The Insect Invasion is Here
It seems to be everywhere on the news- Giant Hornets in the West Coast, Emerald Ash Borers in the Midwest, Spotted Lanternflies in the Eastern States- the list goes on and on. But why are these insects such a problem? How did they get here? And what can be done to stop them?
The world is more connected than ever. We can order products from the other side of the planet, and receive them in days. International travel has made movement between continents and oceans trivial matter. To the natural world, this is unheard of. Spacial separation of two populations is often a cause of evolution into separate species. Islands, for example often harbor many unique species, due to their geographic isolation. When ecosystems organisms develop and evolve separately, mixing them can have drastic consequences. Consider the Great American Biotic Interchange. North and South America were separated by a seaway since the time of the dinosaurs. When they were fully linked by the formation of the Isthmus of Panama, around three million years ago, animals could freely move back and forth between the continents. This was a disaster for South American mammal groups, many of which died out. Introducing a non-native species to a new area is often detrimental to the native inhabitants.
Insects pose a unique challenge as invasive species. Many are small and can travel undetected in shipping containers or plane cargo. Most are r-selected species- they produce many young with shorter generational times. Certain insects can fly great distances to colonize new areas, ignoring barriers that might limit other species, such as a river or canyon. If an insect arrives in an area with plenty of food, and little natural predators, then it may explode in population.
Some of the worst invasive insects are harmful to native plants. One such arthropod is the Japanese Beetle (Popillia japonica), which was likely accidentally brought over in shipments of plant bulbs in the 1910s. They now inhabit most of the United States, and are a major issue for gardeners and farmers. In particularly infested locations, large groups of beetles have stripped the leaves off trees. The Emerald Ash Borer (Agrilus planipennis) is notorious for causing the virtual extinction of Ash trees in many forests across the United States. These tiny terrors were first found in Michigan in 2002. Since then, they have killed billions of Ash trees. Ash Borer larvae feed under the bark, leaving a network of trails and depriving the tree of nutrients. Today in affected areas, most Ash trees visible are now dead. The Spotted Lanternfly (Lycorma delicatula) invaded Pennsylvania in 2014 form China, where it was brought over on landscaping materials. The lanternfly adults feed on sap and stem tissue of economically important plants such as grape, blueberries, and apples, while they are also problematic for trees harvested for their wood, such as maple and black walnut. It has been called “the worst American invasive in 150 years” Officials project this insect could cost Pennsylvania over 300 million a year if it spreads uncontrolled.
Invasive insects also threaten animals. The Asian Giant Hornet (Vespa mandarinia) regularly raids honeybee hives, kill guard bees and consumes bee larvae. They may also occupy and use the hive. In their native home of Japan, Asian honey bees have evolved alongside these hornets. Because of this, they have adapted to fend off attacks. Honey bees will swarm invading hornets and beat their wings, cooking the hornets with heat. Because our native bees in the US, as well as imported honey bees lack this form of defense, spread of these hornets would be devastating for beekeepers. The Red Imported Fire Ant (Solenopsis invicta) was most likely imported on ships in the 1930s. In Florida, it has spread and affected humans, livestock, and pets with painful stings. They can also prey on ground-nesting birds and reptiles. Both Asian Giant Hornets and Red Imported Fire Ants pose a public health risk due to sting allergies.
The reason why so many of these invaders are from East Asia comes largely down to climate and trade. The United States and East Asia are both temperate regions, and share many similar plant species. The end result is a similar habitat, which is easily tolerated by nonnative species. At the same time, the evolutionary divergence between the fauna of these two regions means that invasives commonly lack predators as a means of population control. The United States is an big trader with East Asia, trading over 600 billion with China and nearly 200 billion with Japan. We are at a trade deficit with both nations, meaning we import more than we export. The unintended result is more Asian species coming here during shipping and international travel.
Though it may feel hopeless reading the headlines of all these invasive species, there are a variety of ways we are controlling the spread. Historically, a major way to deal with insect pests has been chemical control, with pesticide use. DDT was liberally sprayed over fields and residential areas alike to decrease populations of mosquitoes. However pesticides often affect non-target species. If a chemical is deadly to one insect, it is likely to be deadly to others. Nicotine-based pesticides have been shown to be harmful to honeybees and other pollinators. DDT is infamous for causing eggshell thinning in raptors, such as eagles. There is also the concern of developing pesticide resistance, requiring ever greater amounts to be used. Another option is biological control. Introduce a species or organism to control the numbers of the invasive. The US Forest Service issued permits for the release of egg parasite insects of the Emerald Ash Borer. The ideal biological control species affects only the numbers of the invasive, although many scientists are hesitant to introduce new species, from the possibility that they themselves will become invasive.
Steps can also be taken regarding the transport of products. In Pennsylvania in areas with Spotted Lanternfly infestation dubbed “quarantine areas”, residents of businesses must follow strict guidelines and obtain permits if they want to ship products to other areas. Embargoes of certain items from these areas may be necessary if the lanternfly problem worsens. Regulatory laws are being proposed to limit spread on shipping containers. Sticky light traps have promise in killing insects that are attracted to light sources. In areas of Emerald Ash Borer infestation, there were regulations on movement of firewood between states, however these proved ineffective and were lifted.
Ultimately, the best policy to reduce the invasive insect problem is prevention, which includes both public awareness of the problem, causing proactive steps by those moving materials which may contain these organisms. Monitoring of areas for these invaders and removal of new populations are most effective early on, before their numbers balloon to an unmanageable level.
The future of invasive insects appears bleak. As climate change worsens and winters get milder, it is likely that the problem will only get worse as they spread to new habitable areas. At the same time, native insect numbers are plummeting. Land managers, scientists, and the general public must work together to keep these invaders under control using a variety of techniques,to preserve both our economy and natural ecosystems.
