POTENTIAL BIOLOGICAL CONTROL OF THE MITE Varroa destructor BY THE ENTOMOPATHOGENIC FUNGUS

FERNANDEZ CECILIA DE LOS A.; COMELLI NORA A.; CONSOLO F. ; EGUARAS M.

San Luis

Congreso; BIOCELL.; 2019

Apis mellífera plays a very important role in beekeeping and in the pollination of crops that man consumes daily. Several potential factors have been studied as possible causes of declining pollinator health, such as parasites and pathogens, exposure to agricultural pesticides, habitat loss and/or climate change. Within the group of biotic stressors is Varroa destructor, an mite that causes a parasitosis called Varroosis; whose main effects are physiological and physical damage when feeding on the hemolymph of bees. Various synthetic miticideshave been developed to target V. destructor mites. However, the long-term application of miticides has resulted in the development of resistance in V. destructor. Biological control is an alternative strategy, based on the total or partial destruction of the pest through the use of its natural enemies; when it comes to fungi capable of causing disease in insects or mites they are called entomopathogens. In this work, the pathogenicity and the susceptibility of an isolates native to the province of San Luis and a commercial strain of Beauveria bassiana were evaluated by bioassays against V.destructor and A. mellífera. The native fungal isolates were obtained from soil samples from different locations in the Province of San Luis, isolated in Chasé medium and characterized to gender from microcultures according to morphological characteristics and the taxonomic key proposed by Barnet and Hunter (1998). For the bioassays performed, mites and bees were collected. They were individually embedded for 10 seconds in 5 ml of the conidia suspension for each treatment (1.108 conidia/ml) and in 5 ml of sterile Tween 80 for control (0.03% w/w). Each group of 5 mites and bees was placed in a sterile Petri dish with 9 cm diameter with food and water ad libitum. 5 repetitions were performed for each treatment. The boxes were placed in an incubator and kept in the dark at 30 ° C and 100% RH (humidity obtained by placing a damp cotton on the base of the plate). The mortality of mites and bees was recorded at 24, 48 and 72 h. Dead mites or bees (which showed no movement or stimulus response) were removed and incubated in 1% water agar at 23 °C. The presence of mycelium on the body of the mite or bees was used as an indicator of fungal-induced mortality. The strains studied were infective producing a mortality of 20% for the native strain and 40% for the comercial strain. Although the native strain was less infective, it is a good indication considering its adaptation to the environment where it would be applied. As for the bioassays in bees, the growth of mycelium on the surface was not observed, which suggests the absence of pathogenicity of the strains tested in bees.