Host range, biology, and thermal tolerance of Lygomusotima stria, a potential biological control agent of Old World climbing fern (Lygodium microphyllum) in the USA

Authors: Wheeler, Gregory; LAKE, ELLEN - Mt Cuba Center; MATTISON, ELIZABETH - Retired ARS Employee; Pratt, Paul; SUTTON, GUY - Rhodes University

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2025
Publication Date: 3/8/2025
Citation: Wheeler, G.S., Lake, E.C., Mattison, E., Pratt, P.D., Sutton, G. 2025. Host range, biology, and thermal tolerance of Lygomusotima stria, a potential biological control agent of Old World climbing fern (Lygodium microphyllum) in the USA. Biological Control. 204. https://doi.org/10.1016/j.biocontrol.2025.105741.
DOI: https://doi.org/10.1016/j.biocontrol.2025.105741

Interpretive Summary: Old World climbing fern is one of the worst environmental weeds of southern and central Florida. The weed climbs over other plants, forming thick mats that block sunlight to native shrubs and trees. In the introduced range, Old World climbing fern invades much of the southern peninsula of Florida where cost-effective, sustainable control methods are needed. A potential biological control agent, the defoliating moth Lygomusotima stria was collected in Thailand and Singapore and examined to determine if it was safe for release. A series of no-choice tests was conducted with recently hatched larvae and middle stage larvae. The results indicated that caterpillar could only feed and complete development on three Lygodium species, Old World climbing fern, another invasive exotic, Japanese climbing fern and the native American climbing fern. Adults laid eggs broadly across many taxa but generally on members of the climbing fern genus. Multigeneration studies indicated that these insects could sustain a population on on three Lygodium species, Old World climbing fern, Japanese climbing fern, and American climbing fern for at least four generations. However, the results of lower lethal temperature studies indicated that the lower lethal temperature for immature stages of the caterpillar ranged from -2.8 to 1.6 °C, indicating these caterpillars will not persist in areas where the more temperate American climbing fern grows. Thus, the caterpillar has a will not feed and develop on other species and we predict it will not pose a threat to the American climbing fern as it has a low tolerance for the colder temperatures where this plant grows naturally. The release of this caterpillar is expected to safely assist in the effort to manage the invasive weed Old World climbing fern.

Technical Abstract: Old World climbing fern, Lygodium microphyllum (Cav.) R. Br., is one of the worst environmental weeds of southern and central Florida. The weed climbs over other plants, forming thick mats that block sunlight to native shrubs and trees. In the introduced range, Old World climbing fern invades much of the southern peninsula of Florida where cost-effective, sustainable control methods are needed. A potential biological control agent, the defoliating moth Lygomusotima stria Solis & Yen, was collected in Thailand and Singapore and examined to determine if it was safe for release. A series of no-choice tests was conducted on neonate and third instars. The results indicated that L. stria could only feed and complete development on three congeners, the target weed, L. microphyllum, another invasive exotic, L. japonicum, and the native L. palmatum. Oviposition tests indicated that adults laid eggs broadly across many taxa but generally on members of the Lygodium genus. Multigeneration studies indicated that L. stria could sustain a population on L. microphyllum, L. japonicum, and L. palmatum for at least four generations. However, the results of lower lethal temperature studies indicated that the LLT50 for L. stria immatures ranged from -2.8 to 1.6 °C, indicating L. stria will not persist in areas where the more temperate L. palmatum grows. Thus, L. stria has a very narrow host range and we predict it will not pose a threat to L. palmatum as it has a low tolerance for the colder temperatures where this plant grows naturally. The release of L. stria is expected to safely assist in the effort to manage the invasive weed Old World climbing fern.