The Epizootic models of Beauveria bassiana in Sawtoothed Grain Beetle, Oryzaephilus surinamensis Populations Feeding on Date fruits

Beauveria bassiana is one of the microbial control agents of sawtoothed beetle Oryzaephilus surinamensis. To study the epizootiology of the entomopathogen in O. surinamensis population, beetles were reared in insectaria filled with date fruits. Before transfer of the insects, date fruits were treated with 50% lethal dose of B. bassiana. Samplings of different life stages of the beetle were done during a 25 week period. The population density of O. surinamensis was estimated in 12 steps. The population fluctuations of the different beetles' life stages were estimated using SIR (Susceptible, Infected and Recovered), Anderson and May and general models. In treated and untreated populations, logistic growth model fitted well to population growth. Comparison of different models showed that the Anderson and May model explain better the various relationships between the populations and the pathogen. A sigmoid trend was observed in the population fluctuation curve in the treated populations, so that the population density of diseased individuals in prepizootic phase increased until attaining the peak where the epizooty took place. Thereafter the postepizootic phase begun with a drop in the density of the affected individual. Five epizootic waves recorded during the sampling period showing the occurrence of five epizootic periods. The peaks of these epizootic waves were recorded in the weeks 3, 13, 21 and 23. The 2nd period was the longest one that lasted 12 weeks being the shortest epizootic wave recorded.