Exposure to cold: aversive Pavlovian conditioning in individual Drosophilamelanogaster

Temperature changes can be especially threatening for ectotherms, such as D rosophila melanogaster (Diptera: Drosophilidea Meigen, 1830), and in this s tudy we tested whether flies can associate olfactory stimuli with a sudden drop in temperature. Such Pavlovian conditioning would allow them to make a ppropriate behavioural and/or physiological responses in the future. We fou nd that exposing individual flies to one of two odours in the presence of a sudden drop in temperature resulted in Pavlovian conditioning with flies s ubsequently avoiding the odour paired with cold. The characteristics of Pav lovian conditioning in flies were comparable to those observed for mammalia n species. Specifically, the strength of conditioning increased with increa sing intensity of the cold and decreased as the time interval between the o lfactory stimulus (CS) and cold (US) was lengthened. Finally, the order in which CS and US were presented affected the strength of conditioning. Learn ing was observed when the CS preceded US and when the US immediately preced ed the CS, but not when the CS preceded the US by 30 s or more. These resul ts provide further evidence for learning in individual flies, and confirm t hat Pavlovian conditioning is a general mechanism used by organisms to obta in information about their environment.