Sugar feeding of parasitoids in an agroecosystem: effects of community composition, habitat and vegetation

Abstract

Abstract Sugar from nectar or from honeydew can prolong parasitoids’ lifespan, enhance their fecundity and foraging ability, and thereby increase their pest suppression efficiency. Sugar sources within crop monocultures are considered to be limiting for parasitoids. Nevertheless, only few studies have measured the sugar feeding of parasitoid assemblages in agricultural areas or in surrounding non‐crop habitats. We used cold anthrone tests to compare the frequency of sugar feeding in parasitoid communities, inside pomegranate orchards and in adjacent natural areas, over two consecutive years. Overall, 40% of the 1610 sampled individuals belonging to 135 species scored positive for sugar. Sugar‐feeding frequency was lower within the orchards than in the neighbouring natural areas. The proportion of sugar‐fed wasps increased with herbaceous vegetation cover, both within and outside the orchards, suggesting that herbs are a sugar‐rich habitat. Parasitoids sampled from trees and from herbs within the orchards had similar frequencies of sugar feeding, despite differences in wasp species composition. Our results probably overestimate sugar‐feeding frequencies in the field because sugar‐fed individuals have higher longevity and hence are more likely to be sampled. We propose a simple model to approximate this over‐sampling bias and apply it to Encarsia inaron (Aphelinidae), one of the most abundant parasitoids in the samples. We conclude that sugar availability potentially limits parasitoid fitness in this agro‐ecosystem. This may be due to the low density of plants in natural areas during the Mediterranean summer, and to herbicide applications within the orchards that further suppress non‐crop herbs.