Time-course analysis of <i>Drosophila suzukii</i> interaction with endoparasitoid wasps evidences a delayed encapsulation response compared to <i>D</i>. <i>melanogaster</i>

<div><p><i>Drosophila suzukii</i> (the spotted-wing Drosophila) appears to be unsuitable for the development of most Drosophila larval endoparasitoids, be they sympatric or not. Here, we questioned the physiological bases of this widespread failure by characterizing the interactions between <i>D</i>. <i>suzukii</i> and various parasitoid species (<i>Asobara japonica</i>, <i>Leptopilina boulardi</i>, <i>Leptopilina heterotoma</i> and <i>Leptopilina victoriae</i>) and comparing them with those observed with <i>D</i>. <i>melanogaster</i>, a rather appropriate host. All parasitoids were able to oviposit in L1 and L2 larval stages of both hosts but their propensity to parasitize was higher on <i>D</i>. <i>melanogaster</i>. <i>A</i>. <i>japonica</i> and, to a much lesser extent, <i>L</i>. <i>heterotoma</i>, were the two species able to successfully develop in <i>D</i>. <i>suzukii</i>, the failure of the parasitism resulting either in the parasitoid encapsulation (notably with <i>L</i>. <i>heterotoma</i>) or the host and parasitoid deaths (especially with <i>L</i>. <i>boulardi</i> and <i>L</i>. <i>victoriae</i>). Compared to <i>D</i>. <i>melanogaster</i>, encapsulation in <i>D</i>. <i>suzukii</i> was strongly delayed and led, if successful, to the production of much larger capsules in surviving flies and, in the event of failure, to the death of both partners because of an uncontrolled melanization. The results thus revealed a different timing of the immune response to parasitoids in <i>D</i>. <i>suzukii</i> compared to <i>D</i>. <i>melanogaster</i> with a lose-lose outcome for parasitoids (generally unsuccessful development) and hosts (high mortality and possible reduction of the fitness of survivors). Finally, these results might suggest that some European endoparasitoids of Drosophila interact with this pest in the field in an unmeasurable way, since they kill their host without reproductive success.</p></div

Time-course of the wasp-host interaction in parasitized <i>D</i>. <i>suzukii</i> larvae.

<p>Live larvae of <i>D</i>. <i>suzukii</i> parasitized by the different parasitoid strains or <i>D</i>. <i>melanogaster</i> YR (YR) parasitized by <i>L</i>. <i>boulardi</i> ISy were dissected at different time (0h-240h) and the main observed steps of the encapsulation response are reported. E, free parasitoid egg; EE, encapsulated parasitoid egg; FL, free parasitoid larva; LC, free parasitoid larva with a thin coat of light-colored cells; DL, dead parasitoid larva; EL, encapsulated parasitoid larva; W, developing wasp. Aj, <i>Asobara japonica</i>; Lv, <i>Leptopilina victoriae</i>; LhGoth, <i>L</i>. <i>heterotoma</i> Gotheron; LhJapan, <i>L</i>. <i>heterotoma</i> Japanese strain; Lbm, <i>L</i>. <i>boulardi</i> ISm strain; Lby, <i>L</i>. <i>boulardi</i> ISy strain; Lb16, <i>L</i>. <i>boulardi</i> strain 16.</p

Suitability of <i>D</i>. <i>suzukii</i> L1 and L2 larval stages for the parasitoid species/strains.

<p>Suitability of <i>D</i>. <i>suzukii</i> L1 and L2 larval stages for the parasitoid species/strains.</p

Parasitoid propensity to parasitize (PP) and infestation rate (IR).

<p>Parasitoid propensity to parasitize (PP) and infestation rate (IR).</p