Testing associational resistance against pine weevils mediated by Lasius ants attending conifer seedlings

Natural enemies attracted to plants may provide those plants with protection against herbivores but may also protect neighbouring plants, that is through associational resistance. Ant attendance may be an important mechanism for the occurrence of such effects because ants can reduce the damage caused by a wide variety of herbivorous insects. Ants have been shown, in a previous field experiment, to decrease the damage caused by the pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae), a pest species that causes high seedling mortality in forest regeneration areas. In this study, we specifically tested whether seedlings planted close to ant-attended seedlings experience associational resistance. We did this under laboratory conditions using the ant species Lasius niger (L.) (Hymenoptera: Formicidae). The feeding damage by pine weevils was significantly reduced on seedlings attended by ants. The neighbouring seedlings, however, did not experience associational resistance. Nevertheless, some associational effects were observed as the number of weevils recorded on both ant-attended and neighbouring seedlings was significantly lower compared with ant-excluded seedlings.