First report of foliar nectar production by Lygodium microphyllum (Lygodiaceae), an invasive fern in Florida

Authors: SEBESTA, NICOLE - Florida International University; JONES, IAN - University Of Toronto; Lake, Ellen

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/12/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Lygodium microphyllum, an invasive fern in Florida, is challenging to manage because of its tolerance of a range of environmental conditions, fast growth and reproduction, and ability to resprout after burning or cutting. Here we share a potential complication to management: production of nectar by L. microphyllum leaves. Numerous small beads of nectar were observed in June 2017 on large (= 2m height) L. microphyllum plants growing inside a greenhouse at Florida International University. The nectar beads appeared uniformly along a leaf’s main rachis (stem) and on many of the frond leaflets. The plant structures producing the nectar are not obvious. Nectar collections from leaflets yielded a mean sugar concentration of 14%. However, there was not enough nectar available to analyze its composition. In a pilot study investigating whether nectar production could be induced, four plants were cut back 50% (to mimic herbivory) and monitored every 6 hours for 2 days for nectar production. Nectar presence was most pronounced 24 hours post-damage; however, there were numerous ants present collecting the nectar, so quantification of volume produced was not possible. That nectar production is inducible suggests that it is a defensive trait and may function to attract predators (often ants) to defend the plant against herbivores. While previous work on the role of nectar in ferns has produced mixed results, the potential repercussions of this defensive strategy could be important to the success of management efforts. Biological control agents released for L. microphyllum management have had variable success, while ants found in the field have been observed removing biocontrol larvae soon after releases (E. Lake, pers. comm.). Could L. microphyllum be responding to damage (management efforts) by producing nectar and attracting defenders in the field? Our next (ant-excluded) experiment will quantify and analyze damage-induced nectar and compare production in L. microphyllum and several congeners.

Technical Abstract: Lygodium microphyllum, a FLEPPC Category I invasive, is challenging to manage because of its tolerance of a range of environmental conditions, fast growth and reproduction, and ability to resprout after burning or cutting. Here we share a potential complication to management: production of foliar nectar. Numerous small beads of nectar were observed in June 2017 on large (= 2m height) L. microphyllum plants housed in the greenhouse at Florida International University. The nectar beads appeared uniformly along a leaf’s main rachis and on many of the frond leaflets; the structures from which the nectar originates, however, are not obvious. Nectar collections from leaflets yielded a mean sugar concentration of 14%; however, not enough nectar was available to allow constituent analysis. In a pilot study investigating inducibility, four plants were cut back 50% (to mimic herbivory) and monitored every 6 hours for 2 days for nectar production. Nectar presence was most pronounced at 24 hours post-damage; however, there were numerous ants present collecting the nectar, so quantification was not possible. That nectar production is inducible suggests that it is a defensive trait and may function to attract predators (often ants) to defend the plant against herbivores. While previous work on the role of nectar in ferns has produced mixed results, the potential repercussions of this defensive strategy could be important to the success of management efforts. Biocontrols released for L. microphyllum management have had variable success, while ants found in the field have been observed removing biocontrol larvae soon after releases (E. Lake, pers. comm.). Could L. microphyllum be responding to damage (management efforts) by producing nectar and attracting defenders in the field? Our next (ant-excluded) experiment will quantify and analyze damage-induced nectar and compare production in L. microphyllum and several congeners.