Is it feasible to use optical brightener technology with a Baculovirus bioinsecticide for resource-poor maize farmers in mesoamerica?

Stilbene-derived optical brighteners greatly enhance the infectivity of a n umber of baculoviruses. This technology has been patented for use with inse ct pathogenic viruses in the United States and Canada. A baculovirus is cur rently being tested for its potential as a biological insecticide of Spodop tera frugiperda (Lepidoptera: Noctuidae), the principal insect pest of maiz e in Mesoamerica. A multiply embedded nucleopolyhedrovirus isolate original ly from Nicaragua was bioassayed alone and in the presence of the optical b rightener Tinopal LPW (1%), using second instar S. frugiperda larvae. The L C50 value of the virus alone was calculated at 82.1 polyhedral inclusion bo dies (PIBs)/mm(2) of diet compared with 0.71 PIBs/mm(2) in the presence of Tinopal LPW. In contrast to other studies, the mean time to death of larvae exposed to virus and Tinopal LPW was significantly extended compared to la rvae inoculated with virus alone. Analysis of the results of eight independ ent held trials in Mexico and Honduras revealed a significant positive rela tionship between log virus dose and percentage mortality observed in S. fru giperda larvae. Virus-induced mortality was approximately 50% at the highes t application rate tested: 1000 larval equivalents (LE) of virus/ha. When t he impact of parasitism was taken into account, larval mortality increased to 45.0-90.7% in plots treated with virus at 250 LE/ha or more. A cost anal ysis indicated that approximately 60% pest control can be achieved as a con servative estimate with virus application and the action of parasitoids for the price of a chemical insecticide. Formulating the virus with an optical brightener appears to be an attractive option based on laboratory findings but requires held testing. The use of optical brightener technology will p robably be feasible for maize growers in Mesoamerica only if it is highly e ffective at very low concentrations (<0.1%) or the volume of the virus appl ication can be reduced. (C) 2000 Academic Press.