Hygienic grooming is induced by contact chemicals in Drosophila melanogaster

Abstract

In social insects, grooming is considered as a behavioral defense against pathogen and parasite infections since it contributes to remove microbes from their cuticle. However, stimuli which trigger this behavior are not well characterized yet. We examined if activating contact chemoreceptive sensilla could trigger grooming activities in Drosophila melanogaster. We monitored the grooming responses of decapitated flies to compounds known to activate the immune system, e.g., dead Escherichia coli (Ec) and lipopolysaccharides (LPS), and to tastants such as quinine, sucrose, and salt. LPS, quinine, and Ec were quite effective in triggering grooming movements when touching the distal border of the wings and the legs, while sucrose had no effect. Contact chemoreceptors are necessary and sufficient to elicit such responses, as grooming could not be elicited by LPS in poxn mutants deprived of external taste sensilla, and as grooming was elicited by light when a channel rhodopsin receptor was expressed in bitter-sensitive cells expressing Gr33a. Contact chemoreceptors distributed along the distal border of the wings respond to these tastants by an increased spiking activity, in response to quinine, Ec, LPS, sucrose, and KCl. These results demonstrate for the first time that bacterial compounds trigger grooming activities in D. melanogaster, and indicate that contact chemoreceptors located on the wings participate in the detection of such chemicals.

Drosophila Chemoreceptors: A Molecular Interface Between the Chemical World and the Brain

“…The anterior margin of the wing contains chemosensory sensilla, which were found to respond to tastants in pioneering studies of Marion-Poll and others [5, 10]. Sensilla on the ovipositor of larger flies have been shown electrophysiologically to have gustatory function [11, 12].…”

Molecular neurobiology of Drosophila taste

“…Interestingly, functional classes of deterrent neurons in the labellum are distinct from those found in the tarsi, suggesting that bitter tastant space may be sampled differentially by different organs [1,2]. Bitter neurons in tarsi and wings also respond to microbial lipopolysaccharides and trigger grooming behaviors [17]. Functional variations between taste organs are supported by the observation that distinct subsets of Gr genes are expressed in labellar, tarsal and pharyngeal organs [1-3], and also that bitter neurons in different organs can have opposite effects on feeding and oviposition behaviors [18].…”

Chemicals and chemoreceptors: ecologically relevant signals driving behavior in Drosophila

“…From the taste organs located in the mouth parts, proboscis, and legs, GRNs transmit directly or through activation of interneurons the gustatory information to the subesophageal ganglion (SOG), a dedicated taste center in the brain . Some taste-like sensilla are also present on the genitalia and on the wing margin, but their precise role is still under investigation (Boll and Noll, 2002;Yanagawa et al, 2014). In the SOG, axonal projections coming from different peripheral tissues are segregated even if they contain the same receptor .…”