By PHILIPPA STEVENSON
A greenhouse thrip costing avocado and citrus growers more than $6 million a year and a menace to home gardens for 70 years is about to come under attack.
A parasitic South American wasp, which has successfully countered greenhouse thrips in California, Hawaii, Israel, South Africa and Italy, was
released in Kerikeri on Friday.
The tiny wasp - adults measure just 0.6mm and 55 pupae fit into a half centimetre circle - was released at HortResearch's Kerikeri research orchard and will also be introduced to commercial operations in Northland and the Bay of Plenty.
Its prey are also barely visible to the naked eye, but thrips wreak havoc on avocado and lemon skins, discolouring and pitting the fruit and reducing their selling prospects.
Citrus exports were worth more than $9.2 million last year, 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 in insecticide costs.
The wasp lays its eggs inside the thrips, eventually killing them.
HortResearch scientist Karyn Froud said the release could have flow-on benefits for home gardeners because thrips have been found to have more than 40 host plants in New Zealand, including rhododendrons and camellias.
Greenhouse thrips had arrived in New Zealand in the 1930s, she said, but the parasitoid wasp did not make it here at the same time, as it did in Australia.
The Environmental Risk Management Authority approved release of the wasp in June after an application by New Zealand Citrus Growers and the Avocado Industry Council, supported by HortResearch.
Ms Froud said extensive evaluation of the wasp, Thripobius semiluteus, had been carried out to ensure it would attack only the greenhouse thrips.
It took several months to track down a suitable source of wasps for breeding in quarantine. Originally from South America, they are established in Australia but were eventually obtained from a research colony in Italy in December.
Once breeding in the laboratory, they had a 250-fold population increase in the first three generations, providing plenty to release into orchards.
Ms Froud said only about two-thirds of the laboratory population would be released. The rest would be kept to build up numbers for further releases.
