Are fruit tree pests proliferating?
Orchard owners are getting some help from Central Otago students to keep an eye on codling and leafroller moths. Their research could help us improve the way we manage fruit tree pests.
Year 5 & 6 students at Wānaka Primary School are taking a closer look at a big agricultural problem in New Zealand: moths that are damaging fruit trees.
The 9-to-11-year olds are focusing on two different kinds of moths - codling moths and leafroller moths. But it is the larvae (young forms), not the adults, that are the culprits.
“The codling moth larvae damage mainly pip fruits like apples, pears and quince. While those of the leafroller moth tends to damage stone fruit trees such as peaches, apricots and plums,” says teacher and project lead Sharon Pendlebury.
She explains that most people have heard more about the codling moth because it’s known for causing big brown areas in the fruit, making the crop completely inedible.
While the leafroller moth is not as immediately damaging as the codling moth, it still affects the bark and leaves – making the tree more likely to develop other infections or diseases.
The students suspect that the moth problem for these fruit trees is on the rise in New Zealand.
To test their idea, they are counting how many moths are caught in the sticky traps they have set up in fruit trees across different parts of Wānaka. Each trap contains chemicals known as pheromones that are irresistible to these moths and are commonly used by orchard owners.
The kids are then going to check for patterns by comparing the numbers of moths in each area and over time, and eventually hope to find out what might be causing these patterns.
Sharon also tells us that there are actually three types of leafroller moth: the light brown apple moth, the brown-headed leafroller and the green-headed leafroller.
So far, they’ve seen hundreds of light brown apple moths but not very many of the others or the codling moth.
They’re not yet sure why, but Sharon thinks it might be because the other moths do their egg-laying later in the season.
Putting the sting into moth control
Alongside their moth-counting research, the students are also learning about the wasps that eat these pests.
“We saw a video showing how one type of wasp paralyses and lays its eggs inside a codling moth larva and then when the eggs hatch the wasp larvae begin to feed on the moth larva, eating it from the inside out!” Sharon says.
“It made my stomach turn a bit because we watched it right after breakfast - but the kids were really into it!”
In New Zealand, there are no native predators for these types of moths. The fruit growers who are trialling using wasps to control moths have to import them from abroad, which can be expensive.
Sharon and her pupils hope that any patterns they might spot in their investigation will help these farmers and orchard owners save costs by targeting the moths better with fewer wasps.
Ten-year-old Jack Wyeth tells us, “I liked putting up and checking the sticky traps most. I was surprised at how many moths have been caught. I really liked learning about the wasp too.”
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About the project
This project is being supported by funding from the Otago Participatory Science Platform (PSP), which is managed by Craig Grant at Otago Museum.
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