Casuarina trees.

Casuarina trees.

Biological control of Australian native Casuarina species in the USA

Species of the Australian native pine, the Casuarinas, have become invasive weeds in parts of the USA.

  • 16 May 2007 | Updated 14 October 2011

CSIRO and the United States Department of Agriculture are working together to control the spread of Australian pine in the United States of America.

The weed

Three species of Australian pine, Casuarina equisetifolia, C. glauca and C. cunninghamiana, have become serious invasive weeds of coastal areas in the United States especially in southern Florida where they are a problem in the Everglades National Park and neighboring areas.

Casuarinas cause many problems:

  • They inhibit the growth of native plants and their associated herbivores, owing to their rapid growth, dense coverage, and thick litter accumulation.
  • Salt-tolerance allows them to grow on coastal dunes, increasing beach erosion and interfering  in nesting by endangered sea turtles and the American crocodile.

However, they also have potential value:

  • They are valued as ornamental shade trees throughout their range.
  • Plans are underway to use C. cunninghamiana as a wind break around citrus groves in Florida.
A number of Australian insects have been identified as potential biocontrol agents for Australian native pines, casuarinas, in the USA.

Control efforts that target the reproductive structures and saplings could reduce the Casuarinas spread into natural areas without affecting their horticultural value.

As these species spread primarily by seed production into natural areas, reducing their reproductive output would decrease their invasiveness. Reproduction can also occur by root suckers, so herbivores attacking young plants would reduce establishment of saplings.

The search for biological control agents

Scientists from the United States Department of Agriculture’s Australian Biological Control Laboratory in Brisbane, Queensland, have been conducting Australian surveys for insect herbivores on the Casuarinaceae since mid 2004. Most of these surveys were in coastal and subcoastal areas from Brisbane to Rockhampton in Queensland.

Casuarinaceae in other areas of northern Australia, far-north Queensland, the Northern Territory, north-west Western Australia and southern Australia have also been included to investigate host range and host specificity of insect herbivores.

Potential biological control agents

A number of Australian insects have been identified as potential biocontrol agents of Casuarina species. Currently, priority is being given to foliage-feeding insects such as gall-forming wasps or defoliating moths.

Seed feeders are also of interest, as they could reduce the invasiveness of casuarinas. However specificity testing may be complicated by difficulties in providing actively growing fruit in quarantine on both host plants and plant species being tested.

The seed-feeding wasp, Bootanelleus orientalis, has been reared extensively from cones of C. equisetifolia in coastal eastern Australia, from Ballina in northern New South Wales to Yeppoon in north Queensland. While this species of wasp may significantly decrease seed production, its culture is complicated by the length of time required for its host to produce seeds in quarantine. For example, it is estimated to take three to five years for C. equisetifolia to produce seed.

Genetic studies are being conducted to determine the variation in Casuarina species in Australia and Florida to locate the source populations of the weed in the introduced range. Research into the evolutionary associations between Casuarina and its associated herbivores is also planned.

Partners

The Australian Biological Control Laboratory (ABCL) is hosted by the CSIRO laboratories at Long Pocket in Brisbane, Queensland, Australia. It is operated by the United States Department of Agriculture, Agricultural Research Service (USDA-ARS).

Find out more about the The US Department of Agriculture‚Äôs Australian Biological Control Laboratory.