Proceedings of tlte Ttl: International Worhng Conference on Stored-product Protection - Yolume 1 Evaluation and standardised testing of diatomaceous earth Zlatko Korumc1 and Peter Ormesher Abstract from Eocene/Miocene Epochs DePOSIts range III tluckness from a few mches to several hundred meters. The deposit Diatomaceous earth (DE) deposits are found around the may be fmely lammated or massive (Quarles and Wmn, world We have extensively tested DE samples collected 1996) . from 80 different sources m Australia, Canada, Chile, When mmed , diatomite contams 50% or more moisture. Chma, Denmark, France, Germany, Japan, Macedonia, The solid component contams about 86 to 94% silica, the MeXICO, Spam , and the USA There was a WIde variation III remamder bemg chIefly alumma and alkalies from clay. The the insecticidal activity of DE samples from different only changes to diatomite dunng processing (chrushing, sources. HIgh msecticidal actrvity was positively correlated drymg , nulling) IS the reduction of the moisture content and WIth gram bulk density reduction The most effective DE mean aggregate particle SIZe MOIsture is reduced to 2 - 6% samples had lower tapped densities « 300 gIL), good and nulling reduces particle SIze to 0.5 to over 100 rmcrons, adherence to the gram (> 70%), a SI(h content greater WIth the majorrty of particles measunng from 10 to 50 than 80%, a pH below 8.5, and reduced gram bulk density microns. The result of this process IS diatomaceous earth, a by more than 2.5 kg/hL when applied at a concentration of fme, talc-like powder or dust considered to be non-toxic to 50 parts per milhon (ppm). Mean particle size (below 15 mammals DE IS extremely stable and does not produce tOXIC microns) and diatom shape were not correlated WIth cherrucal residues or react with other substances in the insecticidal activity. Assessmg these frve physical environment (Quarles, 1992) charactenstics allows for the rapid screenmg of DE sources DIatomaceous earth (DE) IS produced in more than 30 before time consummg bioassays are conducted. countnes World production of DE has been steady at Reduced susceptibility (1 3 - 2.2 fold) of Tribolium approximately 1.4 nulhon tons Major producers are the U. casiameum , Cryptolestes [erruqmeus and Rhyzopertha S. , followed by France and the Republic of Korea These domuuca adults exposed to DE for 5 - 7 generations, as countries accounted for 61 % of the world production. compared With unselected lab strains, suggests that msects Denmark and countries of the former Soviet Union, each may be able to develop physiological or behavioural produces about 7 % of the world production. The prmcipal resistance mechanisms to DE use of diatomaceous earth IS m the filtration of vanous alcoholic beverages, and as a additive in spice and sugar, and pharmaceutical and biotechnological medta The second largest use of DE IS as an absorbent (pet htter and 011 spIl1 Introduction absorbents) DE IS also used as a pestictde carrier, catalyst carrier, roughness and flattmg agent m paint and polishes, an antiblockmg agent III polyethylene film, a soft abrasive m Diatomaceous earth (DE), formed from fossilised diatoms, SIlver and automotive polishes, a bulk extender and a IS composed of almost pure silicon dIOXIde Diatoms are thermal msula tor (Lemons, 1998) unicellular algae and probably the most Widespread group of DE IS probably the most efficacious natural dust used as an plants on earth. They are abundant III all aquatic msectIcide The dust particles adhere to the bodies of the ecosystems, but also occur III terrestrIal enVIronments msects as they walk over It. Damage occurs to the msects' There are more than twenty-five thousand species of dIatoms protective wax coat on the cuticle, mostly by sorption and to With no two havmg the same morphology (Round et al a lesser degree by abraSIon, or both. The result IS the loss 1992). When the dIatoms dIe, the tmy shells smk and form of water from the Illsect's body through deSIccation resultmg thIck layers over the centurIes. Eventually these deposits m death (EbelIng, 1971) The other mode of action of DE IS became fOSSIlIsed and compressed mto a soft, chalky rock repellence caused by the phYSIcal presence of the dust called diatomIte, the unprocessed (mmeral) form of DE. A (WhIte and al , 1966) There are probably other modes of well-documented fossIl record of diatoms extends back to the action of DE that are yet to be dIscovered (Quarles, 1992). mId Cretaceous penod, but the vast majonty of deposits are De has been studIed extenSIvely as a stored-grain 1 Hedley Technologles Inc , 2600 Skymark Avenue, SUite 101- protectant (Quarles, 1992; Banks and Fields, 1994; BUlldmg 4. Mlsslssauga, Ontano, L4W SB2, Canada Korumc, 1994, in press; McLaughhn, 1994; Subramanyam 738 Proceedings of the 7th Internatwnal Workmg Conference on Stored-product Protectwn - Volume 1 et. al , 1994; Quarles and Wmn , 1996; Korumc et al. , 1997 ) Differences m the efficacy of various DE The Difference Among DE's from formulations agamst the same msect species have been Different Geological Locations reported. The efficacy of diatomaceous earth (DE) agamst msects Numerous expenments were conducted With 36 different depends greatly on several physical properties of the diatom natural manne and fresh water diatomaceous earth samples particles (Ebelmg, 1971 ; Quarles and Wmn, 1996 ; collected in 1994 and 1995 from vanous deposits from the Subramanyam, 1995; Korumc, 1997) The analysis of USA, MeXiCO, Canada, Australia, Japan, Chma , and physical and chemical properties of DE is time consummg Macedoma (Koruruc, 1997), and With approximately 40 and expensive, and can be conducted only by experts at additional samples collected dunng 1996 and 1997 from specially equtpped laboratones Therefore, bioassays were Canada, the USA, Chile, France, Germany, Denmark and considered the most important cntenon for the assessment Spam A great difference m efficacy agamst msects was of the efficacy of DE agamst msects. However, this method observed between samples (Korumc, 1997, m press). For is relatively expensive and time consummg, smce it requires example, the L~ (lethal concentration for 90 % of msects expertise and a well-equipped entomological laboratory exposed) in mg of DE per kg of wheat (ppm) for nee By studying different physical properties of DE's, we weevil, Sitopluiu» oryzae (1. ) was 270 ppm for Cehte 209 attempted to discover the correlation between selected (USA), 438 ppm for DE from Austraha, 603 ppm for J 3 properties of DE samples and their efficacy agamst msects (Japan), 829 ppm for DIaFl1 610 (USA), and 1137 ppm for Accordmg to the results we developed a rapid, simple and Melocide DE 100 (USA) For all species tested, there was low-cost procedure for the prediction and the assessment of no mortahty With 1700 ppm of C 16 (Chma ) In many the msecticidal value of DE, Without conductmg bioassays or cases, samples of DE from different locations in the same tnne-consummg and expensive physical and chemical country exhibited a great difference in efficacy (Table 1; analyses Korumc, 1997) Table 1. The efficacy of different diatomaceous earths on Canadian Western Hard Red Spnng wheat agamst nee weevil (RW) and red flour beetle (RFB) (Korumc, 1997). % LC50 (95 CI) - ppm Diatomaceous earth RW after 5 days RFB after 14 days Cehte 209 (USA) 270(213 - 340) 417(328 - 529) J 2 (Japan) 333(263 - 423) 631(506 -787) DE Aus (Australia) 438(346 - 553) 494(383 - 637) Dicalite (USA) 496(393 - 626) 569(438 -738) C 7 (China) 546( 430 - 393) 609( 456 - 812) J 3 (Japan) 603(480-758) 562( 430 -737) Mx 2 (Mexico) 634( 493 - 815) 648(497-847) Perma Guard (USA) 680(555 - 832) 1211 (728 - 2014) DIaFil 610 (USA) 829(561-1223) 1477(447 - 4883) Melocide DE 100 (USA) 1137(546 - 3734) 2047 ( 1178 - 3556) C 2 (China) 1501 (542 - 4154) low mortahty at 1700 ppm Mx 1 (MeXiCO) 1648(515 - 5101) low mortahty at 1700ppm Can 1 (Canada) 2044( 464 - 9007) low mortality at 1700 ppm C 16 (Chma) no mortahty at 1700 ppm no mortality at 1700 ppm Other differences m the vanous DE formulations tested content (Table 2; Korumc, 1997; Table 3; Korumc, m were: diatom species, origin (rnanne or freshwater), pH press) value, particle shape, particle Size distribution, and Si(h 739 Proceedmqs of the 7th Internatwnal Working Conference on Stored-product Proieciuni - Volume 1 Table 2. Some DE's properties * that may influence the efficacy against msects. 50 ppm DE DE Adherence Wheat bulk tapped pH to wheat SIOz Particle SIze distnbution DE density reduction density kernels Mean Below 12 (kg/hl) (gil) (%) (%) m microns microns (%) Cehte 209 (USA) 3.2 222 5.7 84.0 87 82 65 0 J 2 (Japan) 2.9 230 4.5 75.0 80 13.1 46.3 J 3 (Japan) 2.5 230 5.2 73.0 80 7.5 75.7 Mx 2 (Mexico) 2.2 328 8.5 72.0 80 N/A N/A Aus (Australia) 2.6 220 6.5 71.0 85 11.1 57.8 Dlcah te (USA) 2.4 218 7.0 74.0 85 10.4 57.4 Perma Guard (USA) 2.2 286 8.0 70.0 93.0 10.7 62.7 DiaFl1 610 (USA) 2.0 244 8 0 70.0 87.0 7 80 Melocide DE 100 (USA) 1.8 500 7.2 62.0 83.6 11.1 54.8 DlaFl1 620 (USA) 2.0 390 8.0 70.0 87.0 8 80 C 2 (China) 2.0 322 6.2 70.0 83.0 N/A N/A C7 (China) 2.2 234 6.0 70 85 16.4 34.7 DE Can (Canada) 1.9 442 5.9 70.0 70.0 N/A N/A * Methods according to Korumc (1997) Table 3.