Dynamics of Beauveria bassiana and Metarhizium anisopliae Infecting Hypothenemus hampei (Coleoptera: Scolytidae) Populations Emerging from Fallen Coffee Berries

Abstract

The aim of this research was to evaluate the effect of soil sprays of the entomopathogens Beauveria bassiana and Metarhizium anisopliae on coffee berry borer (cbb) adults, Hypothenemus hampei, emerging from fallen berries through time. Each fungus was applied to a plot 5000 m2 in size of the Colombian variety in the third harvest year. The experimental plot was formed with 9 trees, and the experimental unit was the central tree. In this tree all the green uninfested berries were left and the whole tree covered with a screen cage to avoid further cbb infestation or escape. Nine treatments replicated 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 1 109 conidia/tree. Under each experimental 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 applied the same day of the spray and at 2, 5, 10, 15, 20, 25 and 30 days after fungus application. Results showed that infection levels of both fungi on cbb were the highest during the first five days after application, reaching nearly 30% for B. bassiana and 11% for M. anisopliae. However, the infection decreased for 20 days but peaked again at 25 days post-treatment with 24.3% for B. bassiana and 7.7% for M. anisopliae. These results are explained by the formation of propagules in the soil by these fungi, due probably to the accumulation of infective conidia on infected insects which infect other insects leaving the fruits. The two species were recovered from the soil even after two months and fluctuation in numbers of colony forming units was attributed to the rainfall during the study period and the fungus conidiation. B. bassiana was shown to be more infective than M. anisopliae, considering 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 avoid 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 lilacinus.