Assessment of Neonicotinoid Susceptibility in Apis indica F. Population

Abstract

The present study evaluated the susceptibility of Apis indica populations collected from six agro-ecosystems of Trivandrum and Kollam districts along with a feral colony from Mettupalayam to the neonicotinoids viz., imidacloprid 70 WG and thiacloprid 21.7% SC. Acute oral and contact bioassays were conducted to determine lethal concentrations (LC₅₀, LC₉₀), resistance ratio (RR) and safety index (SI). Among the tested populations, the Vellayani (VLY) population showed the highest tolerance, reflected by elevated LC₅₀ and RR values, possibly due to prolonged exposure to insecticides in the field, whereas the feral population was the most susceptible, recording the lowest LC₅₀ values. Imidacloprid exhibited significantly higher toxicity across all populations, with oral and contact RR values up to 6.000 and 2.631, respectively. SI were consistently low (0.004–0.947), classifying imidacloprid as relatively least safe to A. indica in both exposures. In contrast, thiacloprid showed comparatively lower toxicity, with oral and contact RR values up to 18.592 and 3.786, higher SI values (0.054–21.270), indicating relative safety for VLY population in both exposures. Overall, imidacloprid posed significant toxicity risk to A. indica, whereas thiacloprid appeared comparatively safer due to its higher safety margins and lower acute toxicity. The study provides critical baseline data on imidacloprid and thiacloprid susceptibility in indigenous honeybees, emphasizing the need for bee-safety considerations in pesticide selection. These findings suggest for region-specific risk assessment and pollinator-friendly pest management strategies to safeguard A. indica and ensure sustainable pollination services in agricultural ecosystems.