Effects of neonicotinoid imidacloprid exposure on bumble bee (Hymenoptera: Apidae) queen survival and nest initiation

Abstract

Neonicotinoids are highly toxic to insects and may systemically translocate to nectar and pollen of plants where foraging bees may become exposed. Exposure to neonicotinoids can induce detrimental sublethal effects on individual and colonies of bees and may have long-term impacts, such as impaired foraging, reduced longevity, and reduced brood care or production. Less well-studied are the potential effects on queen bumble bees that may become exposed while foraging in the spring during colony initiation. This study assessed queen survival and nest founding in caged bumble bees [Bombus impatiens (Cresson) (Hymenoptera: Apidae)] after chronic (18-d) dietary exposure of imidacloprid in syrup (1, 5, 10, and 25 ppb) and pollen (0.3, 1.7, 3.3, and 8.3 ppb), paired respectively. Here we show some mortality in queens exposed at all doses even as low as 1 ppb, and, compared with untreated queens, significantly reduced survival of treated queens at the two highest doses. Queens that survived initial imidacloprid exposure commenced nest initiation; however, they exhibited dose-dependent delay in egg-laying and emergence of worker brood. Furthermore, imidacloprid treatment affected other parameters such as nest and queen weight. This study is the first to show direct impacts of imidacloprid at field-relevant levels on individual B. impatiens queen survival and nest founding, indicating that bumble bee queens are particularly sensitive to neonicotinoids when directly exposed. This study also helps focus pesticide risk mitigation efforts and highlights the importance of reducing exposure rates in the early spring when bumble bee queens, and other wild bees are foraging and initiating nests.

Effects of neonicotinoid insecticide exposure and monofloral diet on nest-founding bumblebee queens

“…Neonicotinoid insecticides are neurotoxins that interfere with nicotinic acetylcholine receptor signalling, but the full extent of their sublethal effects is currently not well understood. Negative effects on egg laying have been previously found in workers of the species B. terrestris [33,65], and in queens of B. impatiens [40] and B. terrestris [36]. These previous findings, and our similar finding here, may have been caused in part by the negative effect of the insecticide on motor activity, which may reduce egg laying, brood feeding and other activities.…”

Transcriptome analysis reveals nutrition‐ and age‐related patterns of gene expression in the fat body of pre‐overwintering bumble bee queens

“…Neonicotinoids are primarily used to control agricultural pest insect populations, and they accumulate in soil (Bonmatin et al, ) and can be detected in the pollen and nectar of nontarget plants visited by pollinators (David et al, ; Stoner & Eitzer, ). Negative impacts of neonicotinoids have also been observed in bumble bee queens during the nest‐founding stage of their life cycle, which follows the diapause period (Baron, Raine, & Brown, ; Baron, Jansen, Brown, & Raine, ; Wu‐Smart & Spivak, ; Leza et al, ). Our finding that P450s are down‐regulated in queens fed sugar‐limited diets is, potentially, relevant to our understanding of the molecular basis for synergistic interactions between poor nutrition and the susceptibility to pesticides and other stressors in bumble bees.…”

Imidacloprid impairs performance on a model flower handling task in bumblebees (Bombus impatiens)

“…As discussed, colony initiation by queens is a highly demanding and precarious stage of the bumblebee life cycle. Studies have indicated that sub-lethal neonicotinoid exposure can delay and reduce both colony initiation and brood emergence (Baron et al, 2017a;Wu-Smart & Spivak, 2018). Even a slow start could mean the difference between a colony producing queens or not.…”