Wisconsin wetlands are being plagued by purple loosestrife, a nonnative, invasive plant that makes it nearly impossible for native species to grow. ©John T. Andrews

For decades now, climate change has been altering habitats and causing a major shift of ecosystems northward. Unable to adjust quickly enough, some cold-adapted species are being forced to relocate to higher latitudes as warmer temperatures push them out of their traditional environs. For some warm-weather species, habitats are expanding.

Such is the case in Florida, where a mosquito usually found near the equator is moving into Key West, the southernmost U.S. city. The new immigrant is Aedes aegypti, which can spread two diseases: dengue, a viral infection that causes flu-like illness and sometimes death, and chikungunya, which results in fever and severe joint pain. To combat this threat, researchers want to release more Aedes aegypti mosquitoes—genetically modified males that will mate with wild females, whose offspring will then die, thus reducing the population.

Oxitec, the company that is bioengineering the mosquitoes, hopes to release them this spring in Key Haven, a neighborhood of 444 homes on a relatively isolated peninsula at the north end of Key West.

The Arctic fox faces many threats from climate change: shrinking sea ice and tundra habitat, reduced numbers of lemming prey, and increased competition and displacement by the red fox, which is moving northward as temperatures warm. ©Brad Josephs

But could introducing more nonnative species—especially genetically modified ones—be more harmful than helpful to the environment and to us?

A battle between aliens is not new

The strategy proposed for Key West is not the first of its kind. Slowing the spread of exotic plants and insects with the use of chemicals is expensive and often has negative environmental side effects. Finding natural enemies to kill invasive plants or insects is often healthier, more efficient and sustainable.

Last summer, in fact, the National Geographic Society reported that hundreds of thousands of flea-size, parasitic wasps from Pakistan (Tamarixia radiata) were released in California to attack Asian citrus psyllids, potential carriers of a plague called huanglongbing or citrus greening, which could decimate the state’s citrus groves. The U.S. Department of Agriculture recently promised the state $1.5 million to ramp up the program to release about a million wasps a year.


A mosquito, “Aedes aegypti,” usually found near the equator is moving into Key West, Florida’s southernmost point. The new immigrant can spread two diseases: chikungunya and dengue.

In Wisconsin, “beetle ranchers” are raising tens of thousands of tiny Galerucella pusilla bugs—native to Europe and Asia—that will be turned loose in the wild, where it is expected that they and their insatiable appetites will mow down waves of invasive purple loosestrife, a plant native to northwest Africa, Asia, southeastern Australia and Europe. The plant plagues Wisconsin wetlands, where it grows out of control and makes it nearly impossible for native species to grow.

The Wisconsin Department of Natural Resources says the program is cost-effective and environmentally safe. The bugs have been working everywhere they’ve been released, making them one of the most effective biological control projects ever implemented. Minnesota, which has a similar program, says its bio-control purple loosestrife program saves the U.S. Department of Agriculture and the Minnesota Department of Natural Resources about a million dollars a year. The return on investment amounts to $36 in benefits for every dollar invested.

An out-of-control alien

Another case in point involves the Asian lady beetle (Harmonia axyridis), a native of eastern Asia, which was introduced to the United States by the U.S. Department of Agriculture as a biocontrol for aphids and scale insects. It was originally released in Pennsylvania in 1978 and 1981, but the first overwintering beetles were not recorded until 1993.

Public Domain

The “Tamarixia radiata” production team harvests the ectoparasitoid wasps from rearing cages as part of the biological control efforts against Asian citrus psyllids, the vector of citrus greening.

Since 2000, however, populations of the beetle have been increasing uncontrollably in the U.S. and Europe. Germany, especially, has seen a rapid proliferation, and conservationists fear that the Asian lady beetle will outcompete native beetle species. German scientists have now found the reason why this insect is so successful. Apart from strong antibiotic substances and antimicrobial peptides, its body fluid contains microsporidia, which are tiny, fungus-like, protozoa body cells that can cause immense harm. While the Asian lady beetle is obviously resistant to these parasites in its own body, transferred to native species, the cells can be lethal.

So far in the United States, the greatest damage caused by Asian lady beetles is the discomfort they give to homeowners. By the tens of thousands, the beetles tend to congregate in attics, ceilings and wall voids. Due to the warmth of the walls, they will move around and exit into the living areas of the home. In addition to their biting, they exude a foul-smelling, yellow, defensive chemical that will sometimes cause staining on walls and other surfaces. Some people have reported experiencing an allergic reaction and sinus and skin irritations to the excretions.

Introducing foreign DNA

According to the World Health Organization, there are no vaccines or cures for dengue or chikungunya. Although right now U.S. cases remain rare, 50 million people annually worldwide get sick with dengue, and the disease kills 2.5 percent of the half million that get severe cases. Chikungunya infected a million people across the Caribbean last year.

Natives of eastern Asia, Asian lady beetles were introduced to the United States by the U.S. Department of Agriculture and used as a biocontrol for aphids and scale insects. However, their increasing numbers have now gotten out of control. ©Pavel Kirillov, flickr

Throughout the Florida Keys, insecticides are sprayed year-round from helicopters and on the ground. But since Aedes aegypti don’t travel much and are repeatedly doused with the same chemicals, they have evolved to resist four of the six insecticides used against them.

Oxitec says that in 2012, it released 3.3 million modified mosquitoes over six months in the Cayman Islands, suppressing 96 percent of the targeted bugs. It also claims that a later test in Brazil was just as successful, and both countries now want larger-scale projects.

Some worry, however, about the negative consequences that could result if foreign DNA entered a person’s bloodstream after being bitten by an Oxitec mosquito. Even though Oxitec says only nonbiting male mosquitoes would be released, it is inevitable that some females will escape. And, as with the Asian lady beetle, it remains to be seen what the long–term effects of having an alien—and bioengineered—insect among us will be.

Could some introduced, nonnative species prove beneficial to the environment? ©John T. Andrews

Do you think alien species should be used as biocontrols if they can help native species survive?

Here’s to finding your true places and natural habitats,