Effects Of Thiamethoxam On The Survival And Homing Ability Of Apis Mellifera L.

Thiamethoxam as the representative agent for the second generation of neonicotinoid insecticides,is widely used in agricultural production because of its higher activity,higher safety and broader activity than imidacloprid.The re-evaluation of thiamethoxam is urgently needed,following the completion of the re-evaluation project of imidacloprid in China.In this study,the acute oral toxicity of thiamethoxam to Apis mellifera L.and the effect of thiamethoxam on the homing ability of Apis mellifera L.was studied.Additionally,we analyzed the survival risks of thiamethoxam to workers at different ages.The main findings are as follows:?1?The 48 h indoor acute toxicity of thiamethoxam and other four common neonicotinoids?imidacloprid,dinotefuran,acetamiprid and nitenpyram?to Apis mellifera L.were determined.The results showed that the LC₅₀ of thiamethoxam imidacloprid,dinotefuran and nitenpyram to Apis mellifera L.were 8.23,24.09,48.48 and 52.14?g/g respectively.and Apis mellifera L.is more sensitive to which four insecticides than Apis cerana cerana F.(LC₅₀ were 16.45,37.34,50.69,84.48?g/g respectively).For acetamiprid,Apis cerana cerana F.(LC₅₀=285.31?g/g)was more sensitive(LC₅₀=353.36?g/g).?2?Preliminary ascertained the acute toxicity of thiamethoxam to Apis mellifera L.at different ages.Apis mellifera L.larvae are less susceptible to thiamethoxam than adult bees(thiamethoxam for larvae LC₅₀=705.559?g/g).In the adult stages,the sensitivity of Apis mellifera L.to thiamethoxam were also increased with age increasing,in which foragers was the most sensitive to thiamethoxam(LC₅₀=20.019?g/g),the newly emerged bee is least sensitive(LC₅₀=50.371?g/g),which is similar to imidacloprid(for larvae:LC₅₀=294.883?g/g;newly emerged bee:LC₅₀=48.740?g/g;foragers:LC₅₀=19.276?g/g).?3?The effect of thiamethoxam on the homing ability of workers was investigated.When the concentration of thiamethoxam was higher than 7.5 ng/g,the homing percentage of workers decreased significantly and the homing time was significantly prolonged with the concentration increasing.The maximum no observation concentration of thiamethoxam on the homing percentage and homing time was 7.5 ng/g.?4?The he survival risk of sub-lethal dose of thiamethoxam on Apis mellifera L.at different ages were analyzed.The lifespan of the LC₅ and LC₁₅ treatments were not significantly different from the control group for the newly emerged bees,however,its longevity was reduced 19.0 d for the LC₂₅ treatment.For nurse bees,the LC₅ treatment didn't shorten their lifespan,but the LC₁₅ and LC₂₅ treatments reduced the longevity of nurses by 9.2 and 15.0 d,respectively.For forager bees,compared with the control group,no obvious differences were found in the LC₅ and LC₁₅ treatments,yet,the LC₂₅ treatments reduced the lifespan of foragers by 10.9 d.From this study we can draw a conclusion that thiamethoxam was the most toxic to Apis mellifera L.,and the sensitivity of bees were different at different ages.The larvae were the less sensitive to thiamethoxam and foragers were the most sensitive.With the ages of bees increasing,Apis mellifera L.becoms more and more sensitive to thiamethoxam.Furthermore,low doses of thiamethoxam could reduce the homing percentage,prolong their homing time,and shorten the lifetime of worker at different ages.