Biological control of insects

THE INSECT WHISPERER: Forest entomologist Toni Withers of Crown research institute, Scion, made an invaluable contribution to the field trip to Makihoi Forest. Picture supplied

Forest entomologist Toni Withers of Crown research institute, Scion, who accompanied the group, noticed tips in the specimens of Eucalyptus quadrangulata (commonly known in Australia as the white-topped box) had been badly chewed by eucalyptus tortoise beetle (Paropsis charybdis).

The pest has been in New Zealand for more than 100 years. It causes significant damage to shining gum as well as other gums that hold potential for producing ground-durable wood.

Because there are no native tortoise beetles in New Zealand, the pest has few natural enemies to attack it. The tortoise beetle produces two generations a year. Both larvae and adult beetles eat large amounts of young eucalypt leaves for many months of the year.

“These guys are just voracious,” said Toni.

The beetles' sustained feeding damage can stop the trees from growing.

“Biocontrols take out a large portion of their eggs but can't keep up with their rate of reproduction.”

Pupa emerge into adults that climb out of the ground and in Australia, birds and mites have evolved to feed on them — but New Zealand birds don't like them, said Toni.

Scion scientists have been working for six years on a new parasitoid. A specialist parasitoid wasp native to Tasmania has evolved to only attack the larval stage of the eucalypt leaf-feeding beetles' life cycle and nothing else.

When the imported parasitoid was kept in a containment facility at Scion in Rotorua, it was safety tested to see if they attack beetle larvae from different species. They have been shown to be safe. Scion hopes they will be released to help control the tortoise beetle.

A helpful insect species known as Schellenberg's soldier bug is native to New Zealand and Australia and feeds on free-living insects such as caterpillars and beetle larvae.

“This morning, Scion scientists saw them sucking the insides out of many paropsis larvae.”