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research update

Tipping the scales against tipworm

Tiny wasps found to be potential biological control of cranberry pest.

By Judie Steeves

tipworm (Dasineura oxycoccana).

Sheila Fitzpatrick, a research entomologist with the Pacific Agri- food Research Centre in Agassiz, was conducting a study into the reproductive behaviour of the tipworm, and in the process two parasites of the pest were discovered. There is potential to use them in biological control of the tipworm. She noted that they were discovered in cranberry tips infested with tipworm which came from a Pitt Meadows farm where no insecticides had been applied after July 10. Both are tiny wasps that lay eggs in the host larva, killing it, so they are potentially biological control agents. One has been identified as being in the genus Platygaster, platygastridae family, while the other is in the genus Aprostocetus, family Eulophidae. Key to making use of these parasitoids will likely be minimizing insecticide sprays in late July and August, so they are protected to control tipworm populations. Fitzpatrick’s study is the first to describe the pheromone-release or calling behaviour and when the female midges call. The objective is to find a way to monitor and perhaps control populations of the tipworm in the adult or midge stage, by using a pheromone to attract them.

T

here was an unexpected side benefit to research last summer into the sex life of the cranberry

JUDIE STEEVES

Sheila Fitzpatrick of the Agassiz research centre is continuing her study into how cranberry shoots can be protected by a parasite.

However, first the insect needs to be studied to find out when the females release pheromones to attract mates and determine what type of trap would be suited best to monitor cranberry tipworm.

“Cranberry growers are very concerned. It’s very intense production and very valuable land,” noted Fitzpatrick.

The midges are very tiny, so she has had to use a magnifying visor to see them, and they only live for two or three days normally, so timing is critical.

There are usually three to five generations a summer, and females lay more than 40 eggs.

“It’s difficult to put a dollar figure on damage because each upright, or fruiting shoot, doesn’t fruit every year.

Return bloom studies also have to be done,” she said.

In order to study such insects on cranberries, Fitzpatrick says she has to get down on her hands and knees in the field. However, in the lab, she can study them at a more comfortable height.

There is also a similar tipworm that attacks blueberries, called the blueberry gall midge, but it doesn’t seem to cause as much of a problem in B.C., except on young plants. Collaborating with Fitzpatrick on the research are Gerhard and Regine Gries of Simon Fraser University, who she says are among the world’s top researchers into midges.

Work on the pheromones and the tipworm parasitoids is expected to continue this year.

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