Linking aboveground and belowground insect herbivore interactions: a case study with the vine weevil (Otiorhynchus sulcatus)

Interactions between insect herbivores and host plants are fundamental, shaping both ecosystem functions and community structure. One aspect of insect-plant interactions that has received considerable attention recently is the indirect linkages between aboveground and belowground insect herbivores via a shared host plant. To date, the relationship between a maternal insect aboveground and her soil dwelling offspring has been largely overlooked. This study aimed to examine the interactions between the adult insect and soil dwelling larvae of the vine weevil (Otiorhynchus sulcatus) with reference to the preference– performance hypothesis, using an agronomically important host plant, red raspberry (Rubus ideaus). A meta–analysis of aboveground–belowground insect herbivore interactions highlighted that belowground Coleopteran herbivores positively impacted aboveground Homoptera and that general predictions from conceptual models in the literature regarding the direction of interactions between insects were correct, but not statistically significant. In addition it was found that aboveground insect herbivores negatively influenced the survival of belowground herbivores. The preference–performance hypothesis was not supported in the findings for the vine weevil on raspberry. Instead a conflict between larval development and adult egg laying behaviour was observed, with a significant reduction in larval mass recorded when maternal adults fed on the same host plant. Larval mass was decreased by 19% after prior conspecific root feeding, but maternal weevils did not distinguish between plants with and without larvae for oviposition. Significant differences between larval performance (abundances and mass) on the raspberry cultivars Glen Rosa and Glen Ample were not correlated with adult oviposition aboveground. Instead, in some instances, maternal egg laying was correlated with foliar nitrogen content, suggesting that this may be an influential factor in the oviposition behaviour of adult vine weevils. Significant differences seen in larval performance in the laboratory were not reflected in the field, with adult vine weevil populations on Glen Rosa and Glen Ample showing no significant differences in terms of abundance. The findings from this study suggest that mother–offspring relationships in an aboveground–belowground context warrant further consideration. In particular, the identification of potential conflict between mother and offspring highlights another factor influencing aboveground–belowground relationships that could consequently influence terrestrial ecosystems.