Central and North Queensland papaw growers have welcomed the release of a tiny black wasp as a biological control for Oriental scale, a sucking insect responsible: for 10 to 40 percent of commercial papaw production losses.

Ironically, Queensland Department of Primary Industries Nambour-based principal entomologist, Dan Smith, found the Oriental scale parasitic wasp, Comperiella lemniscata, in China three years ago.

The Comperiella wasp has undergone rigorous quarantine testing at Sherwood Quarantine Research facility, Brisbane. Quarantine authorities gave permission for field releases of the wasp in January this year.

The QDPI principle entomologist, Rod Elder, Rockhampton, made the first release at Yarwun on January 6 and a similar release was made at Innisfail. Followup fortnightly surveys of the Comperiella population has shown it has survived at both centres. The wasp has survived the Queensland winter and now populations were again on the increase.

Mr. Elder said, "We estimate this wasp has parasitised up to 80 percent of the adult Oriental scale at our regularly-sampled sites which we consider to be an excellent result."

Releases have now been made at most Queensland papaw plantations with an Oriental scale problem. The wasp has successfully established at all sites.

Last year, QDPI Entomology branch officers made a trial release of another parasitic wasp, Aphytis melinus, initially propagated for the biological control of red scale in citrus orchards. The Aphytis wasp, which must be purchased by growers from biological control insect distributors, parasitises up to 30 percent of the Oriental scale population. Unlike Comperiella, the Aphytis Wasp also kills the adult scales by feeding on them.

Mr. Elder said, "With both wasps, working effectively alongside other natural parasites and predators, papaw growers can look forward to biological control of Oriental scale."

Mr. Elder recommends that growers should buy and release Aphytis wasps whenever an increase in the number of juvenile scales was noticed.

He said, "Our long term aim is to manage the wasp parasite to maximise control of the scale and eventually eliminate insecticide use."

The wasps prefer warm, shaded, high-humidity environmental conditions under trees with solid canopies to protect them from hot, dry conditions. Growers should try to manage their crops accordingly.

Oriental scale insect which occurs in Central and North Queensland was first found in the Torres Strait in the 1950s. It has moved no further south than Yarwun. The scale sucks the fruit, making it unsaleable and also sucks the sap from the tree, reducing plant vigour and allowing entry of rots.

Russ Boadel, Rockhampton QDPI
Extract from Qld. Fruit &anp; Veg News 11.11.1991

DATE: January 1992

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