Investigating the impacts of field-realistic exposure to a neonicotinoid pesticide on bumblebee foraging, homing ability and colony growth

Abstract

The ability to forage and return home is essential to the success of bees as both foragers and pollinators. Pesticide exposure may cause behavioural changes that interfere with these processes, with consequences for colony persistence and delivery of pollination services.We investigated the impact of chronic exposure (5-43 days) to field-realistic levels of a neonicotinoid insecticide (2·4 ppb thiamethoxam) on foraging ability, homing success and colony size using radio frequency identification (RFID) technology in free-flying bumblebee colonies.Individual foragers from pesticide-exposed colonies carried out longer foraging bouts than untreated controls (68 vs. 55 min). Pesticide-exposed bees also brought back pollen less frequently than controls indicating reduced foraging performance.A higher proportion of bees from pesticide-exposed colonies returned when released 1 km from their nests; this is potentially related to increased orientation experience during longer foraging bouts. We measured no impact of pesticide exposure on homing ability for bees released from 2 km, or when data were analysed overall.Despite a trend for control colonies to produce more new workers earlier, we found no overall impacts of pesticide exposure on whole colony size. Synthesis and applications. This study shows that field-realistic neonicotinoid exposure can have impacts on both foraging ability and homing success of bumblebees, with implications for the success of bumblebee colonies in agricultural landscapes and their ability to deliver crucial pollination services. Pesticide risk assessments should include bee species other than honeybees and assess a range of behaviours to elucidate the impact of sublethal effects. This has relevance for reviews of neonicotinoid risk assessment and usage policy world-wide.

Keywords: RFID tagging; agrochemical; bumble bee Bombus terrestris; flower‐visiting insects; insecticide; navigation; neonicotinoids; pesticide exposure; pollination.

Figure 1

Mean daily number of (a) bouts and (b) bout duration (hours) for bees exposed to control or pesticide (2·4 ppb thiamethoxam) treatments. Columns represent means (± SE) across all individuals recorded as foragers (n = 135 individuals in control and 107 pesticide). Letters indicate significant differences (P < 0·05).

Figure 2

The number of bees returning carrying pollen to colonies exposed to control or pesticide (2·4 ppb thiamethoxam) treatments per observation period (443 returning bees observed in total; of these 128 control bees and 78 pesticide bees carried pollen). Data shown are means (± SE) across four colonies of each treatment on 11 observation days.

Figure 3

The proportion of bees that returned from each treatment group – control or pesticide (2·4 ppb thiamethoxam) – from release sites at 1 km and 2 km. Data shown are colony means (± SE), although data were analysed at the individual level with colony as a random effect (n = 27 control and 26 pesticide‐exposed bees released from 1 km, and 24 control and 19 pesticide‐exposed bees released from 2 km). Analysis showed a significant difference between homing performance of control and pesticide treatments at 1 km, but not at 2 km.

Figure 4

Mean daily size (number of individuals, including number of bees that emerged, number of bees that were found dead in the colony, and number of bees that were recorded leaving the colony without returning) of colonies in each treatment. Data points represent means (± SE) across four colonies in each treatment.