Resistance of Drosophila suzukii to the larval parasitoids Leptopilina heterotoma and Asobara japonica is related to haemocyte load

Abstract

Unlike other Drosophila species, the invasive Drosophila suzukii Matsumura (Diptera: Drosophilidae) shows a remarkable pest status. Among the physiological traits that may explain the high level of resistance to parasitoids of Drosophila larvae, the haemocyte load is shown repeatedly to play an important role. To determine whether haemocyte load can explain immunity resistance of D. suzukii to parasitoids, the haemocytes of parasitized and healthy larvae are quantified in two Japanese and three French populations of D. suzukii. Parasitization tests are conducted with two larval parasitoids: the paleartic Leptopilina heterotoma Thomson (Hymenoptera: Figitidae) and the Asian Asobara japonica Belokobylskij (Hymenoptera: Braconidae). Based on morphological and functional criteria, D. suzukii has classes of haemocytes similar to those described in Drosophila melanogaster. However, healthy larvae of the five populations tested possess particularly large numbers of haemocytes compared with D. melanogaster. Haemocyte load is also higher in larvae from the French populations than in the Japanese strains. The ability of D. suzukii larvae to encapsulate eggs of L. heterotoma is associated with a particularly high load of circulating haemocytes. However, it is notable that A. japonica induces a strong depression of the haemocyte population in this resistant host associated with an inability to encapsulate parasitoid eggs. The results show that the cellular immune system plays a major role in the failure of larval parasitoids to develop in most instances in larvae of D. suzukii, possibly contributing to the success of this species as an invader.

Development of Asian parasitoids in larvae Of Drosophila Suzukii feeding on blueberry and artificial diet

“…These results suggest that L. heterotoma's virulence is not strong enough to resist the immune reaction of D. suzukii. This was also observed in other studies (Chabert et al, 2012;Kacsoh & Schlenke, 2012;Knoll et al, 2017;Poyet et al, 2013;Rossi Stacconi et al, 2017).…”

“…These results suggest that L. heterotoma's virulence is not strong enough to resist the immune reaction of D. suzukii. This was also observed in other studies (Chabert et al, 2012;Kacsoh & Schlenke, 2012;Knoll et al, 2017;Poyet et al, 2013;Rossi Stacconi et al, 2017).However, a single female succeeded to complete its development in this study, and higher rates of successful development were observed when testing various geographic strains of the parasitoid (P. Girod A. japonica and L. japonica that attacked and developed in larvae in both substrates, Ganaspis sp. parasitized many more larvae in blueberries compared to artificial diet.…”

“…In the invaded regions, larval parasitoids such as Leptopilina heterotoma (Thompson) (Hymenoptera, Figitidae), Leptopilina boulardi Barbotin, Carton & Keiner-Pillault (Hymenoptera, Figitidae) and Asobara tabida (Nees) (Hymenoptera, Braconidae), which are important natural enemies of local Drosophila spp., are rarely able to develop successfully in D. suzukii larvae, partly because of the strong host immune response of the fly larvae (Chabert, Allemand, Poyet, Eslin, & Gibert, 2012;Gabarra et al, 2015;Poyet et al, 2013;Rossi Stacconi et al, 2015). The main immune defense observed on Drosophila spp.…”

“…In D. suzukii's native range, larval parasitoids in the genera Asobara, Leptopilina and Ganaspis can successfully develop on the host (Buffington & Forshage, 2016;Daane et al, 2016;Kasuya, Mitsui, Ideo, Watada, & Kimura, 2013;Mitsui & Kimura, 2010;Novković, Mitsui, Suwito, & Kimura, 2011). In parasitoids of Drosophila spp., as in other systems, the success in host-parasitoid interaction and the evolution of this interaction are related to two major factors: (i) the immune response of the host and the virulence of the parasitoid (Poyet et al, 2013); (ii) host detection mechanisms at both long and short distances, which can be very different among parasitoids of Drosophila spp. (Vet & van Alphen, 1985).…”

The Avoided Target: The Ceratitis capitata Cellular Encapsulation Response

“…Control wild-type D. melanogaster exhibited zero encapsulation rates. Lastly, a strong correlation between CHC and encapsulation was confirmed in D. suzukii [65]. The upshot of this clear: Drosophila researchers who investigate host-parasitoid interactions are in the habit of asking about correlations between encapsulation rates and CHC.…”