Factors affecting choice of buds by larvae of the ash bud moth Prays fraxinella Bjerk. (Lep., Yponomeutidae), and the implications for ash dieback

Abstract

AbstractAsh dieback is a chronic condition affecting a high percentage of mature pre‐senescent individuals of Fraxinus excelsior L. growing in hedgerows in mainland Britain. The ash bud moth has been mooted as a possible causal agent of dieback through attacking terminal buds of twigs and curbing tree growth: dieback is characterised by failure of terminal buds to flush. Patterns of winter bud utilisation by larvae of the ash bud moth Prays fraxinella were determined by examination of samples gathered during a field survey in 1989. Further twigs gathered in 1993 were used to determine mean values for various characteristics of buds which might influence bud choice by larvae. These bud characteristics were used to generate expected patterns of larval utilisation of buds at different positions on the twig; observed and expected distributions were compared by G‐tests. P. fraxinella larvae display a complex preference for buds situated at different points on the twigs, with preference for buds being strongly affected by bud size, and with preference for buds in the middle of the twigs being higher than that for either apical or basal buds possibly due to interactions between bud size, scales thicknesses, and availability of food within the buds. These findings suggest that failure of terminal buds to flush in instances of ash dieback are not likely to be due to bud moth attack. Size based preference for buds may have deleterious consequences for young trees, however, in which lateral buds are often too small to provide adequate resources for P. fraxinella larvae.