Calibration of a sunlight simulator for determining solar stability of Bacillus thuringiensis and Anagrapha falcifera nuclear polyhedrovirus

The effect of light on survival of entomopathogens is well described and ef forts are underway to develop formulations that may protect an entomopathog en from damage by sunlight. The availability of solar simulators allows for year-round testing of solar protectants. A commercial formulation of Bacil lus thuringiensis Berliner and an unformulated baculovirus isolated from An agrapha falcifera (Kirby) were exposed to various amounts of light from a s olar simulator or the sun to determine the relative effect of each source o n loss of insecticidal activity. Rate of pathogen degradation was essential ly the same for both light sources when original activity remaining was reg ressed against total energy (as measured by joules/m(2)). The amount of tim e required to reduce activity was different, however, because of a differen ce in total energies produced by the solar simulator and natural sunlight. Virus was approximately two times more sensitive to light than bacteria. To obtain 50% reduction of virus activity, exposure to 1.8 x 10(7) joules was required, whereas 3.2 x 10(7) joules was necessary to achieve a similar lo ss of activity for B. thuringiensis. The importance of reporting energy lev els from various solar simulators is discussed.