Dynamics of Beauveria bassiana and Metarhizium anisopliae infecting Hypothenemus hampei (Coleoptera : Scolytidae) populations emerging from fallen coffee berries

The aim of this research was to evaluate the effect of soil sprays of the e ntomopathogens Beauveria bassiana and Metarhizium anisopliae on coffee berr y borer (cbb) adults, Hypothenemus hampei, emerging from fallen berries thr ough time. Each fungus was applied to a plot 5000 m(2) in size of the Colom bian variety in the third harvest year. The experimental plot was formed wi th 9 trees, and the experimental unit was the central tree. In this tree al l the green uninfested berries were left and the whole tree covered with a screen cage to avoid further cbb infestation or escape. Nine treatments rep licated ten times were arranged in a complete randomized design. Conidia of each fungus were suspended in emulsified oil and water and applied on the base of the trees at a dosage of 1 x 10(9) conidia/tree. Under each experim ental tree 350 cbb-infested coffee berries were placed on the soil to serve as a source for aerial infestation of the trees. Infested berries were app lied the same day of the spray and at 2, 5, 10, 15, 20, 25 and 30 days afte r fungus application. Results showed that infection levels of both fungi on cbb were the highest during the first five days after application, reachin g nearly 30% for B. bassiana and 11% for M, anisopliae. However, the infect ion decreased for 20 days but peaked again at 25 days post-treatment with 2 4.3% for B. bassiana and 7.7% for M. anisopliae. These results are explaine d by the formation of propagules in the soil by these fungi, due probably t o the accumulation of infective conidia on infected insects which infect ot her insects leaving the fruits. The two species were recovered from the soi l even after two months and fluctuation in numbers of colony forming units was attributed to the rainfall during the study period and the fungus conid iation. B. bassiana was shown to be more infective than M. anisopliae, cons idering that the latter is more frequently associated to soil habitats. The authors believe efficiency of these fungi can be increased if improvements are made to the formulations, e.g., using a granulated formulation to avoi d leaching of the conidia from the soil during heavy rainy seasons. During this study it was found that H. hampei is a new host of Paecilomyces lilaci nus.