Repellency Bioassay Research Articles

Biting deterrence, repellency, and larvicidal activity of Ruta chalepensis (Sapindales: Rutaceae) essential oil and its major individual constituents against mosquitoes.

The essential oil from aerial parts of Ruta chalepensis L. (Sapindales: Rutaceae) was obtained by hydrodistillation, and its chemical profile was identified using gas chromatography and gas chromatography-mass spectrometry. Compounds, 2-undecanone (43.2%), 2-nonanone (27.9%), and 2-nonyl acetate (10.6%) were the major constituents of the oil. Biting deterrent activity of R. chalepensis essential oil at 10 and 50 microg/cm2, 2-undecanone at 8.5 microg/cm2, 2-nonanone at 9 microg/cm2, and 2-nonyl acetate at 9.3 microg/cm2 was similar to DEET (N, N-diethyl-meta-toluamide) at 4.8 microg/cm2, against Aedes aegypti L. Biting deterrent activity of R. chalepensis oil at 50 microg/cm2 against Anopheles quadrimaculatus Say was statistically similar to DEET at 4.8 microg/cm2, whereas the activity was lower in the other compounds tested. In cloth patch assay, R. chalepensis essential oil was effective at 187 microg/cm2, whereas 2-undecanone was effective at 108.9 microg/cm2 against Ae. aegypti. In larval bioassays, 2-undecanone showed similar toxicity whereas toxicity of R. chalepensis essential oil and 2-nonanone was higher at 24-h posttreatment at the LD50 in An. quadrimaculatus than Ae. aegypti. This study revealed that R. chalepensis essential oil and its major compounds were active biting deterrents against Ae. aegypti at higher application rates whereas only the essential oil showed activity similar to DEET against An. quadrimaculatus. 2-undecanone was the most active compound in in vivo repellency bioassay against Ae. aegypti. Chemical composition of R. chalepensis essential oil varies because of plant production and harvest practices, and the activity level of the essential oil may depend on the source of the sample.

Promising Aedes aegypti repellent chemotypes identified through integrated QSAR, virtual screening, synthesis, and bioassay.

Molecular field topology analysis, scaffold hopping, and molecular docking were used as complementary computational tools for the design of repellents for Aedes aegypti, the insect vector for yellow fever, chikungunya, and dengue fever. A large number of analogues were evaluated by virtual screening with Glide molecular docking software. This produced several dozen hits that were either synthesized or procured from commercial sources. Analysis of these compounds by a repellent bioassay resulted in a few highly active chemicals (in terms of minimum effective dosage) as viable candidates for further hit-to-lead and lead optimization effort.

Repellent effects of essential oils from selected eucalyptus species and their major constituents against Sitophilus zeamais (Coleoptera: Curculionidae)

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.

Insecticidal, repellent and fungicidal properties of novel trifluoromethylphenyl amides

Twenty trifluoromethylphenyl amides were synthesized and evaluated as fungicides and as mosquito toxicants and repellents. Against Aedes aegypti larvae, N-(2,6-dichloro-4-(trifluoromethyl)phenyl)-3,5-dinitrobenzamide (1e) was the most toxic compound (24h LC50 1940nM), while against adults N-(2,6-dichloro-4-(trifluoromethyl)phenyl)-2,2,2-trifluoroacetamide (1c) was most active (24h LD50 19.182nM, 0.5μL/insect). However, the 24h LC50 and LD50 values of fipronil against Ae. aegypti larvae and adults were significantly lower: 13.55nM and 0.787×10−4nM, respectively. Compound 1c was also active against Drosophila melanogaster adults with 24h LC50 values of 5.6 and 4.9μg/cm2 for the Oregon-R and 1675 strains, respectively. Fipronil had LC50 values of 0.004 and 0.017μg/cm2 against the two strains of D. melanogaster, respectively. In repellency bioassays against female Ae. aegypti, 2,2,2-trifluoro-N-(2-(trifluoromethyl)phenyl)acetamide (4c) had the highest repellent potency with a minimum effective dosage (MED) of 0.039μmol/cm2 compared to DEET (MED of 0.091μmol/cm2). Compound N-(2-(trifluoromethyl)phenyl)hexanamide (4a) had an MED of 0.091μmol/cm2 which was comparable to DEET. Compound 4c was the most potent fungicide against Phomopsis obscurans. Several trends were discerned between the structural configuration of these molecules and the effect of structural changes on toxicity and repellency. Para- or meta- trifluoromethylphenyl amides with an aromatic ring attached to the carbonyl carbon showed higher toxicity against Ae. aegypti larvae, than ortho- trifluoromethylphenyl amides. Ortho- trifluoromethylphenyl amides with trifluoromethyl or alkyl group attached to the carbonyl carbon produced higher repellent activity against female Ae. aegypti and Anopheles albimanus than meta- or para- trifluoromethylphenyl amides. The presence of 2,6-dichloro- substitution on the phenyl ring of the amide had an influence on larvicidal and repellent activity of para- trifluoromethylphenyl amides.

Repellent activity screening of 11 kinds of essential oils against Aedes albopictus Skuse: microcapsule preparation of Herba Schizonepetae oil and repellent bioassay on hand skin

The main ingredient of most repellents on the market is DEET, an effective compound that has the disadvantages of toxic reactions as well as damaging effects on plastic and synthetic fabric. DEET alternatives are urgently needed. The repellent activities of 11 kinds of essential oils were tested against Aedes albopictus Skuse by a Y-tube olfactometer. Using essential oils with high repellent activity as core material and gelatin and gum arabic as wall materials, we prepared microcapsules of essential oils and optimized the preparation process. The microcapsule formulation was then subjected to repellent bioassay on hand skin. when the dosage of essential oils was 5 µL, the cinnamon oil repellent rate was 87.5% within 10 min and the Herba Schizonepetae oil (HSO) repellent rate was 98.0% within 3 min. Up to 1.5% (w/v) gelatin and 1.5% (w/v) gum arabic (as wall materials), and HSO (as core material) were used to form microcapsules with a 1:1 ratio of core material to wall material. The ointment preparations effectively protected hand skin exposed to a high-density A. albopictus Skuse rearing cage for 4-5 h. The HSO microcapsule repellent has broad application and development prospects.

Insecticidal and repellence activity of the essential oil of Pogostemon cablin against urban ants species

Ants are highly abundant in neotropical regions, with certain species adapted to the urban environment, where they can cause damage to human health. The main method for controlling ants consists of using organosynthetic insecticides, which are potentially toxic to the environment. Essential plant oils are considered a viable alternative to the use of conventional insecticides. In this study, we analyze the bioinsecticidal activity and repellence of patchouli essential oil (Pogostemon cablin) against three species of urban ants: Camponotus melanoticus, Camponotus novograndensis, and Dorymyrmex thoracicus. The chemical composition of the essential oil was analyzed by GC–MS and GC-FID. The major compounds were patchoulol (36.6%) followed by α-bulnesene (13.95%), and α-guaiene (11.96%). Toxicity and repellency bioassays were performed using the essential oil over the ants, and mortality evaluations were performed at 4, 24, and 48h after performing the bioassays. Mortality percentage of the ants on 7μg/mg was on average 84%. The essential oil of P. cablin displayed toxicity against all three species of urban ants, with the lowest LD50 being observed for D. thoracicus (2.02μg oil/mg insect) after 48h of exposure compared to C. melanoticus (2.34μg oil/mg insect) and C. novogranadensis (2.95μg oil/mg insect). The essential oil of P. cablin was strongly repellent to the three species of ants in all concentrations tested (0.01% and 1% v/v). Considering the potential toxicity and repellency of the P. cablin essential oil to the urban ants, future studies could investigate the practical application of this oil to control of this insects.

Essential oil of Ocotea odorifera: An alternative against Sitophilus zeamais

AbstractNowadays, the maize weevil Sitophilus zeamais—Motsch 1855 is the most relevant pest found during storage of maize grains. Aiming at protecting the agricultural crops, high amounts of synthetic pesticides are used around the world. In this sense, this work aimed at evaluating the insecticidal and repellent effect of essential oil of Ocotea odorifera (Vellozo) Rohwer (Lauraceae) (O. odorifera (sassafras)) leaves against the maize weevil in maize grains. The essential oil's chemical composition showed that sassafras contains camphor (43%) and safrole (42%) as major compounds. Our results show that sassafras oil was insecticidal and repellent to maize weevil. About 100% mortality was achieved using a concentration of 0.32 μl cm−2, after 24 h of exposure. The LD50 value was 14.1 μl or 0.09 μl cm−2 and the study of the effect on insect mortality at the lethal doses (LD50) showed that after 72 h mortality was 100%. The values of the preference index varied from −0.39 (0.065 μl cm−2) to −0.63 (0.659 μl cm−2), demonstrating that the plant oil presents repellent activity. The repellency bioassay simulating small bins showed the repellent effect level from 0.64 (0.36 μl cm−3) to 0.94 (2.9 μl cm−3). The essential oil of sassafras presented insecticidal and repellency against maize weevil. Although from an economical 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.

Evaluation of bioefficacy of three Citrus essential oils against the dengue vector Aedes albopictus (Diptera: Culicidae) in correlation to their components enantiomeric distribution

Laboratory experiments were conducted to study the bioefficacy against Ae. albopictus of three Citrus essential oils, derived from peels of Citrus sinensis, Citrus limon, and Citrus paradise and of their components. Chiral gas chromatography analysis revealed the dominant occurrence of R-(+)-limonene and (-)-β-pinene in all three essential oils while in the case of lemon oil γ-terpinene, neral, and geranial detected also among other components. The tested Citrus essential oils were toxic against mosquito larvae with LC(50) values ranging from 25.03 to 37.03 mg l(-1). Among citrus essential oils components tested, γ-terpinene was the most toxic (LC(50) = 20.21 mg l(-1)) followed by both enantiomeric forms of limonene (LC(50) = 35.99 and 34.89 mg l(-1), for R-(+)-limonene and S-(-)-limonene, respectively). The delayed toxic effects after exposure of larvae to sublethal (LC(50)) doses were also investigated for citrus essential oils and their major component R-(+)-limonene, indicating a significant reduction of pupal survival. In repellent bioassays, lemon essential oil, S-(-)-limonene, citral (mixture of neral\geranial) and (+)-β-pinene were the most effective compared with other citrus essential oils and components against adult mosquitoes. Repellent bioassays also revealed that limonenes and β-pinenes showed an isomer dependence repellent activity. Finally, according to enantiomeric distribution of limonene and α- and β-pinene, the repellency of lemon essential oil is possibly attributed to the presence of citral.

Repellent properties of Nicotiana tabacum and Eucalyptus globoidea against adults of Hyalomma marginatum rufipes

Scientific evaluation of plants for anti-tick properties is a necessary step towards the development of tick control methods that exclude or involve less of synthetic chemicals. In this study, we evaluated the repellent properties of Nicotiana tabacum and Eucalyptusgloboidea against adults of Hyalomma marganitum rufipes using a suitable repellency bioassay. Dichloromethane extract of E. globoidea had more repellent potency against adults of H. m. rufipes compared to ethyle-acetate extract of N. tabacum in all three concentrations (20, 30 and 40% w/v) used. The anti-tick repellent strength of dichloromethane extract of E. globoidea compared favourably with that of the commercial arthropod repellent, N, N-diethyltoluamide (DEET) and was dose dependent. Key words: Nicotiana tabacum, Eucalyptus globoidea, Hyalomma marginatum rufipes, repellency.

Variation in the repellency effects of the leaves of Mentha piperita against adults of Amblyomma hebraeum

The repellency effects of Mentha piperita leaves, collected from two different locations in South Africa, (Ga-Rankuwa and Malelane) on adults of Amblyomma hebreaum were studied. Leaves extraction was carried out using two different solvents (dichloromethane (DCM) and ethylacetate) to make concentrations of 0.24 g/10 ml, 0.24 g/15 ml and 0.24 g/20 ml (w/v). The extracts were tested for repellency on the adults of A. hebraeum using glass plate repellency bioassay. The separation and qualitative analysis of plant extracts (0.24 g/10 ml (w/v)) extracted with DCM were investigated using TLC. Trace elements concentration from the soil and leaves samples from each study areas were determined by ICP – OES. The result shows that plant extract of both DCM and ethylacetate solvents from Ga-Rankuwa plants were more effective at all concentrations in repelling adults’ A. hebraeum when compared with extracts of the plant collected from Malelane. Significantly, higher concentrations of trace metals were reported from the soil and plant collected from Malelane (p < 0.05). TLC plates showed that there are differences in the chemical composition of the DCM extracts of M. piperita from Ga-Rankuwa and Malelane. The study shows that plant species collected from different geographical areas can produce contrasting results. Key words: Mentha piperita, repellency bioassay, Amblyomma hebraeum

English

A suitable in vitro tick climbing repellency bioassay was developed to evaluate the repellent effects of the essential oil (n-hexane extracts of distillate) of Lippia javanica (Burm. F.) Spreng (Verbernaceae) on adults of Hyalomma marginatum rufipes Koch, 1844. The GC-MS analysis of the distillate of the essential oil of Lippia javanica revealed that myrcene (13.4%), 1,8-cineole (8%), dyhydrotagetone (7.9%), ipsenone (9.6%), bicyclo (3.1.1) heptanes-2-one (20.8%) and 2-butanone (13.3%) were the major constituents. A significant (P < 0.05) dose dependent repellency response was observed for the essential oil of L. javanica on adults of H. marginatum rufipes when data were subjected to Kruskal Wallis analysis.

Tanzanian Botanical Derivatives in the Control of Malaria Vectors: Opportunities and Challenges

This paper report on assessment of the chemicals derived from Tanzanian botanical resource as a viable source of safe, environmentally friendly and low cost mosquitocidal agents, but has yet to be developed into simple blends and formulations to be used in malaria control campaigns. Selection of bioactive plant species were based on random screening, phytochemical targeting, ethnobotanical survey, chemotaxonomic approach and targeted screening approach. The crude extracts from leaves, stem and root barks, and pure isolated compounds from over 20 different Tanzania plant species have been established to possess antimosquito activities. The bioassay experiments were based on cytotoxicity screening in BST followed by mosquitocidal assays of larvicidal, tarsal contact and repellency bioassays. The activities were characterized to be larvicidal, growth disruptors, insecticidal and repellents. Seasonal variations, geographical locations, isolation of small amounts of pure compounds, limits in the availability of essential facilities such as NMR spectroscopy, MS and X-ray diffraction analysis for structural elucidation, stereochemical and conformational assignments, have been realised to be among the impediments in the search and establishment of new and biodegradable botanical natural products. The results suggest that the investigated plant species are promising as mosquitocidal agents and could be useful leads for the development of new insecticide products. @JASEM

Repellent, larvicidal and pupicidal properties of essential oils and their formulations against the housefly, Musca domestica

The essential oils of six plant species [peppermint, Mentha piperita, and bergamot mint, Mentha citrata (both, Lamiales: Lamiaceae); blue gum, Eucalyptus globulus (Myrtales: Myrtaceae); lemongrass, Cymbopogon citratus, and khus grass, Vetiver zizanoides (both, Poales: Poaceae), and turmeric, Curcuma longa (Ziniberales: Zingiberaceae)] were screened for repellent, larvicidal and pupicidal activities against the housefly, Musca domestica L. (Diptera: Muscidae). Subsequently, emulsifiable concentrate (EC) formulations of the two most effective oils were prepared and tested in the laboratory as well as in the field. In repellency bioassays, M. piperita (RC(84) , 61.0 µg/cm(2) ) was found to be most effective, followed by E. globulus (RC(84) , 214.5 µg/cm(2) ) and C. citratus (RC(84) , 289.2 µg/cm(2) ). Formulated M. piperita and E. globulus showed RC(84) values of 1.6 µg/cm(2) and 4.1 µg/cm(2) , respectively. Formulated M. piperita and E. globulus achieved larval mortality (LC(50) ) in 72 h at 5.12 µg/cm(2) and 6.09 µg/cm(2) , respectively. In pupicidal bioassays, crude oils of M. piperita and E. globulus suppressed the emergence of adult flies by 100%. Field experiments with the M. piperita formulation showed reductions in fly density (number of flies/h) of 96% on treated cattle and 98% on treated plots. This study demonstrates the effectiveness of EC formulations of selected essential oils in reducing housefly populations in field conditions.

Mosquito Biting Behavior: Statistical Power and Sources of Variation in Toxicity and Repellent Bioassays

Compounds thought to be effective against mosquitoes as either 'insecticides' or 'repellents' have recently been shown to contain properties of both, or possess other behavior-modifying actions. Prompted in part by these reports, we conducted posterior analyses of our data to examine some interrelated statistical issues inherent in our bioassay system. Using a modified K&D module, the responses of over 25,000 adult Aedes aegypti (L.) females exposed to either alphacypermethrin or DEET were compared with the responses of mosquitoes exposed to untreated controls for toxicity and biting (alphacypermethrin) or biting alone (DEET). Our analyses indicated that; (1) our bioassay system has more statistical power to determine a compound's toxicity than its repellent qualities, (2) day-to-day variability is large and needs to be accommodated in analyses; there are other, potentially even larger sources of variability (e.g., mosquito heterogeneity) which invalidate statistical tests that are based on the assumption of binomially or multinomially distributed data (e.g., chi2 tests), and (3) unlike biting mosquitoes exposed to DEET, the proportions of biting mosquitoes exposed to alphacypermethrin are unrelated to the proportions of concurrently tested biting controls, even after adjusting for daily variation in toxicity. Thus, there is a clear behavioral indicator in this bioassay system that the 'repellency' of DEET (a presumed repellent) differs in a fundamental way from that of alphacypermethrin (a presumed toxicant), which may allow the differentiation between classes of compounds based on biting behavior alone.

Mosquito Biting Behavior: Statistical Power and Sources of Variation in Toxicity and Repellent Bioassays

Compounds thought to be effective against mosquitoes as either ’insecticides’ or ’repellents’ have recently been shown to contain properties of both, or possess other behavior-modifying actions. Prompted in part by these reports, we conducted posterior analyses of our data to examine some interrelated statistical issues inherent in our bioassay system. Using a modified K&D module, the responses of over 25,000 adult Aedes aegypti (L.) females exposed to either alphacypermethrin or DEET were compared with the responses of mosquitoes exposed to untreated controls for toxicity and biting (alphacypermethrin) or biting alone (DEET). Our analyses indicated that; (1) our bioassay system has more statistical power to determine a compound’s toxicity than its repellent qualities, (2) day-to-day variability is large and needs to be accommodated in analyses; there are other, potentially even larger sources of variability (e.g., mosquito heterogeneity) which invalidate statistical tests that are based on the assumption of binomially or multinomially distributed data (e.g., χ2 tests), and (3) unlike biting mosquitoes exposed to DEET, the proportions of biting mosquitoes exposed to alphacypermethrin are unrelated to the proportions of concurrently tested biting controls, even after adjusting for daily variation in toxicity. Thus, there is a clear behavioral indicator in this bioassay system that the ’repellency’ of DEET (a presumed repellent) differs in a fundamental way from that of alphacypermethrin (a presumed toxicant), which may allow the differentiation between classes of compounds based on biting behavior alone.

Biological Activity of Essential Oils from Aloysia polystachya and Aloysia citriodora (Verbenaceae) against the Soybean Pest Nezara viridula (Hemiptera: Pentatomidae)

The objective of the current study was to determine the chemical constituents, ovicidal activity, fumigant, contact toxicity and repellent effects of essential oils isolated by hydrodistillation from Aloysia polystachya and A. citriodora against eggs and second instar nymphs of Nezara viridula. The major components were carvone (83.5%) for A. polystachya, and citronellal (51.3%) and sabinene (22.9%) for A. citriodora. The ovicidal activity of both oils was tested by topical application at different concentrations ranging from 1.2 to 12.5 microg/egg; all concentrations had a toxic effect. Data probit analysis showed that the LC50 value for A. polystachya was 2.3 microg/egg and for A. citriodora 1.9 microg/egg. The fumigant activity was evaluated in an enclosed chamber. The toxicity increased with concentration from 11 to 176 microg/mL air, and with exposure times from 1 to 48 h. The LC50 values for A. polystachya and A. citriodora were 29.9 and 13.5 microg/mL air 24 h after treatment, respectively. To evaluate contact activity a glass-vial bioassay was used. The toxicity increased with concentration from 2.8 to 45 microg/cm2 and with exposure time from 1 to 48 h. The LC50 for A. polystachya was 3.4 microg/cm2 and for A. citriodora 8.1 microg/cm2. The repellency bioassay demonstrated that both oils were active at the highest concentration (2.6 and 5.3 microg/mL air) and neutral at 1.3 microg/mL air. These results show that the essential oils from Aloysia polystachya and A. citriodora could be applicable to the management of populations of Nezara viridula.

Repellent activity of DEET against Amblyomma cajennense (Acari: Ixodidae) nymphs submitted to diferent laboratory bioassays

This study was developed to evaluate the repellent activity of N,N-diethyl-3-methylbenzamide (DEET) against Amblyomma cajennense nymphs. Two repellent bioassays were compared and the effective concentration and repellent time were calculated. The fingertip test was accomplished to evaluate in vivo four concentrations of the compound (0.200; 0.100; 0.050 and 0.025 mg.cm⁻²) and the filter-paper bioassay to evaluate in vitro the two highest concentrations.The compound provided repellence higher than 90% in all concentrations and at least 95% repellency in the highest concentration over 5 hours. The effective concentration against 50% of tested nymphs (EC50) was 0.006 mg.cm⁻² and the EC99 was 0.036 mg.cm⁻². Those concentrations were lower than the ones obtained against other tick species, denoting the effectiveness of DEET against A. cajennense. The repellency time against 50% of the ticks (RT50) was 4.8 hours and the RT90 was 2.7 hours. Both bioassays were adequate to evaluate A. cajennense repellency and provided similar results; however the in vivo test is more appropriate to estimate the effective concentration and repellency time.

Toxicity and biochemical efficacy of six essential oils against Tribolium confusum (du val) (Coleoptera: Tenebrionidae)

Six essential oils extracted from garlic (Allium sativum), mint (Mentha piperitaa), basil (Ocimum basilicum), thyme (Thymus vulgaris ) , sesame (Sesamum Indicume) and chamomile (Chamaemelum nobile) were tested for both repellency and toxicity against the confused flour beetle, Tribolium confusum adults and last larval instar. Two kinds of repellency bioassays were performed by using filter paper tests and treated kernels. The toxicological bioassay was performed by topical application. The results showed that the tested oils were highly repellent to the adult insect compared to the larvae. By contrast, the toxicological bioassay showed that larvae were more susceptible to tested essential oils than the adults. Effects of essential oils on five detoxification enzymes were also investigated. A reduction in total activities of the major detoxification enzymes in treated larvae was also observed.

Insecticidal activities of essential oil from the leaves of Mentha longifolia L. subsp. capensis against Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae)

Toxicity of the essential oil from the leaves of Mentha longifolia (Lamiaceae) was evaluated against Sitophilus zeamais, an insect that is the major cause of deterioration in stored grains, including maize. The contact, fumigation and repellency bioassays revealed that the oil was toxic to the insect. Increases in oil concentration and time of exposure resulted in a progressive increase in insect mortality. The dose of essential oil at 0.50 μl/g of maize grains in the contact bioassay caused 100 % mortality of S. zeamais, compared to less than 10 % mortality recorded at 0.125 μl/g. The essential oil demonstrated moderate fumigation toxicity against the test insects at concentrations of 24 and 32 μl of oil per litre of air, respectively. A high repellency was recorded for the oil at all the concentrations tested. Repellency values of as high as 100 % were recorded for most concentrations. Mentha longifolia could be a potential agent for the protection of agricultural stored products against S. zeamais.

Integrating varietal resistance with Xylopia aethiopica (Dunal) A. Richard seed extract for the management of Sitophilus zeamais Motschulsky in stored maize

In search for alternatives to synthetic pesticides in maize (Zea mays, L.) storage, an integrated weevil management scheme involving varietal resistance and Xylopia aethiopica (Dunal) A. Richard seed extract was evaluated in the laboratory. Varying rates of X. aethiopica extract were assessed on three maize varieties (Pajo White, Tsolo Yellow, and DMR-LSR-Y) with differing susceptibility to Sitophilus zeamais. The different rates of X. aethiopica extract significantly interacted with maize varietal resistance and reduced fecundity of S. zeamais and maize seed weight loss due to insect’s feeding. Treatment of seeds with extract at 1.0 ml/20 g seed caused significant (above 50%) mortality at 24 h post treatment in all varieties whereas no mortality was recorded with the control and 0.2 ml/20 g seed. DMRLSR-Y was better protected than the remaining two varieties in the integrated weevil management scheme. A repellency bioassay of the extract also revealed that the extract was strongly repellent to S. zeamais with 73% (Class IV) repellency recorded in 0.4 ml/30 cm2.