Acute Toxicity of Selected Insecticides on Apis mellifera and Ceratina smaragdula: Laboratory and Field Assessments

Abstract

Pollinators are vital to agricultural productivity, yet their populations are declining due to anthropogenic disturbances, including pesticide use. This study evaluated the acute toxicity of selected insecticides to two bee species, the honey bee (Apis mellifera) and the small carpenter bee (Ceratina smaragdula), using laboratory and field experiments. Under laboratory conditions, emamectin benzoate exhibited the highest toxicity to C. smaragdula, with a 12-hour LC₅₀ of 4.69 µg/mL. Moderate toxicity was observed for flubendiamide (LC₅₀ = 60.57 µg/mL) and chlorantraniliprole (LC₅₀ = 57.64 µg/mL), whereas the remaining insecticides showed higher LC₅₀ values ranging from 141.41 to 846.77 µg/mL. After 24 hours, emamectin benzoate remained the most toxic (LC₅₀ = 1.14 µg/mL), and similar toxicity patterns were observed for the other insecticides. In A. mellifera, emamectin benzoate was also the most toxic insecticide at both 12 hours (LC₅₀ = 9.64 µg/mL) and 24 hours (LC₅₀ = 5.10 µg/mL). Moderate toxicity was recorded for flubendiamide and chlorantraniliprole, while the other insecticides exhibited lower toxicity, with 24-hour LC₅₀ values ranging from 56.35 to 589.92 µg/mL. Field applications resulted in significant differences in bee abundance between treated and untreated plots, with the highest abundance in untreated plots and the lowest in bifenthrin-treated plots. Overall, bee abundance increased over time, peaking 72 hours after insecticide application. These findings highlight the need for further investigation into the long-term effects of pesticides, particularly on understudied solitary bee species across diverse ecosystems.