Evaluation of Metarhizium anisopliae var. anisopliae Qu-M845 Isolate to Control Varroa destructor (Acari: Varroidae) in Laboratory and Field Trials

Abstract

The effectiveness of the Metarhizium anisopliae (Metschinkoff) Qu-M845 isolate was evaluated in laboratory and field trials. It was previously selected for thermal resistance (at 30 and 35 °C) and pathogenicity on Varroa destructor (Anderson and Trueman). In the laboratory, the first evaluations were carried out by spraying and increasing the concentration from zero to 108 conidia mL-1 on varroa adults. Lethal concentrations required for 50 and 90% mite mortality (LC50 and LC90) were 3.8 x 105 and 8 x 107 conidia mL-1, respectively (χ2 = 2.03). In the autumn field trials, three application methods (doses of 5 x 1010 conidia per hive) were evaluated. The treatments were: a) conidia stamped on filter paper, located on every second frame inside the hive; b) dry conidia sprinkled on and between frames; and c) dry conidia in a dispenser path at the entrance of the hive. Furthermore, untreated hives were included as controls. After 21 days of treatment, the dry conidia sprinkled on and between frames showed 67% less bees infested by the mite than the control (p < 0.05). Average bee mortality observed was significantly different between treatments (p < 0.05). The sprinkled dry conidia caused the highest mortality of bees. In spring, this treatment produced increased mite mortality and without bee mortality. These results demonstrated that it is possible to develop a biological insecticide based on this isolate to generate an alternative to control V. destructor.