Evaluation of methoprene alone and in combination with diatomaceous earth to control Rhyzopertha dominica (Coleoptera: Bostrichidae) on stored wheat

A series of experiments were conducted in which different formulations of the insect growth regulator methoprene were evaluated for control of Rhyzopertha dominica (F.), the lesser grain borer, a major internal insect pest of stored wheat. In the first test, application rates of 10-ppm R,S-methoprene (a racemic mixture of the R and S isomers of methoprene) and 1 and 5-ppm S-methoprene (S-isomer only) gave 100% suppression of F₁ adult progeny of R. dominica for 24 weeks. In the second test, adult R. dominica were exposed at 27°C and 32°C, 57% and 75% relative humidity (r.h.) on untreated wheat and wheat treated with 1- to 10-ppm S-methoprene dust. Survival after a 3-week exposure decreased with increasing concentration of dust, and ranged from 69% to 99%, but no F₁ adult progeny were produced in treated wheat. In the final test, concentrations of 0, 0.25, 0.50, 0.75, and 1.0 ppm S-methoprene EC were combined with concentrations of 0, 75, 150, 225, and 300 ppm of the commercial diatomaceous earth (DE) Protect-It^®. Within each methoprene concentration, survival generally decreased with increasing concentration of DE, and was generally greater at 75% than at 57% r.h. Only the wheat treated with 0-ppm methoprene contained an appreciable number of F₁ adults. In summary, both the dust and EC formulations of S-methoprene gave 100% suppression of F₁ adult progeny R. dominica at application rates of 1 ppm, and combination treatments involving reduced rates of methoprene and DE gave effective control of R. dominica.     

Behavior of female Rhyzopertha dominica (Coleoptera: Bostrichidae) in a mono-layer of wheat treated with diatomaceous earth

Adult female lesser grain borers (Rhyzopertha dominica [F.]) were observed in a mono-layer of wheat sandwiched between two layers of glass to determine if movement patterns and survival rates differed in wheat that was admixed with diatomaceous earth (DE) compared with untreated wheat. Observations were also made to determine if responses to DE differed depending on the commercial formulation of DE tested at the labeled rates. Mortality was higher in the DE treatments than in the untreated controls, and also varied according to the DE formulation. In wheat treated with 1000 ppm Dryacide^®, 400 ppm Protect-It^®, and 500 ppm Insecto™ (labeled rate for the individual products), mean percentage mortality was 100±0, 71.4±10.1, and 57.1±11.1, respectively. Although total distance traveled and the number of turns taken by the beetles was lower in the Dryacide treatment compared to the untreated controls, the movement patterns were not significantly different among the three DE treatments. Observed differences in mortality are likely related to DE products or amount applied rather than to differences in DE exposure resulting from movement behavior.     

Efficacy of diatomaceous earth and methoprene, alone and in combination, against Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in rough rice

Combination treatments of diatomaceous earth (DE) (Protect-It^®) and the insect growth regulator (IGR) methoprene (Diacon^® II) were evaluated against Rhyzopertha dominica (F.), the lesser grain borer, on stored rough rice. Application rates of DE and methoprene ranged from 0 to 500 ppm and 0 to 1 ppm, respectively, in 25 treatment combinations. Tests were conducted by exposing 20 adults for 2 weeks at 32 °C and 75% relative humidity on single varieties of long-, short-, and medium-grain rough rice, removing adults, and holding the rice for 8 weeks at the same conditions to collect F₁ progeny. In the absence of methoprene, mortality of exposed adults increased as the concentration of DE increased, but even at the highest rate of 500 ppm, mortality was only 57.5±12% and 58.8±9.7% in long and medium-grain rice, respectively, and 26.3±4.7% in short-grain rice. Mortality of R. dominica exposed on short-grain rice was lower than mortality on long-and medium-grain rice at several combinations with 375 and 500 ppm DE. There was also an unexpected increase in adult mortality with the addition of methoprene so that at 1 ppm methoprene and 500 ppm DE, mortality in long-, medium-, and short-grain rice was 77.5±9.0%, 77.5±10.0%, and 58.5±3.0%, respectively. In the absence of methoprene, progeny produced on long- and short-grain rice ranged from 48.0±21.2 to 87.2±9.0, compared to 16.5±5.5 to 33.5±8.6 progeny produced on medium-grain rice. With the inclusion of methoprene there were few progeny produced in any of the treatment combinations, and the overall average was 0.6±0.3. Similarly, with no methoprene the range of insect-damaged kernels (IDK) was 5.2±2.7 to 12.2±3.1%, but with methoprene the overall average was reduced to 1.8±0.2%. While control of R. dominica was somewhat limited with DE, the differences among rice varieties seems to indicate that the specific type and possibly variety of rough rice may influence mortality and reproduction of R. dominica exposed to DE. With methoprene, progeny production was greatly suppressed regardless of DE concentration, but combining DE with methoprene would give some measure of adult control.     

Methods for collecting eggs and monitoring egg-hatch and immature development of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Methods are described for collecting large numbers of R. dominica eggs, assessing the proportion which hatch and rearing first instar larvae to adults. The proportion of eggs which hatched and duration of immature development were estimated at 26 and 30°C, 56% r.h. Mature adults in healthy cultures laid rafts of eggs in between layers of filter papers. The proportion of eggs that hatched was assessed after incubation. The first instar larvae which hatched out of the eggs were reared to adults in individual wells of 96-well polystyrene ELISA plates. They were fed with kibbled wheat while their survival and rate of development was monitored. About half the eggs which were collected shrivelled up without developing. Over 80% of the remaining eggs hatched normally at both temperatures. The mean duration of development from egg to adult through four larval instars was 44 d at 26°C and 34d at 30°C on kibbled wheat. These development times are similar to those on whole wheat reported by other researchers. The methods are much less disruptive or destructive than other methods of monitoring development on flour or whole wheat. Potential applications for these techniques are discussed.     

The influence of the herbs sage and wormwood on the migration of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) populations

The repellent or attractant effects of adding powdered sage, Salvia officinalis, or wormwood, Artemisia absinthium, to wheat on the migratory behaviour of the lesser grain borer Rhyzopertha dominica was investigated. Under conditions permitting the migration of adult R. dominica, the addition of powdered sage to wheat grain resulted in a lower colonisation of this substrate. It was also found that emigration from grain containing sage was very high, especially in the initial period of grain infestation. This leads to the conclusion that sage is a strong repellent. On the other hand, the addition of pulverised wormwood to wheat did not seem to cause significant mortality or migration activity. Females demonstrated a higher sensitivity to the action of herbal chemicals than males, as confirmed by their higher mortality. This resulted in a change in the sex ratio of the population.     

The mortality of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) at moderate temperatures

A method using conductive heating is described for quickly obtaining and maintaining moderate temperatures in grain while minimising grain moisture loss. A model is developed to analyse insect mortality at a range of conditions on log-time logit and log-time probit scales. Values of LT 50, LT 99, and LT 99.9 are presented for adult and immature stages of Sitophilus oryzae in wheat from 42 to 48°C at 12% m.c. and for immature stages of Rhyzopertha dominica in wheat from 45 to 53°C at 9, 12 and 14% m.c. Data show that the heat tolerance of all life cycle stages for both species are different, with a degree of progressive change relative to each other as temperature changes. For R. dominica, the thermal tolerance of life cycle stages also changes relatively with changes in grain moisture content. In general, all stages survive longer at a given temperature as grain moisture increases and the effect of moisture on survival increases as temperature decreases. Values for LT 99.9 for the most heat tolerant stage of R. dominica at 9% m.c. range from 78.22 to 2.49 h between 45 and 53°C. At 12% m.c. they range from 96.81 to 3.36 h, and at 14% m.c. from 114 to 4.14 h. In general, at 12% m.c. the heat tolerance of S. oryzae is about 5°C less than R. dominica with LT 99.9 ranging from 37.36 to 3.71 h between 42 and 48°C. At this level of mortality, immature stage three is generally the most heat tolerant stage of R. dominica, whereas it is stage two for S. oryzae. The results are discussed in relation to practical applications of heat disinfestation and in terms of a general model of mortality. The results are also considered in the context of other available information on the heat treatment of both species.     

Detection of internal wheat seed infestation by Rhyzopertha dominica using X-ray imaging

Standardization for grain grades has been established in most countries to maintain the quality of a crop until it reaches consumers. Different methods have been investigated for their potential to detect insect infestations in grain destined for domestic and export markets. The potential of detecting infestations caused by Rhyzopertha dominica in wheat kernels using a real-time soft X-ray method was determined in this study. Artificially infested wheat kernels were incubated at 30°C and 70% relative humidity and X-rayed sequentially for larval, pupal, and adult stages of R. dominica. Algorithms were used to extract histogram features, textural features, and histogram and shape moments from the X-ray images of wheat kernels. A backpropagation neural network (BPNN) and statistical classifiers were used to identify uninfested and infested kernels using the 57 extracted features. The BPNN correctly identified all uninfested and infested kernels and more than 99% of kernels infested by R. dominica larvae. The classification accuracies determined by the BPNN were higher using all 57 features than when using the histogram and textural features separately. The BPNN performed better than the parametric and non-parametric classifiers in the identification of uninfested and infested kernels by different stages of R. dominica.     

Movement of Rhyzopertha dominica in response to temperature gradients in stored wheat

The movement and temperature preference of Rhyzopertha dominica was determined in a 56 cm diameter cylinder with 9 cm high sides containing 19.9 kg of hard red winter wheat. Two temperature gradients were tested over a 24 h period: 42 to 20 °C and 24 to 20 °C with the cooler temperature being on the periphery of the cylinder. No preference existed when there was no temperature gradient. Beetles preferred the moderate temperature region of the cylinder in the 42 to 20 °C gradient, but avoided the highest temperature region. In the 24 to 20 °C gradient, insects did not move very much during the 24 h period. When a longer duration was used (96 h) for the 24 to 20 °C gradient, there were significantly more insects in the warmest center region of the gradient compared to the middle or outer regions. Compared to other stored grain Coleoptera, such as Cryptolestes ferrugineus, R. dominica appears to move more slowly through the grain into preferred temperature regions.     

Influence of temperature on the functional response of Anisopteromalus calandrae (Hymenoptera: Pteromalidae), a parasitoid of Rhyzopertha dominica (Coleoptera: Bostrichidae)

The functional response of Anisopteromalus calandrae (Howard) parasitizing 4th-instar Rhyzopertha dominica (F.) on wheat was estimated over a range of temperatures and host densities. A functional response equation was used in which a quadratic component that included temperature was substituted for handling time. The instantaneous search rate increased with increasing temperatures. The maximum rate of parasitization was 13 larvae/24 h at 30°C and 35°C. Handling time was lowest at 30°C and highest at 20°C. The ability of A. calandrae to find and parasitize R. dominica over a broad range of temperatures makes it a good candidate for natural control of stored grain pests.     

Relative effectiveness of topical, filter paper and grain applications of deltamethrin, and associated behaviour of Rhyzopertha dominica (F.) strains

The susceptibility of stored grain pests to insecticides may be assessed by different types of bioassay application methods such as topical, impregnated filter papers and grain treatments. Pests may behave differently when in contact with pesticides and these changes in behaviour may contribute to their tolerance of pesticide. To compare the three application methods and determine how Rhyzopertha dominica (F.) behaved on contaminated filter papers and treated grain, experiments were carried out on four strains of this species. The strains were of known susceptibility to deltamethrin; three were from Brazil (BR4, BR6 and BR7) and one from the United Kingdom (UK1). BR4 and UK1 were susceptible strains, and BR6 and BR7 were resistant strains. Behavioural responses of the pest to deltamethrin were compared between resistant and susceptible strains by measuring the walking response of individuals on deltamethrin impregnated filter papers and the repellent effect of treated wheat grain. The body weights of strains were compared. The results showed resistance ratios of 21, 175 and 17 times between the most susceptible and the most resistant strains, following topical, filter paper and grain applications, respectively. The most resistant strain walked less on contaminated filter papers while the most susceptible strain did not change its walking pattern. Deltamethrin showed no repellent effect, neither on impregnated filter papers or in treated wheat grain. The body weights differed among the strains but were not associated with the level of tolerance to deltamethrin.     

Insecticidal effect of three diatomaceous earth formulations, applied alone or in combination, against three stored-product beetle species on wheat and maize

Laboratory tests were carried out to examine the insecticidal effect of three commercially available diatomaceous earth (DE) formulations on wheat and maize against three major stored-grain beetle species: Rhyzopertha dominica, Sitophilus oryzae, and Tribolium confusum. The three DEs tested were Insecto^®, PyriSec^®, and Protect-It^®. These DEs were applied alone or in all possible combinations (Insecto^®+PyriSec^®, Insecto^®+Protect-It^®, PyriSec^®+Protect-It^®, and all three DEs together), at three (total) dose rates: 0.25, 0.5, and 0.75 g/kg of each commodity. Adults of the above species were exposed to the treated commodities for 7 d at 26 °C, and 65% r.h., and after this interval the mortality was measured. For each species, adult mortality was significantly affected by the type of DE, the commodity, and the dose rate. All DEs were less effective against T. confusum, where mortality did not exceed 67%, in comparison with the other two species, where 100% mortality was achieved in some combinations. For all species tested, all DEs were more effective on wheat than on maize. Generally, the mix of two or three DEs was more effective than the application of one DE, for all species and commodities. The results of the present work clearly indicate that a blending of several DEs together may produce a new DE formulation that is highly effective at low dose rates.     

Survival and reproduction of lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) on flora associated with native habitats in Kansas

Capture of Rhyzopertha dominica in pheromone-baited traps located many kilometers away from grain storage suggests that this species may be exploiting non-grain food sources. To investigate the potential for survival of this species on alternative hosts in the absence of grain, we conducted no-choice feeding assays with twigs and seeds of trees, and seeds of grasses, forbs, and shrubs, commonly encountered on Kansas prairie landscapes where R. dominica has been captured. In addition, R. dominica development and progeny production were assessed on seeds that adults were able to survive on for at least two weeks. Adult survival was poor on grass and forb seeds, although 13.4% of individuals survived on Elymus canadensis, Canada wildrye, seeds after two weeks, compared with 80.3% on Triticum aestivum, wheat, and 0.0% survival in the absence of food. Beetles readily tunneled into twigs from a wide range of tree species, but survival was generally low. A few individuals survived up to four weeks on Gleditsia triacanthos, honey locust. In contrast, bioassays showed that R. dominica could survive and reproduce on damaged seeds (acorns) of six species of oak, but not on undamaged seeds. For example, survival was 95.8% on damaged Quercus muehlenbergii, chinquapin oak. A survey of acorns at the original field collection site showed that the majority of the acorns on the ground had been cracked or bored into by insects and small mammals. Furthermore, we recovered three R. dominica adults from acorns collected in the field and held in sealed containers in the laboratory. These findings suggest that R. dominica populations in Kansas can persist on wild acorns when grain is not available.     

A reliable character for sexing live or dead Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

A new, reliable character is described and illustrated for distinguishing the sexes in adult Rhyzopertha dominica (F.). Both live and dead beetles can be sexed accurately using the method.     

Efficacy of diatomaceous earth formulations admixed with grain against populations of Tribolium castaneum

The efficacy of diatomaceous earth (DE) to control stored-products Coleoptera on stored grain was examined against several populations of the red flour beetle, Tribolium castaneum (Herbst). Four commercially available DE formulations were tested: INSECTO^®, Perma-Guard™, Protect-It^® and the diatomite used for the production of Dryacide^®, each at six concentrations (100-1000 ppm). A great variation of efficacy was observed among the DE formulations tested. Protect-It at concentrations up to 400 ppm was found to be the most effective formulation to control red flour beetle populations. However, a concentration of 1000 ppm of Protect-It was necessary to control all adults of all populations. Most T. castaneum populations, except one from Ivory Coast (Asm), were more than 90% controlled with INSECTO and Dryacide DE at 600 ppm. At this concentration, about 88% and 22% Asm adults died with INSECTO and Dryacide DE, respectively. Perma-Guard was the least efficient DE formulation to control T. castaneum adults with three populations exhibiting some survival at 1000 ppm. Reduced susceptibility to DE was observed in two populations, Asm and Lab susceptible from Kansas (Lab-S). As neither population had been previously exposed to DE, it is suggested that red flour beetles may naturally vary in susceptibility to DE. In addition, it was found that some populations can be satisfactorily controlled with some DE formulations but not with others.     

Uneven application can influence the efficacy of s-methoprene against Rhyzopertha dominica (F.) in wheat

The Juvenile Hormone analogue s-methoprene is used to protect stored grain from pests such as the lesser grain borer, Rhyzopertha dominica (F.). The possibility that uneven application influences s-methoprene efficacy against this species was investigated in the laboratory. Adults of methoprene-susceptible strains were exposed for 14 days to wheat treated at doses of up to 0.6 mg kg⁻¹, or to mixtures of treated and untreated wheat giving equivalent average doses. Adult mortality after exposure to treated wheat was negligible in all cases (≤3.3%) and there was no significant effect of either average dose or evenness of application. In contrast, the number of adult progeny depended on both the average dose and evenness of application. Average doses of 0.3 and 0.6 mg kg⁻¹ reduced the number of live F₁ adults by 99–100% relative to the untreated wheat and no effect of evenness of application was detected. At lower doses, however, efficacy tended to decrease with increasing unevenness of application. When adults from the parental generation were transferred to untreated wheat for another 14 days neither the average dose nor evenness of application in the wheat from which they came had any significant effect on reproduction of these adults. This study demonstrates that uneven application can reduce the efficacy of s-methoprene against R. dominica, but that this is unlikely to influence the performance of s-methoprene against susceptible populations at target doses likely to be used in practice (e.g. 0.6 mg kg⁻¹ in Australia). However, the possibility that uneven application leads to underdosing and selects for resistance should be investigated.     

Efficacy and adherence ratio of diatomaceous earth and spinosad in three wheat varieties against three stored-product insect pests

Laboratory tests were carried out in order to evaluate the efficacy of three diatomaceous earth (DE) formulations; Protector, SilicoSec, and Insecto, and one spinosad dust formulation in three commercially available wheat (Triticum durum) varieties, Athos, Pontos, Sifnos, originating from Greek cultures. The efficacy of the above formulations was assessed against adults of Rhyzopertha dominica, Sitophilus oryzae and Tribolium confusum. The DE formulations were applied at three dose levels; 250, 500 and 1000 ppm, while spinosad was applied at 100, 500 and 1000 ppm of the formulation, corresponding to 0.125, 0.625 and 1.25 ppm active ingredient (a.i.), respectively. The adherence ratio of the DE and spinosad formulations to the kernels of the wheat varieties was assessed. Bioassays were carried out at 30°C and 60% r.h. Mortality was recorded after 7 and 14 d in the case of R. dominica and S. oryzae, and after 7 d, 14 d and 21 d of exposure in the case of T. confusum, on the treated varieties. Progeny production of the individuals exposed on the treated varieties was also assessed. Even the lowest dose of spinosad was highly effective (>90%) against R. dominica and S. oryzae. In the case of T. confusum a combination of longer exposures with higher doses was required for each formulation to be effective. Generally, the performance of all formulations was greater in Athos or Sifnos compared to the Pontos. Progeny production of S. oryzae and R. dominica was significantly higher in untreated Pontos than in the other varieties. Progeny production was always greater in untreated than treated substrates. Although adherence ratios for the tested DE and spinosad formulations were generally high (>90%), significant variations in adherence levels among the wheat varieties were recorded.     

Temperature-mediated functional response of Theocolax elegans (Hymenoptera: Pteromalidae) parasitizing Rhyzopertha dominica (Coleoptera: Bostrichidae) in stored wheat

The functional response of Theocolax elegans (Westwood) parasitizing the lesser grain borer, Rhyzopertha dominica (F.) was examined over a range of temperatures. A type II functional response equation was fitted to each temperature regime. The parasitization rate was highest at 30°C (20 hosts per day) and was lowest at 20°C (2 hosts per day). Handling time was inversely proportional to temperature, and ranged from 1.6 days at 20°C to 0.05 days at 30°C. Instantaneous search rate also changed with temperature. It was lowest at 20°C and highest at 30°C. A temperature-mediated functional response equation was fitted to the data, in which handling time was a quadratic function of temperature. The equation explained 74% of the variance in parasitization rate. Theocolax elegans has a narrower optimal temperature range than other parasitic stored-product Hymenoptera. Temperatures greater than 32.5°C caused high parasitoid mortality.     

Efficacy of the insect growth regulators methoprene, fenoxycarb and diflubenzuron against Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) on maize and paddy rice

The activity of fresh deposits of methoprene, fenoxycarb and diflubenzuron against F₁ progeny of Rhyzopertha dominica on maize and paddy was compared with that on wheat, at two equilibrium relative humidities. There were differences between slopes of log concentration-probit (lc-p) lines for different compounds, and for the same compound on different grains. Judging by values of the IC_99.9, i.e. the concentration which inhibited progeny production by 99.9%, the order of activity against F₁ progeny on different grains was: methoprene, wheat and paddy > maize; fenoxycarb, wheat > paddy > maize; diflubenzuron, wheat and maize > paddy. Equilibrium relative humidity (e.r.h.) had no consistent effect on activity—at 90% e.r.h., the IC₅₀ of fenoxycarb on wheat was reduced and the IC₅₀ of diflubenzuron on maize was increased compared with 70% e.r.h., and other treatments were unaffected.

The efficacy of these compounds on maize and paddy against F₁ and F₂ progeny was evaluated during 48 weeks storage at 30°C, 70% r.h. The resolved S isomer of methoprene was also included. Slopes of lc-p lines were greater against the F₂ than against the F₁, particularly using diflubenzuron on paddy, with corresponding smaller values of the IC_99.9. Equally effective concentrations did not decline systematically over 48 weeks. Minimum effective application rates were judged as the concentrations that prevented living F₂ progeny in at least 2 of 3 replicates. Estimates for 48 weeks protection on maize were: methoprene, 2 mg kg⁻¹; S-methoprene, 1 mg kg⁻¹; fenoxycarb, 10 mg kg⁻¹; and diflubenzuron, 5 mg kg⁻¹. Corresponding estimates on paddy were 0.15 mg kg⁻¹, 0.05 mg kg⁻¹, 5 mg kg⁻¹, and 5 mg kg⁻¹.     

Hull characteristics as related to susceptibility of different varieties of rough rice to Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Rhyzopertha dominica (F.), an important pest of stored grains, causes economic damage to rough rice through physical damage to the kernel, resulting in reductions in grain quality. In this test, 28 varieties of commercial rough rice (10 long grain, 11 medium grain, and 7 short grain) were examined for solid, split and cracked hulls, hull thickness, and adult emergence from neonate R. dominica introduced on each individual variety. The percentage of solid hulls ranged from 55.5% on Koshihikari variety to 92.8% on Akita variety, and the percentages of cracked and split hulls were correlated with increased susceptibility. The Dobie index for progeny production showed Wells, Jupiter, and Pirogue varieties as the most tolerant to R. dominica, while Rico and Francis were the most susceptible. The hull thickness of rough rice varied among varieties, but the tolerant varieties appeared to have thicker hulls than the susceptible varieties. There was no difference among rice types (long-, medium-, or short grain) regarding tolerance or susceptibility to R. dominica. Results show that the characteristics of the rough rice hull are important for conferring susceptibility of individual varieties to R. dominica.     

Effectiveness of diatomaceous earth for control of Sitophilus zeamais (Coleoptera: Curculionidae), Tribolium castaneum and Palorus subdepressus (Coleoptera: Tenebrionidae)

The effectiveness of diatomaceous earth (DE) or diatomite has been assessed against three major beetle pests of stored maize: Sitophilus zeamais (the maize weevil), Tribolium castaneum (the red flour beetle) and Palorus subdepressus (the depressed flour beetle). Maize has been treated with four doses of DE (1.5, 3, 4.5 and 6 g/kg) and four doses of Actellic Super™ Dust a chemical insecticide used as a reference (0.25, 0.5, 0.75 and 1 g/kg). The effective mortality was measured for each treatment after 1, 2, 4, 7 and 14 d of exposure. The corrected mortality rates were calculated by considering the mortality in the control group. Diatomaceous earth was as effective as Actellic Super™ Dust but required higher doses. Diatomaceous earth acted faster on S. zeamais and P. subdepressus compared to T. castaneum. The highest dose tested for DE caused the same mortality in T. castaneum as the recommended dose of Actellic Super™ Dust. Diatomaceous earth is a good alternative for the control of these three devastating insect pests of maize stocks and can readily be incorporated into integrated stored products pest management programs.