October 2000. An interesting quarantine dilemma was reported by Cook Islands: An exporter in New Zealand had requested that shipments of Brassicas not be fumigated. Fumigation is prescribed for Brassicas because of the threat of the cabbage white butterfly (Pieris rapae).
Instead of fumigation the shipments of Brassicas (cauliflower and broccoli florets) would be treated as follows: the florets would be trimmed, thoroughly washed and sanitized in a chlorine solution, then immediately vacuum packed and stored below 20C (chilled not frozen).
The question was whether this was an equivalent treatment to fumigation, and whether it gave the Cook Islands that same level of security against the accidental importation of the butterfly.
Members’ provided no definitive answer as to whether the treatment was adequate as a quarantine measure to prevent the introduction of the cabbage white butterfly; they focussed their comments on procedures and what else might be present other than the cabbage white butterfly, and the likelihood of survival and establishment. Cook Islands needed to be satisfied that the proposed processing treatment affords the same or a greater measure of protection than the fumigation treatment, unless Cook Islands was prepared to reconsider the current level of protection that it accepts.
The first question that might be asked was what insects might remain after surface sterilizing with chlorine and chilling, presupposing that all the caterpillars present had been killed. The following are likely:
- cabbage white butterfly eggs
- diamond back moth pupae
- parasites (cocoons or mummified aphids)
- possibly thrips
Some considered that the greatest quarantine threat was the insecticide resistant strains of diamondback moth (DBM). DBM often pupate in the florets or curds and washing, sanitising and chilling will certainly not kill all of them. In New Zealand, there are DBM highly resistant to synthetic pyrethroids and organophosphates. As yet, there is no resistance to Bt sprays or the “new” selective insecticides (Match, Steward and Success).
Historically, Rarotonga has had DBM populations that were also resistant to the same classes of insecticides as in New Zealand, so it may not be such a great issue. However, resistance levels do change over time.
So, some parasite cocoons or mummified aphids may survive, but they are not a major quarantine issue. Likewise, some cabbage white butterfly egg may survive, but this was not thought to be a serious quarantine risk for Cook Islands, as the butterfly is unlikely to survive in the sub-tropics. Thus, the greatest concern is DBM.
Before a decision is made, there needs to be some information on the efficacy of the proposed processing treatment. It is possible that the cabbage white butterfly pupae and perhaps even larvae could survive a chlorinated water wash. However. it is also possible that the associated packing procedures (breaking into florets, visual inspection, vacuum packing and refrigeration) could collectively result in the same level of protection as that afforded by fumigation.
Therefore, Cook Islands was advised to seek evidence from properly conducted trials that the proposed treatment is at least as good as fumigation. If the evidence is acceptable then the procedure should be formalised in a detailed protocol so that the procedures can be monitored by an appropriate authority.