Chronic exposure of imidacloprid and clothianidin reduce queen survival, foraging, and nectar storing in colonies of Bombus impatiens.

Jamison Scholer,Vera Krischik,Peter K Dearden

doi:10.1371/journal.pone.0091573

Abstract

In an 11-week greenhouse study, caged queenright colonies of Bombus impatiens Cresson, were fed treatments of 0 (0 ppb actual residue I, imidacloprid; C, clothianidin), 10 (14 I, 9 C), 20 (16 I, 17C), 50 (71 I, 39 C) and 100 (127 I, 76 C) ppb imidacloprid or clothianidin in sugar syrup (50%). These treatments overlapped the residue levels found in pollen and nectar of many crops and landscape plants, which have higher residue levels than seed-treated crops (less than 10 ppb, corn, canola and sunflower). At 6 weeks, queen mortality was significantly higher in 50 ppb and 100 ppb and by 11 weeks in 20 ppb–100 ppb neonicotinyl-treated colonies. The largest impact for both neonicotinyls starting at 20 (16 I, 17 C) ppb was the statistically significant reduction in queen survival (37% I, 56% C) ppb, worker movement, colony consumption, and colony weight compared to 0 ppb treatments. Bees at feeders flew back to the nest box so it appears that only a few workers were collecting syrup in the flight box and returning the syrup to the nest. The majority of the workers sat immobilized for weeks on the floor of the flight box without moving to fed at sugar syrup feeders. Neonicotinyl residues were lower in wax pots in the nest than in the sugar syrup that was provided. At 10 (14) ppb I and 50 (39) ppb C, fewer males were produced by the workers, but queens continued to invest in queen production which was similar among treatments. Feeding on imidacloprid and clothianidin can cause changes in behavior (reduced worker movement, consumption, wax pot production, and nectar storage) that result in detrimental effects on colonies (queen survival and colony weight). Wild bumblebees depending on foraging workers can be negatively impacted by chronic neonicotinyl exposure at 20 ppb.

Highlights

Honey bees, bumblebees, and other native bees pollinate 30% of the plants that produce the vegetables, fruits, and nuts that we consume and more than 100 crops in North America require pollinators [1,2]
The objectives of this study were to investigate the effects of higher concentrations of imidacloprid and clothianidin, similar to those found in some crops and landscape plants, on individual behavior and colony health of the American bumblebee, Bombus impatiens Cresson by monitoring: 1) queen health, 2) worker behavior, 3) colony health
1 of the 4 treatment residues is lower than the planned treatment and for clothianidin all 4 treatment residues are lower than the planned treatment (Table 1)

Summary

Introduction

Bumblebees, and other native bees pollinate 30% of the plants that produce the vegetables, fruits, and nuts that we consume and more than 100 crops in North America require pollinators [1,2]. In 2007, there were 49.5% fewer managed honey bee (Apis mellifera) colonies in North America than in 1961 [4]. Managed honey bee colony mortality has been estimated to be 30% since 2007 [5,6]. Colony stressors include habitat loss, nutrient deficiencies, Nosema pathogens [7,8], viruses [9], Varroa mites [6], pesticide exposure [10,11,12], interactions between Nosema and imidacloprid [13,14], and Nosema and fipronil [15,16]. North American bumblebee species Bombus occidentalis, B. pensylvanicus, and B. affinus are in decline. These species had significantly higher N. bombi loads and lower genetic diversity compared to healthy populations [17,18]. A combination of factors is most likely to contribute to bee losses [12,19,20]

Objectives

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Conclusion