Effect of Intercropping of Legumes and Rates of Nitrogen Fertilizer on Yield and Yield Components of Maize (<i>Zea mays</i>L.) at Arba Minch

Intercropping of legumes and cereals, an old practice since ancient civilization, plays pivotal role to increase land use efficiency, improve income and food production per unit area and minimize the risks of crop failure for small scale farmers. Thus, field experiment was conducted to determine the effect of intercropping of legumes and rates of nitrogen fertilizer on yield and yield components of maize (Zea mays L.). The experiment consisted of 0, 23, 46, 69 and 92 kg·N·ha-1 and sole maize, maize + commom bean, maize + common bean - mung bean cropping systems with Random Complete Block Design factorial experiment in three replications using maize variety, “BH-140”, common bean variety (Hawassadume) and mung bean variety. Maximum plant heights, dry matter and grain yield, were observed from sole cropped maize and maize + common bean, when applying 92 kg·N·ha-1. Significantly higher total Land Equivalent Ratio of 2.2, Gross Monetary Value of 87,191 birr ha-1, Monetary Advantage of 47,068.2 Birr ha-1, total productivity (80,568.49 birr) and net return (55,214.0 birr) were recorded from maize + common bean - mung bean. The, maximum marginal rate of return was obtained from maize + common bean - mung bean and applying 69 kg·N·ha-1 (1080%). Thus, farmers should be advised to practice cropping of maize + common bean - mung with 69 kg·N·ha-1 to get economical maize production.

Magnitude and Correlates of Contraceptive Use among Females in Reproductive Age in Arba Minch Zuria Woreda: A Community Based Cross-Sectional Study

Background: Despite its positive impact in reducing maternal and child mortality and morbidity, the utilization rate of contraceptives is unacceptably low in many developing countries including Ethiopia. This warrants the investigation of the contributing factors of this low utilization for appropriate interventions. Objective: The objective of this study was to investigate the magnitude and associated factors of contraceptive use in Arba Minch Zuria Woreda, Gamo Gofa Zone, Southern Ethiopia. Methods: A community based cross-sectional study was conducted from April to July 2010 in 9 kebeles of Arba Minch Demographic and Health Development Program. Results: In this study, 28.3% of all women & 32.7% currently married were using any contraceptive methods during the time of the survey. Almost all current users were using modern methods;the most widely used method was injectable (24.2%) followed by implants (2.4%) and pills (1.3%). Current marital status, ethnicity, age, education, presence of radio set in the house hold and discussion about family planning in the last 6 month before the study with their partner were the independent predictors of contraceptive use. Conclusion: The contraceptive prevalence rate is promising but efforts should continue to further increase the contraceptive coverage especially on kebeles with low coverage by targeting men and misconceptions about family planning.

Response of Haricot Bean (<i>Phaseolus vulgaris</i>L.) to Irrigation Frequency and Intra Row Spacing at Arba Minch, Ethiopia

Optimizing irrigation frequency and intra row spacing for specific environment is one the major agronomic practices to improve productivity of haricot bean. Hence, a field experiment was conducted to evaluate the effect of irrigation frequency and intra row spacing on growth, nodulation and agronomic performance of haricot bean at Arba Minch during dry season of 2018/19. The treatments consisted of three levels of irrigation frequency based on IW/CPE ratio (0.5, 0.67 and 1.0) with irrigation depth of 60 mm and three intra row spacing (6, 10 and 14 cm) which were factorially arranged in split plot design with three replications. Data were collected on phenological, nodulation, growth, yield and yield related parameters of the crop. The measured parameters were subjected to analysis of variance using SAS software version 9.0. Among the measured parameters, plant height, pod number per plant, dry matter and seed yield were significantly influenced by interaction effect of the treatments. The maximum seed yield (2873.7 kg ha−1) was recorded with interaction effect of irrigation at IW/CPE of 1 and intra row spacing of 10 cm. As for economic analysis, the same treatment combination also resulted in the highest net benefit (11254.1 Ethiopian Birr ha−1) and marginal rate of return (422.1%). Therefore, it could be concluded that irrigating haricot bean at IW/CPE ratio of 1 and planting at 10 cm intra row spacing could maximize both seed yield and economic benefit of the crop in the study area.

Anemia and Its Associated Risk Factors at the Time of Antiretroviral Therapy Initiation in Public Health Facilities of Arba Minch Town, Southern Ethiopia

Background: Anemia is the most common hematologic abnormality in HIV patients and is associated with disease progression and decreased survival. This study aims to describe the prevalence and predictors of anemia in HIV positive patients at the time of ART initiation at public health facilities of Arba Minch town, Southern Ethiopia. Methods: A total of 411 adults (?15 years) HIV positive patients with complete information on hemoglobin levels and CD4 count and clinical characteristics registered from 2006 to 2013 were assessed for anemia prevalence and risk factors at the ART clinic of the Arba Minch hospital and health center. The measurements of Hemoglobin and CD4 + T cell count were performed using standard methodology at baseline of ART initiation. Results: A total of 411 HIV positive patients (195 males and 216 females) with a mean ± SD age of 33.9 ± 9.0 years were assessed. Hemoglobin levels were between 6.0 and 16.5 mg/dL. The overall prevalence of anemia at the time of ART initiation was 52.3%;with 28.1%, 22.9% and 1.3% mild, moderate and severe anemia respectively. The overall prevalence of anemia was 62.4% among males and 46.7% among females (P < 0.001). An increased risk of anemia was seen in males (adjusted OR = 2.78, 95% CI = 1.77 - 4.35);low CD4 cell counts (adjusted OR = 3.48, 95% CI = 2.09 - 5.79);and history of TB (adjusted OR = 2.89, 95% CI = 1.28 - 6.54). Conclusions: Anemia in HIV-positive patients was highly prevalent at the time of ART initiation. Male gender, low CD4 count and history of TB were associated with higher risk of baseline anemia.

Determination of groundwater potential distribution in Kulfo-Hare watershed through integration of GIS, remote sensing, and AHP in Southern Ethiopia

Identification of groundwater potential areas(GPA)is important in regions facing surface water scarcity,as it assists in effective planning and utilization of groundwater for various purposes.This study employs the methods of remote sensing(RS),geographic information system(GIS)model,and analytical hierarchy process(AHP),multi-criteria decision analysis(MCDA)to locate and map the prospective groundwater areas in the Kulfo-Hare watershed.Seven significant groundwater influencing factors were selected for the determination of groundwater potential in the area:Geology,land use/land cover(LULC),soil,rainfall,slope,drainage density,and lineament density.By applying a five-class classification scheme(very low,low,moderate,high,and very high),the GIS models were used to define the distribution of groundwater potential areas in terms of area coverage(km^(2)),percentage and mapping.The results show that the groundwater potential(GWP)distribution in the research region is as follows:9.7%(6035.9 ha)classified as very high GWP,29.6%(18606 ha)classified as high,24.5%(15245 ha)classified as moderate,18.1%(11431 ha)as low and 18.1%(11492 ha)very low GWP,on the basis of the weighted overlay evaluation.Although a few regions are identifies as extremely low GWP,most of the study area is characterized by very high to moderate GWP.These findings provide valuable insight for sustainable groundwater planning by the government bodies,decision-makers,and private sectors.

Energy efficient indoor localisation for narrowband internet of things

There are an increasing number of Narrow Band IoT devices being manufactured as the technology behind them develops quickly.The high co‐channel interference and signal attenuation seen in edge Narrow Band IoT devices make it challenging to guarantee the service quality of these devices.To maximise the data rate fairness of Narrow Band IoT devices,a multi‐dimensional indoor localisation model is devised,consisting of transmission power,data scheduling,and time slot scheduling,based on a network model that employs non‐orthogonal multiple access via a relay.Based on this network model,the optimisation goal of Narrow Band IoT device data rate ratio fairness is first established by the authors,while taking into account the Narrow Band IoT network:The multidimensional indoor localisation optimisation model of equipment tends to minimize data rate,energy constraints and EH relay energy and data buffer constraints,data scheduling and time slot scheduling.As a result,each Narrow Band IoT device's data rate needs are met while the network's overall performance is optimised.We investigate the model's potential for convex optimisation and offer an algorithm for optimising the distribution of multiple resources using the KKT criterion.The current work primarily considers the NOMA Narrow Band IoT network under a single EH relay.However,the growth of Narrow Band IoT devices also leads to a rise in co‐channel interference,which impacts NOMA's performance enhancement.Through simulation,the proposed approach is successfully shown.These improvements have boosted the network's energy efficiency by 44.1%,data rate proportional fairness by 11.9%,and spectrum efficiency by 55.4%.

水热预处理对提高牛粪厌氧产甲烷性能的研究

为了研究水热预处理对牛粪厌氧产甲烷性能的影响,文章采用不同的温度(50℃,70℃,90℃,100℃,150℃和200℃)分别对牛粪进行预处理(5 min^3 d),再进行中温批式厌氧消化实验。结果表明:最优的预处理条件是70℃预处理3 d,牛粪的甲烷产量最高,达到176.36 mL·g^-1 VS,比未经处理的提高了21.00%;VS去除率为39.64%,比未经处理的提高了6.34%。此外,牛粪经不同水热预处理后的VS水解率达到2.78%~16.25%。部分预处理组的还原糖和VFAs浓度分别达到66.20~118.51 mg·L^-1和8230.14~12135.72 mg·L^-1,分别比对照组提高了7.31%~92.11%和8.03%~59.29%。所以水热温度和时间是预处理过程中的重要影响因素,并且在较低温度下预处理效果最好。

稻草与畜禽粪便混合物厌氧消化快速启动研究

大型沼气工程的启动需要有大量的外源接种物,这使得启动成本增高。为了实现沼气工程低成本快速启动,文章以稻草与粪便(牛粪、猪粪)按0∶1,1∶2,1∶1,2∶1和4∶1(VS比)混合后,在不外加接种物的情况下直接启动。结果表明:除稻草与猪粪4∶1混合外,不同比例的稻草与粪便混合后均能启动成功。添加不同比例牛粪的启动效果优于添加猪粪的启动效果,同时在不外加接种物的情况下,少量稻草与粪便混合的启动效果优于单独粪便的启动效果。稻草与牛粪和猪粪的混合比例均为1∶2时效果最佳,单位VS产气量分别为258 mL·g^-1和187 mL·g^-1,T 80(累积产气量达到总产气量80%时所需的时间)分别为29 d和39 d,氨氮分别为434 mg·L^-1和728 mg·L^-1,碱度为5250 mg·L^-1和5300 mg·L^-1。两种混合方式都可以快速启动且厌氧系统性能稳定,该研究结果可为大型沼气工程启动提供技术支持并可大大节省启动成本。

不同粒径稻草的漂浮特性和厌氧发酵产气性能研究

为提高稻草厌氧发酵产甲烷效益,试验采用批式厌氧消化,研究了不同粒径稻草(40目,20目,10目和5目)的漂浮特性和厌氧发酵性能,对其在厌氧消化过程中的产甲烷性能、粉碎能耗、经济效益以及失水漂浮层变化规律进行分析。结果表明:5目稻草的产甲烷性能和经济效益最好,50 gTS负荷下消化50 d后单位VS产气量为238.47 mL,分别比40目,20目和10目的稻草高出了11.40%,20.09%和9.96%。5目稻草的挥发性固体VS的去除率和纤维素降解率分别为68.65%和59.77%,均优于其他粒径的稻草。稻草粉碎能耗与粒径负相关,5目稻草的耗电量为42 kWh·t^-1,分别比40目,20目和10目稻草的耗电量降低了81.74%,61.82%和40.00%。每吨5目稻草产甲烷净收益为259.1元,比40目,20目和10目稻草的净收益分别高出了228.93%,66.36%和23.26%。在产气高峰期时各试验组失水漂浮层在12 h内达到峰值,随后逐渐下降,而在发酵末期漂浮层厚度增加速率变得十分缓慢。40目稻草形成的失水漂浮层厚度最小且不稳定。本研究提供了一种经济性较优的稻草粒径,对于合理安排搅拌频率、降低能耗成本提供了一定的数据支撑。

酸化处理提高玉米秸秆厌氧消化性能及其优化研究

为了提高木质纤维素的水解效率,酸化相的出料被用来提高玉米秸秆的厌氧产甲烷性能,文章利用单因素方法考察了原料负荷、酸化时间和接种量对挥发酸浓度(VFAs)的影响,采用响应面方法对玉米秸秆酸化相水解产酸构建二次回归模型进行优化,然后将酸化相出料接种厌氧污泥后进行产甲烷试验,比较酸化后玉米秸秆的甲烷产率,得出挥发性脂肪酸产率和甲烷产率关系的数学模型。结果表明,酸化时间为5 d,接种比为6,有机负荷为50 gTS·L^-1时产酸效果最优,VFAs产率为270.50 mg·g^-1 TS。3个因素对VFAs产率的影响依次为接种比>有机负荷>酸化时间。在最优酸化条件下甲烷相出料的系统稳定性好,甲烷产率为285.97 mL·g^-1 TS,比未处理组提高了81.52%,回归性分析结果表明甲烷产率与VFAs产率有较高的相关性。因此,水解酸化可以明显提高木质纤维素的降解效率和甲烷产率。

Effect on anaerobic digestion performance of corn stover by freezing–thawing with ammonia pretreatment

In order to enhance the biomethane production from corn stover, choosing effective pretreatment is one of the necessary steps before starting anaerobic digestion(AD).This study was aimed to analyze the effectiveness of freezing–thawing with ammonia pretreatment on substance degradation and AD performance of corn stover.Three ammonia concentrations(2%, 4%, and 6%) with two different moisture contents(50% and 70%) were used to pretreat the corn stover at two temperatures(-20 ℃ and 20 ℃).The result showed that an optimum pretreatment condition for corn stover was at the temperature of -20 ℃, moisture content of 70% and ammonia concentration of 2%.Under the optimum pretreatment condition, the maximum biomethane yield reached 261 ml·(g VS)^(-1), which was 41.08% higher than that of the untreated.Under different pretreatment conditions,the highest loss of lignin at -20 ℃ with 2% ammonia concentration was 63.36% compared with the untreated.The buffer capacity of AD system was also improved after the freezing–thawing with ammonia pretreatment.Therefore, the freezing–thawing with ammonia pretreatment can be used to improve AD performance for corn stover.This study provides further insight for exploring an efficient freezing–thawing with ammonia pretreatment strategy to enhance AD performance for the practical application.

Improving physicochemical characteristics and anaerobic digestion performance of rice straw via ammonia pretreatment at varying concentrations and moisture levels

Rice straw physicochemical characteristics and anaerobic digestion(AD)performance via ammonia pretreatment at varying ammonia concentrations(2%,4%,and 6%)and moisture contents(30%,50%,70%,and 90%)under a mild condition were investigated.The results showed that the ammonia pretreatment effectively damaged the rice straw structure,increased the soluble organic concentration,and improved rice straw hydrolysis and AD performance.After pretreatment,the ester bond and ether bond were ruptured in lignocellulose and the volatile fatty acids(VFAs)were within the range of 1457.81–1823.67 mg·L-1.In addition,ammonia pretreatment had high selectivity on lignin removal,resulting in a maximum lignin removal rate of 50.80%.The highest methane yield of rice straw was 250.34 ml·(g VS)-1 at a 4%ammonia concentration coupled with a 70%moisture content,which was 28.55%higher than that of the control.The result showed that ammonia pretreatment of rice straw is technically suitable to enhance AD performance for further application.

The relationships among sCOD, VFAs, microbial community, and biogas production during anaerobic digestion of rice straw pretreated with ammonia

This study investigated the effects of soluble chemical oxygen demand(s COD),volatile fatty acids(VFAs),and microbial community on biogas production in the process of rice straw(RS)anaerobic digestion(AD).The results showed that the s COD concentrations and VFA production appeared the same trend,which was inversely related with that of daily biogas production.The cumulative methane yield of RS was 194.9 ml·(g VS)^-1·^-1.The modified Gompertz model is the best fit for measured methane yields of RS in the three kinetic models of first-order kinetic,Cone and modified Gompertz.Firmicutes,Bacteroidetes,and Euryarchaeota were the dominant microbial phyla throughout AD process.At the genus level,the microorganisms mainly composed of Clostridium,Vadin,Terrisporobacter,Methanosaeta,Methanobacterium,and Methanosarcina.Proteiniphilum showed strong relationship with s COD and VFA production.Clostridium and Terrisporobacter displayed relationship with biogas production.Therefore,in order to improve the stability of the AD system,the parameter changes of VFAs,s COD,and biogas yield were monitored in the RS AD process.The study can provide theoretical basis for improving the efficiency of RS AD.

Potential in vitro antimicrobial efficacy of Holigarna arnottiana(Hook F)

Objective:To explore the in vitro antimicrobial potential of Holigarna arnottiana(H.arnottiana)against human and shrimp pathogenic bacteria and use GC-MS analysis to elucidate its antimicrobial principles.Methods:In the present study,organic extract of H.arnottiana was examined for in vitro antimicrobial potency against five clinical human pathogens,seven species of human type culture pathogens,six pathogenic Vibrio strains isolated from moribund tiger shrimp(Penaeus monodon)and seven type cultures(Microbial Type Culture Collection,MTCC)of prominent shrimp pathogens.Results:The extraction of H.arnottiana with ethyl acetate yielded bioactive crude extract that efficiently repressed the growth of all tested pathogens.Among the pathogens tested,shrimp pathogens were the most susceptible organisms while clinical pathogens were found to be a little resistant.The chemical constituents of the H.arnottiana were analysed by GC-MS which revealed the presence of major compounds such as 3,7.1 l,15-tetramethyl-2-hexadecen-l-ol(42.1%),l-lodo-2-methylundecane(34.4%)and squalene(11.1%)which might have a functional role in the chemical defence against microbial invasion.Conclusions:Based on the finding it could be inferred that H.arnottiana would be a reliable source for developing shrimp and human bio-therapeutics in future.

低强度水热法预处理玉米秸秆提高其厌氧消化产甲烷性能

为了提高玉米秸秆厌氧消化产甲烷性能,试验采用低强度水热法处理玉米秸秆,研究了预处理后玉米秸秆的性质变化以及产气性能。结果表明,低强度水热法能够有效提高玉米秸秆产气性能。在80℃,60%含水率和预处理24 h条件下,玉米秸秆产气量达到299.5 mL·g^(-1)VS,比对照组233.8 mL·g^(-1)VS提高了28.1%。在水热过程中添加秸秆干重的2%的NaOH后,50℃,60%含水率和预处理12 h条件下,玉米秸秆产气量达到444.1 mL·g^(-1)VS,比对照组提高了89.9%。因此,在水热预处理过程中添加NaOH能够有效提高玉米秸秆产气性能。

Comparative analysis of residence and diffusion times in rotating bed used for biogas upgrading

Rotating bed can be used in desorption operation of biogas upgrading as a new technology. For enough time to desorb, it is important to study the relationship between the residence time of liquid in rotating bed and the material diffusion time of liquid droplet in desorption process. By theoretical deduction, the exponential relation between residence time and liquid flow rate and rotational speed and kinematic viscosity is obtained. By analyzing the solution of nonlinear partial differential equation, the time law of material diffusion in the droplet is obtained. Moreover, by comparing the residence and diffusion times, the diffusion time can be within or out of residence time range, which has a direct relationship to rotational speed and liquid flow. By experiment, the comparison between residence and diffusion times is more realistic when the rotational speed is higher.

Impact of tree litter identity, litter diversity and habitat quality on litter decomposition rates in tropical moist evergreen forest

Background:Attempts to restore degraded highlands by tree planting are common in East Africa.However,up till now,little attention has been given to effects of tree species choice on litter decomposition and nutrient recycling.Method:In this study,three indigenous and two exotic tree species were selected for a litter decomposition study.The objective was to identify optimal tree species combinations and tree diversity levels for the restoration of degraded land via enhanced litter turnover.Litterbags were installed in June 2019 into potential restoration sites(disturbed natural forest and forest plantation)and compared to intact natural forest.The tested tree leaf litters included five monospecific litters,ten mixtures of three species and one mixture of five species.Standard green and rooibos tea were used for comparison.A total of 1,033 litters were retrieved for weight loss analysis after one,three,six,and twelve months of incubation.Results:The finding indicates a significant effect of both litter quality and litter diversity on litter decomposition.The nitrogen-fixing native tree Millettia ferruginea showed a comparable decomposition rate as the fast decom-posing green tea.The exotic conifer Cupressus lusitanica and the native recalcitrant Syzygium guineense have even a lower decomposition rate than the slowly decomposing rooibos tea.A significant correlation was observed be-tween litter mass loss and initial leaf litter chemical composition.Moreover,we found positive non-additive ef-fects for litter mixtures including nutrient-rich and negative non-additive effects for litter mixtures including poor leaf litters respectively.Conclusion:These findings suggest that both litter quality and litter diversity play an important role in decom-position processes and therefore in the restoration of degraded tropical moist evergreen forest.

Forest cover change and its driving forces in Fagita Lekoma District,Ethiopia

This study investigated forest cover change and the driving forces behind it in Fagita Lekoma District of Ethiopia that resulted in increased forest cover,which might be uncommon outside this case study area.The LULC change analysis was made from 2003 to 2017 based on Landsat images.Socioeconomic analysis was carried out to identify the major driving forces that resulted in LULC change.A questionnaire survey,focused group discussion,key informant interviews and field observation were employed to analyze the link between LULC change and the driving forces.The 15-year period(2003–2017)image analysis revealed that the coverage of forest lands,built-up areas and grassland has increased by 256%,100%and 96%,respectively,at the expense of cultivated lands and wetlands.The increased forest cover is due to the woodlots expansion of Acacia decurrens Willd,which are designed for sustainable livelihoods and a land revitalization strategy in the study area.Rapid population growth,an increasing demand for charcoal and subsequent market opportunities,preferred qualities of A.decurrens or black wattle to halt land degradation as well as to improve land productivity,have been identified as the major driving forces of forest cover change.Chi squared analysis revealed that:a comparative cash income from the sale of A.decurrens;a dependency on natural forests;the distance from the district administrative center;the size of the active labor force,and the area of land owned have significantly affected the cover change.The major forest cover change is due to the expansion of A.decurrens plantations that have socioeconomic and environmental implications to improve rural livelihoods and revitalize the land.Thus,the positive experiences identified in this study should be scaled-up and applied in other similar settings.

Characteristics of grain size distribution and the shear strength analysis of Chenjiaba long runout coseismic landslide

Study on the grain size distribution characteristics and the frictional strength behavior of the slide deposits are helpful to disclose the landslide runout process and understand the mechanism of a long runout landslide. We performed grain size distribution analysis on samples collected from Chenjiaba landslide induced by Wenchuan earthquake. The grain size distribution of samples from the landslide sections quantitatively depicts a gradual coarsening upward grading from shear zone to the top section. Then a multistage-multiphase ring shearing approach was used to determine a comparative shear strength behavior of samples from each landslide section. In this method, a sample was sheared continuously for large displacement and fast rate on different normal stress conditions. The multiphase shear mode with a maximum of 105 mm/min rate has allowed observing the qualitative change and patterns of the frictional resistance behaviors of soils under different normal stresses. The results of coefficient of friction values under multiphase shear mode have shown substantial post peak shear weakening behaviors after large shear displacement that can be narrated with long runout processes. The shear strength test results indicate that the shear zone samples have developed higher friction angle values compared to overlying section samples, on the last phase of shear process, which may be very important to understand the braking mechanism of a long runout landslide.

Bioactivity of essential oils of local plants against adult <i>Anopheles arabiensis</i>(Diptera: Culicidae) in Ethiopia

The adulticidal activities of essential oils of eleven plants namely Chenopodium ambrosioides, Eucalyptus citriodora, Eucalyptus globules, Lippia adoensis, Mentha spicata, Nigella sativa, Ocimum lamiifolium, Ocimum suave, Piper nigrum, Schinus molle and Thymus vulgaris were assessed against a laboratory colony of Anopheles arabiensis in Ethiopia. The Centers for Disease Control and Prevention (CDC) glass bottle bioassay was adopted to conduct bioefficacy tests. For each replicate, ten blood-unfed female An. arabiensis were exposed to different concentrations of essential oils coated in glass bottles, and mortality was recorded at intervals of 5 minutes for one hour to assess the mean percentage mortality and LC50 and LC90 values. The residual toxicity of six essential oils was also assessed by exposing adult An. arabiensis in nylon netting Barraud cages treated by oils. Of all the essential oils assessed for adulticidal activities, O. suave was found to be toxic at low concentration (LC50 = of 0.0014 ml% v/v;LC90 = 0.0027 ml% v/v). The next efficacious oil was that of T. vulgaris with LC50 and LC90 values of 0.0028 ml% v/v and 0.005 ml% v/v, respectively. The lowest activity was due to S. molle, E. globulus and P. nigrum. At a concentration of 0.05 ml% v/v, O. suave killed 100% of An. arabiensis within five minutes of exposure, while P. nigrum at the same duration caused similar rate of mortality at a concentration of 50 fold. Residual toxicity tests revealed O. suave to persist for 15 days, killing all mosquitoes in the first five days and 80% up to 10 days. The lowest residual activity was noted for E. citriodora which persisted only for 2 days. The essential oil O. suave acquired the highest level of toxicity at low concentration and within a short time. The efficacious nature of most plants has an implication for more screening of components of these plants with potential adulticides and develops for mosquito control.