Host manipulation by a herbivore optimizes its feeding behaviour

Plant-manipulating herbivores can modify their host nutrients and defensive compounds to their own advantage. This generally results in enhanced performance of herbivores on modified tissues, but the anatomical and biochemical modifications undergone by host tissues could also modify the herbivores' behaviour. Phloeomyzus passerinii induces a reaction tissue in the bark of its susceptible poplar hosts, suggesting a host-plant manipulation by the aphid. We investigated whether the formation of this reaction tissue, confirmed by histological sections, affected the performance and feeding behaviour of the aphid. In addition we studied how host resistance affected these parameters by comparing two host genotypes of different susceptibility. Aphids developed faster on the preinfested susceptible host genotype, whereas no effect was detected on the resistant one, confirming an improvement in the host's nutritional value due to the preinfestation, in agreement with the nutrition hypothesis. The DC-EPG technique indicated that in both host genotypes, preinfestation shortened the delay until the first probe and increased both the rate and duration of sustained ingestion, and consequently host acceptance. This suggests that host manipulation can adjust not only the nutritional value of plant tissues at an optimal level for development but also host acceptance by the herbivores. In the resistant host genotype though, the number of probes and the duration of parenchyma exploration increased in the galled tissue, which was congruent with extensive cell wall modifications indicated by more extended induced lignification. The adaptive consequences of this modified feeding behaviour are discussed.