TY - JOUR

T1 - Gustatory response and appetitive learning in Microplitis croceipes in relation to sugar type and concentration.

AU - Wäckers, Felix L.

AU - Bonifay, Claire

AU - Vet, Louise E. M.

AU - Lewis, Joe

PY - 2006

Y1 - 2006

N2 - Insects can be conditioned to respond to odours through associative learning. Various learning parameters, such as the rate of odour acquisition, are known to depend on the type of conditioned stimulus. Here we investigate to what extent appetitive conditioning in the parasitoid Microplitis croceipes is also affected by characteristics of the food reward (unconditioned stimulus). We tested 1 M solutions of eight sugars naturally occurring in nectar and honeydew with respect to their effect on parasitoid gustatory response and their suitability as an unconditioned stimulus in the process of associative odour learning. To test for concentration effects, a separate experiment compared parasitoid performance with 1 M and 0.25 M of sucrose, respectively. Only exposure to glucose, fructose, sucrose and melezitose enhanced feeding relative to control individuals provided water. Raffinose, mannose, galactose and melibiose did not increase or decrease consumption, indicating that these sugars are neither phagostimulants nor phagodeterrents. In the conditioning experiments, parasitoids were allowed to feed on a particular sugar solution while being exposed to the floral odour cineole. Parasitoids that had been trained with the stimulatory sugars subsequently showed a clear conditioned feeding response to the cineole. Conditioning with galactose, mannose and melibiose, on the other hand, did not lead to successful odour acquisition. Conditioning with raffinose increased the tendency of the parasitoid to exhibit a conditioned feeding response, even though this response was significantly shorter than the response following training with stimulatory sugars. The level of cineole response was not significantly influenced by the concentration of a sucrose solution, even though the 0.25 M concentration was a weaker feeding stimulant. Our findings indicate that gustatory perception is the principal unconditioned stimulus in appetitive learning. The results with raffinose indicate that postingestive feedback may be involved in food associative learning as well.

AB - Insects can be conditioned to respond to odours through associative learning. Various learning parameters, such as the rate of odour acquisition, are known to depend on the type of conditioned stimulus. Here we investigate to what extent appetitive conditioning in the parasitoid Microplitis croceipes is also affected by characteristics of the food reward (unconditioned stimulus). We tested 1 M solutions of eight sugars naturally occurring in nectar and honeydew with respect to their effect on parasitoid gustatory response and their suitability as an unconditioned stimulus in the process of associative odour learning. To test for concentration effects, a separate experiment compared parasitoid performance with 1 M and 0.25 M of sucrose, respectively. Only exposure to glucose, fructose, sucrose and melezitose enhanced feeding relative to control individuals provided water. Raffinose, mannose, galactose and melibiose did not increase or decrease consumption, indicating that these sugars are neither phagostimulants nor phagodeterrents. In the conditioning experiments, parasitoids were allowed to feed on a particular sugar solution while being exposed to the floral odour cineole. Parasitoids that had been trained with the stimulatory sugars subsequently showed a clear conditioned feeding response to the cineole. Conditioning with galactose, mannose and melibiose, on the other hand, did not lead to successful odour acquisition. Conditioning with raffinose increased the tendency of the parasitoid to exhibit a conditioned feeding response, even though this response was significantly shorter than the response following training with stimulatory sugars. The level of cineole response was not significantly influenced by the concentration of a sucrose solution, even though the 0.25 M concentration was a weaker feeding stimulant. Our findings indicate that gustatory perception is the principal unconditioned stimulus in appetitive learning. The results with raffinose indicate that postingestive feedback may be involved in food associative learning as well.

KW - ODOUR LEARNING

KW - FOOD CONDITIONING

KW - REWARD QUALITY

KW - NECTAR

KW - HONEYDEW

KW - POST-INGESTIVE FEEDBACK

U2 - 10.1163/157075606777304230

DO - 10.1163/157075606777304230

M3 - Journal article

VL - 56

SP - 193

EP - 203

JO - Animal Biology

JF - Animal Biology

SN - 1570-7563

IS - 2

ER -