A meta-analysis of effects of Bt crops on honey bees (Hymenoptera: Apidae)

Abstract

Background: Honey bees (Apis mellifera L.) are the most important pollinators of many agricultural crops worldwide and are a key test species used in the tiered safety assessment of genetically engineered insect-resistant crops. There is concern that widespread planting of these transgenic crops could harm honey bee populations.

Methodology/principal findings: We conducted a meta-analysis of 25 studies that independently assessed potential effects of Bt Cry proteins on honey bee survival (or mortality). Our results show that Bt Cry proteins used in genetically modified crops commercialized for control of lepidopteran and coleopteran pests do not negatively affect the survival of either honey bee larvae or adults in laboratory settings.

Conclusions/significance: Although the additional stresses that honey bees face in the field could, in principle, modify their susceptibility to Cry proteins or lead to indirect effects, our findings support safety assessments that have not detected any direct negative effects of Bt crops for this vital insect pollinator.

Figure 1. Meta-analysis of studies that report survival of honey bees exposed to Bt Cry proteins or plant tissues (pollen) that are active against lepidopterans and coleopterans.

Effect size is Hedge's d, and error bars represent bias-corrected bootstrap 95% confidence intervals. Positive mean effect sizes indicate improved survival when exposed to Cry proteins compared to water or sugar-water control treatments. N = number of lines of independent data summarized by each bar.

Figure 2. Comparison of effect sizes for larval and adult honey bees exposed to different Bt Cry proteins or plant tissues: (A) lepidopteran-active and coleopteran-active proteins combined, (B) lepidopteran-active Bt Cry proteins only, and (C) coleopteran-active protein only.

Error bars and N are as described for Figure 1.