Toxicities of destruxins against Bemisia tabaci and its natural enemy, Serangium japonicum

The bioactivities of destruxins against whitefly, Bemisia tabaci and its natural enemy, ladybird beetle Serangium japonicum were evaluated. Destruxins A and B (DA and DB) showed insignificant ovicidal, oviposition deterrent and systemic insecticidal activities to B. tabaci; however, DA and DB had certain contact virulence to its nymphs. The LC50 values of DA at 120 h to 2nd, 3rd and 4th instars were 89.8 (95% confidence interval as 85.4–94.4), 199.3 (187.7–211.5) and 270.7 (251.5–291.5) mg/L, while the LC50s of DB at 120 h were 96.5 (92.0–101.2), 216.7 (203.0–231.2), 359.4 (326.6–395.4) mg/L, respectively. In addition, DA exhibited moderate acute contact toxicities towards S. japonicum, the LC50s at 48 h were 165.4 (132.3–229.4) and 192.5 (148.1–289.2) mg/L for 4th instar larvae and adults. Furthermore, the results from experiments of residual toxicities of DA towards mortalities of 4th instar larvae and adults, pupation rate, emergence rate, average number of egg/female and hatching rate suggested that DA had minimal effects to the ladybird beetle. Generally, the toxicity decreased about 50% from 1st to 3rd–5th day of post-treatment. Specially, the residual toxicity at 50 mg/L and the 7th day post-treatment was down to a value not differing significantly from the control.