Tiny dynamos work on major problem

TAKE THAT: Entomologist Jenny Dymock fixing the tobacco weed leaf infested with lace bugs on to a new host plant in the Taipa area in 2011.

A tiny South American bug that was released in Northland five years ago to control tobacco weed is spreading well, prompting a call from an insect expert who is tracking its movements for reports of new sightings.

Cable Bay-based entomologist Jenny Dymock, who works with the Northland Regional Council, said despite being just 5mm long, tobacco weed lace bugs (Gargaphia decoris) had now travelled up to "a whopping" 30km from their original 2011 release sites.

They had been found at Kohukohu, Kareponia (near Awanui), Oruru, Mangonui and the Kerikeri Inlet.

DOING THE JOB: Lace bugs are tiny creatures, but dynamite on tobacco weed. PICTURE/NRC

Their only food source was tobacco weed (also known as woolly nightshade, flannel weed and kerosene plant), the New Zealand imports coming from Brazil via South Africa, where they had been used as a biocontrol agent for the past decade.

Dr Dymock said she was keen to hear of any new lace bug sightings in Northland as part of her work to track its spread.

Joe Carr, who chairs the regional council's Environmental Management Committee, said he was excited about the opportunities offered by biocontrol agents like the lace bug.

"Biological control is the use of naturally-occurring enemies and diseases to control pests and weeds, and is very much one of the smarter pest control tools at the council's disposal," he said.

Biocontrol wasn't a "silver bullet solution," as it was not designed to eradicate a species, but once established it was among the most cost-effective control methods available over a wide area and/or remote sites, and could keep target pest populations at low levels.

"Northland's already home to a variety of tiny insects and fungi that have been successfully targeting some of our worst weeds and insects for a number of years, and now help to protect our wider environment, as well as our fruit, vegetable and timber crops," he added.

Cr Carr, an Okaihau beef farmer and forest owner, who represents the council's Hokianga-Kaikohe constituency, said he would be keeping an eye out for lace bugs in his area, and encouraged others to do the same.

Dr Dymock described adult lace bugs as a little like aphids, with patterned lace-like wings and tending to cluster together on the underside of leaves. They fed in groups, sucking the juices out of the leaves, which turned yellow and dropped off.

They also laid extremely small eggs, just 0.5mm long, in batches on the underside of leaves, which hatched into nymphs (smaller, wingless versions of the adult). Adult females guarded eggs and young nymphs from predators, and lace bug colonies were easy to see in the hotter summer months on the underside of leaves.

"As well as the mottled yellow appearance to the leaves, a characteristic sign of lace bug presence to look for is spots of dark frass (insect faeces) hygienically deposited along the edges of tobacco weed leaves," she added.

Go to www.nrc.govt.nz/nasties for more about the regional council's biocontrol programme.