Toxicity of cypermethrin and fenitrothion on the hemolymph carbohydrates, head acetylcholinesterase, and thoracic muscle Na+, K+-ATPase of emerging honeybees (Apis mellifera mellifera. L)

Comparative effects of sublethal doses (0, 0.1, 0.2. 0.4, 0.8, and 1 nmol/bee) of cypermethrin and fenitrothion have been studied on emerging honeybees. The insecticides were injected intrathoracially between the third and the fourth segment. Biochemical effects were determined over a 3-h period. Both cypermethrin and fenitrothion led to a significant hypoglucosemia and hypotrehalosemia 15 min after injection, but cypermethrin seemed more active than fenitrothion at the same doses. A recovery phase appeared for glucosemia and trehalosemia, 60 min after injection. The higher toxicity of cypermethrin than fenitrothion also appeared in this period, where it took a longer time for honeybees to reestablish carbohydrate levels following cypermethrin than fenitrothion injections. The low values of the correlation coefficients (r) for glucose versus trehalose levels led to the supposition that no typical functional interaction between glucose and trehalose could be considered to be involved in this experience. Na+, K+-ATPases activity was significantly inhibited (P< 0.05) by cypermethrin and maximum percentage inhibition was reached (45%) at 1 nmol/bee. The kinetic analysis of honeybee's acetylcholinesterase inhibition by fenitrothion, indicated that this insecticide acts (P< 0.05) on acetylcholinesterase activity. The percentage inhibition exceeded 60% at 0.2 nmol/bee. This result revealed that in general cypermethrin and fenitrothion share common biochemical effects on carbohydrates, although their neurotoxic effects on honeybees might be different.