Just mentioning the name Queensland fruit fly is enough to spook me, and I'm not a commercial grower. Fruit fly is the foot-and-mouth disease, varroa and didymo equivalent of the horticultural world, the ultimate fear factor for growers of many of the region's income earners such as pipfruit, tomatoes, grapes, peppers and berryfruit.

Hopefully, it won't be coming to an orchard or garden near you, because if it does, forget the global financial crisis – we'll have our own homegrown one, only the rest of the world won't really care.

Instead, they will just find somewhere else to source the top-quality produce this country is renowned for, while we struggle to know what hit us, let alone know what to do about it.

The scary thing is that of the above-mentioned pests, three of have now been found in New Zealand in less than a decade. Welcome to the global economy.

You can also add to the mix Psa-V kiwifruit disease, painted apple moth, dutch elm disease, asian paper wasps, american gooseberry mildew, camellia flower blight, southern salt marsh mosquito (the carrier of Ross River virus in Australia) and, close to home in Nelson and Richmond, argentine and red imported fire ants.

You can also throw in a few random brief stowaway survivors such as spiders, snakes and a cane toad or two. Scary, huh?

All this is stuff is why we have biosecurity at the borders. The crucial factor in stopping them in their tracks before they get comfortable here is to be aware of the potential risk pathways. That is the way pests can hitch a ride here.

While there are the obvious ways such as inside travellers' luggage or hiding inside handbags and shoes, as has been the case for some stowaway snakes and toads, the less obvious routes are inside containers and cars imported over the docks. That's why there are monitoring stations for all kinds of potential arrivals within insect flight and movement distances from Port Nelson.

Why should you be concerned in the home garden? Well, while you might feel immune if you grow your own produce, chances are you will also inevitably find yourself battling to control more and more virulent pests in the privacy of your backyard.

Take American gooseberry mildew for instance. While gooseberries may not be top of the pops in your garden, most people know the plant as a tough little battler, capable of withstanding heavy frosts, difficult soils and warding off potential browsers with its nasty spikes.

It's one of those hardy good-doers the early settlers brought with them because it could so easily be grown from hardwood cuttings and was a prolific producer.

It can survive on its own almost anywhere, which is why, nearly 150 years after the Acheron Accommodation House was built at the Hanmer Springs end of Molesworth Station, a few stubborn gooseberry bushes cling to a cold and windswept life among the tussocks.

Although there's no certainty the same bushes that grow there today were planted when Acheron was built, judging by their size and spread, they have obviously been there for a long time.

About 1995, 10 years after American gooseberry mildew arrived in this country in 1984, the Acheron plants were still thriving, surviving on neglect in the back country.

But last February, when I called by again on a trip through the Molesworth, I was dismayed to see these remnants of the hardy pioneering spirit had been struck down by the arrival of the unsightly and debilitating mildew, out there in the middle of nowhere. It was a case of the global pest crisis coming to Acheron, showing there's no escape from the tyranny of spore-borne fungal infection.

Closer to Nelson home gardens, the pesky asian paper wasp has been making a meal of the beloved monarch butterfly. Originally invading New Zealand in the late 1970s, the asian paper wasp spread through the country, arriving in Nelson in the 1990s and has since made itself very much at home here. Not only does it compete with tui and bellbirds for nectar and honeydew supplies, but it also kills and eats monarch butterfly caterpillars, having a significant effect on populations nationally.

Most often the worst time for monarchs is in autumn when the wasps are feeding larvae in the papery, pear-shaped nests they build under eaves and rafters.

Typically, the paper wasps, recognisable in flight with their legs dangling down, will sting a monarch caterpillar, slice it up like steak and carry the pieces back to their nests to feed the larvae. The spread and density of wasp populations are increasing.

While recent news from butterfly supporters' group the Monarch Butterfly Trust is that more butterflies are overwintering in the south, the butterflies used to overwinter in huge numbers in Nelson.

Some people will remember when, in the 1990s, hundreds of monarch butterflies would swarm on the conifer trees on Church Hill each winter, taking refuge in the evergreen canopy. Similarly, huge swarms of the colourful butterflies would overwinter on conifers at Isel Park.

But since then, monarchs have succumbed to the ravages of the vicious paper wasp, which is why the trust helps to highlight the butterflies' plight and support their conservation, even though monarchs also are imported.

What lies ahead if fruit flies became established here could prove far more challenging than the foe the monarchs face. Living as we do at the end of the Earth, trade and travel is our lifeline, but it comes at a price.

The scary threat of fruit fly reminds us there's never a free lunch, especially in the garden.

Check out the Monarch Butterfly Trust at monarch.org.nz and on asian paper wasps at biosecurity.govt.nz/pests/asian-paper-wasp and more on the Queensland fruit fly at biosecurity.govt.nz/files/pests/queensland-fruit-fly/fruit-fly-fact-sheet-may-2012.pdf.

- © Fairfax NZ News