Japanese beetle, Istocheta aldrichi, and Tiphia vernalis - Ask Extension
Istocheta aldrichi and Tiphia vernalis are Japanese beetle predators. Have they been released in Rice County in any systematic way? Can locals here ...
Knowledgebase
Japanese beetle, Istocheta aldrichi, and Tiphia vernalis #587871
Asked August 10, 2019, 9:32 AM EDT
Istocheta aldrichi and Tiphia vernalis are Japanese beetle predators. Have they been released in Rice County in any systematic way? Can locals here help or provide information?
Richard Goerwitz
<personal data hidden>
Rice CountyMinnesota
Expert Response
According to authorities at the University of Minnesota, "two natural enemies of Japanese beetles have been released in Minnesota. The fly Istocheta aldrichi lays eggs on adult Japanese beetles in summer, whereas the wasp Tiphia vernalis parasitizes grubs in the spring. Although both natural enemies became established here, neither is very abundant and they have little impact on Japanese beetle populations."
We don't know if or when these beetle predators might have been released in Rice County, but based on the above statement, it's fair to assume they are present there.
This year Japanese beetle numbers are greatly reducedover last year in some places, including the Twin Cities area.At the same time in some places many beetles
are showing evidence of predation by Istocheta aldrichi .
In response to an inquiry, University of Minnesota Extension Entomologist Jeff Hahn said "I have not noticed this insect (Istocheta aldrichi ) in the past. I have, however, received comments from a few people this year and have seen parasitized JB myself. They have never been very common before but are pretty noticeable this summer. I am not sure what the percent of parasitism is or what this will mean for JB populations. Stay tuned!"
I saw the statement that you also quoted, and it is what initially got me interested, asking the question specifically about Rice County. It can take time for predator and prey populations to mesh, and my immediate area currently carries a heavy load of Japanese beetles.
I have read elsewhere that the climate of North America, being different from that of northern Japan, initially meant that the lifecycle of particularly the winsome fly (Istocheta aldrichi) did not match well with that of the Japanese beetle, but that it is adapting. If in fact there have been releases, I’m curious whether they came directly from Japan, or whether they were taken from local populations that have started the adaptation process.
Yes, the initial observation was that the fly's cycle was out of sync with the beetle's so that only a relatively small percent of beetles were parasitized. However, many parasitized beetles can still be found in some parts of the Twin Cities area which suggests cycle synchrony may have improved here, at least this year.
For a more detailed answer to your question contact Jeff Hahn.
Extension Entomologist
College of Food, Agricultural and Natural Resource Science
