Risk assessments for quarantine pests

4.2.2.1 Arthropod pests

4.2.2.1.1 Bronze beetle

The bronze beetle examined in this pest risk analysis is:

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  Eucolaspis brunnea (Fabricius) [Coleoptera: Chrysomelidae] – bronze beetle.
  

Probability of importation

The likelihood that bronze beetle will arrive in Western Australia with the importation of stone fruit from New Zealand: Very low.

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  The bronze beetle is native to New Zealand and occurs throughout New Zealand (Kay, 1980).
  
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  Bronze beetle feeds mainly on the foliage of host plants, but feeding tends to be haphazard and discontinuous. On broad-leaved plants, they chew from the lower surface of the leaf, penetrating to the upper side and producing a “shot-hole” (Kay, 1980).
  
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  Bronze beetle adults are reported to feed on the foliage and fruit of stone fruit from October to January in New Zealand and may be present on trees at the time of harvest (McLaren et al., 1999).
  
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  Eggs are laid in the soil and larvae develop underground where they feed on grass roots (McLaren et al., 1999). Although sometimes present in large numbers, the damage they do is slight.
  
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  Fully-grown larvae are about 5 mm long whereas adults are 4-5 mm long.
  
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  Adults feed at night, leaving holes in leaves. If disturbed, adults can jump vigorously off the plant and for this reason are sometimes called “flea beetles” (Kay, 1980).
  
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  Bronze beetles have an activity period coinciding with the harvest of early and mid season stone fruit varieties and may be present on harvested fruit as a contaminant.
  
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  Bronze beetle has not been intercepted in Australia on stone fruit from New Zealand during AQIS inspections from 1988 to 2002 (PDI, 2003).
  
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  Post-harvest grading, washing and packing procedures are likely to remove this pest from the fruit.
  

The likelihood that bronze beetle will be distributed to the endangered area as a result of the processing, sale or disposal of stone fruit from New Zealand: Moderate.

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  Distribution of the commodity in Western Australia could be for retail sale, as the intended use of the commodity is human consumption. Adult beetles could be distributed with imported fruit, particularly in unopened cartons.
  
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  Adult bronze beetles are capable of flight and could directly disperse from imported cartons of stone fruit.
  
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  When disturbed, adult bronze beetles are reported to jump vigorously (Kay, 1980). Therefore, this beetle may disperse when cartons of imported stone fruit are opened.
  
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  Bronze beetle has a wide host range including both horticultural crops, ornamentals and native plants. Suitable hosts, including Eucalyptus species, are present in Western Australia.
  

The likelihood that bronze beetle will enter Western Australia as a result of trade in stone fruit from New Zealand and be distributed in a viable state to the endangered area: Very low.

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  The overall probability of entry is determined by combining the probabilities of importation and distribution using the matrix of ‘rules’ for combining descriptive likelihoods (Table 2).
  

The likelihood that bronze beetle will establish based on a comparative assessment of factors in the source and destination areas considered pertinent to the ability of the pest to survive and propagate: High.

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  Bronze beetles have a wide host range including horticultural crops and ornamental species (Kay, 1980) and a number of these hosts are widespread in Western Australia.
  
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  Adults of this species have been recorded on Chenopodium quinoa, Cynodon dactylon, stone fruit, pome fruit, berry fruits (Penman, 1984), pine (Kay, 1980), eucalyptus, acacia, hawthorn, elm, clover, geranium and rose (Lysaght, 1930).
  
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  Bronze beetle is found throughout New Zealand and similar environments are present in Western Australia.
  
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  Adult females lay eggs in dry soil, in batches of 3-14 eggs. Larvae emerge from the eggs after about three weeks and overwinter underground. In early spring they become active again and pupate. Pupation takes about three weeks (Kay, 1980).
  
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  The species has several overlapping generations per year, breeding continuously without diapause.
  
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  The distribution of bronze beetle in New Zealand indicates the species would be restricted to the lower south west of Western Australia.
  

The likelihood that the bronze beetle will spread based on a comparative assessment of those factors in the source and destination areas considered pertinent to the expansion of the geographical distribution of the pest: High.

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  Adult beetles are capable of independent flight and dispersal from favoured hosts, such as blackberry, are considered an important source of infestation in orchards (Tomkins, 2001).
  
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  Long-distance dispersal is through adult flight (Kay, 1980). However, adults are relatively slow flying diurnal beetles that spend most of their time on (or under) foliage or in flowers.
  
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  Natural physical barriers would likely prevent the unaided spread of this pest but larvae could spread undetected via the movement of nursery stock as larvae feed on roots. The limited information available indicates that larvae feed primarily on the root of a variety of grasses (McLaren et al., 1999). The importance of nursery stock as a potential vector for bronze beetle larvae is unclear.
  
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  Bronze beetle is more likely to disperse in association with host material. There are no intrastate quarantine controls in place in Western Australia on the movement of nursery stock.
  
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  The relevance of natural enemies in Western Australia is unknown.
  

The overall likelihood that the bronze beetle will enter Western Australia as a result of trade in stone fruit from New Zealand, be distributed in a viable state to suitable hosts, establish in that area and subsequently spread within Western Australia: Very low.

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  The probability of entry, establishment or spread is determined by combining the probabilities of entry, of establishment and of spread using the matrix of ‘rules’ for combining descriptive likelihoods (Table 2).
  

Consequences (direct and indirect) of the bronze beetle: Low.

Unrestricted risk estimate

The unrestricted risk estimate for the bronze beetle, determined by combining the overall ‘probability of entry, of establishment and of spread’ with the ‘consequences’ using the risk estimation matrix (Table 4): Negligible.