Mortality and progeny production of four stored-product insect species on three grain commodities treated with Beauveria bassiana and diatomaceous earths

Laboratory bioassays were conducted to estimate the effectiveness of the entomopathogenic fungus Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) at 1.5 × 10⁸ and 1.5 × 10¹⁰ conidia/kg grain alone or mixed with the diatomaceous earths (DEs) Protect-It at 150 ppm and DEBBM at 50 ppm against adults of the rusty grain beetle, Cryptolestes ferrugineus Stephens (Coleoptera: Laemophloeidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the psocid, Liposcelis paeta Pearman (Psocoptera: Liposcelididae). The adult insects were exposed to treated grains for 7, 14 and 21 days. For progeny emergence data, the treated units were remained under the same conditions for 62 days for all beetles and 30 days for psocids. The results revealed significant differences in mortalities of insect species among treatments and grains. The combined use of B. bassiana, at the highest dose, and DE increased adult mortalities of all species. In general, the treatments were least effective against T. castaneum and most effective against L. paeta. More numbers of dead insects were found on wheat than on rice or maize. The emergence of progeny was considerably reduced on grains treated with B. bassiana, at the highest dose, plus DE. The results of the present study suggest that the effectiveness of B. bassiana is fortified by the addition of DEs, but it varies among exposed insect species and commodities.     

Efficacy of spinosad in layer-treated wheat against five stored-product insect species

The biological insecticide spinosad was evaluated in laboratory bioassays as a surface treatment for wheat to control adult Rhyzopertha dominica, Sitophilus oryzae and three psocid species, Liposcelis paeta, L. bostrychophila, and Lepinotus reticulatus. Spinosad was applied at 1 ppm to 35 g of wheat placed in a vial or to the upper one half, one fourth, or one eighth layer of the wheat; insects were either added to the vials before or after the wheat. When R. dominica were introduced into the vials after the wheat, mortality was 100% except for 83% mortality in the one eighth layer treatment. In contrast, when adults were placed in the vials before the wheat, mortality was 100% only when all of the wheat was treated. Mortality of S. oryzae was lower compared to R. dominica but there was some evidence of upward movement into the treated layers. Mortality of L. paeta and L. bostrychophila was <50% when the entire quantity was treated, in contrast to 100% mortality of L. reticulatus. However, for all psocid species, overall mortality decreased with decreasing depth of the treated layer. The results of this laboratory study show that while spinosad has some effectiveness as a layer treatment on a column of wheat, efficacy will be dependent on the target species, the depth of the treated layer, and the upward or downward mobility of the insect species.     

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.     

Insecticidal activity of three diatomaceous earths on lesser grain borer,Rhyzopertha dominica F., and their effects on wheat,barley, rye,oats and triticale grain properties

This study aimed to evaluate insecticidal activity of three diatomaceous earths DEs, two originated from Serbia (DE S-1 and DE S-2) and one commercial formulation (Protect-It, Hedley Technologies Ltd. Canada) applied at rates of 0.5, 1.0 and 1.5 g/kg (500, 1000 and 1500 ppm) on Rhyzopertha dominica in wheat, barley, rye, oats and triticale grains and their effects on mass of kernels and several properties: adherence, hectolitre mass, moisture, protein and ash contents. Mortality of R. dominica adults increased with exposure duration and DEs rates. In all tested grains after the longest exposure period (21 days), 1.0 and 1.5 g/kg rates of Protect-It, and 1.5 g/kg rate of DE S-1 and DE S-2 (in barley) caused 95–100% mortality. Offspring reduction of ≥95% was recorded after the application of 1.0 and 1.5 g/kg of Protect-It and 1.5 g/kg of DE S-1. The lowest weight of damaged grain was found after applying 1.0 and 1.5 g/kg of DEs to all grain types, and the highest in rye and wheat treated with 0.5 g/kg DE S-1 and DE S-2, respectively. The highest DEs adherence of 83–95% was detected in wheat, and 87–92% in oats, and the lowest of 71–77% in rye and 59–73% in triticale. All DEs significantly reduced hectolitre mass of all grains, especially Protect-It, 3.6–8.8%. No negative effects of DEs were detected on moisture contents, and the contents of proteins and ashes in the grains. The changes were due to the activity of 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.     

Insecticidal effect of spinosad dust, in combination with diatomaceous earth, against two stored-grain beetle species

Laboratory bioassays were carried out to determine the efficacy of spinosad applied alone or combined with the diatomaceous earth (DE) SilicoSec against adult rice weevils, Sitophilus oryzae and confused flour beetles, Tribolium confusum. Efficacy was assessed on wheat and maize at three dosages of spinosad dust formulation (corresponding to 0.0625, 0.1875 and 0.625 ppm of active ingredient [AI] for S. oryzae and to 0.1875, 0.625 and 1.25 ppm of AI for T. confusum), alone or combined with SilicoSec at 150 ppm for S. oryzae and 250 ppm for T. confusum. The mortality of S. oryzae exposed for 14 d on wheat treated with spinosad ranged between 83% and 100%. Conversely, the mortality of S. oryzae on maize treated with DE or on maize treated with lower doses of spinosad dust did not exceed 19% and was only 59% on maize with the highest spinosad dust treatment. Generally, the presence of SilicoSec combined with spinosad did not significantly increase S. oryzae mortality compared with spinosad alone. For T. confusum, mortality on both commodities was lower than for S. oryzae. After 14 d of exposure on wheat, mortality was 14% at the highest dose of spinosad, but increased to 33% in the presence of DE. Similar results were also obtained for T. confusum exposed on treated maize, which indicated a joint action between spinosad and DE. In the case of S. oryzae, the inclusion of DE reduced progeny production in comparison with spinosad alone. Progeny production of T. confusum was relatively low in all treatments, compared to progeny production of S. oryzae. The results of the study show the potential of combination treatments of spinosad dust and DE, but efficacy varies with the target insect species and commodity.     

Efficacy of filter cake and Triplex powders from Ethiopia against three externally developing stored product insect species

Efficacy of filter cake and Triplex powders was evaluated against the red flour beetle, Tribolium castaneum (Herbst); saw-toothed grain beetle, Oryzaephilus surinamensis (L.); and Indian meal moth, Plodia interpunctella (Hübner). Mortality of T. castaneum and O. surinamensis was determined 14 d after exposing 20 adults to 100 g of maize and wheat treated with 0, 0.3, 0.5, 0.7, 1, 2, and 3 g/kg of filter cake and 0, 0.5, 0.7, 1, 2, 3, 6, 8, and 10 g/kg of Triplex. Adult progeny production was determined at 42 d. Live larvae at 21 d and adults of P. interpunctella that emerged at 42 d were determined by exposing 100 eggs to 0, 0.2, 0.3, 0.5, 0.7, 1, 2, and 3 g/kg of filter cake and 0, 0.3, 0.5, 0.7, 1, 2, 3, 6, and 8 g/kg of Triplex treated maize and wheat. On both grains, 100% mortality of T. castaneum and O. surinamensis adults was observed after exposure to 2–3 and 1–3 g/kg of filter cake, respectively. On wheat, 100% mortality only of O. surinamensis was observed in 2–3 g/kg Triplex treatment. Adult progeny production of T. castaneum and O. surinamensis was completely suppressed on both grains treated with 0.7–3 g/kg of filter cake. Adult progeny production of T. castaneum was completely suppressed at 1–3 g/kg of Triplex treated grains, whereas complete suppression of O. surinamensis was achieved only on maize treated with 2–3 g/kg of Triplex. Both live larvae at 21 d and adults of P. interpunctella that emerged at 42 d were completely suppressed when eggs were exposed to 2–3 and 0.5–3 g/kg filter cake treated maize and wheat, respectively, and on 6–8 and 3 g/kg Triplex treated maize and wheat, respectively. Filter cake was more efficacious compared to Triplex on both grains.     

Diatomaceous earth enhances the toxicity of garlic, Allium sativum, essential oil against stored-product pests

Laboratory bioassays were carried out to determine the efficacy of garlic, Allium sativum L. (Amaryllidaceae), essential oil applied alone or with diatomaceous earth (DE) against adult rice weevils, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and red flour beetles, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). The results showed that the combination treatment was significantly more effective than either treatment alone. In addition, the results also showed that the simultaneous application of essential oil plus DE significantly reduced the concentration of essential oil alone required for an effective treatment and the application rate of DE can be reduced when combined with essential oil. Moreover, the activity of the combination treatment lasted longer than that of essential oil alone and the survival of eggs or larvae to adult stage was significantly inhibited in the combined treatments against both species, compared with the use of essential oil alone. Our results suggested that garlic essential oil combined with DE has a strong additive effect, and therefore may have potential as an alternative to synthetic insecticides for the control of insect pests of stored products.     

Efficacy of two Nigeria-derived diatomaceous earths against Sitophilus oryzae (Coleoptera: Curculionidae) and Rhyzopertha dominica (Coleoptera: Bostrichidae) on wheat

We investigated the effectiveness of two raw diatomaceous earths (DEs) obtained from Bularafa and Abakire districts in Yobe State, Nigeria, against the rice weevil, Sitophilus oryzae (L.) and the lesser grain borer, Rhyzopertha dominica (F.). Insecto, a commercialized DE, was also tested as standard check. Adults of the two species were exposed on wheat admixed with the respective DEs at a dose rate of 1000 ppm, at 30 °C and 55% RH. Relative to R. dominica, Insecto, Bularafa and Abakire DEs induced 14-d corrected adult mortalities of 73.6, 61.2 and 40.4%, respectively. Corrected 14-day adult mortalities against S. oryzae were 100, 100 and 81%, respectively. Mortality increased with increasing exposure duration. Bularafa and Insecto DEs were more effective than Abakire DE both in terms of adult insect mortality and F1 progeny suppression in the two species investigated. Both species avoided contact with DE-treated wheat. Bularafa and Insecto DEs contain higher levels of silica (81.0% and 87.0%, respectively) than Abakire DE (60.2%), and also have smaller particle sizes than Abakire DE. These differences in silica level and particle size probably explain why Bularafa and Insecto DEs are more effective against S. oryzae and R. dominica than Abakire DE. The decreasing order of efficacy of the three DEs against the two pest species is Insecto > Bularafa > Abakire. Bularafa DE has potential for the management of insect pests of stored grain in Nigeria.     

Effectiveness of spinosad combined with diatomaceous earth against different European strains of Tribolium confusum du Val (Coleoptera: Tenebrionidae): Influence of commodity and temperature

Laboratory bioassays were carried out to assess the effects of combining spinosad at 0.01, 0.1 and 0.5 ppm, with the diatomaceous earth (DE) formulation SilicoSec at rates of 150, 300 and 600 ppm, against larvae and adults of three different populations of Tribolium confusum du Val (Coleoptera: Tenebrionidae), originating from different European countries (Greece, Portugal and Denmark). Tests were conducted on wheat and maize at 25 and 30 °C. Survival of T. confusum larvae was assessed after 7 d exposure and survival of adults was assessed after 7 d and 14 d of exposure. At each dose of spinosad, survival of T. confusum individuals decreased as the rate of DE increased. As temperature increased, the efficacy of spinosad and Silicosec applied either alone or in combination also increased. The efficacy of spinosad alone was slightly higher on maize than wheat, while the reverse was noted for all the tested combinations of spinosad with DE as well as in the case of the application of DE alone. The strain from Portugal was always the least susceptible of the three tested. Our study indicates that it is possible to combine low doses of DE (<600 ppm) with spinosad (<1 ppm) to control adults and larvae of T. confusum, especially at temperatures >25 °C.     

Susceptibility of stored product insects to high concentrations of ozone at different exposure intervals

Ozone is a highly reactive gas with insecticidal activity. Past studies have indicated that ozone technology has potential as a management tool to control insect pests in bulk grain storage facilities. The objective of this study was to determine the efficacy of short periods of exposure to high ozone concentrations to kill all life stages of red flour beetle (Tribolium castaneum (Herbst)) (Coleoptera: Tenebrionidae), and Indianmeal moth (Plodia interpunctella (Hübner)) (Lepidoptera: Pyralidae), adult maize weevil (Sitophilus zeamais (Motsch.)) (Coleoptera: Curculionidae) and adult rice weevil (S. oryzae (L)) (Coleoptera: Curculionidae). Insects were treated with six ozone concentrations between 50 and 1800 ppm. The specific objective was to determine minimal time needed to attain 100% mortality. The most ozone-tolerant stages of T. castaneum were pupae and eggs, which required a treatment of 180 min at 1800 ppm ozone to reach 100% mortality. Eggs of P. interpunctella also required 180 min at 1800 ppm ozone to reach 100% mortality. Ozone treatments of 1800 ppm for 120 min and 1800 ppm for 60 min were required to kill all adult S. zeamais and adult S. oryzae, respectively. The results indicate that high ozone concentrations reduce the treatment times significantly over previously described results. Our results also provide new baseline information about insect tolerance to ozone treatment.     

Freezing for control of stored-product psocids

A series of studies was conducted by exposing young and old eggs, nymphs, and adults of the psocids Liposcelis bostrychophila (Badonnel), L. paeta (Pearman), L. decolor (Pearman), and L. entomophila (Enderlein) to −18 °C for various time intervals. Survival was assessed as initial and final, at different times depending on the life stage. Young eggs of L. bostrychophila were the most tolerant life stage of any of the species, with scattered survival out to 120 h of exposure to −18 °C. Eggs were the most tolerant life stage for each species, requiring 24, 12, and 2 h of exposure for complete kill of L. paeta, L. decolor, and L. entomophila, respectively. Nymphs and adults of all species were far more susceptible than eggs, with no final survival after two hours of exposure. Results show the extreme variation between different psocid life stages and species to cold temperatures, and provide guidelines for using cold as a control strategy for psocids. Our results show that 24 h at −18 °C is sufficient to kill all life stages of the psocid species tested, except for young L. bostrychophila eggs which will require at least 128 h of exposure at −18 °C for complete mortality.     

Laboratory assessment of insecticidal effectiveness of natural zeolite and diatomaceous earth formulations against three stored-product beetle pests

The insecticidal effectiveness of two natural zeolite formulations (Minazel plus and Minazel), applied to wheat at selected rates of 0.25, 0.50 and 0.75 g/kg, and a diatomaceous earth formulation (DE) (Protect-It™), applied at the recommended rates of 0.15 g/kg for Sitophilus oryzae, 0.20 g/kg for Rhyzopertha dominica and 0.30 g/kg for Tribolium castaneum, were tested under laboratory conditions (24 ± 1 °C temperature and 45 ± 5% relative humidity). The highest adult mortality was observed after the longest exposure period of 21 days and 7 days of recovery, when all three zeolite dosage rates and the recommended DE dosage caused 97-100% mortality of S. oryzae and 94-100% of T. castaneum. On the other hand, 100% mortality was not achieved in any test variant involving R. dominica; the highest (about 92%) was detected for DE, while 52% and 79% mortality was achieved with the zeolites at the highest rate of 0.75 g/kg. Progeny reduction by >90% was achieved after 21 days of contact of all three beetle pests with DE-treated wheat, while the same level of reduction was achieved for S. oryzae and T. castaenum only after contact with the highest rate of the zeolite product, Minazel. Thus the two zeolite formulations are comparable to diatomaceous earth in controlling adult S. oryzae, R. dominica and T. castaneum, but only the Minazel formulation could effectively protect wheat from attack by S. oryzae or T. castaneum, and only with a higher rate of application than for the DE formulation.     

The influence of Rhyzopertha dominica (F.) on the technological quality of cereal grains treated with diatomaceous earth

Laboratory bioassays (temperature 26 ± 1 °C and 60 ± 5% r. h.) were performed to evaluate the insecticidal effect of three different diatomaceous earths (DE) against Rhyzopertha dominica (F.) in wheat, triticale and rye. In order to achieve this, the amount of damaged kernels, amount of debris, wet gluten content, gluten index and rheological properties were assessed in infested samples, infested samples treated with DE Protect-It and two DEs originating from Serbia (S-1 and S-2) and were compared to control (uninfested) samples using Chopin Mixolab. The most susceptible to beetle infestation were rye sample and wheat variety Planeta. The lowest weight of damaged grain was found after applying DE Protect-It to all grain types. The amount of damaged kernels, the amount of debris and loss of mass were the highestin sample treated with DE S-2. While infestation resulted in increase in the amount of damaged kernels and debris and decrease in wet gluten content, and provoked weakening of gluten network structure as well as starch damage, an addition of DE, especially Protect-It, resulted in grain samples of similar technological quality to control (uninfested) sample. The susceptibility of different cereals used in breadmaking to infestation by R. dominica, as well as their response to the insecticidal effect of diatomaceous earth largely varied. Both cereal type and quality, as measured by wet gluten content and gluten index, influenced grain response to infestation. Insecticidal effect of diatomaceous earth, especially DE S-1and DE S-2, was the least effective in terms of triticale. These findings suggest that the application of DE in cereals storage management might largely be affected with grain type as well as grain composition and technological quality.     

Persistence and efficacy of indoxacarb against three stored product insect species on wheat and maize

In the present study, we investigated the insecticidal efficacy of indoxacarb on wheat and maize, against adults of three major stored-grain species, the rice weevil, Sitophilius oryzae (L.) (Coleoptera: Curculionidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and the confused flour beetle, Tribollium confusum Jacquelin Du Val (Coleoptera). For this purpose, bioassays were carried out with indoxacarb at the doses 0.1, 1 and 10 ppm. Moreover, the treated grains were left at the laboratory for a period of six months, in order to examine the residual effect of indoxacarb, by conducting bioassays at monthly intervals. For S. oryzae and R. dominica, adults were exposed in the treated grains for 7 and 14 d, while for T. confusum adults were exposed for 14 and 21 d, in order to estimate the mortality level. After the termination of this interval, the treated samples were left for an additional period of 65 days, on which progeny production was recorded. R. dominica was by far more susceptible than S. oryzae, given that mortality, in many cases, reached 100% even after 7 d of exposure, even at the lowest dose rate of 0.1 ppm. At the same time, for this species, progeny production was low. For S. oryzae, mortality was low at 0.1 ppm, with high levels of progeny production. T. confusum was the least susceptible of the species tested. Generally, during the experimental period, the efficacy of indoxacarb was decreased, but mortality was higher on wheat than on maize. Indoxacarb residues determination by GC-ECD indicated that after 6 months 33% of the insecticide remains in grains at 0.1 ppm dose, about 40–50% at 1 ppm and about 40–60% at 10 ppm dose. Based on the results of the present work, indoxacarb is an effective grain protectant, at least in the case of R. dominica and S. oryzae.     

Field trials on the efficacy of Beauveria bassiana,diatomaceous earth and Imidacloprid for the protection of wheat grains from four major stored grain insect pests

We assessed the insecticidal efficacy of Beauveria bassiana, diatomaceous earth (DE) and the neonicotinoid Imidacloprid against four major insect species of stored grain pests during field trials conducted on small farms located in four districts of Punjab, Pakistan. In each district, a 40 kg lot of wheat grain was admixed with B. bassiana (3 × 10¹⁰ conidia kg⁻¹), DE (150 ppm) and Imidacloprid (5.0 ppm) alone and in different combinations. Each lot was divided subsequently into four equal parts (10 kg each), packed in polypropylene bags, artificially infested, labeled and stored at the farms under natural environmental conditions up to 6 months. Sampling was carried out every 30 d to record the total number of dead and alive adults, as well as the percent of grain damage in treated and untreated (control) grains. Results revealed a significant difference among the treatments, test insect species and the storage period. For each district, the combined treatments provided better control of all tested insect species compared with each treatment alone. The least number of surviving adults and minimum percent grain damage was observed for Imidacloprid and DE combination, but was outperformed by the DE treatment with B. bassiana for long-term protection. For all grain protectants, we obtained the same order of susceptibility level among the test species (i.e. Liposcelis paeta > Cryptolestes ferrugineus > Rhyzopertha dominica > Tribolium castaneum). The results of the present study suggested that DE, insect pathogenic fungi and Imidacloprid can be effectively used for the protection of wheat stored at small-scale farmer's fields.     

Effectiveness of spinosad as a grain protectant against resistant beetle and psocid pests of stored grain in Australia

Effectiveness of the bacterium-derived insecticide, spinosad, was determined against eight storage pests of Australia. Laboratory experiments were carried out on relevant resistant strains of four beetle and four psocid species, with the aim of determining the potential of spinosad as a new grain protectant. To explore the possibility that spinosad could have delayed effects, we exposed all insects for 14 d initially and then a further 14 and 28 d for psocids and beetles, respectively. Adult insects of each strain were exposed to untreated wheat (control) and wheat treated with spinosad at 0.1, 0.5 and 1 mg [a.i.]/kg of grain, and adult mortality and reduction of progeny were determined. Among beetles, spinosad was most effective against Rhyzopertha dominica (F.), with 100% adult mortality and progeny reduction after 14 d exposure at 1 mg [a.i.]/kg. Efficacy of spinosad was less with Sitophilus oryzae (L.), and least with Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (L.). Against the psocids, spinosad was most effective against Liposcelis entomophila (Enderlein), with 100% adult mortality after 28 d exposure at 1 mg [a.i.]/kg and 92% progeny reduction after 14 d exposure and 100% subsequently. Spinosad was only moderately effective against Liposcelis bostrychophila Badonnel, L. decolor (Pearman) and L. paeta Pearman. Our findings suggest spinosad to be a potential protectant against R. dominica and L. entomophila in stored grain in Australia. This potential use would be in combination with another protectant capable of controlling other members of the pest complex.     

Responses of phosphine susceptible and resistant strains of five stored-product insect species to chlorine dioxide

Adults of phosphine susceptible laboratory strains and phosphine resistant field strains of five stored-product insect species were exposed in vials with 0 or 10 g of wheat for different time periods to 0.54 g/m³ (200 ppm) of chlorine dioxide gas. After exposure, adult mortality was determined 5 d later at 28 °C and 65% r.h. The 5-d mortality was 100% in laboratory and field strains of the red flour beetle, Tribolium castaneum (Herbst); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); lesser grain borer, Rhyzopertha dominica (F.); maize weevil, Sitophilus zeamais Motschulsky; and rice weevil, Sitophilus oryzae (L.) that were exposed in vials with 10 g of wheat to chlorine dioxide for 26, 16, 24–34, 18–24, and 15–18 h, respectively. Corresponding exposure durations for these species and strains in vials without wheat were 15, 3, 18–20, 7–15, and 5–7 h, respectively. Dosages of chlorine dioxide producing 99% mortality (LD₉₉) of T. castaneum, O. surinamensis, R. dominica, S. zeamais, and S. oryzae strains in vials with wheat ranged from 14.79−22.57, 8.20–8.41, 15.79–21.60, 10.66–14.53, and 7.67–12.20 g-h/m³, respectively. In vials without wheat, corresponding LD₉₉ values for T. castaneum, R. dominica, and S. zeamais strains were 6.51–8.66, 11.46–23.17, and 5.79–10.26 g-h/m³, respectively. LD₉₉ values for O. surinamensis and S. oryzae could not be computed, because of 100% mortality after a 3–5 h exposure to chlorine dioxide. No adult progeny production of T. castaneum and O. surinamensis was observed after 8 weeks in control and chlorine dioxide-exposed samples. Adult progeny production of Sitophilus spp. was found only in the control samples. The dosage for 99% adult progeny reduction relative to control for R. dominica strains ranged from 10.07 to 18.11 g-h/m³. Chlorine dioxide gas is effective in killing phosphine susceptible and resistant strains of five stored-product insect species and suppressing adult progeny production of three out of the five species.     

Tanacetum vulgare essential oil as grain protectant against adults and larvae of four major stored-product insect pests

In this study the adulticidal and larvicidal effect of tansy, Tanacetum vulgare L. (Asteraceae) essential oil (EO) was estimated against four noxious stored-product insect species; Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), Tenebrio molitor L. (Coleoptera: Tenebrionidae) and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). The EO chemical composition, as determined by GC-MS, was dominated by oxygenated monoterpenes (68.2%), with borneol (13.6%), umbellulone (11.7%), artemisia ketone (9.3%), cis-chrysanthenol (6.9%), camphor (5.9%), and terpinen-4-ol (5.5%) as the major constituents. This profile was quite different from those previously reported from other T. vulgare European accessions which are characterized by high content of the toxic trans-thujone. The T. vulgare EO was applied as wheat protectant at two concentrations of 500 and 1000 ppm. Adult and larval mortality levels were estimated after 4, 8 and 16 h and 1, 2, 3, 4, 5, 6 and 7 days. Tanacetum vulgare EO caused complete mortality (100%) to T. castaneum larvae, but only 25.6% to adults at 1000 ppm 6 and 7 days post-exposure, respectively. The mortality rates of T. confusum larvae and adults were 56.7 and 8.9% on wheat treated with 1000 ppm EO, respectively after 7 days of exposure. The ΕΟ caused moderate mortality to T. molitor adults (52.2%), and low mortality to larvae (8.9%), at 1000 ppm at the end of the experimental period. High mortality of O. surinamensis larvae (93.3%) was noticed at 1000 ppm after 7 days of exposure, while only 13.3% of the exposed adults were dead at the same concentration and exposure interval. Overall, the T. vulgare EO could be considered as a potential wheat protectant for the management of important stored-product insects. However, its efficacy depends on the species and the life stage of the target pest.     

Evaluation of six insecticides against adults and larvae of Trogoderma granarium Everts (Coleoptera: Dermestidae) on wheat,barley, maize and rough rice

We evaluated the following six insecticides: cypermethrin, deltamethrin, pirimiphos-methyl, silicoSec, s-methoprene and spinosad, that are registered as grain protectants, against adults or larvae of the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) on wheat, barley, maize and rough rice. Three doses were tested: the half of the label dose, the label dose and the double label dose for each insecticide and mortality was assessed after 1, 3, 7 and 14 days (d) post exposure. For parental adults, progeny production was estimated after an additional period of 46 d of exposure. All tested insecticides were able to suppress T. granarium adults, even at the lowest dose. Pirimiphos-methyl and silicoSec were found to be most effective than the other insecticides, as these were the only ones that caused application resulted in 100% mortality at the 7-d exposure interval, at the half label or label dose. Conversely, the majority of the insecticides tested were found to be ineffective against T. granarium larvae. Pirimiphos-methyl was the only insecticide on which larval mortality reached 100% on all commodities tested and by far more effective than the other insecticides. For both adults and larvae, mortalities were generally higher on wheat and barley, than on rough rice and maize, for most of the combinations tested. Our findings indicate that the biological stage (i.e., adults or larvae) and the type of infected commodity should be seriously considered when insecticidal management strategies with cypermethrin, deltamethrin, pirimiphos-methyl, silicoSec, s-methoprene or spinosad are planned against T. granarium.