Underestimated Damage Caused by the European Hazelnut Weevil, Curculio nucum (Curculionidae)

Abstract

Hazelnut is an important food resource for the larvae and adults of the hazelnut weevil, Curculio nucum. While wormy nuts reflect the impact of such weevils at harvest time, little is known about the other types of damage they cause. To establish a comprehensive list of damages, and thereby identify the period of hazelnut vulnerability, male and female weevils were collected weekly and isolated on fruiting branches for 1 week. Based on nut development, higher rates of dropped nutlets, belted nuts, and blank nuts were observed at harvest. Marks specific to weevils, including wormy nuts, riddled shells, and larvae paths on the basal scar, were recorded during nut lignification. Belted nuts and blank nuts are empty nuts and constituted the main damage. The feeding activities of both the adults and larvae, but also the oviposition punctures, are likely to be the main causes of embryo abortions. The greatest damages occurred during kernel growth and when the shell had almost reached its final size. The larvae failed to penetrate fully lignified shells, with dead larvae mainly being found on the basal scar, the later softer part of the hazelnut. In Ségorbe cultivars, the dynamic of hazelnut development is the main factor involved in its susceptibility to C. nucum, with aborted nuts being the most underestimated damage.