Draft non-regulated risk analysis report for table grapes from the Republic of Korea

1.15Spotted wing drosophila

Drosophila suzukii ^EP

Biosecurity Australia has undertaken a pest risk analysis to assess the quarantine risks

posed by Drosophila suzukii from all countries and for all commodities (Biosecurity Australia 2010a). This pest attacks a range of soft fruits including grapes, strawberries, cherries, blueberries, caneberries and stone fruit. This draft pest risk analysis report identified fresh fruit and fresh flower imports as potential pathways for the introduction of D. suzukii with an unrestricted risk that exceeds Australia’s acceptable level of protection (ALOP). A summary of background information and biology of this pest, as detailed in the Final pest risk analysis report for Drosophila suzukii (Biosecurity Australia 2010a), is outlined below.

An unidentified species of Drosophila was first recorded attacking a range of soft fruits in California in 2008 (Hauser et al. 2009). Drosophila are known to be attracted to fermenting, over-ripe and rotting fruit and are well known nuisance pests in restaurants, grocery stores, fruit markets and homes (Jacobs 2010). When damage continued in 2009 samples were submitted for further identification and were determined to be D. suzukii, a species which causes damage to fruit in Japan (Hauser et al. 2009). D. suzukii has subsequently been confirmed to be present in Canada (NAPPO 2010a), several states in the USA (NAPPO 2010b), Italy (EPPO 2010), Spain and France (Calabria et al. in press). D. suzukii is native to several Asian countries including Korea, Japan and China (Hauser et al. 2009).

The potential for the introduction of D. suzukii into Australia, via imports of currently traded host fruit, resulted in Australia introducing emergency quarantine measures prior to the re-commencement of trade. The emergency measures were announced on 7 April 2010 for table grapes (Vitis spp.), cherries, strawberries and stone fruit and for human consumption from all countries.

The total development time of D. suzukii (egg to adult) ranges from 8–28 days. The duration is dependent on seasons, with shorter lifecycles in summer. Typically eggs hatch in 1 day, with larval development taking 3–10 days, and pupation taking 4–14 days. Adults become sexually mature in 1–2 days and live for 21–66 days. Females can lay an average of 380 eggs in their life (Kanzawa 1939).

The larval feeding of early instars causes the fruit to collapse around the oviposition scar and if attack rates are high the entire fruit can collapse. The oviposition scar exposes the fruit to secondary attack by pathogens and other insects (Hauser and Damus 2009). The damage caused by D. suzukii larvae renders the fruit unsuitable for sale (Bolda et al. 2010).

D. suzukii preferentially oviposit on ripe fruit but will also lay eggs in unripe and over-ripe fruit (Kanzawa 1939). Larvae feeding in fruit that is very acidic fail to complete development (Kanzawa 1935). Oviposition trials on wine and table grapes have shown that fully ripe table grapes are attacked at high levels but that oviposition does not occur on undamaged grapes with low sugar levels. Damaged fruit with low sugar levels will be oviposited in but larvae develop poorly and fail to pupate (Malguashca et al. 2010).

During the 1930s in Japan, D. suzukii was trapped in vineyards at high levels and there are reports of damage as high as 80% (Kanzawa 1939). More recently there have been reports of outbreaks of D. suzukii on grapes in Hokkaido (CFIA 2010). In the USA, D. suzukii has been recorded from grapes though infestation rates remained low last season (OSU 2010).

In its native and introduced range, D. suzukii has been recorded to cause damage to a range of fruits including grapes, cherry, blueberry and red bayberry, mulberries, peaches, plums, strawberries and various caneberries. Studies in Japan have shown severe crop losses of 80% for grapes and 26–100% for cherries (Kanzawa 1939).

The risk scenario of concern for D. suzukii is the presence of the larvae in mature bunches of grapes.

As D. suzukii on table grape imports was covered in the Draft Pest Risk Analysis for Drosophila suzukii (Biosecurity Australia 2010a) the likelihood estimates from that report are outlined here.

1.15.1Probability of entry, of establishment and of spread

Probability of importation on table grapes: HIGH

Probability of distribution: HIGH

Overall probability of entry: HIGH

Probability of establishment: HIGH

Probability of spread: HIGH

1.15.2Overall probability of entry, establishment and spread

The overall probability of entry, establishment and spread is determined by combining the probabilities of entry, of establishment and of spread using the matrix of rules shown in Table 2.2.

The likelihood that D. suzukii will enter Australia as a result of trade in table grapes from Korea, be distributed in a viable state to a susceptible host, establish in Australia and subsequently spread within Australia: HIGH.

1.15.3Consequences

The consequences of the establishment of D. suzukii in Australia were estimated previously for all commodities for the Draft pest risk analysis report for Drosophila suzukii (Biosecurity Australia 2010a). This estimate of impact scores is provided below.

Plant life or health F

Other aspects of the environment B
Eradication, control etc. E
Domestic trade E
International trade E
Environment D

Based on the decision rules described in Table 2.4, that is, where the consequences of a pest with respect to one or more criteria are ‘F’, the overall consequences are estimated to be HIGH.

1.15.4Unrestricted risk estimate

Unrestricted risk is the result of combining the probability of entry, establishment and spread with the estimate of consequences. Probabilities and consequences are combined using the risk estimation matrix shown in Table 2.5.

Unrestricted risk estimate for Drosophila suzukii
Overall probability of entry, establishment and spread	High
Consequences	High
Unrestricted risk	High

As indicated, the unrestricted risk estimate for D. suzukii of ‘high’ exceeds Australia’s ALOP. Therefore, specific risk management measures are required for this pest.