DES MOINES ? State and federal insect experts say it likely will be next year before they will be able to tell whether a swarm of stingless wasps introduced in Iowa are helping suppress a destructive pest that has attacked ash trees in 52 of Iowa?s 99 counties.
Three species of parasitic wasps were released in 2016 at two biocontrol sites ? 11,000 in the Whitham Woods in Jefferson County and 14,000 at the Mt. Hosmer park in the Allamakee County town of Lansing ? as a natural predator of the Emerald Ash Borer, a devastating exotic beetle whose larvae eats away ash trees from within, said Mike Kintner, Iowa Department of Agriculture and Land Stewardship Emerald Ash Borer and gypsy moth coordinator.
This year the program was expanded to three more locations where stingless wasps were released ? Lake Iowa Park in Iowa County, West Lake Park in Scott County and Millrace Flats in Louisa County ? to target EAB larval and egg stages.
Kintner said researchers want a full two years of experience under U.S. Department of Agriculture guidance to assess the release and recovery efforts. It likely will be the fall/winter of 2018 at the earliest before they evaluate parasitoids at the two Jefferson and Allamakee sites by peeling trees and placing insect traps to get indications of wasp-related activity.
?We?ll just have to see how well they worked,? said Kintner, by eventually determining not just that the parasitic wasps are killing Emerald Ash Borer but also that they actually are reproducing natural areas.
With the arrival of fall weather, Kintner said the destructive insects have moved into a resting phase but he added it was ?pretty safe today? they likely will expand to more Iowa counties once the dormant period ends next spring. ?We?re on a track record here from basically 2013 where we?ve been seeing a lot of counties added every year and I would see no reason why that wouldn?t continue next year as well,? he noted.
Another natural predator in Iowa is the woodpecker that currently are offering some local control, he said, ?but unfortunately there aren?t enough of them and there are just too many Emerald Ash Borer. But that does offer some level of control.?
All ash tree species are susceptible to attack by an invasive bug. The larval stage of this insect kills ash trees by tunneling under the bark and feeding on the part of the tree that moves water and nutrients throughout the tree.