Title "Evaluation of different fungal applications to increase varroa controlling by Metarhizium anisopliae"

The most serious threat to European honey bees is the ectoparasitic mite Varroa destructor. Varroa can be defeated with chemicals, but residues in honey bee products and arisen resistances to chemicals make it necessary to find new control methods. In this in-field trial we evaluated if a special isolate of the entomo-, acaro-pathogenic fungus Metarhizium anisopliae var. anisopliae BIPESCO 5 is a possible biological control agent against V. destructor. For this purpose 16 Dadant bee hives were set-up at Maso Franch, Lavis, Trentino (Italy). The hives were divided in 2 groups, 8 hives were disposed for control and 8 hives for the treatment with the fungus. From 13 June until 3 July the 'Metarhizium' treatment group was dusted weekly (4 times) with conidia of BIPESCO 5. After waiting 14 further days the 16 colonies were split in nucleus colonies. In this occasion the parental families without brood were exposed to a follow-up oxalic acid treatment. The nucleus colonies were observed for further 24 days until all brood hatched and then treated with oxalic acid. During the experiment live phoretic mites were sampled weekly with the powdered sugar method and dead mites were count on mesh bottom board. Residual mite-fall was assessed until 2 weeks after the oxalic acid treatment. During the experiment colony strength and health status was monitored weekly. Pre-oxalic acid treatment mite-fall on nucleus colonies was significantly reduced in the colonies where the fungus was applied, compared with the control hives, which imply that there were less reproductive mites at the moment of the hive split in the 'Metarhizium'-treated group.