Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/1996
Publication Date: N/A
Interpretive Summary: In a copperative effort between Mexican and USDA-ARS scientists, a new way of preparing biological pesticides was discovered. Biological pesticides are being considered as replacements for broad-spectrum chemical pesticides, but current technology related to the biologicals is generally not satisfactory. Biological pesticides are usually short-lived in the environment after application and are therefore not effective for more than a few days. One of these biological pesticides is an insect active bacteria called Bacillus thuringiensis or Bt. We have demonstrated that Bt can be treated with corn flour that has been specially modified, and other common ingredients like sugar and corn oil, such that these materials closely adhere to the Bt. The formulation is sprayable and the extra ingredients help the Bt survive in response to damaging sunlight after application. In addition, the materials stimulate insects to eat the Bt, something the insects usually find unpalatable.
Technical Abstract: Spray dried Bacillus thuringiensis formulations, comprised of citric or lactic acid, pregelatinized corn flour, cornstarch, isopropyl alcohol, sugar, and corn oil, were used in leaf and diet incorporation bioassays, to determine the effects of solar radiation and rain on insecticidal activity. In diet incorporation tests against Helicoverpa zea, Trichoplusia ni, Heliothis virescens and Spodoptera exigua, insecticidal activity of spray-dried B. thuringiensis did not decrease when compared with unformulated technical B. thuringiensis. Cotton leaf bioassay tests using Ostrinia nubilalis showed that insecticidal activity of formulations exposed 8 hr to artificial solar radiation was higher than technical B. thuringiensis exposed to solar radiation, suggesting the formulations provided protection against solar radiation. In cotton leaf bioassays, when five different starches were used individually in the formulations, insecticidal activity was reduced after exposure to solar radiation in only one case. Cotton leaf bioassays also showed a reduction in insecticidal activity due to exposure to solar radiation as the amount of active ingredient (w/w) in the formulation increased. Throughout all tests, rainfastness of formulations was not consistently better than technical B. thuringiensis alone.