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Protecting and providing habitat for beneficial insects is the first step in conservation biocontrol. Unless beneficial insects are also protected from insecticides, however, their populations may never increase enough to make a significant contribution to pest control.
The concept of Integrated Pest Management (IPM) provides a decision-making framework for reducing pesticide use in both conventional and organic farming systems. IPM employs a four-phase strategy:
The goal of IPM is to reduce pesticide use while still controlling pest populations below economically damaging levels. Conservation biocontrol can be a core component of the first phase of IPM, in which a farmer works to reduce conditions that favor pest populations.
When truly adopted, IPM can help protect beneficial insects, the environment, and you, your family and your farmworkers from unnecessary pesticide use. Cooperative Extension staff can assist with the development of farm-specific IPM programs, and financial support for transitioning to IPM is available through the USDA Natural Resources Conservation Service (NRCS).
Organic farming practices are typically much safer for beneficial insects. Keep in mind, however, that even some organic-approved insecticides can harm beneficial insects.
Insecticides have an impact on beneficial insect populations, whether it’s because the poisons kill the insects directly or because they persist in the landscape, causing sublethal effects that inhibit foraging and reproduction among beneficial species. Even herbicides, which do not directly kill insects, can kill native grasses and wildflowers that host beneficial insects and reduce the amount of foraging and egg-laying resources available.
If you must use insecticides, try to apply them only when beneficial insects are not active. Many beneficial insects prefer warm daylight hours for active feeding, so nighttime spraying with active ingredients that have short residual toxicities is a simple strategy for reducing harm. Note, however, that residual toxicity of many insecticides can last longer in cool temperatures, and dewy nights may cause an insecticide to remain active on the foliage the following morning. Also note that some very important pest predators, including most predaceous ground beetles, are nocturnal.
New research is demonstrating that under some circumstances neonicotinoid insecticides are extremely persistent in the environment, with residues sometimes remaining active for years after they were originally applied. Additionally, neonicotinoid concentrations may increase to very high levels in perennial plants that are treated year after year, although how widespread the phenomenon is remains unknown. Finally, there are concerns about flowering weeds absorbing neonicotinoids from the soil around nearby treated plants and potentially poisoning flower visitors like pollinators and other beneficial insects.
Because of these concerns, and because neonicotinoids are highly mobile in soil and water, we recommend caution if they must be used. For more information about the impact of neonicotinoids on beneficial insects, check out the Xerces publication Beyond the Birds and the Bees: Effects of Neonicotinoid Insecticides on Agriculturally Important Beneficial Insects, available at: www.xerces.org/pesticides.
Even when you’re careful, insecticides will affect beneficial insect populations. When insecticide use is unavoidable, use products with the lowest possible impact on beneficial insects.
Insecticide labels may list some of the known hazards to beneficial insects. If this information is absent, toxicity information about honey bees, if available, can help you identify how relatively toxic a particular product may be to other beneficial insects. However, some products that are not toxic to honey bees may be toxic to beneficial insects, given that many beneficial insects are much smaller than honey bees and are affected by lower doses of pesticides. Also, unlike honey bees, predatory and parasitoid insects forage wherever their prey populations reside, including where no flowers are present. If they continue to feed on prey dying from pesticide exposure, they or their offspring may die as well.
The best approach to insecticide selection is to choose products, when possible, that are toxic to only a narrow range of insect species. For example, Bacillus thuringiensis (Bt) is a natural bacterium with many strains, each of which is toxic to a specific group of insects; Bacillus thuringiensis var. kurstaki (Btk) typically is used to control various moth caterpillars. While such selective insecticides may not prevent all harm to nontarget insects, they are a better choice than chemicals with broad-spectrum toxicity to all insect groups. For more information on Bt, see Microbial Insecticides and Nematodes (next page).
A newer class of insecticides, known as neonicotinoids, has been promoted in recent years despite being toxic to a wide range of good and bad insects. Because of their low toxicity to mammals, these chemicals have been widely embraced by various agricultural and landscape industries. Neonicotinoid products mimic the toxins found in nicotine, and are applied as seed and root treatments, foliar sprays, and trunk injections. The chemicals are then absorbed and transported by the vascular system throughout the plant. Research demonstrates that these chemicals are sequestered in flower nectar and pollen, and nectar- and pollen-feeding insects such as lacewings, parasitoid wasps, and lady beetles may be poisoned as a result. Predatory beneficial insects can also be exposed and harmed when they ingest pests that were exposed but not killed. It is unclear whether neonicotinoids can be integrated with biocontrol. Because of the long-term impacts of these products on beneficial insect populations, we recommend avoiding their use when possible.
Finally, the popularity of organic farming has been increasing at a tremendous rate. However, it is important to note that even organic pesticides can harm beneficial insects. Some organic-approved products are just as lethal as conventional insecticides. Pyrethrin and spinosad, two common pesticides used in organic farming, are broad-spectrum insect killers, destroying pest and beneficial species alike. Some other organic-approved products are safer to use as long as they are not applied where beneficial species are active. Those less-toxic pesticides include horticultural oils and insecticidal soaps.
If pesticide labels list a risk to bees, they should be considered potentially harmful to all beneficial insects. The dead bumble bees in this photo were killed when they were exposed to a neonicotinoid insecticide present in the nectar of blooming trees.
As an alternative to synthetic insecticides, some farmers use microbial insecticides consisting of bacteria, fungi, viruses, or even nematodes for pest control. Most of these products are allowed under organic certification standards, and they are often touted as being safer than conventional insecticides for beneficial insects.
In some cases, this is true. For example, most formulations of the naturally occurring soil bacterium Bacillus thurengensis (Bt) are selectively toxic to different groups of insects; the bacterium creates holes in the gut wall of insects that feed on it, releasing those gut contents into the bloodstream. Most commercial Bt products consist of a specific subspecies, such as B. thurengensis var. kurstaki, which only affects caterpillar pests, or B. thurengensis var. san diego, which only affects beetle larvae. While these toxins may also kill nonpests such as butterfly caterpillars or beneficial beetle species, they are at least considered safe for parasitoid wasps, lacewings, and bees.
In other cases, microbial toxins are less safe for beneficial insects. Spinosad, the active ingredient derived from another soil bacterium, Saccharopolyspora spinosa, is toxic to a wide range of insects, including bees and parasitic wasps, when they contact the spray droplets. Spinosad functions by disrupting the nervous system of insects, leading to muscle loss, eventual paralysis, and death.
Similarly, the soil-dwelling fungus Beauvaria bassiana also has variable toxicity to many different insect groups, and its effects on some beneficial insects are not well documented. Beauvaria is applied as a spray containing the fungal spores. When an insect walks across treated surfaces, it picks up the spores on its body, where they later germinate and produce threadlike hyphae that penetrate the insect’s body and result in a widespread infection, eventually killing the insect. Because it is a living fungus, Beauvaria tends to require specific environmental conditions (usually cool, humid environments) to thrive. Until more is known about the impact of different formulations on various beneficial insects, use Beauvaria with caution.
Insect viruses are available for the control of some pests such as codling moth, corn earworm, and tobacco budworm. The insecticides formulated from these viruses are promoted as being host specific, and are not documented to harm beneficial insects. However, viruses that infect other animal species are sometimes known to undergo genetic recombination that alters their virulence or host range. Because the commercial availability of insect viruses is now fairly limited, the risks to beneficial insects are probably very low. As a broad category, however, the development of new insect viruses should be approached with extreme caution to prevent unintended harm to nonpest insects.
Sprayer equipment strongly influences the potential for pesticide drift. In the case of boom sprayers, they should be operated as close to the crop canopy as possible.
Live nematodes (microscopic roundworms) are another group of infectious agents used for pest control. While there are more than 16,000 known parasitic nematodes found in soil and water, only a few species, primarily Heterorhabditis bacteriophora, Steinernema carpocapsae, and Steinernema feltiae, have been identified and commercially propagated for pest control. These nematodes tend to dwell in the upper soil profile, and are parasites of insects such as beetles and flies, often in the larval stage. Nematodes attack their hosts by sampling the air around them for the presence of insect respiration and thus locating them in the soil. Once a host insect is located, the nematode usually enters it through the mouth, anus, or a tracheal breathing tube and begins feeding, reproducing, and defecating. The latter is typically what kills the host: the host’s bloodstream is poisoned with bacteria.
Nematodes are usually commercially available combined with vermiculite for mixing into potting media, or absorbed into sponges for soaking into a tank of water. The water is then subsequently sprayed over crop fields.
While nematodes may help control a wide range of crop pests, including black vine weevils, cucumber beetles, carrot rust flies, squash vine borers, Japanese beetles, and corn rootworms, their wide host range means they are likely to attack many beneficial soil-dwelling insect species as well.
Because of this, the ultimate pest control effectiveness of nematodes may be hard to assess under real-world conditions. It may be that in field crops, released nematodes reduce pest and beneficial insect populations equally and consequently have negligible pest control value. Depending on local conditions, it is even possible that some of the beneficial insects killed by released nematodes may be suppressing secondary pests that are not the target of original nematode release. For example, if nematodes are released into a field for the control of cucumber beetles, and in the process they also reduce populations of beneficial soldier beetle larvae, then aphids, which the soldier beetles were previously preying upon, may explode in numbers.
Because of such interactions, and the uncertainty of how nematodes impact resident beneficial insect populations, we do not recommend their release. It is worth noting, however, that healthy soils with an abundance of organic matter that are protected from compaction typically have existing populations of nematodes, including parasitic species, and may already be providing natural suppression of some pests.
Some farms do not use pesticides at all to maintain crop quality and yield. As unlikely as pesticide-free farming may seem today, consider that it was the norm in the not-so-distant past. In the past, farmers used nonchemical strategies such as:
These three fundamental strategies are still used today by farmers who don’t use pesticides.
In addition, protective barriers such as floating row covers or spray-on kaolin clay emulsions now provide alternatives to pesticides. For example, apple and pear growers in Japan protect their crops with specialized cloth bags that surround each developing fruit. Amazingly, the majority of Japan’s commercial apple crop is produced this way, and special Japanese fruit bags, as well as other similar products, are becoming increasingly available in the United States.
Kaolin clay is increasingly used as an alternative to insecticides. Applied as a liquid slurry, the clay covers leaf surfaces to inhibit feeding and egg-laying by crop pests.
Row covers can exclude fruit and vegetable pests and eliminate the need for insecticides in some cases. Keep in mind, however, that they also exclude beneficial insects.
Beyond simple pest barriers, mate-finding pheromones are commercially available for some pest insects and can be sprayed near crop fields or incorporated into dispensers that are hung in crop plants. These pheromones confuse or disrupt the mating of insect pests, making it more difficult for mates to find each other. These same pheromones are often commercially available in the form of monitoring traps that attract and catch pest insects on sticky cardboard landing pads. Other, nonpheromone sticky traps capture pest insects using scents and brightly colored surfaces to which they are naturally attracted (such as red sphere traps used to catch apple maggot flies). Although the primary purpose of these traps is to monitor pest populations, they may also contribute to pest control on smaller farms.
Pheromone traps and mating disruption pheromones are nontoxic pest control strategies that target specific species and complement conservation biocontrol.
The USDA Natural Resources Conservation Service offers an Integrated Pest Management Conservation Practice, geared toward guiding farmers to adopt pest management practices that have reduced risk to natural resources. Growers interested in IPM can receive cost-share assistance, as well as technical assistance, with the implementation of IPM practices. Through this conservation practice, the NRCS may be able to help farmers work with crop consultants to develop a custom IPM plan for their farm. To learn more, visit your local USDA Service Center (http://offices.sc.egov.usda.gov/locator/app).
Crop-specific guidance on these pesticide alternatives also may be available from your local Cooperative Extension service. When these nonchemical strategies are combined with habitat enhancement for beneficial insects, the result can be farm systems with fewer pest problems.
Although you might expect that most pesticides are applied on farms, in actuality more pesticides are applied per acre in suburban settings than in agricultural areas, according to the United States Geological Survey. In 2004, the Environmental Protection Agency estimated that over 78 million homes applied garden or lawn pesticides. Beneficial insects are susceptible to many products used to kill garden or landscape pests, so reducing or eliminating pesticide use is important if you want beneficial insects for pest control.
Whenever you apply insecticides, control spray drift to prevent poisoning of beneficial insects and other wildlife in noncrop areas. Spray drift occurs when spray droplets, pesticide vapors, or windborne contaminated soil particles are carried on air currents beyond the crop field. In some cases pesticide drift may be limited only to adjacent field border areas, but even that can pose a problem if you are trying to maintain those areas as beneficial insect habitat. In more extreme cases, pesticide drift has been known to cause damage to more than a mile from the site of application. The weather, your application method, and your equipment settings can all affect the extent of drift.
Weather-related pesticide drift increases under several conditions:
In the case of windborne drift, the effects can be reduced by spraying in the early morning or evening when winds are calmer. Pesticide labels sometimes provide specific guidelines on acceptable wind velocities for a particular product.
For drift caused by warm temperature conditions, midday spraying is less desirable because as the ground warms, rising air can lift the spray particles in vertical convection currents. These droplets may remain aloft for some time and can travel many miles.
Drift can also occur during temperature inversions, when spray droplets become trapped and move laterally above the ground in a cool, lower air mass. Inversions often occur when cool night temperatures follow high day temperatures; they are often characterized by foggy conditions.
Optimal spray conditions for reducing drift occur when the air is slightly unstable, with a very mild, steady wind of 2 to 9 miles (3 to 15 km) per hour. Ideally, temperatures and humidity should be moderate. Contact your local Cooperative Extension for specific guidance about your region.
Your spray application methods and equipment settings also strongly influence the potential for drift. Since small droplets are most likely to drift long distances, avoid aerial applications and air-blast sprayers whenever possible. Operate standard boom sprayers at the lowest effective pressure and set the nozzles as low to the ground as possible. Nozzle type also has a great influence on the amount of drift a sprayer produces. Select nozzles capable of operating at low pressures (15 to 30 psi) to produce larger, heavier droplets that will deliver the insecticide within the crop canopy, where it is less likely to be carried by wind currents.
New electrostatic sprayers can also help reduce off-target pesticide applications. These sprayers apply the pesticide with special nozzles that electrically charge the droplets, which are then attracted to the leaf surfaces. This approach delivers chemicals more effectively and efficiently than traditional nozzle technology does, and can reduce off-target applications by over 50 percent. Regardless of the chemical or the type of application equipment you use, make sure your sprayers are properly calibrated to ensure that you’re not applying excess amounts of pesticide.
Newer spray technology such as tower sprayers and electrostatic sprayers can reduce the potential for insecticide drift.
Air-blast sprayers and aerial crop dusting create pesticide mist that can be difficult to keep precisely on target.
Finally, nonflowering windbreaks and conservation buffers can act as barriers to reduce pesticide drift from neighboring fields. For example, windbreaks of dense evergreen trees, which typically attract relatively few beneficial insect species, can be used as a simple barrier for reducing pesticide drift and protecting adjacent beneficial insect habitat. The USDA Natural Resources Conservation Service can provide guidance and financial support for the construction of pesticide drift barriers.
There are several web resources that can help you choose pesticides that are least harmful to beneficial insects.
The University of California system has a statewide Integrated Pest Management program to dispense advice. Their main website provides information about IPM and crop-specific guidance about pesticides and alternatives for managing pests. The crop index can guide you to pages specific to the crop of your choice, and provides a link to pages with information about the relative toxicities to beneficial insects of pesticides used in that crop. You can find information about pesticide selectivity or mode of action, and the duration of their impact to beneficial insects in the crop index at: www.ipm.ucdavis.edu/PMG/crops-agriculture.html.
The publication How to Reduce Bee Poisoning from Pesticides, from Pacific Northwest Extension, focuses on ways to protect bees from hazards associated with pesticides, and contains tables that provide the toxicity of various pesticides to bees. While many pesticide labels may not list hazards to other beneficial insects, products with labels that mention a hazard to bees should also be considered toxic to all beneficial insects. A pdf of the publication is available here: www.xerces.org/pesticides.
For farmers wanting to protect insect habitat from pesticide drift, or protect their organic crops from a neighbor’s conventional pesticide drift, a carefully designed windbreak can be an effective tool. Trees and shrubs, particularly small-needled evergreens, are known to be exceptionally good at capturing spray drift. Don’t use plants that attract beneficial insects, of course.
Research shows that a windbreak that allows some of the wind to pass through it (a feature described as porosity) is more effective than one that doesn’t. A solid windbreak of overly dense trees deflects the wind upward, creating eddies on the leeward side that could bring drifting pesticides back down to the surface, an effect known as downwash.
The best pesticide drift protection comes from a windbreak made of several rows of trees and shrubs that include small-needled evergreens. These trees are two to four times as effective as broadleaf plants in capturing spray droplets, and provide year-round protection. While a windbreak with multiple rows of trees is the optimum, even a single row can substantially reduce drift if space is limited.
The shape, structure, and width of the windbreak can all affect its droplet-capture effectiveness. The ideal windbreak is made up of five rows of small-needled evergreens, starting with a shrub row on the windward side, with the rows behind increasing in height. Minimum height at maturity should be one and a half times the spray release height.
Spacing between rows should be 12 to 20 feet (3.6 to 6 m) and should allow room for mowers and other equipment. The exact distance will be guided by the mature width of the plants and your own equipment and maintenance practices. Where possible, row spacing should be closest on the windward and leeward sides, and farthest between the innermost rows. Designs with a mixture of shrubs and trees or with fewer rows can be planted a little more densely.
The reality is that this ideal may not be achievable. Where not enough space is available to establish five rows of trees, even just two rows of evergreens can help reduce drift. However, if the windbreak is not dense enough, it may need to be twice the spray height to provide meaningful benefits.
The best windbreaks for capturing pesticide drift are evergreens that allow some of the wind to pass through them, while at the same time capturing most of the drift on their needles.
Generally, you should align windbreaks to intercept prevailing winds, although the location will be dictated by site conditions and available space. While some crops benefit from being sheltered from wind, others may not thrive with less light, so your design needs to balance wind reduction with the effects of shade. You might place the windbreak on the windward side of a field or farm to protect it from drift, or you might want to place it instead on the leeward side of crop fields to prevent movement of chemicals off-site and into adjacent insect habitat.
When designed correctly, windbreaks can be effective, but they make up only one component of best management practices for minimizing chemical drift. Other key actions include timing your spraying to avoid high wind conditions and active times for beneficial insects; selecting appropriate nozzles, with the understanding that smaller droplets travel farther and are less easily captured by vegetation; and regular sprayer calibration to avoid overapplication.
Windbreaks provide a unique opportunity to address conservation threats to beneficial insects and, at the same time, address a wide variety of other resource concerns, from crop production and reduced soil erosion to wildlife habitat. They continue to be a flexible and useful tool for conservation on agricultural lands and an important feature for sustainable farms.
— Nancy Lee Adamson, Thomas Ward, Mace Vaughan, The Xerces Society and USDA Natural Resources Conservation Service Adapted from Inside Agroforestry, Vol. 20.
At the foot of the Appalachian Mountains, in the main fruit-growing region of southern Pennsylvania, lies a three-generation family farm that produces fresh market apples and tart processing cherries. Now run by three grandsons of the founder, the 800-acre Lerew Brothers Farm in York Springs was among the first in the state to move away from broad-spectrum organophosphate and carbamate insecticides to control leafroller and codling moths. In the mid-1990s the Lerews transitioned to using more pest-selective insecticides that were also safer to farmworkers.
Throughout this transition, and in the years since, the Lerews worked closely with the nearby Pennsylvania State University (PSU) Fruit Research and Extension Center to adopt models for predicting pest outbreaks that guide the timing of insecticides. As a result, the Lerews were able to reduce the number of sprays for the main moth pests from seven per season to only three. They also enjoyed much-improved fruit quality.
Later, in 2003, PSU entomologist Dr. David Biddinger began to find greater numbers of beneficial insects in the Lerews’ orchards. These good bugs significantly reduced outbreaks of secondary pests such as mites, aphids, and leafminers. Most striking was the lack of outbreaks by the European red mite, a major pest in the past. Most other fruit growers at the time were averaging $150 to $200 per acre in pesticide costs, with about one-third of this being spent on mites. Because mite predators survived in the Lerews’ orchards, they had not sprayed for pest mites in more than five years.
In typical Pennsylvania orchards, PSU researchers found only three insecticide-resistant mite predators, a Stethorus lady beetle and two species of predatory mites. These predators were only partially effective in reducing mite injury. In the Lerews’ orchards, however, pest mite populations were 10 to 15 times lower than in other growers’ orchards; mite damage to the leaves never occurred. We discovered that the predatory mite Typhlodromus pyri, which had never before been seen in Pennsylvania, was responsible. This mite had been used in effective biocontrol programs in New York, New England, and Washington state orchards, but never in the mid-Atlantic. It had been generally thought that T. pyri was a cool-weather predator that could not adapt to warmer regions. An intensive survey of other Pennsylvania farms in 2004 found T. pyri to be present at low levels on farms that were using selective insecticides, but this beneficial mite was not seen at all on farms still using broad-spectrum insecticides.
Although no bigger than the period at the end of this sentence, predatory mites can help keep spider mites and rust mites in check in fruit and vegetable crops.
The majority of predators move into the orchard only when pest populations are high, and already causing significant leaf damage. In contrast, T. pyri spends its entire life on the tree, feeding on pollen and fungal spores at times when the pest mite populations are very low. Because it never leaves the apple tree, T. pyri is a much more effective mite predator and could effectively regulate pest mite populations throughout the season. However, because T. pyri lives permanently on the apple trees, a toxic insecticide application anytime during the season would completely eliminate it.
Typhlodromus pyri can be easily transferred to new orchards by clipping branches and placing them in other orchards. Using the Lerew Brothers Farm and the PSU research orchards as two T. pyri “seed sites,” PSU quickly established the predator in the majority of Pennsylvania’s 22,000 acres of apples. This expansion was facilitated by financial incentives provided to the growers through NRCS conservation programs, and informed by conservation guidelines provided by PSU. Current Penn State University recommendations for establishing and conserving biological mite control with T. pyri are regularly updated at: http://extension.psu.edu/ipm/resources/nrcs/programs/conventreefruit/biocontrolmites/view.
Because of this conservation biocontrol program, it is estimated that the amount of miticides used in Pennsylvania orchards has been reduced by more than a ton of active ingredients each year, and growers save more than $1 million in pesticide costs.
— Dr. David Biddinger Biocontrol Specialist & Senior Research Associate, Penn State University Department of Entomology;
Jim Lerew, Farmer, Lerew Brothers Farm;
Dr. Ed Rajotte, Professor of Entomology and IPM Coordinator, Penn State University Department of Entomology