Weeds - Phase 1 - Research Highlights

Biological Control of Gorse in Australia

 

What the report is about

The purpose of this project was to confirm previous work on the host specificity of the gorse pod moth, Cydia succedana, to enable its release for biological control of gorse in Australia. Three folivores and one seed feeder have already been released but, although efficacy studies have shown that these four agents will contribute to gorse control, an additional agent or agents will still be required to significantly reduce gorse vigour. The seed-feeding gorse pod moth is widely established in New Zealand and, in combination with the gorse seed weevil, has resulted in seed destruction at levels ranging from 75 to 85 per cent at some sites. The gorse pod moth, therefore, has the potential to play an important role in the biological control of gorse in Australia.

Click here for the full report.

Background

The gorse pod moth, Cydia succedana (Lepidoptera: Tortricidae), was approved for release in Australia in 2001 following host specificity studies on 79 species or cultivars of plants. The moth's release in Australia was, however, postponed when field surveys in New Zealand revealed that the moth could exploit some exotic species in the genera Lupinus and Lotus.

Subsequent New Zealand studies from 2003 to 2006 found that the release of untested moths from Portugal, coupled with asynchrony between the flight period of the gorse pod moth and gorse flowering, explained the unanticipated non-target attack in New Zealand.

Furthermore, the results of repeated host testing on Lotus and other species, using moths from England, concurred with the original tests and suggested that the English populations would be unlikely to exploit non-target species.

Methods used

To confirm that pod moths from England would not be a major risk to commercial lupin species or cultivars grown in Australia, a host specificity study was conducted on selected cultivars in quarantine at Frankston, Victoria, in 2009-10.

Commercial cultivars of lupins chosen for the quarantine host specificity testing of the gorse pod moth in Australia were Lupinus luteus L. cv. ‘Pootalong', Lupinus albus L. cv. ‘Kiev' and Lupinus angustifolius L. cv. ‘Wonga'.

Studies showed that these cultivars could be induced to produce flowers and immature pods in about eight weeks under glasshouse conditions of 20-24°C and a minimum photoperiod of 16L:8D. Flowering and pod production in these cultivars were therefore easier to synchronise with the importation of moths during the European spring; for other species and cultivars, flowering and pod production took longer than 12 weeks.

Nine lupin species and cultivars were grown at testing facilities. Observation trials at Frankston in Victoria and in Hobart, Tasmania, were used to determine the most suitable species and cultivars for use in the host testing trials. Three of the lupin species sown-L. angustifolius (narrow-leafed lupin), L. albus (white or albus lupin) and L. luteus (yellow lupin)-are the primary commercial species grown in Australia.

Four consignments of gorse pod moth were received separately in May and June 2009 and again in May and June 2010. All adults were immediately collected, sexed and placed in plastic storage containers to enable mating and oviposition. At least 1600 eggs were obtained from the four consignments and put into sterile Petri dishes lined with moist filter paper. Newly hatched larvae were collected and used for either culturing or host testing. Only larvae that were collected within two hours of hatching were used for host testing.

Results/key findings

Standard no-choice larval starvation tests provided additional confirmation that English populations of the gorse pod moth display a preference for gorse, Ulex europaeus, over the lupin species tested. Two methods-referred to as ‘Petri dish' and ‘whole-plant'-were used.

In the Petri dish tests the mean number of larvae surviving to the pupal stage on gorse (44.4 per cent) was significantly higher than on L. luteus cv. ‘Pootalong' (14 per cent), L. albus cv. ‘Kiev' (20 per cent) and L. angustifolius cv. ‘Wonga' (2.9 per cent).

Whole-plant tests were included in order to determine whether the use of live plant material could increase survival.

In the whole-plant tests two larvae (4 per cent) survived to adult stage on L. luteus and only one larva (2 per cent) survived to adult stage on L. albus. Although 10 per cent of larvae placed on the gorse controls developed to adult stage, this was lower than the 26 per cent that developed to adult stage in earlier culturing tests using potted gorse plants.

The poor survival of larvae to the adult stage on the gorse controls in the whole-plant tests is an indication that some refinement of this technique will be necessary if it is to be considered a more valid testing method than the use of severed pods in Petri dishes.

Implications for relevant stakeholders

Host testing of gorse pod moth obtained from Yately Common, England, has confirmed previous results: the moths display a preference for gorse over other test plant species.

Results from our tests on lupins showed that cultivars of L. angustifolius are at low risk of attack. The higher level of development on L. albus and L. luteus in no-choice tests suggests that some low-level impact on cultivars of these species could occur, but this is considered unlikely, especially under normal conditions in the presence of gorse.

Even so, on the basis of these results, choice oviposition tests will now be required to enable completion of a risk analysis report for the gorse pod moth on lupins; that report will be submitted to Australian quarantine authorities.