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

Abstract

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 (LD₅₀) and hazard quotients (HQs), respectively. Based on LD₅₀ 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 LD₅₀ 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 LD₅₀ 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.