Use of native Bacillus Thuringiensis rt to control Spodoptera Frugiperda in maize plants

Abstract

Bacillus thuringiensis (Bt), which produces the delta-endotoxin, is widely used in the biological control of Spodoptera frugiperda (Sf) (Lepidoptera: Noctuidae), a key pest of corn in northwest Argentina.The native Bt RT (16S rDNA partial sequence deposited in GenBank, accession number EF638795) was used. Entomopathogenic cultivation was developed at 30ºC in a fermentor (Labfors 3) with a working volume of 3 l, using a culture medium formulated with agroindustrial wastes. The product was applied on maize plants usingan airbrush (n=15 for each condition). Bioassays were conducted in a climate chamber with third stage Sf larvae (corn biotype). The following lots were analyzed: a) uninfected plants, b) infected plants, c) infected plants sprayed with sterile culture medium, d) infected plants treated with Bt. After 7 days, the experiment was stopped and mortality was calculated according to the Henderson-Tilton formula, using as control treatment b. The dry weight of aerial parts of plants was also assessed. After 5 days of incubation, the culture reached 1,164 x 106 crystals/ml, 83 x 106 spores/ml and 76 x 106 vegetative cells/ml. The mortality after 7 days was 76%. There were no significant differences between the dry weights of aerial parts of uninfected plants and those treated with Bt.