Host range, biology, and climate suitability of Callopistria exotica, a potential biological control agent of Old World climbing fern (Lygodium microphyllum) in the USA

Authors: Wheeler, Gregory; LAKE, ELLEN - Mt Cuba Center; SUTTON, GUY - Rhodes University

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Old World climbing fern, has rapidly invaded southern Florida. The weed climbs over other plants, including tall trees, forming massive walls of vegetation. It also forms thick mats on the ground that smother native plants. Currently, the weed has spread throughout most of the Florida peninsula. The weed is a severe problem in many of the most important parks and preserves in south Florida including Loxahatchee National Wildlife Refuge, the Panther Refuge, Audubon Corkscrew Sanctuary, J. Dickinson Park, Fakahatchee Strand State Preserve State Park, and Everglades National Park. First detected in Everglades National Park in 2001, the weed occupied an estimated 900 hectares of coastal marsh spread over 40 miles. Old world climbing fern is a suitable target for biological control as it causes harm to infested areas, no cost-effective, sustainable control methods are available, and because there are few close relatives in Florida, there is little threat to non-target species. To test the suitability of the new potential biological control agent, the defoliator Callopistria exotica, a series of no-choice tests was conducted on 68 plant species. The results indicate that C. exotica is highly specific to Old-World climbing fern and one other species that is also an exotic invasive, Lygodium japonicum. Thus, we conclude that this proposed biological control species is highly specific and will not survive typical winter temperatures north of Florida. We request permission for the release of C. exotica against Old World climbing fern.

Technical Abstract: Old World climbing fern, Lygodium microphyllum (Cav.) R. Br., is one of the worst environmental weeds of southern Florida. The weed climbs over other plants, forming thick mats on shrubs and trees that block sunlight to native plants. In the invaded 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 defoliator Callopistria exotica, was collected in Hong Kong and examined in quarantine to determine if it was safe for release. Climate modeling analysis was also performed to predict the potential climate suitability of C. exotica in the invaded range. A series of no-choice tests was conducted on 68 plant species from 45 genera, 33 plant families, and 18 orders. The results indicated that C. exotica is highly specific to the target weed, L. microphyllum and a congener that is also an exotic invasive, L. japonicum. The results indicated that the neonates fed and matured to the adult stage on the target weed L. microphyllum (0.71 ± 0.02 proportion survived) and on another invasive fern, L. japonicum (0.84 ± 0.04 proportion survived). While no C. exotica neonates survived when fed L. oligostachyum, a low proportion survived to the adult stage when fed the non-targets L. palmatum (0.07 ± 0.03), L. venustum (0.01 ± 0.01), and L. volubile (0.07 ± 0.03). Additionally, though few larvae survived to the adult stage when fed L. palmatum and L. volubile their development time were greater (1.3-1.5 - fold longer) and pupal weights were lower (0.7-0.9 - fold less) than those fed the target weed. All neonates perished within 3 days when fed the remaining 62 species evaluated in these no-choice tests. Climate modeling indicated that the suitability of North American climates for the establishment of C. exotica are very high in south Florida but very unsuitable north of the L. microphyllum invaded range. These results indicated that, this potential biological control agent, is highly specific to L. microphyllum and L. japonicum and will have no, or very low survival on other non-target species. The release of C. exotica will assist in the effort to manage the invasive weed Old World climbing fern.