Combating invasive insects

Blog 9
February 22, 2021

National Invasive Species Awareness Week runs February 22-28, 2021. But what does that mean? What are invasive species and how do they impact our local habitats? In this post, we’ll explore how we combat those species.

A non-native species may not become established when introduced into a new habitat. Of those that do, few will be invasive. Their negative impacts, however, can be astounding especially when it comes to invasive plant-eating, herbivorous, insects. Native plants have coexisted with their native herbivores long enough to develop at least some level of innate resistance to them. These plants do not share this evolutionary history with recently introduced insects, leaving them susceptible to herbivory. By invading a new habitat, insect herbivores are also able to escape the natural predators, parasitoids, and pathogens of their original habitat. With this new widely available food source and with fewer natural population controls insect populations can grow rapidly in their new habitat and cause extensive damage, which is what makes them invasive.

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Anoplophora glabripennis grub specimens in the Peggy Notebaert Nature Museum of the Chicago Academy of Sciences collection.

Invasive insect threats in Illinois include spongy moth (Lymantria dispar), which if left unchecked can defoliate trees damaging entire forest ecosystems. Emerald ash borer grubs (Agrilus planipennis) tunnel inside ash trees, eventually killing the tree and leading to the destruction of entire ash populations in urban and natural areas. Asian longhorned beetle (Anoplophora glabripennis) once threatened hardwood trees like ash, maple, and poplar in Chicago. Spotted lanternfly (Lycorma delicatula), while not yet in Illinois, provides an imminent threat to, but not limited to, a wide range of crops such as apples, cherries, peaches, plums, grapes, and hops.

Tackling these harmful pests requires extraordinary coordination between governments, industries, and communities. There are any number of different strategies that can be used to stop their movement, reduce their impacts, and in some cases eliminate them completely. Let’s explore a few!

The first strategy is in place before potential invasive pests even arrive. The Plant Quarantine Act of 1912 gave the federal government authority to inspect agricultural products at the country’s borders and prevent infested material from entering. This is now carried out by the Animal and Plant Health Service (APHIS) of the USDA. Most non-native insects are brought over accidentally in plants, shipping containers, wooden pallets, or other cargo. Occasionally non-native insects will slip through and become an invasive pest. When this happens APHIS will work with local governments to establish targeted quarantines and monitoring programs. Spotted lanternfly was first detected in Pennsylvania in 2014 and has since spread to at least five other states along the East Coast. Estimates of spotted lanternfly’s potential range, if uncontrolled, has a high probability of covering most of Illinois and Missouri, extending into Kansas. They are known hitchhikers that will lay egg masses on trees, plants, trains, cars, and even clothing. Quarantines and inspections of transport containers on the East Coast currently protect us from the rapid invasion of these destructive pests.

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Asian longhorned beetle specimen from the Peggy Notebaert Nature Museum of the Chicago Academy of Sciences collection.

If an invasive insect is identified shortly after introduction with a localized distribution it makes a good candidate for complete removal, aka eradication. This often requires early detection. It’s difficult, many eradication programs fail, are expensive, and have potential for non-target impacts but if successful can prevent so much damage. Asian longhorned beetle was successfully eradicated from Chicago, thanks in part to its early detection by a Skokie Park District employee who discovered the beetle in firewood originating from the Ravenswood neighborhood in 1998. The employee promptly reported their sighting to APHIS who determined the beetle was carried to Ravenswood via wooden shipping pallets. APHIS worked with local agencies and the community to implement robust monitoring programs, coordinate tree removal, and apply insecticides. Asian longhorned beetle was declared officially eradicated from Chicago in 2008.

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Emerald ash borer (Agrilus planipennis). Photo from USDA APHIS PPQ.

Eradication is not feasible for every invasive insect, but control strategies can still be implemented to lessen their spread and impact. Emerald ash borer, for instance, was already well established when first detected in Michigan in 2002 as it was likely introduced years prior. Emerald ash borer destroys ash trees, but it can take up to three years for damage to be visible. Sanitation is an important control strategy which for emerald ash borer involves the removal and chipping of any infested trees as well as potential host trees in the surrounding areas. This intended to reduce their movement and prevent them from quickly spreading to new areas on their own. For emerald ash borer this means cutting down and chipping infested ash trees and the removal of healthy trees surrounding areas of high infestations.

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Spongy moth (Lymantria dispar). Photo from USDA APHIS PPQ.

If an invasive pest has already been around long enough to be widespread and well established what can be done? Suppression programs aim to reduce the population sizes to manageable levels where their ecological impacts are lessened. Spongy moth was first introduced to New England in 1869. They were brought over intentionally in an attempt to cultivate an alternative to the silk moth (Bombyx mori). Perhaps unsurprisingly the non-native moths raised in outdoor containers escaped. They have since spread through much of the Northeast and Great Lakes regions. The masses of caterpillars can defoliate entire swaths of forest trees, leaving them vulnerable to pests and diseases. They also outcompete native moths by quickly consuming their food sources. The use of targeted insecticides, such as a strain of Bt that only affects caterpillars, can prevent defoliation. While other caterpillar species can be directly harmed by these insecticides, studies show positive long-term effects on native moth biodiversity by reducing competition from spongy moths.

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Spotted lanternfly (Lycorma delicatula). Photo from USDA APHIS PPQ.

A single strategy on its own is rarely enough to adequately control an invasive species threat. Typically, the use of multiple tactics is required and that is integrated pest management. Using every tool at our disposal not only provides better control but reduces our reliance on chemical insecticides and reduces the likelihood the insects will develop resistance to any one control method. Early detection, sanitation by removing infested trees, and the use of insecticides together allowed for the successful eradication of Asian longhorned beetles from Chicago. Quarantines not only help to prevent spotted lanternfly from reaching us, they are also giving us time to implement sanitation by removing their native host, tree of heaven (which is itself a highly invasive plant)! Parasitoid wasps and beetle pathogens are deployed as biocontrol agents to suppress emerald ash borer.

What Can You Do?

So far we’ve looked at methods the government and other agencies use to control invasive insects. Here are some ways you can help prevent their spread too:

  • Promptly remove any infested trees or plants and woodchip them.
  • Remove all tree of heaven. It is a preferred host for spotted lanternfly and invasive itself, get rid of it before they arrive!
  • Check your belongings and vehicles for hitchhiking eggs or critters before you move.
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