Early memory in the parasitoid wasp Nasonia vitripennis.

We studied early memory in Nasonia vitripennis, a parasitoid of fly pupae and emerging model organism for ecological questions in the context of learning. After associative training consisting of one drilling experience in a host in the presence of cinnamon, females showed a preference to cinnamon for at least 24 h. To study sensitisation, wasps were trained by one drilling in a host without cinnamon. These wasps were not attracted to cinnamon immediately afterwards. Obviously, sensitisation is not involved in early memory. Wasps that were anaesthetised by CO2 directly after associative training did not react to cinnamon 30-45 min later, but after 1 and 24 h. CO2 treatment≥5 min after training did not erase the reaction to cinnamon. This indicates the existence of four early memory phases. (a) One phase<5 min after training, in which CO2 has to be applied to become effective. (b) One subsequent phase which is resistant to CO2. (c) One phase<1 h in which memory can be erased by CO2 treatment directly after training. (d) One phase 1-24 h not affected by CO2 treatment. Together with earlier data this enables us to establish a complete memory structure for N. vitripennis.

Olfactory host finding, intermediate memory and its potential ecological adaptation in Nasonia vitripennis.

Associative learning of host-associated chemical cues was studied in Nasonia vitripennis, a parasitoid of fly pupae in nests of hole-nesting birds. When females encountered a fly pupa and performed one sequence of host recognition behaviour including drilling the ovipositor into the host in the presence of the artificial odour furfurylheptanoate (FFH), they were afterwards arrested by FFH in olfactometer experiments. The response vanished after 4 days and could be blocked after 3 days by feeding wasps with ethacrynic acid prior and after the training. This indicates the formation of an intermediate form of memory by one host experience in N. vitripennis. Interestingly, the trained wasps avoided odours that were not present during the host encounter, although naive wasps did not react to these odours. This unique behaviour probably causes wasps to focus during host searching on those chemical cues they have experienced in the host environment. Studies in nests of hole-nesting birds revealed that about 30% of all nests contained only one fly pupa, and laboratory studies showed that N. vitripennis females are able to parasitise around 100 fly pupae in their life. It is discussed that under these conditions, the formation of a non-permanent intermediate memory for host-associated odours after one host encounter is adaptive to avoid costs involved with formation and maintenance of memory for misleading cues. The demonstration of associative olfactory learning in N. vitripennis, the first parasitoid species with sequenced genome, opens the gate to study molecular mechanisms of memory formation and its ecological adaptation in parasitoids.