Browsing by Author "Tekie, Habte(PhD)"

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    Abundance, Distribution and Insecticide Resistance of Anopheles Mosquitoes (Diptera: Culicidae) and Malaria Transmission Intensity in Relation to Agro-ecology in Sekoru District, Southwestern Ethiopia
    (Addis Ababa University, 2017-06) Ejeta, Desta; Tekie, Habte(PhD)
    Malaria is a leading cause of morbidity and mortality in several sub-Saharan African countries. Environmental/ecological changes due to anthropogenic activities are among the determinant factors for malaria transmission. Agricultural practices are among anthropogenic activities that contribute to malaria incidence and transmission. Understanding association of ecological changes due to anthropogenic activities on mosquito species composition, abundance, distribution, dynamics, insecticide resistance and malaria transmission intensity is important to plan and implement effective vector control intervention strategies. Thus, the aim of this study was to investigate species composition, abundance, distribution and infectious rate of Anopheles mosquitoes and their knockdown resistance (kdr) status in relation to agricultural practices. A longitudinal entomological study was conducted from January to December 2015 in Sekoru District, southwestern Ethiopia. Anopheles mosquito larvae and adults were collected using different methods from villages with different agro-ecology. The mosquitoes were identified to species level using standard keys. Molecular identification of Anopheles gambiae complex and detection of knockdown insecticide resistance (kdr) was conducted using species-specific PCR and allele specific PCR techniques. Moreover, Plasmodium circumsporozoite protein was detected for both Plasmodium falciparum and P. vivax using Enzyme-linked Immunosorbent Assay (ELISA). Eight Anopheles mosquito species (Anophelesarabiensis,An. demeilloni, An. squamosus, An. garnhami, An. christyi, An. pretoriensis, An. longipalpis and An. marshallii) were identified, of which An. arabiensis was the predominant species (46.2%; n=715). The highest number of Anopheles mosquitoes (66%; n=1019) was collected from the irrigated village. The xvi infection rate of An. arabiensis was higher in the irrigated village (10.8 infective bites/person/month) as compared to rain fed agriculture practicing village (5.99 infective bites/person/month) and human settlement village (zero infective bite). Anopheles gambiaes.l. larvae were the predominant (57.4%) larval species identified. The highest larval density (2.12 larvae/dip) was recorded from the irrigated village. Only West African kdr mutation (L1014F) was detected with an allelic frequency of 83.88%. The distribution and frequency of kdr allele were significantly associated with study villages (X2=133.85, df=2, P <0.001). The kdr allele frequency was 95%in the irrigated village, 78.87%in village with rain fed agriculture, and 3.89% in the human settlement village. In conclusion, Anopheles mosquito abundance, distribution, infection rate and insecticide resistance were significantly associated with agro-ecology. Agro-ecological practices need to be considered in the management of Anopheles vectors of malaria. Keywords: Anopheles mosquitoes, Agro-ecology, Insecticide resistance, Irrigation, Larval habitats, Malaria, Sekoru District
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    Development of Lures and Local Traps and Their Application for Field Management of Pachnoda Interrupta (Olivier) (Coleoptera: Scarabaeidae) in Sorghum in Ethiopia
    (Addis Ababa University, 2014-06) Atenafu, Getnet; Tekie, Habte(PhD)
    Sorghum (Sorghum bicolor (L.) is one of the major nutritious cereals in Africa widely cultivated in eastern regions including Ethiopia. Sorghum chafer Pachnoda interrupta (Coleoptera: Scarabaeidae) is a polyphagous insect whose adults are serious pests of sorghum (Sorghum bioclor) in the fields. The damage by the sorghum chafer during the milky stage of the seed contributed to low production of sorghum in many regions of Ethiopia. The adult beetle uses visual and olfactory cues (specific blends of compounds) in their search for food sources, mate selection, and oviposition sites. The present study focused on evaluation of the attractiveness of lures and catch performance of locally designed cheap traps in P. interrupta field management strategies in naturally infested regions of northeastern Ethiopia. Optimal and constant release rates of previously identified volatile compounds phenylacetaldehyde, 2,3-butanediol, methyl salicylate, eugenol, isoamyl acetate were determined from dispensers in the laboratory. Field experiments testing the efficacy of different single- and multi-component baits and different types of traps were conducted in close collaboration with farmers. Various blends/single compounds and the natural attractant banana fruit were tested in both the mating season in July and the feeding season for newly emerged adults in October. Different locally affordable trap designs were evaluated and compared with the previously proven efficacy of a commercial Japanese beetle trap. In addition, novel attractant blends were also tested in the field. These blends were synthetic replicas of odors from overripe banana fruit and fermentation volatiles identified by solid-phase micro extraction combined with gas chromatography-mass spectrometry analysis in the laboratory. After a two-choice behavioral bioassay, the promising component blends tested in the laboratory were evaluated in the mating and feeding seasons in 2013. The iv results of the beetle catch revealed that traps baited with the multiple-dispenser blend of the five compounds, and the mixture of the five compounds formulated in one dispenser, were the best lures. It was also demonstrated that the longevity of the lure in the field coincided with the flying period of P. interrupta during the mating and feeding seasons. Among the field tested trap designs, four locally affordable cheap traps were found to be as efficient as the commercially produced Japanese beetle trap in trapping P. interrupta . Among the blends from volatile chemicals released from overripe banana and fermentation volatiles, a blend of eleven compounds was proven effective in behavioral responses both in the laboratory choice bioassay and the P. interrupta trapping in the field. This indicates that the compounds identified are behaviorally relevant and can be used as potential candidates for further field tests. In conclusion, the work has produced both efficient and cheap local traps baited with best attractant compounds blend.
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    Ecology and Distribution Pattern of Anopheles Mosquitoes and Malaria Transmission in Ghibe River Basin, Southwestern Ethiopia
    (Addis Ababa University, 2017-05) Getachew, Dejene; Tekie, Habte(PhD)
    Malaria is a leading public health problem in Ethiopia. Though malaria prevalence showed high reduction in many parts of the country, its transmission is likely to be more and more focal with some areas still having substantial risk of malaria. There was paucity of information on the malaria vectors and malaria transmission pattern in the study area. So that, the objective of this study was to investigate the species composition and monthly distribution of Anopheles mosquitoes, their blood meal sources, sporozoite infection rates and level of insecticide susceptibility in the Ghibe River basin, southwestern Ethiopia. Study on Anopheles mosquitoes distribution and malaria transmission was conducted in two study sites. Longitudinal larval and adult Anopheles mosquitoes collections were carried out monthly from November 2014 to October 2016. Late instar larvae were morphologically identified. Habitats containing Anopheles larvae were identified and their environmental variables were recorded. Adult Anopheles mosquitoes were collected from selected houses near to or far from the river with CDC light traps, pyrethrum spray catches, pit shelter and mouth aspirator. Adult female Anopheles mosquitoes were morphologically identified and their parity rate, blood meal sources and malaria infections were analysed using Enzyme-linked immunosorbent assay (ELISA). Anpheles larvae and pupae were collected from their breeding sites, allowed to emerge into adult, morphologically identified, and exposed to insecticides using WHO discriminating concentrations. Awarness of the communities towards malaria prevention and control were also investigated. Multiple regression analysis was used to identify the most predictor larval habitat environmental variables with the occurrence of Anopheles larvae. Human blood index (HBI) was calculated as the ratio of blood-fed mosquitoes that had fed on human to the total tested expressed in percent. Sprorozoite rate was expressed as the proportion of mosquitoes with xvii sprorozoite to the number of mosquitoes tested. Insecticide susceptibility was determined based on mean mortality of the four replicates after 24 hour exposure. In total, 9,277 larvae of Anopheles mosquitoes were sampled. Mean Anopheles larval densities were higher in the pools in drying river beds (35.2 ± 7.9 larvae/dip), borrow pits (14.3 ± 8.6 larvae/dip) and pools at river edges (13.0 ± 2.1 larvae/dip) in Darge, and in borrow pits (11.2 ± 6.3 larvae/dip) and rain pools (11.9 ± 5.1 larvae/dip) in Ghibe. From totally identified Anopheles mosquitoes larvae more than 95% of them were An. gambiae s.l. Temperature at the time of collection (p = 0.03) and emergent vegetation (p = 0.003) were the best predictors of Anopheles larval density. In total, 2,669 adult female Anopheles mosquitoes were collected and morphologically identified. In Ghibe, mean density of An. gambiae s.l. (=An. arabiensis) using CDC light trap was higher outdoors (1.8/CDC light trap/night) as compared to indoors (0.7/CDC light trap/night) but in Darge 0.125/CDC light trap/night indoor and 0.07/CDC light trap/night outdoor. In Ghibe, the HBI for An. arabiensis was 58.0% from CDC light trap collections indoors and 16.0% outdoors but in Darge it was 14.0% indoors and 13.0% outdoors. Overall sporozoite rates of An. arabiensis for P. vivax and P. falciparum were 0.06% each. Anopheles arabiensis developed insecticide resistance to all the insecticide classes tested with, except fenitrotion. Study on awareness showed, there was knowledge gap in the communities towards the way malaria is transmitted. In conclusion, An. arabiensis is the predominant species of malaria vector in the study area. Malaria prevalence and vectors infection rates were very low. However, the outdoor abundance and the development of resistance to the major insecticides need to look for alternative control options in addition to LLINs and IRS. Keywords: Anopheles gambiae s.l., CDC light trap, Darge, Ghibe, human blood index, larval habitat, sporozoite rate.
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    Entomological Impact of Combined and Separate Use of Indoor Residual Spraying and Long-Lasting Insecticidal Nets for Malaria Prevention in Adami Tullu District, South-Central Ethiopia
    (Addis Ababa University, 2016-06) Kenea, Oljira; Tekie, Habte(PhD)
    Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are the key frontline malaria prevention interventions in Ethiopia. Both target Anopheles arabiensis, the sole primary malaria vector. Universal coverage of both interventions has been promoted and there is a growing demand in combination of interventions for malaria control and elimination. However, available evidence is contradictory wether the combined intervention is better than either IRS or LLINs alone. To investigate whether IRS and LLINs combination provides added protective impact on An. arabiensis compared to either IRS or LLINs alone, a cluster randomized controlled trial was carried out in Adami Tullu district, south-central Ethiopia. Villages were randomly allocated to four study arms: IRS+LLINs, IRS, LLINs, and control. All households in the IRS+LLINs and LLINs arms were provided with LLINs (PermaNet 2.0) free of charge. Households in the IRS+LLINs and IRS arms were applied with propoxur before the main malaria transmission season in 2014 and 2015. Adult mosquitoes were collected in randomly selected villages in each arm using CDC light trap catch (LTC) set close to a sleeping person, pyrethrum spray catch (PSC), and artificial pit shelter (PIT), for measuring host-seeking density (HSD), indoor resting density (IRD), and outdoor resting density (ORD) of the anophelines. Human landing catch (HLC) was performed in selected villages to monitor the impact of the interventions on local mosquito biting behaviours (biting location, time and host preference). Collected anophelines were identified to species by use of standard morphological keys and additional use of molecular methods to separate sibling species of the An. gambiae complex. Enzyme-linked immunosorbent assay (ELISA) was used to detect malaria infections in mosquitoes and the sources of mosquito blood meals. Mean densities were compared using incidence rate ratio (IRR) calculated by negative binomial regression. Parity rate (percentage of xxii parous females) was also determined by ovarial dissection. Human blood index (HBI) was expressed as the proportion of mosquitoes with human blood divided by the total number of blood-fed mosquitoes tested. A total of 1786 female anophelines of four species (An. arabiensis, An. pharoensis, An. ziemanni and An. funestus s.l.) were collected over two transmission seasons during the intervention period (2014-2015). Anopheles numbers were highest in the control arm (41.3% of total) followed by LLINs (25.4%), IRS (18.0%), and IRS+LLINs (15.8%). In most of the vector parameters estimated, the impact of IRS and LLINs combined and separate interventions were significantly higher in communities that recieved the interventions (in experimental groups) compared with untreated communities (control group). The mean HSD of An. arabiensis in the IRS+LLINs arm was similar to the IRS arm (0.03 vs. 0.03/ house/LTC/night) but lower than the LLINs arm (0.03 vs. 0.10/house/LTC/night, p=0.07) and so was the difference in IRD and ORD between the IRS+LLINs compared to the IRS arm. However, both IRD and ORD of An. arabiensis were higher in LLINs compared to IRS+LLINs (p < 0.001 for indoors). Parity rate of An. arabiensis were similar among the intervention arms. None of the 1786 samples of four species tested by ELISA was positive for P. falciparum and P. vivax CSP infection in all of the study arms. Anopheles arabiensis preferred mainly bovine and human hosts for blood meal sources with high HBI in the LLIN alone. Indoor resting habit of An. arabiensis was less impacted by LLINs alone intervention compared to IRS + LLINs or IRS alone. In conclusion, the IRS+LLINs and the IRS alone each was similarly most effective against An. arabiensis as compared to the LLINs alone. The IRS+LLINs provided added impact on An. arabiensis compared to LLINs alone. The LLINs alone had poor impact on densities and human biting rates of An. arabiensis in this study setting.
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    Repellence and Larvicidal Efficacy of Some Selected Plant Oils and Extracts Against Adult Anopheles Arabiensis (Patton) and Larvae of Aedes Aegypti (Linnaeous) (Culicidae: Diptera) Under Laboratory Conditions
    (Addis Ababa University, 2017-05) Berhe, Melete; Tekie, Habte(PhD)
    Insecticides and repellent chemicals are among the major tools of controlling disease vectors. In this study, the knock-down, adultcidal and repellence activities of crude ethyl alcohol extracts of the leaves of spearmint (Mentha spicata) and rosemary (Rosemarinus officinalis) were tested against the larval and adult stages of malaria vector Anopheles arabiensis. The larvacidal effect of seed powder of neem (Azadrichiata indica) was evaluated under laboratory condition against the fourth instar larvae of Aedes aegypti. Extracts of M. spicata and R. officinalis caused moderate knock-down and mortality activity after 1 h and 24 h of exposure, respectively, but higher repellency effects at 1 h. M. spicata caused average percent knock-down, mortality and repellency effects ranging from 8 to 32%, 0 to 28% and 95 to 97%, respectively at six different concentrations used. Whilst R. officinalis induced between 0 and 36%, 0 and 32% and 63 and 74% mean percent knock-down, mortality and repellency effects, in that order. Adult mosquito mortality increased with increasing concentration of the extracts but there was no significant variation among all concentrations of extracts of both plants used (P>0.05), except 0.1 and 1 percent concentrations which were significant (P<0.05). M. spicata showed much superior average percent repellency. No significant variation was shown on repellency effect among the different concentrations (P>0.05). A significantly higher repellency effect was observed in the different concentrations of extracts of R. officinalis (P<0.05) as compared to the control. The mean percent larval mortality against A. agypti caused by seed powder of A. indica at concentration of 5g/250ml was 58% at 24 h and 81% at 48 h. There was no significant difference in larval mortality between 24 and 48 h of exposure (P>0.05). In conclusion, M. spicata and R. officinalis can’t be considered as sources of potential adulticides based on WHO standards as their extracts failed to produce >60% mortality but can be regarded as potential sources of viii repellents against An. arabiensis. Besides, A. indica could be a potential source of larvicides against the larvae of Ae. aegypti. Keywords: Adulticides, Anopheles arabiesnis, Aedes agepti, Larvicides, Plant extracts
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    Study on the Electrophysiological and Behavioral Responses of Bactrocera dorsalis, B. zonata, B. cucurbitae, B. oleae and C. capitata to protein lures
    (Addis Ababa University, 2015-03) T/ Mariam, Haimanot; Tekie, Habte(PhD)
    The family of Tephritidae are economically important agricultural pests. Among them Bactrocera is the most devastating genus known that damages fruits and lads to economic losses. To control these pests female targeted attractants are essential. Previous work has shown that females of fruit flies are attracted to protein baits. The objective of the present work was to identify volatiles from a mixture of five different lures (brewery yeast, baker’s yeast, torula yeast, GF-120 and anamed) that elicit antennal response of our experimental species. The experiment was carried out on five species of fruit flies (Ceratitis capitata, Bactrocera dorsalis, Bactrocera zonata, Bactrocera cucurbitae and on Bactrocera oleae). We scored the similarity and dissimilarity of these species in the antennal response to volatiles from mixed fermentation and protein lures using gas chromatography electorantennography detection (GC-EAD). Nine compounds were identified that elicited an antennal response. Of these nine compounds in C. capitata, seven compounds in B. zonata, six compounds in B. dorsalis and B. cucurbitae and two compounds in B. oleae gave an antennal response. The active compounds were identified using gas chromatography coupled to mass spectrometry (GC-MS). In olfactometer assay flies were attracted to brewery yeast and a mixture of fermentation and protein lures made. The findings are discussed in the potential of developing a bait that attracts these fruit flies. Key words: protein baits, antennal response, GC-EAD, GC-MS, Bactrocera and Olfactometer