Patogenicidade de Beauveria bassiana, Isaria javanica e I. farinosa sobre Tetranychus urticae

Abstract

Brazil bears the title of second largest producer of papaya, however, some problems limit the cultivation of papaya, such as frequent manifestations of mites. Among the mites that attack this crop, Tetranychus urticae Koch has spread causing great damage to the producers. Aiming at an alternative control method of this pest, the objective of this study was to verify the efficiency of different strains of the entomopathogenic fungi Beauveria bassiana and Isaria spp. in the biological control of Tetranychus urticae in vitro. In order to meet the objectives, the work was carried out from two bioassays: the first one on the still phases of the mite, with application of the treatments in the egg phase and evaluation until the adult stage; and the second on the mobile phases with application in the protoninfa phase and evaluation until the adult stage. The treatments were formulated from four fungal strains corresponding to Isaria facinora (URM1355), Isaria javanica (URM4995), Beauveria bassiana (URM202) and Beauveria bassiana from commercial sources for comparison with Spirodiclofen and Abamectin as controls. The fungi were grown in Potato-Dextrose-Agar (BDA) medium, in Petri dishes incubated in a BOD (Biological Oxygen Demand) chamber at 28 ± 1 ° C, RH 60

± 10%, and were adjusted to the concentration of 1 x 108 conidia / ml, diluted in sterile water containing Tweem 80 (0.05% v / v), to be applied by simple spraying in plots containing 22 plates / treatment with 5 copies of organisms arranged in wet leaf discs. The treatments were maintained throughout the evaluation period in conditioned chambers (B.O.D.) at 25 ± 1ºC, with relative humidity (RH) of 60 ± 10% and photoperiod of 12 h. The bioassay of the immobile phases revealed that only the treatment with Spirodiclofen presented maximum lethal effect (100%), preventing the hatching of eggs. In addition to spirodiclofen, Beauveria bassiana commercial treatment also obtained lethality reaching 61% of the total deaths. The results showed that in addition to spirodiclofen, the Beauveria bassiana commercial treatment also obtained lethality reaching 61% of the total deaths. The bioassay of the mobile phases did not obtain significant results in any of the treatments to assert their efficiency, only Abamectin was effective in the control. Thus, it can be concluded that only the commercial fungal line of B. bassiana presents a lethal effect to the mite under the conditions tested.