Post-release support of host range predictions for two <i>Lygodium microphyllum</i> biological control agents

Abstract Classical biological control of weeds is a strategy for managing invasive plants, reassociating coevolved herbivores with their hosts in weeds’ adventive ranges. A modified open field test was conducted to assess the ecological host range of two biological control agents, Floracarus perrepae Knihinicki &amp; Boczek (Prostigmata: Eriophyidae) and Neomusotima conspurcatalis (Warren) (Lepidoptera: Crambidae), on nontarget ferns. These biological control agents are released to aid in the management of Lygodium microphyllum (Cav.) R. Br. (Lygodiaceae), an invasive fern that has had detrimental effects on ecosystems in south and central Florida. We examined nontarget ferns at four sites in Florida for evidence of biological control agent presence/damage, which would be an indication of an expanded ecological host range compared to the physiological host range determined during quarantine studies. The sites were visited multiple times between July 2021 and March 2023, and ferns were examined for evidence of feeding, larval presence, and oviposition. Neither agents nor indicators of their presence were observed on nontarget species. The mite F. perrepae was observed at the three sites on the eastern coast but failed to establish itself at the location on the western coast. In contrast, N. conspurcatalis was found at all locations, although its presence was not consistent across sites over time. Population monitoring indicated both agents were present in sufficient numbers to enable observation of spillover effects, but none were observed. This ecological host range testing validated the predicted physiological host ranges for the two biological control agents, confirming their high specificity to the target fern as observed during laboratory host range testing.