Development of microbial control for lepidopteran pests of the corn ear
The problems associated with chemical pesticide misuse have led to the search for alternative forms of insect pest management such as microbial control that are environmentally and ecologically sound. The efficacy of three Bacillus thuringiensis Berliner (Bt) products and Anagrapha falcifera multiple nuclear polyhedrosis virus (AfMNPV) to control Helicoverpa zea (Boddie) was evaluated in the laboratory and in the field on corn. The virulence of the entomopathogens for Ostrinia nubilalis (Hubner) and Spodoptera frugiperda (J. E. Smith) was also evaluated in the laboratory;Three Bt products (HD-1-S-1980, Javelin°ler, and XenTari°ler) and AfMNPV were tested in the laboratory. The relative virulence, from estimates of LC[subscript]50s, of the Bt materials for H. zea and S. frugiperda was Javelin > XenTari > HD-1-S-1980 and for O. nubilalis it was Javelin > XenTari and HD-1-S-1980. AfMNPV was most toxic for H. zea, followed by S. frugiperda, and then O. nubilalis. Mixtures of two entomopathogens (XenTari and AfMNPV) either had no effect on mortality when compared to either pathogen alone or mortality of the virus was reduced with the addition of Bt;In the field, applications of the three entomopathogens, Javelin, XenTari, and AfMNPV, significantly decreased damage by H. zea and increased the percentage of corn ears without damage and of marketable ears; AfMNPV provided as good or better protection than the Bt products. Within this experiment, a starch-sucrose product was also tested for its compatibility with the pathogens. The starch-sucrose product did not affect the efficacy of the pathogens to manage H. zea, however additional testing with AfMNPV was recommended;In addition two sunlight protectants, Congo red and a starch-sucrose product, were mixed singly and in combination with AfMNPV to evaluate their effect on the field persistence of the virus. The treatments were sprayed on corn silks, and the silks were collected immediately after application (Day 0) and 1, 3, 6, and 9 days after application. Bioassay results for viral residuals retrieved from the silks showed no significant differences in persistence between the virus alone and virus+starch-sucrose; the virus alone maintained a high degree of activity (≈80%) after 9 days. The addition of Congo red negatively affected results of the residual bioassays.