted bodily sugars, glycogen, and lipids at a slower rate than wasps fed low sucrose diets, there was no effect on bodily protein levels. Given these findings, further research is now needed to identify floral resources that are compatible, attractive, and nutritionally-sufficient for optimal H. pennsylvanicus reproductive fitness, which could lead to enhanced parasitism of L. zonatus in crop systems.

Finding an egg in a haystack: variation in chemical cue use by egg parasitoids of herbivorous insects

Egg parasitoids of herbivorous insects use an interplay of short- and long-range chemical cues emitted by hosts and host plants to find eggs to parasitize. Volatile compounds that attract egg parasitoids can be identified via behavioral assays and used to manipulate parasitoid behavior in the field for biological control of herbivorous pests. However, how and when a particular cue will be used varies over the life of an individual, as well as at and below species level. Future research should expand taxonomic coverage to explore variation in chemical cue use in more natural, dynamic settings. More nuanced understanding of the variability of egg parasitoid host-finding strategies will aid in disentangling the underlying genetics and further enhancing biological control.