Conjugation of δ-endotoxin from Bacillus thuringiensis with abamectin of Streptomyces avermitilis as a new type of biocide, GCSC-BtA, for control of agricultural insect pests

Abstract

Conjugation of δ-endotoxin from Bacillus thuringiensis with abamectin, a toxin of Streptomyces avermitilis, was carried out to form a new type of biocide, GCSC-BtA based on “Germany-China Scientific Cooperation” research, for the control of agricultural insect pests. The strategy for biochemical linkage was designed by conjugating an amino group in B.t. protoxin with a carboxyl group in carboxylated abamectin under the treatment of conjugator EDC [1-Ethyl-3-(3-dimethylaminopropyl carbodiimide Hydrochloride)]. The formation of B.t. protoxin was processed by solubilizing B.t. crystal in 25 mM dithiothreitol (DTT) at 37 °C for 2 h. The carboxylated abamectin was formed by carboxylating the NaH-activated abamectin with 10 mg/ml butyric anhydride at 111 °C in a water-circumfluent condensation device for 2 h. The conjugating reaction, consisting of 5 mg/ml B.t. protoxin, 10 mg/ml carboxylated abamectin and 19.17 mg/ml EDC, was successfully conducted at room temperature for 24 h. Significant differences were found between pure abamectin, carboxylated abamectin and the conjugated BtA by means of UV-photo absorptions recorded at wavelengths 354, 438, 518, 600 nm (P < 0.01). LT₅₀ of the conjugated GCSC-BtA to the 3^rd instar larvae of Plutella xylostella (L.) (Lep., Plutellidae) was 35.27 μg a.i./ml, about 62 % and 76 % of that caused by the B.t. protoxin and the caxboxylated abamectin, respectively. The conjugated GCSC-BtA caused 87.14 % mortalities in larvae of P. xylostella, 93.75 % in adult Myzus persicae (Sulzer) (Hom., Aphididae) and 89.33 % in adult Phyllotreta vittata Fabricius (Col., Chrysomelidae) as compared to 48.33 % by the B.t. crystal only in P. xylostella. The symptoms caused by conjugated GCSC-BtA in the 3^rd instar of P. xylostella were black color in the head part and white-yellow in the abdomen of dead larvae, which differed from the black color or the white-yellow all along the body caused by either the B.t. crystal or the abamectin, respectively. It was concluded that the conjugated GCSC-BtA biocide had a broader host spectrum and a faster killing speed than either the B.t. crystal or abamectin alone for the control of agricultural pests.