Mud and maccas mix

NSW DPI entomologists Craig Maddox and Dr Ruth Huwer
NSW DPI entomologists Craig Maddox and Dr Ruth Huwer inspect a macadamia nutborer lure in a mangrove swamp near Ballina.

What do muddy mangroves and macadamia farms have in common?

It’s hard to imagine but researchers from NSW DPI at Alstonville have identified a significant link – both are favoured sites for macadamia nutborer (MNB).

“MNB is a well-known and damaging pest of the $100 million macadamia industry but we only recently discovered that one of its main hosts is the mangrove,” said DPI entomologist Dr Ruth Huwer.

“We knew MNB was finding a refuge apart from macadamia plantations but it has been a fairly lengthy search to find the major alternate host,” she said.

“We started looking in mangroves after reading a scientific paper from Japan where they noticed a similar moth frequenting mangroves.

“The result was that we found macadamia nutborer here in our mangroves in large numbers.

“We also found them in mangroves near Brisbane airport and even on islands off the Gold Coast – a long way from any macadamia farm.”

Fellow DPI entomologist Craig Maddox says it makes sense for two reasons:

  • The husk of the mangrove pod is of a similar texture to the macadamia husk, and
  • A rearing project at Alstonville in the hills above Ballina has found that sub 15 degree C winters are too harsh for the nutborer moth. Mangroves are at sea temperature of about 18 degrees C minimum in winter.

“Now we know the main host, we can watch the populations to predict the borer’s impact on macadamia orchards which are mostly located 10 kilometres or further inland,” he said.

“The theory is that much larger than normal moth populations may move from the mangroves after floods,” he said.

“It may explain why we get MNB population surges in macadamias.

“By monitoring population levels in the coastal mangroves and understanding when and why the MNB moths move, we will be in a much better situation to control the pest in macadamias.”

The NSW DPI researchers at Alstonville have already done encouraging work with a tiny wasp which is achieving significant savings for macadamia growers - and the environment - in reduced chemical sprays.

The parasitic wasp, Trichogrammatoidea cryptophlebiae, a South African native, was introduced to Australia only eight years ago and is now proving to be an excellent biological control agent for the damaging borer.

The wasp lays eggs in nut borer eggs, and the developing larvae eat the contents of the nut borer eggs.

Releasing the wasps in an orchard at critical times when MNB are on the move from mangroves may be very effective, said Dr Huwer.

The research team at Alstonville is also on the lookout for another parasite that kills the nutborer.

“We are sure there will be another native parasitoid which we may be able to use in biological control as well,” she said.

“By baiting estuarine areas with fresh host egg cards we can collect live parasitoids and rear them in the insectary."