Toxicityofdifenoconazoleandazoxystrobinonthegrowthanddevelopmentof<italic>Bombyxmori</italic>

In order to evaluate the influence of 10% difenoconazole water dispersible granule (WG) and 250 g/L azoxystrobin suspension concentrate (SC) on silkworms in mulberry gardens and surrounding agricultural fields, the acute toxicity and developmental toxicity were investigated in laboratory by exposing both fungicides to silkworm, Bombyx moril. The 2^nd instar larvae of silkworm was continuously fed with leaves exposed to fungicides. The results of acute toxicity showed that the 96 h-LC₅₀ for the 2^nd instar larvae to 10% difenoconazole WG and 250 g/L azoxystrobin SC were 353.58 mg/L and 498.66 mg/L, respectively. The results of the development toxicity experiments showed that the highest dose (200 mg/L) and the lowest dose (50 mg/L) of 10% difenoconazole WG had significantly effect on the development duration of the 2^nd-4^th instars larvae of silkworm, however the influence gradually became less obvious with instar. 250 g/L azoxystrobin SC had significantly effect on silkworms. The development duration of larvae was prolonged, and the development was seriously irregularity. The mortality of high concentration group (250 mg/L) was significantly above the average. Compared with the control, the development duration and the weight of molting silkworm larvae had obvious differences. In addition, the pupal stage without cocooning was observed. Although 10% difenoconazole WG and 250 g/L azoxystrobin SC have low toxicity and low risk to silkworm, they can influence the development duration, silkworm weight, fecundity and other major economic traits of silkworm. Therefore, when using these two fungicides in silkworm area, to control the loss of silkworm production, mulberry leaf pollution should be avoided.