In a November article on the BBC News, Dr. Matthew Cock, chief scientist for CABI, a UK-based agri-environment research organization, presented his list of the worst plant pests that threaten crops throughout the world. His intent was to raise awareness of the diversity of pests and diseases that threaten crops, not to recommend where government funding should go. If you would like more information about Dr. Cock or to address him with your concerns, go to his Plantwise blog.

The list below does not necessarily represent the priorities of the Southern Region IPM Center.

THE LIST

Worst historical pest:

• Desert locust, Schistocerca gregaria, an insect that flies in from time to time, consumes a very wide range of crops and strips a field bare in an hour.
• Human beings, for introducing invasive pests to habitats both accidentally and sometimes deliberately (as in the case of witches’ broom disease of cocoa in Brazil)

Hardest pest to control:

• South American rubber blight, Microcyclus ulei
• Coffee wilt disease, Fusarium xylarioides

Most expensive pest to control:

• Western corn rootworm, Diabrotica virgifera, a highly resistant pest to GM crops, although there are recent signs that resistance may be breaking down.

Pest of greatest human impact:

• Potato blight, Phytophthora infestans, which caused the Irish potato famine (1845-1852), decreasing the population in Ireland by 24%.
• Coffee leaf rust, Hemilaea vastatrix, said to have led to the switch to tea drinking in the UK.

Worst stored product pest:

• The Khapra beetle, Trogoderma granarium, which feeds on a variety of dried materials and is resistant to insecticides. Infestations can cause up to 70% grain loss.

Worst climate change threat:

• Mountain pine beetle, Dendroctonus ponderosae, which has killed 13 million hectares of lodgepole pine forest in British Columbia, Canada, releasing an estimated 270 million tons of carbon.

Most imminent threat:

• Wheat stem rust strain Ug99, Puccinia graminis tritici

Most resilient pest:

• Colorado potato beetle, Leptinotarsa decemlineata, which has developed resistance to 52 compounds belonging to all major insecticide classes.

For the entire article and explanation, go to the original BBC article.

That’s where adelgid populations are highest, the study found. Results of the study were published in the December issue of the Journal of Economic Entomology.

To combat hemlock woolly adelgid (Adelges tsugae), many researchers have released two species of beetles, Laricobius nigrinus and Sasajscymnus tsugae, which eat the adelgid. The beetle releases have been fairly successful at controlling the adelgid each year, but populations must be replenished at the beginning of each season, and the beetles are expensive to rear.

Scientists raise the beetles on infested hemlock branches that are kept alive with a mixture of insecticide and fertilizer. When a significant population of beetles is on the branches, the branches are tied to the lower third of infested hemlock trees.

That, the study says, may be one of the reasons why beetles do not survive from year to year. Their prey—the adelgids—seem to populate the upper third of the tree instead. Scientists have not studied how the beetles move to find their food, but they say that the larvae remain rather stationary, and many of them do not survive.

The beetles face a number of challenges depending on the location of the forest. Hemlocks die quickly after the initiation of an attack—often no more than three years—and as tree health fades, adelgid populations diminish. In areas with colder winters, adelgid populations often die back in winter, leaving little food for beetle predators. Finally, unlike adelgid populations, which seem to stay massive despite declining forest health, beetle populations have not been able to reach a mass significant enough to help them overwinter.

Other pest management strategies for hemlock woolly adelgid include imidacloprid injections, which are not always appropriate and are prohibitively expensive, and resistance breeding, research on which is being conducted by the Alliance for Saving Threatened Forests.

The research team observed two of the hemlock woolly adelgid’s three generations: the progrediens—wingless females that lay eggs and feed on the needles—and sistens—nymphs that develop from the eggs and eventually overwinter into adults. (see the Canadian Food Inspection Agency website for a more detailed description of the adelgid’s life cycle)

Results showed that adelgid ovisacs (egg sacs) were more abundant in the upper third of the tree crown than in the lower crown. Researchers found fewer progrediens and their eggs in the lower crown than in the upper and middle crown. Sistens populations were significantly greater in the upper crown than in the lower crown. Sistens densities were also greater in the upper crown when adelgid infestations were low or had just begun.

“Most predator releases have been made on the lower third of the hemlock tree crown,” quotes the article. “Although adult predators can fly, their ability to locate and colonize branches based on adelgid density is not well-understood. Because larval mobility is limited, predator larvae might have a greater chance of survival if placed on shoots having a patch of high adelgid density.”

When they compared the location of new growth to the area of the tree, the team found that new growth was not concentrated in the upper third. This finding made the location of adelgid densities more remarkable, since other studies have concluded that adelgids prefer the new growth over mature branches.

Concentrating predator releases in the sector where more adelgids are likely to live may increase the chance of survival and reproduction for the beetles, which co-author Kris Bramen says are like “diamonds over the canopy.”

The University of Georgia press release is available online at http://news.uga.edu/releases/article/uga-study-offers-hope-for-hemlock-attack/.

The Journal of Economic Entomology article is online at http://www.bioone.org/doi/full/10.1603/EC11022.

In the Ngara district in northwest Tanzania is a small village with some of the ideal conditions for mosquitoes. Villagers lack the income to pay for the typical mosquito protection. Many are wary of chemical sprays used on their property or inside the house. Because the village was nearly ideal for mosquitoes, it was also ideal for a group of British researchers who wanted to test the effectiveness of an exotic invasive plant on repelling mosquitoes.

The idea of using one pest to control another is not new; however, using an exotic invasive plant to control a pest insect presented a new set of problems, as the research team discovered. The experiment also raises the recent debate over whether exotic invasive plants have any redeeming value in an ecosystem.

In Tanzania, the typical technology for mosquito prevention is a process called house screening. House screening involves modifications to a house including physical screens and insecticide treated curtains. Although the practice is common in urban areas, many people in the poorer rural areas cannot afford the $25 to implement the screening. In addition, many of those families live in mud brick houses where screens are not practical.

Lantana camara

So in 2008, scientists from a large Tanzanian nonprofit, Concern Worldwide Tanzania, and from universities in London, England, decided to test the efficacy of plants known to have chemicals that repel mosquitoes. Their findings were published in a peer-reviewed article in PLoS ONE in October 2011. The scientists experimented with planting Lantana camara, an aggressive, non-native weed that grows rampant in eastern Tanzania.

The Ngara district is popular to migrating refugees from Burundi and subject to migrating Tanzanians seeking more land. The district is located in the Kagera region of Tanzania, one of the most remote regions in Tanzania, where 33% of the households fall below the poverty line. According to demographics collected during the study, most families had lived in the village for fewer than 5 years. The majority were also subsistence farmers, had low levels of education and had little disposable income. Many villagers were familiar with mosquito control and prevention, but several were not. Malaria-carrying mosquitoes are endemic to the region; in fact, a mosquito collection in 2008-09 revealed a plethora of Anophales gambiae mosquitoes, the vector for African malaria.

The study team was seeking a method of mosquito control that would be simple for villagers to use and affordable enough for them to be practical. Lantana contains caryophylene and alpha-pinene that are known to repel mosquitoes. Plants can be purchased for $1.50, and because the species is invasive, it is easy to grow but must be regularly pruned.

The team collected data for one year and had to discontinue the study after the government began their own mosquito spray program in the district. The data showed some modest reductions in mosquito populations, but they team had not collected population data before and after planting, so they could not attribute the reductions specifically to the Lantana.

Concern Worldwide planted Lantana only at 231 houses whose residents had requested the plants, and they collected data from 90 additional residents with no repellent plants. Reactions to the plants were mixed; some residents thought Lantana had reduced the number of mosquitoes around their home, while others complained about the amount of labor it took to keep the plants from becoming overgrown. One owner of a banana plantation removed the plants after he said that they invaded his fields and reduced his banana yield.

As has been found in other studies, knowledge about mosquitoes and prevention strategies varied. The baseline survey included a question about how malaria could be prevented, to which 41% of participants mentioned bednets and 14% mentioned filling in puddles. However, 12% thought that eating cleaner food could prevent malaria, and 21% did not know how to prevent it. In fact, only 81% of participants knew that mosquitoes caused malaria, and 60% knew that mosquitoes bred in standing water.

In terms of preventing mosquito bites, most residents said that they covered themselves in long clothes (79%), and 52% used bednets. However, 53% of residents did not have a bednet at all—one percent more than those who claimed to use one.

Probably the most interesting—and troubling—finding involves the attitudes of the majority of residents toward mosquito and malaria prevention. According to the data, residents perceived malaria as an inevitable part of life, while having to do additional labor to control an aggressive plant was considered a serious impediment to their quality of life. Researchers noted, however, that the increase in labor would need to be studied, especially since many children are involved in household labor. In addition, the study noted that the plants should be used in concert with other mosquito control technologies, not relied on as the sole pest management strategy.

In the United States, our war against exotic invasive plants involves issues much less opaque. Weeds typically reduce our quality of life, whether they are choking native vegetation in a public forest or reducing crop yield on a farm. Most families in the U.S. can afford some kind of spray for mosquitoes, and those who prefer not to spray deal with a pest that is, for the most part, just an incredible annoyance. It’s not often that we have to decide between preserving the health of native vegetation or saving people’s lives.

This post is not here to point out the benefits of invasive plants. Clearly, for the most part, their costs far outweigh any advantages. I pose the debate here purely for the sake of discussion and to tender a reminder that in some situations, the solutions are not always clear cut.

Most of us don’t think of invasive species in terms of their disappearance. In fact, the term “invasive” implies a conquest of sorts, taking over an ecosystem from insect, animal or plant inhabitants that already live there. However, according to Dr. Meghan Cooling, an ecologist at the Centre for Biodiversity and Restoration Ecology in Wellington, New Zealand, invasive species are susceptible to population collapse, sometimes regardless of whether or not they are managed.

Argentine ant

Native to South America, the Argentine ant (Linepithema humile) is listed as one of the world’s worst invasive species. Colonies are usually large, and the ant displaces competing ant colonies, including fire ants (NCSU Insect Note). Argentine ants have been in the United States since the late nineteenth century, and are a serious problem in the southeastern and southwestern U.S.

First observed in New Zealand in 1990, Argentine ants have spread through the country, largely through accidental introductions by travelers. Some scientists have speculated that the species’ survival depends on warm temperatures, and currently Argentine ants inhabit regions that have more temperate climates. The climate in New Zealand varies from north to south; northern New Zealand has almost a tropical climate, while temperatures drop further south (and farther from the equator). Dr. Cooling and her team concentrated their research in Auckland, which is near the northern tip of New Zealand.

Cooling and her colleagues wanted to know how invasive insect species such as the Argentine ant might respond to future warmer temperatures as climate change progresses, especially in areas with more temperate climates. First, they posed the question about the present persistence of Argentine ant colonies and how climate variables like temperature and rainfall contributed to colony survival or collapse. Second, how might the warming temperatures associated with climate change affect ant colony collapse? And after colonies have collapsed, can the ant species that they displaced repopulate the area?

The team used three types of ant communities in Auckland, New Zealand, in their experiment: communities with high populations of Argentine ants, communities where Argentine ant colonies had disappeared, and communities that had never been invaded with Argentine ants. In January and February 2011, the researchers observed 150 locations where ant colonies had been reported between 1990 and 2008. They used approved models to estimate survival and climate change. In addition, ant colonies in research areas were not managed by human intervention.

In the 150 locations observed, ant colonies disappeared from 60 of them. Of the colonies that remained, most were in areas with warm temperatures. Rainfall reduced ant colony survival.

Climate change model predictions indicated that Argentine ants may be more likely to survive in areas that currently were seeing colonies collapse. In fact, prediction maps locate ant colonies in New Zealand, based on a climate change model, much further south than colonies are currently surviving. However, Dr. Cooling states that areas where Argentine ant populations have a greater than 80 percent chance of surviving for 15 years increases only from 0.25 to 1.29 percent with warming temperatures.

The team observed that areas that had seen a collapse of Argentine ant colonies were now rich with diverse species of native ants; in fact, native ant species in areas where Argentine ant colonies had disappeared were indistinguishable from areas that had never had Argentine ants.

Controlling Argentine ants had been predicted to cost the country up to $68 million per year. Cooling says that New Zealand may be able to save that money if colonies continue to disappear on their own.

However, she admits, the evolution of Argentine ants in New Zealand is not necessarily a model to be applied to other species or countries.

“Other invasive species and climate change clearly contribute to the current global biodiversity crisis, and their costs may be substantial,” she writes. “Determining which species are susceptible and the mechanisms for these collapses should be a high priority for invasion biologists.”

Source: Cooling, M., Hartley, S., Sim, D.A., and Lester, P.J. “The widespread collapse of an invasive ant species: Argentine ants (Linepithema humile) in New Zealand.” Biology Letters, 30 Nov 2011, DOI: 10.1098/rsbl.2011.1014. Online.

In the November/December issue of Sierra magazine, writer Nate Seltenrich raises the topic of Christmas tree pests with a short article about Phytophthora cinnamomi, a root mold that affects not only Fraser fir, but other trees as well, including chestnut, avocado and other firs.

That article brought to mind several other diseases and pests that Christmas tree farmers fight every year. You most likely won’t see symptoms of these pests and diseases when looking for a tree, but some symptoms don’t show up until well after Christmas is over. Therefore, although these problems should not influence your Christmas tree purchasing, you may reconsider the fate of the tree after Christmas.

Diseases

Sand pine with p.cinnamomi. Photo by Edward L. Barnard

Phytophthora cinnamomi: Since I’ve already brought it up, I figured I’d start with this one. P. cinnamomi is a root-rot pathogen that causes certain death once it has infected a plant. The pathogen originated in Papua New Guinea and spreads through the soil, so infected trees that are planted can spread the infection to other susceptible plants. According to Seltenrich, the disease originally plagued the Southeast but is beginning to move north.

Rhizosphaera pini: Although not found in the southern US, R. pini is a common plant pathogen in the Lake States, Northeastern States and Canada. R. pini is often considered to be a weak pathogen, occurring on stressed foliage or foliage killed by other causes. However, it has been observed causing significant damage on balsam fir and Fraser fir. It appears to be particularly damaging in shaded, damp areas and when the trees are under other stress. (Source: Forest Service Pest Alert)

Insect pests

Bent tops caused by balsam woolly adelgid

Balsam woolly adelgids (Adelges piceae): BWA is native to central Europe and was discovered in the southern Appalachians in the 1950s, where it had already destroyed acres of Fraser fir in the Mount Mitchell area. Research is currently being done to produce BWA-resistant Fraser firs both for Christmas tree and to supplement regrowth in the North Carolina mountains. See the Alliance for Threatened Forests website for more information.

BWA infested trees do not develop symptoms for several months; however, the insects themselves are visible as adults during the summer. They appear as small cotton-like pinpoints on the trunk of Fraser fir. One of the first symptoms of BWA attack is a crooked top (see photo). Other symptoms include dead branches, swelling around the shoot nodes, a stiff trunk and growth rings with red, hard wood instead of the usual white wood. BWA is typically treated in the Christmas tree farm with insecticides, but it is very expensive to control. If you live in an area where BWA is present (see map), consider discarding your Fraser fir after the holidays are over rather than replanting. Christmas tree farmers must use more pesticides to treat their trees if they are near untreated residential trees.

Symptoms of balsam twig aphid

Balsam twig aphids (Mindarus abietinus): These aphids are small, pale green insects that feed on fir and spruce in the spring. Symptoms of past infestation are curled needles and stunted growth, although heavy damaged trees are usually not sold.

Spruce spider mites (Oligonychus ununguis): These tiny mites suck sap from the needles. Infested needles look speckled when viewed up-close, and as the number of mites increases, needles can turn bronze or brown in color. Most growers practice strategies that reduce the incidence of infestation from these mites.

Symptoms of spruce spider mites

Rust mites (Nalepella spp.): These tiny mites are not visible to the naked eye; you need a hand lens or microscope to see them. Damage usually occurs in the summer, where infested needles turn brown and die, and often are confined to one area of the tree.

Rosette Bud Mites (Tricetacus spp.): These mites cause deformed buds on Fraser fir, rounded instead of pointed. The buds do not break in the spring, and if they do, they form weakened shoots. A tree with several of these buds will develop holes in the canopy and typically is not sold.

Nothing can be warmer and homier than the smell and sight of a real Christmas tree. Below are more links to webpages with tips on how to choose and care for your real Christmas tree. After the holidays, though, you may want to inspect your tree for signs of any of the above pests and diseases, and if you’re unsure, it’s best to leave that tree by the curb for pickup than to plant it in your backyard and risk affecting neighboring trees, especially if you live near a Christmas tree farm.

The information about insect pests comes from NC State University’s webpage on North Carolina Christmas Trees.

For general information about choosing a Christmas tree, see http://www.ces.ncsu.edu/fletcher/programs/xmas/xmas_treetypes.html

For tips on where to buy your real tree, see http://www.ces.ncsu.edu/fletcher/programs/xmas/xmastreefinder.html

For information about how to judge the freshness of a market Christmas tree, see http://www.ces.ncsu.edu/fletcher/programs/xmas/treefreshness.html

Designing, maintaining and operating buildings and grounds with pest prevention in mind is an enormous time and money saver! Here we focus on doors, windows, exterior lighting and landscaping in new construction and existing school buildings.

According to Dr. Michael Merchant, professor and extension urban entomologist at Texas AgriLife Extension Service, pests are much like people in that “Doorways are probably the number one entry point for pests into a school.” It’s important to ensure that all doors are well designed and installed, and are equipped with either rubber or nylon brush door sweeps. All doors should be inspected after installation, ensuring that there are no gaps or spaces around the frame and the door closes tightly. Dr. Chris Geiger, municipal toxics reduction coordinator for the San Francisco Department of the Environment, emphasizes that doors should have no more than 1/4 inch of clearance. If you can slide a pencil under the door, the gap is too big. University of Florida data shows that effective door sweeps alone can cut pest complaints by 65%!

In addition to making pest access into the building more difficult, door sweeps also block air flow, keeping dirt out and reducing heating and cooling losses. Self-closing doors can be used to prevent doors from being left open inadvertently. Dr. Merchant asserts that schools need to take responsibility for these details; architects and building contractors simply don’t have pest prevention at the top of their priority lists.

Windows are another common pest entry point. All windows should be tight-fitting and should include well-maintained screens. An article by Sewell Simmons in the Journal of School Business Management entitled “Pest Prevention Construction Guidelines and Practices ” states that, “Screens on windows, crawl spaces, and vents are often damaged in school buildings. Check these carefully for needed repair or replacement.” Dr. Geiger suggests looking into Teflon coatings or bird repellant gels for exterior window ledges, which may provide a surface that’s too slippery or sticky for birds to roost comfortably.

School IPM 2015: A Strategic Plan for Integrated Pest Management in Schools in the United States recommends that “weep holes, or openings in masonry to allow moisture to escape, are screened to prevent pest access, e.g., stinging insect nesting.” Fine net screens or stainless steel batting can be used to prevent pest entry through weep holes, as long as they allow water to escape.

Lights Out on Pests!

We’re all familiar with how insects can be drawn in by sources of light at night. Since doorways are so critical to keeping pests out, sources of light should not be mounted above doorways, but rather on poles away from the building, with the light directed where needed. The International Dark-Sky Association provides guidelines on lighting that reduces light pollution. Low-UV-production bulbs, such as yellow insect Quick Links School IPM 2015 Homepage Get Involved! About School IPM 2015 Make a Contribution! lights can help reduce attraction. Sodium vapor lights are also an option, however these require special light fixtures rather than simply replacing a bulb.

Pest-Free Landscaping

One of the easiest mistakes to make in landscaping is choosing plants based on their dimensions when planted, rather than size at maturity. Shrubs are often planted too close together, obscuring the ground and creating harborage for rodents and insects. Low-growing vegetation that conceals the ground encourages rodents and insect problems. Trees can grow into power lines or too close to buildings, allowing branches to provide easy access for insects and animals to buildings. Tree and shrub branches should be kept at least six feet away from structures, and ten feet if tree squirrels are a problem.

Decorative elements such as lattices and vines climbing up the side of buildings can also provide bird roosting sites and a handy ladder for roof rats–avoid these if possible. Dr. Merchant also suggests choosing native plants and those that are well-adapted to your area. These varieties may be more resistant to the common pests in your locale, requiring less pest prevention and elimination. If you have questions about pest-resistant plants, consult your cooperative extension service for recommendations.

Sidewalk cracks can provide an ideal place for weeds to thrive, and can also act as pathways for insects such as ants. Any cracks should be filled with an appropriate sealant or concrete. Dr. Geiger suggests installing concrete, brick or paver mowing strips under fences and around buildings and plantings to prevent weeds from growing in locations that can’t be easily mowed. Mowing strips save on labor and reduce the need for pesticides to control weeds in unmowable areas.

Good moisture control can help with the management of subterranean termites, carpenter ants and some wood-boring beetles. Simmons’ article provides good tips for reducing moisture, such as using moisture barriers in both above-ground and slab foundations. Additionally, all exterior grades should be sloped away from the building to provide good drainage and prevent moisture from building up. Sprinkler irrigation heads should be aligned and/or shielded to keep spray from hitting buildings. Foundation wall vents should be included to provide cross-ventilation for buildings with crawl spaces.

In the early 1900s, for instance, insects and parasitoids were sometimes released after little testing on nontarget effects. As a result, the biocontrol agents often found meal sources that were more appetizing than the ones they were supposed to eat—and sometimes became a threat to a native insect or plant.

To combat the gypsy moth in 1906, for example, the parasitoid Compsilura concinnata was released in North America. Scientists knew that C. concinnata was polyphagous (pursued multiple hosts) but though that their variable appetite would ensure greater success in controlling the moth pest. Instead, C. concinnata attacked several native moths, including giant silkworm.

Florida cactus inadvertently became the preferred diet of Cactoblastis cactorum, released initially in Australia in 1926 to control prickly pear. The predator moth was so successful at lowering the prickly pear population in Australia that scientists released it in 1957 on Nevis Island in the Caribbean, close enough to the Florida coast for the moth to travel to the state and feed on several native cacti species, one of which it extinguished.

More recently (1990) a European thistle weevil, Larinus planus, was released into several western states to control Canada thisle.  By 1999, L. planus was feeding on a rare thistle species in Colorado, while ignoring the Canada thistle growing nearby.

Evens such as these led scientists to adopt new practices that would limit the chances of a biocontrol agent to attack a nontarget population. Scientists introducing biocontrol agents for weeds must present, to a federal panel, a detailed plan for host range testing based on specified protocols.

Procedures for testing biocontrol agents for insect pests do not involve a federal panel, but scientists often carefully screen close relatives of the target organism to see if the biocontrol agent will attack it, given no other food option. Organisms that adapt readily to hosts other than the target are typically rejected for use.

However, each organism presents its own risks as soon as it is released into the natural environment. In the controlled environment of a laboratory, with a limited time period, scientists cannot observe or predict how an organism may adapt over a period of years, after it has reproduced several generations and adjusted to its new climate and surroundings. The question asked is always, “do the benefits outweigh the risks, or are the possible consequences not worth the risk?”

Contrary to my usual conclusions, I’m not going to make one in this argument. I want to let those who are interested to guide the discussion. You may be a passionate advocate of biocontrol. Or you may have seen some of the past damage and now fear every biocontrol implementation. As is true with many IPM practices, there are no universal right or wrong answers. Each scientist must decide how to handle each case individually and decide what may work for today.

Genetically Modified Mosquitoes Could Be an Important Tool in the Fight against Disease
By Mark Q. Benedict

Current technologies we use against mosquitoes simply are not adequate: existing measures are losing the war. The choice of implementing GM mosquitoes is not a choice of no risk versus risk, it is a matter of choosing the least risky among all existing choices in a war against very real continuing disease risk. Read more.

The Danger of Genetically Modified Mosquitoes
By Helen Wallace

The release of genetically modified (GM) insects should follow a precautionary approach, because what appears well understood in the lab can have unintended consequences when released on a large scale into the environment. On release, GM mosquitoes become part of a complex system involving predators and prey, other mosquito species, four types of dengue virus, other tropical diseases transmitted by mosquitoes, and the humans—including children—who are being bitten and infected. Read more.

Exotic invasives, whether they are insects, diseases or weeds, cause about $100 billion in damage every year. In public settings such as state forests, pest management specialists use extreme caution when using pesticides. Because of visitors, trees cannot be sprayed. Some infested areas are near streambeds or other areas where rare or endangered species live, species that may be sensitive to the chemicals. Some chemical pesticides persist in the soil, making them unsuitable for use in ecologically sensitive areas. On farms, consistently using pesticides, especially where only one or two have been labeled for use on a crop, encourages pesticide resistance and can eventually become useless for controlling the pest.

Every insect has a natural enemy. One of the main differences between native pests and exotic pests is the proximity of the enemy. For a pest indigenous to the U.S., for instance, specialists search for natural enemies within the immediate area. For a population of thrips attacking a fruit farm, for instance, many specialists will recommend that the grower use pesticides sparingly to conserve the natural enemies (usually lady beetles). Pest insects seem to develop resistance to chemical pesticides long before beneficial insects do.

In Texas, extension specialist Monti Vandiver encourages his growers to scout their fields for insects, both destructive and beneficial. In one instance, he encouraged a cotton grower to delay spraying for cotton thrips because he noticed a population of ladybugs developing nearby. In a week, the ladybugs descended on the thrips and annihilated the population. The cotton field was saved without a single spray. Read the story.

The enemies of an exotic invasive are usually in the invasive’s native land, too far away to help control the pest in the U.S. In those cases, scientists will return to the insect’s native land and try to breed a population of natural enemies, studying the natural enemies under several different situations to be sure that the new insect does not become a pest in a new country.

To control the invasive fire ant, for example, scientists traveled to the ant’s homeland of South America to find the phorid fly. In South America, fire ant populations are only 20 percent of what they are in the U.S. Auburn University has been at the forefront of finding predators and fungal diseases to control fire ants and has released phorid flies in several counties, with success. These biocontrol technologies are helping to reduce fire ant populations to lower the amount of chemical applications necessary to pour on fire ant mounds.

The Cornell University site has a few additional success stories about invasive pests that are currently being managed through biological control methods.

However, as any other intervention, biological control has risks. Next week I’ll look at some of the risks of biocontrol.

Although the news of O’Neill’s discovery and plan for release was generally well-received, some public radio listeners expressed concern about a new virus in the environment. Responses to NPR’s blog echoed some typical concerns about biological control in general. Are we unleashing a new threat into the environment? What if we can’t control the new virus?

The comments gave me a great excuse to write a blog post (or three) on biological control, or biocontrol, as those of us in the IPM field call it. This series is not going to be propaganda on why you should believe in biocontrol; the series will tell you what biocontrol is, why it’s used, it’s risks and it’s benefits.

What IS Biocontrol?

In their native environment, insect pests typically have natural enemies that control their population naturally. Unless the pest populations have very high numbers, people don’t usually need to add other types of control. Even if pesticides are used, fairly low amounts are needed because they are augmenting the natural control already in place. For instance, lady beetles keep native aphid populations low enough that farmers spend little on pesticides.

However, when an insect pest is not native, it has no natural controls. In addition, some of them have protective shells or seek cover in seeds so that pesticides can’t reach them. Left unchecked, those pest populations can grow to devastating numbers. Prime examples are the hemlock woolly adelgid, the emerald ash borer and the Asian longhorned beetle. In those cases, biocontrol is an option for controlling the pest, by bringing the enemies from the pest’s native land into the new area. Biocontrol is the reduction of pest populations by the introduction of natural enemies through artificial means. (Cornell University, Biological Control)

Natural enemies exist in three groups: predators, pathogens and parasitoids. Predators are insects that consume other insects and therefore control their populations. Pathogens are disease-causing organisms such as bacteria, fungi and viruses. Parasitoids are insect species that develop inside of another insect host, killing the host.

Effective natural enemies should be able to reproduce quickly and multiply numerously, consume one prey or host species, be able to adapt to various environmental conditions and be able to adapt as its prey or host adapts.

The Cornell University website goes into depth about the different types of biocontrol; however, I’m going to focus on the type that seems to cause angst when it is publicized: classical biological control, which involves bringing predators from the pest’s native country in to the U.S.

How Biocontrol “Agents” are chosen

The process for classical biological control is quite extensive; scientists first must study the pest itself, figure out where it came from, and then visit the pest’s origin and observe its interactions with its environment. Hemlock woolly adelgid, for instance, is not as devastating in its native Asian home as it is in the eastern mountains of the U.S., because it has predators that feed on it and the Asian hemlocks have developed a tolerance to the adelgid’s bite.

Once scientists have learned enough about the pest’s native enemies to understand how they might control the pest, they begin a long process of testing the enemy. First, the scientist must apply to the US Department of Agriculture, Animal and Plant Health Inspection Service (APHIS) for a permit to study the “biocontrol agent” in quarantined conditions, usually in the pest’s native country. Next, the scientist must find climates that match the climate the insect is infesting. The scientist will collect the biocontrol agent population from that area.

The scientist will then spend copious amounts of time making sure that the pest insect is the only insect that the biocontrol agent will attack. To study this, the scientist places the biocontrol agent in an isolated chamber with another species that has similar characteristics to the pest insect. Optimally, the biocontrol agent will die rather than consume insects other than the pest insect. If the biocontrol agent attacks several species (called “non-target species) in addition to the pest species, the biocontrol agent is usually not introduced, or it may be introduced in countries where the non-target species do not exist (Van Lenteren, 2009). Biocontrol agents that attack weed species go through a separate screening by a panel of government agencies, to reduce the risk that the natural enemy will destroy non-target rare plant species (Orr).

Typically before a biocontrol agent is released into the environment, it must satisfy several conditions:

• Establishment should be short-term, based on the existence of the pest
• It should not attack valuable non-target organisms
• Dispersal should be moderate or local
• Effects from the biocontrol agent’s presence should be limited and short-term rather than permanent. (Van Lenteren, 2009)

If the scientist is satisfied that the risks to releasing the biocontrol agent will be minimal, he or she will begin to introduce the agent to the environment. It takes most satisfactory biocontrol agents several years to become established.

Sources:

Biological Control: A Guide to Natural Enemies in North America. Cornell University College of Agricultural and Life Sciences, http://www.biocontrol.entomology.cornell.edu

Van Lenteren, J.C., Bale, J., Bigler, F., Hokkanen, H.M.T., and Loomans, A.J.M. “Assessing Risks of Releasing Exotic Biological Control Agents of Arthropod Pests.” Annu. Rev. Entomol. 2006, 51:609-34.

David Orr, NC State University entomology faculty, personal communication, Aug. 31, 2011

Next: The Risks of Biocontrol