The performance of six grain storage technologies for the control of insect pests in maize was evaluated over a 36-week (9-month) storage period. The six technologies used were: two ZeroFly® hermetic bag brands (laminated and non-laminated); Purdue Improved Crop Storage (PICS) bag; non-hermetic ZeroFly® bag; woven polypropylene (PP) bag containing maize grain treated with Actellic Gold® Dust (pirimiphos-methyl 1.6% + thiamethoxam 0.3%) and woven PP bag containing untreated grain. Each bag was filled with 50 kg maize grain and four replicates of each were set up. With the exception of the non-hermetic ZeroFly® bag, 50 live adults of the larger grain borer Prostephanus truncatus and of the maize weevil Sitophilus zeamais, were introduced into all the bags. Insects were not introduced into the non-hermetic ZeroFly® bag to assess its effectiveness in repelling infestation from outside. Parameters recorded were gas composition (oxygen and carbon dioxide) levels inside the bags; weight of flour generated by insect feeding activities; grain moisture level; live adult insect counts; grain damage and weight loss; grain germination rate and aflatoxin level. At termination, the plastic liners of the hermetic bags were examined for perforations. Results show that oxygen depletion and carbon dioxide evolution were faster in ZeroFly® hermetic compared to PICS bags. Throughout the 36-week storage trial, grain damage remained below 4% and weight loss below 3% in all the treatments except in the untreated PP bags in which it increased to 81.1 and 25.5%, respectively. The hermetic PICS, ZeroFly® and Actellic Gold dust-treated PP bags maintained grain germination at 60%, which was lower than the initial 90%, while in untreated control, it reduced to 4.7%. The mean aflatoxin levels fluctuated between 0.39 and 3.56 parts per billion (ppb) during 24 weeks of storage in all the technologies tested, which is below the acceptable maximum level of 10 ppb in maize. Based on the evaluation results, it can be concluded that hermetic PICS and ZeroFly® bags and woven PP bag with Actellic Gold dust-treated grain effectively protected stored maize grain from insect attack and weight losses. Appropriate strategies and mechanisms for the effective and efficient adoption of hermetic storage bag technology at scale would contribute towards global food security.

The possibility that Sitophilus zeamais Motschulsky prefers a particular grain side and a grain side area for feeding, and the implications and value in maize programmes' breeding for resistance were investigated in the laboratory at ambient temperature (32.7 °C) and relative humidity (70.4%) using standard techniques. A total of 20 elite maize varieties were used: TZBRCOMP.2C1F1, TZBRELD3C5, PVASYN-3F2, PVASYN-6F2, DTSYN-11-W, BR9943DMRSR, IWDC3SNY-W, WHITEDTSTRSYN, 2008DTMA-YSTR and 2000SYNEE-WSTR, obtained from the Maize Breeding Unit of International Institute for Tropical Agriculture (IITA), Ibadan, Nigeria, and ILE-1-OB, IFEMAIZEHYBRID-1, IFEMAIZEHYBRID-2, IFEMAIZEHYBRID-5, IFEMAIZEHYBRID-6, ARTCOMPOSITE-A-Y, ARTCOMPOSITE-B-Y, ART/98/SW1-OB, ART/98/SW4-OB and ART/98/SW5-OB, obtained from the Institute of Agricultural Research and Training (IAR&T), Moor Plantation, Ibadan, Nigeria. The flat side of a maize grain at the point of penetration was significantly preferred (P≤ 0.05), possibly because it provided much needed space for anchorage and feeding. The South locus of the flattened side of a maize grain was also significantly preferred (P≤ 0.05), possibly because of its soft nature and proximity to the nutrient-rich embryo. The findings of the study have implications for seed viability and can be considered in breeding for resistance to infestation by S. zeamais in stored maize.

Maize (Zea mays L.) is Kenya's most important staple crop with annual production fluctuating between 2.6 and 3.1 million tons in 2012 and 2011, respectively. However, frequent food shortages are still experienced in the country. These have been attributed to pests and diseases and post-harvest constraints. The dominant post-harvest pest of maize is Sitophilus zeamais (Motsch.), which causes losses between 10 and 20% of harvested grain. The objective of this study was to establish the repellent activity of essential oils extracted from selected eucalyptus species against S. zeamais. Essential oils were extracted from the fresh leaves of Eucalyptus saligna Sm., Eucalyptus globulus Labill., Eucalyptus camaldulensis Schlecht and Eucalyptus citriodora Hook by steam distillation using a Clevenger-type apparatus. A repellency bioassay, with varying concentrations (0.002, 0.02, 0.2 and 2 μl/μl) of the oils, was carried out against the maize weevils using a Y-shaped olfactometer. Repeated measures of analysis of variance were applied to test the different doses and repellents, and their interactions against S. zeamais. The essential oils of E. camaldulensis and E. citriodora presented better repellent activity at the 2 μl/μl concentration (74.35 and 69.15%, respectively) followed by those of E. globulus (53.68%) and E. saligna (40.5%). Gas chromatography (GC)–mass spectrometry and GC co-injections with authentic samples showed the presence of the following major constituents in: (i) E. camaldulensis oil: 1,8-cineole (18.9%), α-cardinol (6.4%) and β-phellandrene (2.6%); (ii) E. citriodora oil: 1,8-cineole (11.2%), β-pinene (3.2%) and 4-terpineol (3.1%); and (iii) E. globulus oil: 1,8-cineol (17.2%), α-pinene (7.1%) and spathulenol (6.5%). The results provide a scientific rationale for the use of eucalyptus oils in the protection of maize against weevils.

Powdered maize cobs were tested as an alternative for pesticide use in stored maize. Five doses (2, 4, 6, 8 and 10 g/250 g seed) of powdered maize cobs applied at particle sizes of 1.4 and 0.4 mm diameter were compared with actellic powder against Sitophilus zeamais Motschulsky for 120 days. Mortality and survival data showed that cob powders did not act as fumigant but exerted a potent inhibition of progeny on direct contact with S. zeamais adults. The particle size of powdered cobs had no effect on maize damage and losses. At doses equal to or higher than 6 g powdered maize cobs/250 g grain maize, i.e. 2.4% (w/w), damage to grain was < 5% and weight losses < 1%. The protection offered at the highest dose was comparable to the pesticide control. The use of powdered maize cobs is discussed as a natural alternative to synthetic pesticides for protection of maize against S. zeamais.

Botanical insecticides are among the most promising alternatives to synthetic insecticides for stored product protection. Calneem oil from Ghana and local neem oils from two localities in northern Cameroon (Garoua and Maroua) were tested at 0 (untreated control), 2, 4, 6, 8 and 12 ml/kg, on the adult and immature stages of the maize weevil Sitophilus zeamais (Motschulsky), for mortality and reproduction inhibition. The neem oils from Cameroon were extracted using the traditional kneading method and a hydraulic press in the laboratory (refined). Maize grains were coated with the five neem seed oils (Calneem, Garoua traditional and refined, and Maroua traditional and refined, respectively) and adult mortality was recorded at 1, 3, 7 and 14 days after exposure. Within 1 day of exposure, the highest tested concentration (12 ml/kg) of Calneem, Garoua traditional, Garoua refined, Maroua traditional and Maroua refined oils caused similar weevil mortality of 86.3, 93.8, 93.8, 97.5 and 97.5%, respectively. The 24-h LC50values for the oils in the same order were 7.0, 6.0, 5.0, 5.0 and 4.8 ml/kg, respectively. The lowest (2 ml/kg) and highest (12 ml/kg) concentrations of the oils suppressed progeny production by over 80 and 98%, respectively. The oils arrested the development of the hidden eggs and immature stages in the maize grains. The results suggested that neem seed oils from different localities of northern Cameroon, irrespective of the method of extraction, were effective for the protection of stored maize against S. zeamais. The promotion of natural neem seed oils as stored grain protectants in Cameroon would boost food security, alleviate poverty and reduce environmental degradation.

The larger grain borer Prostephanus truncatus Horn and the maize weevil Sitophilus zeamais Motschulsky are important pests of stored maize in the tropics, particularly where maize is stored on-farm with little control of moisture content and without use of pesticides. This study was undertaken to determine level of resistance among new experimental maize hybrids against P. truncatus and S. zeamais. Out of the 54 experimental hybrids tested, eight hybrids were resistant, six were susceptible and the remaining 40 hybrids were moderately resistant. Five hybrids showed considerable reduction in losses for both P. truncatus and S. zeamais (CKPH08013, CKPH08021, CKPH08003, CKPH08004 and CKPH08009), suggesting that they contained genes that confer resistance to the two pests. Low grain weight loss, powder production and low insect multiplication on resistant grains reduce the negative impact of the two beetle pests. Therefore, host plant resistance can be used as a vital component of an integrated pest management strategy against P. truncatus and S. zeamais.

Sitophilus zeamais Motschulsky is an important field-to-store pest of maize in several parts of Africa including Cameroon. Although synthetic insecticides are effective at controlling the pest, the environmental and health hazards of these chemicals are of increasing concern. This study assesses the efficacy of ashes of local plant material against S. zeamais in the western highlands of Cameroon as an alternative to synthetic insecticides. Laboratory studies on toxicity against F1 progeny of S. zeamais were conducted using leaf ashes of Cupressus arizonica, Eucalyptus grandis, Ocimum gratissimum and root ash of Vetiveria zizanioides at the rates of 0.1, 0.25, 0.5 and 1.0 g/25 g maize grains in Kilner jars. Toxicity of E. grandis ash extract was also evaluated. The ashes of E. grandis and O. gratissimum at the rate of 0.25 g/25 g grains significantly reduced the number of emerged weevils. Eucalyptus grandis ash showed toxicity (1.0 F1 progeny emerging at 0.25 g/25 g grains compared with 16.5 for the control). Eucalyptus grandis ash at 20 g/2 kg grains significantly reduced grain weight loss and protected grains for 6 months without adversely affecting the germination of the seeds. Ethanolic E. grandis ash extracts at rates of 50,000 and 100,000 ppm significantly (P < 0.05) reduced the number of emerged F1 progeny of S. zeamais.

The penetration of adult Sitophilus zeamais Motschulsky through maize grain bulks (0.75 m deep), treated with Protect-It®, a diatomaceous earth (DE) at 0, 0.05, 0.1 and 0.2% (w/w), was determined 12 weeks after weevils were released at the upper surface of the grain. Maize was stored in columns in polyvinyl chloride (PVC) pipes, under controlled conditions of 26±2°C and 70±10% RH. Grain samples were collected from various pre-determined depths and the numbers of S. zeamais adults counted. Differences in insect numbers between treatments and at different depths from which samples were collected were highly significant (P<0.001). The bottom 2–3 layers (0.65–0.75 m deep) had significantly more insects than the upper layers for all the DE concentrations. No significant differences in total insect numbers (live+dead) were found between the DE concentrations. Dead S. zeamais weevils were found at the bottom of grain treated with Protect-It®, indicating that insects can penetrate through DE-treated grain 0.75 m deep but then subsequently die. There was no strong evidence that DEs admixed with bulk grain restrict S. zeamais movement within the grain.

Laboratory experiments on the role of humidity, density and species of prey were conducted in order to better understand the ecology of Teretriosoma nigrescens Lewis (Coleoptera: Histeridae), a predator introduced into West Africa to control the larger grain borer, Prostephanus truncatus. Developmental time of T. nigrescens was very similar among individuals exposed to 30,40, 70 and 90% relative humidity at 30°C, although survivorship varied. At optimal temperature and humidity larvae fed only first-instar Sitophilus zeamais as prey took longer to develop and weighed less at emergence, than those raised on first-instar P. truncatus. Larvae feeding on Tribolium castaneum took longer to develop with only 10% surviving to the adult stage. None of the larvae offered Gnatocerus maxillosus as prey survived. In an analysis of prey consumption rates, no T. nigrescens larvae survived on one P. truncatus first-instar larva per day; 50% survived on two per day, and almost 90% survived on five larvae per day. In an analysis of density effects on T. nigrescens reproduction and survivorship, there was no difference in the number of Fl offspring at T. nigrescens:P. truncatus ratios of 15:300,30:300,60:300 or 90:300, suggesting that the lowest predator: prey production ratio was the most efficient one.

Four maize varieties, 8321–21-W, DMR-LSR-W, ACR-83TZUT-W and TZB were simultaneously fed to Sitophilus zeamais in a completely randomized design. Susceptibility was assessed on such parameters as weight loss of grains caused by the weevil infestation, number of progenies at 42 days after infestation and the percentage of damaged kernels. The least susceptible in terms of loss of weight of grains was TZB. Losses in the other three were not significantly different at 5% level (P ≻ 0.05).

The least percentage mortality of adult weevils and the highest number of punctured kernels were observed in var. 8321–21-W (48%), 27 kernels respectively while var. DMR-LSR-W had the highest mortality score (80%) and ranked second in the total number of kernels punctured (13). Details of the description of maize varieties used and the analysis of damage caused by the weevil are discussed in the paper.

The major alkanone constituents of the resin of Commiphora rostrata, 2-decanone and 2-undecanone, and a series of structural analogues were bioassayed for their repellency against the maize weevil, Sitophilus zeamais in olfactometric assays. All the aliphatic ketones and aldehydes showed comparable or greater activity than the synthetic commercial insect repellent N, N-diethyl toluamide (DEET). In the 2-alkanone series the C-8 and C-9 compounds demonstrated significantly higher activity than their shorter- and longer-chained congeners. Analogues differing in the relative positions of the carbonyl group, including aldehydes, showed a variable pattern of repellency. Alkanols appeared to be mildly attractive to the weevil. The results support our previous suggestion that the resin constituents may play an allomonal role in the ecosystem where the plant thrives.

The susceptibility of maize germplasm from CIMMYT — Mexico, Malawi and Zimbabwe — to attack by the maize weevil, Sitophilus zeamais (Motsch.) was investigated under controlled temperature (28°C) and r.h. (70–75%). An index of susceptibility (I), derived from the numbers of F1 progeny and the mean development period was used as the basis for measurement of the susceptibility. The indices of susceptibility of the CIMMYT germplasm ranged from 9.25 for Rattray Arnold (I) 8149 to 14.48 for Poza Rica 7737. Of the 17 collections of Malawi local maize evaluated MLM#20 was the least susceptible (I = 10.72), while MLM#24 was the most susceptible (I = 13.25). The least susceptible of the Zimbabwean germplasm was a local collection of an indigenous maize, Variety 8 (I = 10.61), while the most susceptible was a hybrid PNR 6334 (I = 14.74). Further, the nine Mexican materials and a local hybrid SR 52 were evaluated under field conditions in small farmers' granaries. Rattray Arnold (I) 8149 and Population 68 were the least damaged and produced the lowest numbers of weevils. Maize classified as susceptible in laboratory tests also suffered high damage levels in on-farm storage trials.

Various components of the neem tree, Azadirachta indica A. Juss were tested for their insecticidal effects on Sitophilus zeamais Motsen in stored maize. Seed kernel, leaf, flower and bark from the tree in powdered and extract (80% ethanol) form were used at the rate of 2.5g and 2ml respectively per 50g of grain, infested with 20 insects. Pirimiphos methyl and ethanol applied at 25mg and 2ml served as comparative treatment, and control neem products were efficient where used as a preventive measure. The degree of infestation was 3.2 as compared with 53 recorded in curative assay. Ethanolic extracts showed higher toxicity to S. zeamais than the powdered form. Insects after being confined 72 hr to treated grains had a mortality ranging between 29 and 96.4% (powder) and 32.5 to 100% (extract). The index of susceptibility varied from 0.45 (kernel) to 3.87 (bark) in powdered and 0 (kernel or leaf) to 1.76 (bark) for extracts. When leaf or kernel powder was used to protect grain over a 60 day storage period in aerated and non-aerated environment, insect mortality was 100% (kernel), whereas the leaf powder did not show complete insect control in aerated environment (88.1 %). A very high rate of population increase of S. zeamais was observed in the control.

The effect of 10, 20, 30, 40, and 50 adult Sitophilus zeamais on the quality of 1 kg lots of white maize maintained at 25−30°C and 65−85% r.h. was observed. Per cent moisture, oil, Free Fatty Acid (FFA) content and germination were determined at 2-week intervals for 10 weeks.

Moisture content of infested maize ranged from 11.51 to 12.92%. There was a significant correlation between moisture content and degree of infestation (r = 0.88; P < 0.05; Y = 11.908 + 0.006 x). The range of oil content of infested maize was 4.83−5.75%. There was a significant correlation between oil content and degree of infestation (r = −0.097; P < 0.05; Y = 5.08 −0.0076 x). The free fatty acid (FFA) of infested maize was 5.82−6.86%. The heterogeneity at various infestation levels was significant (F = 81.38; d.f. = 5; P < 0.001). There was an increase in FFA, with increasing infestations, although the correlation was not significant.

The germination of maize, 10 days after planting, at various infestation levels was 43.0−97.5%. There was a decrease in germination, as level of infestation increased. The heterogeneity in germination at various infestation levels was significant (F = 19.21; d.f. = 5; P < 0.001). Possible reasons for the results obtained, are presented.

Tanzanian strains of Tribolium castaneum (Herbst), Gnatocerus maxillosus (F.), Sitophilus oryzae (L.) and Sitophilus zeamais Motschulsky were confined to maize grain treated with a dilute dust of permethrin at the rates of 1.5, 3.0 and 6.0 ppm active ingredient. The adult mortality and resulting F1 generation were recorded. G. maxillosus was very susceptible to the insecticide and even the lowest dose brought complete control. T. castaneum adults survived all treatments but few F1 were produced. Adult survival of s. oryzae and S. zeamais was progressively reduced by increasing dosage, although S. zeamais was much less susceptible to the treatment than S. oryzae.

The repellency of grain, treated with 3.0 ppm permethrin, to S. oryzae, S. zeamais and T. castaneum was tested in a simple choice chamber. Neither male nor female T. castaneum were repelled but significantly fewer eggs were laid on treated grain. For both Sitophilus spp there was no significant difference between the numbers of females or eggs observed on treated or untreated grain, but males were repelled from permethrin.

The importance of these results is discussed in relation to a recent recommendation that the treatment of shelled grain with 3.0 ppm permethrin should be adopted in Tanzania in order to control Prostephanus truncatus (Horn), a new and serious storage pest.