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

AbstractConjugation 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 3rd 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 3rd 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.