Investigating the abundance and diversity of sawflies (Hymenoptera, Symphyta) within commercial Sitka spruce plantation forests in mid‐Wales

Abstract

Sitka spruce is a widely planted and economically important tree species in the United Kingdom; hence, identifying any future biotic or abiotic threats to its productivity is important. Defoliating insects are widely considered to be major forest disturbance agents, and these can include the sawflies (Symphyta), which are well known to reach high population densities that can cause significant outbreak events, leading to tree mortality or impacts on growth. The aim of the current study was to investigate the abundance and diversity of sawflies within stands of Sitka spruce over an elevation range and to evaluate whether there were any potentially important species present. Experimental plots were established in two commercial forest plantations in mid‐Wales, and the adult sawfly community was assessed over a 3‐year period using yellow pan traps. Sixty species of sawfly were caught over the 3‐year period, which accounted for >11% of all known British sawfly species. Results indicated that there were generally greater abundance and diversity of sawflies at lower elevational plots, where temperatures were higher. The most abundant sawfly species captured in the study was the notable defoliator species, the mountain spruce sawfly (Epicenematus montanus), which was found in particularly high numbers in the low‐elevation plot in Hafren forest. A further seven spruce‐associated sawfly species were also caught across the experimental plots. The study highlighted the presence of a number of notable spruce‐associated sawfly species (E. montanus and Pristiphora spp.), some of which have caused significant defoliation of spruce (Picea) species in Europe. The generally higher abundance of these sawflies at lower elevations indicated that Sitka spruce may potentially become more vulnerable to defoliation events caused by sawfly outbreaks in the future, especially when considering current projected climate change predictions.