Richard W. Mwangi

The effects of a tsetse DNA virus infection on the functions of the male accessory reproductive gland in the host fly Glossina morsitans centralis (Diptera; Glossinidae).

Abstract. Freshly deposited third instar Glossina morsitans centralis larvae were infected with the tsetse DNA virus by microinjection, and at emergence adult males were separated from the females and fed on rabbit blood every second day for 8 days. A control group treated with sterile saline were handled similarly. They were dissected, and comparative observations made on the appearance and size of the accessory reproductive glands (ARG) in infected and control males. Regularly fed 8-day-old males from infected and control groups were mated to 2-day-old normal females obtained from the insectay. After separation from copula, the females were dissected and the uteri examined for the presence and quality of the spermatophore. The spermathecae were also examined for insemination. ARG tissues from the control and virus infected regularly fed 8-day-old male flies were fixed and processed for electron microscopic studies.The ARGs from control flies were found to be milky in appearance, whereas those from virus-infected flies were transparent in most parts. The ARGs from virus-infected males were significantly smaller in diameters (F = 42.26, p < 0.0001) and shorter (F = 200.4, p < 0.0001) than those of the controls.Most of the virus-infected males failed to form a complete spermatophore, whereas almost all the controls formed complete spermatophore as observed in the uteri of the female mates (Χ2 = 111.661, p < 0.0001). The infected males that formed partial spermatophores and those that did not form any at all failed to inseminate their female mates.Histological studies of the ARGs revealed some lesions in the epithelial cells characterized by degeneration of cytoplasmic organelles and detachment of the muscle layer from the basal plasma membrane. However, no virus particles were observed in the affected cells.

The Effects of a DNA Virus Infection on the Reproductive Potential of Female Tsetse Flies, Glossina morsitans centralis and Glossina morsitans morsitans (Diptera: Glossinidae)

Reproductive anomalies associated with the tsetse DNA virus infection in the female tsetse hosts, Glossina morsitans centralis Machado and Glossina morsitans morsitans Westwood, inoculated with the virus during the 3rd instar larval stage were studied and the data compared to those obtained from the control females injected with sterile physiological saline. Virus infected flies had significantly longer first and second pregnancy cycles (P < 0.0001) and produced pupae that were of significantly less weight in milligrams (P < 0.0001) compared to controls. Transmission of the virus to progeny was not absolute and only 21% of G. m. centralis and 48% of G. m. morsitans first progeny flies from infected females developed salivary gland hypertrophy as a result of transmission from mother to progeny. The virus infected females produced significantly fewere pupae compared to the controls during the experimental period (P < 0.00001).

Seasonal population changes and malaria transmission potential of Anopheles pharoensis and the minor anophelines in Mwea Irrigation Scheme, Kenya.

A study in 1984 and 1985 showed that Anopheles gambiae s.l. and An. pharoensis were the major anophelines in Mwea Irrigation Scheme, Kenya, constituting 83.86% and 15.69% of the catch respectively. Four minor species made up the remaining 0.45%. The irrigation phase of the rice cultivation cycle in August, which linked the flooding effects of the two rainy seasons, resulted in major population increases of An. pharoensis and enabled continuous breeding for up to 9 months per year. The average of mean monthly proportions of unfed, bloodfed, and gravid females was 26.6, 58.8, and 14.6% respectively. The Plasmodium falciparum sporozoite rates for An. pharoensis were 1.3% by ELISA and 0.68% by dissection, while those for An. funestus were 1.7% by ELISA and 1.25% by dissection. An. pharoensis can contribute to the epidemiology of Malaria in the Mwea area.

The chemotactic effect of Phlebotomus duboscqi (diptera: psychodidae) salivary gland lysates to murine monocytes

The possibility that salivary gland lysates of Phlebotomus duboscqi are able to attract vertebrate monocytes was investigated. In vitro studies showed that salivary gland lysates of P. duboscqi, the vector of Leishmania major in Kenya, are chemotactic to mouse peritoneal monocytes. This attraction of monocytes by vector salivary gland lysates may form part of the mechanisms through which sandfly saliva ensures successful parasitization of macrophages in a susceptible host by Leishmania parasites.

Field studies of larval Anopheles arabiensis Patton of Mwea Irrigation Scheme, Kenya

Between May 1984 and December 1985, the population of immature stages of Anopheles arabiensis was sampled by the dip method at sites close to two villages in Mwea Irrigation Scheme, Kenya. Larval presence corresponded to rainy seasons and the flooding phase of the rice cycle. No larvae were found during the postharvest dry season. The instar composition, age distribution and survivorship curves for the different stages were determined. Pupal productivity for Mwea rice fields was estimated to be 1% of the total immature population.RésuméEntre mal 1984 et décembre 1985, la population des larves de Anophèles arabiensis etaient etudiés par la méthode d’immersion près des deux villages de la région irriguée de Mwea au Kenya. La présence des larves correspondaient avec les saisons pluvieux et l’inondation des champs de riz. Ils n’avaient pas les larves trouvaient près de la moisson, pendant la saison sèche. La composition des larves, la distribution de l’âge, et les courbes de survie étaient résolus. La productivité des mostiques An. arabiensis de Mwea étaient estimés être 1% de la population total pas mûr.

Effects of a biologically active fraction from melia volkensii on culex quinquefasciatus

Abstract—A chromatographically enriched fraction designated Fraction B from dry fruits of the plant Melia volkensii (family Meliaceae) was evaluated with the objective of determining its toxic and growth inhibiting effects on the larvae and adults of Culex quinquefasciatus mosquitoes. The fraction was purified from a crude methanolic extract by cold precipitation and elution of the precipitate dissolved in a hexane-ethyl acetate solvent system through a silica gel column. Larval treatments involved rearing the larval stages in water containing the fraction at concentrations of between 5 and 200 ppm. The LC50 for this fraction was found to be 34.72 μ/ml in 48 h. Second instar larvae were found to be more susceptible to fraction B when compared to fourth instar larvae. All fourth instar larvae that survived the treatment moulted into larval-pupal intermediates that were short-lived. The extract was also found to be an oviposition deterrent at a concentration of 20 ppm and above. It is concluded that M. volkensii extract has potential in the control of Culex quinquefasciatus.Résumé—Une fraction enrichie chromatographiquement et designée Fraction B des fruits secs de la plante Melia volkensii (famille Meliaceae) a été évaluée pour déterminer sa toxicité et ses effets inhibiteurs de croissance sur les larves et adultes de Culex quinquefasciatus. La fraction a été purifiée à partir de l’extrait méthanolé brut par précipitation à froid et elution du précipité dissoit dans un mélange de solvent hexane-ethyl acetate à travers une colonne de silica gel. Des traitements destinés aux larves impliquaient l’élevage des stades larvaires dans le l’eau contenant la fraction aux concentrations comprises entre 5 et 200 ppm. La DL50 pour cette fraction a été de 34.72 μg/ml en 48 heures. On a trouvé que les larves du 2nd instar ont été les plus susceptibles à la fraction B, comparées aux larves du 4ème instar. Toutes les larves du 4ème instar qui ont survécu au traitement ont mué en intermédiares larve-pupe dont la durée de vie a été écourtée. L’extrait s’est aussi révelé un dissuadant de l’oviposition à la concentration de 20 ppm et au dessus. On en a conclu que l’extrait de M. volkensii offre un moyen potentiel de lutte contre Culex quinquefasciatus.

Population and cytogenetic observations on Anopheles arabiensis Patton of Mwea irrigation scheme, Kenya.

A study of the mosquito fauna of the Mwea Rice Irrigation Scheme, Kenya, carried out during 1984 and 1985 identified 13 species, with Anopheles gambiae s. l. comprising 65.71% of the total collection. X-chromosome identification of 652 semi-gravid females resulted in 649 (99.5 %) positive identifications of An. arabiensis, implicating it as the noxious member of the An. gambiae complex present. Inversion polymorphism of chromosomes 2Rb and 3Ra karyotypes was studied in one village population. Seasonal population changes were found to be heavily dependent on rice field surface water. Artificial irrigation for rice farming greatly extended the breeding period per year by linking up the two wet seasons. Adult females fed more frequently on bovids than humans. The mean percentage gonotrophic condition of all females caught in the villagesof Karima, Thiba, Mucii-wa-Urata and Rurumi by pyrethrum spray-sheet collections, miniature light-traps and exit window traps was 69 % bloodfed, 18 % unfed and 13 % gravid. These proportions were statistically shown to be within predictable limits over time and space. The sporozoite infection rate in adult females was 0.55% by manual dissections and 1.2% by the ELISA technique.RésuméUne etude de la faune des moustiques de la région irriguées de Mwea au Kenya, effectuée en 1984 et 1985 a identiné 13 espèces avec Anopheles gambiae s. l. composant 65.71 % de la collection totale. Les identification de chromosome X sur 652 demi-gravide femelles donne 649 (99.5%) identifications positives de An. gambie, l’implicant comme membre nocive de An. gambiae complexe presente. Nous avons etudié dans une population villageoise la polymorphisme inversive des karyotypes des chromosomes 2Rb et 3Ra. Les changements saisonieres dans la populations dependant enormement de la surface d’eau du terrain. L’irrigation artificielle de la culture de riz prolonge considerablement la period de croissance annuelle en rapprochant les deux saisons pluvieuses. Les femelles des adultes se nourrissent plus frequenment sur les bovides que sur les humains. La pourcentage moyenne de la condition gonotrophique de toutes les femelles capturées dans les villages de Karima, Thiba, Mucii-wa-Urata et Rurumi en utilisant 3 methodes de capture, c’est a dire, par le pyrethe, par le piège lumière et par le piège de le fenðre d’exit est de 69 % nourri de sang, 18% non-nourri, et 13% de gravide. Ces proportions statistiquement restent dans les limites de prediction sur l’espèce et le temps. Le taux d’infection de sporozoite chez le femellesdes adultes est de 0.55% par dissection manuelle et de 1.2% par le technique ELISA.

Toxicity and growth-inhibitory activity of Polygonum senegalense (Meissn.) surface exudate against Aedes aegypti larvae

Laboratory studies were conducted to assess the toxicity and growth-inhibitory activity against Aedes aegypti larvae, of the crude acetone extracts of Polygonum senegalense (Meissn.) leaves, itsflavonoid component 2′,6′-dihydroxy-4′-methoxydihydrochalcone and the internal tissue flavanol quercetin. The first two showed significantly high insecticidal and growth-inhibitory activity even at low concentrations, whereas quercetin was toxic only at concentrations above 7μg/ml.RésuméDes études au laboratoire ont été menées pour déceler l’effet toxique et inhibiteur de croissance chez les larves d’Aedes aegypti, par emploi des extraits bruts à l’acétone obtenus des feuilles de Polygonum senegalense (Meissn.) et en comparaison avec ses composants flavonoïdes: 2′,6′- dihydroxy-4′-méthoxydihydrochalcone et du flavonol quercitine des tissus internes de la plante. Les deux premiers produits ont montré une activité hautement significative du pouvoir insecticide et d’effet inhibiteur de croissance même à des basses concentrations, au moment où la quercitine était seulement toxique à des concentrations supérieures à 7 μg/ml.

A simple method for maintaining, detecting and recovering virulent Leishmania donovani in hamsters

The ability of hamsters (Mesocricetus auratus) to retain amastigotes of Leishmania donovani at cutaneous sites was examined. Following intradermal inoculation of L. donovani stationary phase culture promastigotes in fore and hind footpads, nasal area and belly skin, cultures of aspirates taken fortnightly from these sites showed that amastigotes can survive in the skin for up to 10 months without visceralizing. Hairless cutaneous sites were better at retaining L. donovani amastigotes than the hairy belly skin. L. donovani promastigotes cultivated from aspirates of sites of inoculation were highly virulent. The skin is suggested as one of the sites where viscerotropic L. donovani can remain cryptic for a long time before the infection either visceralizes or is aborted. Skins of hamsters when inoculated intradermally can serve as an easy site for maintaining, detecting and recovering virulent L. donovani without killing the hamster.

Growth, development and life cycle of Icerya pattersoni (Newstead) (Homoptera: Margarodidae), a coffee pest in Kenya.

Experiments carried out in a coffee plantation to determine the developmental period of Icerya pattersoni (Newst.) showed that the female and male scales lasted 157 and 129 days on average, respectively. The different stages of I. pattersoni females were found to be recognizable by the number of antennal segments. The antenna of the stage I nymphal instar is six segmented, stage II is nine segmented and stage III is eleven segmented. The antenna of adult males is eighteen segmented. Females are neotenic but the males possess a pair of grey wings and atrophied mouthparts. In the field the I. pattersoni pest population size is highest in the heavy rainfall months of April and May.RésuméLes expériences menées pour détermine la période de dévelopment de Icerya pattersoni (Newst.) sur la variété du café SL 28 ont montré que les échelles des males et des fameules onto duré 157 et 129 jours en moyenne, respectivement. La maturité de la plante s’est montrée a influer sur le dévelopment et la fécondité moyenne de l’échelle. Les jeunes plantes étant moins favorables que les plantes mûres. Les étapes différentes des fameules I. pattersoni se sont montrées identifiables par le nombre des ségments anténaux. Le “nymphal instar antenna” de l’Etape I a six ségements, de l’Etape II neuf ségments et de l’Etape III onze ségments. L’antenne des males adults a dixhuit ségments. Les fameules sont “neotenic” mais les males possèdent un paire des ailes grises et des parties de boucheatrophiées.