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Biocontrol Aid For Avocado And Citrus Growers

A parasitoid wasp, so tiny that 55 pupae fit into a half centimetre circle, and the adult size is only 0.6 of a millimetre, is being released in Kerikeri this Friday (9 March). Further releases will be made in other selected Kerikeri and Bay of Plenty orchards.

This new parasitoid Thripobius semiluteus, is targeted at greenhouse thrips which damage citrus and avocados. Both citrus and avocados are commercially important crops. Citrus earned more than $9.2 million in exports in the year to June 2000, and avocados brought in more than $25.2 million. Growers estimate that greenhouse thrips cost about $6.25 million a year in fruit rejected for export and control costs using insecticides.

The New Zealand Citrus Growers and the Avocado Industry Council, supported by HortResearch lodged an application to release the parasite to the Environmental Risk Management Authority (ERMA). ERMA gave the go-ahead for the release last June but it took several more months to track down a suitable source for breeding in quarantine. Originally from South American they are established in Australia but in the end scientist Karyn Froud said it was easier to get some from a research colony in Italy.

The minute wasp lays its eggs inside greenhouse thrips, eventually killing them. Ms Froud and her team went through an extensive and careful evaluation of Thripobius semiluteus, as required by ERMA, to ensure that it would attack only the greenhouse thrips.

The little wasp arrived here in December 2000 and in the first three generations it had a 250-fold increase in its population providing plenty to release into citrus and avocado orchards in Northland, and the Bay of Plenty.

Ms Froud said only about two thirds of the laboratory population will be released. The remaining third will be kept to build up numbers for further releases.

The introduction of the new parasitoid could well have flow on benefits for home gardeners for although the greenhouse thrips is a serious pest on citrus and avocados they also attack some deciduous trees and such plants as rhododendrons and camellias. In fact it has been found in over 40 host plants in New Zealand.

Greenhouse thrips first arrived in New Zealand in the 1930s, unfortunately the parasitoid did not make it here at the same time, as it did in Australia.

This parasitoid has been successfully introduced into California, Hawaii, Israel, South Africa and Italy.

For further information contact
Karyn Froud, HortResearch Mt Albert, Tel: 09 815 420, or 025 293 1080.

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