Phenology, damage and parasitoids of the apple leaf cutter Coenorhinus pauxillus (Germ.) (Col.: Attelabidae)

Abstract

An outbreak on apple permitted a closer look at Coenorhinus pauxillus (Germar) (Col.: Attelabidae). The adult weevils emerge from mid-March onwards and attack the first unfolding leaves. Infested leaves drop when the larvae are in the 1^st or 2^nd instar, and it takes a further 4 weeks before the larvae are ready to pupate. Rearing of field-collected eggs and larvae is described. Leaf decomposition is an essential condition for pupation, as the fully-grown larvae do not leave their mine actively. Part of the population pupates more or less immediately and produces adult weevils in autumn. However, up to 70 % of the weevils remain in prolonged diapause; their pupation does not take place before the summer of the following year. Damage by the weevil involves not only the loss of leaves of flower clusters and shoots, but also feeding damage to young fruits. Two parasitoids were found. Observations indicate that 3 – 4 subsequently more abundant generations of Anaphes brachygaster Debauche (Hym.: Mymaridae) develop in eggs of C. pauxillus. Probles brevicornisHorstmann (Hym.: Ichneumonidae, Tersilochinae) emerges in May and oviposits in young weevil larvae on the tree. The parasitoid does not develop into a pupa until its host starts pupating. The outbreak of apple leaf cutter did not decline over three years, but did not spread into adjacent plantings.