Evaluar la susceptibilidad de Plutella xylostella (L.) a dos cepas locales posibles Bacillus thuringiensis en comparación con producto comercial bajo condiciones in vitro.

Abstract

The Plutella xylostella (L.) moth is a primary pest that causes great damage and economic loss to Brassicaceae vegetable growers around the world. Its genetic plasticity and being multivoltine has allowed it to develop rapid resistance to different synthetic insecticides. The objectives of the bioassay were to characterize the studied strains phenotypically; evaluate the mortality, DL50 and TL50 in vitro of three strains of Bacillus thuringiensis (Berliner); one commercial and two local. The three strains were studied at doses of 1x104 , 1x106 , 1x108 , 1x1010, 1x1012 CFU / ml and an absolute control was tested on second instar larvae under in vitro conditions. A randomized design with six treatments, five replications, and repetition with five larvae was used for each of the three strains. Mortality evaluated every 12 hours until the total death of the larvae or the emergence of adults. Data was analyzed with SPSS, using Probit Tests to calculate DL50. The two local strains presented characteristic colonies of the genus Bacillus sp. The forest soil strain caused mortalities of 100% at lower doses than the other two strains, the 1x104 concentration caused 84% mortality, not so for the other two strains where the mortalities were below 76%. Although the DL50 were very similar to 1x108 among the three strains; the TL50 if they were different, where the forest floor strain caused the mortality of 50% of the population at 19 hours; while the commercial strain the DL50 was 52 hours and for the agricultural soil strain it was 48 hours. The forest floor strain is considered a good candidate as a bioinsecticide, as it has been shown to be more lethal than the commercial strain.