The impact of stem galls induced by Hemadas nubilipennis Ashmead on shoot characteristics of lowbush blueberry

Abstract

The effect of galls induced by Hemadas nubilipennis Ashmead (Hymenoptera: Pteromalidae) on the morphology and reproduction of lowbush blueberry (Vaccinium angustifolium Aiton) was studied over two seasons in three Nova Scotia blueberry fields. Comparisons of galled and non-galled shoot characteristics, and position on shoots of galls formed in the years of vegetative and reproductive growth were made. In June 1999, 30 newly galled vegetative shoots were arbitrarily selected, tagged and measured along with similar sized non-galled shoots on the galled clone and a neighbouring non-galled clone. Shoot characteristics were measured in the reproductive season during bloom and after harvest. At two sites, the dry weights of leaves and stems on galled shoots measured in the reproductive season were significantly less than non-galled shoots, but at a third site there was no difference in stem allocation. Galls reduced berry production on shoots at two sites. Proportions of terminally positioned galls differed significantly among study sites in the reproductive season. Shoots with terminal galls were significantly shorter, lighter and allocated less weight to leaves and stems than shoots with basally positioned galls. If the reports of increasing gall populations in Nova Scotia during the 1990s are correct, there may be good reason to believe that there will be significant economic loss of blueberries in the future. Key words: Gall, blueberry (lowbush), Hemadas nubilipennis, Vaccinium angustifolium