OCCURRENCE OF THE ENTOMOPATHOGEN BEAUVERIA-BASSIANA (BALSAMO) VUILLEMIN IN DIFFERENT TILLAGE REGIMES AND IN ZEA-MAYS L AND VIRULENCE TOWARDS OSTRINIA-NUBILALIS (HUBNER)

The entomopathogen, Beauveria bassiana (Balsamo) Vuillemin, is an important component in the com (Zea mays L.) agroecosystem; this pathogen was found in soil, living com plants, and field com residue. Beauveria bassiana occurs naturally in the soil within different tillage systems (plow, chisel, no-tillage), with an average of 51-74 colony forming units g-1 of soil. The natural inoculum was present in the crop residue from the different tillage systems, killing up to 84% of European corn borer larvae (Ostrinia nubilalis (Hubner), Lepidoptera: Pyralidae) overwintering in the no-tillage regime. Of the larvae collected from com late in the season, 100% of those killed by Beauveria bassiana were from plants colonized by Beauveria bassiana applied foliarly at the whorl-stage (chi2 = 19.1, P < 0.01). However, the lack of mycosis in the totalanubilalis population may have been a function of low concentrations of the fungus in the plants. Fungal samples isolated from internodal and nodal tissue of those plants maintained virulency, killing from 23-100% of exposed larvae. Beauveria bassiana has potential for environmentally safe insect suppression, in that it occurs naturally and can also be applied to field com. Understanding the unique relationship between the soil, Beauveria bassiana, and Z mays will be invaluable in furthering development and utilization of such fungi to manage insect pests of food plants.