Multisystem effects of ready-mix insecticides on stingless bee Melipona scutellaris Latreille (Hymenoptera: Meliponini)

Melipona scutellaris, a generalist Brazilian stingless bee, is considered a key pollinator of natural vegetation and cultivated plants. Ready-mix insecticides are usually formulated with two active ingredients and have been used to control the most problematic pests but most likely have adverse effects, such as harming non-target insects. Therefore, we assessed the effects of chronic exposure to residual concentrations of five ready-mix insecticides, acetamiprid + bifenthrin, chlorantraniliprole + abamectin, chlorantraniliprole + lambda-cyhalothrin, thiamethoxam + chlorantraniliprole, and thiamethoxam + lambda-cyhalothrin, on the survival of M. scutellaris forager bees. We also determined the histopathological and physiological effects on the brain, midgut, and fat body of M. scutellaris. Chronic exposure to these insecticides adversely affected the survival and physiology of forager bees. Histopathological analysis revealed damage to the midgut, fat body, and brain with notable cell morphology and enzyme activity injuries. Acetamiprid + bifenthrin and chlorantraniliprole + abamectin induced significant changes in the midgut and fat body, whereas all the ready-mix insecticides induced morphological changes in the brain. Additionally, enzymatic biomarkers showed decreased alkaline phosphatase (ALP) activity in the gut and increased carboxylesterase-3 (CaE-3) activity in the abdomen of the exposed bees. These findings underscore the potential risks posed by ready-mix insecticides to the health of M. scutellaris and, consequently, to bee conservation and crop pollination.