Open access publications in the SLU publication database

Abstract

Ants interact with plants in various ways and ant presence on plants can decrease local abundance or activity of herbivores, which in turn increases plant fitness. Red wood ants (Formica rufa group) are common species in forests of northern Europe. A large part of their diet consists of honeydew produced by ant-tended arboreal aphids and ants have been shown to affect a wide range of herbivores both in tree canopies and undergrowth. The pine weevil, Hylobius abietis (L.), is an economically important forest pest species. Adult beetles feed on stem bark of transplanted conifer seedlings and cause severe seedling mortality in forest regeneration areas. In this thesis, interactions between ants and pine weevils were investigated to evaluate whether ants can affect weevils’ damage to conifer seedlings. The results showed that pine weevil damage to conifer seedlings with a food source attended by ants was significantly lower (by ca. 30%) compared to control seedlings. This effect was mainly ascribed to non-consumptive interactions i.e., the presence of ants distracted pine weevils from feeding. Observations of ant-weevil interactions supported this hypothesis, as ants frequently attacked pine weevils close to ant-attended seedlings and weevils’ locomotion behaviour increased during ant attacks. The effects of ant-attendance may be generalized to other aggressive ant species, as ant-attended seedlings visited by Lasius ants suffered lower damage by weevils compared to ant-excluded seedlings. Differences in ant abundance on the ground, however, did not affect damage to unbaited spruce seedlings, because similar feeding damage was recorded in areas with high and low abundance of red wood ants. Further, weevils’ damage to seedlings that were planted in close proximity to ant-attended seedlings was comparable to that of ant-excluded seedlings. This suggests that seedling protection by ants is probably mainly related to the ants' protection of food sources whereas abundance of ants has less effect on weevils’ feeding. Understanding the role of ants may have important implications for future strategies aiming to control pine weevil damage.