Chemical bases for maize grain resistance to infestation and damage by the maize weevil,Sitophilus zeamais Motschulsky

It was suggested that the factors that confer resistance on a maize variety against Sitophilus zeamais Motschulsky are chemically based. To test this hypothesis, resistance indices of the weevil were assessed using a new scale developed by Nwosu et al. (2015a) after performing detailed chemical analysis of the whole-maize grain using twenty elite maize varieties under ambient temperature and relative humidity of 30.7 °C and 74.5% respectively. Increases in maize varietal crude fibre, phenolic acid and trypsin inhibitor increased significantly mortality of S. zeamais adults and reduced significantly survival rate of S. zeamais adults, percent of grain damage, percent of weight loss, weight of grain flour and oviposition by the adult females. The level of cystein proteinase inhibitor (a natural protectant of plants against insect attack) in the grains was not on its own responsible for increased mortality, reduced grain damage and reduced oviposition. The study identified crude fibre, phenolic acid and trypsin inhibitor of whole-maize grain as the bases for resistance. Their significant increase in grains resulted in low infestation. Whereas, increased protein, zinc, magnesium, calcium, sodium, phosphorus, manganese, iron, cobalt and starch rendered the elite maize grains susceptible to S. zeamais attack. Therefore, significant incorporation of the bases for resistance and significant reduction of the bases for susceptibility in maize grains during breeding programmes is advocated; provided this does not adversely affect palatability and nutritional needs of man. Eighty-five percent of the elite maize varieties were at least resistant to S. zeamais infestation and damage. The resistant varieties, particularly 2000SYNEE-WSTR and TZBRELD3C5 maize with high resistance should be promoted for growing. Antibiosis, antixenosis and preference were the mechanisms of maize grain resistance to S. zeamais attack.     

Resistance of selected Mozambican local and improved maize genotypes to maize weevil,Sitophilus zeamais (Motschulsky)

Maize weevil Sitophilus zeamais (Motschulsky) is one of the most important pests of on-farm stored maize in thetropics, particularly where there is no control of moisture content and application of pesticides. This study aimed todetermine the level of resistance among Mozambican maize genotypes against S. zeamais. A total of 17 genotypes,composed of seven experimental hybrids developed from S5 inbred lines from five populations, one released hybrid,two improved open pollinated varieties (OPV), three landraces from Mozambique, two resistant and two susceptiblechecks from Kenya were screened for their resistance to S. zeamais. Four hybrids were screened at their F1 and F2generations. The genotypes were evaluated in the post-harvest laboratory, Kiboko, Kenya in a completely randomizeddesign, replicated 4 times. Data was collected on the number of emerged insects, seed weight loss, seed damage,median development period; and protein, starch and oil contents. The Dobie index of susceptibility was used to groupthe genotypes. Six of the of the eight hybrids at the F1 generation were resistant while two were moderately resistant.Three of the four hybrids evaluated at the F2 generation were moderately resistant while one was susceptible. Two ofthe five OPVs evaluated (EV8430DMRSR and landrace Kandjerendjere) were resistant. Genotypes with high proteincontent showed resistance while those with high starch contents showed susceptibility. Weevils fed on the resistantgenotype produced low number of F1 progeny, had a high median developmental time, caused low seed damage andlow seed weight loss. The resistant genotypes can be either used as cultivars or as sources of resistance in a breedingprogram for weevil resistance.     

Desiccation resistance and water balance in populations of the maize weevil Sitophilus zeamais

Water balance is a challenge for insects due to their small size and body with high surface area-to-volume ratios, and it is particularly important for insects that inhabit dry environments, such as stored grains, and warm climates. This subject has been curiously neglected in stored product insects, including the maize weevil Sitophilus zeamais Motschulsky, were broad population differences have been reported with management consequences. Here, we assessed variation in desiccation resistance and water balance among three strains of the maize weevil exhibiting differences in body mass. The survival of male and female weevils from three strains was therefore assessed at relative humidities ranging from 0 to 100%, in which their water content and water loss were also assessed. The effect of insect aggregation (1–25 insects per group) on water balance was also assessed, as was the water gain by the drinking of free water and drinking preference when exposed to insecticide-contaminated water. The median survival time (LT₅₀) of individual insects increased with relative humidity and varied significantly among the weevil strains. The larger strain exhibited 60–80% higher LT₅₀ at 50% relative humidity (r.h.) and above, with little difference between strains at 0% r.h. Heavier weevils exhibited higher water content and lower overall rates of water loss; these qualities made heavier weevils more resistant to dehydration. Larger groups of weevils facilitate water retention in individual insects. Weevils actively drink water to achieve favorable water balance when dehydrated, which is a major source of water intake. Under dehydration, weevils in general were not able to discriminate between insecticide-contaminated and uncontaminated water. However, females of the insecticide-susceptible strain avoided contaminated water.     

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.     

Deleterious effects of Myracrodruon urundeuva leaf extract and lectin on the maize weevil,Sitophilus zeamais (Coleoptera,Curculionidae)

Deterioration and degradation of grains by storage insect pests lead to economic losses of several billion dollars and affect food security. Sitophilus zeamais is responsible for pre- and post-harvest damages to maize. The high toxicity of synthetic insecticides and the development of resistance by insects to the chemicals currently used stimulate the investigation of plant-derived insecticides as new alternatives for pest control. In this study, we report the effects of diets containing Myracrodruon urundeuva leaf extract (10–150 mg/g) and lectin (MuLL; 3–150 mg/g) on the survival, feeding, and nutrition of the storage pest S. zeamais. The digestive enzyme activity in gut extracts from the insects reared on the leaf extract (25 mg/g) or MuLL (15 mg/g) diets was also evaluated. The leaf extract induced mortality (LC₅₀: 72.4 mg/g), while MuLL (30–150 mg/g) exerted strong feeding deterrence. The leaf extract and MuLL promoted the loss of biomass, as reflected in the negative values for relative biomass gain rates and efficiencies in converting ingested food. Protease, trypsin-like, acid phosphatase, and amylase activities in the insects reared on leaf extract or MuLL diets were significantly (P < 0.05) lower than those in the control insects. MuLL ingestion also significantly reduced (P < 0.05) endoglucanase and alkaline phosphatase activities. In conclusion, the leaf extract and MuLL have the potential for S. zeamais control by killing adults and preventing the use of a food source, respectively. The deleterious effects of the extract and lectin on S. zeamais may be linked to enzyme inhibition and consequent suppression of digestive processes.     

Potential of three enhanced diatomaceous earths against Sitophilus zeamais Motschulsky and Prostephanus truncantus (Horn) on stored maize grain

Global health and environmental concerns against synthetic pesticides in stored-grain coupled with high cost, unavailability and inaccessibility of modern non-chemical grain treatment technologies in Africa are driving the need for low-cost and low-dose combination of readily available alternatives. Laboratory studies were conducted to determine the efficacy of non-registered low-dose food grade diatomaceous earths enhanced with natural grain protectants: IBS at 50, 75 and 100 ppm; IPE1 at 200, 300 and 400 ppm; IPE2 at 100, 150 and 200 ppm against Prostephanus truncatus and Sitophilus zeamais adult insects on maize. Adult insect mortality was assessed at 7, 14 and 21 days after treatment (DAT) while progeny emergence was assessed at 49 and 70 DAT for S. zeamais and P. truncatus, respectively. IBS caused significant (p < 0.05) P. truncatus and S. zeamais adult mortality at 14 and 21 DAT, respectively. Except for IPE1 at 400ppm, lower doses of IPE1 and IPE2 showed significantly low adult mortality (p < 0.05) (54-74%) on Sitophilus zeamais compared to IBS and the positive control. All rates of IPE1 and IPE2 were also not effective on P. truncatus adults, with significantly low mortality (p < 0.05) (18–38% compared to positive control). IBS at 75 and 100 ppm were effective on progeny suppression on both S. zeamais and P. truncatus but IPE1 at 400 ppm was effective on S. zeamais only. These results suggest the potential of IBS and IPE1 (at 400 ppm) as effective sustainable alternatives to synthetic grain protectants for small-scale farmers in sub-Saharan Africa who may not afford the modern non-chemical grain protection technologies. Field efficacy of these materials under typical farmer conditions is required.     

The implication of kernel phenology in convening resistance to storage weevil and varietal development in sorghum

Storage weevil is a major biotic insect pest attacking sorghum during late harvest or in storage condition. In developing countries, the infestation can be up to 83% within first six months, and may cause grain loss of 15–77% within the period. Kernel phenotypic characteristics such as pericarp thickness, testa, hardness and kernel size contributes to host plant resistance; through provision of physical barrier for insect penetration and space for oviposition. These traits have connections with several biochemicals associated with antibiosis and antixenosis effects to storage weevils including phenolic compounds. On contrary, little has been reviewed regarding the potential of these traits in varietal development. The insufficient collated information makes weevil management difficult. Both conventional and genomics approaches could be useful in transferring source of resistance to preferred sorghum cultivars for better management of weevils.     

基于线粒体COI和COII基因的米象与玉米象的分子鉴定

为建立基于线粒体COI和COII基因序列的米象和玉米象的分子鉴定方法。采自全国6个地理种群的米象和2个地理种群的玉米象,PCR扩增试虫线粒体COI和COII基因,将获得的基因序列在GenBank中进行BLAST比对,分析基因序列相似性,分别计算基于COI和COII基因序列的遗传距离,并构建系统发育树。结果表明在本研究所分析的2种象虫样本中,米象COI基因的种内相似度在98.17% 以上,米象和玉米象COI基因的种间相似度为85.84%~86.92%;米象COII基因的种内相似度在98.37% 以上,玉米象COII基因的种内相似度在97.77% 以上,2种象虫COII基因的种间相似度为86.27%~88.31%。米象的种内遗传距离为0.002~0.020(COI)和0.011~0.015(COII),玉米象的种内遗传距离为0.001~0.023(COII)。两种象虫的种间遗传距离为0.145~0.185(COI)和0.128~0.154(COII),基于COI和COII基因的种间遗传距离显著高于种内遗传距离。系统发育树结果显示,在2个基因的系统发育树上,米象、玉米象的基因序列分别位于不同的进化支,同种象虫的基因序列位于相同的进化枝。根据本研究所用的线粒体COI和COII基因序列的差异性可以进行米象和玉米象的分子鉴定。     

热处理对玉米象保护酶活性的影响

分别以43、47、51、55℃对玉米象(SitophiLus zeamais)成虫进行热处理,测定不同处理时间后其超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)的活性。在43、47℃的高温处理条件下,保护酶活性存在应激性升高的阶段,最大值分别达到13.49 U/mgSOD、0.39 U/mgPOD、4.20 mgH_2O_2/(min·mg)CAT,酶活性显著增强,随着处理时间的延长活性受到抑制。51、55℃高温处理后,CAT活性均不高于对照水平,最低值仅为对照组的70%,SOD、POD活性在55℃处理不同时间后,明显低于43、47、51℃处理后的酶活性。结果表明,玉米象成虫体内3种酶活性与高温处理温度、处理时间有一定的相关性,升高温度和延长高温处理时间能导致保护酶活性降低。     

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.     

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.     

应用S-烯虫酯小麦防治米象和玉米象持效性模拟研究

为明确S-烯虫酯在储粮实仓中对米象和玉米象成虫及子一代种群的持效性和敏感性差异,本实验分别扦取了经S-烯虫酯处理90 d和365 d后的小麦样品,在(27±1)℃,相对湿度(70±1)％的条件下对米象和玉米象2种常见储粮害虫进行持效性模拟研究.结果表明,施药时间为90 d时,S-烯虫酯处理下玉米象成虫的校正死亡率为(4...     

Insect-corn kernel interaction: Chemical signaling of the grain and host recognition by Sitophilus zeamais

In living organisms, the cuticle has structural functions and is involved through chemical signaling in biological interactions such as plant-insect and provides protection against biotic and abiotic factors, thereby avoiding desiccation or the attack of predators. The objective of this study was to investigate the participation of the epicuticle in the maize kernel-Sitophilus zeamais interaction. The GC-MS analysis of the epicuticle extract demonstrated the presence of aliphatic hydrocarbons, alcohols, ethers, fatty acids, sterols and their derivatives. The results of bioassays show that the epicuticle of maize has a primordial role in its interaction with S. zeamais, and participates in the recognition and attraction to the food source, as well as regulating its reproduction. In addition the compounds present in the epicuticle extract may act as signal molecules and development regulators. This study reveals the effect of the maize kernel cuticle on Sitophilus behavior and contributes to the understanding of the interaction.     

Insecticidal and repellency activity of essential oil of Eucalyptus sp. against Sitophilus zeamais Motschulsky (Coleoptera, Curculionidae)

BACKGROUND: The objective of this work was to evaluate the insecticidal and repellent effect of essential oils of Eucalyptus dunnii, E. saligna, E. benthamii, E. globulus and E. viminalis in the control of Sitophilus zeamais in maize grains. RESULTS: The essential oils chemical composition showed that the E. benthamii presents the cis‐ocimene (56.88%) as major compound. Results permitted us to verify that the evaluated species presented different insecticidal action under Sitophilus zeamais. About 100% of mortality was achieved with doses of 65, 100 and 400 µL for E. dunnii, E. saligna and E. benthamii, respectively. After regression analysis the LD₅₀ values were calculated and E. dunnii was shown to be the most efficient (25.03 µL), followed by E. saligna (37.93 µL) and E. benthamii (121.09 µL). Using the previously calculated LD₅₀ values, the repellency activity was calculated, allowing us to conclude that all species presented significant values in terms of this important parameter. CONCLUSION: The essential oil of Eucalyptus sp. presented insecticidal and repellency against Sitophilus zeamais Motschulsky (Coleoptera, Curculionidae). Although from an economic point of view synthetic chemicals are still more frequently used as repellents, natural products (essential oils) have the potential to provide efficient and safer repellents for humans and the environment. Copyright © 2010 Society of Chemical Industry     

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.     

Responses and genetics of maize germplasm resistant to the maize weevil Sitophilus zeamais Motschulsky in West Africa

The maize weevil, Sitophilus zeamais Motschulsky causes considerable damage to maize grain during storage in the tropics. The objectives of this study were to determine through two experiments the genetic basis of resistance to S. zeamais in African maize germplasm of open-pollinated cultivars, lines and hybrids. The first experiment tested for resistance of 20 maize cultivars (10 white and 10 yellow-grained) developed for lowland Africa grown in three relatively weevil-free savanna locations. The second experiment tested two sets of diallel crosses without reciprocals of 66 F₁ progeny from 12 inbred lines and 78 F₁ crosses from 13 inbred lines of subtropical and temperate origins. Variables studied for the first experiment included husk cover, grain texture, number of egg plugs, number of weevils produced, and number of grains damaged by the weevil. Results showed highly significant differences among the 20 maize cultivars tested. Significant cultivar×location interactions for egg plug and weevil production indicate the importance of environmental effects and complexity in weevil resistance. Of the 20 cultivars tested, Ikenne 83-TZSR-W-1 (open pollinated) and 8329-15 (hybrid) were the most promising for restricted weevil production and minimal grain damage. The results of genetic studies in the second experiment with 144 crosses indicated the presence of genetic differences in maize lines to weevil attack. General combining ability (GCA) and specific combining ability mean squares were highly significant, suggesting that the maize weevil resistance was controlled by both additive and non-additive gene actions and the inheritance was quantitative and polygenic. Among the lines used in the crosses, the two most weevil resistant lines with high GCA effects were TZi 30 (International Institute of Tropical Agriculture) and FLA2BT 106 (Florida).     

石菖蒲根茎提取物对玉米象和谷蠹有效杀虫活性成分初步分析

采用硅胶柱层析和气相色谱-质谱(GC-MS)联用法,以玉米象(Sitophilus zeamais Motsch.)和谷蠹(Rhizopertha dominica Fab.)成虫为试虫,对石菖蒲(Acorus gramineus)根茎提取物的有效杀虫活性成分进行了初步分析.结果表明石菖蒲根茎提取物含有多种对玉米象和谷蠹具有生物活性的化合物,主要活性物质为β-细辛醚.未知化合物2可能为石菖蒲根茎内新发现的一种杀虫活性物质,但其分子结构、活性作用方式需要进一步予以研究.     

Development of Sitophilus zeamais Motschulsky,in maize kernels and pellets made from maize kernel fractions

As a means of studying certain aspects of resistance of maize varieties to Sitophilus zeamais, various types of pellets were prepared using ground maize and compared with whole, pericarpless, and germless kernels. Numbers of weevil progeny (from six females and three males, and usually a 7-day oviposition period) were greatest in pellets made of flour moistened with water containing agar. More progeny was produced in pellets than in whole kernels. Damaged kernels (hot-water treated, pericarpless, germless) were more susceptible than undamaged kernels and fewer weevil progeny were produced in pellets made of germless kernels than from pellets of whole kernels. Additions of small amounts of extra germ tissue to whole maize flour enhanced the susceptibility of pellets to the weevil, but adding larger amounts of germ of pericarp reduced progeny number, weight and developmental speed.     

A note on the influence of kernel hardness on the extractability of wheat proteins

By using different grinding techniques, which resulted in whole wheatmeals ranging from 0.5 to 2.0 mm in particle size, it was shown that the amount of protein which could be extracted from the coarser meals was significantly less than that which could be extracted from fine meals. The standard error per determination was also higher for the coarser meals. The differences in extractability were significantly correlated with kernel hardness, but not with protein content. The significance of the findings is discussed in relation to modern colorimetric methods of protein determination.