Comparison of the toxicity and potential ecological risks of various pesticides for nurses of honey bee (Apis mellifera. L)

The honey bee ( Apis mellifera . L) is an important pollinator worldwide, but it is facing significant population declines due to the influence of various factors, particularly the use of pesticides. Forager bees come into contact with pesticides during their foraging activity, while nurse bees are exposed to pesticides within the hive when they consume contaminated food sources. Based on established pesticide exposure routes, the present study assessed the oral toxicity and ecotoxic risks of 13 pesticides, including two organophosphates [coumaphos (COU) and fenitrothion (FEN)], two pyrethroids [τ-fluvalinate (τFLU) and cypermethrin (CYP)], four neonicotinoids [acetamiprid (ACE), imidacloprid (IMI), thiamethoxam (THIA), and flupyradifurone (FLU)], two carbamates [carbaryl (CAR) and carbofuran (CAB)], two avermectins [abamectin (ABA) and ivermectin (IVE)], and one phenyl pyrazole, fipronil (FIP) for nurse bees using the median lethal dose (LD 50 ) and hazard quotients (HQs), respectively. Based on LD 50 data from bioassays and previous reports, ranking pesticides by their toxicity for nurse bees resulted in the following order: FIP = THIA > ABA > IVE > CAB > IMI = FEN > CAR > CYP > FLU > ACE > COU = τFLU. The HQs were calculated using the LD 50 and arithmetic field-detected concentration for each pesticide in bee bread and honey based on the previous studies. The HQ results indicated THIA had the highest potential risk for honey bees, followed by FIP, CAR, FLU, CYP, CAB, FEN, IMI, COU, τFLU, and ACE. Quadrant-based analysis subsequently revealed that high LD 50 values were not necessarily associated with high HQs for nurse honey bees. These findings suggest that differences in the residue concentration of the pesticides due to differences in their chemical properties and usages can influence their actual risk in natural systems, which is not in direct accordance with their toxicity. This study thus highlights the importance of assessing the effect of agrochemicals on honey bees in an ecological context. • Oral toxicity of 13 pesticides was evaluated in nurse honey bees. • Fipronil and thiamethoxam exhibited the highest toxicity based on LD₅₀ values. • Thiamethoxam posed the greatest risk according to hazard quotient (HQ) analysis. • LD 50 and HQ values did not always show a direct correlation across pesticides. • Results highlight the need for evaluating pesticides in an ecological context.