**1. Introduction**

Focusing on the interactions of insects with plants and microbes has been considered the key to better understand various mechanisms behind ecosystem functioning [1]. The significance of insects is modulated by their abundance and the diversity of biotic interactions, most prominently of those with various natural enemies. As insects cause grea<sup>t</sup> losses in forestry and agriculture, the understanding of the biology of their natural enemies is of high importance also in the applied context [2–4]. Thus far, parasitoids and vertebrates have received most research effort in the context of ecological studies on insects [5,6]. Naturally, pathogens have also not escaped attention as antagonists of insects [7–9]; among those, viruses have had a central role in ecological studies [10]. Moreover, from the late 1990s, there has been an exponential growth in studies focusing on the use of fungi as biocontrol agents [2,11]. However, the knowledge about the role of entomopathogenic fungi in natural settings is still scarce, despite the almost two centuries long awareness about these organisms in the scientific community [12].

To contribute to filling this gap, we recorded the diversity and prevalence of lethal fungal pathogens in laboratory rearing of lepidopteran larvae that represented offspring of field-collected females, fed with field-collected host plants. The assemblage of fungal pathogens in the laboratory was compared to that recorded in a field experiment in which

**Citation:** Gielen, R.; Meister, H.; Tammaru, T.; Põldmaa, K. Fungi Recorded on Folivorous Lepidoptera: High Diversity Despite Moderate Prevalence. *J. Fungi* **2021**, *7*, 25. https://doi.org/10.3390/jof7010025

Received: 28 November 2020 Accepted: 29 December 2020 Published: 5 January 2021

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moth larvae were reared in a seminatural setting. The focus was set on plant- and airborne fungal infections relevant for folivorous larvae, with the interactions of soil-dwelling pupae [2,3] remaining beyond the scope of the present paper. We discuss the patterns of diversity and abundance of insect-associated fungi on lepidopteran hosts, and report taxa not recorded on this group of insects previously.

#### **2. Materials and Methods**
