When it comes to invasive insects, much of our attention is directed towards those that cause a great deal of damage, such as Japanese beetles and emerald ash borer. However, there are some other invasive insects present in Illinois that pose a threat to our plants and even us that you should be aware of.

Asian tiger mosquito (Aedes albopictus)

Asian tiger mosquitoes were first discovered in the United States in 1985 in Texas and have spread to more than 20 states, including Illinois. It is believed they were introduced into the U.S. in rainwater in tires and have spread throughout the country this way.

They get their name due to their white and black color pattern. Adults have black and white bands on their legs and a white stripe running down the center of their heads.

Asian tiger mosquitoes are daytime feeders. They are commonly found in shaded areas where they will rest on foliage near the ground. While they may not have particularly painful bites, they are persistent.

In addition to their annoying bites, these insects can carry and transmit Zika, dengue, or chikungunya viruses. However, they aren’t nearly as efficient vectors of these diseases as some other species of mosquitoes and these diseases are not currently a concern in Illinois (May 2021).

Management

Females will lay eggs on the sides of water-holding containers like tires, birdbaths, and tree holes. The eggs will hatch when they become covered in water, usually due to rain. The mosquitoes don’t fly very far. Therefore, eliminating egg-laying habitats (they can develop in as little as one cup of water) will go a long way in reducing populations. Wearing shoes, socks, long pants, and long-sleeved shirts can help prevent bites. Additionally, using insect repellent containing DEET, picaridin, or lemongrass oil can help prevent bites from Asian tiger and other mosquitoes.

Spotted wing drosophila (Drosophila suzukii)

Spotted wing drosophila (SWD) was first found in the continental U.S. in 2008 in California. Since then, it has spread throughout the country, including to Illinois, in 2012. It has likely been spread in infested fruits.

Most fruit flies will lay their eggs in fruit that is already ripe or overripe. On the other hand, SWD will lay their eggs in ripening fruit just before it’s ready to harvest. When the small, white, and cylindrical larvae of hatch inside the fruit, they will begin to feed, and the fruit will begin to collapse in as little as two days. Once this happens, fungi may move in and further degrade the fruit.  

SWD is primarily a pest of fruits like strawberries, raspberries, and blueberries. They will also attack fruit like cherries, peaches, grapes, and tomatoes. It will also feed on ‘alternate’ hosts such as elderberry, pokeweed, and dogwood. If you grow any of these fruits, you can build a trap to monitor for them.

SWD are small flies (1/8 inch) with red eyes, a brown thorax, and black stripes on the abdomen, similar to many other types of fruit flies. To differentiate SWD from other fruit flies, you can look at the wings of the males. Male SWD will have a dark spot on their wings near the wing tip. Female SWD are a little harder to ID (they don’t have wing spots), but they have a rather large ovipositor (structure used to lay eggs) with serrations. These serrations allow the females to lay eggs in unripe fruit.

Management

Good sanitation is important when it comes to managing SWD. Don’t leave damaged or overripe fruit in your garden since these can act as a food source for SWD. Composting and burying fruit is not an effective way to kill SWD (the can survive being buried 18 inches deep). Instead, place the fruit in a clear bag and leave them in the sun to kill any flies that may be present. 

Netting can also be used to protect plants from SWD. Since these insects are small, you'll need netting with small holes, like 80-gram insect netting. This netting can also help keep birds away from fruits. The drawback of netting is that it may need to be removed in order for flowers to be pollinated and for fruit to be harvested, which may allow SWD to get in. 

Make sure to harvest fruit frequently, to make sure ripe fruit isn't in the garden very long. After harvesting refrigerate fruit as soon as possible. This will slow the development of any larvae that may be present, prolonging the shelf life of the fruit. 

Insecticides can also be used to manage populations. When applying insecticides apply them in the evening to avoid killing pollinators. Products containing carbaryl, malathion, spinosad and pyrethrin can be used. Make sure to read and follow all label directions.

Viburnum leaf beetle (Pyrrhalta viburni)

Viburnum leaf beetle (VLB) is native to Europe and was found in North America in Canada in 1947. In 1996 it was found for the first time in the U.S. in New York. It was first found in Illinois in 2009 in the Chicago area.

Both the adults and larvae will feed on viburnum leaves. The larvae will often feed in groups and cause leaves to look lace-like (like Japanese beetles). The adults will create oblong holes in leaves. If beetle populations are high enough, they can defoliate plants, which will weaken them over time and can eventually cause death.

In May, the larvae will hatch and are yellowish-green in color and have black spots and dashes on their bodies. They will feed for around a month and begin to pupate in the ground in early to mid-June. Adults are around ¼ inch long and golden-brown and will start to emerge in mid-to-late July. During the summer and fall, females will chew pits in twigs, lay eggs, and then cover the eggs with chewed pieces of wood. Females can lay up to 500 eggs over their lifetime, and these eggs will hatch the following spring. Adults will be active until the first frost.

Management

Viburnum species will vary in their susceptibility to attack from VLB. Some species like arrowwood (V. dentatum) and American cranberrybush (V. opulus var. americana) viburnums are highly susceptible and can be killed in as little as 2-3 years. In contrast, some species like Koreanspice (V. carlesii) and Judd (Viburnum x juddii) viburnum are resistant.

If you plan on planting viburnum and live in an area with VLB, avoid planting susceptible varieties. If you have viburnums, inspect your plants between fall and spring for twigs that have eggs laid in them. If you find any, prune them out and destroy them.

Chemicals can also be used to manage the beetles. Horticultural oil can be used on plants before leaves emerge in spring. The oil will cover and suffocate eggs, reducing the number of larvae that hatch. After leaves have emerged contact pesticides can be used. These pesticides will be most effective on the young larvae, so apply early in the season. Spraying adults is less effective.

Learn more about Illinois invasive species. 

Good Growing Tip: Want to learn more about spotted wing drosophila? Check out this video by Extension's Kelly Allsup.

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Photo: "Spotted-winged Drosophila, Drosophila su" (CC BY 2.0) by Judy Gallagher