Efficacy evaluation of the mycopesticide Naturalis (Beauveria bassiana strain ATCC 74040) against spider mites (Acari: Tetranychidae) in Serbia

Abstract: Biological efficacy of a B. bassiana-based product (trade name Naturalis, containing min. 2,3×107 viable conidiospores/ml; strain ATCC 74040) in spider mites control was investigated in two field trials and one greenhouse trial in Serbia. The product was applied twice at rates of 0.1% v/v (i.e. Naturalis-LR) and 0.15% v/v (i.e. Naturalis-HR), at 3-5 days intervals, and its efficacy was compared to abamectin (a microbiological acaricide), and acrinathrin and clofentezine (chemical acaricides), applied once at their label rates. The trial against two-spotted spider mite (Tetranychus urticae) on pepper was conducted in a commercial greenhouse at Padinska Skela locality (N44°57.010′; E020°25.734′), where Naturalis was applied twice at 5-day intervals, and the efficacy was assessed 8 and 18 DAT1 (= days after the first treatment). In the assessments, lower and higher rate of Naturalis achieved high efficacy (> 97%) in T. urticae control. Abamectin and acrinathrin also showed high efficacy (> 99%). The trials against summer population of European red mite (Panonychus ulmi) were conducted in commercial apple orchards at Morović (N45°00.856′; E019°15.449′) and Slankamen (N45°07.588′; E020°15.602′) localities, and acaricides were applied at 75 BBCH growth stage. In Morović, the second treatment with Naturalis was three days after the first treatment, and the efficacy was assessed 6, 17, and 27 DAT1. Naturalis-LR achieved 78.6%, 85% and 90.6% efficacy, respectively, and Naturalis-HR achieved 74.4%, 95.8%, and 95.5% efficacy, respectively, while abamectin efficacy was 89%, 99.3%, and 97.5%. In Slankamen, the second treatment with Naturalis was four days after the first treatment, and the efficacy was assessed 11 and 24 DAT1. Efficacy of Naturalis-LR was 65.6% and 54.2%, and of Naturalis-HR it was 89% and 75.8%. Abamectin achieved 83.4% and 82.6% efficacy, while the efficacy of acrinathrin was 91.1% and 94.5%. Clofentezine efficacy was only 53.1% and 66.2%, which is probably the consequence of intense selection pressure on P. ulmi population at this locality in the previous years. The obtained results indicate that application of mycopesticide Naturalis can provide an efficacy in spider mite control which is comparable to the efficacy of standard acaricides. The results are discussed in the light of possible improvement of spider mite management by alternative use of this mycoacaricide as a control measure.