Evaluating conditions for producing spray-dried formulations of Anagrapha falcifera nucleopolyhedroviruses (AfMNPV)

We investigated how altering parameters during the production of spray-dried lignin formulations affected the insecticidal activity of a baculovirus (AfMNPV), which was originally isolated from celery looper, Anagrapha falcifera (Kirby). Exposure to high temperature, varied pH of the dryer feedstock, substitution of formulation ingredients, and different commercial production lots of virus were evaluated for their effect on the insecticidal activity of AfMNPV. Insecticidal activities of treatments were determined by droplet-feeding assays using neonate Trichoplusia ni (Hübner) for dosage response or single-dosage comparisons. Unformulated virus exposed to 68^oC for 2 h showed no loss of insecticidal activity, whereas exposure to 90^oC for 30 min caused >20% loss of activity. Thus, residence at higher temperatures in drying systems could adversely affect virus activity. Spray-dried formulations made with Indulin AT lignin (pH 8.5, 9.5, and 10.5) lost insecticidal activity with increasing alkalinity of the dryer feedstock. In contrast to Indulin AT, the same formulations made with PC-1307 lignin did not lose insecticidal activity with increased alkalinity. Adding corn flour to spray-dried Indulin AT-based formulations improved insecticidal activity of the virus. These experiments demonstrated the importance of carefully selecting feed-stock ingredients and processing conditions when spray drying AfMNPV.