<i>Drosophila</i> Avoids Parasitoids by Sensing Their Semiochemicals via a Dedicated Olfactory Circuit

Abstract

<div><p>Detecting danger is one of the foremost tasks for a neural system. Larval parasitoids constitute clear danger to <i>Drosophila</i>, as up to 80% of fly larvae become parasitized in nature. We show that <i>Drosophila melanogaster</i> larvae and adults avoid sites smelling of the main parasitoid enemies, <i>Leptopilina</i> wasps. This avoidance is mediated via a highly specific olfactory sensory neuron (OSN) type. While the larval OSN expresses the olfactory receptor Or49a and is tuned to the <i>Leptopilina</i> odor iridomyrmecin, the adult expresses both Or49a and Or85f and in addition detects the wasp odors actinidine and nepetalactol. The information is transferred via projection neurons to a specific part of the lateral horn known to be involved in mediating avoidance. <i>Drosophila</i> has thus developed a dedicated circuit to detect a life-threatening enemy based on the smell of its semiochemicals. Such an enemy-detecting olfactory circuit has earlier only been characterized in mice and nematodes.</p></div