Australian Quarantine Review Secretariat Australian Quarantine a shared responsibility

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4 PESTS OF PLANTS

4.1 Pests and Hosts Considered

4.1.1 Crop, Ornamental and Nursery Plants

The Australian Quarantine Review Committee did not commission a report on pests of plants because of the availability of a major review completed in mid-1996 for the Bureau of Resource Sciences by Dr Geoff Clarke of the CSIRO Division of Entomology (Clarke in prep.). This report is a more comprehensive review of insect pests than any of the reports contracted by the Australian Quarantine Review Committee. The report covered insect pests of both animals and plants.
Because it commenced before the establishment of the Australian Quarantine Review Committee, the terms of reference for this report were not the same as for the four reports commissioned specifically for the Review. Its terms of reference were to:
· document the introduction of insects and related arthropods into Australia between 1971 and 1995;
· identify where possible the probable means of introduction;
· document the economic and environmental cost of introduction, including control and eradication measures; and
· provide recommendations for quarantine procedures to minimise future introductions with reference to major potential pests.

4.1.2 Forest Pests

To ensure that forest pests were fully considered, the Review Committee commissioned a report on them as part of the report on forest pests and pathogens. The section in this report that dealt with forest pests was prepared by Drs Fred Neumann and Nick Collett of the Centre for Forest Tree Technology of the Victorian Department of Natural Resources and Environment. Like Dr Clarke's report, the commissioned report focused on insect pests and did not include other taxa (e.g. snails).

The report concluded that during the past 25 years, only two species of forest insect pest have established in Australia, and one spread from Tasmania to mainland Australia:
· the elm bark beetle (Scolytus multistriatus), a potential vector of the Dutch elm disease fungus (Ophiostomas ulmi) was detected in Melbourne, Victoria, in 1974;
· the elm leaf beetle (Pyrrhalta luteola), a severe defoliator of Ulmus spp. was detected on the Mornington Peninsula 40 km south of Melbourne in 1989; and
· European wasp (Vespula germanica) was first recorded in Tasmania in 1959, but on the mainland in Sydney, New South Wales, not until 1975.

Dr Clarke's review of insect incursions also identified these forest pests, and the first two of these pests are included in the following discussion and tables on pests of plants. For the purposes of this appendix, European wasp is omitted because its initial establishment in Tasmania preceded the study period of 1971 to 1995. To ensure that individual agents are not counted more than once (by being included in more than one of the reports summarised in this appendix), insect pests of animals (i.e. varroa mite and Asian honeybee) included in Dr Clarke's review are also omitted from consideration here, but are included in the section on animal pests and diseases in this appendix.

4.2 Number and Rate of Incursions

Table 5 summarises information on insect pests of plants that established in Australia between 1971 and 1995. The significance of targeted surveillance is shown by the number of detections effected by the Northern Australia Quarantine Strategy (NAQS — see Section 9.5.1.1 of this Report). NAQS commenced in 1989, and detected six 'new' incursions of exotic pests and diseases during surveys of the Torres Strait region in its first two years of operation. Four of these detections occurred during the first NAQS survey in 1990 but were probably not introduced in that year, only first detected then because the NAQS survey specifically looked for potentially significant pests and diseases in that region. The effect of the NAQS detections is illustrated in Table 5, which shows the number of detections of established incursions of plant pests in five-year periods with and without the inclusion of those detected by NAQS.

Table 5: Insect pests (of plants) that established between 1971 and 1995

	Number established
Period	Total	Excluding NAQS
1971–75	3	3
1976–80	9	9
1981–85	11	11
1986–90	13	9
1991–95	9	7
Total	45	39

In addition, Clarke (in prep.) regards five of the species that established during the study period as 'innocuous', and Table 6 shows the effect on the number of incursions of pests of quarantine concern if these five species are excluded.

Interpretation of trends is problematic with low numbers, as pertain in this case. Clarke analysed the data (including the three incursions excluded here — Asian honeybee, varroa mite and European wasp) and concluded that if the NAQS detections are included, there is a trend towards an increasing rate of incursions that established during the study period. However, analysis after excluding the NAQS detections did not support any change in rate of establishment of exotic insect pests of plants. Clarke concluded that this analysis supports the argument that any apparent increase in the number of exotic insect pests of plants establishing in the past few years is the result of more extensive surveillance (through NAQS). If the five 'innocuous' species are also omitted from the analysis, there is definitely no suggestion of any trend to an increasing rate of incursions of significant insect pests of plants during the study period.
Table 6: Insect pests (of plants) that established between 1971 and 1995, excluding 'innocuous' species

	Number established
Period	Total	Excluding NAQS
1971–75	3	3
1976–80	9	9
1981–85	9	9
1986–90	12	8
1991–95	7	5
Total	40	34

4.3 Cost of Plant Pests

4.3.1 General

Dr Clarke's review and the commissioned report on forest pests were able to identify little information on the economic effect of plant pests that established in Australia during the past 25 years. Dr Clarke's review provides detailed estimates of the potential cost of recently established insect pests based on a series of assumptions including their establishment across the full geographical range of their preferred host species and cause a specific percentage loss in crop volume and value depending on their pest status (Clarke in prep.). Such calculations result in estimates of quite significant potential annual costs from both control costs and losses from decreased production (e.g. some $750 000 and $4.7 million, respectively, for all of the incursions considered). Calculations based on the sort of assumptions used by Dr Clarke tend to over-estimate the real cost because pests rarely behave as the assumptions imply (e.g. spreading across the full range of their host species). Thus estimates based on such assumptions need to be interpreted with some care — at best they provide an approximate figure that is likely to be an upper limit, and they should not be quoted out of context without reference to the underlying assumptions.

Additional information on costs associated with plant pathogens was provided to the Review Committee by AQIS, which prepared a background paper on costs of plant pest and disease control and eradication funded through the SCARM process between 1977 and 1992. The paper was prepared as input to the deliberations of the SCARM Task Force on Incursion Management (see Section 10.1 of the Report). Approximate costs attributed to joint Commonwealth–State control and eradication of plant pests between 1977 and 1992 are shown in Table 7. Note that the table includes snails, which were not otherwise specifically considered in Clarke's review (which focused on insect pests) and other sources examined by the Review Committee. Although incomplete, these data provide an indication of the costs to governments alone for the control and eradication of incursions of plant pathogens in Australia. The major additional expected cost since then is of the $55 million anticipated expenditure for the control and expected eradication of papaya fruit fly.

Table 7: Approximate costs attributed to joint Commonwealth–State control and eradication of plant pests between 1977 and 1992 (amounts in $000)

Program	Joint	State
giant African snail (Queensland, 1977)	6.5	7.6
green snail (Western Australia, 1981–89)	476.1	138.9
warehouse beetle (New South Wales, 1978–82)	991.5	–
Total	$1474.1	$146.5

4.3.2 Forest pest costs

The commissioned report on forest pests could not identify any detailed reviews of the economic effect of these pests. The report provides only an incomplete indication of the scale of their effect in that:

· control programs against elm bark beetle have cost some rural municipalities about $5000 a year;
· research on the distribution, ecology and control of the elm leaf beetle since 1990 has cost about $55 000 a year, and annual control costs vary from $29 200 to $180 000 per affected municipality, depending on the number of trees that need treatment; and
· continuing control measures against European wasp cost about $644 000 in 1989 alone.

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