Characterization of Bacillus thuringiensis isolates toxic to cotton boll weevil (Anthonomus grandis)

Abstract

The cotton boll weevil (Anthonomus grandis) is the major cotton pest in the Americas. One of the alternatives for its control is the utilization of Bacillus thuringiensis (Bt), an entomopathogenic bacterium characterized by its production of insecticidal crystal proteins. Embrapa Genetic Resources and Biotechnology has a collection of Bacilli in which diVerent isolates of Bt are stored. A method for rearing and maintenance of Anthonomus grandis on artiWcial diet in the laboratory was developed, and a robust larval bioassay protocol was established for the selection of B. thuringiensis isolates toxic to boll weevil. After preliminary bioassays performed with 215 isolates, 5 were selected that demonstrated a good level of toxicity and these were analyzed in more detail. The most toxic were S601 and S1806 presenting LC 50 (lethal concentration to kill 50% if the larvae) of 0.14 mg/ml and 0.30 mg/ml, respectively. S601 showed an LC 50 value that was half that of the standard B. thuringiensis subspecies tenebrionis and S1806 demonstrated similar values of LC 50 to the standard. S601 contained the cry1B gene and S1806 had the cry4A, cry4B, cry10, cry11, cyt1 and cyt2 genes like B. thuringiensis subspecies israelensis.

Optimal control in a multistage physiologically structured insect population model

“…Many such pests are insects as, for example, the boll weevil (Anthonomus grandis) in the cotton crop 13 , the European grapevine moth (Lobesia botrana) in the wine industry 8,18 , or the apple leaf midge (Dasineura mali) in apple crops 6 . The methods used to control these pest populations are mainly application of insecticides (e.g.…”

“…The methods used to control these pest populations are mainly application of insecticides (e.g. Bt, growth regulator), mating disruption to a lesser degree 19 , and other modern methods currently in the testing process, such as biological control 20 or development of transgenic plant mutants resistant to the particular insect 13 .…”

Cry10Aa Protein is Highly Toxic to <i>Anthonomus grandis</i> Boheman (Coleoptera: Curculionidae), an Important Insect Pest in Brazilian Cotton Crop Fields

“…The cotton productive chain is one of the most important in Brazil and in the world, as it generates thousands of direct and indirect jobs and annually only the Brazilian cotton industry generates around US $ 1.5 billion (Martins et al, 2007). The cotton boll weevil, Anthonomus grandis (Coleoptera: Curculionidae), is a devastating cotton pest responsible for more than 50% of insecticide costs in Brazilian cotton crop fields.…”

“…The cotton boll weevil, Anthonomus grandis (Coleoptera: Curculionidae), is a devastating cotton pest responsible for more than 50% of insecticide costs in Brazilian cotton crop fields. Moreover, A. grandis larvae resides inside floral buds and results in the destruction of fiber quality and hampers chemical control, causing considerable yield losses (Martins et al, 2007). However, due to A. grandis economic importance, the search for Cry toxins specific to this species is as essential as the knowledge on the toxic processes involved.…”

“…israelensis (Bti) S1804, is a Brazilian soil strain serotype H-14, toxic to Aedes aegypti (Diptera: Culicidae). Previous work, performed with another Bti strain, have shown that Bti was also toxic to A. grandis and this toxicity was not due to Cry4A, Cry4B, Cry11 and Cyt proteins individually or their combination (Martins et al, 2007). So, in order to find out which protein was responsible for the high level of toxicity we investigated the action of Cry10Aa towards A. grandis, since Bti strains also have a cry10A gene.…”