Toxicity difference of different acetamiprid formulations againstBemisia tabaci and reasons

The fate of pesticide droplets on plant leaves is significantly influenced by the fine structures of leaf surfaces and the characteristics of pesticide solutions. Deposition quantity is the main factor that influences pesticide toxicity. Using appropriate pesticide formulations greatly increases pesticide utilization and efficiency while it at the same time reduces environmental pollution. Cabbage and cucumber leaves were used as bioassay carriers in order to explore the differences in toxicity among different acetamiprid formulations to Bemisia tabaci Gennadius. The toxicities of five different acetamiprid formulations - emulsifiable concentrate (EC), microemulsion (ME), soluble liquid (SL), soluble powder (SP) and wettable power (WP) - were examined in a laboratory study. The mechanisms of the different toxicities were analyzed through detections of leaf critical surface tension, acetamiprid solution surface tension, dynamic contact angle and leaf retention volume of liquid. The results showed that differences among the pesticide formulations were more obvious when cabbage leaf was used as bioassay carrier. However, differences among the formulations were not so notable when cucumber leaf was used as bioassay carrier. Toxicities differences of SL, SP and WP between two bioassay carries were larger than those of EC and ME. Critical surface tension of cabbage and cucumber leaves were 30.73 mN·m^-1 and 57.91~63.30 mN·m ^-1, respectively. The solution surface tensions of EC and ME were less than critical surface tensions of cabbage and cucumber leaves, if acetamiprid active ingredient concentration reached 7.81 mg·L^-1. For SL, SP and WP, however, solution surface tensions were only less than critical surface tensions of cabbage when acetamiprid active ingredient concentration exceeded 500 mg·L^-1. Contact angle was significantly lower than 90° when ME droplets instantly dripped on plant leaf surface of two plants. Cabbage leaf retention volumes of low concentration ME and EC solutions were higher than the other three formulations. There was no obvious difference in retention volumes of cucumber leaf for the 5 acetamiprid formulations. Differences in leaf surface characteristics and solution surface tensions were the main reasons for the variations in toxicities of different formulations.