broom twig- mining moth
Transcription
broom twig- mining moth
Weed Biological Control Pamphlet No. 9 April 2008 BIOLOGICAL CONTROL OF ENGLISH BROOM: MINING MOTH BROOM TWIG- Background English broom, Cystisus scoparius (also known as broom and Scotch broom) is a leguminous shrub that is native to central and western Europe and has now spread to many temperate areas of the world. English broom has now become naturalised over large areas of south-eastern Australia. In Tasmania, it occurs throughout areas of human settlement but is particularly common in higher rainfall areas. Plants are locally abundant on roadsides, waste areas, poor quality pastures and in disturbed bushland. In pastures, English broom causes production losses by forming thickets that prevent grazing. Mature bushes are relatively unpalatable to sheep and cattle and contain alkaloids that are potentially toxic to stock. Dense thickets also provide cover for pest animals such as rabbits and inhibit access to bushland and recreational areas. English broom can be controlled to varying extents by herbicides, burning, mechanical clearing and grazing using sheep and goats. Grazing with sheep and goats is effective in pasture situations. However, the limited success, expense and difficulty in controlling English broom in many areas has resulted in biological control being investigated. Many insect species have been recorded on English broom in its native range and several of these have been under investigation to determine whether they have a sufficiently narrow host range to enable them to be released safely in Australia as biological control agents. These investigations resulted in the broom twig-mining moth, Leucoptera spartifoliella, which occurs in northern and central Europe, being released in New South Wales in 1993. It has since been released in Victoria and is now established on English broom in both states. The moth was released in Tasmania in 1995 and again in 1998, but there is no evidence that the moth established from these releases. However, field collected stock was again imported from southern NSW in November 2004. Some of this consignment was released directly into the field at a site near Oatlands in December 2004. The remaining stock was used to commence glasshouse rearing at New Town Laboratories. Moths produced from this culture are being used for field releases to get the broom twig-mining moth widely established in Tasmania. If this program is successful, the established sites will be used to collect and redistribute the moth to sites around the state in order to accelerate its dispersal. Description, life cycle and biology The moths (adult stage) (Fig. 1) are small, 3-4mm Figure 1. Broom twig-mining moth (Photo: W. Chatterton, TIAR). long and mostly white, with dark markings near the tips of the forewings. There is one generation each year. The moths start to emerge from pupae in early summer (December), with numbers reaching a peak around mid-summer (January). Eggs are white and oval shaped about 0.5 mm long and laid singly in the furrows of young stems. They hatch over a period of 2-3 weeks. The tiny, flat, legless larvae perforate the underside of the egg, bore into the stem and then tunnel through the tissue beneath the bark. Mature larvae are about 3 mm long, olive green with a dark stripe visible along the upper and lower body surface. Larval feeding continues throughout the remaining summer and autumn but slows and may cease during the cooler winter months. Feeding resumes in spring with fully developed mines often reaching 30-50 cm in length. The larvae pass through six stages (instars) during their development. First and second instar larvae are very small. Mines created by these young larvae are no more than 10 mm long and only about 0.5 mm wide. They are therefore difficult to see with the naked eye. Once the mines reach 30 mm in length, the mine is 0.5-1mm wide and more readily visible. Most damage to the plant is caused by the fifth and sixth instar larvae in spring, at which stage the mines become raised and up to 2 mm wide (Fig. 2). During spring, from about October, the fully developed larvae leave their tunnels and spin a white cocoon (Fig. 3) from which the moths emerge. When broom plants are heavily infested, the stems become covered with white cocoons. In general, the pupal period lasts about one month, but may be longer depending on weather conditions. Figure 2. Stem mines caused by larvae of the broom twig-mining moth (Photo: W. Chatterton, TIAR). Although larval feeding activity will not by itself be capable of controlling English broom, it has the potential of causing considerable damage to the plant, weakening it and making a useful contribution to its control. Introductions of more biological control agents are planned and these will place additional stress on plants, reduce their vigour and ultimately decrease the density of infestations. Biological control should be considered as a longterm program that is best used on large, chronic infestations with a low priority for control by other methods. Acknowledgments CSIRO and NSW Agriculture conducted the host specificity testing and importation for the broom twig-mining moth that enabled its initial release in Australia. CSIRO and DPI, Frankston, Victoria provided information on the biology of the moth. Figure 3. Pupa of broom twig-mining moth (Photo: W. Chatterton, TIAR). Damage Branches that become heavily infested with tunnelling larvae can die. With continued heavy attack, plants become less vigorous and display a large amount of dead wood. Plant growth and seed production can be significantly reduced. For further information on this project contact: John Ireson Tasmanian Institute of Agricultural Research, 13 St. John’s Avenue, New Town, 7008. Phone: (03) 6233 6821; Fax: (03) 62782716 Email: John.Ireson@dpiw.tas.gov.au
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