Wednesday, July 6, 2022

New grass grub predator found

The discovery of an unknown predator of one of New Zealand’s most costly agricultural pests has scientists puzzled.

In November last year researchers from the Foundation for Arable Research, who were collecting grass grub pupae for a grass grub feeding project, found them being eaten alive in the soil by unknown maggot-like larvae.

Foundation research manager Richard Chynoweth said at first they couldn’t believe what they were seeing.

“Grass grub is one of NZ’s most costly, and therefore most researched pest insects, but we had no knowledge of this sort of predation occurring.”

The team gathered as many of the larvae as it could and assembled an expert team from across the world to learn more.

“Larvae of this fly had never been found and studied before, although adult flies were in several NZ museum insect collections. They had also never been recorded as having any sort of association with grass grub, another native species.”

Richard Chynoweth

Foundation for Arable Research

Several months of laboratory rearing, DNA testing, and combing the scientific literature ensued, after which the group learned it had found something new.

“We discovered that the larvae were Ostenia robusta, a native, but not well-recorded carnivorous fly,” Chynoweth said.

“Larvae of this fly had never been found and studied before, although adult flies were in several NZ museum insect collections. They had also never been recorded as having any sort of association with grass grub, another native species.

“Our main aim for this project now is to learn more about the distribution and the biology of this insect and to confirm that last year’s finding wasn’t just a one-off.

“Once we have more information about Ostenia robusta we can start to make decisions about whether or not is has potential for use within integrated pest-management systems.”

The work was presented to the science community at the New Zealand Plant Protection Society in Napier last month.

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