Non-target effects of Metarhizium brunneum (BIPESCO 5/F 52) in soil show that this fungus varies between being compatible with, or moderately harmful to, four predatory arthropods

Abstract

Biological control with entomopathogenic fungi is a feasible option for regulation of pest insect populations. However, possible effects on beneficial arthropods must be considered. We assessed the non-target effects of the microbial biological control agent Metarhizium brunneum (isolate BIPESCO 5/F 52) applied in soil on four different predatory arthropods: the predatory mite Gaeolaelaps aculeifer (Canestrini), the predatory bug Orius majusculus (Reuter), the rove beetle Dalotia coriaria (Kraatz) and the gall midge Aphidoletes aphidimyza Rondani. All are widespread and naturally occurring in Europe, they represent different classes of arthropods and different insect orders; furthermore, their life cycles involve different levels of contact with the soil. Adult G. aculeifer, O. majusculus, and D. coriaria, and last instar A. aphidimyza larvae were exposed to natural soil (control) or natural soil inoculated with M. brunneum at a concentration of 5 x 10 6 conidia/g of soil; this represents a worst-case scenario. Mortality, longevity, fecundity and Metarhizium outgrowth on dead individuals were assessed for the first three species; for A. aphidimyza, only mortality (non-emergence rate) and fecundity of emerged females were assessed. The fungal treatment resulted in a significantly higher mortality of O. majusculus and D. coriaria, 96%, and 7.3% respectively, compared with 19%, and 2% for their respective controls. Mortality of G. aculeifer was not significantly affected by exposure to the fungus in the soil. Longevity of O. majusculus and D. coriaria was significantly reduced following exposure to the fungus in the soil (log-rank test: p< 0.0001, Wilcoxon test p< 0.0001 and log-rank test: p=0.029, Wilcoxon test: p=0.027, respectively), while G. aculeifer longevity was not affected. Fecundity of O. majusculus and D. coriaria was negatively affected following exposure to the fungus in the soil, which reduced their oviposition by 20% and 4%, respectively, compared with the control, while G. aculeifer fecundity was not affected. Aphidoletes aphidimyza larval mortality was higher following exposure to the fungus in the soil (60% dead) than in the control (40% dead) but its fecundity was not statistically significantly affected by treatment. In conclusion, the predatory arthropods studied demonstrated a range of fitness responses to M. brunneum exposure in the soil, from no response (G. aculeifer), to intermediate (D. coriaria and A. aphidimyza) and high response (O. majusculus). This study demonstrates the relevance of using several fitness parameters and different arthropod species to determine whether a biological control agent should be considered a low-risk substance with respect to non-target effects.

Standard non-target tests for risk assessment of plant protection products are unsuitable for entomopathogenic fungi—a proposal for a new protocol

“…Since then, studies have aimed to close this gap. Tests on soil-dwelling non-target arthropods have been conducted in the laboratory (de Azevedo et al 2019;Saito and Brownbridge 2016), in the field (Babendreier et al 2015;Fischhoff et al 2017), and under semi-natural conditions (de Azevedo et al 2018). However, studies vary in product formulation, concentration, exposure method, and length as well as endpoints and quality control, complicating their comparison and thus subsequent risk evaluation.…”

“…In the presented experiment, viability was assessed through germination tests of conidia. The minimum germination threshold was set to 95% for all samples in accordance with de Azevedo et al (2019) to ensure that sufficient infective propagules were present. In performing this simple test, misleading trials using a nonviable test agent can be avoided.…”

First steps towards biological control of the pear gall midge (Contarinia pyrivora) with the insect pathogenic fungus Metarhizium brunneum

“…Metarhizium brunneum isolate BIPESCO 5 (alias Ma43, alias ATCC 90448, alias BIPESCO 5, alias F52 [Eilenberg et al 2008]) is a widely used isolate for biocontrol studies (Azevedo et al, 2017, 2019; Rauch et al, 2017). It was grown on 4% Sabouraud dextrose agar for 2 weeks at 22°C in darkness.…”

“…The same procedure was done to provide control soil except that inoculum was replaced with 0.05% Triton X‐100. Treatment and control soils were maintained at room temperature overnight and, before use, sieved again through a 3 mm mesh to ensure an even conidial distribution in the treatment soil (Azevedo et al, 2019). Inoculated soil was placed into 385 ml plastic beakers each with 50 g of soil, which were subjected to one of the three treatments, four beakers were made of 5 × 10 5 conidia/g of soil, three beakers of 5 × 10 6 conidia/g of soil and 7 beakers of the control.…”

“…The generalist insect pathogenic fungus Metarhizium brunneum (Hypocreales: Clavicipitaceae) is a good candidate for biological control of C. pyrivora since that fungus exists as commercial products to control different insect pests (Hajek and Eilenberg, 2018). The fungus works well as a biocontrol agent against soil pests, even in combination with other biological control agents (Azevedo et al, 2017; Azevedo et al, 2019; Gonzalez et al, 2016; Rauch et al, 2017).…”