Parasites doing well in apple orchards
3 July, 2002
Helpful Parasite Alive And Well In Hawke’s Bay Orchards
A tiny parasite wasp released into Hawke’s Bay apple orchards in February 2001 appears to be thriving.
The new biocontrol agent for the obscure mealybug was released in New Zealand after 6 years work and following approval from ERMA.
This was the culmination of co-ordinated research and support from HortResearch, ENZA, the IFP20 Group of apple growers, NZ Pipfruit, FRST and, finally, approval from ERMA in August 2000. The wasp, with the scientific name Pseudaphycus maculipennis, is called Pmac (‘peemac’) for short.
About 60,000 Pmac were released into six apple orchards around Hastings in February 2001, and have been left to their own devices since then. A trapping programme in April this year showed that they have already established in at least two of the orchards.
“This is good news” said John Charles, the HortResearch scientist leading the programme, “as it shows that they can survive the winter and the normal orchard management programme, and also are able to find sufficient numbers of mealybugs in the orchards to live on and then disperse”.
An additional 140,000 or so Pmac were released to a total of 13 Hawke’s Bay orchards last summer. They have already been recovered from one of these orchards.
“It is too early to tell what impact they are having on mealybug populations in these orchards” Mr Charles said, “but we hope to be able to measure Pmac’s success in controlling mealybugs over the next couple of years. We also plan to release more Pmac into Hawke’s Bay, and to expand the release programme to Nelson apple orchards – and, indeed, any other places and crops where obscure mealybug is a problem.”
The economically damaging obscure mealybug was first found in New Zealand in 1922, and until now it has had no significant natural enemies here. It lives in cracks and crevices in trees or fruit, as well as on leaves and roots of host plants. In apple trees they move into the apple calyx when the fruit is quite small. They feed and grow inside the apple and excrete honeydew. Sooty mould fungi grow on the honeydew and appear as a black deposit around the calyx. Although the fruit is unharmed, and the sooty mould is purely cosmetic, those apples are rejected for export and downgraded to domestic or other uses.
The mealybugs also infest other fruit crops such as peaches and grapes, where they transmit grapevine leafroll disease.
Mr Charles said that with the fruit industries’ rapid move into organics and integrated fruit production (IFP) methods there were increased opportunities for successful biological control. These parasites will be extremely important in further reducing the dependence on insecticides for mealybug control.