Improving detection probabilities for pests in stored grain

BACKGROUND: The presence of insects in stored grain is a significant problem for grain farmers, bulk grain handlers and distributors worldwide. Inspection of bulk grain commodities is essential to detect pests and thereby to reduce the risk of their presence in exported goods. It has been well documented that insect pests cluster in response to factors such as microclimatic conditions within bulk grain. Statistical sampling methodologies for grain, however, have typically considered pests and pathogens to be homogeneously distributed throughout grain commodities. In this paper, a sampling methodology is demonstrated that accounts for the heterogeneous distribution of insects in bulk grain. RESULTS: It is shown that failure to account for the heterogeneous distribution of pests may lead to overestimates of the capacity for a sampling programme to detect insects in bulk grain. The results indicate the importance of the proportion of grain that is infested in addition to the density of pests within the infested grain. It is also demonstrated that the probability of detecting pests in bulk grain increases as the number of subsamples increases, even when the total volume or mass of grain sampled remains constant. CONCLUSION: This study underlines the importance of considering an appropriate biological model when developing sampling methodologies for insect pests. Accounting for a heterogeneous distribution of pests leads to a considerable improvement in the detection of pests over traditional sampling models. Copyright © 2010 Society of Chemical Industry     

Distribution and migration of insects and mites in flat storage containing wheat

Studies were conducted in a flat storeroom in central Greece, filled with approx. 90 tons of wheat, in order to evaluate insect and mite species abundance, and changes in population density and distribution among sampling units and locations. The surface of the grain bulk was divided into two sampling zones: the central and the peripheral (edge). At 10-day intervals, five wheat samples were taken from the central zone and eight from the peripheral zone, with a non-partitioned grain trier (1.6-m length, 250-g capacity). Fifteen insect species and 12 mite taxa were found during the sampling period, (June 1999–Feb. 2000). The most abundant insect species wereSitophilus oryzae (L.),Cryptolestes ferrugineux (Stephens),Tribolium castaneum (Herbst) andLatheticus oryzae Waterhouse; the most abundant mite species wereAcarus siro L.,Lepidoglyphus destructor (Shrank), and the predatorsBlattisocius tarsalis (Berlese) andB. keegani Fox. Grain temperature decreased during the storage period, more slowly in the central than peripheral zone; grain moisture content increased. The highest population densities for both insects and mites were recorded during September and October. The most numerous species of insects and mites showed an aggregated spatial pattern, as indicated by Iwao’s Patchiness Regression.     

储藏物害虫生物性防治技术研究现状和展望

有效的杀虫剂和熏蒸剂种类的减少,以及它们对环境的污染和对人畜健康的影响,使得生物性的防治技术在储藏物害虫的控制上显得越来越重要。近年来,有关储藏物害虫生物性防治技术的研究报道越来越多。根据过去20年的文献,特别是根据刚出版的第七届国际储藏物保护会议的有关论文,评述了储藏物害虫生物性防治技术的研究现状,展望了将来的发展。内容涉及到天敌昆虫、昆虫信息素、病原微生物、抗虫品种和遗传防治等领域,着重于它们在实践中的应用。     

Management of Stored Wheat Insect Pests in the USA

Management of stored-grain insect pests by farmers or elevator managers should be based upon a knowledge of the grain storage environment and the ecology of insect pests. Grain storage facilities and practices, geographical location, government policies, and marketing demands for grain quality are discussed as factors influencing stored-grain insect pest management decisions in the United States. Typical practices include a small number of grain samples designed to provide grain quality information for segregation, blending and marketing. This low sampling rate results in subjective evaluation and inconsistent penalties for insect-related quality factors. Information on the efficacy of insect pest management practices in the United States, mainly for farm-stored wheat, is discussed, and stored-grain integrated pest management (IPM) is compared to field-crop IPM. The transition from traditional stored-grain insect pest control to IPM will require greater emphasis on sampling to estimate insect densities, the development of sound economic thresholds and decision-making strategies, more selective use of pesticides, and greater use of nonchemical methods such as aeration. New developments in insect monitoring, predictive computer models, grain cooling by aeration, biological control, and fumigation are reviewed, their potential for improving insect pest management is discussed, and future research needs are examined.     

Insecticidal efficacy of beauveria bassiana,diatomaceous earth and fenitrothion against rhyzopertha dominica and tribolium castaneum on stored wheat

Bioassays were conducted in stored grains to evaluate the combined use of the entomopathogenic fungus Beauveria bassiana, diatomaceous earth (DE) and fenitrothion against adults of Rhyzopertha dominica and Tribolium castaneum. The insecticide agents were applied to wheat as follows: the fungus at 1 × 10⁸ conidia/kg of wheat, DE at 3 g/kg of wheat and fenitrothion at a rate of 0.15 ml/kg of wheat (25% of field dose rate). Surviving insects and progeny production were monitored at thirty-day intervals until four months. For both insect species, significantly less progeny was produced on wheat treated with fenitrothion and DE + B. bassiana formulations in comparison with controls. The effect of insecticides on the grain damage, germination power of wheat and bulk density was also evaluated. After four months, B. bassiana mixed with DE reduced the damaged insect grains by 50% in comparison with both fenitrothion and control treatments. Trials using DE caused a reduction in bulk density while there were no significant differences for germination testing between treatments.     

Management of five stored-product insects in wheat with pirimiphos-methyl and pirimiphos-methyl plus synergized pyrethrins

Hard red winter wheat was treated with pirimiphos-methyl at 4, 6 and 8 mg kg(-1), synergized pyrethrins at 0.38, 0.75, 1.13 and 1.5 mg kg(-1), and combinations of the two insecticides, to conduct laboratory bioassays against four beetle pests of stored grain, red flour beetle Tribolium castaneum (Herbst), rusty grain beetle Cryptolestes ferrugineus (Stephens), lesser grain borer Rhyzopertha dominica (F), and rice weevil Sitophilus oryzae (L), and one moth pest, Indianmeal moth Plodia interpunctella (Hubner). Beetle adults and P interpunctella larvae survived well on control wheat, producing a large number of progeny (65-1037 insects per container). Kernel damage in control wheat among the insect species ranged from 9 to 99%. On pirimiphos-methyl-treated wheat, mortality of R dominica adults was > or =72%, but that of the other beetle species and P interpunctella larvae was 100%. Progeny were not produced on pirimiphos-methyl-treated wheat, and the kernel damage was negligible (< or =1%). Synergized pyrethrins were ineffective against the five insect pests. Pirimiphos-methyl combined with synergized pyrethrins was not superior to pirimiphos-methyl alone against the five insect pests. Pirimiphos-methyl is not registered in the USA for use on wheat, but our results suggest that it could be a viable grain protectant at rates of 4-8 mg kg(-1).     

Efficacy of a diatomaceous earth against mite and insect populations in small bins of wheat under conditions of low temperature and high humidity

Twenty‐five kilograms of wheat, at 16 and 17% moisture content (MC) were treated with ‘Dryacide’, a diatomaceous earth, at 3 and 5 g kg⁻¹ and stored in metal bins. The bins were then infested with mixed populations of mites (Acarus siro and Lepidoglyphus destructor) and insects (Sitophilus granarius and Oryzaephilus surinamensis) at approximately 100 and 10 per kg, respectively. The grain was held at a constant temperature of 15 °C and relative humidities of 75 and 80%, chosen to simulate bulk surface conditions in UK stores, and monitored for 42 weeks. At 16% MC, the mite and insect populations were suppressed within 2 and 13 weeks, respectively, at both doses. At 17% MC, the mites took 5 weeks to die out and F₁ adults of S granarius emerging within 22 weeks were controlled after a further 5 weeks. After 23 weeks the bins were re‐infested with mites and these were completely suppressed after a further 3 weeks. There was no decline in efficacy throughout the experiment. © Crown Copyright 2000. Reproduced with the permission of Her Majesty's Stationery Office. Published for SCI by John Wiley & Sons, Ltd.     

寄主与粮粒对雅脊金小蜂寄生和发育的影响

从三级营养关系出发,研究了不同粮食（小麦和玉米）和寄主（米象和玉米象）对雅脊金小蜂发育和寄生的影响。结果表明：4个三级营养系统中雅脊金小蜂实验种群在4种虫源寄主中均能正常发育,其卵-成虫的发育历期在4种虫源寄主中由短至长依序为：玉米粒-玉米象〈小麦粒-玉米象〈小麦粒-米象〈玉米粒-米象;4种蜂源中雅脊金小蜂对小麦中的米象或玉米象的寄生率、刺死率和总致死率均显著高于对玉米中的米象或玉米象。因此用雅脊金小蜂控制小麦中的米象或玉米象,其效果较之玉米中的米象或玉米象的效果更好。     

Post-harvest entomology research in the United States Department of Agriculture-Agricultural Research Service

This is a review of current post-harvest entomology research conducted by the Agricultural Research Service, the research branch of the US Department of Agriculture. The review covers both durable and perishable commodities. Research on biochemistry, genetics, physiology, monitoring and control of insects infesting stored grain, dried fruits and nuts, and processed commodities is reviewed. Research on development of quarantine treatments, particularly for fruit flies, is also reviewed, including research on thermal and irradiation treatments and a discussion of risk management for quarantine pests. Two areas of research are covered more extensively: a project to map the genome of the red flour beetle, Tribolium castaneum, and the use of near-infrared spectroscopy for detection of hidden infestations in grain, quantification of insect fragments in food, determination of quality in dried fruits, identification of insect species and age-grading insects. Future research directions are identified.     

溴虫氟苯双酰胺对小菜蛾的毒力及相关酶活性的影响

溴虫氟苯双酰胺是一种全新的双酰胺类杀虫剂,主要用于防治鳞翅目、鞘翅目、白蚁以及蚊蝇等害虫。为了明确溴虫氟苯双酰胺对小菜蛾的生物活性及解毒酶活性的影响,本研究选择氯虫苯甲酰胺为对照药剂,采用叶片药膜法测定了溴虫氟苯双酰胺对小菜蛾的生物活性,并测定了亚致死剂量(LC20、LC40)的溴虫氟苯双酰胺和氯虫苯甲酰胺对小菜蛾多功能氧化酶、谷胱甘肽S-转移酶和羧酸酯酶活性的影响。结果表明,溴虫氟苯双酰胺与氯虫苯甲酰胺对小菜蛾的生物活性相当,两者对小菜蛾的LC50分别为0.042和0.056μg/mL。与氯虫苯甲酰胺相似,亚致死剂量的溴虫氟苯双酰胺能够诱导小菜蛾体内羧酸酯酶活性升高,但溴虫氟苯双酰胺对多功能氧化酶和谷胱甘肽S-转移酶活性没有显著影响。     

五种出口农产品仓储昆虫群落结构的数量特征

利用群落物种的丰富度、生态优势度、多样性、均匀度等群落特征指数，研究了临沂市5种出口农产品仓储昆虫群落结构的数量特征，并分析了它们的相似性。通过系统聚类分析将5种群落分为4类，脱水蔬菜和中药材仓储昆虫群落同属于一类，其它3种农产品仓储昆虫群落各属一类。除大蒜群落结构合理外，其它群落结构都不合理，粮谷群落结构尤其不合理。结合仓储昆虫群落结构特征指数、害虫及天敌的发生情况，分析了4大类群落的特点，并提出了对应的仓储管理意见。利用群落特征指数，对粮谷昆虫群落时间格局的结构特点进行了研究，根据不同时间害虫及天敌的发生情况，提出了相应的害虫管理措施。     

The Feasibility of Environmental Control for the Protection of Stored Grain

Relevant data on the possibilities of changing the stored grain environment, for the sake of better preservation of grain in storage, are reviewed. The grain bulk is regarded as an ecosystem, in which the impact of damaging organisms can be controlled by ambient conditions. The influence of humidity, temperature, composition of atmospheric gases, atmospheric pressure and light is discussed. Lowering humidity and grain temperatures are well known effective and practical ways for the prevention of storage damage. The modification of atmospheric gas compositions has been subjected to very extensive research, on which new methods for insect control could be based. Lowering the absolute pressure in storage containers has detrimental effects on storage insects; the practical implementation of this technique is discussed. Research on the effects of changing light conditions on stored grain insects is in its earliest stage, but shows promise. Studies on an integrated approach using several environmental elements for the containment of grain insects and microflora are proposed.     

Improved efficacy of ethyl formate against stored grain insects by combination with carbon dioxide in a 'dynamic' application

Ethyl formate is being evaluated as a fumigant for stored grain as it is a potential alternative to the ozone-depleting fumigant methyl bromide and to phosphine, which is under pressure owing to the development of strong resistance in stored grain insects. However, use of ethyl formate faces significant challenges, such as poor penetration through grain, significant losses to grain sorption, high concentrations of fumigant required to control insects, and flammability risks, which have limited its further development. In this study it was found that the combination of carbon dioxide (5-20%) with ethyl formate significantly enhanced efficacy of the fumigant against external living stages of the rice weevil, Sitophilus oryzae (L.), the lesser grain borer, Rhyzopertha dominica F., and the flour beetle, Tribolium castaneum (Herbst). Dynamic application of ethyl formate and carbon dioxide mixture (100 mg litre-1 ethyl formate, 20% CO2) pumped through a model silo containing wheat (50 kg) for one gas exchange was also investigated. A flow rate of 6 litres min-1 gave a relatively even distribution of fumigant throughout the grain column and similar mortality levels among cultures of S. oryzae and T. castaneum placed at three positions, the top, middle and bottom of the column. Mortality of 99.8% of mixed stage cultures of T. castaneum and 95.1% of S. oryzae was achieved in 3 h exposures to 111 and 185 mg ethyl formate h litre-1 respectively applied by the dynamic method. It is concluded that the combination of carbon dioxide with ethyl formate and dynamic application enhances distribution and efficacy of the fumigant against stored grain insects.     

Comparison of four methods for the detection of Coleoptera adults infesting stored wheat: efficiency and detection sensitivity

In order to evaluate trapping and standard sampling methods for Coleoptera adult detection in bulked wheat, three commercial types of traps (WBII, Pitfall Cone Trap and Grain Probe Trap) and a 2-m long grain trier (9 openings, 750 g capacity) were compared. The comparison, which took place in 9 steel bins containing wheat in Central Greece, indicated that the traps were more effective in detecting adults belonging to the 21 beetle species that were found. Traps contained up to 45 times more adults than the grain trier samples, while at the same time traps produced noticeable levels of detection sensitivity for all species found, as compared to the grain trier samples. For most species, mean trap catches in WBII and Pitfall Cone traps were significantly higher than the means of the other two methods. The correlation coefficient values between trap catches and adult numbers in samples were not significantly different than zero, indicating that the effort to relate trapping to absolute estimation sampling methods is a very complex procedure.     

Comparison of four methods for the detection of Coleoptera adults infesting stored wheat: efficiency and detection sensitivity

In order to evaluate trapping and standard sampling methods for Coleoptera adult detection in bulked wheat, three commercial types of traps (WBII, Pitfall Cone Trap and Grain Probe Trap) and a 2-m long grain trier (9 openings, 750 g capacity) were compared. The comparison, which took place in 9 steel bins containing wheat in Central Greece, indicated that the traps were more effective in detecting adults belonging to the 21 beetle species that were found. Traps contained up to 45 times more adults than the grain trier samples, while at the same time traps produced noticeable levels of detection sensitivity for all species found, as compared to the grain trier samples. For most species, mean trap catches in WBII and Pitfall Cone traps were significantly higher than the means of the other two methods. The correlation coefficient values between trap catches and adult numbers in samples were not significantly different than zero, indicating that the effort to relate trapping to absolute estimation sampling methods is a very complex procedure.     

Effect of phosphine dose on sorption in wheat

BACKGROUND: In spite of the extensive use of phosphine fumigation around the world to control insects in stored grain, and the knowledge that grain sorbs phosphine, the effect of concentration on sorption has not been quantified. A laboratory study was undertaken, therefore, to investigate the effect of phosphine dose on sorption in wheat. Wheat was added to glass flasks to achieve filling ratios of 0.25-0.95, and the flasks were sealed and injected with phosphine at 0.1-1.5 mg L(-1) based on flask volume. Phosphine concentration was monitored for 8 days at 25 degrees C and 55% RH. RESULTS: When sorption occurred, phosphine concentration declined with time and was approximately first order, i.e. the data fitted an exponential decay equation. Percentage sorption per day was directly proportional to filling ratio, and was negatively correlated with dose for any given filling ratio. Based on the results, a tenfold increase in dose would result in a halving of the sorption constant and the percentage daily loss. Wheat was less sorptive if it was fumigated for a second time. CONCLUSIONS: The results have implications for the use of phosphine for control of insects in stored wheat. This study shows that dose is a factor that must be considered when trying to understand the impact of sorption on phosphine concentration, and that there appears to be a limit to the capacity of wheat to sorb phosphine.     

Influence of killing agents and water on the capture of six coleoptera species in probe traps

The introduction of propylene glycol, DDVP and water inside perforated probe traps was evaluated on the basis of their effectiveness in trapping adults of six species of Coleoptera infesting stored cereals. Adults ofSitophilus oryzae, Tribolium castaneum, Cryptolestes ferrugineus, Tenebroides mauritanicus, Rhyzopertha dominica andOryzaephilus surinamen-sis were placed in plastic cylindrical bins each containing 14 kg of wheat. One probe trap was then introduced into each container and the adults trapped were counted 72 h later. Experiments were conducted at two population densities, of 30 adults (approx. one insect per 0.5 kg of wheat) and 90 adults (approx. three adults per 0.5 kg of wheat) of each species per container. The highest percentage of adults trapped was observed forC. ferrugineus andT. castaneum, and the lowest forR. dominica andS. oryzae. No significant differences in number of adults captured (% of the total number of adults) was noted between the two population density levels. At the lower density, the presence of killing agents in the traps did not increase the captures significantly; on the other hand, at the higher density, the killing agents helped to increase significantly the catches of 5.oryzae, T. castaneum, T. mauritanicus andO. surinamensis, as compared with the catches in the control traps. No significant differences were noted forC. ferrugineus andR. dominica.     

Interstitial air movement in model grain silos

Sulphur hexafluoride, SF₆, was used as a gaseous tracer to determine the rate of unassisted air movement in the microclimate of grain stored in steel bins. The airspeeds were influenced by the nature of the stored products, the size and geometrical shape of the kernels and the storage temperature. Air movement rates varied from 3 to 108 in/h depending on the temperature gradients. This is the first quantitative evidence of the ultraslow speed of air movement in stored grain.     

小麦不同生育期地下害虫为害程度与其虫口密度的关系

为明确小麦不同生育期地下害虫为害程度与其虫口密度的关系,采用棋盘式10点取样法,在调查秋播前麦田地下害虫种类和数量的基础上,研究冬前秋苗期和春季返青拔节期地下害虫为害造成的麦苗死亡率。在陕西武功,秋播前麦田地下害虫有20种,其中以金针虫和蛴螬为优势种,分别占地下害虫发生总量的58.66%和21.91%。地下害虫为害引起的死苗现象主要发生在冬前秋苗期,供试5块田的死苗率达4.4%～9.1%;春季返青拔节期的死苗率较低,仅为1.0%～2.3%。相关分析表明,地下害虫为害造成的冬前秋苗期和春季返青拔节期死苗率与其虫口密度密切相关。     

不同温度和水分小麦中不同谷蠹发生状态时二氧化碳变化研究

［目的］ 研究不同储藏温度、粮食含水量条件下,粮食、微生物、储粮害虫谷蠹与二氧化碳浓度变化的对应关系,以期为通过检测气体监测害虫发生提供参考依据。 ［方法］ 在20、25、30 ℃下检测含水量分别为12%、13%和14%的小麦样品感染谷蠹后不同时间的二氧化碳浓度,并与自然带菌无虫和灭菌无虫小麦进行比较。［结果］ 在前期30 d中,感染害虫（10头/kg）的小麦中二氧化碳浓度明显大于自然带菌和灭菌无虫样品,其中12%含水量,25 ℃感染害虫小麦中二氧化碳浓度最高达2.676%,自然带菌样品中为0.214%,灭菌样品中为0.148%。二氧化碳浓度随温度升高及粮食水分增大而显著升高。［结论］ 二氧化碳浓度与粮食中害虫发生状况显著相关,一定条件下可通过检测二氧化碳浓度了解储粮粮情和害虫发生状态。