SELECTION AND MOLECULAR CHARACTERIZATION OF BACILLUS THURINGIENSIS BERLINER WITH TOXIC ACTIVITY AGAINST TRICHOPLUSIA NI HUEBNER (LEPIDOPTERA: NOCTUIDAE)

ABSTRACT

Trichoplusia ni is a polyphagous pest that is becoming a major pest in plantations of cruciferous crops, soybeans and cotton. This study was aimed to select and molecularly characterize efficient isolates of Bacillus thuringiensis (Bt) for the control of T. ni. For the bioassays of pathogenicity, an aliquot with a 3 x 108 spores/mL suspension of Bt of each isolate was applied on the surface of the artificial diet disk, previously distributed on acrylic plates with 50 larvae, distributed in 5 repetitions. In bioassays to obtain the LC₅₀, only isolates with 100% mortality were

preselected, and tests were carried out at the concentrations 10², 5 x 10², 10³, 2 x 10³, 4 x 10³, 6 x 10³, and 8 x 10³ spores/mL, and the treatments consisting of 120 larvae, distributed in 3 repetitions. A molecular characterization was performed to detect the genes cry1, cry2 and Vip for the isolates which obtained mortality over 95%. Isolates HD-1 (Standard), Bt-1043N-V, Bt-1034F, Bt-1009K, Bt-1000 and Bt-969A caused 100% mortality in the test for pathogenicity and presented an LC₅₀ of 1.17 x 10³, 1.45 x 10³, 1, 46 x 10³, 1.01 x 10³, 9.43 x 10², 1.22 x 10³, respectively. Genes cry1, cry2 and

Vip were not found in the isolates tested, and other Cry toxins may have been causing the mortality of T. ni, since the isolates tested are specific for the Lepidoptera order. These isolates showed potential for the control of T. ni, being aggressive to this insect, with a potential to be used in a pest management program for this species.

KEY WORDS
IPM; biological control; entomopathogen; Cry toxins