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The tomato russet mite (TRM), Aculops lycopersici (Tryon) (Eriophyidae) is a major pest of tomato crops worldwide, responsible for extensive plant damage and substantial yield losses. The limited availability of chemical control options for this pest, particularly in the European Union, highlights the need for alternative management strategies. The aim of this study was to assess the pathogenicity of the entomopathogenic fungus Beauveria bassiana strain ATCC74040 (in the form of biopesticide Naturalis®) against TRM females and eggs under laboratory conditions (25 ± 2 °C, 80% RH, 16:8 L/D), using a graded series of concentrations (103–107 CFU mL−1). At the two highest levels tested (106 and 107 CFU mL−1), direct spraying caused mean mortalities of 61.7% and 88.6% of TRM females after five days, respectively, whereas in the residual assay (exposure to plants treated 24 h earlier) the same concentrations resulted in only 8.2% and 16.4% mortality, correspondingly. The lethal concentrations required to cause 50% and 90% mortality of directly treated females within five days (LC50 and LC90) were 2.65 × 105 CFU mL−1 (95% CI 1.87 × 105–3.74 × 105) and 1.51 × 107 CFU mL−1 (95% CI 8.12 × 106–2.83 × 107), respectively. In contrast, in residual assays, LC50 and LC90 values were substantially higher—1.15 × 109 (95% CI 1.41 × 108–9.36 × 109), and 7.81 × 1012 CFU mL−1 (95% CI 1.80 × 1011–3.46 × 1014), in turn—highlighting the markedly lower efficacy of indirect application. At a concentration of 106 CFU mL-1, the fungus also exhibited ovicidal activity, reducing TRM hatching by average 42% compared to the control. The highest concentration tested (107 CFU mL-1) induced phytotoxic symptoms on tomato plants (cv. ‘Mei Shuai’) suggesting that cultivar-specific sensitivity may occur. Further research is needed to assess this risk across a wider range of tomato varieties, as this phenomenon could be critical for the practical use of Naturalis-based biocontrol strategies. The results indicate that B. bassiana can reduce TRM populations under direct application, but also underscore the limitations related to residual activity. These findings provide an essential basis for future semi-field and field trials to optimize application strategies and evaluate their integration into tomato crop protection programs.
Sybilska et al. (Mon,) studied this question.