Biological control of Australian pine
Three species of Australian pine, Casuarina equisetifolia, C. glauca and C. cunninghamiana(Casuarinaceae), have become serious invasive weeds in the United States especially in southern Florida, including the Everglades National Park and neighboring areas. With its rapid growth, dense coverage, and thick litter accumulation, Australian pine dramatically alters the habitat of infested areas inhibiting the growth of native plants and their associated herbivores. A salt tolerant species, C. equisetifolia may be found on coastal dunes where it increases beach erosion and interferes in the nesting of endangered sea turtles and the American crocodile. Because this species spreads primarily by seed production into natural areas, a reduction in reproductive output would decrease its invasiveness. Reproduction may also occur by root suckers and thus herbivores attacking young plants would reduce establishment of saplings. Australian pine is highly valued as an ornamental tree providing shade throughout its range. Casuarina cunninghamiana has also been suggested for use as a wind break around citrus groves to inhibit the spread of citrus canker. Control efforts that target the reproductive structures and saplings of Australian pine would potentially reduce its spread into natural areas while not affecting its horticultural value or agricultural application. Preliminary surveys of the insect herbivore fauna associated with the Casuarinaceae commenced in Australia in mid 2004.
Australian Pine in Florida, photo courtesy ABCL
Surveys have been conducted to search for insects associated with Casuarina spp. that might be developed for biological control. The surveys have resulted in a list of 90 herbivore species, most of which have yet to be identified to species. These insects were found attacking mostly the leaves, but also branches and fruit of the trees. Of particular interest is the Torymidae wasp that has been reared from the cones of Casuarina spp. This wasp, identified as Bootanelleus orientalis, has been collected from New South Wales, Queensland, and South Australia from Casuarina fruit. It appears to be specific to Casuarina and was recovered from at least six species including C. equisetifolia, C. glauca, and C. cunninghamiana. There are also leaf-feeding weevils, moth species (Lepidoptera), and sap-sucking bugs (Hemiptera) in the native range that could be used against root suckers.
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