Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2000
Publication Date: 4/15/2000
Citation: TAMEZ-GUERRA, P., MCGUIRE, M.R., BEHLE, R.W., SHASHA, B.S., GALAN-WONG, L.J. ASSESSMENT OF MICROENCAPSULATED FORMULATIONS FOR IMPROVED RESIDUAL ACTIVITYOF BACILLUS THURINGIENSIS. JOURNAL OF ECONOMIC ENTOMOLOGY. 2002. v. 93(2). p. 219-225. Interpretive Summary: Insect pests are generally controlled by the application of synthetic chemical pesticides. The chemical may affect nontarget organisms or otherwise cause undesired effects in the environment. Alternatives to chemicals are currently under development and include microorganisms that infect and kill a very small number of insect pest species. Bacteria, most notably Bacillus thuringiensis or Bt, have been successful as alternatives to chemicals. However, Bt does not stay active in the field after application very long. Our manuscript reports the use of surplus farm commodities as materials that can be used to formulate Bt to improve its residual activity. A novel method was developed to combine Bt with the protective materials. We demonstrated in the laboratory and field that corn flour and lignin can protect Bt from sunlight and rainfall longer than a commercial formulation. This information should be useful to scientists conducting work on mechanisms that affect persistence of Bt and to companies interested in improving biopesticides.
Technical Abstract: Bacillus thuringiensis Berliner is a very efficacious bioinsecticide used to control lepidopteran pests in the field. Unfortunately, it has limited residual activity on plants because sunlight inactivates spores and crystals or they can be washed off by rain. B. thuringiensis stability, after simulated sunlight (xenon light/8 h) and rain (5 cm/50 min), was improved using formulations based on lignin, corn flours, or both, with up to 20% of the active ingredient, when compared with technical powder or Dipel 2X in laboratory assays. Two formulations, made with corn flours or lignin + pregelatinized corn flour (PCF), killed 51.6% and 75.3% of Ostrinia nubilalis Hubner neonates after rain, respectively, versus 27% for technical powder. When the insecticidal activity was tested after simulated sunlight, corn flour-based formulations killed 78.5% of test larvae, while the lignin + PCF formulation killed 70.4%, in contrast to technical powder which caused an average of 29% mortality. In a field test, formulations were applied to cabbage; and insecticidal activity was determined against Trichoplusia ni Hubner neonates exposed to treated leaves. Insecticidal activity of the corn flour-based formulations was comparable to Dipel 2X for 4 d after treatment, but was significantly better than Dipel 2X 7 d after application. A lignin and PCF-based formulation showed significantly higher residual activity than Dipel 2X, 4 and 7 d after application.