| The microbe-derivated insecticide, Bt (Bacillus thruingiensis ) preparation, has excellent characteristics, including the safety to environment and non-target organisms, residue free, and being difficult to form resistance. However, its drawbacks, such as slow efficiency and short persistence, restrict its potency against pests in fields. Avermectin, whose mode of action is different from Bt, may fetch up disadvantages associated with application of Bt, thanks to avermectin's natures, including high efficiency, low toxicity, and broad spectra. Based on this idea, the mixture of avermectin and Bt was studied, aiming at developing a new avermectin-and-Bt-based product.1. The bioassay under laboratory conditions with Potter Method indicated that the values of LC50(48h) of 1.8% Avermectin EC and 8000IU/mg Bt WP against Plutella xylostella L. (2nd instar) were 0.65 mg/L and 155.63 IU/mg, respectively.2. Based on the extensively screening, 4 combos with good bioactivity were selected to undergo the laboratory bioassay against P. xylostella L. (2nd instar). The results showed that their values of Combined Toxicity Coefficient (CTC) were over 120. The Combo 2 with synergism displayed the strongest toxicity with a LC50 of 73.23 IU/mg and a CTC of 212.52.3. The Combo 2 was further studied in the formulation aspect. The potential formulation of Combo 2 is the wettable powder (0.1%) , including 23.89 % SiO2-(H2O)n, 16% surfactant, 0.11% avermectin chemicals, and 50.0% B.t crude powder. The standard of this product should match: Bt protein≥ 1.0%, avermectin≥ 0.1%, 6≤pH 8, water≤3.0%, and particle size≤44um.4. The results in field demonstrated that the controlling efficiency of 0.1% this mixture WP with the dosage of 50-75g/mu, against P. xylostella L., was 60% 1d after application, 75-93% 3-7 d after application, 65-92% 7 d after application, and 34% 14 d after application, respectively.
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