On the track of insects responsible for misshaped apples

Abstract: With the broad use of specific control strategies against primary apple pests, secondary pest species such as fruit piercing insects gained importance. Although some of the species misshaping apples such as the apple fruit weevil (Tatianaerhynchites aequatus) or the forest bug (Pentatoma rufipes) are well known, we nevertheless suspect that a whole complex of insects might provoke similar fruit deformations. We tried to unravel this complex by weekly beating samples in young, mature and old apple orchards. 15 times more apples were pierced on untreated cider trees than in conventional orchards. Moreover, the number of misshaped fruits was correlated with the number of phytophagous Heteroptera as well as the number of folivorous weevils of the genus Phyllobius. In order to study these weevils’ ability to pierce fruits, adults of Phyllobius betulinus and P. oblongus were each released inside of sleeve cages enwrapping apple inflorescences. Contrary to our expectations, no indications of misshaped apples were observed in these sleeve cages. This indicates that these two Phyllobius species do not directly feed on apples and that their presence within attacked orchards is probably associated with a moderate use of pesticides. However, our exposure experiment also highlighted that the apple fruit weevil T. aequatus is able to misshape apples heavily. Overall, these investigations will help to unravel the complex of fruit piercing insects in order to identify the principal species responsible for misshaped fruits and to adapt IPM control strategies against these secondary apple pests.