The invasive pest Drosophila suzukii uses trans-generational medication to resist parasitoid attack

Abstract

Animal medication is a behavioral strategy to resist enemies based on the use of substances from the environment. While it has been observed in several animals, whether invasive species can use medication to resist new enemies during its expansion is unknown. Here, we show that the worldwide invasive pest Drosophila suzukii performs trans-generational prophylactic medication by adapting its oviposition behavior in the presence of enemies. We find that flies preferentially lay their eggs on media containing atropine - an entomotoxic alkaloid - in the presence of parasitoids. We further show that flies developing on atropine more efficiently resist parasitization by parasitoids. Finally, we find that developing in hosts reared on atropine strongly impacts the life-history traits of parasitoids. This protective behavior is reported for the first time in a pest and invasive species, and suggests that animal medication may be an important driver of population dynamics during invasions.

Figure 1. Number of eggs laid by D. suzukii on regular or atropine medium in the absence (dotted lines) or presence of parasitoids (solid lines).

(A) In the absence or presence of T. cf. drosophilae (n = 200 experimental replicates). (B) In the absence or presence of A. japonica (n = 200 experimental replicates). Bars represent Standard Errors of the mean.

Figure 2. The effect of atropine on drosophila-parasitoid interaction.

We recorded emergences (A) in control conditions, without parasitic pressure; (B) in case of parasitization by T. cf. drosophilae; (C) in case of parasitization by A. japonica. Light gray boxes: Mortality Rate of the fly-parasitoid pairs; Yellow boxes: Successful parasitoid emergence; Green boxes: Successful drosophila emergences (n = 100 experimental replicates for each modality).

Figure 3. Impact of atropine in drosophila developmental medium on two life history traits of adult parasitoids.

We recorded tibia size and number of eggs per ovary in (A) T. cf. drosophilae. (B) A. japonica. Broken black lines: parasitoids emerged from hosts reared on regular medium; solid red lines: parasitoids emerged from hosts reared on atropine medium.