Research into the introduction of a parasite for elm leaf beetle larvae began in 1991. We were fortunate to be able to call on extensive, long-term research from the United States where the European parasitical fly Erynniopsis antennata was introduced in the 1930s. Dr Don Dahlsten from the University of California – Berkeley visited Australia and helped to establish the research here. The Erynniopsis antennata were released in Victoria in January 2002, so the research has extended, off and on, over a period of more than a decade.

When selecting natural enemies of the elm leaf beetle, only predators that specialise on the target pest were considered. These predators are termed "host-specific". To ensure that natural enemies introduced to Australia are host-specific and pose no threat, each natural enemy must undergo extensive screening and host-specificity study. The fly has been tested against a range of native Australian insects and beneficial species and was found to only attack elm leaf beetle larvae. This was supported by studies of the parasitic fly in its natural range, where it is only known to attack elm leaf beetle. The results of these tests were submitted to Environment Australia, responsible for ensuring there is no threat to native flora and fauna, and the Australian Quarantine and Inspection Service (AQIS), which considers potential threats to primary industry. In addition, the application to introduce a natural enemy such as the elm leaf beetle parasitic fly is reviewed by the CSIRO, and every State government department of Agriculture and Conservation. Each of these organisations must agree that the introduction is safe and poses no threat to primary industry or the Australian environment. The elm leaf beetle parasitic fly has met all the requirements for its introduction to Australia.

It is still an unknown quantity at the moment and it will take several years before the true outcome will be known. In 1993 we released a predatory wasp species that has also been used in the US for elm leaf beetle control, but they failed to establish here, primarily because the climate was too cold for them. The fly, while it involved much more research, is better suited to our climate, so we are hopeful that it will establish well. In California, introduction of the fly achieved a 40% reduction in beetle populations, so we can use that as a guide to what we can expect here. It is possible that our outcome may even surpass the American result because a hyper-parasite of the fly (ie a parasite that attacks a parasite) was inadvertently introduced into the US along with the fly, thus reducing its effectiveness. Fortunately we have been able to avoid the same mistake here.

Firstly, especially within the establishment phase, it is important that gardeners continue to take other steps to control the elm leaf beetle. The flies have been released in three locations - Birramung Marr Park in the city centre, Lilydale and Alexandra. It will take several years for the populations to spread.

Secondly it is important to choose control measures that are compatible with bio-control ie measures that will not kill off the parasitic flies as well as the beetles. There are two main ways to do this.

Confidor is a low-toxicity, systemic insecticide that is now registered for control of elm leaf beetles and can be applied to the soil. (This insecticide does not affect the parasitic flies because they do not eat leaves.) The directions for soil application are on the label. Where there are large valuable trees or large stands of trees, then high pressure soil injection with Confidor carried out by arborists or tree surgeons is well worthwhile.

Treating the trunks of elms by spraying or painting 40cm wide bands of carbaryl right around them will kill elm leaf beetle larvae as they migrate down to pupate in the soil. This must be done just prior to Christmas in Australia. It is effective for about 6 weeks. While this will not kill off all the larvae (some will drop directly to the soil), it will significantly reduce the population. This restricted use of carbaryl will have little or no effect on the parasitic flies. This strategy is simple and inexpensive, but will not prevent elms from being reinfested with pests from nearby trees, so it is important to work together with neighbours to protect all the elms in the one area.

APR 2002

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