Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2007
Publication Date: 6/1/2008
Citation: Madeira, P.T., Pemberton, R.W., Center, T.D. 2008. A molecular phylogeny of the genus Lygodium (Schizaeaceae) with special reference to the biological control and host range testing of Lygodium microphyllum . Biological Control, Vol. 45, Issue 3, June 2008, pgs. 308-318. Interpretive Summary: Lygodium microphyllum, sometimes known as “Old World Climbing Fern”, is a non-native plant that was naturalized in the 1960’s and has become an invasive plant by aggressively spreading throughout forested wetlands in southern and central Florida. This climbing fern creates thick mats as it climbs over native shrubs and trees. These mats smother the underlying vegetation and can carry ground fires into the forest canopy. Foreign surveys for biological control agents identified 20 insect species and 2 mite species as potential agent. Four agents were collected and tested (host range testing) on a variety of plants, including five Lygodium species native to the United States and the West Indies, to see if they can complete their life cycles on any non-target species. This study used DNA sequencing to look at the phylogeny (family tree) within the genus Lygodium to see how this would correlate with the host range testing. The study found three major branches of the Lygodium family tree with Lygodium microphyllum far out on one branch. One native to the U.S., Lygodium palmatum, was on a second older branch and the other Lygodium natives were on a third younger branch. All the natives were about equally distant (10%) in relationship from Lygodium microphyllum so factors other than relatedness appear to be primary in determining whether the biological control agents can succeed on them. Several agents did well on Lygodium palmatum, perhaps because millions of years ago its ancestors were widely available as a food source for the biological control agent’s ancestors. However, Lygodium palmatum is a temperate plant and the biological control agents are subtropical so this is not considered problematic to their use.
Technical Abstract: Lygodium microphyllum, first naturalized in the 1960’s, has aggressively invaded forest dominated wetlands in southern and central Florida. The indeterminate growth of this invasive climbing fern creates thick rachis mats which climb over shrubs and trees smothering the underlying growth and the carrying ground fires up into the forest canopy. Foreign surveys for natural enemies identified 20 species of insects and two species of mites. Host range testing of three insect species and one mite included five Lygodium species (L. palmatum, L. volubile, L. cubense, L. venustum, and L. oligostachyum) native to the United States and the West Indies. A molecular phylogeny of the genus was conducted using the trnL intron and the trnL-F intergenic spacer of chloroplast DNA to determine the relationship of L. microphyllum to other Lygodium species. Three major clades appeared, one with L. palmatum and L. articulatum (the most ancient species in the genus), a second with L. reticulatum and L. microphyllum, and a third comprised of the other species examined. L. microphyllum appeared at the end of a long branch approximately equidistant from all species of interest preventing the correlation of genetic distance and host range behavior. However, inspection of host range experiments showed an apparent relationship between the presence of a related biotype or species of the insect on a related alternate host and the ability of that insect to develop on that alternate host. Ancestral host usage is suggested as an explanation for the widespread acceptance of L. palmatum by the insects and mite.