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 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.     

Performance of diatomaceous earth and imidacloprid as wheat,rice and maize protectants against four stored-grain insect pests

Laboratory experiments were conducted in Pakistan to investigate the effectiveness of the diatomaceous earth (DE) formulation, Protect-It, at 150 ppm and imidacloprid, at 1.25, 2.5 and 5.0 ppm, alone or in combination, against 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 bioassays were conducted at 25 °C, 65% relative humidity (r.h.) and continuous darkness by using adults of each insect pest that were exposed on treated or untreated wheat, rice and maize. Adult mortality counts were performed 1, 2, 4 and 7 days post-exposure. Progeny production was also evaluated 62 and 30 days after the last mortality count for beetles and psocid respectively. Results showed that mortality was increased with the increase of dose and exposure interval. Imidacloprid was more effective at the highest dose than the DE alone. The combination of DE plus imidacloprid resulted to higher mortalities than DE or imidacloprid alone at almost all exposure intervals. There was higher mortality on wheat than on rice or maize. In general, T. castaneum was the most tolerant insect species to any treatment while L. paeta was the least tolerant. The highest progeny production was observed for T. castaneum (i.e., 33.1 individuals per vial) while the lowest for L. paeta (i.e., 11.1 individuals per vial) on maize treated with Protect-It alone. The findings of the current study indicate that the combined use of DE and imidacloprid, as wheat, rice and maize protectants, may provide adequate level of management to several important stored-product insects.     

Diatomaceous earth low-lethal dose effects on the fitness of entomopathogenic fungus,Beauveria bassiana,against two coleopteran stored product pests

Efficacy of different doses of the Beauveria bassiana-IRAN441C alone (66,125, 250, 500, 1000 mg conidia. Kg⁻¹ grains) and combined with a low-lethal dose (LD₂₅) of diatomaceous earth (DE) SilicoSec® as lethal agents were assessed against the adults of Callosobruchus maculatus (F.) (Chrysomelidae) on mung, and cowpeas, and Oryzaephilus surinamensis (L.) (Silvanidae) on wheat and barley seeds. In both species, mortality reached 60–73% in B. bassiana alone and 83–100% in fungus combined with the DE at the highest dose. A synergistic effect between B. bassiana conidia and the DE was confirmed. The DE low-lethal dose alters fungal mycosis and sporogenesis (conidia mL⁻¹) rates in the infected cadavers. The adult populations of both species were suppressed desirably despite a decrease in the number of cadaver-derived mycosis and their spore production at the highest combination doses (1000 mg kg⁻¹+ LD₂₅ of DE). Seed type had no significant effect on mycosis and sporogenesis on both insects in several combination doses. The cadaver-derived aerial conidia germination rate was increased in the presence of DE low-lethal dose, but it declined by increasing the fungal dose. Type of commodity failed to affect the germination rate of O. surinamensis-derived conidia; however, the mung bean intensified this case for another insect. In both beetles, offspring's emergence was suppressed dose-dependently seven weeks after removing exposed parents to the lethal agents as well it was more in doses mixed with DE. The most significant reduction in progeny production of treated C. maculatus occurred on cowpeas and that of treated O. surinamensis on wheat seeds. Our findings demonstrate that DE's low-lethal dose enhances the virulence of B. bassiana in the various mixtures synergistically, and co-applications of the two substances were feasible. As well, the lethal agents' adverse effects were found to carry over onto both species' offspring during two-month storage time.     

Efficacy of diatomaceous earths and their low-dose combinations with spinosad or deltamethrin against three beetle pests of stored-maize

A key element in postharvest IPM is the reduction of chemical residues in food through the use of reduced dosages of less toxic grain protectants. Two laboratory experiments were conducted: Experiment I determined the efficacies of straight diatomaceous earths (DEs) – “Chemutsi” (African raw DE), MN51 (new formulation) and Protect-It^® (enhanced DE), and two new food grade DE-based formulations (A2 and A3) against adult Prostephanus truncatus (Horn), Sitophilus zeamais (Motschulsky) and Tribolium castaneum (Herbst) admixed with shelled maize. In Experiment II, Chemutsi and Protect-It^® were further tested in varying combinations with low-dose deltamethrin and spinosad. At 21 days post-exposure, MN51 800 ppm and 1000 ppm, Chemutsi 1000 ppm, Protect-It^® 600 ppm and food grade A3 150 ppm caused S. zeamais mortalities that were not significantly different from the positive control (Protect-It^® 1000 ppm). However, after the same exposure period, all the straight DEs (applied at ≤ 1000 ppm) and the DE-based food grade formulations were not effective on P. truncatus and T. castaneum. In low dose combinations, 7 day mortalities showed high S. zeamais susceptibility to both DE-spinosad and DE-deltamethrin while P. truncatus was more susceptible only to DE-spinosad and T. castaneum to Protect-It^®-deltamethrin only. At 21 days, all DE-spinosad and DE-deltamethrin treatments were effective and not significantly different from the commercial grain protectant (fenitrothion 1.0% w/w (10000 ppm) + deltamethrin 0.13% w/w (130 ppm)) on all test species. DE-spinosad and DE-deltamethrin combinations significantly suppressed (P < 0.001) F₁ progeny for the three test species whereas straight DEs and DE-based food grade formulations did not. Our results showed that at half the label rates or lower, DE-spinosad and DE-deltamethrin combinations were effective alternative grain protectants that are safer and possibly cheaper. We also give the first report on the effectiveness of Chemutsi in combination with spinosad or deltamethrin on maize grain.     

Efficacy of different entomopathogenic fungal isolates against four key stored-grain beetle species

The development of resistance in stored-grain insect pests can be effectively reduced by using biological control methods. Entomopathogenic fungi have been under consideration as complementary and alternative agents to synthetic insecticides. The aim of this study is to identify the pathogenic potential of four different fungal isolates of Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) (WG-47, WG-48, WG-50, WG-51) and three isolates of Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae) (WG-46, WG-49, WG-52) against the adult stages of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) at 1 × 10⁶, 1 × 10⁷, 1 × 10⁸ and 1 × 10⁹ conidia/kg wheat. Mortality was found dose dependent among all the tested species. Rhyzopertha dominica was the most susceptible followed by S. granarius, T. castaneum and T. granarium. Among the different isolates B. bassiana caused higher mortality compared to M. anisopliae. The isolates WG-50 and WG-51 of B. bassiana provided maximum mortality among the different tested species and led to lower F1 individuals compared to the controls. Our study indicates that entomopathogenic fungi have an elevated potential to successfully manage the aforementioned coleopteran species on stored wheat.     

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.     

Assessing efficacies of insect pest management methods for stored bagged maize preservation in storehouses located in Nigerian markets

Stored product insect pests cause significant losses in maize in sub-Saharan Africa (SSA). Control of these pests with conventional insecticides is fraught with health and environmental risks. Globally, several reduced-risk methods have been deployed as alternatives to conventional insecticides. In this study, conducted in February–December 2016, efficacies of five treatments to control insects in bagged maize stored in Nigerian market storehouses were evaluated. Treatments included a botanical (Piper guineense), Bularafa diatomaceous earth (DE), permethrin powder (Rambo™), PICS (hermetic) bags and ZeroFly® bags. The study also had a negative control comprising untreated maize in polypropylene bags. Study locations were in three grain markets, namely Eleekara market in Oyo town and Arisekola market in Ibadan, Oyo State, South West Nigeria, and Ago market in Ilorin, Kwara State, North Central Nigeria. Except in the case of PICS bags, each storehouse had six 100-kg bags for each storage method or treatment; these bags were sampled monthly. For PICS, each storehouse had 18 bags (∼80 kg each) and six were destructively sampled every 4 months. Psocids (total 3,614) and S. zeamais (total 1,255) were the most abundant types of insects found during the study. However, among all treatments, PICS bags were the most effective at mitigating population growth of all species of stored product insects encountered, and the number of psocids and S. zeamais found in PICS bags during the entire study were 0 and 8, respectively. The order of effectiveness of the treatments were PICS > Permethrin > ZeroFly > DE > Botanical > control. Data showed PICS, Permethrin, ZeroFly, and DE when used according to manufacturer’s instructions or label are effective and can be incorporated in integrated pest management of stored-product insects in maize storehouses. More research is required to explore how P. guineense can be made more efficacious.     

Comparative toxicity of nanostructured alumina and a commercial inert dust for Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) at varying ambient humidity levels

The widespread concern for environmental and human health has raised the need for new reduced-risk control strategies and the search for new chemical classes of pesticides. Recently, a novel type of particulate material, nanostructured alumina (NSA) has been found to induce mortality in insects exposed to wheat treated with NSA dust. Preliminary studies have shown insecticidal activity of NSA particles on two insect species, Sitophilus oryzae (L.), and Rhyzopertha dominica, (F.), major pests of stored grain. We investigated the toxicity of NSA and Protect-It^® diatomaceous earth (DE) using dry dust applications at three different relative ambient humidity levels. Results showed that NSA was more effective in killing S. oryzae than Protect-It^® and was equally toxic to R. dominica. Treatment with both products also reduced progeny production. In addition, R. dominica was less susceptible to inert dusts than S. oryzae. Our results suggest that NSA might prove a good alternative or complement to DE based products, and encourage further testing with other insect pests and systems, plus experiments on delivery options to further enhance NSA products.     

Moisture content,insect pests and mycotoxin levels of maize at harvest and post-harvest in the Middle Belt of Ghana

Grain moisture content (MC), insect pest infestation and mycotoxin contamination of maize are challenges to food safety and security, especially in the tropics where maize is a staple grain. However, very little documentation is available on the impact of these factors on maize in Ghana. This study focused on post-harvest losses of maize and assessed grain MC, insect pests and mycotoxin (aflatoxin and fumonisin) levels on-farm at three stages, during the major and minor seasons (primary and secondary harvest seasons, respectively). Grain MC decreased significantly from the field stage (17.2–19.0%) to the post-drying stage (12.4–14.2%). The mean grain MC was significantly greater in the major season (20.4%) than in the minor season (12.5%). Maize weevil, Sitophilus zeamais Motschulsky, Angoumois grain moth, Sitotroga cerealella Olivier, square-neck grain beetle, Cathartus quadricollis Guerin-Meneville, and corn sap beetle, Carpophilus dimidiatus Fabricius were the dominant insect species that attacked maize on-farm. Mean numbers of each species were generally significantly greater in the minor season than in the major season, but in both seasons, greater numbers were detected at the heaping stage compared to field and post-drying stages. Percentage insect damaged kernels and weight loss were significantly lower at the field stage than at both the heaped and post-drying stages; statistically similar levels were observed in the latter two stages. Mean aflatoxin (ppb) and fumonisin (ppm) levels were significantly higher in the major season (29.1 ppb, 1.6 ppm) than in the minor season (3.5 ppb, 1.0 ppm). Results showed variation between locations sampled, but in general more insect damage and quality deterioration occurred during the major season compared to the minor season. Farmers should dry immediately after harvest to reduce risk of damage from insect pests and mycotoxins.     

Enhancement the efficacy of spinosad for the control Sitophilus oryzae by combined application with diatomaceous earth and Trichoderma harzianum

Laboratory tests were carried out to evaluate the effect of diatomaceous earth (DE) originated from Egypt and Trichoderma harzianum on the efficacy of spinosad applied at low application rates against Sitophilus oryzae adults in stored wheat. Spinosad was assessed at 0.05, 0.1 and 0.5 mg/kg (ppm) alone or combined with DE at 100, 500 and 1000 mg/kg (ppm) or with T. harzianum at 3.3 × 10⁶, 6.6 × 10⁶ and 2.1 × 10⁷ spores/kg. Adult mortality after 7, 14 and 21 days, progeny reduction after 45 and 90 days, and wheat weight loss were determined for all individual and binary treatments. Adult mortality increased with respect to increased exposure interval and application rate. Complete adult mortality (100%) was achieved after 21 days using 0.5 mg/kg of spinosad with all tested doses of DE and with 2.10 × 10⁷ spores/kg of T. harzinum). Progeny production of S. oryzae was significantly reduced at all treatments compared to untreated wheat. No progeny was observed in the wheat treated with the combined treatments (0.5 mg/kg of spinosad + 1000 mg/kg of DE) and (0.5 mg/kg of spinosad + 2.10 × 10⁷ spores/kg of T. harzinum) after 45 and 90 days. Similar trends were noted for wheat weight loss as the combined treatments at highest rates preserved the wheat intact and free from damage caused by S. oryzae for 90 days. Our findings suggest the combinations of spinosad at low rates with DE or T. harzianum can be effectively used for the control S. oryzae and provide long-term protection of stored wheat.     

Effects of spinosad on the heat tolerance and cold tolerance of Sitophilus oryzae L. (Coleoptera: Curculionidae) and Rhyzopertha dominica F. (Coleoptera: Bostrichidae)

Sitophilus oryzae and Rhyzopertha dominica are serious insect pests of stored products in Sri Lanka. Currently pirimiphos methyl and phosphine fumigation are used as control measures but grain handlers seek for alternatives. Exposure to high or low temperature is popular in stored-product insect pest management but is expensive. Spinosad is effective against certain stored-product insects but has not yet been tested for its synergy with heat or cold. This experiment was conducted to evaluate the effect of spinosad on the heat tolerance and cold tolerance of S. oryzae and R. dominica adults. The experiment was a two-factor factorial, complete randomized design with four replicates. The spinosad concentration and exposure period were changed. Adults of S. oryzae and R. dominica were first exposed to a series of spinosad concentrations. Later they were held at higher (40 °C) or lower (6–11 °C) temperatures than room temperature for different durations.Pre exposure of S. oryzae adults to Spinosad at 18 ppm or above synergized the adult mortality at high or low temperature showing a dose response. Pre-exposure of R. dominica adults to spinosad concentrations 12.5 ppm or higher synergized the mortality at high temperature whereas the spinosad synergized the mortality of R. dominica at low temperature when exposed to 6.25 ppm or higher concentrations; the effects followed a dose response. This study shows that heat and cold tolerance of S. oryzae and R. dominica adults are reduced by pre-exposure to spinosad. Therefore, spinosad is a potential grain protectant at high or low temperatures against these two insect species.     

Insecticidal effect of spinetoram against six major stored grain insect species

Spinetoram is a novel insecticide that belongs to the spinosyn class of insecticidal chemicals. The efficacy of spinetoram against numerous insect pest species in a variety of field crops has been well demonstrated. However, there are no data available for the effectiveness of spinetoram against stored grain insects. In the present study, we evaluated spinetoram as a grain protectant, against six stored-product Coleoptera. The species tested were: the rice weevil, Sitophilus oryzae, the lesser grain borer, Rhyzopertha dominica, the larger grain borer, Prostephanus truncatus, the confused flour beetle, Tribolium confusum, the granary weevil, Sitophilus granarius and the sawtoothed grain beetle, Oryzaephilus surinamensis. All species were tested at the adult stage, on wheat (or maize in the case of P. truncatus) treated to achieve spinetoram concentrations of 0.01, 0.1, 0.5, 1, 2, 5 and 10 ppm. Mortality was recorded after 1, 2, 7, 14 and 21 d of exposure, and 65 d later the wheat and maize were examined for offspring emergence. Among the species examined, P. truncatus and R. dominica were by far the most susceptible, given that mortality was close to 100% after 7 d on wheat treated or maize with 0.1 ppm of spinetoram. At this concentration, progeny production of P. truncatus and R. dominica was negligible. On the other hand, T. confusum was the least susceptible; mortality reached 95% only at 10 ppm, and only after 14 d of exposure. Similarly, O. surinamensis was of limited susceptibility to spinetoram; mortality reached 95% only after 14 d of exposure on wheat treated with 5 ppm. Nevertheless, offspring emergence of these species was extremely low. For S. granarius and S. oryzae, complete (100%) mortality was recorded after 14 d of exposure, at 0.5 and 1 ppm, respectively. At these concentrations or higher, progeny production was notably reduced. The results of the present study demonstrate that spinetoram is effective as a grain protectant, but its efficacy varies according to the target species, concentration and exposure interval.     

Evaluation of diatomaceous earth formulations enhanced with natural products against stored product insects

The insecticidal effect of prepared insecticide formulations labelled as Natural P, Inert Natural P and Py EC on Sitophilus oryzae, Rhyzopertha dominica and Tribolium castaneum have been evaluated on wheat grains. Formulation Natural P contains diatomaceous earth (DE), amorphous silica gel (3%), pyrethrin, flax oil, lavandin essential oil (EO) and un-activated yeast. Formulation Inert Natural P contains DE, amorphous silica gel, lavandin EO and food grade bait whereas formulation Py EC contains pyrethrin, piperonyl butoxide (PBO), flax oil, polysorbate, methyl oleate and amorphous silica gel (5%). Celatom® MN-51 (diatomaceous earth – DE) was used as a standard insecticide. Inert Natural P and Natural P were applied as dust at four different doses and Py EC was applied as emulsions on grain by spraying. All three formulations showed higher insecticidal efficacy and higher progeny inhibition on all three tested insect species and had lower impact on wheat bulk density reduction compared with Celatom® MN-51. The LD₅₀ and LD₉₀ values of Inert Natural P were 48.7 and 163.7 ppm respectively for S. oryzae, 15.2 and 178.0 ppm for R. dominica and 115.2 and 171.3 ppm for T. castaneum. The LD₅₀ and LD₉₀ values of Natural P were 83.6 and 97.9 ppm respectively for S. oryzae, 19.5 and 97.9 ppm for R. dominica and 75.4 and 105.6 ppm for T. castaneum. Applied Py EC at concentration of 2.0 ppm a.i. pyrethrin exhibited 100% mortality after 2 d of S. oryzae and T. castaneum and after 6 d of R. dominica. In addition, all three formulations caused significant reduction of progeny (F1) population compared to control, providing promising approach of integrated pest management strategy.     

Base-line susceptibility of field populations of Rhyzopertha dominica (F.) to spinosad in Australia

Spinosad has recently been registered in several countries for long-term protection against a range of stored grain insects including the lesser grain borer, Rhyzopertha dominica (F.). The potential for development of resistance to spinosad is demonstrated by the existence of resistance in many insect pests of agriculture. The aim of this study was to determine the base-line susceptibility of R. dominica to spinosad, to provide a basis for future resistance monitoring. Eighteen insect populations of R. dominica were collected from field storage sites across four States within Australia, and exposed to a range of spinosad rates, including its current registered rate of 1 mg kg⁻¹ (1 ppm). Base-line susceptibility was assessed based on adult mortality and production of F₁ adults. Comparison of LC₅₀ and LC_99.9 indicated the existence of low level of variation among the tested R. dominica populations, in their susceptibility to spinosad. For adults, there was a narrow range of LC₅₀ values with the highest (0.027 ppm) being 2.5 × the lowest (0.011 mg kg⁻¹). Similarly, LC_99.9 values showed a narrow range with the highest (0.36 mg kg⁻¹) being 3.6 × the lowest (0.10 mg kg⁻¹). For adult progeny produced in spinosad treated grain, there was a narrow range of LC₅₀ values with the highest (0.025 mg kg⁻¹) being 5 × the lowest (0.004 mg kg⁻¹) and the highest LC_99.9 values (0.67 mg kg⁻¹) being 5 × the lowest LC_99.9 (0.13 mg kg⁻¹). Based on the data generated from this study, we recommend a dose of 1 mg kg⁻¹(1 ppm) to be used to discriminate between susceptible and resistant populations for future resistance monitoring programs.     

Evaluations of the new deltamethrin-treated all-in-one hermetic bag for the control of the Khapra beetle,Trogoderma granarium (Everts)

The khapra beetle, Trogoderma granarium (Everts), is a highly destructive stored product insect that presents a significant threat to stored bagged grain. Hermetic packaging is designed to maintain the quality and safety of stored grain, while continually protecting the grain from insect infestations during storage. The objective of this research was to evaluate a prototype deltamethrin, all-in-one treated hermetic bag on contact efficacy, larval mobility, and the control of T. granarium in artificially infested wheat. The insecticidal activity of the deltamethrin-treated packaging was tested against larvae and adults of T. granarium through contact bioassays. There was a significant reduction in responsive adults after 5 day and >86% of larvae were unresponsive after 9 d of exposure on the treated bag. Trogoderma granarium movement toward a food bait was <10% after a 24 h exposure on the treated bag compared to ~45% of larvae on untreated bag. Lots of 15 kg of wheat were artificially infested with 100 T. granarium larvae and placed inside treated and untreated storage bags, sealed, and stored in a semi-field warehouse, and observed after 2, 6, and 8-weeks for T. granarium survival and grain quality attributes. The weight and number of insect damaged kernels was lower across all storage intervals for grain held in the treated bags, as compared with control bags. Live adult T. granarium were observed at 2-weeks in treated and untreated bags, but there were no live adults observed after 8-weeks of storage in both bags. The new prototype hermetic bags maintained positive grain qualities, however more information on the hermetic parameters are needed to understand how some individuals survived.     

Evaluation of dosimeter tubes for monitoring phosphine fumigations

Within integrated pest management options, fumigation of stored products is one method to help control post-harvest insect infestations in our food and agricultural products. Fumigant gas concentration monitoring is important to confirm that the treatment was adequate to achieve the desired insect control, but monitoring can be relatively expensive and labor intensive. This study evaluated how accurately dosimeter tubes could monitor phosphine fumigation treatments. The dosimeter tube is designed to continuously react with phosphine gas during the fumigation period and yields a measurement in terms of concentration 1 time product or CT, which can be interpreted as cumulative exposure. Two models of dosimeter tubes were evaluated (high range and low range). The reference method for these trials were wireless phosphine monitoring sensors, which recorded gas concentrations at hourly intervals during an exposure, and from this a CT product was also calculated. Model LPG-1, high-range dosimeter tube, measured within ± 25% of the phosphine monitoring sensors for CT dosages less the 70,000 ppm1hr. Model LPG-2, low-range tube, tended to significantly over-estimate phosphine CT dosage by 50%–100% of the phosphine monitoring sensor references. Secondly, bioassays of fumigant efficacy were performed using susceptible and resistant adult Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), lesser grain borers, and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), red flour beetle, for estimating insect control at the varied fumigation CT treatments. For the susceptible strains, CT dosages ∼5000 ppm1hr controlled both species. However, the insect control varied from 60% to 100% for resistant adults at CT dosages of ∼20,000 ppm1hr. The dosimeter tubes function in these ranges of dosages where each insect species are controlled and the dosimeter tube model LPG-1 provides reasonable estimates of the fumigation dosage for a given treatment level.     

Insect population dynamics in commercial grain elevators

Data were collected in 1998-2002 from wheat stored in commercial grain elevators in south-central Kansas. Bins at these elevators had concrete walls and were typically 6-9 m in diameter and 30-35 m tall. A vacuum-probe sampler was used to collect grain samples in the top 12 m of the wheat in each bin. The primary insect species found in the wheat samples were: Cryptolestes ferrugineus, Rhyzopertha dominica, and Tribolium castaneum. In the top 3.7 m of grain, R. dominica, C. ferrugineus, T. castaneum and Sitophilus oryzae made up 44, 36, 19 and 1% of the insects found in the samples, respectively. From 3.8 to 12.2 m, R. dominica, C. ferrugineus, T. castaneum and S. oryzae were present at 84, 8, 8, and 1%, respectively. The most prevalent species also changed over time. In June, the start of wheat harvesting and storage in Kansas, insect density was low in the bins. At this time, C. ferrugineus was the most common insect, and it was found mostly in the top grain sample (0-1.2 m). In September through November, C. ferrugineus and R. dominica were at similar densities; however, from February to March, R. dominica was more common.Generally, insect density was greatest at the top and decreased with grain depth. Very few insects were found in samples collected from greater than 12 m (most of the bins contained grain to depths of 24-36 m). Insect density for all species increased rapidly from June through October. During this period less than 20% of the bins had economically significant insect densities (>2 insects/kg). From October until February, the average insect density remained fairly constant but it was greatly reduced in April, May, and June. Bins that had insect densities >2 insects/kg tended to be located adjacent to other heavily infested bins.     

Sensitivity of different life stages of Indian meal moth Plodia interpunctella to gaseous chlorine dioxide

Gaseous chlorine dioxide (ClO₂), a possible alternative to the fumigant methyl bromide, is a strong disinfecting agent that has strong oxidizing properties and penetration ability. The Indian meal moth, Plodia interpunctella, is one of the most important insect pests of stored food, but its sensitivity to gaseous ClO₂ at different life stages has not yet been studied. We exposed all the life stages of P. interpunctella (i.e., eggs, larvae, pupae, and adults) to ClO₂ at different concentrations for different time periods. The results showed that 100 ppm and 200 ppm ClO₂ for 48 h and 24 h, respectively, resulted in 100% mortality of all P. interpunctella life stages. The order of sensitivity of P. interpunctella to gaseous ClO₂ was: egg > larva > pupa at 50 ppm and 100 ppm, and egg > pupa > larva at 200 ppm. The gas treatment affects the subsequent life stage of P. interpunctella: the gas-treated larvae fail to pupate or emerge as adults. These results suggest that gaseous ClO₂ is a possible alternative to methyl bromide, and it can effectively control all stages of P. interpunctella.     

Spinosad: A new natural product for stored grain protection

Spinosad is a reduced-risk insecticide derived by fermentation from the soil actinomycete, Saccharopolyspora spinosa Mertz & Yao. Spinosad is currently registered in several countries as a grain protectant at a maximum labeled use rate of 1 ppm (1 mg a.i./kg of grain) and with the Maximum Residue Level (MRL) or tolerance on grains set at 1 or 1.5 ppm. Global launch of spinosad as a grain protectant is expected in the near future, pending final acceptance of international residue tolerances for spinosad by major grain importing and exporting countries. Spinosad effectively controls economically important beetle and moth pests associated with stored grain and is also effective against certain psocid species. Spinosad provides grain protection through control of adult and/or immature life stages of pest insects. The pest spectrum of spinosad under commercial grain storage conditions is still being defined, but it is clear from available laboratory and field evaluations on various grains that the lesser grain borer, Rhyzopertha dominica (F.); larger grain borer, Prostephanus truncatus (Horn); rusty grain beetle, Cryptolestes ferrugineus (Stephens); flat grain beetle, Cryptolestes pusillus (Schönherr); red flour beetle, Tribolium castaneum (Herbst); confused flour beetle, Tribolium confusum Jacquelin du Val; Indian meal moth, Plodia interpunctella (Hübner); rice moth, Corcyra cephalonica (Stainton); Angoumois grain moth, Sitotroga cerealella (Olivier); almond moth, Cadra cautella Walker; and the psocid species Lepinotus reticulatus Enderlein and Liposcelis entomophila (Enderlein) are susceptible to spinosad and complete control is to be expected. Other pest species such as the maize weevil, Sitophilus zeamais Motchulsky; rice weevil, Sitophilus oryzae (L.); and sawtoothed grain beetle, Oryzaephilus surinamensis (L.) are susceptible to spinosad to varying degrees, but their overall level of control remains to be verified under commercial grain storage conditions. Spinosad residues are highly stable on grains stored in bins, with a length of protection ranging from 6 months to 2 years. Numerous factors have been shown to impact the overall performance of spinosad, including insect pest species, pest life stage, grain type, grain variety, and formulation type. Spinosad possesses a unique mode of action in insects and controls insect strains resistant to other grain protectants. When launched globally, spinosad will represent a valuable new addition to the limited arsenal of grain protectants and can positively impact global food security. Its combination of high efficacy, broad insect pest spectrum, low mammalian toxicity, and sound environmental profile is unique among existing products currently used for stored-grain protection.