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.     

Protection of stored maize from insect pests using a two-component biological control method consisting of a hymenopteran parasitoid, Theocolax elegans, and transgenic avidin maize powder

The hymenopteran parasitoid, Theocolax elegans (Westwood), and transgenic avidin maize powder were tested to determine if their individual or combined use would protect stored grain from infestation by both internal and external insect pests. Small-scale tests were conducted in plastic jars containing 3 kg of non-transgenic maize. We tested treatments of 0.3% powdered avidin maize, the parasitoid wasp, and the combination of the parasitoid plus 0.3% powdered avidin maize. One pair each of Sitophilus zeamais Motschulsky, Tribolium castaneum (Herbst), and Cryptolestes ferrugineus (Stephens) was added to each jar. After 8 weeks, the entire contents of each jar were examined for adult insects. Control and avidin maize powders had no detrimental effects on the beneficial insect parasitoid T. elegans. The parasitoid suppressed populations of the internal feeder S. zeamais. The avidin maize powder treatment had no effect on S. zeamais because these larvae developed inside the maize kernels where no avidin maize powder was present. For S. zeamais, the combination treatment was not significantly different from the parasitoid treatment. In contrast, populations of the external feeder T. castaneum were not suppressed by the parasitoid but were suppressed by the avidin maize powder treatment. The parasitoid-avidin combination treatment produced the greatest percentage reduction for all three insect species and resulted in 78%, 94%, and 70% reductions in populations of S. zeamais, T. castaneum, and C. ferrugineus, respectively, when compared to the control treatment. The percentage reductions for the parasitoid treatment were 70%, 8%, and 20% for S. zeamais, T. castaneum, and C. ferrugineus, respectively. For the avidin maize powder treatment, populations of S. zeamais, T. castaneum, and C. ferrugineus were reduced by 10%, 85%, and 40%, respectively. The combination treatment of avidin maize powder plus the release of parasitoid wasps was superior to either treatment alone when applied to mixed populations of internal and external feeders.     

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.     

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.     

Trans-2-hexen-1-ol as a tool for the control of Fusarium verticillioides in stored maize grains

Fusarium verticillioides infects stored maize grains. In the present study, we first evaluated the effects of ten volatile organic compounds on F. verticillioides growth in culture medium. Subsequently, based on the antifungal activity obtained in the present study and the insecticidal effect against Sitophilus zeamais reported previously, trans-2- hexen-1- ol was selected to analyzed its effect on the fungus in stored maize. All the compounds tested showed inhibitory activity on fungal development, being the most active compounds geraniol, nerol, isovaleraldehyde and linalool, followed by trans-2-hexen-1-ol, cis-3-hexen-1-ol, cis-2-hexen-1-ol and trans-3-hexen-1-ol. Besides its antifungal activity against F. verticillioides, trans-2-hexen-1-ol inhibited FB₁ production. In this study it was also demonstrated that S. zeamais favors F. verticillioides dispersion, confirming the importance of these insects as mechanical vectors of fungal spores. These results reveal the ability of trans-2-hexen-1-ol as a potential tool to control F. verticillioides in a natural approach as an alternative to synthetic pesticides.     

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.     

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.     

Influence of medium and physical disturbances during rearing on development and numbers of Sitophilus progeny

Four Sitophilus populations (Sitophilus zeamais Motschulsky from Mexico, S. zeamais from Arkansas, U.S.A., Sitophilus oryzae L., and Sitophilus granarius L.) were studied. Hard red winter wheat, sorghum, and maize were used to determine effects of rearing media on progeny production of insects from the four populations.Mechanically disturbing infested samples to remove newly-emerged adult weevils every 48 hr reduced numbers of progeny surviving to the adult stage, especially for Arkansas S. zeamais and S. granarius reared in any of the three grains.With one exception, reproduction for all populations in all three grains was highest when parents were reared in wheat; other differences are discussed. Also, progeny developmental periods for all four populations were shortest when parents were reared in wheat. Progeny of all four populations had the longest developmental periods when reared in maize regardless of the medium in which their parents were reared.In 250 g samples of wheat, and 125 g samples of sorghum, 50 parent S. oryzae produced statistically as many progeny as in 500 g and 625 g samples of wheat and 250, 500, and 625 g samples of sorghum, respectively. In maize, 625 g samples produced significantly more progeny than 500 g samples.Sex ratios of progeny from each grain were 1:1, except that females of S. oryzae reared in maize outnumbered males.     

Influence of rearing medium on size and weight of adults of four Sitophilus populations and on weight loss of host kernels (Coleoptera: Curculionidae)

Four populations of Sitophilus (S. zeamais Motsch. from Mexico, S. zeamais from Arkansas, U.S.A., S. oryzae (L.) and S. granarius (L.) were studied. Hard red winter wheat (“Cloud” variety), brown commercial sorghum, and yellow and white “dent” maize (mixed varieties) were used to determine the effect of parent-and progeny-rearing media on the adult elytron length in each population. Kernel weight loss caused by individuals of each population and weevil weights were determined.Elytron lengths of S. oryzae progeny were significantly (P < 0.05) but only slightly longer, when parents were reared in wheat rather than sorghum or maize; otherwise parent-rearing medium had no effect. Progeny-rearing medium, not parent size, was most responsible for differences in elytron lengths. S. granarius progeny from wheat were significantly larger than those from maize or sorghum; progeny from all other populations were significantly larger from maize than from wheat or sorghum.S. oryzae caused less weight loss in kernels of wheat and sorghum, and were significantly lighter (P < 0.05) than other insects. The Arkansas S. zeamais was significantly heavier than Mexican S. zeamais in wheat, otherwise their weights were similar. Weight losses (actual and percentages) of kernels of all grains were similar for Arkansas S. zeamais and Mexican S. zeamais. S. granarius were heavier and produced greater weight loss in wheat kernels than other populations did.     

Impact of moisture content and maize weevils on maize quality during hermetic and non-hermetic storage

The objective of this study was to determine the impact of moisture content and Sitophilus zeamais Motschulsky on maize quality during hermetic and non-hermetic storage conditions. Commercial Channel 211-97 hybrid maize kernels were conditioned to 14, 16, 18, and 20% moisture content (wet basis), and then three replications of 300 g of maize grain were stored in glass jars or triple Ziploc^® slider 66-μm(2.6-mil) polyethylene bags at four conditions: hermetic with weevils, hermetic no-weevils, non-hermetic with weevils, non-hermetic no-weevils. All jars and bags were stored in an environmental chamber at 27 °C and 70% relative humidity for either 30 or 60 d. At the end of each storage period, jars and bags were assessed for visual mold growth, mycotoxin levels, gas concentrations, pH level, the numbers of live and dead S. zeamais, and maize moisture content. The maize stored in non-hermetic conditions with weevils at 18 and 20% exhibited high levels of mold growth and aflatoxin contamination (>150 ppb). Conversely, very little mold growth was observed in maize stored in hermetic, and no aflatoxins were detected in any moisture level. CO₂ increased and O₂ gradually decreased as storage time increased for maize stored in hermetic conditions (with or without weevils) in all moisture level. No significant difference in pH was observed in any storage conditions (P < 0.05). Total mortality (100%) of S. zeamais was observed in all hermetically stored samples at the end of 60 days storage. Moisture content for hermetically stored maize was relatively constant. A positive correlation between moisture content and storage time was observed for maize stored in non-hermetic with weevils (r = 0.96, P < 0.05). The results indicate that moisture content and the number of S. zeamais weevils plays a significant role in maize storage, both under hermetic and non-hermetic conditions.     

Field trials to control insect pests of farm-stored maize in Zambia

Severe infestations of Sitophilus zeamais Motsch and Sitotroga cerealella Oliv. occur in maize cobs stored under farm conditions in Zambia causing up to 92% damaged grains 8 months after harvest. Shelling the maize reduced S. cerealella damage to low levels and also stabilized the moisture content of the grain providing a more suitable substrate for insecticide application and c control of S. zeamais. Malathion at 12 ppm a.i., tetrachlorvinphos (12 ppm), and jodfenphos (12 ppm), applied as dust admixtures to shelled maize in traditional mud-walled, timber and thatch storage cribs, all kept damaged grains below 10% up to 10 months after harvest. Pirimiphos-methyl (4 ppm) and fenitrothion (2 ppm) maintained these low damage levels up to 8 months after harvest, but there was evidence of continued S. cerealella infestation with these two insecticides.     

Rolliniastatin-1, a bis-tetrahydrofuran acetogenin: The major compound of Annona mucosa Jacq. (Annonaceae) has potent grain-protective properties

The widespread use of synthetic insecticides results in insecticide-resistant populations of maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae), a primary pest species of stored corn worldwide. Thus, new active ingredients with different modes of action are needed for integrated pest management (IPM) of stored grains. Thus, toxicological bioassays (using S. zeamais as bioindicator) associated to chromatographic techniques were performed to isolate insecticidal compounds from the grain-protective ethanolic extract of Annona mucosa Jacq. (Annonaceae) seeds. The acetogenin bis-tetrahydrofuran rolliniastatin-1 was identified as major bioactive constituent from A. mucosa seeds based on bioassay-guided fractionation, along with rolliniastatin-2, deethylrollinastatin-1, jimenezin and fractions containing triglycerides. This compound produced 51.1% of mortality of adult weevils when applied at 57.66 mg kg⁻¹, drastically reducing F₁ progeny and their damage to corn grains. Although the acute toxicity level was lower than that with the formulation based on diatomaceous earth at a concentration 17.3 times higher (Insecto®^, at recommended rate) used as a positive control, rolliniastatin-1 protected grain statistically similar to that of the positive control. Furthermore, bioassays indicate that compounds of different chemical natures have a synergistic effect on the overall biological activity of seed derivatives of A. mucosa. Efficacy and technical viability of the process to obtain rolliniastatin-1 from the seeds of A. mucosa should allow the production of a botanical insecticide to control populations of S. zeamais at corn warehouses.     

A simple curve describing the development pattern of some beetles breeding on stored products

The curve representing the emergence pattern of a generation of Sitophilus zeamais Motsch. developing upon maize was investigated, and it was found that the relationship between the cumulative number of emerged insects (y) and time (t) could be described by the asymptotic model log_ey = a ? bp^t. The model also satisfactorily fitted data for the emergence of S. zeamais breeding on triticale and on barley, Callosobruchus maculatus (F.) breeding on cowpeas and Prostephanus truncatus (Horn) breeding on maize.     

Prey-specific contact kairomones exploited by adult and larval Teretrius nigrescens: A behavioural comparison across different stored-product pests and different pest substrates

Prostephanus truncatus is a serious exotic beetle pest of stored maize and cassava in Africa. Teretrius nigrescens is a classical biological control predator of this pest that was released into Africa in 1991. In previous work it was shown that adult T. nigrescens are arrested in the presence of dust and frass produced by P. truncatus feeding on maize, and both adult and larval T. nigrescens are arrested by solvent extracts of this dust/frass when presented on filter paper. The current study used these two complementary bioassay approaches to test crude dust/frass and then solvent extracts of the same materials. Results demonstrate that T. nigrescens adults are arrested more strongly by the dust/frass of P. truncatus than the dust/frass of six other beetle pests of stored grain. Similar behaviours are observed for responses of both adults and larvae to solvent extracts. However, extract of dust/frass from Sitophilus zeamais is repellent to adults and larvae of T. nigrescens. Collections of dust/frass from P. truncatus cultured on maize, cassava and an artificial maize substrate previously stripped of all hexane extractable compounds, are all shown to arrest adult T. nigrescens when presented in their crude form and to arrest both adults and larvae when presented as solvent extracts. These experiments demonstrate that P. truncatus produces a species-specific kairomone that is independent of the food or tunnelling substrate. Findings are discussed in the context of prey location, particularly in natural habitats.     

The effect of grain stability on damage caused by Prostephanus truncatus (Horn) and three other beetle pests of stored maize

In an experiment where grain was presented to Prostephanus truncatus (Horn), Rhyzopertha dominica (F), Sitophilus zeamais Motsch, and Tribolium castaneum (Herbst) in four different ways, it was found that on simulated maize cobs P. truncatus caused much more damage than on loose maize, whereas the reverse was true for the other species. Damage was measured as percentage weight loss over a 6 week period, starting with adult beetles. It is suggested that such differences in the biology of the pests should be taken into account when investigating the inherent susceptibility to infestation of different maize varieties.     

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).     

Resistance of Tripsacorn to Sitophilus zeamais and Oryzaephilus surinamensis

One strategy that has been used to find germplasm for developing improved plant varieties is to test ancestral germplasm for the desired traits. Although the progenitors of commercial maize are not known, a hybrid (called Tripsacorn) developed from a perennial teosinte, Zea diploperennis, and eastern gamagrass, Tripsacum dactyloides, resembles the earliest known samples of primitive domesticated maize. We tested resistance of whole Tripsacorn to the primary storage pest (primary storage pests can infest intact kernels) the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), and resistance of ground Tripsacorn to the secondary storage pest (secondary pests usually cannot infest intact kernels) the sawtoothed grain beetle, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). Tripsacorn was immune to attack by S. zeamais. The weevils were unable to lay eggs in the Tripsacorn, and we hypothesized that the hardness of the fruitcase was responsible for lack of weevil oviposition. Oryzaephilus surinamensis were able to complete immature development on ground Tripsacorn, but duration of development was longer and weight of emerged adults was less than for beetles developing on wheat. Hardness of the fruitcase may have been a primitive mechanism of defense against insects and other pests, but probably would not be an acceptable trait in commercial varieties. It remains to be determined whether the possible antibiotic effect demonstrated in ground Tripsacorn would be a useful trait in commercial maize hybrids.     

Tolerance of Sitophilus zeamais (Coleoptera: Curculionidae) to heated controlled atmosphere treatments

Combination heat and controlled atmosphere (CA) postharvest phytosanitary treatments are environmentally friendly alternatives to chemical fumigants. A controlled atmosphere/heating block system (CA-HBS) was used to rapidly assess tolerances of adult maize weevil, Sitophilus zeamais, both under regular air (RA) and CA (1% O₂ and 15% CO₂) conditions. In the RA treatment, thermal death kinetics for S. zeamais adults were determined at temperatures between 46 °C and 52 °C at a heating rate of 5 °C/min. The results showed that thermal death curves of S. zeamais adults followed a 0th-order kinetic reaction model. The required holding times for achieving 100% mortality were 165, 40, 14, and 4 min at 46, 48, 50 and 52 °C, respectively. The activation energy for killing S. zeamais adults was 526.7 kJ/mol. The effects of CA at various temperature-time combinations and heating rates on insect mortality were evaluated. The mortality of S. zeamais adults was higher under CA treatment than in the heat treatment alone. The slowest heating rate (0.1 °C/min) achieved the highest insect mortality in CA treatments but lowest mortality in RA treatments. The information obtained from the CA-HBS can be used to develop combination heat and CA treatments against S. zeamais.     

Bioactivities of cymol and essential oils of Cupressus sempervirens and Eucalyptus saligna against Sitophilus zeamais Motschulsky and Tribolium confusum du Val

The essential oils extracted from Eucalyptus saligna and Cupressus sempervirens leaves were analysed by GC-MS and evaluated along with cymol, one of their main constituents for their repellent and toxic effects on Sitophilus zeamais and Tribolium confusum. Contact toxicity assayed by impregnation on filter paper discs or coating onto maize grains showed that these chemicals caused significant mortality of the test insects. Eucalyptus oil was more toxic than Cupressus oil to both insect species (LD₅₀=0.36 μl/cm² for S. zeamais and 0.48 μl/cm² for T. confusum) on filter paper discs, and was more toxic to S. zeamais on maize (LD₅₀=38.05 μl/40 g grain). Both oils considerably reduced the F₁ progeny production and grain weight loss. Moreover, both crude oil extracts produced a stronger repellent activity against the test insects than did cymol. These results suggest that the essential oils from E. saligna and C. sempervirens may be used in grain storage against insect pests.     

Relationship between seed physical traits and maize weevil (Sitophilus zeamais) damage parameters in selected Quality Protein Maize (QPM) varieties

The vulnerability of Quality Protein Maize (QPM) varieties to Sitophilus zeamais Motschulsky attack causes substantial postharvest loss to farmers. A study was conducted in the Institute of Agricultural Research and Training, Moor Plantation, Ibadan, Nigeria, to evaluate the response of the newly released QPM and High Protein Maize (HPM) varieties of the Institute to Sitophilus zeamais infestation. Five varieties comprising two QPM (ART/98/SW6-OB and ILE 1-OB); one HPM (ART/98/SW1) and two conventional maize varieties (KU1414SR/SR and TZPB) were used for the experiment. Two hundred seeds of each variety were artificially infested with eggs of Sitophilus zeamais and arranged in a completely randomized design with three replicates under two storage conditions (dark room and opened well-ventilated room) for three months. Data were collected on seed traits and weevil damage parameters. Results showed that there were significant differences among the varieties and between the storage conditions for most of the traits. Both QPM varieties significantly harbored Sitophilus zeamais as the number of emerged adult insects at 3 weeks after infestation (WAI), damage rating, total number of insects at termination and grain weight loss were highest in both, though higher in ILE 1-OB. The conventional inbred line (KU1414SR/SR) experienced less damage. Grain weight loss was positively correlated with insect damage rating, while seed coat thickness was negatively correlated with grain weight loss and other damage parameters. The released QPM varieties of the Institute are highly susceptible to Sitophilius zeamais infestation and therefore require genetic improvement. Seed coat thickness and damage ratings are important traits to be considered in improvement programmes for resistance to Sitophilus zeamais in QPM varieties.