Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/1997
Publication Date: N/A
Interpretive Summary: Biological insecticides such as viruses, bacteria and fungi are sensitive to sunlight and must remain viable in the environment in order to exert effective control over insect pests. Sunlight, however, completely inactivates these biologicals within two days of application. Viruses formulated with a UV-protectant such as a carbon powder, could enhance the field persistence and effectiveness of biological insecticides. In laboratory and simulated field tests viral formulations with carbon that were exposed to sunlight were as stable as the same formulations not exposed to sunlight. This information should help manufacturers, growers and scientists involved in formulating more sunlight-stable biological pesticides.
Technical Abstract: Benzopurpurin (a disazo dye) and carbon provided the best protection when polyhedral inclusion bodies (PIB) of Baculovirus heliothis were exposed to simulated sunlight-ultraviolet (SUV). Greater than 75% of the original PIB activity was still present after 48 h of SUV. When sprayed on soybeans, and exposed to natural sunlight, only formulations with carbon provided significant protection of PIB. The half-life (in hours) of formulations with: PIB-only ; PIB + polymer (pyrrolidone-based sticker); PIB + polymer + benzopurpurin; and PIB + polymer + carbon were 4.9 + or - 1.4, 3.3 + or - 0.6, 3.4 + or - 0.7 and 27.7 + or - 5.2, respectively. PIB of B. heliothis tenaciously adhere to soybean leaflets after spraying and drying. Less than 6% of the PIB activity was lost after a drenching, simulated rainfall. Addition of a polymer sticker, as evidenced by the SUV exposure data, significantly increased adherence of carbon particles to soybean leaflets but not of PIB per se. More than 97% of the original PIB activity of carbon formulations was still present on soybean leaflets after 10 h of exposure to sunlight-UV. In contrast less than 20% was present for formulations without carbon.