High Hemocyte Load Is Associated with Increased Resistance against Parasitoids in Drosophila suzukii, a Relative of D. melanogaster

Abstract

Among the most common parasites of Drosophila in nature are parasitoid wasps, which lay their eggs in fly larvae and pupae. D. melanogaster larvae can mount a cellular immune response against wasp eggs, but female wasps inject venom along with their eggs to block this immune response. Genetic variation in flies for immune resistance against wasps and genetic variation in wasps for virulence against flies largely determines the outcome of any fly-wasp interaction. Interestingly, up to 90% of the variation in fly resistance against wasp parasitism has been linked to a very simple mechanism: flies with increased constitutive blood cell (hemocyte) production are more resistant. However, this relationship has not been tested for Drosophila hosts outside of the melanogaster subgroup, nor has it been tested across a diversity of parasitoid wasp species and strains. We compared hemocyte levels in two fly species from different subgroups, D. melanogaster and D. suzukii, and found that D. suzukii constitutively produces up to five times more hemocytes than D. melanogaster. Using a panel of 24 parasitoid wasp strains representing fifteen species, four families, and multiple virulence strategies, we found that D. suzukii was significantly more resistant to wasp parasitism than D. melanogaster. Thus, our data suggest that the relationship between hemocyte production and wasp resistance is general. However, at least one sympatric wasp species was a highly successful infector of D. suzukii, suggesting specialists can overcome the general resistance afforded to hosts by excessive hemocyte production. Given that D. suzukii is an emerging agricultural pest, identification of the few parasitoid wasps that successfully infect D. suzukii may have value for biocontrol.

Development, Reproductive Output and Population Growth of the Fruit Fly Pest <I>Drosophila suzukii</I> (Diptera: Drosophilidae) on Artificial Diet

“…In D. suzukii cultures, earlier oviposition occurs on natural food substrates, i.e., intact thin-skinned fruits, a discovery made by Kacsoh & Schlenke (2012), who added thawed, frozen raspberries to standard drosophila diet media. Our findings concur with those of Kacsoh & Schlenke (2012); adding intact fruit to drosophila media prompted earlier oviposition by D. suzukii. These researchers, however, reported no concomitant increase in overall fly production.…”

“…Fruit-amended diets for D. suzukii commonly have included purees of fresh fruit, either peach or raspberry, with (Stewart et al 2014) or without the addition of an agar thickener (Hardin et al 2015). Whole berries (e.g., raspberries), one or perhaps more, can be dropped into a rearing vial onto the soft diet media (Kacsoh & Schlenke 2012). These authors did not describe the quantities of ingredients or microbial contamination caused by adding or pureeing fruit in the D. suzukii diet.…”

“…The rearing method described here is similar to the fruit-based diet described by Kacsoh & Schlenke (2012). However, we discuss problems encountered while rearing locally captured D. suzukii and solutions found to optimize this species' diet.…”

Male killing Spiroplasma protects Drosophila melanogaster against two parasitoid wasps

“…Numerous species of parasitoid wasps attack Drosophila flies . D. melanogaster alone is an adequate host to at least 14 species from four families of parasitic Hymenoptera that use diverse strategies to circumvent host defenses (Kacsoh and Schlenke, 2012). Our study examined whether Spiroplasma and Wolbachia influence the outcome of parasitism by two cosmopolitan congeneric wasps that differ in their host range and attack strategies: the Drosophila generalist Leptopilina heterotoma (Lh) and the melanogaster-group specialist L. boulardi (Lb).…”

The Uniqueness of Achatina fulica in its Evolutionary Success

“…Total hemocyte count in mollusc has been considered as an important immune parameter [43]. Elevation of the total hemocyte count indicates augmentation of immunity of invertebrates [44]. Phagocytosis is an established strategy of immune defense in invertebrates including mollusc.…”