Little known lace bug, a relatively new pest which attacks macadamia flowers with devastating results, is the target of new research.

NSW Department of Primary Industries entomologist, Ruth Huwer, at the Centre for Tropical Horticulture at Alstonville, finds increased levels of damage to macadamia crops over the the last few seasons by lace bugs disturbing, because they are normally considered to be a minor pest.

"In some of the worst affected orchards, we are seeing up to 85 per cent of flowers with lace bugs present, and in 2005, we measured 40pc reduction in nut yield due to this pest," she said.

Dr Huwer explained it’s very important to monitor closely for lace bug damage early during the flowering season, before opening of the flowers.

"Growers need to time their control treatments on affected trees before populations get to a damaging level."

Lace bug (Ulonimea sp.) is a small insect.

"Adults are three to four millimetres in size, slender and light to dark brown in colour with red eyes," Dr Huwer said.

Eggs are usually inserted through a hole in the flower petal and laid into unopened florets, but can also be found on the outside of a floret.

"First instar nymphs emerge inside the florets, leave an empty egg shell behind and are therefore usually covered in pollen."

"The wingless nymphs have an oval shape and are yellow green in colour in the early instar and reddish brown in the later instar."

According to Dr Huwer, adult bugs and nymphs attack flowers and suck sap from the buds. The florets consequently desiccate and wither.

Black withered florets on the bottom tip, but also the middle of a flower raceme, are signs of lace bug damage.

As a result, damage can result in poor nut set or even failure of nut set.

"Observations suggest that their life-cycle is short, possibly two weeks from egg to adult," Dr Huwer said.

"We don’t know how many eggs they can lay, but number and damage can increase rapidly in some affected areas.

"Details on the life-cycle need to be examined.

"We have recorded a 42pc reduction in crop size in the 741 variety in a sprayed versus unsprayed comparison in 2005 at Alstonville, due primarily to lace bug activity which was observed as late as November."

There is no information on other host plants for this species, but most affected areas in orchards are near scrub.

Host plants outside the macadamia orchard need to be investigated.

Because the insect attacks flowers, insecticide application to control the pest and timing of the application is a bit of a dilemma, as spraying during flowering is adverse to pollination and pollen viability.

The current recommendation is to spot spray affected trees with an appropriate registered insecticide.

"We are setting up a small trial at Alstonville to test the efficacy of a number of insecticides," Dr Huwer said.

Contact Dr Ruth Huwer, Alstonville, (02) 6626 2451