MODELING THE PERSISTENCE OF QUIESCENT CONIDIA OF THE ENTOMOPATHOGENICHYPHOMYCETE PAECILOMYCES-FUMOSOROSEUS EXPOSED TO SOLAR-RADIATION

Persistence of conidia of the entomopathogenic fungus Paecilomyces fum osoroseus exposed to artificial and solar radiation at a constant temp erature was studied by monitoring the ability to germinate and to form colonies (colony-forming units, CFUs). The photic effect of radiation on each of these variables was modelled by a decreasing function of U VB irradiation (in J m(-2)). Germination ability was represented by a logistic function and viability (log CFU) by an infinitely decreasing function. Experiments carried out under artificial conditions, at thre e different UVB irradiances (from 0.3 to 1.6 W m(-2)), similar to thos e observed in nature, confirmed the adequacy of the predictor variable and of the functions chosen for describing these data. The proposed m odels appeared to be irradiance independent. Under solar radiation, th e models were able to describe data collected on three different summe r days in France (48 degrees 51'N, 2 degrees 06'E). However, it took a greater amount of solar UVB radiation to produce the same effect as t hat achieved indoors. This could be explained by differences in radiat ion spectra. For each model, one set of parameters was sufficient for representing all three sets of data: this constitutes an initial valid ation of the models proposed.