Food Sweetener Safely Slays Insects

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.

Silicon Bed Bug Weaponry

BED BUGS CAN be spiked and trapped by tiny spears like leaf hairs, and can become dehydrated or dessicated and rendered harmless by certain forms of silicon, the second most abundant element in planet Earth’s crust (28%) after oxygen (47%). That silicon can be the bane of bed bugs is indeed odd when one considers that silicon permeates our world from beach sands, opals, agates and quartz crystals to sandpaper, semiconductors, glasses, ceramics, optical fibers and cosmetic products. Indeed, the famous French scientist and silkworm entomologist, Louis Pasteur, whose name has become synonymous with the germ theory of medicine, predicted silicon’s eventual service in human medicine; though Pasteur was probably not thinking along the lines of silica gels and desiccant diatomaceous earth dusts as remedies for the 21st century’s worldwide medical plague of bed bugs.

Despite its commonness in nature and the human environment and potential uses in human medicine, the use of silicon products comes with caveats to users, who might want to wear sufficient protective clothing and respirators to avoid inhaling the products. Strangely enough, that much maligned metabolic waste product, carbon dioxide, which along with sunlight is essential to photosynthesis and life on planet Earth, is perhaps a safer component (e.g. as a lure or attractant) when integrated into bed bug traps. Food grade diatomaceous earth made from freshwater diatoms is considered relatively nontoxic; whereas filtering grade diatomaceous earth (e.g. the type used for swimming pool filters) is a crystalline form with inhalation toxicity.

“Louis Pasteur (1822-95) said that silicon would prove to be a treatment for many diseases and in the first quarter of the twentieth century there were numerous reports by French and German doctors of sodium silicate being used successfully to treat conditions such as high blood pressure and dermatitis,” wrote British chemist John Emsley in his superb compendium, Nature’s Building Blocks (An A-Z Guide to the Elements). “By 1930, such treatments were seen to have been in vain and the medication fell out of favor. So things rested, until the discovery that silicon might have a role to play in human metabolism, and then followed suggestions that it could have a role in conditions such as arthritis and Alzheimer’s disease, but no new treatment based on these suggestions has yet emerged. Meanwhile, silicon continues to be linked with a disease of its own: silicosis. Miners, stone-cutters, sand-blasters and metal-grinders develop this lung condition which is a recognized occupational disorder caused by the inhalation of minute particles of silica…” Symptoms include coughing, wheezing and shortness of breath; a more aggressive form of silicosis associated with certain types of asbestos can develop into lung cancer and has been a rich source of litigation for occupational exposure in the USA.

While silica products should be used sparingly (a caution that should also apply to most sprays) or not at all by some people (e.g. existing respiratory problems; perhaps seek a medical opinion before using), they might prove for many others the tipping point for winning the bed bug war as part of an integrated approach that controls bed bugs (many of which are pesticide resistant) using a multiple arsenal of weapons including herbal oils, clutter reduction, heat, sealing crack and crevice harborages, traps, pheromones, carbon dioxide, vacuuming under baseboards, etc.

At the 2014 Entomological Society of America (ESA) annual meeting, Kyeong-Yeoll Lee of South Korea’s Kyungpook National University (Daegu) reported that silica in the form of diatomaceous earth (Perma-Guard(TM) or Fossil-Shell(R)) acted as a synergist when heat (hot air) fumigations substituted for chemical fumigants such as methyl bromide. Though the test insect was Indian meal moth, a worldwide pest of stored grain and many other packaged agricultural products, it would not be surprising to find that heat treatments combined with silica products like diatomaceous earth will also prove efficacious and perhaps also synergistic against bed bugs. Indeed, heat treatments may induce bed bugs to move around more, which could hasten contacting diatomaceous earth and water loss.

At the same 2014 ESA meeting, Virginia Tech (Blacksburg, VA) researcher Molly Stedfast provided some impressive results via the time-consuming process of first educating apartment residents about bed bugs and then painstakingly vacuuming along baseboards to suck up as many bed bugs as possible before applying the silica products under the baseboards to further reduce bed bug populations. This integrated (IPM; integrated pest management) approach required quite a bit of manual labor, as furniture had to be moved to gain access to the baseboards before vacuuming and then applying silica gel or dust products.

Stedfast tested two silica products, Mother Earth(TM) D, a highly-absorptive desiccant dust made from 100% freshwater diatomaceous earth, and CimeXa(TM) Insecticide Dust, a 100% amorphous silica gel. The silica dust or gel injures the insect cuticle (outer protective “skin”), letting water leak out and leading to dehydration (providing relative humidity is not extremely high, above 81%; and free water is unavailable). Both the diatomaceous earth and silica gel products were “very effective at killing bed bugs even at 10% of the label rate.” Going above the label rate was a waste of resources, as only so much product can contaminate the bed bugs. Bed bugs can die within 24 hours of contacting the silica products, but air currents that blow the dusts around can be a problem; also the products need to stay moist and not dry out to be effective. Among Stedfast’s biggest headaches is the application equipment, which was not very robust.

The patent literature reveals that inventors such as Roderick William Phillips in Vancouver are working on improved spray apparatuses for applying diatomaceous earth: “There is disclosed a spray apparatus for holding contents comprising diatomaceous earth and a compressed propellant for propelling the diatomaceous earth. There is also disclosed use of diatomaceous earth to control a population of bedbugs…diatomaceous earth, a naturally occurring siliceous sedimentary rock that includes fossilized remains of diatoms. However, known methods of applying diatomaceous earth can be cumbersome. For example, known methods of applying diatomaceous earth may undesirably require handling the diatomaceous earth, for example to transfer the diatomaceous earth from a container not having an applicator to a separate applicator apparatus. Also, known applicator apparatuses may apply diatomaceous earth unevenly, which may be wasteful or ineffective. In general, known methods of applying diatomaceous earth may be sufficiently complex so as to require professional involvement, which may undesirably add to cost and delay of bedbug treatment. Also, numerous types of diatomaceous earth are available, and different types of diatomaceous earth vary widely and significantly from each other. It has been estimated that there are approximately 100,000 extant diatom species…and may vary widely and significantly in size and shape across a very large number of diatom species…”

At the University of British Columbia (Vancouver), Yasmin Akhtar and Murray Isman demonstrated that both diatomaceous earth and herbal or botanical compounds such as neem, ryania and rotenone are to varying degrees transported by adult bed bugs and contaminate other adults and younger bed bug nymphs. “Our data clearly demonstrate horizontal transfer of diatomaceous earth and botanical insecticides in the common bed bug,” said Akhtar and Isman. “Use of a fluorescent dust provided visual confirmation that contaminated bed bugs transfer dust to untreated bed bugs in harborage. This result is important because bedbugs live in hard-to-reach places and interaction between conspecifics can be exploited for delivery and dissemination of management products directed at this public health pest…This result is important because bedbugs live in hard-to-reach places (cracks, crevices, picture frames, books, furniture) and as such interaction between the members of the colony can be exploited for delivery and dissemination of control products.”

At the 2014 ESA annual meeting, Akhtar suggested protecting travelers and suppressing bed bug transit by building diatomaceous earth into luggage, mattresses and fabrics. Diatomaceous earth provided 96% repellence; bed bug mortality was zero at 24 hours, but 93% after 120 hours. Diatomaceous earth could also be applied to box springs, dressers and headboards, and under carpets and inside drywall. A diatomaceous earth aerosol provided 81% bed bug mortality at 30 days, and was still active and being transferred from dead bed bugs to live bed bugs.

Diatom species mined for diatomaceous earth are stunning in their architectural variety and beauty. Ultimately, the silicon secrets of living diatoms has the potential to transform “the manufacture of siloxane-based semiconductors, glasses, ceramics, plastics, elastomers, resins, mesoporous molecular sieves and catalysts, optical fibers and coatings, insulators, moisture shields, photoluminescent polymers, and cosmetics,” wrote UCSB marine scientist Daniel E. Morse. “The manufacture of these materials typically requires high temperatures, high pressures or the use of caustic chemicals. By contrast, the biological production of amorphous silica, the simplest siloxane [(SiO2)n], is accomplished under mild physiological conditions, producing a remarkable diversity of exquisitely structured shells, spines, fibers and granules in many protists, diatoms, sponges, molluscs and higher plants. These biologically produced silicas exhibit a genetically controlled precision of nanoscale architecture that, in many cases, exceeds the capabilities of present-day human engineering. Furthermore, the biological productivity of siloxanes occurs on an enormous scale globally, yielding gigatons per year of silica deposits on the floor of the ocean. Diatomaceous earth (composed of the nanoporous skeletons of diatoms) is mined in great quantities from vast primordial deposits of this biogenic silica.”