Natural control name of the game
The WOW! Factor
By VIRGINIA WINDER - Taranaki Daily News
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Things are getting hot in the glasshouse. The allies are battling the enemies in a case of biological warfare.
At stake are tomatoes, cucumbers and capsicums - tender young things susceptible to attacks from the bad guys, or, in this case, bad bugs. You might know them as whitefly, aphids, two- spotted spider mites, sciarid flies and thrips.
The battleground is NZ Hothouse, a hydroponic operation encompassing 20 hectares of glasshouses near Pukekohe in South Auckland. This is the source of many of the vine-ripened tomatoes and telegraph cucumbers that appear in supermarkets and fruit marts around New Zealand.
The writer is there on a vegetables.co.nz tour with her In Season food page hat on. Witt chef tutor John Hudson is alongside, wielding the camera. But when the subject turns from grub to grubs, and a few involuntary "wows" are whispered by the tourists, the science lover can't help herself.
"Our main problem is whitefly," says general manager Simon Watson. "Ten or 15 years ago, growers would nuke the place with insecticide."
Not now.
"We have harnessed nature to put ourselves in a position where we don't need to use harmful chemicals."
This is where the biological warfare comes into play, but don't imagine a sci-fi scenario of vile viruses in vials. Envisage instead, a battle of bugs.
"We breed our own wasps to kill the whitefly," Watson says.
Grower Mark Clifton stands outside a closed-in space where the wasps, Encarsia formosa, and other insects are bred.
The tiny parasitic orange and black wasp lays its eggs into second, third and fourth nymphal stages of whitefly. The wasp's egg then hatches inside the whitefly scale and the wasp larva feeds inside the scale. The scale will turn black within two weeks and a wasp will emerge soon after.
"That breaks the cycle of whitefly," Clifton says.
"Whitefly is an incredibly quick-breeding killer. You might have a few whiteflies one week and a month later have so many your whole crop can be wiped out."
Pollinating the plants is also a natural process. Bumblebees have this job. These buzzing balls of black and gold fluff are bought by the boxful and released into the 20ha of hothouses. These are welcome critters, but there are still more enemies lurking among the leaves.
"Thrips can make cucumbers hook like a banana, but Amblyseius cucumeris keeps them on the straight and narrow," a sign on the bug house says.
The cucumeris critters are also used to keep capsicum plants healthy. Like in the wasp and whitefly war, cucumeris attacks foes while they are just developing. The predator feeds on the young stages of thrips because the adults are too large for it to kill. Thrips also come under attack from Hypoaspis miles. These tiny mites are also deadly enemies of the sciarid fly, also known as the fungus gnat. In another hothouse skirmish, it's mite against mite.
On one side we have the two-spotted spider mite, which lives on the underside of leaves, spins protective silk webs and causes damage by puncturing plant cells to feed.
On the other is the mighty mite, Phytoseiulus persimilis, which keeps its cousin under control. And, finally, aphids are given a sting by Aphidius colemani. The female wasp lays its eggs into the body of the aphid. The egg hatches inside and the larva feeds and develops into a fully formed wasp, killing the aphid in the process. The aphid bodies bloat and develop crusty shells called mummies.
When the wasp is mature, it cuts an escape hole in the back of the aphid and emerges to mate and feed and the female then searches for aphids to lay more eggs.
A couple of fungi are part of NZ Hothouse's natural arsenal against damaging insects. Verticillium lecanii and Beauveria bassiana are fungi that infect and kill unwanted mites, aphids and whitefly.
B. bassiana infects insects with white muscardine disease.
"When the microscopic spores of the fungus come into contact with the body of an insect host, they germinate, penetrate the cuticle and grow inside, killing the insect within a matter of days. Afterwards, a white mould emerges from the cadaver and produces new spores," Wikipedia says.
"That's what happens in the wild," Watson says. "It's a natural way of doing things."
