Synergism between local- and landscape-level pesticides reduces wild bee floral visitation in pollinator-dependent crops

The hazard pesticides pose to pollinators are well-understood from laboratory studies. However, the field-level response of pollinators to pesticide use in agroecosystems is not well-established, nor is it clear if synergisms between pesticides affect pollinator visitation to crops. Here, we evaluated if fungicide and insecticide use posed a hazard to wild and honeybees at 87 cucurbit-pumpkin, cucumber, watermelon-farms in the Midwestern United States. We also evaluated if synergisms between local- (i.e. focal cucurbit field) and landscape-level (i.e. surrounding crops) pesticide use influence wild and honeybee visitation to crop flowers. We found that bees were exposed to pesticides above regulatory levels of concern and that synergisms between a few local insecticides and landscape-level fungicides reduced wild bee visitation to cucurbit flowers. Honey and bumblebee visitation to crops was not strongly influenced by synergisms between pesticides used at the local and landscape level. Synthesis and applications. We found pesticides posed hazards to honey and wild bee species. However, pesticides were less likely to affect short-term visitation rates of honeybees compared with wild bee species. Thus, there is a need for changes in pesticide use at large spatial scales to reduce reliance on honeybees and maximize wild bee visitation to pollinator-dependent crops. We suggest that a multifaceted approach, involving collaborations between farmers, consumers and policymakers, will be fruitful to promote changes in pesticide use and wild bee pollinators.

Automated summary

While laboratory studies have established the hazards pesticides pose to pollinators, their field-level response in agroecosystems remains unclear. This study found that bees were exposed to pesticides above regulatory levels of concern, with synergisms between certain local insecticides and landscape-level fungicides reducing wild bee visitation. However, honey and bumblebee visitation to crops was not greatly influenced by pesticide synergisms.