Mary Ndungu

Cleome monophylla essential oil and its constituents as tick (Rhipicephalus appendiculatus) and maize weevil (Sitophilus zeamais) repellents

The repellency of the essential oil of the shrub Cleome monophylla (Family: Capparidaceae) and identified constituents of the oil were evaluated against the livestock tick, Rhipicephalus appendiculatus and the maize weevil, Sitophillus zeamais. In a tick climbing repellency bioassay, the oil of C. monophylla exhibited repellency which, at the highest dose, was comparable to that of the commercial arthropod repellent N, N‐diethyl toluamide (DEET). In a Y‐tube olfactometer bioassay, C. monophylla oil showed higher or comparable repellency against S. zeamais relative to DEET at all the doses tested. 14 Compounds were identified in the C. monophylla oil by GC, GC‐MS and coinjection with authentic samples. Terpenolene was found to occur in largest quantity (14%) followed by 1‐α‐terpeneol (10%), pentacosane (9%), (α + β)‐humulene (8%), phytol (5%) and 2‐dodecanone (4%). The most repellent components against R. appendiculatus and S. zeamais were 1‐α‐terpeneol and 2‐dodecanone. The overall pattern of repellency activity of the C. monophylla constituents with respect to the two arthropods was, however, different. The potential of C. monophylla in tick and maize weevil control is discussed.

Gynandropsis gynandra Essential Oil and Its Constituents as Tick (Rhipicephalus appendiculatus ) Repellents

Abstract The repellency of the essential oil of the previously reported anti-tick pasture shrub Gynandropsis gynandra and identified constituents of the oil were evaluated against the livestock tick, Rhipicephalus appendiculatus. In a tick-climbing repellency bioassay, the oil of G. gynandra exhibited a repellency effect which at the highest treatment levels was higher than that of the commercial arthropod repellent N,N-diethyltoluamide. Twenty eight compounds were identified in the G. gynandra oil by GC, GC-MS and coinjection with authentic samples. Carvacrol was found to occur in largest quantity (29.2%), followed by trans-phytol (24.0%), linalool (13.3%), trans-2-methylcyclopentanol (7.2%) and β-caryophyllene (4.4%). m-Cymene, nonanal, 1-α-terpineol, β-cyclocitral, nerol, trans-geraniol, carvacrol, β-ionone, trans-geranylacetone, and nerolidol were the most repellent components against R. appendiculatus. Methyl isothiocyanate which occurred in the G. gynandra oil at a relative percentage of 2.1 and which was not tested in the bioassay due to its toxicity may also contribute significantly to the repellency of the oil. The repellency of the oil of G. gynandra supported earlier findings by other workers that G. gynandra repelled R. appendiculatus ticks.

Relationship between virulence and repellency of entomopathogenic isolates of Metarhizium anisopliae and Beauveria bassiana to the termite Macrotermes michaelseni

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 termites 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.

Comparison of volatile blends and gene sequences of two isolates of Metarhizium anisopliae of different virulence and repellency toward the termite Macrotermes michaelseni

Previously, we reported an interesting relationship between virulence and repellency of different isolates of the fungus Metarhizium anisopliae towards the termite Macrotermes michaelseni: the higher the virulence of a given isolate, the greater its repellency. In the present study, we compared the volatile profiles of two isolates, one that was more virulent (and repellent) and one that was less virulent (and repellent) to the termite. The prominent components of the two blends were characterized by gas chromatography-mass spectrometry and authenticated by gas chromatography coinjections with synthentic standards. There were both qualitative and quantitative differences between the two blends. The repellencies of synthetic blends of 10 prominent constituents of the volatiles of the two isolates were compared and that of the more virulent isolate was found to be significantly more repellent. Subtractive bioassays were carried out with one of the constituents of each of the two 10-component blends missing at a time to determine its relative contribution to the overall repellency. The results indicated that the repellency of the volatiles of each isolate was primarily due to synergistic effects of a smaller number of constituents. Intraspecific differences between the two isolates were also reflected in their nucleotide sequences.

Laboratory evaluation of some eastern African Meliaceae as sources of larvicidal botanicals for Anopheles gambiae

Root bark extracts of five Meliaceae species (Turraea abyssinica Hochst., Turraea wakefeldii Oliv., Turraea mombassana Hiern ex C.DC., Trichilia roka (Forsk) Chiov. and Melia volkensii Guerke.) and different fractions thereof (following chloroform extraction and column chromatographic separation) were compared for their immediate toxicity and long-term effects on Anopheles gambiae Giles sensu stricto (Diptera: Culicidae). Larvicidal effects of the extracts appeared to be largely associated with limonoids of medium polarity with M. volkensii and T. mombassana extracts being more potent than those of the other Meliaceae. Long-term (6–8 days post-exposure) observations at lower doses showed that 100% cumulative mortality can be achieved with some extracts (particularly those of T. mombassana and M. volkensii) with interesting growth-inhibition effects. Follow-up studies that are needed and practical implications of the results in terms of development of larval control strategies for African malaria vectors are discussed.RésuméDes extraits d’écorce de racines de cinq espèces de Meliaceae (Turraea abyssinica Hochst., Turraea wakefieldi Oliv., Turraea mombassana Hiern ex C.DC., Trichilia roka (Forsk) Chiov. et Melia volkensii Guerke.) et différentes fractions de ces extraits (après extraction au chloroforme et séparation par chromatographie en colonne) ont été comparées en terme de toxicité immédiate et de leurs effets à long terme sur des larves d’Anopheles gambiae Giles sensu stricto (Diptera: Culicidae). Les effets larvicides des extraits semblent en grande partie associés aux limonoides de polarité moyenne des extraits de M. volkensii et T. mombassana, qui sont plus actifs que ceux des autres Meliaceae. A long terme (6–8 jours après exposition) les traitements à faibles doses peuvent provoquer près de 100% de mortalité cumulée avec certains extraits (en particulier ceux de T. mombassana et M. volkensii) avec des effets d’inhibition de la croissance intéressants. On discute des futures voies d’investigation et des implications pratiques de ses résultats dans le cadre du développement de stratégies de lutte larvaire contre les vecteurs de la malaria Africaine.

Comparative responses of ovipositing Anopheles gambiae and Culex quinquefasciatus females to the presence of Culex egg rafts and larvae

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.

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

Maize (Zea mays L.) is Kenya’s most important staple crop with annual production fluctuating between 2.6 and 3.1 million tons in 2012 and 2011, respectively. However, frequent food shortages are still experienced in the country. These have been attributed to pests and diseases and post-harvest constraints. The dominant post-harvest pest of maize is Sitophilus zeamais (Motsch.), which causes losses between 10 and 20% of harvested grain. The objective of this study was to establish the repellent activity of essential oils extracted from selected eucalyptus species against S. zeamais. Essential oils were extracted from the fresh leaves of Eucalyptus saligna Sm., Eucalyptus globulus Labill., Eucalyptus camaldulensis Schlecht and Eucalyptus citriodora Hook by steam distillation using a Clevenger-type apparatus. A repellency bioassay, with varying concentrations (0.002, 0.02,0.2 and 2 μl/μl) of the oils, was carried out against the maize weevils using a Y-shaped olfactometer. Repeated measures of analysis of variance were applied to test the different doses and repellents, and their interactions against S. zeamais. The essential oils of E. camaldulensis and E. citriodora presented better repellent activity at the 2 μl/μl concentration (74.35 and 69.15%, respectively) followed by those of E. globulus (53.68%) and E. saligna (40.5%). Gas chromatography (GC)-mass spectrometry and GC co-injections with authentic samples showed the presence of the following major constituents in: (i) E. camaldulensis oil: 1,8-cineole (18.9%), α-cardinol (6.4%) and ß-phellandrene (2.6%); (ii) E. citriodora oil: 1,8-cineole (11.2%), ß-pinene (3.2%) and 4-terpineol (3.1%); and (iii) E. globulus oil: 1,8-cineol (17.2%), α-pinene (7.1%) and spathulenol (6.5%). The results provide a scientific rationale for the use of eucalyptus oils in the protection of maize against weevils.

Evidence for Potential of Managing Some African Fruit Fly Species (Diptera: Tephritidae) Using the Mango Fruit Fly Host-Marking Pheromone

ABSTRACT We investigated conspecific and heterospecific oviposition host discrimination among four economically important fruit fly pests of mango in Africa (Ceratitis capitata, Wiedemann; C. fasciventris, Bezzi; C. rosa, Karsch, and C. cosyra, Walker) with regard to host-marking behavior and fecal matter aqueous solutions. The objective of the study was to get insight into the potential of managing these pests using the host-marking technique. Observations were done on mango slices marked by the flies and treated with aqueous solutions of fecal matter of the flies, respectively. In both host-marking and fecal matter experiments, C. cosyra, which is the most destructive species of the four on mango, was exceptional. It only discriminated against hosts treated with its fecal matter but with lower sensitivity while C. capitata and C. fasciventris discriminated against hosts marked by it or treated with its fecal matter and with higher sensitivity. Our results provide evidence for potential of managing some of the major fruit fly species infesting mango in Africa using the host-marking pheromone of the mango fruit fly, C. cosyra.

Bio-Assay Guided Fractionation of Anti-Mosquito Limonoids from Turraea abyssinica and Turraea cornucopia

Malaria, transmitted by mosquitoes of the genus Anopheles, is the most important parasitic disease worldwide. It affects 40% of the global population mostly within the tropical world. Yearly, over one million children under the age of five die in Africa as a result of malaria. The genus Turraea belongs to the family Meliaceae. Meliaceae is characterized by the presence of tetranortriterpenoids (limonoids), a group of compounds that exhibit a wide variety of biological properties including anti-insect, anti-protozoa, anti-bacterial and anti-fungal activities. In the present study, the root bark of T. abyssinica and T. cornucopia were extracted with methanol and partitioned between water and chloroform. The activity of crude methanol and chloroform extracts was tested against larvae and adults of Anopheles gambiae sensu stricto (Diptera: Culicidae). As larvicides, the methanol extract of T. cornucopia was the most active (LD50 202 ppm). The chloroform extract of T. cornucopia was the most active as an adulticide (LD50 302.1 ppm). Partitioning of the methanolic extracts between chloroform and water, followed by silica gel chromatography of the organic extract gave limonoids-rich fractions that had larvicidal activity higher than those of the corresponding crude extracts. Column chromatography of the chloroform fraction followed by semi-preparative HPLC yielded 1α-12α-diacetoxy-1,2-dihydro-7-deacetyl-3β-7α-dihydroxyazadiron,12α-acetoxy-7-deacetylazadiron and mzikonone. The structures of these compounds were elucidated using spectroscopic methods (IR UV, MS, 1H-, 13C- NMR, gradient COSY, and gradient HMBC experiments). Stereo chemical assignments were made by gradient NOE spectroscopy. These plants offer a significant potential for mosquito control as larvicides and adulticides.

Identification of Glutamic Acid as a Host Marking Pheromone of the African Fruit Fly Species Ceratitis rosa (Diptera: Tephritidae)

Host marking pheromones (HMPs) deposited by female fruit flies deter other females from overexploiting the same fruit for egg laying. Using a bioassay-guided approach, we identified the HMP of the Natal fruit fly species Ceratitis rosa as glutamic acid, 1, from the aqueous fecal matter extract of ovipositing females by liquid chromatography-quadrupole time-of-flight-mass spectrometry (LC-QTOF-MS). Dual choice oviposition assays showed that both the fecal matter extract and 1 significantly reduced oviposition responses in conspecific females of C. rosa. Glutamic acid levels were 10-20 times higher in fecal matter than in the ovipositor or hemolymph extracts of females. Identification of 1 as a host marking pheromone in females of C. rosa improves our understanding of fruit fly chemical ecology and provides evidence that it could be used as a potential component in the integrated management of this fruit fly species.