December 2009. Fresh fruit export is always restricted if it has scales, mealybugs, thrips or aphids. Samoa is planning research on how to deal with these pests on fresh fruit exports. Would anyone like to comment on the approach to take?

Detailed replies are provided in full because of their importance:

1) This is a complicated issue and the pests you mention raise several important but complex problems for risk assessors and developing a research project will not be easy. However, the first question to ask is “Do I really need to do anything?”; this needs to be asked for each of these pest types individually and for each crop.

As you know, risk analysis is a combination of “the likelihood of entry, establishment and spread” and “the cost of the consequences” but arguably the most important component, I suggest, is “entry and establishment”, that is, in IPPC terms “introduction”. Often it is possible for an organism to enter a country on a commodity but there is no or little likelihood of establishment. If the fruit is going from a tropical environment to a temperate environment then the likelihood of establishment is even lower.

For example, there is a very strong case to say that scale insects are very unlikely to ever establish in a new country following importation attached to commercial fruit. Fruit in commercial trade (note: I do not say this for hand carried fruit) will have very low populations of any pest; the fruit will have been in cold storage for days and possibly weeks before arriving and will primarily go to a fridge or fruit bowl inside a house. The scale is stuck to the fruit, any young that emerge are only capable of crawling a few metres at most before they must find a host or they will die; most scale insects have a very narrow host range and will therefore have a hard job finding a host. The likelihood that establishment will occur under these circumstances is negligible. If you combine this with the small number (relative to exports from other countries) of fruit you might actually export at one time then the likelihood is near to zero. Note: this does not apply to fruit hand carried or picked from the wild or someone’s garden.

Mealy bugs are a little different as their young can walk further before they desiccate and die and they generally have a wider host range. But even here the likelihoods must be considered to be very low.

Thrips and aphids are more difficult again as they can fly and aphids don’t need to mate. Remember numbers on commercial fruit will be low, also if the insect is a bona fide quarantine pest the consignment should have been at least inspected and found free of the insect; they will arrive in the country after days, even if air freighted, of cold storage, possibly as a life stage not suited to survive a winter (especially if tropical); they will then be held in a cold store till sold and then either consumed quickly or held in a fruit bowl or fridge till consumed. I suggest that unless there are large numbers of the pest in a consignment (which if the quarantine inspection is done properly there shouldn’t be) then the likelihood of establishment from infested commercial fruit is very low, even for thrips and aphids.

I guess what I am trying to say is that severe treatments like fumigation are not usually needed, especially for pests like scales, mealybugs, thrips and aphids. In these circumstances it is usually possible to put in place a systems approach where a number of different procedures are applied each with a different effect, with none giving 100% control by themselves but combined they have an excellent effect. For example, in modern packing houses powerful water washers remove most contaminants on the surface of fruit and could easily be incorporated into a packing line if not already there. Often there are activities which are part of the normal quality processing that will have a significant effect on the pests and all that is needed is some process to verify that this has been done.

The above does not necessarily apply for fruit flies or insects that bore into fruit but for the insect types you mention I suggest you try to avoid chemicals and move more towards the use of a systems type approach, e.g. a verified programme of field control to get the numbers down at harvest, rigorous packhouse cleaning and quality control followed by cold storage and then enhanced quarantine inspection. You could follow the numbers of the pests on the fruit through that process and present data to the importing country that shows the numbers to be very low. This is likely to be cheaper and possibly at least as effective as chemical methods; it fits with the idea of only exporting high quality produce to get the best price and it is more environmentally friendly.

2) However, if you wish to undertake export then the importing regulatory authority will not be that interested in the ‘potentially low invasive biology’ of the organism particularly if it has already been deemed to be undesirable as part of the established import agreement.

Trade barriers are being established constantly under the guise of phytosanitary protection – even by countries that already have the species established ??? and that is contrary to WTO-SPS guidelines.

I am responsible for the phytosanitary programmes for a large New Zealand
horticultural export crop and know exactly where both yourself and Bob are coming from with your comments. The system approach is really the only way to move forward on this.

My suggestion and advice would be to establish integrated control programmes for the organisms you are concerned with (scale, mealybug, thrips and aphids) during the production phase. This will be the first step in your system and should ensure that the level of infestation at harvest and therefore the proportion of crop that is unsuitable for a particular market is low. It then becomes necessary as suggested above to have good post-harvest inspection and grading system in place to ensure the crop meets market requirements.

While the suggestion above, to try and avoid chemicals is a sound one, phytosanitary
regulators unfortunately like the belt and braces approach and usually require to see how you will monitor and intervene so that low fruit infestation levels are going into the pack house. They can be comfortable then that the packer is really only grading and confirming the low phytosanitary risk status of the consignment. This approach will certainly help generate the data you will need to gain acceptance of such a system to present to the regulators.

The ants you mentioned associated with these organisms (particularly the aphids,
scale and mealybugs) will try to protect them from any biological control agents you employ – the ants see the honeydew excreted by these organisms as an important food source.