Plant guttation is a fluid from xylem and phloem sap secreted at the margins of leaves from many plant species. All previous studies have considered guttation as a water source for insects. Here, we hypothesized that plant guttation serves as a reliable and nutrient-rich food source for insects with effects on their communities. Using highbush blueberries as a study system, we demonstrate that guttation droplets contain carbohydrates and proteins. Insects from three feeding lifestyles, a herbivore, a parasitic wasp and a predator, increased their longevity and fecundity when fed on these guttation droplets compared to those fed on control water. Our results also show that guttation droplets, unlike nectar, are present on leaves during the entire growing season and are visited by numerous insects of different orders. In exclusion-field experiments, the presence of guttation modified the insect community by increasing the number of predators and parasitic wasps that visited the plants. Overall, our results demonstrate that plant guttation is highly reliable, compared to other plant-derived food sources such as nectar, and that it increases the communities and fitness of insects. Therefore, guttation represents an important plant trait with profound implications on multi-trophic insect–plant interactions.

Native to southeast Asia, the spotted-wing drosophila (Drosophila suzukii (Matsumura); Diptera: Drosophilidae) has become a major pest of small fruits in the Americas and Europe. Field studies were conducted over a two-year period (2015–2016) in cultivated highbush blueberry (Vaccinium corymbosum Linnaeus; Ericaceae) fields and adjacent non-crop habitats containing wild blueberries in New Jersey (United States of America). We tracked seasonal changes in D. suzukii adult abundance and fruit infestation throughout the ripening period (June–August). In both years, D. suzukii adult counts post-harvest were generally higher in traps located in non-crop habitats compared with those located in highbush blueberry fields. Wild and cultivated fruits synchronised in maturation, and the numbers of eggs laid and of emerged adults in both fruit types were comparable for most of the season, although sometimes these numbers were higher in wild fruits post-harvest. Overall, immature success (measured as the per cent egg-to-adult survival) was also mostly higher in wild than in cultivated fruits. Altogether, these studies document that non-crop habitats, and wild hosts therein, are used by D. suzukii during fruit ripening and may serve as potential sources of infestation to nearby highbush blueberry fields. Hence, methods that reduce D. suzukii populations in non-crop habitats may help manage this pest in neighbouring highbush blueberries.