Synergistic effects of Metarhizium anisopliae mixed with three pesticides against Galeruca daurica

In order to provide reference for the coordination of chemical pesticides and biological control agents against Galeruca daurica Joannis, the joint lethal effect of three insecticides (abamectin, indoxacarb and rotenone) mixed with Metarhizium anisopliae var. acridum on the third instar larvae of G.daurica was measured by topical application method. The results showed that the toxicity of abamectin to the larvae was the highest among the three insecticides tested, with LD50 value of 4.80 ng/larva; the toxicity of indoxacarb and rotenone was lower than that of abamectin, with LD50 value of 10.47 ng/larva and 53.21 ng/larva, respectively. Meanwhile, the inhibition of different concentration of insecticides on the germination of conidia of M.anisopliaewas determined after treatment for 24 h and 48 h. All the three pesticides showed inhibition on the spore germination of M. anisopliae, but the inhibition rates were less than 20%, and the inhibition decreased as the concentration decreased and the time prolonged. Indoxacarb showed the least influence on M. anisopliae after 24 h and 48 h, and the average inhibition rates were 1.89%±0.57% and 0.89%±0.39%, respectively. The mixture of spore suspension of M.anisopliae and three pesticides against the third instar larvae of G.daurica was more effective than that of M.anisopliae alone, displaying clear synergetic activity, and the synergism of indoxacarb and M.anisopliae was the best. The LT50 values of mixtures of M.anisoplia +indoxacarb,M.anisopliae +abamectin and M.anisopliae +rotenone against G.daurica decreased by about 8.12 d, 7.60 d and 6.45 d, respectively, comparing with those of M.anisopliae alone.