Biological Control of Dock: Enhanced Distribution of the Dock Moth

Summary

Docks (Rumex spp) have long been recognised as difficult weeds for producers to control throughout the high rainfall pasture areas of southern Australia. In 1982, biological control was identified as a possible means of economically controlling docks whilst minimising the use of herbicides on pastures, and improving pasture production and utilisation. Agriculture Western Australia, in a collaborative project with Meat & Livestock Australia (then Meat Research Corporation) and the CSIRO, identified and imported two clearwing moths, which are natural enemies of docks. One of these Synansphecia (formerly Chamaesphecia) doryliformis (Lepidoptera: Sesiidae) from Morocco, was re-synchronised to southern hemisphere conditions, and successfully reared on potted field collected dock plants.

The first releases of the dock moth into pastures of south-west Western Australia were made in 1989. Assessment of these releases showed that although the moth was capable of surviving in the Australian environment, its one-year life cycle dictated that population numbers in the field would increase only gradually, and that dispersal from release sites would also be slow. Clearly, large numbers of moths would need to be released in many locations to establish the insect in pastures, and to gain maximum benefit from its Introduction.

Further research funded by MLA between 1991 and 1994 resulted in the development and refinement of a semi-natural mass rearing system based on dock root pieces in a temperature controlled environment in the laboratory. This made possible the large scale production of dock moths required for release. Another important development was the eggstick machine, which enabled the robust moth eggs to be glued onto toothpicks. The eggsticks were then inserted into the cut stems of mature dock plants in the field. This technique greatly reduced the labour requirement of field releases and improved the efficiency of laboratory production by overcoming the critical constraints of using newly emerged larvae. The easily handled eggsticks also made possible the distribution and introduction of dock moth into affected pastures Australia wide.