Foliar fertilizers differentially affect larval survival and adult metal load in a Neotropical stingless bee

Pollinators are frequently exposed to agrochemicals, yet the toxicological risks posed by foliar fertilizers remain largely understudied despite their current key role in modern agriculture. This study assessed the effects of three widely used foliar fertilizers [copper sulfate (CuSO₄; 240 g kg⁻¹ Cu and 110 g kg⁻¹ S), boron (141.7 g L⁻¹ B), and a commercial micronutrient mixture (50.80 g L⁻¹ S, 6.35 g L⁻¹ B, 7.62 g L⁻¹ Cu, 38.10 g L⁻¹ Mn, 0.76 g L⁻¹ Mo, and 63.50 g L⁻¹ Zn] on immature development, adult morphology, body weight, locomotor behavior, and metal bioaccumulation in the stingless bee Melipona quadrifasciata. Immature development was assessed by egg hatching success, daily survival, pupation, and adult emergence, whereas locomotor behavior was evaluated through resting time, walking time, distance traveled, walking velocity, and the frequency and duration of freezing, moderate, and vigorous movements. CuSO₄ led to 100% mortality during immature development within 12 days after egg hatching. Boron reduced egg hatching to 42.7%, with only 20% of individuals surviving to day 20 and fewer than 5% successfully emerging as adults, whereas the micronutrient mixture allowed 80% adult emergence. Adults emerging from the micronutrient mixture treatment showed a 6.1% reduction in body mass but no changes in locomotor behavior, except for a slight increase in the frequency of moderate movements in grouped bees. These adults also exhibited elevated body concentrations of manganese, copper, and zinc. These findings underscore the toxicity of CuSO₄ and boron at field levels, and the comparatively lower toxicity but notable bioaccumulation potential of the micronutrient mixture, highlighting the need for broader toxicological assessments of foliar fertilizers on native pollinators.