Payam Nour University. From the SelectedWorks of Adel Khashaveh

Transcription

1 Payam Nour University From the SelectedWorks of Adel Khashaveh 2007 Effect of five diatomaceous earth formulations against Tribolium castaneum (Coleoptera: Tenebrionidae), Oryzaephilus surinamensis (Coleoptera: Silvanidae) and Rhyzopertha dominica (Coleoptera: Bostrychidae) Adel Khashaveh Available at:

2 Using diatomaceous earths against stored-product pests 359 Effect of five diatomaceous earth formulations against Tribolium castaneum (Coleoptera: Tenebrionidae), Oryzaephilus surinamensis (Coleoptera: Silvanidae) and Rhyzopertha dominica (Coleoptera: Bostrychidae) MASUMEH ZIAEE 1 and ADEL KHASHAVEH 2 1 Department of Zoology, Young Researcher Club of Urmia Islamic Azad University, Urmia, 2 Department of Entomology, Agricultural Faculty, Urmia University, Urmia, Iran Abstract Laboratory bioassays were conducted to determine the effect of food source on the survival of Tribolium castaneum Herbst, Oryzaephilus surinamensis L. and Rhyzopertha dominica F., after exposure to five diatomaceous earth (DE) formulations: Protect-It, Insecto, Perma-Guard TM, Dryacide and SilicoSec. Adults of these species were exposed to DEs at the rate of 0.5 mg/cm 2 for 1 day on filter paper inside plastic Petri dishes. After exposure, the initial mortality was counted and live individuals of the three species were held for a week in glass vials containing 50 mg wheat flour, rice and whole wheat, respectively. In the second experiment, after 1 day exposure to DEs, beetles were transferred to Petri dishes without food and held for a week to determine if the presence of food source would decrease the mortality of beetles. Experiments were carried out at 27 o C and 55% RH in the dark. The initial mortality in both of the experiments reached 100% for the three species exposed to Protect-It and in the case of R. dominica and O. surinamensis exposed to Dryacide. In contrast, low level of mortality (< 10%) was observed for T. castaneum exposed to Perma-Guard TM and Insecto. The mortality after the post-treatment period on food was decreased for the three species exposed to Perma-Guard TM and in the case of T. castaneum and R. dominica exposed to Insecto and SilicoSec. Adults of O. surinamensis were the most susceptible followed by R. dominica and 100% adult mortality was obtained, whereas T. castaneum were the least susceptible beetles to DEs. Protect-It and Dryacide were the most efficient DE formulations and can be used effectively in a stored grain integrated pest management program. Key words diatomaceous earth, initial mortality, food, delayed mortality, Oryzaephilus surinamensis, Rhyzopertha dominica, Tribolium castaneum DOI /j x Introduction In stable, well organized societies, infestations of storage pests are mostly held under control. However, the costs of Correspondence: Masumeh Ziaee, Department of Zoology, Young Researcher Club of Urmia Islamic Azad University, Urmia, Iran. Tel: ; fax: ; masumeh_ziaee@yahoo.com keeping insects under control are significant and damaging infestations can occur if mistakes or neglect occur. Over the life of a given batch of commodity, protection against insect attack may account for several percent of its value (Rees, 2004). For control of stored grain insect pests several methods exist, but nowadays researchers seek reduced-risk methods. Diatomaceous earth (DE) has long been known as a potentially useful grain protectant because it is safe to use, does not affect grain end-use quality, provides long-term protection and is comparable in cost to 359

3 360 M. Ziaee & A. Khashaveh other methods of grain protection and dust formulations are more likely to be adopted in developing countries (Korunic et al., 1996; Korunic, 1998; Athanassiou et al., 2005a, b; Moras et al., 2006; Ziaee et al., 2007). Diatomaceous earths are composed of amorphous silicon dioxide and formed from fossilized diatoms (single-celled algae). They have low mammalian toxicity, and their use is compatible with other, reduced-risk, integrated pest management (IPM)-based control methods in storage facilities (Subramanyam & Roesli, 2000). DE particles adhere to the body of the insect and damage the protective waxy layer of the insect cuticle by absorption, and to a lesser degree, by abrasion. Death is caused from loss of water from the insect s body (Ebeling, 1971). Apart from treating the entire mass of the grain commodity, DEs can be used for surface treatment of bulk-stored grains. White and Loschiavo (1989) conducted studies in which the effects of exposure interval, type and quantity of food after exposure to silica aerogel on the survival of Oryzaephilus mercator F. (Coleoptera: Silvanidae) and Tribolium confusum Jaquelin duval (Coleoptera: Tenebrionidae) were determined. Mortality of beetles increased with exposure interval but the efficacy of silica aerogel was reduced when beetles were provided with food after exposure. Extensive comparisons among different DEs against stored-grain insect species have been carried out by other researchers as well (Fields & Korunic, 2000; Athanassiou et al., 2004, 2005b; Kavallieratos et al., 2005; Athanassiou, 2006; Vayias et al., 2006a, b; Athanassiou et al., 2007; Ziaee et al., 2007). Arthur (2000a) carried out an experiment to determine the effects of temperature and relative humidity on the toxicity of Protect-It placed on filter paper inside plastic Petri dishes against T. castaneum and T. confusum. He confirmed that mortality of both species increased with exposure interval. Furthermore, Arthur (2000b) investigated the impact of food source on the survival of T. castaneum and T. confusum. He reported that accumulated food material reduces the residual efficacy of the DE treatment. The aim of the current study was: (i) to compare the efficacy of different DE formulations applied on an inert filter paper against T. castaneum, O. surinamensis and R. dominica; and (ii) to determine whether the presence of food can affects survival of T. castaneum, O. surinamensis and R. dominica after exposure to DEs. Materials and methods Insects Adults of T. castaneum, O. surinamensis and R. dominica were used in the tests. The T. castaneum adults were taken from a culture that was kept on wheat flour plus 5% brewers yeast (by weight); adults of O. surinamensis were taken from a culture that was kept on rolled oats and 5% brewers yeast (by weight); and R. dominica adults were taken from a culture that was kept on whole wheat; at 28 o C, 65% ± 5% RH and continuous darkness. All species were kept in laboratory cultures for > 3 years. Adults used in the experiments were <14 days old. DE formulations Five commercially available DE formulations were used in the tests: 1. Protect-It is a mixture of freshwater DE (Hedley Technologies Inc., Mississauga, ON, Canada) with 10% silica aerogel to enhance insecticidal activity. It contains approximately 83.7% amorphous silicon dioxide, 5.6% Al 2, 2.3% Fe 2, 0.9% CaO, 0.3% MgO, and 1.9% other oxide (e.g. Ti, P 2 ), and 3%-5% moisture content (m. c.). The median particle size is 5 μm (Korunic & Fields, 1995). 2. Insecto is a marine DE (Natural Insects Products, Inc., Orange, CA, USA) with 10% food-grade bait. It has 87% (w/w) amorphous silicon dioxide, with 2%-4% m.c., and a chemical composition of approximately 3% Al 2, 1% Fe 2,<1% CaO, MgO, Ti, and P 2. The median particle size is approximately 8.2 μm (Subramanyam et al., 1994). 3. The freshwater DE Perma-Guard TM D-10 (Perma- Guard TM Inc., Albuquerque, NM, USA) contains 93% SiO 2, 3% Al 2, 1.3% Fe 2, 1.1% CaO, 0.6% Na 2 O, 0.3% K 2 O and 0.2% Ti and maximum 4.5% m.c. The median particle size is approximately 11.7 μm (Arnaud et al., 2005). 4. The marine DE Dryacide (Dryacide USA LLC, San Diego, CA, USA), is a white dust that contains 91%-92% amorphous silicon dioxide, 3%-5% clay minerals and 3%-5% m.c. with a mean particle size of μm (A. McLaughlin, personal communication). 5. SilicoSec is a freshwater formulation of DE obtained from Biofa GmbH, Münsingen, Germany and it is composed of 92% SiO 2, 3% Al 2, 1% Fe 2 and 1% Na 2 O. The median particle size is 8-12 μm (Athanassiou et al., 2005b). Post-treatment period on food A standard plastic Petri dish with an external radius of 10 cm, internal radius of 8.8 cm and an area of 62 cm 2 served as the exposure arena. Beetles were exposed for a day to five DE formulations at the rate of 0.5 mg/cm 2. Therefore 31 mg of each DE formulation was placed on filter paper inside plastic

4 Using diatomaceous earths against stored-product pests 361 Petri dishes. The dishes were shaken for a minute to distribute the DE which due to static electricity tends to stick to the filter paper. After shaking, the Petri dishes were left undisturbed for at least 1 minute in order to settle the DE particles on the filter paper. Subsequently, 15 adults were introduced in each dish and the dishes were covered with lids. Petri dishes were placed in the incubator set at 27 o C and 55% RH in the dark. The desired RH was maintained by using a saturated salt solution of sodium bromide, as recommended by Greenspan (1997). Each treatment of DEs plus untreated dishes containing filter paper alone, were replicated four times for each species (24 Petri dishes per species). After a day of exposure to DEs, insects were assessed as live if able to move normally and to respond to stimuli or as dead if unable to do either and initial mortality was recorded; then live individuals of T. castaneum, O. surinamensis and R. dominica were held for a week in glass vials containing 50 mg wheat flour, rice and whole wheat, respectively under the same conditions. The moisture content of commodities was measured by drying 10-gram samples of each commodity in a ventilated oven at 110 o C. The moisture content of wheat flour, rice and wheat was 13.4%, 12.8% and 11.3% m.c., respectively. The level of 55% RH corresponds to moisture content values 13% for wheat flour, 11.5% for wheat and 12.5% for rice, respectively (Pixton, 1967; Pixton & Warburton, 1971; Henderson & Pixton, 1982). After 1 week, the insects were discarded from the samples and the number of live and dead individuals was assessed as above. Post-treatment period without food All exposure conditions were the same as mentioned in experiment 1. Petri dishes were lined with filter paper and 31 mg of each DE placed on them. Each DE treatment was replicated four times for each insect and the untreated dishes containing filter paper alone served as a control with four replications (24 Petri dishes per species). Fifteen adults of each species were exposed to DEs for 1 day. Upon completion of the exposure, beetles were classified as live or dead and initial mortality was recorded; then live adults were transferred to new Petri dishes lined with filter paper alone; without food, and returned to the incubator for a week. After the 1-week holding period, the mortality of adults was measured. Trials were conducted at 27 o C and 55% RH in the dark as described for the first experiment. Data analysis Control mortality was zero for insects and no corrections were necessary. The data were analyzed by using analysis of variance (ANOVA) and the t-test was used to determine significant differences between mortality of adults after the post-treatment period without food and on food for each species and DE formulation (SAS, 2000). To equalize variances, mortality percentage was transformed using the square-root of the arcsin. Means were separated by using the Tukey-Kramer (HSD) test at P = 0.05 (Snegecor & Cochran, 1989). Results Post-treatment period on food The effect of DE formulation on adult mortality of T. castaneum, O. surinamensis and R. dominica after the posttreatment period on food and without food was significant at P < 0.01 level (Tables 1, 2). The initial mortality and percentage mortality of T. castaneum, O. surinamensis and R. dominica adults held for 1 week on the food source is presented in Table 3. Initial mortality ranged between 3.33% for T. castaneum exposed to Perma-Guard TM and 100% in the case of R. dominica and O. surinamensis exposed to Dryacide and all three species exposed to Protect-It were dead after 1 day of exposure. All adults of O. surinamensis were dead 1 week after their exposure to SilicoSec. Post-treatment period without food Initial mortality and percentage mortality of beetles after the post-treatment period without food is recorded in Table 4. Table 1 ANOVA parameters for mortality levels of Tribolium castaneum, Oryzaephilus surinamensis and Rhyzopertha dominica adults exposed to five diatomaceous earth (DE) formulations and after post-treatment period on food (df treatment = 4; df total = 19). Source Insect species DE formulation 1 day of exposure 1 week on food F P F P T. castaneum O. surinamensis R. dominica Table 2 ANOVA parameters for mortality levels of Tribolium castaneum, Oryzaephilus surinamensis and Rhyzopertha dominica adults exposed to five diatomaceous earth (DE) formulations and after post-treatment period without food (df treatment = 4; df total = 19). Source Insect species DE formulation 1 day of exposure 1 week without food F P F P T. castaneum O. surinamensis R. dominica

5 362 M. Ziaee & A. Khashaveh Table 3 Initial mean mortality and mortality (%)±SEM of Tribolium castaneum, Oryzaephilus surinamensis and Rhyzopertha dominica adults after post-treatment period on food. DE formulations T. castaneum O. surinamensis R. dominica 1 day of 1 week 1 day of 1 week 1 day of 1 week exposure on food exposure on food exposure on food Dryacide 91.6 ± 7.2 a Perma-Guard TM 3.3 ± 4.1 c 31.1 ± 1.9 c 73.3 ± 2.9 c 91.6 ± 5.2 b 38.3 ± 1.8 c 68.3 ± 2.6 c Protect-It Insecto 8.3 ± 5.2 bc 30.0 ± 3.6 c 76.6 ± 2.9 c 96.6 ± 4.1 ab 43.3 ± 6.1 bc 81.6 ± 1.2 c SilicoSec 33.3 ± 5.0 b 81.6 ± 5.7 b 93.3 ± 4.3 b ± 2.5 b 93.3 ± 4.3 b Means within columns followed by the same letter are not significantly different; -: 100% mortality was observed, Tukey-Kramer-HSD test at P = Table 4 Initial mean mortality and mortality (%) ±SEM of Tribolium castaneum, Oryzaephilus surinamensis and Rhyzopertha dominica adults after post-treatment period without food. DE formulations T. castaneum O. surinamensis R. dominica 1 day of 1 week 1 day of 1 week 1 day of 1 week exposure without food exposure without food exposure without food Dryacide 91.6 ± 4.8 b Perma-Guard TM 6.6 ± 4.3 d 45.0 ± 2.4 b 66.6 ± 1.6 c ± 1.1 c 86.6 ± 2.3 b Protect-It Insecto 6.6 ± 0.0 d 60.0 ± 1.6 b 75.0 ± 2.0 c ± 0.9 c 96.6 ± 4.1 a SilicoSec 36.6 ± 1.1 c 96.6 ± 4.1 b 86.6 ± 2.3 b ± 2.2 b - Means within columns followed by the same letter are not significantly different; -: 100% mortality was observed, Tukey-Kramer-HSD test at P = After the post-treatment period without food, the mortality of T. castaneum exposed to DEs was 45% ± 2.4% to 100%, and for R. dominica mortality ranged between 86.6% ± 2.3% to 100%, whereas; the entire population of O. surinamensis adults were dead after being held for 1 week without food (Table 4). The comparison between mortality of beetles with and without food after the 1 week holding period for each species indicated that the presence of a food source may decrease the mortality of beetles (Table 5). Discussion There are several reports on the increased survival of stored product beetles when they are given food after exposure to inert dusts. However, the magnitude of these effects can vary depending on the specific dusts, exposure conditions, type of food material and insect species (Arthur, 2000b; Athanassiou et al., 2003, 2004, 2005b, 2007; Athanassiou & Kavallieratos, 2005; Kavallieratos et al., 2005; Athanassiou, 2006). Dowdy (1999) exposed T. castaneum to different DE Table 5 Mortality (%) of Tribolium castaneum, Oryzaephilus surinamensis and Rhyzopertha dominica after post-treatment period without food versus mortality (%) of beetles after posttreatment period on food. DE T. O. R. formulations castaneum surinamensis dominica Dryacide P NC NC NC t Perma-Guard TM P 0.02* 0.04* 0.006** t 4.29* 3.25* 6.71 Protect-It P NC NC NC t Insecto P 0.035* 0.18NS 0.016* t SilicoSec P 0.010* NC 0.04* t Differences between mortality (%) of adults after post treatment period without food and on food for each species and DE formulation was determined by the t test (SAS, 2000). NC: cannot be calculated because the variance of data was zero; NS: no significant difference; * and ** indicate that mortality of adults without food > mortality on food at P < 0.05 and P<0.01, respectively.

6 Using diatomaceous earths against stored-product pests 363 samples at the rate of 0.5 mg/cm 2 for a 15 and 30 minute duration at 34 and 50 o C. After exposure, beetles were held for 1 week at 34 o C and 60% ± 5% RH in empty dishes or on dishes with 500 mg of flour. He stated that the mortality during 7 days slowly increased, in comparison with the initial mortality. White and Loschiavo (1989) exposed O. mercator and T. confusum to silica aerogel at the rate of 0.72 mg/cm 2. The beetles were either starved after exposure or given 125 mg to 1 g of whole rolled oats, ground rolled oats, or ground breadcrumbs. All starved beetles were dead within 3 days, whereas the mortality of both species in the food treatments was greatly delayed. These findings were similar to the results of our experiment. The mortality of three species exposed to Protect-It and Dryacide and for O. surinamensis exposed to SilicoSec after the 1-week holding period on food were 100% which was expected after the high level of mortality (> 90%) recorded after initial exposure. However, the insects that survived after 1 day of exposure may be able to remove the dust particles from the cuticular surface. Therefore, insects provided with a food source are going to survive far better than those left to starve. Chapman (1971) stated that stored-product beetles have well-developed cryptonephridial systems to remove water from dry foods such as cereals. At the same time, the physiological stress of an insect that can eat after exposure is far less than that of an insect left to starve and this will make the former far more capable in replenishing the lost protective waxy layer and terminating the water loss through the exposed cuticle. In our study comparing the mortality of beetles after the post-treatment period with and without food indicated that the mortality of beetles exposed to the most effective DEs (Protect-It and Dryacide ) had not decreased, even when they are given food after exposure. In contrast, the mortality of adults was low, if they had access to food after exposure to the less effective DEs (Perma-Guard TM, SilicoSec and Insecto ). Cook (2003) recorded complete mortality of T. castaneum when exposed to dishes treated with 10 g/m 2 SilicoSec for 48 h, followed by a 7-day recovery period. Mason (1997) also reported 94% adult mortality against T. castaneum with 7 g/m 2 application of Protect-It. Arthur (2000b) emphasizes the importance of sanitation to reduce the occurrence of food material within the storage environment and to eliminate harborage sites and refuge when possible. The effect of different DEs on various stored product insects has been studied by numerous researchers (Korunic, 1998; Athanassiou et al., 2003, 2004, 2005a, b, 2006, 2007; Athanassiou & Kavallieratos, 2005; Kavallieratos et al., 2005; Vayias et al., 2006a, b). Korunic et al. (1997) found that on the same commodity, there was a significant variation in the susceptibility of different insect species to the DE-based formulation Protect-It. The insects, in order from the most susceptible to the least were Cryptolestes ferrugineus Stephens (Coleoptera: Cucujidae); O. surinamensis; Sitophilus granarius L. (Coleoptera: Curculionidae); Sitophilus oryzae L. (Coleoptera: Curculionidae); R. dominica; T. castaneum; and Prostephanus truncatus Horn (Coleoptera: Bostrychidae). Several studies documented that Tribolium spp. are probably the most tolerant stored-product beetle species to DEs (Arthur, 2000a, b, Athanassiou et al., 2004, 2005a, Vayias & Athanassiou, 2004). However, according to Athanassiou et al. (2006), they have different susceptibilities to DEs. In the same study, strains from Denmark, United Kingdom and Germany were the most susceptible to Insecto, Protect-It, Protectot, PyriSec and SilicoSec whereas the strain from Portugal was the least susceptible. In this study, the DE Protect-It and Dryacide were the most efficient DE formulations against the three provided species, even in the presence of the food source. On the other hand, Perma-Guard TM and Insecto were the least efficient DEs; therefore, high rates would be required to control infestations of stored product insect pests. Among the species tested, T. castaneum is less sensitive to DE dusts than R. dominica and O. surinamensis. Further experiments will need to assess the efficacy of DEs on surfaces such as concrete and wood against the most tolerant insects to provide a more realistic challenge to DE efficacy. Farm-scale trials will also provide information on DE efficacy in the field and allow for dose recommendations to be provided. In conclusion, these laboratory tests have found that when applied to surfaces Protect-It and Dryacide were the most effective treatments against beetles with doses of 0.5 g/cm 2 producing 100% mortality in the insect species. These results would encourage the use of DE and inert dusts in general, as they appear to be among the most promising alternatives to pesticides in a storedproduct IPM program. Acknowledgments The authors wish to thank Dr. Alan McLaughlin for advice and helpful comments and special thanks to Dr. Christos G. Athanassiou for reviewing the manuscript. References Arnaud, L., Lan, H.T.T., Brostaux, Y. and Haubruge, E. (2005) Efficacy of diatomaceous earth formulations admixed with grain against populations of Tribolium castaneum. Journal of Stored Products Research, 41,

7 364 M. Ziaee & A. Khashaveh Arthur, F.H. (2000a) Toxicity of diatomaceous earth to red flour beetles and confused flour beetles (Coleoptera: Tenebrionidae) effects of temperature and relative humidity. Journal of Economic Entomology, 93, Arthur, F.H. (2000b) Impact of food source on survival of red flour beetles and confused flour beetles (Coleoptera: Tenebrionidae) exposed to diatomaceous earth. Journal of Economic Entomology, 93, Athanassiou, C.G. (2006) Influence of instar and commodity on insecticidal effect of two diatomaceous earth formulations against larvae of Ephestia kuehniella (Lepidoptera: Pyralidae). Journal of Economic Entomology, 99, Athanassiou, C.G. and Kavallieratos, N.G. (2005) Insecticidal effect and adherence of PyriSec in different grain commodities. Crop Protection, 24, Athanassiou, C.G., Kavallieratos, N.G. and Andris, N.S. (2004) Insecticidal effect of three diatomaceous earth formulations against adults of Sitophilus oryzae (Coleoptera: Curculionidae) and Tribolium confusum (Coleoptera: Tenebrionidae) on oat, rye and triticale. Journal of Economic Entomology, 97, Athanassiou, C.G., Kavallieratos, N.G., Economou, L.P., Dimizas, C.B., Vayias, B.J., Tomanovic, Z. ˇ and Milutinovic, M. (2005b) Persistence and efficacy of three diatomaceous earth formulations against Sitophilus oryzae (Coleoptera: Curculionidae) on wheat and barley. Journal of Economic Entomology, 98, Athanassiou, C.G., Kavallieratos, N.G., Peteinatos, G.G., Petrou, S.E., Boukouvala, M.C. and Tomanovic, Z. ˇ (2007) Influence of temperature and humidity on insecticidal effect of three diatomaceous earth formulations against larger grain borer (Coleoptera: Bostrychidae). Journal of Economic Entomology, 100, Athanassiou, C.G., Kavallieratos, N.G., Tsaganou, F.C., Vayias, B.J., Dimizas, C.B. and Buchelos, C.Th. (2003) Effect of grain type on the insecticidal efficacy of diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Crop Protection, 22, Athanassiou, C.G., Korunic, Z., Kavallieratos, N.G., Peteinatos, G.G., Boukouvala, M.C. and Mikeli, N.H. (2006) New trends in the use of diatomaceous earth against stored-grain insects. Proceedings of 9th International Working Conference on Stored-Product Protection, São Paulo, Brazil, October 15-18, 2006, Athanassiou, C.G., Vayias, B.J., Dimizas, G.B., Kavalieratos, N. G., Papagregoriou, A.S. and Buchelos, C.Th. (2005a) Insecticidal efficacy of diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Tribolium confusum Du Val (Coleoptera: Tenebrionidae) on stored wheat: Influence of dose rates, temperature and exposure interval. Journal of Stored Products Research, 41, Chapman, R.F. (1971) The Insects Structure and Function. 2nd edn. Cambridge University Press, London. 749 pp. Cook, D.A. (2003) The efficacy of high temperature and diatomaceous earth combinations against adults of red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae) and the grain weevil Sitophilus granarius (Coleoptera: Curculionidae). Proceedings of the BCPC International Congress Crop Science and Technology. The British Crop Protection Council, Alton, UK, Dowdy, A.K. (1999) Mortality of red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae) exposed to high temperature and diatomaceous earth combinations. Journal of Stored Products Research, 35, Ebeling, W. (1971) Sorptive dust for pest control. Annual Review of Entomology, 16, Fields, P.G. and Korunic, Z. (2000) The effect of grain moisture content and temperature on the efficacy of diatomaceous earths from different geographical locations against stored-product beetles. Journal of Stored Products Research, 36, Greenspan, L. (1977) Humidity fixed points of binary saturated aqueous solutions. Journal of Research of the National Bureau of Standards-Physics and Chemistry, 81, Henderson, S. and Pixton, S.W. (1982) The relationship between moisture content and equilibrium relative humidity of five types of wheat flour. Journal of Stored Products Research, 18, Kavallieratos, N.G., Athanassiou, C.G., Paschalidou, F.G., Andris, N.S. and Tomanovic, Z. ˇ (2005) Influence of grain type on the insecticidal efficacy of two diatomaceous earth formulations against Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). Pest Management Science, 61, Korunic, Z. (1998) Diatomaceous earths, a group of natural insecticides. Journal of Stored Products Research, 34, Korunic, Z. and Fields, P.G. (1995) Diatomaceous earths, insecticidal composition. USA Patent 5, Korunic, Z., Fields, P.G., Kovacs, M.I.P., Noll, J.S., Lukow, O. M., Demianyk, C.J. and Shibley, K.J. (1996) The effect of diatomaceous earth on grain quality. Postharvest Biology and Technolology, 9, Korunic, Z., Fields, P.G., Timlick, B., Ormesher, P. and VanNatto, C. (1997) The enhanced diatomaceous earth, a safe, effective and long lasting grain protectant. Food and Agriculture Organization, VIII Round Table on Prevention of Post-Harvest Food Losses, Columbia, Cartagena, August 13-15, Mason, L. (1997) Activity of Product-It in empty granaries against two stored-product pests. Report Prepared by Department of Entomology, Food and Pest Management Purdue University, USA, 4 pp. Moras, A., Gelain, J., Romano, C.M., Lorini, I., Gularte, M.R. and Elias, M.C. (2006) Effects of diatomaceous earth used to control stored grain pests on technological, physical and cooking characteristics of parboiled and conventionally processed rice. Proceedings of 9th International Working Conference on Stored Product Protection, October 15-18, 2006, Campinas,

8 Using diatomaceous earths against stored-product pests 365 São Paolo, Brazil, Pixton, S.W. (1967) Moisture content-its significance and measurement in store products. Journal of Stored Products Research, 3, Pixton, S.W. and Warburton, S. (1971) Moisture content / relative humidity equilibrium of some cereal grains at different temperatures. Journal of Stored Products Research, 6, Rees, D.P. (2004) Insects of Stored Products. CSIRO Publishing, Collingwood, Victoria, Austrilia. col. illus., 192 pp. SAS (2000) The SAS System Version 7 for Windows. SAS Institute, Cary, Nc. Snedecor, G.W. and Cochran, W.G. (1989) Statistical Methods. 8th edn. Iowa State University Press, Ames, 503 pp. Subramanyam, Bh. and Roesli, R. (2000) Inert dusts. Alternatives to Pesticides in Stored-Product IPM (eds. Bh. Subramanyam & D.W. Hagstrum), pp Kluwer Academic Publishers, Dordrecht. Subramanyam, Bh., Swanson, C.L., Madamanchi, N. and Norwood, S. (1994) Effectiveness of Insecto, a new diatomaceous earth formulation, in suppressing several stored-grain insect species. Proceedings of 6th International Working Conference on Stored-Product Protection, April 17-23, 1994, Canberra, Australia, 650 (eds. E. Highley, E.J. Wright, H.J. Banks & B.R. Champ), pp University Press, Cambridge, U.K. Vayias, B.J. and Athanassiou, C.G. (2004) Factors affecting the insecticidal efficacy of the diatomaceous earth formulation SilicoSec against adults and larvae of the confused flour beetle, Tribolium confusum Du Val (Coleoptera: Tenebrionidae). Crop Protection, 23, Vayias, B.J., Athanassiou, C.G., Kavallieratos, N.G., Tsesmeli, C.D. and Buchelos, C.Th. (2006a) Persistence and efficacy of two diatomaceous earth formulations and a mixture of diatomaceous earth with natural pyrethrum against Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) on wheat and maize. Pest Management Science, 62, Vayias, B.J., Athanassiou, C.G., Kavallieratos, N.G. and Buchelos, C.Th. (2006b) Susceptibility of different European populations of Tribolium confusum (Coleoptera: Tenebrionidae) to five diatomaceous earth formulations. Journal of Economic Entomology, 99, White, N.D.G. and Loshciavo, S.R. (1989) Factors affecting survival of the merchant grain beetle (Coleoptera: Silvanidae) and the confused flour beetle (Coleoptera: Tenebrionidae) exposed to silica aerogel. Journal of Economic Entomology, 82, Ziaee, M., Nikpay, A. and Khashaveh, A. (2007) Effect of oilseed type on the efficacy of five diatomaceous earth formulations against Tribolium castaneum Herbst (Coleoptera: Tenebrionidae). Journal of Pest Science (in press). Accepted June 1, 2007