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Liquid flow along a charged interface is commonly described by classical continuum theory, which represents the electric double layer by uniformly distributed point charges. The electrophoretic mobility of hydrophobic nanodroplets in water doubles in magnitude when the pH is varied from neutral to mildly basic (pH 7 → 11). Classical continuum theory predicts that this increase in mobility is due to an increased surface charge. Here, by combining all-optical measurements of surface charge and molecular structure, as well as electronic structure calculations, we show that surface charge and molecular structure at the nanodroplet surface are identical at neutral and mildly basic pH. We propose that the force that propels the droplets originates from two factors: Negative charge on the droplet surface due to charge transfer from and within water, and anisotropic gradients in the fluctuating polarization induced by the electric field. Both charge density fluctuations couple with the external electric field, and lead to droplet flow. Replacing chloride by hydroxide doubles both the charge conductivity via the Grotthuss mechanism, and the droplet mobility. This general mechanism deeply impacts a plethora of processes in biology, chemistry, and nanotechnology and provides an explanation of how pH influences hydrodynamic phenomena and the limitations of classical continuum theory currently used to rationalize these effects.

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The prediction of dipeptide assembly into crystals or gels is challenging. This work reveals the diverging conformational landscape that guides self-organization towards different outcomes. In silico and experimental data enabled deciphering of the electronic circular dichroism (ECD) spectra of self-assembling dipeptides to reveal folded or extended conformers as key players.

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We present insights into the nature of structural heterogeneities in liquid water by characterizing the empty space within the hydrogen bond network. Using molecular dynamics simulations, we show that density fluctuations create regions of empty space characterized by a diverse morphology - from spherical to fractal-like voids. These voids allow for the identification of low and high density patches of the liquid, encompassing short (0.3-0.5 nm) as well as long (1-2 nm) length-scales. In addition, we show that the formation of these patches is coupled to collective fluctuations involving the topology of hydrogen-bonded rings of water molecules. In particular, water molecules in the high density patches tend to be slightly more tetrahedral - which is consistent with the predictions of the hydrophobic effect.

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In this work, we examine the importance of nuclear quantum effects on capturing the line broadening and vibronic structure of optical spectra. We determine the absorption spectra of three aromatic molecules indole, pyridine, and benzene using time dependent density functional theory with several molecular dynamics sampling protocols: force-field based empirical potentials, ab initio simulations, and finally path-integrals for the inclusion of nuclear quantum effects. We show that the absorption spectrum for all these chromophores are similarly broadened in the presence of nuclear quantum effects regardless of the presence of hydrogen bond donor or acceptor groups. We also show that simulations incorporating nuclear quantum effects are able to reproduce the heterogeneous broadening of the absorption spectra even with empirical force fields. The spectral broadening associated with nuclear quantum effects can be accounted for by the broadened distribution of chromophore size as revealed by a particle in the box model. We also highlight the role that nuclear quantum effects have on the underlying electronic structure of aromatic molecules as probed by various electrostatic properties.

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Previously, essential oil of Conyza newii (Asterale: Asteracea, Oliv. & Hiern) growing in the northern part of West Pokot (35°E, 1°N) of Kenya was shown to be highly repellent [RD50 = 8.9 × 10(-5) mg/cm(2) , 95% confidence interval (CL)] to Anopheles gambiae s.s. Fumigant toxicity of the oil to the mosquito was also demonstrated. The major constituents of the oil were found to be monoterpenoids, including (S)-(-)-perillyl alcohol, (S)-(-)-perillaldehyde, geraniol, (R)-(+)-limonene, trans-ß-ocimene and 1,8-cineol. In this study, the chemical composition and repellency of essential oils of the plant seedlings collected from West Pokot (35°E, 1°N) and propagated in seven different geographical regions of Kenya [West Pokot (35°E, 1°N), Kilome (37°E, 1°S), Naivasha (36°E, 0°), Webuye (34°E, 1°N), Nyakach (34°E, 0°), Kericho (35°E, 0°) and Nairobi (36°E, 1°S)] were compared. There were significant variations (P < 0.01, 95% CL) in the relative proportions of the six constituents and this was reflected in the repellency of the essential oils (P < 0.01, 95% CL). Higher repellency of the oil was associated with greater proportions of (S)-(-) perillyl alcohol, (S)-(-)-perillaldehyde and geraniol, and lower repellency was associated with an increased proportion of (R)-(+)-limonene. The results suggest significant epigenetic (chemotypic) variations in the repellency and composition of C. newii essential oils growing in different regions of Kenya.

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Counter flow geometry (CFG) traps (American Biophysics) baited with foot odours (adsorbed overnight on a combination of a nylon and a cotton socks) from 4 groups of 4 male volunteers were initially used in a screen-house to compare and grade the attractiveness of Anopheles gambiae Giles sensu stricto to these odours. Ten individuals were then selected from the 4 groups for further grading in which mosquito attractiveness to odours adsorbed on socks worn by each of the individuals was compared against a control (clean, un-worn cotton and nylon socks). A gradation of attractiveness was found, with the most attractive foot odour catching 8-fold more mosquitoes than the least attractive one (t-test, p=0.001). For comparison of the chromatographic profiles of the foot odours and identification of their constituents, six adsorbents (tenax, chromsorb, porapak Q, activated charcoal, reverse phase octadecyl and octyl bonded silica) were evaluated for their suitability in trapping the volatiles in a static mode. Of these, porapak Q was found to be the most effective. Comparison of the gas-chromatographic (GC) and gas chromatography-linked mass spectrometry (GC-MS) profiles of blends collected from the most and least attractive feet on porapak Q adsorbent revealed both qualitative and quantitative differences. The implication of our finding on differential attraction of An. gambiae to their preferred feeding site of different human subjects is highlighted.

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Isolates of the fungus Beauveria bassiana have different levels of virulence and repellency against the termite Macrotermes michaelseni. In the present study, we compared the volatile profiles and gene sequences of two isolates of the fungus with different levels of virulence and repellence to the termite. Gas chromatography-mass spectrometric analyses showed quantitative and qualitative differences in the composition of volatiles of the two isolates. The repellencies of synthetic blends of 10 prominent components that mimicked the volatiles of each of the two isolates were significantly different. Subtractive bioassays showed that the repellency of each isolate was due to synergistic effects of a few constituents. As previously reported for isolates of Metarhizium anisopliae, some differences also were found in the nucleotide sequences of the two isolates of B. bassiana, suggesting a genetic basis for the observed intra-specific differences in their repellency and virulence against the termite.

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Field observations have demonstrated that gravid Anopheles gambiae Giles s.s. (Diptera: Culicidae) are selective in their choice of oviposition sites. For example, immature stages of An. gambiae s.s. are rarely found in water that contains Culex quinquefasciatus Say immatures. The possibility that this may, in part at least, reflect a response by ovipositing An. gambiae s.s. females to volatile signals associated with Culex juveniles was evaluated by testing the response of An. gambiae s.s. females to varying densities of Cx. quinquefasciatus egg rafts and/or larvae in oviposition choice assays. For comparison, the oviposition choices of Cx. quinquefasciatus to conspecific egg rafts and/or larvae were similarly assayed. At a low density of Cx. quinquefasciatus egg rafts (1-15 egg rafts/100 mL water), An. gambiae s.s. females laid more eggs in the treatment water than in the control, with a maximum of twice as many in the treatment water at 5 egg rafts/100 mL water. At higher egg raft densities and in all treatments that included Cx. quinquefasciatus larvae, oviposition decreased significantly in the treatment dishes in a density-dependent manner. As previous studies have indicated, ovipositing Cx. quinquefasciatus females were attracted to and laid egg rafts in dishes containing conspecific egg rafts and, interestingly, also in dishes containing larvae.

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The global rate of heavy metal pollution is rapidly increasing in various habitats. Anopheles malaria vector species (Diptera: Culicidae) appear to tolerate many aquatic habitats with metal pollutants, despite their normal proclivity for 'clean' water (i.e. low levels of organic matter). Investigations were conducted to establish whether there are biological costs for tolerance to heavy metals in Anopheles gambiae Giles sensu stricto and to assess the potential impact of heavy metal pollution on mosquito ecology. Anopheles gambiae s.s. were selected for cadmium, copper or lead tolerance through chronic exposure of immature stages to solutions of the metals for three successive generations. Biological costs were assessed in the fourth generation by horizontal life table analysis. Tolerance in larvae to cadmium (as cadmium chloride, CdCl(2)), copper [as copper II nitrate hydrate, Cu(NO(3))(2) 2.5 H(2)O] and lead [as lead II nitrate, Pb(NO(3))(2)], monitored by changes in LC(50) concentrations of the metals, changed from 6.07 microg/L, 12.42 microg/L and 493.32 microg/L to 4.45 microg/L, 25.02 microg/L and 516.69 microg/L, respectively, after three generations of exposure. The metal-selected strains had a significantly lower magnitude of egg viability, larval and pupal survivorship, adult emergence, fecundity and net reproductive rate than the control strain. The population doubling times were significantly longer and the instantaneous birth rates lower in most metal-selected strains relative to the control strain. Our results suggest that although An. gambiae s.s. displays the potential to develop tolerance to heavy metals, particularly copper, this may occur at a significant biological cost, which can adversely affect its ecological fitness.

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Experiments were carried out to evaluate the efficacy of Metarhizium anisopliae (Metsch.) Sorok. (Ascomycota: Hypocreales)-treated semiochemical-baited traps for control of Amblyomma variegatum Fabriscius (Acari: Ixodidae) under field conditions. Unfed A. variegatum adults (118) were seeded in each 100-m plot and allowed to acclimatise for 3 days. On the fourth day (Day 4), an emulsifiable formulation of M. anisopliae (consisting of 49.5% sterile distilled water, fungal conidia, 49.5% corn oil and 1% Tween 80) titrated at 10(9)conidia ml(-1) was applied in semiochemical-baited traps (900 cm(2)) which were placed at five spots within the plot. The control and fungal treatments were repeated after 14 and 28 days soon after rotating the traps clockwise (45 degrees ) in order to cover different sections of the plot. In the control plots, emulsifiable formulation without fungus was applied in the semiochemical-baited traps. Six weeks after the initiation of the experiments, five semiochemical-baited traps (untreated) were deployed in each plot for 3 successive days to trap ticks in the treated and control plots. The percentage of ticks recovered in the fungus-treated plots were significantly lower (31.1+/-5.2%) than in the control plots (85.6+/-3%) (P<0.001), which represented a relative tick reduction of 63.7%. Mortality of 93.8+/-2.3% was observed among the ticks that were recovered from the field and maintained in the laboratory for 2 weeks; while only 3.3+/-0.9% died from the control plots. The results of this study open up the possibility of developing an environmentally friendly and low cost application strategy to control Amblyomma ticks.

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Termites encounter a diverse array of potentially useful and harmful fungi in their subterranean habitats. These vary from symbiotic to harmful species with varying levels of virulence. How these hemiedaphic insects survive in habitats with infective fungi is not well understood. Possible mediation of olfactory signals in avoiding contact with entomopathogenic fungi has been explored by a number of workers. In the present study, we initially found that Macrotermes michaelseni detected a virulent isolate of Metarhizium anisopliae from some distance and avoided direct physical contact. We hypothesized that there may be a relationship between virulence and repellency of different isolates of M. anisopliae and Beauveria bassiana to the termite. We compared these for selected isolates of the two fungi. Positive correlations between the two parameters for both sets of isolates of the fungi were obtained. The results show an interesting co-evolutionary phenomenon in which the termite's response to either M. anisopliae or B. bassiana is directly related to potential harm these fungi can inflict on the insect and that the virulent strains are more likely to be recognized from some distance and avoided.

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The antiplasmodial, anti-trypanosomal and anti-leishmanial activity of 25 plant extracts obtained from seven Tanzanian medicinal plants: Annickia (Enantia) kummeriae (Annonaceae), Artemisia annua (Asteraceae), Pseudospondias microcarpa (Anacardiaceae), Drypetes natalensis (Euphorbiaceae), Acridocarpus chloropterus (Malpighiaceae), Maytenus senegalensis (Celastraceae) and Neurautanenia mitis (Papilonaceae), were evaluated in vitro against Plasmodium falciparum K1, Trypanosoma brucei rhodesiense STIB 900 and axenic Leishmania donovani MHOM-ET-67/82. Out of the 25 extracts tested, 17 showed good antiplasmodial activity (IC50 0.04-5.0 microg/ml), 7 exhibited moderate anti-trypanosomal activity (IC50 2.3-2.8 microg/ml), while 5 displayed mild anti-leishmanial activity (IC50 8.8-9.79 microg/ml). A. kummeriae, A. annua, P. microcarpa, D. natalensis, M. senegalensis and N. mitis extracts had good antiplasmodial activity (IC50 0.04-2.1 microg/ml) and selectivity indices (29.2-2,250 microg/ml). The high antiplasmodial, moderate anti-trypanosomal and mild anti-leishmanial activity make these plants good candidates for bioassay-guided isolation of anti-protozoal compounds which could serve as new lead structures for drug development.

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Experiments were conducted to explore the use of a semiochemical bait to enhance exposure of Amblyomma variegatum Fabricius (Acari: Ixodidae) to different formulations of the entomopathogenic fungus Metarhizium anisopliae (Metsch.) Sorok. (Ascomycota: Hypocreales). Initially, the relative efficacies of attraction-aggregation-attachment pheromone (AAAP), made up of o-nitrophenol, methyl salicylate and nonanoic acid in the ratio 2:1:8, 1-octen-3-ol and butyric acid, were evaluated in an olfactometer. Only AAAP and 1-octen-3-ol were found to elicit attractive responses to the tick. Simultaneous release of 1-octen-3-ol and AAAP together with CO(2) from a trap in semifield plots attracted up to 94.0+/-6% of adult ticks from a distance of 6m, and up to 24.0+/-5.1% from 8m. Formulations of M. anisopliae (dry powder, oil, and emulsifiable) applied within the trap baited with AAAP, 1-octen-3-ol and CO(2) resulted in high levels of contamination of the ticks attracted to the traps. However, 48h after autoinoculation, 89.1 and 33.3% of conidia were lost in dry powder and oil formulations, respectively. Emulsifiable formulation showed least loss of propagules (17.1%). Samples of ticks attracted to the baited traps were transferred to plastic basins containing grass and maintained for 5 weeks. The experiment was conducted in rainy and dry seasons. Emulsifiable formulation gave the highest relative tick reduction in both seasons: 54.7 and 46.5% in rainy and dry seasons, respectively, followed by oil formulation (32.0 and 23.8%) and powder formulation (38.0 and 24.4%).

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In the present study the methanolic extract of Albizia gummifera was fractionated into various fractions. These fractions were tested against choroquine sensitive (NF54) and resistant (ENT30) strains of Plasmodium falciparum. All other fractions apart from the alkaloidal fraction showed low activity with IC 50 above 3 microg/ml. The alkaloidal fraction exhibited strong activity against NF54 and ENT30 with IC 50 of 0.16+/-0.05 and 0.99+/-0.06 microg/ml, respectively. Five known spermine alkaloids were isolated from the alkaloidal fraction. These alkaloids exhibited activities against NF54 and ENT30 with IC 50 ranging from 0.09+/-0.02 to 0.91+/-0.10 microg/ml. Four of the alkaloids were further evaluated for in vivo activity against rodent malaria parasite Plasmodium berghei. The alkaloids showed percentage chemosuppression of parasitaemia in mice ranging from 43 to 72%. The use of the extracts A. gummifera for treatment of malaria in traditional medicine seems to have a scientific basis.

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Anopheles gambiae Giles s.s. (Diptera: Culicidae) is known to feed on plant sugars, but this is the first experimental study to consider whether it discriminates between plant species. Thirteen perennial plant species were selected on the basis of their local availability within the vicinity of human dwellings and larval habitats of An. gambiae s.s. in western Kenya. Groups of 100 or 200 mosquitoes were released into cages either with a cutting of one plant type at a time (single-plant assay) or with cuttings of all 13 plants simultaneously (choice assay), respectively, and left overnight. In the choice assay, direct observations of the percentages of mosquitoes perching or feeding on each plant were recorded over four 1-h periods each night. For both types of assay, mosquitoes were recaptured and the percentage that had fed on plants was assessed by testing them individually for the presence of fructose. To identify which plants the choice-assay mosquitoes had fed on, gas chromatography (GC) profiles of samples of mosquito homogenates were compared with GC profiles of extracts from relevant parts of each plant. Four of the plants that were observed to have been fed on most frequently in the choice assay (Parthenium hysterophorus L., Tecoma stans L., Ricinus communis L., and Senna didymobotrya Fresen) were also shown to have been ingested most often by mosquitoes in both types of assay, suggesting that An. gambiae is differentially responsive to this range of plants, regardless of whether the plants were presented singly or mixed together. Significantly more females than males fed on plants, with the exception of P. hysterophorus L., one of the plants most frequently fed on. For most plant species (ten of 13), GC profiles indicated that An. gambiae obtained sugars primarily from flowers. The exceptions were P. hysterophorus L., Lantana camara L. and R. communis L., on which An. gambiae fed more often from leaves and stems than from flowers.

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We did cross-sectional surveys in Kwale District, Kenya to determine the epidemiology of bovine trypanosomosis and livestock owners' perceptions of the disease. The surveys involved relative importance of trypanosomosis, examination of the current disease constraints, current control practices and drug-use patterns. Informal meetings were held with farmers and cattle census undertaken. Tsetse-fly densities and trypanosomosis prevalences in cattle were determined. A total of 132 farmers were interviewed. Trypanosomosis, anaplasmosis, East Coast fever, foot-and-mouth diseases were reported to be the major constraints to livestock production. Trypanosomosis was the most important compared to other diseases. Chemotherapy was the most widely used method of controlling the disease. Farmer-based tsetse-control technologies were poorly adopted. Respondents were quite knowledgeable on the symptoms, causes and treatment of trypanosomosis. Glossina austeni, G. brevipalpis and G. pallidipes were found in the area; the latter was the most common (0.2-738 flies/trap). Trypanosoma congolense and T. vivax were found in cattle with the former more prevalent. Infection prevalences in cattle varied between 0 and 25% (median: 22%).

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Investigations were commenced to study the potential use of the fungi, Beauveria bassiana, Metarhizium anisopliae, and the attraction-aggregation-attachment pheromone (AAAP) for the control of Ambloyomma variegatum as an environmentally friendly technology. The objective of the study was to develop and test a device, which could be used for pheromone and carbon dioxide delivery and infection of ticks with the fungi in an attempt to control the tick populations in the vegetation. Using a pheromone-baited device treated with the fungi mixture, 79% of the ticks released were attracted and exposed to the fungi and of these, 78% died during incubation in the laboratory. In another set of experiments, of the released ticks that were similarly exposed to fungi using the pheromone-baited device and left in the vegetation, 33.8% were recovered compared to recoveries of between 76 and 84% in the controls. These results were significantly different at the 5% level, an indication that the pheromone/fungi mixtures had significant effect in reducing the tick population in the field.

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The effect of formulation, fungal concentration, type and seasonal changes on the mortality of the tick Amblyomma variegatum was investigated. A previous study demonstrated high pathogenicity of strains of the fungi Beauveria bassiana and Metarhizium anisopliae against the ticks Rhipicephalus appendiculatus and Amblyomma variegatum (Kaaya et al. J Invertebr Pathol 1996; 67: 15-20). The present study was undertaken to explore possible additive or synergistic effects of the two fungi on A. variegatum. The effects of oil and water formulations at different concentrations of each fungus and combination of the two on the mortality of A. variegatum in the laboratory and in the field during the wet and dry seasons were determined and compared. The oil formulation performed better in all assays, with highest tick mortality of 92% occurring during the wet season at conidia concentration of 1 x 10(10) conidia/ml of the mixed fungi compared to 49% for the water formulation at similar conidia concentration. However, at the same conidial concentration during the dry season, mortalities in the field were relatively low with the mixture of the fungi recording 24% and 17% tick mortality for the oil and water formulation respectively. The effect of infecting the ticks with a cocktail of the two fungi was inconclusive under more controlled conditions in the laboratory but field results under both wet and dry seasons indicated significant differences between the separate and mixed fungi infections. The results demonstrate a potential of cocktail formulations in the control of ticks and possibly of other arthropod pests.

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The essential oils from 15 species of African plants selected by ethnobotanical considerations and field inspection (odour and presence of insects) were screened for fumigant toxicity to Anopheles gambiae s.s. in the laboratory. Essential oils from 6 species showed varying levels of toxicity, with Conyza newii (Compositae) and Plectranthus marruboides (Labiateae) being the most potent. Fifty compounds representing approximately 74% of the essential oil of C. newii were identified by GC-MS and GC-coinjection (for available standards). The major and some of the minor constituents of the two oils were assayed at different doses. Two compounds, from C. newii, perillaldehyde and perillyl alcohol, exhibited higher fumigant toxicity (LD50 = 1.05 x 10(-4) and 2.52 x 10(-4) mg cm(-3), respectively) than the parent oil (2.0 x 10(-3) mg cm(-3)). GC-MS analysis of the essential oil of P. marruboides gave results similar to that previously reported. Interestingly, none of its components were active, suggesting that the insecticidal activity of the oil results from either some of the minor components or as a blend effect of some of the major constituents.

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The propensity of the malaria vector mosquito Anopheles gambiae Giles (Diptera: Culicidae) to ingest sugars from various plants, and subsequent survival rates, were assessed with laboratory-reared males and females offered eight species of plants commonly cultivated and/or growing wild in western Kenya. In cages (no-choice bioassay), mosquitoes given the opportunity to feed on castorbean (Ricinus communis L.) had the longest survival times (mean and median survival time of 6.99 +/- 0.23 and 5.67 +/- 0.17 days, respectively), comparable to mosquitoes given 6% glucose (mean and median survival time of 8.70 +/- 0.23 and 6.67 +/- 0.33 days, respectively). Survival rates of An. gambiae were low on the other plants, comparable to mosquitoes given only water. Three plants: sweet potato (Ipomoea batatas L.), wild sage (Lantana camara L.) and castorbean provided levels of sugar ingestion by both sexes of An. gambiae detectable using the cold anthrone method, showing a positive correlation between median survival and sugar consumption (Spearman rank correlation coefficient = 0.905, P < 0.0001). Equal numbers of males and females were released in an enclosed semi-field screenhouse system containing a range of local plants, but no host for blood, and allowed to feed ad libitum: 6.7 +/- 0.5% (11/64) of those recaptured were found to contain detectable fructose (all females). Common plants are clearly a viable source of nutrition for adult female An. gambiae, as well as males, and may constitute and important resource for this important malaria vector.

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