Behavioural Brain Research 95 (1998) 23 – 29 The foraging gene affects adult but not larval olfactory-related behavior in Drosophila melanogaster S.A. Shaver a,c , C.J. Varnam b,c , A.J. Hilliker a , M.B. Sokolowski c, * a Department of Genetics and Molecular Biology, Guelph Uniersity, Guelph, Ont. N1G 2W1, Canada b Department of Zoology, Uniersity of Toronto, Toronto, Ont. M5S 1A1, Canada c Department of Biology, York Uniersity, Toronto, Ontario M3J 1P3, Canada Received 24 March 1997; received in revised form 19 August 1997; accepted 26 August 1997 Abstract This study investigates the ability of larvae and adult rover and sitter Drosophila melanogaster to detect and migrate towards the source of a fly medium attractant using larval plate assays and an adult olfactory trap assay. Allelic variation at the foraging locus which encodes a cGMP-dependent protein kinase (PKG) did not affect larval olfactory response in the larval plate assays. In contrast, adult males of the sitter mutant for s2 exhibited an olfactory trap response (OTR) which was significantly greater than that of males of the wild type for R strain from which for s2 was derived and further genetic analysis showed that this was attributable to the for s2 allele. The olfactory responses of for R and for s2 flies to three odours (propionic acid, ethyl acetate and acetone) in a T-maze assay was normal indicating that they did not have general olfactory deficits. The finding that adult flies who differ in their PKG enzyme activities differ in foraging behaviours and olfactory trap responses to yeast odours suggests that PKG signalling pathways are involved in olfactory related responses to food. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Olfaction; Foraging; Behavior; Genetics; Drosophila 1. Introduction The senses are the means by which organisms obtain information regarding their surroundings. Drosophila are sensitive to a wide variety of odourants and are capable of odour discrimination. The third antennal segment and maxillary palp of the adult and the dorsal organ of the larval antenno – maxilary complex have been identified as the main olfactory organs of this organism [2,5,35,36]. The underlying signal transduc- tion processes which mediate the olfactory avoidance, attraction and adaptation responses which result when an odour is detected by these olfactory organs are not well defined. However, mutagenesis experiments have begun to identify a number of genes which mediate the manner and/or rate with which Drosophila melanogaster respond to various odours (olfactory response). The products of several of these genes have been character- ized and have been found to play a role in a number of signal transduction pathways (e.g. [13,20,24,27,38,43]). The natural habitat of Drosophila is a complex one which is continually changing. Adult females of many species deposit eggs on substrates (e.g. fruit) [6] which contain microorganisms such as yeasts, which metaboli- cally alter these substrates and release products such as alcohols, acids, esters, ketones and aldehydes [6,22]. Thus, while foraging for food, Drosophila are exposed to an abundance of olfactory stimuli. It is likely that olfactory response plays an important role in the selec- tion of food [3] and in the identification of hazardous substances [21]. D. melanogaster larvae forage for food by shovelling with their mouth hooks while moving along the surface of the feeding substrate [23,37]. This foraging behaviour is measured as the distance a larva travels on a nutritive * Corresponding author. Tel: +1 416 7365391; fax: +1 416 7365989; e-mail: mbsoko@yorku.ca 0166-4328/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0166-4328(97)00206-4