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It's war on the farm as aphids invade, wasps swarm, and it will most likely will be won by ... native ladybirds, says Bruce Wills

It's war on the farm as aphids invade, wasps swarm, and it will most likely will be won by ... native ladybirds, says Bruce Wills
Giant willow aphids

By Bruce Wills*

Having watched the movie ‘World War Z,’ about a fictional pandemic of zombies, I have a story to tell of a farming pandemic involving giant aphid Clones.

This is my ‘World War C’ and it’s spawning a wasp plague.

This is made all the more real by fellow sheep and beef farmer Janet Kelland’s tangle with wasps on her Taumaranui farm - an experience that nearly cost her life.

The where, what, why, when and how will come but the Giant Willow Aphid genie was confirmed on Christmas Eve.  

Tuberolachnus salignus was confirmed in Auckland on 24 December and by February had invaded Bay of Plenty.

A few weeks ago I can now add my farm in Hawke’s Bay and, as of 19 March, the South Island’s West Coast.

They’ll be almost everywhere by now.

I am astounded by its rapid spread.

My farm is like an island surrounded by pine trees but somehow my willows were sniffed out.

These aphids are female clones and breed so fast asexually that they make rabbits look like monks.

While the Ministry for Primary Industries is right to say it’s too late to eradicate we need to know just how this bug got here.

The first time I noticed these aphids at Trelinnoe was when the trunk of a willow appeared sooty black.  Walking closer it was a seething mass of aphids.

So much so my hand could sweep hundreds off at a time to expose the tree beneath.

I hopped on my quad bike and checked tree after tree and sure enough each willow was covered in these dark pen shaped aphids. As giant aphids they’re name is no misnomer because they’re about 6mm long.

So how will someone be hurt, or worse?

As these aphids feed on my willows, the injured tree releases honeydew and what aggressive insect likes sweet things?  Approaching one tree to do maintenance the drone of wasps was like standing beside a 737.

I encounter wasps all the time and I can promise you on several occasions I would have left Usain Bolt trailing in my wake.

Recently I went to cut a branch and disturbed a nest and I must confess to Worksafe NZ that my helmet was left behind as I sped away on my quad bike with a black cloud of wasps in hot pursuit.


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As Janet Kelland noted after release from hospital we seem to have an explosion in wasp numbers.

Given our beech forests also suffer from the wasp plague we are going to be in for much larger numbers over the next few years.

From Nelson we have already seen children and adults hurt when a nest was disturbed and now we have a farmer medevac’d in Taumarunui. 

With more food thanks to the Giant Willow Aphid it means more nests and that means more over wintering queens.  That adds up to more of a wasp plague until the aphids at least are brought under control.

Right now, it means the beekeepers I work with have to relocate hives because wasps attracted by honeydew are also raiding honeybee hives. If our bees did not have enough issues to deal with.

So what is the answer to the aphid curse outside of nurseries?

It isn’t a spray but does come from nature and it is called the ladybird. 

Yes that pretty little native insect is an aphid munching machine and I have seen them making a beeline for the Willow Aphid.

While I am no bug whisperer I imagine they are in seventh-heaven but the ratio is like one to thousands.

It means we can expect the ladybird population to massively expand but that will take a few years and until that time, I am steeling myself for perhaps the loss of young trees and a number of wasp stings.  My current record being 30 when I accidentally laid over a nest to cut a branch.

So if you are a home gardener then please buy chemicals specifically labelled bee or butterfly friendly because it will be ladybird friendly and we need every ladybird possible. 


Bruce Wills is Federated Farmers President

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or not buy chemicals at all...
Or maybe warmer winters is letting pests survive? couldnt be an outcome of global warming could it?  aka the pine beetle?

I'm going to disagree here and say it is just that with international shipping stuff eventually gets in (the better the border control, the longer you can keep things out). And for Wasps, they are a species comfortable with a temperate climate, and don't seem to be too put out by warming. This is why NZ beech forests have been estimated to have a greater weight of wasps than birds.

I am the person who originally discovered the aphid in N.Z. in December 2013. We really don't know how long the aphid has been here, or how fast it has spread. We don't have an efficient system for detecting new insect pests early. I discovered the species only because I randomly went to Western Springs Park and happened to notice a huge (the body is only about 4mm long, but the legs are very long) winged aphid sitting on a leaf of a random plant (not a willow). Only after I identified it back in the lab did I go back and look at the willows, and there was a big infestation! Indications are that it hasn't been here very long, but we may never know for sure. Once word of it got out, only then did people started finding it all over the place. The honeydew certainly does attract wasps, but unless you mess with them, they are too busy drinking the honeydew to be aggressive. Overall wasp numbers may increase as a result of the aphids, but we have no hard data yet to confirm that this is happening. I have observed ladybird larvae eating the aphids. I'm not sure why Bruce Wills speaks of "native ladybirds", as introduced species are most likely to eat these aphids. I haven't yet noticed any significant sooty mould growth. The "wall to wall" aphids themselves tend to appear as a dark encrustation on the willow stems, but this should not be confused with sooty mould. It is interesting that the species has not been reported in Australia. The situation parallels the 1990s invasion of the willow sawfly (Nematus oligospilus), which was only subsequently found in Australia. In summary, we may never know how GWA got here, or how long it has been here. We should wait to see what happens rather than indulging in "scaremongering" about wasps, etc. It is however a good example of indirect effects of new organisms (particularly the kiwifruit concerns, which probably would not have been predicted). I wonder if Bruce Wills and others are equally concerned with the potential for indirect effects from newly released species of dung beetles??

Thank you.

Thanks for that Stephen.