The toxic effects of new insecticide isoflualanam on Apis mellifera

The toxicity risk of the new insecticide isoflualanam to Apis mellifera adults and larvae was evaluated in the laboratory using 95% technical material (TC) and its six formulations. Its toxicity was compared with two structurally similar diamide insecticides, broflanilide 100 g/L suspension concentrate (SC) and cyantraniliprole 97% TC. The results of the acute toxicity test on adult honey bees indicated that the acute toxicity of 95% isoflualanam TC was lower than that of broflanilide 100 g/L SC and cyantraniliprole 97% TC, with toxicity reductions by a factor of 2.6 to 100. The acute toxicity of isoflualanam 100 g/L capsule suspension (CS) to adults and larvae of bees was significantly lower than that of 30 g/L emulsifiable concentrate (EC) and microemulsion (ME). The toxicity of polyurethane microcapsule suspension to bee adults was 3.2 to 100 times lower than that of polyurea (P < 0.05). In the larval toxicity assays, the results show that the acute toxicity of isoflualanam 95% TC to larvae was lower than that of broflanilide 100 g/L SC and cyantraniliprole 97% TC. The chronic toxicity of isoflualanam 95% TC to larvae was comparable to that of cyantraniliprole 97% TC, and its no-observed-effect dose (NOED) was higher than that of broflanilide 100 g/L SC. Both the acute and chronic toxicities of isoflualanam 100 g/L CS to larvae are significantly lower than those of its EC and ME formulations. Regarding capsule materials, polyurethane and polyurea CS with a 2 µm particle size exhibited higher toxicity to honeybee larvae than those with a particle size of 50 µm, ranging from 3.4 to 36 times higher. However, no consistent toxicity trend was observed for acute toxicity in adult bees. The results indicate that the novel isoxazoline insecticide, isoflualanam, exhibits a superior safety profile for honeybees compared to broflanilide and cyantraniliprole. The safety of isoflualanam to honeybees can be further improved by formulating it as a microcapsule suspension and selecting a capsule wall material with higher safety.