Isn’t it just amazing how well adapted the tiny parasitic wasps are? Parasitoids want to lay their eggs in good, yummy caterpillars. Yummy caterpillars are those feeding on high quality plants. Quality of plants is partly determined by if their roots have been eaten by below ground herbivores. Plants smell differently above ground, depending on if their roots have been eaten or not. These odour variations are learned by the parasitic wasps when identifying the high quality hosts.
These results are presented in the new Early View paper “Effect of belowground herbivory on parasitoid associative learning of plant odours” by Marjolein Kruidhof and her co-workers. Here’s Marjolein’s own summary:
Only experienced parasitic wasps adapt their preference for plant odours in the presence of root feeders
Although hidden in the soil, insects that feed on plant roots often do not go unnoticed by insects living aboveground. Upon root feeding, the odour the plant emits into the air changes. Tiny parasitic wasps, which lay their eggs inside the body of host caterpillars that feed on the plant leaves, use these plant odours to locate their hosts. Researchers from the Netherlands Institute of Ecology (NIOO-KNAW) in the Netherlands tested whether two closely-related parasitic wasp species, Cotesia glomerata and C. rubecula, expressed a preference for plants with or without Delia radicum root feeders. As inexperienced wasps of both species did not respond to the presence of root feeders, they continued to investigate whether the parasitic wasps could develop a preference after gaining experience when parasitizing caterpillars on root-infested or root-uninfested plants. Indeed, both wasp species adapted their preference for plant odours to the presence of root feeders, but did so in an opposite direction. While C. glomerata learned to prefer the odour of plants with intact roots, C. rubecula learned to prefer the odour of root-infested plants. These findings stress the importance of not only assessing the influence of root herbivores on the responses of inexperienced parasitic wasps, but of also taking learned responses into account. In a publication that will soon appear in Oikos the authors discuss the possible reasons why these two parasitic wasp species respond so differently towards the presence of root feeders.