Pollinators and plant nurseries: how irrigation and pesticide treatment of native ornamental plants impact solitary bees

Abstract

A key conservation goal in agroecosystems is to understand how management practices may affect beneficial species, such as pollinators. Currently, broad gaps exist in our knowledge as to how horticultural management practices, such as irrigation level, might influence bee reproduction, particularly for solitary bees. Despite the extensive use of ornamental plants by bees, especially little is known about how irrigation level may interact with insecticides, like water-soluble neonicotinoids, to influence floral rewards and bee reproduction. We designed a two-factor field cage experiment in which we reared Megachile rotundata (Fabricius) (Hymenoptera: Megachilidae) on containerized ornamental plants grown under two different irrigation levels and imidacloprid treatments (30% label rate dosage of a nursery formulation or an untreated control). Lower irrigation was associated with modest decreases in nectar volume and floral abundance in untreated plants, whereas irrigation did not affect plants treated with imidacloprid. Furthermore, higher irrigation decreased the amount of imidacloprid entering nectar. Imidacloprid application strongly reduced bee foraging activity and reproduction, and higher irrigation did not offset any negative effects on bees. Our study emphasizes the impact of a nursery neonicotinoid formulation on solitary bee foraging and reproduction, while highlighting interactions between irrigation level and neonicotinoid application in containerized plants themselves.

Ornamental roses for conservation of leafcutter bee pollinators

“…Installing bee hotels is a popular way of managing leafcutter bees 20 . Yet, recent meticulous field and controlled experiments have documented suboptimal propagation of the brood in bee hotels 16 , 22 . Studies have related this to an increasing parasitism rate in bee hotels 16 , 56 and poor choice of nesting materials 16 .…”

“…Yet, recent meticulous field and controlled experiments have documented suboptimal propagation of the brood in bee hotels 16 , 22 . Studies have related this to an increasing parasitism rate in bee hotels 16 , 56 and poor choice of nesting materials 16 . A recent study found 75% brood loss (N = 40 brood cells) to parasitism for Megachile lanata in the bee hotels in Bangalore 56 .…”

“…Leaves and petals of a range of plant species, including rose, have been unearthed in the nest tubes of leafcutter bees 15 , 16 , 18 , 23 , 57 . Plant surveys have reported an even greater number of leaf-foraging plant species in parts of southwest USA 15 and Asia 18 , 58 .…”

“…Several promising bee pollinators of crops require non-flower parts of plants for their biological and ecological processes 14 – 16 . Leafcutter bees, for instance, need young leaves for constructing brood cells 17 (Fig.…”

“…Leafcutter bees require fresh young leaves for collecting leaf discs to build brood chambers inside bee hotels or other suitable cavities. A pilot study in controlled conditions recently showed that the nesting material could drive the brood success in leafcutter bees 16 . Although we have some empirical studies for the leafcutter bees’ leaf foraging plants 15 , 18 , 23 , no recommendations have been made for the practitioners.…”