Laboratory evaluation of Beauveria bassiana strain ATCC74040 as a potential biocontrol agent of Aculops lycopersici

Abstract

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.

Keywords: Beauveria bassiana; Biological control; Entomopathogenic fungi; Eriophyoid mites.

Fig. 1

(a–c) Survival/mortality of Aculops lycopersici females after direct treatment with Beauveria bassiana strain ATCC74040. For each time point (one, three, and five days), the Kruskal–Wallis test was used to compare the mortality rates across different fungal concentrations. According to Dunn’s test, at a significance level of 0.05, the same letters indicate homogenous groups.

Fig. 2

(a–c) Residual effect of Beauveria bassiana strain ATCC74040 on survival/mortality of Aculops lycopersici females placed on plants 24 h after spraying with the biopesticide. The Kruskal–Wallis test was used to compare the mortality rates across different fungal concentrations. According to Dunn’s test, at a significance level of 0.05, the same letters indicate homogenous groups.

Fig. 3

Effect of direct spraying with different Beauveria bassiana strain ATCC74040 concentrations (color grey) on Aculops lycopersici egg hatching. According to Dunn’s test, at a significance level of 0.05, the same letters indicate homogenous groups.

Fig. 4

Aculops lycopersici egg hatching in the following days after treatment Beauveria bassiana strain ATCC74040 at concentration 10⁶ CFU mL^-1. Asterisks indicate statistically significant differences between control and experimental groups (p < 0.05), based on Dunn’s test.

Fig. 5

A Probit analysis plot used to model the relationship between the logarithm of time (Log(T)) and the probability of Aculops lycopersici mortality (Probit(P)).