Responses of different clonal lines of Imperata cylindrica (cogongrass) to herbivory when grown in different nutrient environments

Authors: Wheeler, Gregory; Arismendi, Giselle

Submitted to: Florida Entomological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/30/2023
Publication Date: 7/31/2023
Citation: Wheeler, G.S., Arismendi Baena, G. 2023. Responses of different clonal lines of Imperata cylindrica (cogongrass) to herbivory when grown in different nutrient environments. Florida Entomological Society Annual Meeting.

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 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. Fires can be carried quickly to the tops of trees by the burning fern and then spread by the floating pieces. The native range is the Old World from Africa to India, Southeast Asia, Australia, and some Pacific Islands. 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 due to its phylogenetic isolation, 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 from 45 genera, 33 plant families, and 18 orders. The results indicate that C. exotica is highly specific to the target weed, Old-World climbing fern Lygodium microphyllum and one other congener that is also an exotic invasive, Lygodium japonicum. In no-choice starvation tests, the neonates fed and matured to the adult stage on the target weed L. microphyllum (0.71 ± 0.02 proportion survived) and another non-target invasive fern, L. japonicum (0.84 ± 0.04 proportion survived). While no C. exotica neonates survived to the adult stage when fed L. oligostachyum, a very low proportion survived to the adult stage when fed the non-target species L. palmatum (0.07 ± 0.03), L. venustum (0.01 ± 0.01), and L. volubile (0.07 ± 0.03). All neonates perished within 3 days when fed the remaining 62 species evaluated in these no-choice tests. Additionally, though few larvae completed development when fed L. palmatum and L. volubile their development rate to the adult stage and pupal weights were significantly lower than those fed the target weed. These few that survived on these non-targets will face further challenges as they will be exposed to natural enemies longer in the vulnerable larval stage and due to smaller weights, will likely be less fecund. Studies conducted to examine egg and larval tolerance to cold temperatures indicated no eggs hatched when exposed to 15 °C (59 °F). 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.