Pest Risk Analysis for Stone Fruit from New Zealand into Western Australia

Introduction and spread probability

The likelihood that codling moth will arrive in Western Australia with the importation of stone fruit from New Zealand: Extremely low.

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  Codling moth has been recorded on stone fruit but is not considered a significant pest of these commodities. Codling moth is considered to occur only very rarely on stone fruit (McLaren et al., 1999).
  
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  Larvae have been recorded feeding on fruit of peach, plum, apricot, cherry, orange, persimmon, pomegranate and chestnut but the species is essentially a pest of pome fruit (Hely et al., 1982).
  
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  Eggs are preferentially laid on apple trees (Wearing et al., 1973) because apples release a naturally occurring oviposition stimulant for codling moth (Wearing & Hutchinson, 1973).
  
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  Studies indicate that eggs are not laid on nectarine or cherry when these species are exposed to potential oviposition by codling moth (Wearing & McLaren, 1996).
  
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  On pome fruit, the larvae often enter through the calyx and bore down to the core of the fruit, leaving a prominent entry hole. Codling moth feeding causes premature fall of infested fruit (Hely et al., 1982).
  
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  Studies in New Zealand show that there was no damage to stone fruit despite the presence of codling moth damage in apples nearby (Wearing & McLaren, 1996).
  
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  Fully-grown larvae are 20 mm long and pupae are 8.0 to 11.5 mm. Consequently, there is a high likelihood that codling moth would be detected during pre-export inspection.
  
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  Post-harvest grading and packing procedures are likely to remove infested fruit as the entrance hole and frass deposited by developing larvae is easily detected.
  

The likelihood that codling moth 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 the PRA area would be for retail sale, as the intended use of the commodity is human consumption. Waste material would be generated.
  
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  Early instar larvae escaping detection are likely to survive cold storage and distribution to the endangered area. Codling moth would enter the environment via adult emergence from pupae in waste that has been discarded from a distribution centre before the fruit desiccates or decays.
  
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  Adult females would need to locate a male to mate with and then find a susceptible host on which to lay eggs.
  
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  Female are capable of flying up to 600 m and males up to 1 km (HortResearch, 1999).
  

The likelihood that codling moth 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: Extremely 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 codling moth 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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  Although apple and pear are the main host plants for codling moth (Howell et al., 1992), it can complete its life cycle on other hosts. Larvae are known to be polyphagous and have been reported to also feed on cherry (Moffitt et al., 1992), nectarine (Curtis et al., 1991), prune (Yokoyama & Miller, 1999) and walnut (Vail et al., 1993). However, codling moth develops poorly on some potential hosts and cherries are noted to be a very poor host, or even a non-host (Wearing and McLaren, 2001). Codling moth hosts are widespread in Western Australia.
  
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  Codling moth has been reported from New South Wales, Queensland, South Australia, Tasmania and Victoria. Current legislation in Western Australia prohibits the importation of apples and pears into Western Australia. However, several codling moth outbreaks have occurred in Western Australia and been successfully eradicated, indicating that climatic conditions are suitable for its establishment in Western Australia.
  
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  Females vary in their fecundity (Wearing & Ferguson, 1971). Adult females usually lay approximately 250-300 eggs over 4 to 7 days and live for about 4 days after the last oviposition.
  
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  Females lay eggs singly on leaves or, later in the season, on apple fruit (English, 2001). After hatching, the larvae burrow immediately into a fruitlet. Larvae pass through five instars whilst feeding within the fruit, and then leave the fruit.
  
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  The number of generations per year varies from 1 to 4 depending on the climate and the host plant. During each generation a small proportion of the larvae enter diapause for up to two years (Yothers & Carlson, 1941).
  

The likelihood that codling moth 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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  Codling moth is thought to have originated in the Palaearctic region and has spread along with the cultivation of apples to most temperate regions of the world, including Europe, China, North and South America, South Africa, Australia and New Zealand (Bradley et al., 1979).
  
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  Codling moth has also spread in the eastern states of Australia and successfully entered Western Australia several times, indicating the environment in Western Australia would be suitable for its spread.
  
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  Dispersal of codling moth is by the movement of infested fruit, or of cocoons in fruit containers (Hely et al., 1982). Natural physical barriers may prevent unaided long-distance spread of this pest but adult forms may spread undetected via the movement of fruit.
  
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  Codling moth is rather sedentary for a winged species. Individual females spread over no more than five to ten trees in most orchards, while the males are more mobile (Hely et al., 1982).
  
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  Studies indicate that males can fly for one km from a point of release and some individuals have been recovered up to 11 km away. On the other hand, females have been captured within 300m of their release point and maximum dispersal may be as low as 600 m (HortResearch, 1999).
  
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  Many natural enemies have been reported to attack codling moth larvae and pupae and some are present in Western Australia. Trichogramma minutem, a minute parasite of codling moth eggs, is known to occur in Western Australia.
  

The overall likelihood that codling moth 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: Extremely 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).