Microbial control of the cotton leafworm Spodoptera littoralis (Boisd.) by Egyptian Bacillus thuringiensis isolates

Abstract

Four local Bacillus thuringiensis (Bt) isolates that had been serologically identified as Bt var. kurstaki (Btk2, Btk3, and Btk66) and Bt var. mexicanensis (Btm27), in addition to two reference strains (4D20 and 4AC1), were laboratory assayed as microbial control agents against the Egyptian cotton leafworm Spodoptera littoralis (Boisd.). Polymerase chain reaction (PCR) amplification analysis revealed that each of the six experimental strains carries, at least, a cry1 type gene which expresses a protein toxin active against lepidopterous insects. Additionally, PCR amplification results demonstrated that 4D20 and Btk66 contain the Lepidoptera- and Diptera-active cry2 type gene and that Btk66 contains Coleoptera-active cry7 and cry8 genes. Among the six strains, Btk66 and Btm27 were the most promising microbial control agents against S. littoralis. The present findings were the first to report that Btm27 (classified as B. thuringiensis var. mexicanensis) is a very potent microbial control agent against S. littoralis-tested larvae. For more characterization of these two isolates, the sspO gene was investigated as a molecular chronometer. The DNA sequencing results proved that Btk66 and Btm27 carry sspO open reading frames with identical nucleotide sequences, suggesting a strong phylogenetic relationship between the two strains.

Genome Sequence of Bacillus thuringiensis Strain Btm27, an Egyptian Isolate Highly Toxic to Cotton Leafworm

“…Besides its role as biopesticide, further promising biotechnological applications included the production of industrially important enzymes ( 5 ) for cytotoxic effects on cancer cells ( 6 ). As recently demonstrated by Alfazairy et al ( 7 ), the sequenced Egyptian strain Btm27 is a potent control agent against cotton leafworm. Structural and functional genomic analyses of the strain will allow one to better characterize its insecticidal efficiency and biotechnological potential.…”

Cry3Aa Toxin Is Not Suitable to Control Lepidopteran Pest Spodoptera littoralis (Boisd.)

“…Cry1 act on lepidopteran pests, and therefore Cry1Ab suppresses Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) [ 5 , 6 , 7 ]. On the other hand, Cry3 toxins are specific to coleopteran species [ 8 , 9 , 10 ]; Cry3Aa is used against potato pest Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae).…”