Citation: Hajek, A.E.; Everest, T.A.; Clifton, E.H. Accumulation of Fungal Pathogens Infecting the Invasive Spotted Lanternfly, Lycorma delicatula. Insects 2023, 14, 912. https:// doi.org/10.3390/insects14120912 Academic Editor: Mieczyslawa Irena Bogu´ s Received: 30 October 2023 Revised: 21 November 2023 Accepted: 24 November 2023 Published: 27 November 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). insects Article Accumulation of Fungal Pathogens Infecting the Invasive Spotted Lanternfly, Lycorma delicatula Ann E. Hajek 1, * , Thomas A. Everest 1 and Eric H. Clifton 1,2 1 Department of Entomology, Cornell University, Ithaca, NY 14853, USA; te97@cornell.edu (T.A.E.); eclifton88@gmail.com (E.H.C.) 2 Research & Development, BioWorks Inc., Victor, NY 14564, USA * Correspondence: aeh4@cornell.edu Simple Summary: Populations of the invasive spotted lanternfly in the eastern United States threaten vineyards and pose a public nuisance. Methods for control are being investigated, with an interest in mortality caused by insect-specific pathogens and naturally occurring predators. Two species of insect- pathogenic fungi caused extensive mortality in spotted lanternfly populations in fall 2018, and two additional fungal pathogens have been reported. Our extensive surveys, which emphasized a year with a summer drought, document that while Beauveria bassiana was most abundant, fifteen additional fungal pathogens killed spotted lanternflies. Although levels of infection for many pathogen species were low, infection was greatest in adults sampled in September and October, when spotted lanternfly reproduction occurs. Thus, we report an increased diversity of naturally occurring generalist fungal pathogens attacking this relatively new invasive planthopper. Abstract: In the eastern United States, populations of the invasive spotted lanternfly, Lycorma deli- catula, are abundant and spreading. Four species of naturally occurring entomopathogenic fungi have previously been reported as infecting these planthoppers, with two of these causing epizootics. Nymphal- and adult-stage lanternflies in Pennsylvania and New York were surveyed for ento- mopathogenic fungal infections from October 2021 to November 2023, and assays were conducted to confirm the pathogenicity of species that were potentially pathogenic. Beauveria bassiana was the most abundant pathogen, but we report an additional 15 previously unreported species of ento- mopathogenic fungi infecting spotted lanternflies, all in the order Hypocreales (Ascomycota). The next most common pathogens were Fusarium fujikuroi and Sarocladium strictum. While infection prevalence by species was often low, probably impacted to some extent by the summer drought in 2022, together these pathogens caused a total of 6.7% mortality. A significant trend was evident over time within a season, with low levels of infection among nymphs and higher infection levels in mid- and late-stage adults, the stages when mating and oviposition occur. Keywords: entomopathogenic fungi; invasive; opportunistic fungal pathogens; planthopper; biological control 1. Introduction The success of invasive species in their introduced ranges is often attributed to es- cape from natural enemies that provide control in native regions [1]. However, over time, natural enemies can adapt to using an invasive species through host shifts, evolu- tionary changes in resident enemy populations, or introductions of co-evolved natural enemies [2–4]. In the case of pathogens, the accumulation of pathogens attacking invasives has been hypothesized to potentially (1) lead to population decline of invasives or (2) create increases in pathogen populations that could spill over to impact co-occurring native host species [4]. With no saturation in numbers of invasive insect species predicted over time [5], Insects 2023, 14, 912. https://doi.org/10.3390/insects14120912 https://www.mdpi.com/journal/insects