Direct Effects of Carpophagous Insects on the Germination Ability and Early Abscission of Oak Acorns

Abstract

Carpophagous insects play an important role in decreasing the viability of acorns in both direct and indirect ways. Therefore they significantly influence the reproductive potential of oaks. As a direct effect, their feeding on the embryo and on the cotyledons may prevent the germination of the acorn and on the other hand, their damage causes premature acorn abscission. During 3 years, 60 acorn samples from five oak species (Turkey oak – Quercus cerris, pedunculate oak – Quercus robur, sessile oak – Quercus petraea, downy oak – Quercus pubescens, red oak – Quercus rubra) have been investigated. The average rate of damage varied a lot between years, but was always significant (2000: 36%, 2001: 61%, 2002: 51%). The insects’ influence causing premature acorn abscission was significant both for pedunculate and Turkey oaks. The premature acorn abscission was 34% of the total crop in 2000 for pedunculate oak (Curculio spp. 26%, Cydia spp. 2% and Andricus quercuscalicis 6%) and 39% in 2001 (Curculio spp. 14%, Cydia spp. 2%, Andricus quercuscalicis 13%, Callirhytis glandium 10%). In case of Turkey oak it was 29% in 2001 (C. glandium 16%, Neuroterus saliens 13%, and 12% in 2002 (C. glandium 10%, N. saliens 2%).