**Acetamiprid A**ff**ects Destruxins Production but Its Accumulation in** *Metarhizium* **sp. Spores Increases Infection Ability of Fungi**

#### **Monika Nowak 1, Przemysław Bernat 1, Julia Mrozi ´nska 2 and Sylwia Ró ˙zalska 1,\***


Received: 10 August 2020; Accepted: 5 September 2020; Published: 11 September 2020

**Abstract:** *Metarhizium* sp. are entomopathogenic fungi that inhabit the soil environment. Together, they act as natural pest control factors. In the natural environment, they come into contact with various anthropogenic pollutants, and sometimes, they are used together and interchangeably with chemical insecticides (e.g., neonicotinoids) for pest control. In most cases, the compatibility of entomopathogens with insecticides has been determined; however, the influence of these compounds on the metabolism of entomopathogenic fungi has not ye<sup>t</sup> been studied. Secondary metabolites are very important factors that influence the fitness of the producers, playing important roles in the ability of these pathogens to successfully parasitize insects. In this study, for the first time, we focus on whether the insecticide present in the fungal growth environment affects secondary metabolism in fungi. The research revealed that acetamiprid at concentrations from 5 to 50 mg L−<sup>1</sup> did not inhibit the growth of all tested *Metarhizium* sp.; however, it reduced the level of 19 produced destruxins in direct proportion to the dosage used. Furthermore, it was shown that acetamiprid accumulates not only in plant or animal tissues, but also in fungal cells. Despite the negative impact of acetamiprid on secondary metabolism, it was proofed to accumulate in *Metarhizium* spores, which appeared to have a stronger infectious potential against mealworm *Tenebrio molitor*, in comparison to the insecticide or the biological agen<sup>t</sup> alone.

**Keywords:** entomopathogens; mycoinsecticides; secondary metabolites; insect pathogenesis; acetamiprid accumulation

**Key Contribution:** Acetamiprid represses destruxins production by *Metarhizium* sp.; Spores of *M. brunneum* with accumulated acetamiprid have increased infectivity against *T. molitor*.
