Associative learning and memory duration in the parasitic wasp Lariophagus distinguendus

Lariophagus distinguendus (Pteromalidae, Hymenoptera) is an ectoparasitoid of larvae of the granary weevil Sitophilus granarius which develop inside grains. Female parasitoids were trained by keeping them for 1 h on grains infested with their hosts in the presence of the odorant furfurylheptanoate (FFH). In olfactometer experiments, these wasps afterwards preferred the odour field containing FFH as compared to control fields. Control experiments with; i) naïve wasps; ii) wasps exposed to infested grains only; iii) to FFH only; and iv) to infested grains first and FFH later, did not reveal any response to FFH. This indicates that the reaction to FFH is caused by associative learning due to host experience as unconditioned stimulus. Experiments on the durability of the learned response demonstrated that host experience in the presence of FFH induces a memory that can be observed for at least 144 h and most likely is equivalent to long-term memory in honey bee Apis mellifera and Drosophila melanogaster.