Periodic disturbance time interval for suppression of the maize weevils,Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in stored maize (Zea mays L.)

Sitophilus zeamais Motschulsky threaten maize (Zea mays L.) storage in the tropical regions of low-income countries where maize is a staple. Disturbance of maize during storage can be an alternative to chemical treatment in suppressing populations of S. zeamais. Disturbance has been successful against insect pests of stored products, i.e. bean weevils, Acanthoscelides obtectus (say) (Coleoptera: Chysomelidae: Bruchinae) and lesser grain borers Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae). Prior research has not established a standard disturbance interval. This study tested various disturbance intervals to see determine suppression of S. zeamais populations in stored maize with four treatments: stationary jars (control) and jars disturbed at intervals of 8, 12 and 24 h. Jars contained 1 kg of 16 ± 0.7% wet basis moisture maize and 234 ± 51 adult S. zeamais stored at 27 °C, 70% r. h. and 12 h light and dark phases. Periodically, electric motors rotated jars through about 1.25 revolutions in 3 s. Three jars were selected randomly from each treatment every 40 d up to 160 d for analysis. Reduction in S. zeamais populations was 75%, 95% and 94% for 8, 12 and 24 h disturbance intervals, respectively, compared to the stationary jars after 160 d. The average quality of maize in all disturbed jars was better than in stationary jars, respectively, for moisture content (13 ± 1.1% vs. 21 ± 1.0%), bulk density (553.5 ± 1.1 kg/m³ vs. 231.7 ± 1.2 kg/m³), broken corn and foreign material (9 ± 1.2% vs. 68 ± 3.9%), insect damage (70 ± 4.5% vs. 100 ± 0.0%), and mold damage (0.4 ± 0.2% vs. 27 ± 17.2%). Disturbances of 12h and 24 h (once per day) proved the best intervals in suppressing S. zeamais populations and maintaining the quality of maize, much longer than previously reported. Of these two intervals, the less frequent 24 h disturbance interval may be an effective non-chemical approach to control S. zeamais in maize stored by smallholder farmers, requiring less effort.     

蓖麻限制性酶解蛋白功能特性和抗氧化活性研究

目的研究蓖麻限制性酶解蛋白的功能特性和抗氧化活性,为进一步开发利用蓖麻蛋白提供一条新途径。方法以蓖麻子为原料,通过粉碎、脱脂、乙醇洗涤、沸水脱毒、冷冻干燥等操作步骤制备蓖麻浓缩蛋白,再分别用碱性蛋白酶(alcalase)、风味蛋白酶(flavourzyme)、复合蛋白酶(protamex)、中性蛋白酶和木瓜蛋白酶水解得到5种蓖麻限制性酶解蛋白,并进行功能性质和抗氧化活性研究。结果蓖麻浓缩蛋白色泽洁白、无异味,其蛋白含量为73.08%,脂肪含量为1.13%,是一种优质的植物蛋白;蓖麻浓缩蛋白经蛋白酶限制性酶解后功能性质和抗氧化活性增加,功能性质大小顺序为:复合蛋白酶、中性蛋白酶、木瓜蛋白酶、碱性蛋白酶和风味蛋白酶,抗氧化活性大小顺序为:复合蛋白酶、风味蛋白酶、中性蛋白酶、碱性蛋白酶和木瓜蛋白酶。结论采用复合蛋白酶限制性酶解蓖麻蛋白,可得到功能特性和抗氧化活性都较好的限制性酶解蓖麻蛋白。     

Susceptibility of selected maize seed genotypes to Sitophilus zeamais (Coleoptera: Curculionidae)

Studies were carried out under laboratory conditions of 25 ± 2 °C and 70 ± 5% RH in an incubator to determine the relative susceptibility of eighteen maize genotypes to attack by the maize weevil, Sitophilus zeamais Motschulsky. The experiment was laid out in a Completely Randomized Design (CRD) with three replications. Adult mortality, number of F₁ progeny, weevil development time, susceptibility index, percentage seed damage, percentage weight loss, and weight of powder produced were determined after storage period of three months. The susceptibility index was determined using Dobie’s formula and the genotypes were classified into different susceptibility groups. The genotypes exhibited varying degrees of susceptibility to S. zeamais attack. Only Aseda was regarded as resistant and TZE-Y POP STR as moderately resistant to S. zeamais. Kpari-Faako, Tintim, WACCI-M-1215, WACCI-M-1594 and Wang-Dataa were regarded as moderately susceptible to S. zeamais. However, Abontem, Bihilifa, Ewul-Boyu, Sanzal-Sima, TZE-I 17, WACCI-M-1205, WACCI-M-1508 and WACCI-M-1510 were regarded as susceptible genotypes. Furthermore, Aburohemaa, Obaatanpa and Omankwa were regarded as highly susceptible to S. zeamais. Number of F₁ progeny, seed damage, seed weight loss, weight of dust produced and seed moisture content had positive relationship with varietal susceptibility while adult weevil mortality, median development period and seed germination after infestation had an inverse relationship with susceptibility in maize. The use of insect resistant genotypes would offer a sustainable way of minimizing postharvest losses of seeds in storage especially for smallholder farmers who keep harvested grains for future use as food and seed.     

苦杏仁精油对玉米象的驱避活性研究

采用饲料混药法研究了含HCN和除去HCN两种苦杏仁精油对玉米象的驱避活性,结果显示苦杏仁精油对玉米象的驱避活性随着处理时间的延长而降低,两种苦杏仁精油在24 h内对玉米象的驱避率达到了Ⅴ级,但是随着时间的延长,对玉米象的驱避率效果下降至Ⅰ级。玉米象的死亡率随着处理时间的增加而逐渐增大,最终达到了100%的死亡率。另外,含HCN和除去HCN的苦杏仁精油对玉米象的驱避活性研究结果表明含HCN的苦杏仁精油的活性显著高于除去HCN的苦杏仁精油。     

内蒙古地区蓖麻材料种子中脂肪酸组成的测定及分析

采用索氏提取法、毛细管气相色谱法,首次对内蒙古地区8个品种、4个品系共12个蓖麻材料种子中的粗脂肪含量、脂肪酸组成进行测定,用IMB SPSS Statistics 19软件对数据进行分析,为内蒙古地区蓖麻高油品质育种研究及化工原料的选择提供参考数据。试验结果表明:12个蓖麻材料的种子百粒质量、种仁百粒质量、种仁率、百粒种子中粗脂肪含量、种子中粗脂肪含量、种仁中粗脂肪含量差异均达到极显著水平;蓖麻油酸是蓖麻粗脂肪的主要成分;12个材料的粗脂肪中8种脂肪酸含量、种子中8种脂肪酸含量差异均达极显著水平;基于种子中粗脂肪含量和种子中8种脂肪酸含量进行聚类的结果不相同,基于种子中8种脂肪酸含量和种子中蓖麻油酸含量进行聚类的结果基本一致。对种子中粗脂肪含量和8种脂肪酸含量进行线性回归分析,从回归方程可以看出,种子中的粗脂肪含量与硬脂酸、花生酸、亚油酸、蓖麻油酸含量呈正相关,与棕榈酸、油酸、亚麻酸、花生一烯酸含量呈负相关。     

不同大小蓖麻籽中脂肪酸组分的测定与分析

以32个品种不同大小的蓖麻籽为研究对象,采用索氏提取法、毛细管气相色谱法对籽中粗脂肪含量、脂肪酸组分进行测定分析,研究籽的大小与含油量之间的关系,为蓖麻高油品质育种研究提供依据。结果表明,32个品种的籽在长、体积、容重、百粒质量方面差异均极显著;籽中的粗脂肪、蓖麻油酸含量差异极显著。籽中粗脂肪含量和大小指标的多元回归方程:y_1=(-5.156x_1-8.747x_2+1.977x_3+0.324x_4+44.462)×100%;籽中蓖麻油酸含量和大小指标的多元回归方程为:y_2=(2.282x_1-19.553x_2+2.448x_3+0.286x_4+32.147)×100%。     

Susceptibility of Brazilian maize landraces to the attack of Sitophilus zeamais (Coleoptera: Curculionidae)

Landraces are used in breeding programs as a source of resistance and compose a small group of genetic materials accepted under organic seed production. The goal of this study was to evaluate the susceptibility of Brazilian landraces grains to the attack of Sitophilus zeamais. Ten different landraces were subjected to the attack of S. zeamais in choice and no-choice experiments. We evaluated the number of emerged insects and the weight reduction of the damaged grains. The Presidente Amarelo landrace received 4.4 and 5.4 times less insects than Colorado and Cateto in the choice experiment. Also, the Ligeirinho and Presidente Amarelo landrace provided the emergence of 4.2 times less adults than Cateto. The landraces presented different results when submitted to choice and no-choice experiments. However, Cateto grains presented the highest susceptibility to attack in both experiments. Presidente Amarelo, on the other hand, presented the highest resistance to the attack of S. zeamais and so might be considered to be used as a source of resistance in breeding programs.     

Efficacy of recovered diatomaceous earth from brewery to control Sitophilus zeamais and Acanthoscelides obtectus

Diatomaceous earth (DE) is an inert dust that can be used as a filter in breweries and to control stored-product pests. Experiments were carried out with two DE types to identify their persistence in mini-silos, control of progeny, and mortality of Sitophilus zeamais and Acanthoscelides obtectus in maize and common bean grains. We used DEs from a brewing industry, a conventional DE (directly used as a filter for beer clarification) and a residue DE (a DE recovered after its use as a filter). Experiments were conducted considering the exposure time of insects to the DEs (1, 3, 5, and 7 days for A. obtectus and 5, 7, 10, and 18 days for S. zeamais), concentration (0.5, 1.0, 1.5 and 2.0 g/kg) and persistence (evaluations performed every 30 days). Mortality of both insects increased with concentration (96 and 59% for A. obtectus at the most efficient concentration and 80 and 9% for S. zeamais at 2.0 g/kg for conventional and residue DE respectively) and exposure time (100 and 90% for A. obtectus and 98 and 51% for S. zeamais at the highest exposure time for conventional and residue DE respectively). We observed a decrease of insects in the progeny (>80% at the highest concentration or period of exposure). Persistence control was high for A. obtectus in both DEs (>95% control after 70 days of exposure) while for S. zeamais conventional DE was better at maintaining low insect populations (87 and 50% for conventional and residue DE respectively on the 50th day of exposure). The use of DEs from the brewery industry can be considered as an alternative tool to control populations of stored-product pests.     

Radio frequency heating against Sitophilus zeamais Motschulsky in white maize

Radio frequency treatments were evaluated for the control of Sitophilus zeamais Motschulsky in white maize, and their effects on physiological and biochemical properties were evaluated. A 12 kW, 27.12 MHz radio frequency machine was used with an electrode gap of 20 cm; batches of 10 and 20 kg of white maize (11.8% moisture content, w.b.) were treated. Radio frequency heating treatments at 50 °C for 3 min or 60 °C in white maize were effective to achieve 100% mortality of Sitophilus zeamais 4th instar larvae. Significant changes were observed in the moisture content, water activity and color in the corn kernels after the treatments (P < 0.05); however, they were within the range established by the Mexican Standard. As an advantage, the viability and germination of the grain were not affected by the treatments (P > 0.05). Radio frequency has potential to be a postharvest treatment against this pest without damage to white maize.     

Efficacy of combining varietal resistance with harvest time and planting date for the management of Sitophilus zeamais Motschulsky infestation in stored maize

The combination of varietal resistance with three harvest times and planting dates for efficient storage of maize against Sitophilus zeamais infestation was evaluated in the Niger Delta region of Nigeria for two seasons. Seven maize varieties made up of three susceptible local maize cultivars (Akparike, Bende and Ogbia muno) and four improved resistant varieties (ACR.97 TZL COMP.1-W, TZL COMP.4C2, ADV.NCRE-STR and BG 97 TZE COMP.3XL) were used. There were significant differences in the number of teneral adults among harvest times in all the planting dates in both years. Maize harvested when the cobs were completely dry at the latest harvest time (HVT 3) suffered significantly higher weight losses. In 2009, the highest susceptibility was apparent in a local variety Akparike planted on 17 October (PD 1) and harvested at HVT 3 by which time the cobs had completely turned yellow. Combining early planting and early harvest with resistant varieties could be an appropriate tactic for resource-poor farmers to effectively manage maize weevils in the store in the Niger Delta agro-ecological zone.     

Effect of CO2 modified atmosphere packaging on aflatoxin production in maize infested with Sitophilus zeamais

The weevil Sitophilus zeamais (Motschulsky), the maize weevil, is a pest of stored maize that can cause feeding damage and lead to the proliferation of toxigenic fungi. The application of modified atmospheres with a high concentration of CO₂ is an alternative method for the control of S. zeamais and the inhibition of fungal growth. The objectives of the study were to determine the effect of S. zeamais infestation, grain damage and grain moisture content on aflatoxin production by Aspergillus flavus on maize, and the impact of high CO₂ modified atmosphere packaging on pest infestation and aflatoxin production. Mycotoxin production was only recorded when maize was infested with S. zeamais and had A. flavus inoculum. However, production of mycotoxins was not recorded when the maize was mechanically damaged and stored at 18% moisture content, indicating that the biological activity of the insect was determinant in the production of mycotoxins. The high CO₂ modified atmosphere packaging tested (90% CO₂, 5% O₂ and 5% N₂) prevented mycotoxin production.     

Evaluation of the insecticidal activity of Moringa oleifera seed extract and lectin (WSMoL) against Sitophilus zeamais

The maize weevil Sitophilus zeamais is a pest of remarkable economic importance as it attacks stored grains, processed cereals, and industrial foods. In this study, a water extract (WE) from Moringa oleifera seeds and water-soluble lectin (WSMoL) isolated from it were investigated for insecticidal activity against S. zeamais adults. The insects were maintained for 10 days on plates containing an artificial diet composed of wheat flour supplemented with WE (60.0–640.0 mg/g) or WSMoL (0.5–60 mg/g). Mortality rate, insect biomass, and amount of food consumed were recorded. The effects of WE and WSMoL on trypsin-like, α-amylase, and endoglucanase activities from insect guts were also investigated. Phytochemical analysis revealed the presence of flavonoids, tannins, saponins, phenylpropanoids, alkaloids, and reducing sugars in the WE. Furthermore, the presence of rutin and ellagic acid was confirmed by HPLC. The extract was toxic to S. zeamais (LC₅₀: 214.6 mg/g) while WSMoL caused slight mortality (12.0 ± 2.7%) at the highest tested dose (60 mg/g). The intake of WE exerted moderate to strong deterrent effects. Moreover, WSMoL decreased the relative biomass gain rate and efficiency in the conversion of ingested food but did not exert deterrent action. The WE stimulated α-amylase and endoglucanase activities, while WSMoL stimulated trypsin-like activity from S. zeamais gut. In conclusion, the WE was toxic to S. zeamais probably due to its feeding-deterrent activity, while WSMoL did not cause acute mortality but negatively affected the nutritional physiology of the insects, which can have long-term impacts.     

Pasta preference and ability to penetrate through packaging of Sitophilus zeamais Motschulsky (Coleoptera: Dryophthoridae)

Results of bioassays of the maize weevil, Sitophilus zeamais, on different types of special commercial pasta are reported. The attraction to eight types of pasta was compared: barley and buckwheat, dietetic, egg pasta, gluten-free, spelt and lentils, tricolour pasta (a mixture of semolina, tomato, and spinach), vitamin enriched, and whole wheat semolina. The results obtained demonstrated that adult S. zeamais revealed significant preferences for whole wheat semolina and tricolour pasta, followed by vitamin enriched pasta, egg pasta, spelt and lentils pasta, gluten-free pasta, barley and buckwheat pasta, and dietetic pasta. The ability of S. zeamais to penetrate packages of commercial pasta was also determined using a folded carton box or a plastic pillow pouch with or without gussets. Sixteen types of commercial pasta packages were compared. S. zeamais was found inside packages of barley and buckwheat pasta, durum wheat pasta, egg pasta, five cereals pasta, kamut pasta, rice pasta, spelt pasta, spelt and lentil pasta, tricolour pasta, vitamin enriched pasta, and whole wheat pasta. The adults entered into carton boxes and infested the pasta through openings not well sealed by glue. The large or enlarged air vent micro-holes present on polypropylene pasta packages facilitated the entry of adults.     

Evaluation of stirring to suppress weevils in stored maize

The maize weevil (Sitophilus zeamais Motschulsky) is found throughout the world and is among the most destructive pests of stored grain and grain products. Maize weevil suppression is difficult and chemical insecticides are frequently employed. Stored grain insects can also be suppressed by physical disturbance which involves movement of individual kernels with respect to one another. Stirring grain in a silo disturbs individual kernels but we don't know of any study on the effects of stirring on maize weevils. The objective of this research was to determine the effects periodic stirring weevil-infested maize has on maize weevil population density and on maize quality. Six 0.12-m³ (4.2-ft³) steel experimental containers were used in this study. Three of the containers were equipped with Sukup Fastir®™ stirring machines. All containers were loaded with 30 kg of maize and unsexed adult weevils were placed in each container at a density of 25 live weevils per kg of maize. Stirring machines were programmed to travel one length of the stirred containers every 12 h. At 40 days and at 80 days, no live weevils were found in samples from the stirred containers, but at 80 days, reached 18 weevils per kg in control containers. Stirring increased BCFM in the stirred maize by seven percentage points and decreased maize moisture by 0.2 percentage points compared to control containers. Mechanical damage and bulk density changes were inconsequential. Stirring shows promise as an effective non-chemical method for suppression of maize weevils, but studies at silo scale are needed.     

Efficacy of filter cake and Triplex powders from Ethiopia applied to wheat against Sitophilus zeamais and Sitophilus oryzae

The efficacy of filter cake and Triplex powders applied to wheat was evaluated in the laboratory against the maize weevil, Sitophilus zeamais Motschulsky and rice weevil, Sitophilus oryzae (Linnaeus)—two most common insect pests associated with stored grain in Ethiopia. Efficacy of these powders was determined by exposing 20 adults of each species to 100 g of wheat treated with 0, 100, 500, 700 and 1000 mg/kg of filter cake and Triplex. Adult mortality was determined 7 and 14 d after exposure. In addition, adult progeny production, percentage of insect damaged kernels, and percentage of grain weight loss at each species-powder-concentration-time combinations were determined after 42 d. The 7 and 14 d mortality was 100% for adults of both species exposed to 1000 mg/kg of filter cake; only the 14 d mortality of Sitophilus species was 100% for adults exposed to 700 mg/kg. Mortality of S. oryzae adults was 100% when exposed for 14 d to1000 mg/kg of Triplex. Mortality of S. zeamais never reached 100% in any Triplex treatments. Adult progeny production of S. zeamais was completely suppressed at filter cake concentrations of 700 and 1000 mg/kg, whereas 1000 mg/kg was necessary for complete suppression of S. oryzae adult progeny production. Complete suppression of adult progeny production was not observed in any Triplex treatments. Complete reduction in percentage of insect damaged kernels and percentage of grain weight loss were obtained when S. zeamais and S. oryzae adults were exposed to 1000 mg/kg of filter cake; similar reductions with S. zeamais occurred only at 1000 mg/kg of Triplex. In the case of S. oryzae, complete reduction of insect damaged kernels and grain weight loss were not achieved at any concentration of Triplex. These powders can be used as alternatives to chemical insecticides for management of Sitophilus species.     

Antinutritional effects of the chitin-binding lectin from Microgramma vacciniifolia rhizome (MvRL) on Sitophilus zeamais

Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) is one of the most common and destructive storage pests in the world and its control depends mostly on the utilization of synthetic pesticides. The hazards of synthetic chemicals to people and the environment, together with the development of resistance by the insects, stimulate the investigation of alternative methods. In the present study, we determined the effects of the ingestion of artificial diet containing the Microgramma vacciniifolia rhizome lectin (MvRL) on survival, feeding and nutrition of S. zeamais adults. MvRL was incorporated into the artificial diets at concentrations ranging from 10 to 130 mg/g. Mortality rate, ingested food and variation in the weight of the insects were determined after 7 days. In addition, the in vitro effects of MvRL on the activity of insect digestive enzymes were investigated. MvRL did not increase the mortality rates but disrupted the nutritional status of the insects since the biomass variation and efficiency in conversion of ingested food were negative. The lectin was able to inhibit in vitro β-glucosidase and α-amylase activities. In conclusion, MvRL showed anti-nutritional properties on S. zeamais adults, which may be due interference with digestive enzymes. MvRL may be useful as an additive or synergistic agent for reduced pest fitness by affecting the food conversion into biomass.     

Chemical composition and bioactivity of peel oils from Citrus aurantiifolia and Citrus reticulata and enantiomers of their major constituent against Sitophilus zeamais (Coleoptera: Curculionidae)

Peel oils from Citrus aurantiifolia and C. reticulata cultivated in northeastern Brazil were analyzed using gas chromatography with flame ionization detection and gas chromatography-mass spectrometry. The insecticidal activity of the oils and both enantiomeric forms of the main constituent – limonene [(R)-(+)-limonene and (S)-(−)-limonene] – was evaluated against Sitophylus zeamais under laboratory condition. The results were compared with deltamethrin as the positive control. Chromatographic analysis of the Citrus oils demonstrated limonene to be main constituent, accounting for 38.9% of the C. aurantiifolia oil and 80.2% of the C. reticulata oil. Peel oil from C. reticulata proved to be more toxic to S. zeamais adults in the contact, ingestion and fumigant tests (LC₅₀ = 71.18 μL mL⁻¹, 1.52 μL g⁻¹ and 41.92 μL L⁻¹ of air, respectively) than the C. reticulata oil. A non-significant different was found between (R) and (S)-limonene in the contact and fumigant tests. However, (R)-limonene exhibited greater toxicity against S. zeamais than the (S)-limonene during the ingestion assay. Deltamethrin was much more toxic in the contact and ingestion bioassays than the Citrus oils and the two enantiomeric forms of limonene. The C. reticulata oil was more repellent than C. aurantiifolia. In the repellency test, S zeamais adults were more susceptible to (S)-limonene than (R)-limonene. The results of the present study suggest that these Citrus oils and the two enantiomeric forms of limonene have toxic effects on S. zeamais in different ways (i.e., via the cuticle, digestive system and respiratory system) as well as a behavioral effect (repellency).     

Efficacy of combining Niger seed oil with malathion 5% dust formulation on maize against the maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae)

The combined effects of Niger seed oil and malathion, 5% dust, against the maize weevil, Sitophilus zeamais, were evaluated to determine the minimum effective rate(s) of the combinations that can provide adequate protection to maize seed against attack by weevils. Niger seed oil at the rates of 0%, 10%, 20%, 30%, 40%, 50% and 100% of the recommended application rate, 5 ml kg⁻¹, was combined with malathion at the respective rates of 100%, 50%, 40%, 30%, 20%, 10% and 0% of the recommended application rate, 0.5 g kg⁻¹. All combinations provided complete protection to maize seed from the maize weevil up to 90 days after infestation. To determine the residual effects of the treatments, weevils were reintroduced to the grain that had been treated 90 days previously. In addition to 100% malathion, 10% Niger seed oil + 50% malathion, and 20% Niger seed oil + 40% malathion, were fully effective in controlling S. zeamais for a further 156 days after this re-infestation. Therefore, these combinations could be considered as a potential component in an effort to establish integrated management of the maize weevil. Residual performance of both oil and malathion against the weevils was primarily affected by the dose of malathion, with higher doses of malathion providing greater protection for a longer period. Niger seed oil treatment lowered the level of seed germination at the application rate of 5 ml per kg of maize.     

New insecticide delivery method for the control of Sitophilus zeamais in stored maize

Maize kernel deterioration caused by the action of insects has led to an urgent need to develop new control methods against the maize weevil, Sitophilus zeamais, one of the major pests found in silo bags during the storage of maize. Here, we evaluated the insecticidal efficiency of plasticized and unplasticized cotton matrices (deliveries), loaded with R-(+)-pulegone, (−)-carvone, 2-decanone and trans-2-hexenol against S. zeamais. R-(+)- pulegone was the only compound that produced weevil mortality. Plasticized delivery loaded with R-(+)-pulegone achieved a 90% mortality on the 12th day, with mortality values recorded of above 96% over the course of 30 days. R-(+)-pulegone from plasticized delivery was released more slowly compared to unplasticized delivery. Moreover, delivery loaded with R-(+)-pulegone did not show phytotoxicity in maize kernels. Hence, due to its effectiveness against the weevil and the lack of phytotoxic activity against maize kernels, plasticized delivery loaded with R-(+)-pulegone represents a promising material for S. zeamais control. However, large-scale studies are needed in order to evaluate its potential use in grain storage systems.     

Degradation of azadirachtin A on treated maize and cowpea and the persistence of Azadirachta indica seed oil on Callosobruchus maculatus and Sitophilus zeamais

Azadirachta indica seed oil has long been used in many parts of the world for the control of various insect pests. The quantification of its known insecticidal compound Azadirachtin A on treated commodities remains a challenge. The degradation of Azadirachtin A in treated cowpea and maize was determined with HPLC-MS as well as the toxicity of A. indica seed oil on their respective major pests is storage between 0 and 180 days. Azadirachtin A degraded slowly on treated maize from 1.31 mg/kg (0-day) to 0.38 mg/kg (180-day) while on cowpea it degraded from 1.14 mg/kg (0-day) to 0.43 mg/kg (180-day). A. indica oil caused a significant day-dependent mortality of adults Callosobruchus maculatus and Sitophilus zeamais and its effectiveness decreased with time. The tested oil was more persistent for inhibiting progeny production than on adult mortality. Further studies are needed to evaluate the quality of treated grains at different storage times.