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Synergistic activity of Bacillus thuringiensis δ‐endotoxin and TMOF against Culex pipiens and Spodoptera littoralis larvae
Author(s) -
Mohammed Ahmed M.A.,
Diab Mervat R.,
Khalil Sayed M.S.
Publication year - 2018
Publication title -
entomological research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.421
H-Index - 20
eISSN - 1748-5967
pISSN - 1738-2297
DOI - 10.1111/1748-5967.12257
Subject(s) - spodoptera littoralis , culex pipiens , biology , bacillus thuringiensis , spodoptera , midgut , glutathione , toxin , microbiology and biotechnology , toxicity , larva , escherichia coli , noctuidae , biochemistry , enzyme , botany , bacteria , recombinant dna , chemistry , genetics , organic chemistry , gene
Trypsin Modulating Oostatic Factor (TMOF) is a decapeptide hormone that inhibits the biosynthesis of digestive enzymes in the mosquito midgut. The hormone inhibits food digestion and ultimately leads to starvation and death. It has been used as a biological insecticide to control mosquitoes. In an attempt to increase the insecticidal activity of TMOF, a combination of CryIC (δ‐endotoxin from Bacillus thuringiensis ) and TMOF was determined. Eight recombinant proteins fused with GST (glutathione‐S‐transferase) were expressed in Escherichia coli cells. Their insecticidal activities were determined against Culex pipiens and Spodoptera littoralis larvae. Purified GST‐TMOF and its analogue GST‐YDPAS exhibited a moderate toxicity on C. pipiens larvae with LC 50 of 145.9 and 339.9 μg/mL, respectively. Unexpectedly, no mortality was observed in first instar larvae of S. littoralis . Puirified GST‐TMOF and GST‐YDPAS together with Bt toxin showed a synergistic toxic effect on both Culex and Spodoptera larvae. In the presence of 100 μg/mL GST‐TMOF and GST‐YDPAS, the median lethal concentration of entomocidus on culex larvae decreased from 52.1 to 16.7 and 31.9 μg/mL, respectively. Likewise, GST‐TMOF and GST‐YDPAS incorporated with 0.07 μg/cm 2 of enotmocidus showed insecticidal activity against S. littoralis with LC 50 of 16.4 and 21.9 μg/cm 2 . The E. coli lysates containing GST‐CryIC and its 3′‐truncated version showed low toxicity against the lepidopteran insect (10.8 and 16.6 μg/cm 2 ) compared to 0.15 μg/cm 2 of the native crystalline form of CryIC. Similarly, the mosquitocidal activity of the recombinant Bt toxins was low.