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.
Highlights
Insects, especially Diptera, devote a considerable amount of time to self-grooming
We demonstrate for the first time that grooming activities in D. melanogaster adults are triggered by bacterial suspensions of E. coli, its surface compound, LPS, and by aversive chemicals like quinine and NaCl at a high concentration
Mechanosensation is not required to elicit this response as sucrose and water did not induce grooming, and Poxn70 mutants deprived of their external taste receptors were insensitive to LPS
Summary
Grooming involves brushing the body and the wings with the legs, and cleaning the legs and the antenna with the mouthparts. Stereotyped grooming occur in response to mechanical stimulation of dorsal bristles in flies (Burg et al, 1993), of eye bristles in cricket (Hensler, 1986), or of leg and wing hairs in locusts (Burrows and Newland, 1994; Newland and Burrows, 1994, 1997; Page and Matheson, 2004). Grooming or scratching is observed in response to noxious molecules in flies (Dethier, 1972) and in locusts (Newland, 1998; Page and Matheson, 2004). Grooming serves a number of purposes, related to maintaining the integrity of the body and avoiding noxious stimuli
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