That’s a sure sign good wasps are working to remove unwanted insect pest populations in arable or other crops.
Other beneficial predators or parasitoids include ladybirds, but unlike wasp maggots they don’t, in gruesome fashion, eat their hosts inside out.
Dissecting caterpillars is part of the job for the entomologist, who set up IPM Technologies in Melbourne to help farmers control pests with minimal use of pesticides.
"I like pulling them apart ," Dr Horne said at an Ashburton workshop hosted by the Foundation for Arable Research (Far). "Every farmer I’ve met if I show them a caterpillar they squash it."
He said it was part of the approach to integrated pest management (IPM).
"The reason it’s important is you can’t tell the level of parasitism in a caterpillar — you can’t tell if it is parasitised or not. It’s a really important question because if it is parasitised you don’t need to do anything as it’s not going to turn into a moth. So the way to tell is to pull it apart. If it’s got a maggot inside of it then it’s parasitised."
While growers could not stop this generation from eating a crop, they would know the next generation would not turn into a moth and lay 900 eggs, he said.
Some wasp maggots busted out of a parasitised caterpillar while they were still alive.
The company still worked with farmers, but a lot of the time assisted advisers to help them work out if they needed to spray a crop and which was the best pesticide to use.
A small lab tested pesticides including for chemical companies and their products. Often the tests were carried out to find out what the insecticides and fungicides did to beneficial insects.
"When we meet people for the first time it’s usually ‘we’ve got this pest that needs to be sprayed’ — simple as that — and ‘what product do we need to use?’ But pesticides are only one of three control options."
Farmers using pesticides had to consider residues left in produce and worker and environmental safety.
This was becoming important because companies might not want a chemical to be used even though it it may be legal.
Rather than relying on one option he supported IPM and combined pesticides, cultural controls and biological agents to control pests.
Cultural controls included providing habitats and alternative food for beneficial insects, controlling weeds, irrigating to control numbers, trap crops, selecting varieties and planting at certain times, retaining stubble and using minimum tillage and cleaning machinery to make sure pests did not spread.
The biological controls were insects which ate pests — predators, parasitoids or pathogens.
"The most important thing is there’s nothing else. So if you accept that, this is what we’ve got. However you control a pest on any given day depends on what’s available. So pesticides come and go. Things you are using now might not be available in five years’ time. They might not be available next year. They could be withdrawn, banned or the market you are supplying might not want them, so all these things change."
Pest resistance to pesticides was growing in Australia.
If farmers were only using pesticides they were only using one-third of the available tools, Dr Horne said.
If they were using pesticides which also killed beneficial insects they were making the pest problem worse and it was best to roll the controls together.
The starting point was always to identify pests and work out what ate them, he said.
It would be better if people changed to IPM before there was a crisis, he said.
In Indonesia he came across a "massive crisis" where shallot growers were found over nine weeks to be using 90 insecticides, spraying every two days to try to control the caterpillar, beet armyworm, before it hatched.
When they arrived growers were abandoning crops.
He told them he could get their chemical use down to seven insecticides for better results, but there were no takers. Only when they guaranteed the market value for one-quarter of a crop did they get one East Java grower on board.
By the end of the project 1500 growers had adopted IPM.
"The point is we got far better results with far less insecticides. ... They are not on their own. It’s the same everywhere — it’s the same here and it’s the same in Australia."
The normal reaction for a pesticide programme that started to fail was to use a bit more and use it more often.
Australia was dealing with a crisis at the moment with the diamondback moth resistant to just about every pesticide.
Cabbage crops damaged by the moth could not be sold to the market, while a grower who lost a third of a Brussels sprout crop in the Yarra Valley now used an IPM approach with a "fraction" of his previous pesticides and had a crop to sell.
Strawberry growers calling a crisis meeting near Melbourne were abandoning crops in March instead of having a crop through to May, despite spraying every three days.
"So the same story and same again. We worked with growers in the same way and it took four years to go from zero adoption of IPM to 100% adoption. There is now no ... full-spectrum insecticides used at all. The good news is you can get positive results by careful use of pesticides."
