Tag Archives: New Invasives

Caterpillars, Garden Insects, Invasive Species, Moths

Purple Carrot Seed Moth Appears in Wisconsin

In a given year at the UW Insect Diagnostic Lab, I typically document 2-3  new, non-native, potentially-invasive insects in Wisconsin. In some cases, these species make an appearance only to fade into the background with little impact, while other exotics become heavy-hitting invasive pests (e.g., emerald ash borer and gypsy moth). The latest non-native pest to make an appearance in the state is the tiny “purple carrot seed moth” (Depressaria depressana) and its impacts are not yet fully known. This species has a wide native range and can be found from western Europe through Russia to China.  It was first documented in North America in 2008 and is so new that few images exist and it’s not included in the common caterpillar and moth field guides on the market.

Purple carrot seed moth. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

In the last decade, the purple carrot seed moth has been documented in many locations in southern Canada and the northeastern US and has also been spotted in a few scattered locations in Michigan, Indiana, and Illinois. In mid-July of 2018, two reports came into the UW Insect Diagnostic Lab in rapid succession—Kewaunee and Dodge counties in Wisconsin. These cases were confirmed through images and caterpillar specimens that were reared to adult moths. After discussing the purple carrot seed moth on a recent episode of Wisconsin Public Radio’s The Larry Meiller Show, several additional suspected cases were reported in the state: Racine (Racine Co.), Random Lake (Sheboygan Co.), Burnett (Dodge Co.), and Franklin (Milwaukee Co.).

These insects get their name due to their association with flowers (umbels) of plants in the carrot family (Umbelliferae). The caterpillars of the purple carrot seed moth are small (3/8 inch long when mature), but dozens can feed on a single umbel. The caterpillars are dark green or reddish with many conspicuous white spots on their bodies. In addition to feeding on the flowers, the caterpillars tie together floral parts with silken webbing, which can make herbs like dill unusable. Eventually the caterpillars pupate within the webbing and emerge as adult moths a short time later. The adult moths are 3/8 inch long with a pale patch near the head; their purplish-grey wings are folded back along the body when not flying.

Caterpillar of the purple carrot seed moth, note the many conspicuous white spots on the body. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

The impacts of this non-native insect are not fully known for our area. The reports of plant damage in Wisconsin thus far have only been on dill. Due to the plant parts attacked (flowers), the impact on carrots, celery, and parsnip crops will likely be minor. The biggest impacts would be expected with umbelliferous crops commonly grown for seeds: dill, fennel, and coriander. Luckily, several organic control products may offer help on herbs: insecticidal soap and Neem oil are two low-impact products expected to help control this pest, if needed.  Cutting out and destroying infested flower heads may be another helpful tactic.

Damage from the purple carrot seed moth on dill. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

Because this pest is “new” in Wisconsin, if you believe you’ve found it on dill or other plants from the carrot family, please snap some pictures and contact me to help document this species in the state.

If you’d like to learn more about this insect and its potential impacts check out this video through the Wisconsin First Detector Network.

June 2020 Update: A current distribution of known PCSM sightings can be found below.  If you encounter this insect this summer in Wisconsin, feel free to let me know, so I can better keep track of its activity in the state.        —PJ

County records of the Purple Carrot Seed Moth in Wisconsin. Map Credit: PJ Liesch, UW Insect Diagnostic Lab
Beetles, Invasive Species, Ornamental Pest, Shrubs

The “New” Japanese Beetle in the Midwest

Move over Popillia japonica, there’s a new “Japanese beetle” in town.

As is typical in a given year, Wisconsin sees a few new invasive species in the state each year.  In 2016, one of the surprises was the arrival of the “two banded Japanese weevil” (Pseudocneorhinus bifasciatus), often simply called the “Japanese weevil”.  Weevils themselves are technically a type of beetle from the hyper-diverse family Curculionidae, which contains a plethora of weevils, curculios, and multitudes of bark beetles.  When talking to the public, it’s amazing how often the Japanese beetles feeding on landscape plants during the summer are mixed up with the Asian lady beetles (Harmonia axyridis), which invade homes in the fall.  Given the name of this new “Japanese weevil”, I’m expecting this creature to confuse the situation even more.

What is the Japanese Weevil?

The Japanese weevil (P. bifasciatus) is a non-native beetle that feeds on a wide variety of landscape plants, particularly shrubs.  Adult Japanese weevils are ~ ¼” long with a gray or brownish, pear-shaped body with black bands across the wing covers (elytra).  The pale larvae (grubs) live in the soil and feed on roots of suitable host plants.  We haven’t had this pest in Wisconsin long enough to fully understand the local life cycle, but given the pattern in other states, this insect will most likely complete one generation per year, with adult presence and feeding damage occurring during the summer from late June through August.

Photo Credit: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org
The invasive two banded Japanese weevil (Pseudocneorhinus bifasciatus). Photo Credit: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org

Where’s the Japanese weevil from?

Very similar to the Japanese beetle (Popillia japonica), the Japanese weevil is native to Japan and first popped up in the US in 1914, via the transport of infested nursery stock.  Like the Japanese beetle, the Japanese weevil feeds on a wide range of landscape plants.  When it first showed up in Wisconsin in 2016, the Japanese weevil was found on a variety of ornamental plants in Madison, WI.  How this species got to Wisconsin remains a mystery, but the movement of infested potted plants is the most likely explanation, as this insect is not capable of flight.  While the Japanese beetle is common across many parts of eastern North America, the Japanese weevil has a much more scattered distribution and can be found primarily in the Mid-Atlantic region with scattered cases in the Illinois, Iowa, Wisconsin and Oklahoma.

What does this insect mean for Wisconsin?

Luckily, it seems that the Japanese weevil may not be nearly as big of a threat to landscape plants as the Japanese beetle.  When lots of Japanese beetles are present, entire trees can have their leaves nibbled into a lace-like skeleton.  In contrast, when the Japanese weevil feeds, it tends to cut notches out of the edges of leaves.  This damage can resemble the feeding of many caterpillar species, and healthy plants should be able to tolerate the feeding.  Reports from other states suggest that this insect unlikely to cause very severe damage.

The invasive two banded Japanese weevil (Pseudocneorhinus bifasciatus). Photo Credit: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org
The invasive two banded Japanese weevil (Pseudocneorhinus bifasciatus). Photo Credit: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org

Think you’ve found the Japanese weevil?

If you come across any beetles in Wisconsin feeding on landscape plants that resemble the Japanese weevil, send digital images and/or physical specimens to the UW Insect Diagnostic Lab for confirmation, so we can track this new arrival in the state.