Interplanting, Ancient Roots

November 26, 2009

INTERPLANTING IS ANCIENT. It predates agriculture. Interplanting even predates the dinosaur, going back to the first plants growing side-by-side on planet EARTH. Indeed, interplanting is a natural ecological phenomena, existing much like the stars in the night sky.

On farms and gardens, interplanting is sometimes called companion planting. Ancient farmers observed natural interplanting or companion planting in their fields, along with winds, rains, heat, cold, insects, solstices and lunar and planetary movements across the sky. Today, much of the natural interplants occurring in farm fields and gardens is derisively referred to as weed growth (though major crops like maize and wheat still contain the genes of weed ancestors). Indeed, it is a value judgment when native wildflowers like prairie sunflowers are labeled weeds and destroyed by cultivation or herbicides.

In the U.S. state of Tennessee in the 1930s, during America’s Great Depression, the insect factor in interplanting was first subjected to scientific experimentation by an entomologist named Marcovitch. Writing in a 1935 issue of the Journal of Economic Entomology, a still extant publication of the Entomological Society of America (ESA), Marcovitch traced his interest to experiment station reports by other entomologists. Much like the ancient farmers who based planting decisions on empirical and astronomical observations, an entomologist writing in 1906 “advocated for the control of the melon louse the planting of mustard or kale or rape around the melon field. The lady beetles would thus become plentiful after feeding on the cabbage aphids and be ready to attack the melon louse.”

Marcovitch’s penchant to begin the modern era of experimental companion planting was also inspired by a 1929 entomological report that woodlots fostered populations of aphid-eating syrphid flies that destroyed aphids in garden peas. In contrast, pea fields away from woodlots were devastated by aphids and sometimes yielded no crop. Figuring that aphid damage to vegetables was a consequence of an absence of biological control by aphid natural enemies, Marcovitch began a series of scientific interplanting experiments to boost natural biological control in crop fields.

Tennessee turnip strips planted in March yielded aphid natural enemies like lady beetles and small parasitic wasps that migrated later into adjacent strips of peas, beans, corn, okra, cotton, cucumbers and watermelons. Aphid populations declined in the main crops, thanks to the adjacent natural enemy-laden turnip rows. In contrast, “control” watermelon plots lacking adjacent turnip rows to provide natural enemies were destroyed by aphids early in the season.

Since Marcovitch’s pioneering 1935 report in the Journal of Economic Entomology, books have been written on interplanting experiments to increase natural biological control in crops.


Wintergreen = Biocontrol Aromatherapy

September 18, 2009

WHEN ENTOMOLOGISTS hip to chemical ecology speak of HIPPOs, they mean HERBIVORE INDUCED PLANT PROTECTION ODORS, not the massive hippopotamus native to riverine Africa. At Washington State University (WSU), David James and his entomological colleagues have spent the last several years testing fragrant wintergreen oil, a common HIPPO produced by distressed plants, as a means to boost biological control of crop pests by natural enemies.

The same fragrant wintergreen oil (high in methyl salicylate) used in mints and mouthwashes can be formulated into slow-release dispensers to attract beneficial insects into crops in greater numbers earlier in the season than would otherwise be the case. The dispensers minimize environmental and worker health impacts and crop damage (phytotoxicity). Also, the dispensers can last 3-4 months, providing extended periods of natural enemy attraction. Sprays evaporate more quickly, potentially meaning more applications. Nevertheless, spray technologies are still very popular and 2% wintergreen oil in canola oil is being test sprayed worldwide in crops ranging from hops and cotton to soybeans, strawberries and sweet corn.

In their earliest hop yard and grape vineyard field tests, James and his coworkers found that wintergreen oil attracted significantly higher numbers of pest natural enemies like predatory green lacewings, minute pirate bugs (Orius spp.), spider mite-eating lady beetles (Stethorus spp.), and aphid-eating syrphid flies. By getting higher numbers of natural enemies into the fields earlier than might otherwise have been the case, pests like spider mites were kept under biological control all season long. Leafhopper numbers were also lower, leading James to suspect that parasitic wasp species attacking this pest were also boosted by wintergreen oil.

This is the basis for commercial products such as PredaLure, sold by Rincon-Vitova Insectaries and others to maximize natural enemies providing biological pest control. Plants are virtual chatterboxes of chemical communication, and wintergreen oil and methyl salicylate are just the tip of the iceberg in terms of natural compounds awaiting field testing. Farnesene, caryophyllene and the male-produced lacewing aggregation pheromone iridodial are among the other green lacewing attractants attracting research attention.

When attacked by insects, spider mites, and pathogens (e.g. viruses, bacteria, fungi) or under environmental stress (e.g. chilling, drought, salinity), plants can ooze chemical exudates from their roots into the soil and waft a variety of communication chemicals into the wind. Thereby neutralizing pathogenic soil microbes, luring in pest-eating natural enemies and tipping off downwind neighbors in the plant community to ramp up their immune response in preparation for impending pest attacks.

We have only scratched the surface of what exists and what is possible to develop for biological insect control.


Planet Moth

September 7, 2009

WITH 200,000 known species, Earth is almost Planet Moth. Only beetle species are more numerous. Moths have been denizens of Earth since prehistoric times, long before the ascent of man. Mostly nocturnal, secretive and nondescript, moths play a quiet ecological role, doing some vital pollination of plants and nourishing the food chain by feeding birds, bats, lizards, fish, frogs and many other critters.

Silkworm moths, domesticated as a crop on mulberry trees in China about 5,000 years ago, are famous in the textile industry. Clothes moths are infamous for feeding on garments, and have spurred herbal pest control innovations since ancient times. Humankind has sprayed billions of tons of synthetic pesticides against cotton bollworm moths, Indian meal moths, diamondback moths, cabbage loopers, leafrollers, leafminers, stemborers, codling moths, corn earworms, inchworms, armyworms, spruce budworms, gypsy moths and bagworms, to name but a few. However, alternatives like pheromones are becoming more widely used to monitor, trap, and confuse moths and prevent mating and egg laying (eggs hatch into caterpillars that eat, pupate and beget new moths).

Biocontrol by natural enemies, including birds, bats, toads, spiders and other insects, is part of the ancient planetary rhythm for controlling moths and maintaining global ecological balance. From Texas, Arizona, California and Mexico to China, Russia, Central America and Australia, microscopic Trichogramma wasps are among the most popular insectary-reared natural enemies released to stop moth egg hatching. Cotton growers escaping the pesticide treadmill have traditionally been big users of Trichogramma wasps. Tomatoes, corn, grapes, tree fruits, ornamental nurseries and many other crops also use Trichogramma, green lacewings and a wide array of other natural enemies purchased from Rincon-Vitova and other insectaries to lessen moth attacks and minimize pesticide use.

Of course, the moth wars are not all one-sided. Spray pesticides too often and moths become resistant. And moths can elude and make life challenging for their natural enemies. For example, many moth species respond to bat ultrasound echo-location signals with evasive aerial maneuvers and jamming signals. Moth immune systems may even encapsulate and prevent parasites from providing biocontrol. Each female of one fat Australian moth species can lay 18,000 eggs, the ultimate defense, essentially ensuring survival by sheer numbers.


Bed Bugs, Turning Up the Heat

August 21, 2009

PESTICIDE RESISTANCE and bedbugs’ innate ability to avoid toxicant contact by hiding in cracks and crevices during daylight hours make alternatives like traps and heat hot topics at Entomological Society of America annual meetings. In contrast to ticks, where researchers have at least investigated biocontrols like micro-wasps, insect-killing nematodes and fungi, bedbug natural enemies have mostly escaped scientific scrutiny and testing.

Rutgers University’s Changlu Wang, an IPM (Integrated Pest Management; using multiple techniques) expert, is better known for his cockroach trapping skills in large public housing and apartment complexes in Indiana. Against bedbugs, Wang uses natural diatomaceous earth in bedbug interceptor traps (Climbup(TM); Susan McKnight, Inc.). This is in addition to clutter removal, bagging and washing infested belongings, new encased mattresses, and steam treatment (vaporized hot water) of floors, drapes and sofas.

Interceptor traps are designed to monitor bedbug infestations, and provide researchers population data. But these bedpost traps are also good control tools: In 10 weeks capturing 50% of the 8 to 1,103 bedbugs per one-bedroom apartment in Indiana. Though bedbugs can still crawl up from walls or behind headboards if a bed is flush against them, or even drop from ceilings.

Unlike “moat” traps surrounding bedposts, interceptor traps have a small container (which Wang fills with 20 ml of antifreeze for insect collection) inside of a larger container that Wang fills with an insecticidal formulation of diatomaceous earth. Future bedbug traps may also be able to take advantage of recently discovered airborne bedbug aggregation pheromones.

At the University of Florida Institute of Food and Agricultural Sciences, Roberto Pereira and others are working on heat fumigation to kill bedbugs. When test tubes containing bedbugs are placed in 111-113 F (44-45 C) hot tubs, these hardy insects survive an amazing 2 to 6 hours.

However, specialized pest control companies in the southern California counties of San Diego and Orange routinely use heat (hot air) fumigation instead of chemical pesticides against drywood termites embedded deep in wooden structures. It requires skill to arrange fans to circulate hot air in buildings. Temperature readings inside the wood are needed every half hour or so to calculate the heat dose needed to cook the insects. If it can be done economically with termites living in walls, heat fumigation can also be done with bedbugs. But expect stiff resistance to heat technologies from established companies with large fixed investments in traditional chemical fumigation skills and equipment.

A cheaper alternative to whole room or whole building heat fumigation is relatively low-cost portable heat chambers. Small heat chambers (e.g. constructed of foam boards) costing $400 or less are already used by the hotel industry, shelters and others to disinfest furnishings. In Florida, portable heat chambers stop the annual spread of bedbugs on preowned beds and furnishings purchased by students. Hospitals have used heat to disinfest wheelchairs of patients too sensitive for pesticide treatments.


Beating the Bed Bug Blues

July 15, 2009

“SUCH BUGS and goblins in my life,” said Shakespeare’s Hamlet during the medieval era when “bug” meant bed bug. Indeed, bedbugs have been part of the human condition from prehistoric times. By 400 B.C. the ancient Greeks were scratching bedbug bites and singing the Big Bed Bug Blues. Bat caves, bird nests and animal barns are the natural habitats supporting bed bugs and their goblin-like natural enemies like itch mites, assassin bugs, assorted ants, centipedes, and spiders.

Though bedbug biocontrol by the currently-known crop of natural enemies seems better left to the Batcave and more rustic outdoorsy habitats, natural ecological principles still apply in human dwellings. Contrary to the DDT-nostalgia (interestingly, lacking scientific citations) infesting Wikipedia, pesticides cannot substitute for human smarts in fighting bedbugs. Even in the heyday of DDT bed bugs were hard to kill and there was pesticide resistance, Clemson University urban entomologist Eric Benson told an Entomological Society of America (ESA) annual meeting. Indeed, overdoing pesticides is likely to kill natural enemies and stimulate outbreaks of new indoor pests (e.g. rat mites).

An integrated pest management (IPM) approach pits human ingenuity and a multiplicity of tactics against bedbugs. Shripat Kamble of the University of Nebraska told an ESA annual meeting of traditional bedbug remedies rememebered from a childhood in India: “People commonly used in the summertime heat treatment. Keeping the cot outside in the hot sun,” and shaking the bed so the bugs spilled onto bare ground hot enough to kill. “Another treatment that was commonly done was boiling water, and then pouring boiling water through all the hiding areas of the bed bugs…A lot of times it worked, and sometimes we still had problems.”

Nobody, not even the professionals, has a surefire remedy guaranteed to work against bedbugs every time in every household. Like Shakespeare and the ancient Greeks, bedbugs are likely to remain a part of the modern human condition.


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