Sunlight Stability and Rain-Fastness of Formulations of Baculovirus heliothis

Abstract

Sunlight-Ultraviolet, with an activity spectrum from 290 to 400 nm, is the most destructive factor affecting the persistence of baculoviruses. Benzopurpurin (a disazo dye) and carbon provided the best protection when polyhedral inclusion bodies (PIB) of Baculovirus heliothis were exposed to an artificial spectrum simulating sunlight-UV (UV). Greater than 75% of the original PIB activity was still present after 48 h of sunlight-UV. When sprayed on soybeans and exposed to natural sunlight, only formulations with carbon provided significant protection of PIB. The half-life of formulations were PIB-only 4.9 ± 1.4 h (mean ± SE), PIB + polymer (pyrrolidone-based sticker) 3.3 ± 0.6 h, PIB + polymer + benzopurpurin 3.4 ± 0.7 h, and PIB + polymer + carbon 27.7 ± 5.2 h. PIB of B. heliothis tenaciously adhere to soybean, Glycine max (L.) Merrill, leaflets after spraying and drying. Less than 6% of the PIB activity of nonformulated PIB was lost after a drenching, simulated rainfall. 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, <20% was present for formulations without carbon.