Quality of aphid honeydew for a parasitoid varies as a function of both aphid species and host plant

Abstract

Honeydew i.e., the sugar-rich excretion of phloem-sap feeders, is the most available sugar source in agroecosystems which enables parasitoids to increase their fitness. For the parasitoids of honeydew-producing insects, honeydew is associated with host presence, suggesting that parasitoids can find carbohydrate sources and hosts at the same place. Hence, these parasitoids may have evolved to efficiently use the honeydew produced by their main hosts as a carbohydrate source. In this context, we assessed the relationship between the adult fitness (in terms of longevity and fecundity) of the aphid parasitoid Aphelinus abdominalis (which prefer attack aphid species belonging to the Macrosiphini tribe), fed on honeydew produced by 19 different plant-aphid combinations, and parasitoid preference (i.e., the choice of female to oviposit) and ability to produce offspring in these combinations. Honeydew quality was modulated by both the plant and aphid host species. The honeydew produced by eight aphid species (e.g., Macrosiphum euphorbiae and Aphis craccivora) resulted in high parasitoid longevity (same longevity as the honey-fed positive control) and an increase in egg load between 24 and 48 h, compared to the negative control (fed only water). In contrast, nine aphid species (e.g., Brevicoryne brassicae and Aphis nerii) excreted low-quality honeydew that did not increase parasitoid longevity or egg load (similar to the negative control water-fed parasitoids). There was no relationship between A. abdominalis adult fitness when fed various honeydews and its preference as well as its ability to produce offspring in the hosts producing these honeydews. Several hypotheses that may explain this lack of relationship are discussed.