Ferguson H.M.,Ifakara Health Institute |
Ferguson H.M.,University of Glasgow |
Dornhaus A.,University of Arizona |
Beeche A.,International Development Research Center |
And 7 more authors.
PLoS Medicine | Year: 2010
Existing front-line vector control measures, such as insecticide-treated nets and residual sprays, cannot break the transmission cycle of Plasmodium falciparum in the most intensely endemic parts of Africa and the Pacific. The goal of malaria eradication will require urgent strategic investment into understanding the ecology and evolution of the mosquito vectors that transmit malaria. Priority areas will include understanding aspects of the mosquito life cycle beyond the blood feeding processes which directly mediate malaria transmission. Global commitment to malaria eradication necessitates a corresponding longterm commitment to vector ecology.
Onyambus G.K.,Jomo Kenyatta University of Agriculture and Technology |
Maranga R.O.,Jomo Kenyatta University of Agriculture and Technology |
Gitonga L.M.,Jomo Kenyatta University of Agriculture and Technology |
Knapp M.,International Center for Insect Physiology and Ecology
Experimental and Applied Acarology | Year: 2011
The spider mite Tetranychus evansi has a broad range of host plants. Control of T. evansi has been a big challenge to tomato farmers due to its fast rate of reproduction, development of resistance to chemical pesticides and its ability to use weeds as alternative hosts when the tomato plants are not available. The aim of the current study was to determine the host plant acceptance and the relative contributions of trichomes in the control of the red spider mite by comparing the survival, development and oviposition rates of the red spider mite on eight tomato accessions. Leaflets from eight tomato varieties were assayed with the spider mites to determine the egg laying capacity and developmental time of the spider mites on the tomato accessions as well as the trichome densities. Densities of trichome types I, IV, V and VI varied among the tomato accessions. Variation in types I, IV and VI accounted for most of the variation in mite responses. The varieties with high densities of types IV and VI had the highest fecundity and mite development did not go beyond the larval stage. The developmental time varied significantly among the tomato accessions. The results indicated that the higher the density of trichome type I the lower the adult survival. The findings indicated possible resistance of some of the tested tomato accessions against T. evansi which is partially associated with trichomes types and density. © 2011 Springer Science+Business Media B.V.
Tamiru A.,International Center for Insect Physiology and Ecology |
Getu E.,Addis Ababa Institute of Technology |
Jembere B.,Addis Ababa Institute of Technology |
Bruce T.,Rothamsted Center for Sustainable Pest and Disease Management
Bulletin of Entomological Research | Year: 2012
The spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), is one of the most important insect pests attacking maize and sorghum in Ethiopia. Recent studies have indicated that the pest is spreading to new locations where it was not reported before. In the current study, laboratory investigations were carried out to determine the combined effect of different levels of relative humidity and temperature regimes on the development and fecundity of C. partellus, as these physical factors are known to play an important role in the life cycle of insects and adaptability to local climate. Developmental time, longevity, potential fecundity and realized fecundity of C. partellus were measured under controlled conditions. Three temperature regimes (22°C, 26°C and 30°C) and three relative humidity levels (40%, 60% and 80%) were tested. It was found that temperature, relative humidity (RH) and their interaction significantly affected the developmental time, adult longevity, potential fecundity and realized fecundity of the pest. Developmental time was inversely related to temperature. Mean duration of C. partellus life cycle was 70.2 days at 22°C and 80% RH, whereas it took only 26.5 days to complete its life cycle at 30°C and 40% RH. Male and female longevity were similar in most cases. The adult life span ranged between 6.9-11.1 days at 22°C and 3.1-7.2 days at 30°C for different levels of relative humidity. The most suitable conditions for C. partellus development and fecundity were 26-30°C temperatures regimes and 60-80% RH levels. © Copyright Cambridge University Press 2011.
Fischer A.,International Center for Insect Physiology and Ecology |
Fischer A.,Kenya International Livestock Research Institute |
Shapiro B.,Pennsylvania State University |
Muriuki C.,Kenya International Livestock Research Institute |
And 6 more authors.
PLoS ONE | Year: 2012
The 'Mycoplasma mycoides cluster' comprises the ruminant pathogens Mycoplasma mycoides subsp. mycoides the causative agent of contagious bovine pleuropneumonia (CBPP), Mycoplasma capricolum subsp. capripneumoniae the agent of contagious caprine pleuropneumonia (CCPP), Mycoplasma capricolum subsp. capricolum, Mycoplasma leachii and Mycoplasma mycoides subsp. capri. CBPP and CCPP are major livestock diseases and impact the agricultural sector especially in developing countries through reduced food-supply and international trade restrictions. In addition, these diseases are a threat to disease-free countries. We used a multilocus sequence typing (MLST) approach to gain insights into the demographic history of and phylogenetic relationships among the members of the 'M. mycoides cluster'. We collected partial sequences from seven housekeeping genes representing a total of 3,816 base pairs from 118 strains within this cluster, and five strains isolated from wild Caprinae. Strikingly, the origin of the 'M. mycoides cluster' dates to about 10,000 years ago, suggesting that the establishment and spread of the cluster coincided with livestock domestication. In addition, we show that hybridization and recombination may be important factors in the evolutionary history of the cluster. © 2012 Fischer et al.
Muga G.O.,University of Nairobi |
Onyango-Ouma W.,University of Nairobi |
Sang R.,International Center for Insect Physiology and Ecology |
Affognon H.,International Center for Insect Physiology and Ecology
American Journal of Tropical Medicine and Hygiene | Year: 2015
Health researchers have advocated for a cross-disciplinary approach to the study and prevention of infectious zoonotic diseases, such as Rift Valley Fever. It is believed that this approach can help bring out the social determinants and effects of the zoonotic diseases for the design of appropriate interventions and public health policy. A comprehensive literature review using a systematic search strategy was undertaken to explore the sociocultural and economic factors that influence the transmission and spread of Rift Valley Fever. Although the findings reveal a paucity of social research on Rift Valley Fever, they suggest that livestock sacrificial rituals, food preparation and consumption practices, gender roles, and inadequate resource base for public institutions are the key factors that influence the transmission. It is concluded that there is need for cross-disciplinary studies to increase the understanding of Rift Valley Fever and facilitate appropriate and timely response and mitigation measures. Copyright © 2015 by The American Society of Tropical Medicine and Hygiene.
Fand B.B.,Indian Council of Agricultural Research |
Tonnang H.E.Z.,International Center for Insect Physiology and Ecology |
Kumar M.,Indian Council of Agricultural Research |
Kamble A.L.,Indian Council of Agricultural Research |
Bal S.K.,Indian Council of Agricultural Research
Crop Protection | Year: 2014
The temperature-dependent population growth potential of Phenacoccus solenopsis Tinsley, a highly polyphagous and invasive mealybug species, was studied on sprouted potatoes under laboratory conditions at six constant temperatures (15-40°C). Several non-linear equations were fitted to the obtained data to model temperature-dependent population growth and species life history. The established equations for each life age/stage of the species were compiled to obtain an overall temperature-dependent phenology model. The life table parameters of P.solenopsis were estimated using stochastic simulation centred on a rate summation and cohort up-dating approach. The theoretical lower development threshold temperatures estimated using linear regressions applied to mean development rates were 11.2, 8.9, 9.8 and 12.7°C, and the thermal constants for development were 93.7, 129.8, 97.1 and 100.0 degree days (DD) for nymph 1, nymph 2, nymph 3 and male pupa stages, respectively. The developed phenology model predicted temperatures between 25 and 35°C as the favourable range for P.solenopsis development, survival and reproduction. P.solenopsis population attained a maximum net reproductive rate (107-108 females/female/generation) and total fecundity (216.6-226.5 individuals/female/generation) at temperatures between 25 and 30°C. Mean length of generations decreased from 75.6 days at 15°C to 21 days at 40°C. The maximum finite rate of increase (1.12-1.16 females/female/day) and shortest doubling time (4.3-6.1 days) were also observed at temperatures between 25 and 35°C. The simulation of phenology model at fluctuating temperatures indicated that P.solenopsis populations might potentially increase with a finite rate of 1.06 females/female/day with an average generation time of 58.7 days and a doubling time of 12.1 days. The obtained life table parameters were reasonably similar when compared with literature data. The present model can be simulated spatially for estimating the pest risk and undertaking agro-ecoregion specific pest management strategies. © 2013 Elsevier Ltd.
Birkett M.A.,Rothamsted Research |
Hassanali A.,International Center for Insect Physiology and Ecology |
Hassanali A.,Kenyatta University |
Hoglund S.,Swedish University of Agricultural Sciences |
And 2 more authors.
Phytochemistry | Year: 2011
The repellent activity of the essential oil of the catmint plant, Nepeta cataria (Lamiaceae), and the main iridoid compounds (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone, was assessed against (i) major Afro-tropical pathogen vector mosquitoes, i.e. The malaria mosquito, Anopheles gambiae s.s. and the Southern house mosquito, Culex quinquefasciatus, using a World Health Organisation (WHO)-approved topical application bioassay (ii) the brown ear tick, Rhipicephalus appendiculatus, using a climbing repellency assay, and (iii) the red poultry mite, Dermanyssus gallinae, using field trapping experiments. Gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS) analysis of two N. cataria chemotypes (A and B) used in the repellency assays showed that (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone were present in different proportions, with one of the oils (from chemotype A) being dominated by the (4aS,7S,7aR) isomer (91.95% by GC), and the other oil (from chemotype B) containing the two (4aS,7S,7aR) and (4aS,7S,7aS) isomers in 16.98% and 69.83% (by GC), respectively. The sesquiterpene hydrocarbon (E)-(1R,9S)-caryophyllene was identified as the only other major component in the oils (8.05% and 13.19% by GC, respectively). Using the topical application bioassay, the oils showed high repellent activity (chemotype A RD 50 = 0.081 mg cm -2 and chemotype B RD 50 = 0.091 mg cm -2) for An. gambiae comparable with the synthetic repellent DEET (RD 50 = 0.12 mg cm -2), whilst for Cx. quinquefasciatus, lower repellent activity was recorded (chemotype A RD 50 = 0.34 mg cm -2 and chemotype B RD 50 = 0.074 mg cm -2). Further repellency testing against An. gambiae using the purified (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone isomers revealed overall lower repellent activity, compared to the chemotype A and B oils. Testing of binary mixtures of the (4aS,7S,7aR) and (4aS,7S,7aS) isomers across a range of ratios, but all at the same overall dose (0.1 mg), revealed not only a synergistic effect between the two, but also a surprising ratio-dependent effect, with lower activity for the pure isomers and equivalent or near-equivalent mixtures, but higher activity for non-equivalent ratios. Furthermore, a binary mixture of (4aS,7S,7aR) and (4aS,7S,7aS) isomers, in a ratio equivalent to that found in chemotype B oil, was less repellent than the oil itself, when tested at two doses equivalent to 0.1 and 0.01 mg chemotype B oil. The three-component blend including (E)-(1R,9S)-caryophyllene at the level found in chemotype B oil had the same activity as chemotype B oil. In a tick climbing repellency assay using R. appendiculatus, the oils showed high repellent activity comparable with data for other repellent essential oils (chemotype A RD 50 = 0.005 mg and chemotype B RD 50 = 0.0012 mg). In field trapping assays with D. gallinae, addition of the chemotype A and B oils, and a combination of the two, to traps pre-conditioned with D. gallinae, all resulted in a significant reduction of D. gallinae trap capture. In summary, these data suggest that although the nepetalactone isomers have the potential to be used in human and livestock protection against major pathogen vectors, intact, i.e. unfractionated, Nepeta spp. oils offer potentially greater protection, due to the presence of both nepetalactone isomers and other components such as (E)-(1R,9S)-caryophyllene. © 2010 Elsevier Ltd. All rights reserved.
Smith D.A.S.,Eton College |
Gordon I.J.,International Center for Insect Physiology and Ecology |
Allen J.A.,University of Southampton
Ecological Entomology | Year: 2010
1. The aim of this paper is to investigate mechanisms of reinforcement between two semi-isolated semispecies of the African savannah butterfly Danaus chrysippus. The biogeography of colour genes suggests that four semispecies evolved in once isolated refugia. They expanded their ranges in response to Holocene climatic changes to form a hybrid zone in central-east Africa. 2. Danaus chrysippus is a superspecies within which cycles of alternating cladogenesis and reticulation among semispecies have probably operated over some 4 Myr. Semispecies are inter-fertile but show Haldane rule effects in crosses; gene flow is massive but subject to isolation by distance. 3. One semispecies shows linkage disequilibrium, vis- à-vis others, for haplotype, karyotype (W-linkage of colour genes which function as reproductive isolating barriers) and all-female broods caused by a male-killer endosymbiont. Introgression of colour genes between D. c. dorippus and D. c. chrysippus is constrained by sex linkage and male killing. 4. Reinforcement in hybrid zones comprises allochronic migration, assortative mating, (assumed) sex chromosome incompatibility and sex-ratio distortion. Gene introgression from D. c. dorippus to other semispecies is maintained by a high frequency of backcrossing between hybrid males and females of the latter. © 2010 The Royal Entomological Society.
Metcalfe K.,University of Exeter |
Metcalfe K.,University of Kent |
Ffrench-Constant R.,University of Exeter |
Gordon I.,International Center for Insect Physiology and Ecology
ORYX | Year: 2010
Sacred sites, particularly in forests, often form unofficial protected areas because their biodiversity is preserved and protected by the local people looking after the sites. Here, we survey the biodiversity of the Three Sisters Cave complex, a sacred site or kaya in a fragment of East African coastal forest in south-east Kenya. We show that, despite the tiny size of this non-gazetted forest reserve, it contains many of the threatened species of both flora (121 species) and fauna (46 species) representative of Kenya's coastal forest. Following the overexploitation and widespread destruction of coastal rainforests in Kenya, such sacred sites represent key biodiversity hotspots as well as forest islands in the now largely deforested coastal plain. Other non-gazetted forest sacred sites may represent undocumented sources of biodiversity that may contribute towards conservation of this threatened coastal habitat. © 2009 Fauna & Flora International.
Gordon I.J.,International Center for Insect Physiology and Ecology |
Ireri P.,International Center for Insect Physiology and Ecology |
Ireri P.,Kenyatta University |
Smith D.A.S.,International Center for Insect Physiology and Ecology |
Smith D.A.S.,Eton College
Biological Journal of the Linnean Society | Year: 2014
Danaus chrysippus (L.) in Africa comprises four substantially isolated semispecies that are migratory and hybridize on a seasonal basis throughout the eastern and central part of the continent. In the hybrid zone (but not elsewhere), the butterfly is commonly host to a male killing endosymbiotic bacterium, Spiroplasma sp., which principally infects one semispecies, Danaus chrysippus chrysippus in Kenya. A W-autosome mutation, inherited strictly matrilinearly, links B and C colour gene loci, which have thus gained sex-linkage in chrysippus. We have monitored variation in sex ratio and genotype at the A and C colour gene loci for two extended periods of 18 months (2004-5) and 12 months (2009-10) in adults reared from wild eggs laid on trap plants in Kasarani, near Nairobi, Kenya. Additionally, in 2009-10, all surviving adult butterflies were screened for Spiroplasma infection. The hybridizing Kasarani population is highly atypical in three respects, and has apparently been so for some 30 years: first, the sex ratio is permanently female-biased (as expected), although subject to seasonal fluctuation, being lowest (male/female) when D.c. chrysippus (cc) peaks and highest when Danaus chrysippus dorippus (CC) predominates; second, the population is invariably dominated by Cc heterozygotes of both sexes but especially females; and third, cc males are always scarce because they are systematically eliminated by male killing, whereas the CC genotype is male-biased. It is this imbalance of sex versus genotype that determines the massive departure from Hardy-Weinberg equilibrium in the population, in part because cc females have little choice but to pair with C- males. We suggest that: first, Cc hybrids of both sexes fail to disperse in the company of either parental semispecies; second, Spiroplasma positive females carrying the W-autosome mutation have a selective advantage over females that lack the translocation; third, the endoparasite and the translocation create a 'magic trait' linkage group that underlies hologenomic reproductive isolation between two emerging species, D.c. chrysippus and D.c. dorippus; and, fourth, that the predominance of males in dorippus suggests that individuals must be protected by a male-killing suppressor gene. By contrast to the C locus, Aa heterozygotes are in substantial and permanent deficit, suggesting either assortative mating between AA (chrysippus and dorippus) and aa (Danaus chrysippus alcippus), or heterozygote unfitness, or both. © 2013 The Linnean Society of London.