Food Sweetener Safely Slays Insects

August 27, 2015

CERTAIN SUGARS CONSIDERED SAFE as sweeteners in the human food supply can double as environmentally-friendly pest remedies, and even make biological control of insects by beneficial fungi more practical for households, farms and gardens. Considering that caffeine from coffee grounds can be used against deadly dengue mosquitoes and that a variety of traditional herbs can blast away bed bugs, insecticidal sugar compounds should come as no surprise. Perhaps the only remedy more surprising is that rain water or simulated rain sprays from hoses or irrigation equipment can safely wash away pests with no toxic pesticide residues to worry about in the environment.

Using sugars directly to slay insects is somewhat unusual. However, sugars are commonly used as attractants, for instance to lure fruit flies, moths or ants to baits and traps both for population control and as a survey method or monitoring tool. California citrus growers have a long history of using sugar sprays as an IPM (integrated pest management) strategy to lure fruit-scarring citrus thrips to organic or botanical formulations of ryania (“from woody stem and root materials of plants of the genus Ryania”) or sabadilla (alkaloids from seeds of a lily bulb, Schoenocaulon officinale). “INTEGRATED PEST MANAGEMENT implies that techniques used to manage one pest species should not disrupt techniques used to manage other pests of the same crop,” wrote J.D. Hare and Joseph Morse in the Journal of Economic Entomology. “In citrus pest management in California, this situation is well illustrated in the choice of pesticides for the management of one major pest, citrus thrips, Scirtothrips citri (Moulton), without disruption of several effective biological control agents of the other major pest, California red scale, Aonidiella aurantii (Maskell).”

That sugars can be lethal to pests and be a source of environmentally-friendly pesticides is not exactly intuitive. “Potential of the non-nutritive sweet alcohol erythritol as a human-safe insecticide” was the strangely intriguing title of Drexel University’s Sean O’Donnell’s presentation at the Entomological Society of America (ESA) annual meeting. Many of the details were previously published in PLoS ONE, an open access journal, and in part because of the origins of the research in a grade school science project by one of the researcher’s sons, aspects of the story have been widely reported in various media. “Erythritol is a zero-calorie sweetener found in fruits and fermented foods,” summarized Lauren Wolf in Chemical & Engineering News, and “is Generally Recognized As Safe by the Food & Drug Administration and has been approved as a food additive around the globe.”

“Many pesticides in current use are synthetic molecules such as organochlorine and organophosphate compounds,” and “suffer drawbacks including high production costs, concern over environmental sustainability, harmful effects on human health, targeting non-intended insect species, and the evolution of resistance among insect populations,” write the researchers in PLoS ONE. “Erythritol, a non-nutritive sugar alcohol, was toxic to the fruit fly Drosophila melanogaster. Ingested erythritol decreased fruit fly longevity in a dose-dependent manner, and erythritol was ingested by flies that had free access to control (sucrose) foods in choice and CAFE (capillary feeding assays) studies…

“We initially compared the effects of adding five different non-nutritive sugar substitutes (Truvia, Equal, Splenda, Sweet’N Low, and PureVia,” wrote the researchers in PLoS ONE. “Adult flies raised on food containing Truvia showed a significant reduction in longevity…We noted that adult flies raised on food containing Truvia displayed aberrant motor control prior to death. We therefore assayed motor reflex behavior through climbing assays…Taken together with our longevity studies, these data suggested some component of the non-nutritive sweetener Truvia was toxic to adult Drosophila melanogster, affecting both motor function and longevity of this insect…

“Our initial analysis of sweeteners included two sweeteners that contained extracts from the stevia plant, Truvia and Purevia. While adult flies raised on food containing Truvia showed a significant decrease in longevity compared to controls, this was not the case for flies raised on Purevia. These data suggest stevia plant extract was not the toxic element in these sweeteners. Purevia contains dextrose as a bulk component, while Truvia contains erythritol as a bulk component…To determine if erythritol was the toxic component of Truvia, we repeated our longevity studies on food containing equal weight/volume (0.0952 g/ml) of nutritive sugar control sucrose, and non-nutritive sweeteners Truvia, Purevia, and erythritol. We assured the flies were successfully eating the foods containing these sweeteners through dye labelling the food with a non-absorbed blue dye (blue food), and visual confirmation of blue food present in fly abdomens and proboscises daily…The average percentage of blue abdomens throughout the study were 97.46%.”

“These data confirm all treatment foods (including Truvia and erythritol treatments) were consumed by adult flies, and suggest mortality was not due to food avoidance and starvation…A large body of literature has shown that erythritol consumption by humans is very well tolerated, and, indeed, large amounts of both erythritol and Truvia are being consumed by humans every day throughout the world. Taken together, our data set the stage for investigating this compound as a novel, effective, and human safe approach for insect pest control. We suggest targeted bait presentations to fruit crop and urban insect pests are particularly promising.”

Interestingly, a few decades ago UK researchers found that the sweeteners (sugar alcohols; polyols) erythritol, glycerol and trehalose rendered more effective several insect biocontrol fungi, Beauveria bassiana, Metarhizium anisopliae and Paecilomyces farinosus. These insect-killing fungi need a relative humidity (RH) near 100% for germination of their conidia (seed-like propagules). “Conidia with higher intracellular concentrations of glycerol and erythritol germinated both more quickly and at lower water activity,” wrote UK researchers J.E. Hallsworth and N. Magan in the journal Microbiology. “This study shows for the first time that manipulating polyol content can extend the range of water availability over which fungal propagules can germinate. Physiological manipulation of conidia may improve biological control of insect pests in the field…Although fungal pathogens have been used to control insect pests for more than 100 years, pest control has been inadequate because high water availability is required for fungal germination.”

Curiously, erythritol and glycerol, besides being sweetening substances, also function as antifreeze compounds. Certain Antarctic midges, known as extremeophiles for living in an ultra-cold habitat, ingest and sequester erythritol from their food plants; and as antifreeze it protects the adult flies from freezing. Indeed, many mysteries remain. Besides being found in green plants like stevia and in lower amounts in fruits, erythritol is found in certain mushrooms, lichens and algae. Human and animal blood and tissues apparently have low endogenous levels of erythritol; and erythritol is a yeast fermentation product (hence in sake, beer, wine). In human medicine, erythritol has been used for coronary vasodilation and treating hypertension; and according to Japanese microbiologists, erythritol ingestion may mean fewer dental cavities (caries) than sucrose sugar.

Doggone Birds (Fruit Protection)

September 13, 2012

Many bird species provide biocontrol by eating a wide range of insect pests, and are worth encouraging for controlling flies, mosquitoes, locusts, caterpillars, ticks, rodents and other pests around homes, forests, farms and gardens. Other bird species are considered pestiferous when feeding on our food plants, and can be repelled in various ways, including by loud noises, eyespot balloons, reflecting tape, scarecrows and scare devices, sensor networks and dogs.

Among the beneficial birds when they are not causing damage to utility poles or annoying people with their racket are woodpeckers. Personally, I like hearing woodpeckers working urban and forest trees, and was heartened to learn from Michigan State University’s Andrew Tluczek’s presentation to the Entomological Society of America (ESA) annual meeting that: “Woodpecker predation has caused up to 90% mortality of emerald ash borer (Agrilus planipennis) larvae in some sites.”

A 2006 tick control article in BioScience magazine devoted considerable discussion to birds for tick biocontrol. In Africa, birds known as oxpeckers (Buphagus spp.) provide biocontrol of ticks on mammals by consuming hundreds of adult ticks or thousands of nymphal ticks per day. Free-ranging guinea fowl experimentally tested around New York (USA) lawns reduced adult blacklegged tick numbers; but unfortunately the smaller nymph stage blacklegged ticks transmitting Lyme disease apparently were missed and not stopped very well.

The list of bird benefits for biocontrol, like barn owls for rodent biocontrol in Israel, Palestine, Malaysia and elsewhere could go on and on.

“Bird damage situations throughout the world are similar, involving many of the same crops and genera of birds,” wrote John W. De Grazio a few decades ago in the <em>Proceedings of the 8th Vertebrate Pest Conference. Seed-eating red-winged blackbirds, ring-necked pheasants, sparrows, crows, doves, parrots, munias, queleas, weavers and waterfowl are sometimes pests of corn, rice, wheat, sorghum, sunflowers, almonds, pecans, peanuts, etc. Starlings, sparrows, finches, grackles, robins, parakeets, etc. consume grapes, blueberries, and other fruit in yards, vineyards and orchards.

Dogs are used in pest control for sniffing out termites and bed bugs, and the natural proclivity of some dog breeds to chase birds can be harnessed to keep birds from destroying fruit in orchards and vineyards. In researching a grant proposal to travel to and write about Japan, which I failed miserably to qualify for, my Internet research for the proposal took me to the Japanese Journal of Farm Work Research. Being one of a select 4% of the USA population to have worked in agriculture, the journal title intrigued me enough to browse through several years of tables of contents, where I came across an intriguing article title: “Protection of Citrus From Bird Damage by a Dog.”

Not reading Japanese, I had to rely on the visual diagrams and English summary by researchers Hiromichi Ichinokiyama and Masami Takeuchi at the Kinan Fruits Tree Laboratory and Mie Prefectural Science and Technology Promotion Center:

“Effectiveness of a dog (Canus lupus familiaris) for protecting citrus fruits from bird damage was investigated using a citrus orchard (5.8 a in area) in the harvest season. In Experiment 1, a Border collie shepherd (male) was tied to a wire extended along one side of the square orchard to allow him to run along the inner side of the orchard. This watchdog system was effective in reducing fruit damage by birds (mainly brown-eared bulbul) only in the citrus tree row nearest to the dog runway.”

However, the researchers had better success letting the dog run free in the orchard:

“In Experiment 2, the orchard was enclosed with a tall chain-link fence and the same dog was allowed to move freely in the orchard. In this case, he persevered in chasing birds until they flew away from the orchard. This watchdog system effectively reduced bird damage to citrus fruits all over the orchard, resulting in an increase in crop yield…Further study is needed on the optimum number of dogs released per unit orchard area and the effectiveness of the watchdog system in case when this bird control system is spread to all orchards in the citrus-growing area.”

Like Richard Feynman’s Nontoxic Ant Ferry, dogs chasing birds away from trees laden with fruit or nuts is more a proof-of-concept awaiting further development than a fully developed technology you can order on the Internet.

Thank you to the organizations and people who created and are advancing the Internet, as even finding this sort of information would have been nearly impossible a few decades ago. Amazing how this high-tech infrastructure can advance low-tech solutions like the old-fashioned four-legged, tail-wagging dog as a bird-chaser in service of better fruit harvests.

Carbon Dioxide Gas Combats Bed Bugs

July 24, 2012

CARBON DIOXIDE GAS, an essential nutrient for photosynthesis and the human and animal food chain consuming green plants, can also play a key role in bed bug control. As an attractant, carbon dioxide (CO2) is useful for monitoring and trapping bed bugs and other vampire-like blood-suckers attracted to the gas, including ticks, mosquitoes, and assorted biting flies. Carbon dioxide gas, which has been used to fumigate everything from stored grain and food products to freight containers, museum collections, and hotel and motel rooms, can also be used to fumigate clothing, furnishings, books, electronics, and other bed bug-infested items.

Carbon, carbon dioxide, and the carbon cycle are integral to our very existence on planet Earth. “The carbon of the Earth comes in several forms,” writes University of Cambridge chemist John Emsley in his fascinating Oxford University Press book, Nature’s Building Blocks (An A-Z Guide to the Elements). “Most of what we eat –carbohydrates, fats, proteins and fibre – is made up of compounds of carbon…most ingested carbon compounds are oxidized to release the energy they contain, and then we breathe out the carbon as carbon dioxide. This joins the other carbon dioxide in the atmosphere, from where it will again be extracted by plants and become part of the carbon cycle of nature…The cycle rules the tempo of life on Earth and turns over 200 billion tonnes of carbon each year…In this way carbon is passed up the various food chains, with each recipient releasing some as carbon dioxide, until most carbon is back where it started.”

Does this mean that using carbon dioxide for bed bug control is environmentally acceptable, since it is kind of a “miracle of life” gas behind photosynthesis and plant life? Or is carbon dioxide really more the evil greenhouse or global-warming gas causing global climatic havoc and deserving of punishment via carbon taxes and elimination from the atmosphere via geological carbon sequestration (storage) schemes? Perhaps we should offset carbon dioxide releases for bed bug pest control with offsetting carbon dioxide injections into greenhouses, where elevated CO2 levels increase yields of greenhouse roses, tomatoes, cucumbers, peppers and other crops.

“Carbon is probably the most important element from an environmental point of view,” writes Emsley in Nature’s Building Blocks. “The Earth’s early atmosphere may have contained a lot of carbon dioxide and methane, but once life evolved that began to change. Today, there is very little of these gases and a lot of oxygen instead, thanks chiefly to the action of plants which convert carbon dioxide and water into carbohydrate and oxygen by photosynthesis. The Earth’s atmosphere contains an ever-increasing concentration of carbon dioxide and carbon monoxide, from fossil fuel burning, and of methane, from paddy fields and cows. Human contributions to these sources are still minor compared with natural sources: most carbon dioxide comes from plants, microbes and animals, while methane is given off by swamps, marshes and termite mounds.”

Obviously best to avoid bed bug infestations, and not have to think about remedies like carbon dioxide trapping or fumigations. Italian chemist Primo Levi makes the most persuasive literary argument: “Carbon dioxide, that is, the aerial form of carbon…this gas which constitutes the raw material of life, the permanent store upon which all that grows draws, and the ultimate destiny of all flesh, is not one of the principal components of air but rather a ridiculous remnant, an ‘impurity,’ thirty times less abundant than argon, which nobody even notices. The air contains 0.03 percent; if Italy was air, the only Italians fit to build life would be, for example, the 15,000 inhabitants of Milazzo in the province of Messina. This, on the human scale, is ironic acrobatics, a juggler’s trick, an incomprehensible display of omnipotence-arrogance, since from this ever renewed impurity of the air we come, we animals and we plants, and we the human species, with our four billion discordant opinions, our millenniums of history…”

Bed bugs concern themselves little with environmental correctness, and just tune into characteristics like the heat and carbon dioxide released by metabolizing warm-blooded meal hosts like humans, poultry, rodents, rabbits, etc. A flush from a CO2 cartridge is enough to flush bed bugs from their harborages or hiding places onto a bed in search of a meal. But more naturally, bed bugs follow CO2 gradients to locate live hosts for their blood meals.

“Carbon dioxide has been shown by several researchers to be the most effective attractant for bed bugs,” University of Florida-Gainesville entomologist Philip Koehler told a recent Entomological Society of America (ESA) annual meeting. Humans produce about 700 mg (0.02 oz) of CO2 per minute. “Thus, detectors with very slow CO2 releases cannot compete with human hosts,” said Koehler. “A rapid CO2 release is a better mimic to the human breathing pattern. Detectors with fast CO2 release captured about 4x more bed bugs than detectors with slow release.”

Trapping or monitoring bed bugs with CO2 is complicated by the fact that at different times in the life cycle bed bugs seek out hosts (releasing CO2) for blood meals when hungry; and then when well-fed, instead of CO2 bed bugs seek shelter in groups or cracks and crevices. So although CO2 is the better lure for hungry bed bugs, bed bugs that have fed have different needs and respond to different lures.

A commercial product, FMC’s Verifi(TM) trap, is a dual-action detector combining “fast CO2 generation with liquid kairomone and pheromone lures to attract both host-seeking bed bugs and aggregation-seeking bed bugs,” Koehler told the ESA. Carbon dioxide and the kairomone lure blood-seeking bed bugs into a pitfall part of the trap from which there is no escape. A pheromone lures harborage- or aggregation-seeking bed bugs seeking shelter in cracks and crevices into another part of the trap.

“An inexpensive detector that can be left in place and routinely serviced is needed to aid pest management professionals,” Ohio State University’s Susan Jones told the ESA. “Rutger’s do-it-yourself dry ice (frozen CO2) traps are a cheap and effective method for overnight surveys of potentially infested habitations.” An experiment in a 13-story high-rise apartment building in Columbus, Ohio compared (see You Tube video) 3 Verifi(TM) bed bug detectors per room with 1 CO2-generating dry ice trap per room and canine (dog) detection teams (2 dogs/room; same handler).

Verifi(TM) traps detected bed bugs in 11 of 17 infested rooms in the first 24 hours; and in 14 of 17 infested rooms within a week. Dry ice traps had similar efficacy. Dogs detected bed bugs in 19 rooms, including 3 rooms where neither visual inspections nor dry ice or Verifi(TM) traps detected anything. But the dogs were also not perfect, as each dog also missed 1 room rated positive for bed bugs. So the quest to capture bed bugs with carbon dioxide and other lures goes on.

Human ingenuity seems almost unlimited when it comes to traps. Carbon dioxide, heat and other attractants are all being tested with traps as varied as Susan McKnight Inc.’s Climbup bed bug trap and pitfall traps made from inverted dog bowls painted black on the outside. Rutgers’ Narinderpal Singh tested CO2, heat, and lures such as nonanol, octanol, 1-octen-3-ol, coriander, and spearmint with inverted dog bowl pitfall traps. CO2 had an additive effect with multiple-component lures in inverted dog bowl traps, and may be developed into an inexpensive monitoring system for detecting low levels of bed bugs. Trials with baited traps are continuing.

Both carbon dioxide and ozone show fumigant potential against bed bugs. Purdue University’s Kurt Saltzmann told the ESA of “Two devices capable of delivering ozone to laboratory fumigation chambers.” One device delivered a short exposure to high ozone levels, and the other long exposure to low ozone levels. “Preliminary experiments showed that adult male bed bugs were susceptible to relatively short periods of ozone exposure when high concentrations of ozone were used,” said Saltzmann. “100% mortality was achieved when bed bugs were exposed to 1800 ppm ozone for 150 minutes.” Low ozone fumigation is also being tested with 1-2% hydrogen peroxide for up to 72 hours.

Carbon dioxide (CO2) is used by libraries, museums, and others as an insect-killing fumigant. Indeed, dry ice (frozen CO2) to release CO2 gas is cheaper than washing and drying fabrics to kill bed bugs, Rutgers University’s Changlu Wang told the ESA. At an 80% concentration, CO2 kills all bed bug eggs in 24 hours (eggs are the toughest bed bug life stage to kill). A 50% CO2 concentration for 8 hours is sufficient to kill bed bug nymphs (immatures) and adults.

Wang’s CO2 fumigations involved filling Husky garbage bags 90% full of items such as mattress covers and fabrics, leaving little room for air. Then the bags were sealed with dry ice inside for several hours. Books, electronics, toys and other items damaged by heat treatments might benefit from the low temperatures created by dry ice treatments. However, for safety reasons Wang recommends wearing gloves and turning on fans for ventilation when opening many bags filled with carbon dioxide gas (fumigant).

Earthworm Compost, Medicinal Honey & Fewer Hive Sprays Avert Bee Collapse

April 4, 2012

HONEY BEE COLONY COLLAPSE DISORDER and subtle learning and memory pesticide effects were among Biocontrol Beat topics detailed in Feb. 2011 (Honey Bees, 24-Hour Surveillance Cameras & Pesticides). For many attendees of Entomological Society of America (ESA) annual meetings, the two reports on pesticide effects on honey bees and bumble bees in the 30 March 2012 issue of Science magazine were just two more data bits, nothing particularly surprising; albeit good headline news fodder and a bit troubling. Perhaps a slight feeling of déjà vu for those familiar with Rachel Carson and her book of more than half a century ago, Silent Spring.

To imbibers of energy-boosting, nervous system stimulants like coffee, tea, and the many other caffeinated beverages flooding the marketplace, the idea that a common natural (e.g. botanical) or synthetic chemical might affect behavior is almost a no-brainer, though not necessarily self-evident. Caffeine has gone from fruit fly studies to mosquito control remedy recently. Natural nicotine from tobacco family plants has had almost an opposite trajectory, having once been widely used (e.g. burned as a fumigant) and recommended (e.g. soaking cigarette butts in water) for pest control in agriculture, greenhouses, and organic gardens; and now shunned because of its toxicity to humans and beneficial insects.

Neonicotinoid pesticides, like the widely used imidacloprid, had their design inspiration in natural nicotine molecules; but are safer to humans and other animals. But perhaps not totally without adverse effects, if indeed it is possible to have a substance that is toxic and yet totally safe. The Science reports associate neonicotinoid chemicals like imidacloprid with reduced bumble bee colony size and queen production, as well as lower honey bee survival and foraging success.

Though the scientific data will be subjected to further debate and future studies may confirm or refute the results, Science magazine writer Erik Stokstad, in an accompanying news and analysis, marshaled a stunning statistic to go with the reports: “In the United States alone, 59 million hectares of crops are protected by systemic pesticides. Seeds are treated with these neurotoxins before planting, and the poison suffuses the tissues, pollen, and nectar…”

Nonetheless, as ESA annual meeting habitués may know: genetics, pathogens, parasites, and beekeeper practices apparently also figure into the still mysterious honey bee Colony Collapse Disorder (CCD). Perhaps aptly for a confusingly mysterious disorder, CCD, the acronym for Colony Collapse Disorder, is confusingly the same as the Community College of Denver, charged-coupled devices (like those capturing images in digital cameras), Confraternity of Christian Doctrine, and The Convention Centre Dublin, to mention but a few highly-ranked “CCD” terms in Google.

Those who put their faith in scientific panels, better testing, and more government regulation will be heartened to know that Stokstad says more is on the way in Europe and the USA. Those wanting to do something practical right now to help the honey bees and native bumble bees pollinating their backyards and fields might find more encouragement in some of the presentations coming out of the Entomological Society of America (ESA) annual meetings.

For example, North Carolina State University soil ecologist Yasmin Cardoza, who has shown that earthworm compost produces plants more resistant to caterpillar pests and aphids, more recently told the ESA that amending a cucumber soil (model system) with earthworm compost (vermicompost) helped bumble bees and other native pollinators become heavier, healthier, and more fecund.

Cucumber plants grown in soils amended with earthworm compost had flowers (pollen, nectar) with significantly more protein and a bit more sugar. These more nutritious flowers grown with earthworm compost attracted more bumble bees and native pollinators. Plus the bumble bees had more and larger ovary cells and egg tubes (i.e. an indication of enhanced reproduction), weighed more, and had fewer disease pathogens. Whether earthworm compost can reverse or prevent Colony Collapse or create Colony Expansion would make for an interesting study.

Beekeeping methods also take a hit for exacerbating honey bee problems; and are illustrative of how mites, insect pests and pesticides make for the type of challenging problem that in previous centuries were solved by privately-funded freelance scientists like Louis Pasteur. Pasteur’s freelance entomological endeavors included almost single-handedly rescuing the nineteenth-century silk industry from a similar mysterious collapse of silkworm colonies (insect colonies seem particularly prone to epidemic collapse when you want them; but resistant to collapse when you would rather be rid of them, like termite and fire ant pests). Rene Dubos’ account in his 1950 book, Louis Pasteur Free Lance Of Science, is well worth reading for free on the Internet (pdf, Kindle versions). By early twenty-first century standards, Pasteur seems almost like a Rambo of science, accomplishing with a few assistants what would seem impossible today.

Even if the cause of honey bee colony collapse is still mysterious, like silkworm colony collapse was prior to Pasteur, there is no doubting the reality of the problem.

“In Virginia, the number of managed honey bee colonies have declined by about 50% since the late 1980s due to the introduction of parasitic mites,” Virginia Techie (Blacksburg, VA) Jennifer Williams told the ESA. “Excessive reliance” on fluvalinate (a pyrethroid miticide) and coumaphos (an organophosphate miticide) have “been implicated in numerous problems to honey bees, including impaired reproductive physiology, reduced ability of colonies to raise queens, reduced sperm viability in drones (males), and increased queen failure and loss.” Often these miticides are found in combination with imidacloprid (systemic insecticide), chlorothalonil (broad-spectrum fungicide), and the broad-spectrum antibiotics oxytetracyline and streptomycin used by beekeepers to combat American foulbrood disease in honey bee hives.

Fluvalinate, coumaphos, coumaphos-oxon, and chlorothalonil are found in almost half of North American honey bee colonies at ppb (parts per billion) levels that can be acutely toxic. Combining miticides, pesticides, and antibiotics is a toxic cocktail recipe boosting honey bee mortality 27-50%, according to Williams. In other words, it is a vicious circle in which beekeeping practices (e.g. miticides, antibiotics, substituting sugar water for honey) may have deleterious effects offsetting curative effects on already weakened and mentally confused bees feeding on plants treated with pesticides rather than healthy composts like those being studied by Cardoza.

As if honey bees did not have enough health problems, the small hive beetle (Aethina tumida) is now part of the mix. “In their native range in South Africa, these beetles cause relatively little damage,” Natasha Wright of the University of Arkansas told the ESA. “However, they can be destructive to honey bee colonies in the United States and Australia. The adults and larvae feed on bee brood and bee products. They also cause honey to ferment, which results in unsellable honey. Little is known about the biological control agents.”

“Identifying new mechanisms that support honey bee health will be pivotal to the long-term security and productivity of American agriculture,” Emory University’s Lydia McCormick told the ESA. “Hydrogen peroxide is a potential natural defense/stress response to small hive beetle,” a pest which can devastate a honey bee colony in weeks or months. Not to knock beekeepers, who have enough problems already, but their practice of feeding bees sugar water rather than honey laced with hydrogen peroxide may be part of the problem. Honey bees produce more hydrogen peroxide in their honey to combat stressors like the hive beetle.

“Extremely low concentrations of hydrogen peroxide in sugar-water fed samples may represent a problem in this common method of hive management,” said McCormick. “Honey bees may selectively regulate higher brood honey hydrogen peroxide as a strategic oxidant defense. Given that brood cells contain honey bee larvae, high honey hydrogen peroxide may help protect against pests.” Indeed, small hive beetle survival is lower with hydrogen peroxide in the honey.

Honey containing hydrogen peroxide has been marketed for its antibacterial, wound healing, and skin care potential; and prescriptions for medical-grade honey are a possibility. New Zealand professor Peter Charles Molan published an interesting historical review on honey for wound healing in 2001. Besides hydrogen peroxide, honey may have healing botanical compounds (phytochemicals). Perhaps the bee’s loss is humankind’s medical gain. Though if the bees are lost as pollinators in the process, it is not a sustainable practice in the longer-term.

Moth-Eye Reflections

September 8, 2011

“ANTI-REFLECTION MOTH-EYE ARRAYS are now widely applied in panels of instruments, like cellphones and in window panes,” wrote Doekele G. Stavenga of the Department of Neurobiophysics at the University of Groningen (The Netherlands) in Functional Surfaces in Biology -Little Structures With Big Effects, Volume 1. The editor, Stanislav Gorb of the University of Kiel (Germany), thanked senior publishing editor Zuzana Bernhart (Plant Pathology and Entomology; Springer, Holland) for her “belief in this topic and her personal help.” Bernhart said that a big dose of the inspiration for the two book volumes came from what have become regular symposia on insect-inspired innovations at the Entomological Society of America (ESA) annnual meetings.

At nanotechnology events, insects and entomology are acknowledged frequently as inspiration. For example, at the California NanoSystems Institute on UCLA’s campus, Tomohide Takami, a researcher visiting from the Division of Quantum Phases and Devices at Konkuk University (South Korea), said “we have fabricated a bio-mimetic probe called ‘nano-mosquito’…to explore nano-world.” In a prior lecture Xiaodong Chen visiting from Nanyang Technological University (Singapore) noted: 1) energy storage devices, lightweight aerospace materials, and self-assembly inspired by diatoms and honey bee honeycombs; 2) Singapore’s waterfront Esplanade Theatres on the Bay is an architectural shape perhaps inspired by fly eyes and tropical fruit (durian); 3) moth eyes that are anti-reflective (so enemies do not see the glint of their eyes) and provide better vision at night and in fogs inspire solar cells that harvest more light.

“Anti-reflective moth-eye arrays could produce up to 12% more energy than those employing single layer anti-reflective coatings,” via “a reduction of up to 70% of the light reflected from the surface,” said Stuart Boden and Darren Bagnall of the University of South Hampton (UK) in their poster display (“Bio-mimetic nanostructured surfaces for near zero reflection from sunrise to sunset”). Via electron beam lithography and dry etching (subwavelength): “We have fabricated a range of moth-eye arrays in silicon. Reflectance measurements confirm the low reflectivity of these arrays over the visible and near infra-red wavelengths, making them excellent candidates for reducing reflection on solar cells.”

“Insects have facetted, compound eyes, consisting of numerous anatomically identical units, the ommatidia,” wrote Doekele Stavenga and his colleagues in the Proceedings of the Royal Society B (22 March 2006. 273(1587):661-667), a journal whose roots date back over 200 years to London in 1800. Back in the 1960s, researchers discovered that the outer surfaces of moth eyes had “an array of cuticular protuberances termed corneal nipples” which reduce light reflection to 1%. Thus, moth night vision is improved by allowing 99% of light to enter moth eyes. Fewer reflections or less glint from the eyes makes moths harder for predators to detect. [Moth defenses against bat echo-location is another story, for another time]

“Moths thus realize a much higher light sensitivity than butterflies, allowing a nocturnal instead of diurnal (daylight) lifestyle,” wrote Stavenga et al. “A moth with large, glittering eyes will be quite conspicuous, and therefore its visibility is reduced by the eye reflectance decreasing… The insight that nipple arrays can strongly reduce surface reflectance has been widely technically applied, e.g. in window panes, cell phone displays and camera lenses.”

Moth-eye antireflection coatings (ARCs), “which are inspired by the grainy microstructures on the corneas of moths consisting of a non-close-packed hexagonal array of conical nipples, can suppress reflection over a broader range of wavelengths and wider angles of incidence than traditional multilayer dielectric ARCs,” wrote Chih-Hung Sun and other chemical engineering colleagues at the University of Florida, Gainesville, in an article titled “Large-scale assembly of periodic nanostructures with metastable square lattices.”

Moth-eye ARCs, reported Sun et al., “are widely utilized in eliminating the “ghost images” for flat-panel displays, increasing the transmittance for optical lenses, improving the out-coupling efficiency of semiconductor light emitting diodes, and enhancing the conversion efficiency of solar cells.”

“Since all biological structures are multifunctional, it makes them even more interesting,” wrote Stanislav Gorb in his introduction to the Springer book, Functional Surfaces in Biology. “Small surface structures at the micrometer and nanometer scales (i.e. very very small) are often vitally important for a particular function or a set of diverse functions…Because of the structural and chemical complexity of biological surfaces, exact working mechanisms have been clarified only for some systems.”

Some other possible innovations from the micro-world described in the Springer book: Protective slime coatings that protect seeds from rotting (e.g. pathogens) and stimulate or inhibit seed germination as needed. Water-repellent hairs have been “invented” by spiders. Water bugs can inspire waterproofing, anti-submersion fabrics, and surfaces promoting water runoff. Self-cleaning plant surfaces that cause water to form spheres and roll off are inspiration for water-repellent surfaces that might also trap air underwater for breathing. The plant world’s system of water transport pipes (xylem) can yield ideas for water transport systems. Feather microstructures could inspire aerodynamic innovations to complement lessons learned from insect flight.

We have barely scratched the surface of the ingenious natural world that we inhabit and share.

Natural vs Synthetic Repellents

March 30, 2010

SYNTHETIC OR NATURAL? Which is best? Since the 1950s the synthetic chemical DEET (N, N-diethyl-m-toluamide) has been the standard to which all other mosquito, tick and biting fly repellents have been compared. DEET is still the standard of comparison, but the long search for natural or organic repellents is finally yielding a number of potential alternatives, some from the plant world and others from such unlikely places as human sweat.

The progress in besting DEET has been so stunning that the Entomological Society of America (ESA) presented a four-hour symposium with a dozen 20-minute talks, Celebrating the Success of Global Insect Repellent Science Research. Habitues of the ESA know that in the world view of a female mosquito, humans are little more than scented apes put on Earth to be protein-rich blood meals to begat new generations of what we call vermin and they consider kin.

Sweat, heat, and carbon dioxide, that greenhouse gas that humans respire into the atmosphere with every exhaled breath, tip off mosquitoes and other bloodsuckers that the human food wagon has arrived. Actually, that’s putting it a bit crudely. Mosquitoes are actually connoisseurs, and sniff out humans like a gourmet would a fine wine. To be even more accurate, females are the true connoisseurs and gourmands, the bloodsucking vampire sex of the mosquito world. Male mosquitoes are true flower children, pacifists abhorring the bloodsucking life and mostly passing the time pollinating plants.

Longtime scholars of mosquito feeding habits on humans, like Willem Takken at Wageningen University in The Netherlands, have tallied 300 to 350 compounds mosquitoes can use to identify humans. About 60 of these odors are common to every person, and the rest give each human a slightly different scent. Thus, we oftentimes remember a person by their distinctive smell. Elegant experimental techniques like gene silencing and transferring mosquito olfactory genes to fruit flies allows the mapping of mosquito odor preferences. Some mosquito species, such as the malaria-vector Anopheles gambiae, can zero right in on humans. Other mosquito species may bypass humans in favor of cows, livestock or other animal species.

From a practical standpoint, if diseases like malaria, dengue and yellow fever are not a concern and you need protection for only an hour or two, one of the many commercial botanical repellents is likely to suffice as an alternative to DEET. Lemon eucalyptus products, including Quwenling from China, get high marks from the CDC. Daniel Strickman at the USDA-ARS in Beltsville, MD, and others have compiled long lists of botanicals good for about an hour of repellency, including: clove, geranium (geraniol), citronella, celery, lemon, lime, neem, pyrethrum, fringed rue, patchouli, pennyroyal, soybean, thyme, niaouli (Melaleuca viridiflora), makaen (Zanthoxylum limonella), Mexican tea (Chenopodium ambrosioides), Labrador tea (Ledum groenlandicum), and lily-of-the-valley.

However, natural or organic does not automatically mean safe or lacking in toxicity. Natural compounds, like synthetics, can also be sources of skin irritation, toxicity, and carcinogenicity. Even lemon eucalyptus oil can be an eye irritant. And as some herbal tea drinkers have learned the hard way (as is documented in the medical journals), the active ingredients in pennyroyal, violets and other botanicals can be dangerously toxic in too high a dose or with prolonged use.

The U.S. EPA can give what is known in legalese as FIFRA 25(b) Exemptions (Minimum Risk Pesticides), the USDA’s Strickland told the ESA repellent symposium. This allows some natural compound active ingredients to be used as repellents without testing. Examples include cedar oil (from eastern red cedar), citronella, garlic, geranium, lemongrass, peppermint, soybean oil and thyme. The International Fragrance Association investigates active ingredients to avoid lawsuits over cosmetics, though even this is not a guarantee against allergic reactions.

In short, caution is the watchword. Try a little bit first, and to be really safe use long sleeves and pants so that minimal repellent directly contacts the skin (as both natural and synthetic chemicals may penetrate the skin and enter the bloodstream).

Joel Coats’ lab at the University of Iowa provided the ESA symposium with a glimpse of the future. Coats’ lab is well-known in entomological circles for its pioneering work with naturally occurring monoterpene and sesquiterpene chemicals in plants such as catnip (Nepeta cataria), Osage orange (Maclura pomifera), West Indian sandalwood (Amyris balsamifera), and Siam-wood (Fokenia hodginsii). In short, the chemicals known as monoterpenes provide a broad spatial repellency, and the “oxygenated sesquiterpenes” provide contact repellency. And a mixture of the two provides both modes of action and the best repellency. You will probably want to wait for the testing to be completed and commercial products to be formulated.

But back to the question of which is best, natural or synthetic. Some of the best natural compounds, and there are too many to list, can outperform DEET. Even some new synthetics can outperform DEET in some ways. If you have a job that keeps you in the field and exposed to mosquitoes, biting flies and ticks for 12 or 24 hours at a time, then you need some heavy-duty, long-lasting protection. Indeed, that is the holy grail for organizations like the U.S. Army.

Life may have seemed simpler in the 1960s when Mr. Robinson told Dustin Hoffman in the movie The Graduate that the future was in plastics. Quantitative structure-activity relationships (QSAR) is the future in 2010, say Coats and his graduate student Gretchen Paluch. They forsee a leapfrogging future where natural repellents better than DEET lead to new synthetic spinoffs of nature’s best molecules better than anything yet known.

They believe that patchouli, cedar oil and other natural compounds can (via QSAR) provide the skeleton for designing new repellent molecules. However, it may not be so simple, as a fine ecological balance has evolved in nature. Though it may seem contradictory, even so-called repellent plants like catnip, which is famous for repellent molecules like neptalactone, also contain attractant molecules. Possibly the best repellents will also contain elements of attraction. But that is another story for another time.

Coffee Grounds for Mosquito Control

August 2, 2009

RECYCLE BIODEGRADABLE coffee grounds and simultaneously knockdown mosquitoes vectoring dengue, yellow fever, West Nile virus, malaria and other diseases. Hermione Bicudo at Universidade Estadual Paulista in Sao Paulo, Brazil, has been working towards that goal since the early 1980s. Mosquito control alternatives are needed, as mosquitoes are rapid, prolific breeders that rapidly develop resistance to pyrethroid, organophosphate and other types of insecticides.

Bicudo’s lab began studying caffeine effects on Drosophila fruit flies in the early 1980s. Drosophila fruit flies are a model insect widely used from the early twentieth century to unravel the mysteries of inheritance and genetics. Caffeine has been used relatively safely for centuries, and is found in medicines, cosmetics and food and beverages like coffee, tea, guarana and chocolate. Used coffee grounds are a ubiquitous waste product in modern caffeinated societies.

A resurgence of yellow fever mosquito, Aedes aegypti, in Brazil prompted Bicudo’s lab to test whether deleterious caffeine effects on Drosophila fruit flies (e.g. less frequent mating, less egg laying capacity, shorter life spans) might also slow mosquito population growth. Approximately four full soup spoons of used coffee grounds in a 250 mL glass of water killed 100% of aquatic mosquito larvae. This translated into fewer adult mosquitoes (the biting, blood-sucking stage) and less new mosquito egg laying (thus, lower mosquito populations over time). Used coffee grounds also have fertilizer value for plants, and can be dusted onto Bromeliads and other garden plants (possibly also puddles, ponds, tree holes, used tire breeding sites, etc.) where accumulated water forms potential mosquito breeding sites.

In contrast to other researchers, Bicuda’s lab found that caffeine solutions became more effective against mosquitoes with age. Day-old caffeine solutions took 20 days to kill 100% of mosquito larave; 25-day old caffeine solutions killed 100% of mosquito larvae in 1 day. Combined with elimination of mosquito breeding sites, used coffee grounds or caffeine solutions could prove very useful in IPM (integrated pest management) programs to slow pesticide resistance and reduce mosquito breeding.