Dispersion factors in the arboreal snail Sitala jenynsi (Gastropoda: Ariophantidae)

Sitala jenynsi snails from the University and Wazo populations of Dar es Salaam, Tanzania, were released on grass, and on forest terrain, in both regions during the dry (February, March) and the rainy seasons (April). Snail dispersion was assessed as weekly quadratic means and as the overall Diffusion Coefficient 0.423 nr/week. The coefficient was enhanced by grassy habitats, continuous vegetation cover, absence of edible plants and rainy weather; conversely, dispersion was retarded by shrubs, vegetation discontinuities, presence of edible plants and dry weather. There were differences in the rate of dispersion between populations, snails from the University Campus being faster. In each release a broadly unidirectional dispersion was recorded. The populations in question, seasons and the direction of origin of the snails seemed immaterial to directionality of dispersion, The dispersion rates of Sitala jenynsi exceeded those of the helicids Cepaea nemoralis and Theba pisana and of the partulid Pariula taeniata. While observed dispersion rates of S jenynsi may warrant the mixing of individuals in a population, they seem insufficient to facilitate appreciable migration of snails between neighboring populations

Snail arboreality: the microdistribution of Sitala jenynsi (Gastropoda: Ariophantidae)

The habitats and patterns of vertical migration of the shell banding morphs of the snail Sitala jenynsi (Pfeiffer) were studied in Dar es Salaam and Wazo regions of central coastal Tanzania Both dimorphic and trimorphic populations were arboreal throughout the year. The snails occurred randomly within mid-heights 180 to 360 cm. without apparent morph differences in micro-distribution. The pattern of circadial vertical distribution consisted of upward migrations during mornings and downward shifts during late evenings. These oscillations regressed negatively on relative humidity (RH), a unit advance in RH representing an eight-fold descent of snails on daytime height. Variations in RH accounted for much of the total variance in the mean vertical distance. During high RH, however, temperature and mating behaviour probably exerted major influences on snail micro-distribution. The effects of arboreality on snail survival and initiation of differentiating subpopulations are proposed

Karyology of three evolutionarily hexaploid southern African species of yellowfish, Labeobarbus Rüppel, 1836 (Cyprinidae)

The karyotypes of three species of yellowfish, namely Labeobarbus marequensis (A. Smith, 1841), L. capensis (A. Smith, 1841) and L. polylepis (Boulenger, 1907), were examined by Giemsa staining using an approach improved for the description of high chromosome numbers. In each case, 2n = 150; no heteromorphic chromosomes were detected; chromosomes in all morphological categories ranged smoothly from large to small, with no distinctly large submetacentric pairs; and metacentric chromosomes showed little variation in size. Labeobarbus marequensis had 26 metacentric (m), 44 submetacentric (sm), 42 subtelocentric (st) and 38 acrocentric (a) chromosomes and a fundamental number (FN) of 262; L. capensis had 16 m, 58 sm, 42 st and 34 a chromosomes and FN = 266; and L. polylepis had 18 m, 60 sm, 42 st and 30 a chromosomes and FN = 270. These results, combined with published literature, imply that Labeobarbus Rüppel, 1836 is an evolutionarily hexaploid African lineage and support its removal from synonymy with the evolutionarily tetraploid Asian genus Tor Gray, 1834. A review of fundamental numbers for conspecific Labeobarbus species examined in different studies implicated karyological technique as a confounding factor in assessing details of karyotypes, leading to recommendations for future karyological studies of barbine fishes. Potential synapomorphies are pointed out in karyological characters of species within Labeobarbus

Quantification of shell banding polymorphism in the East African tree snail Sitala jenynsi (Pulmonata: Ariophantidae)

In eastern Africa, populations of the tree snail Sitala jenynsi are monomorphic, dimorphic or trimorphic for the width of the upper brown band on their shells.We measured the variation in the width of this band in several populations and analysed it using two mutually verifiable methods: arithmetical probability paper and  regressions of log-transformed shell metrics. The demarcations of the three morphs in areas of spatial overlap between the band-width states have been defined. We recognized existence of type I narrow-banding which associates monomorphism, and type II narrow-banding, medium banding and wide-banding forms which associate polymorphism. We have also quantified the variation in three other characters, two of which are also polymorphic: a lower pigmented band and an upper unpigmented ‘ghost band’. The evolutionary implications of the findings are discussed. Continued use of varietal names to describe the banding polymorphism of S. jenynsi is recommended, in  preference to the multidimensional colour pattern notation commonly applied to gastropods.Key words: Mollusca, Gastropoda, Pulmonata, Ariophantidae, Sitala jenynsi,  arboreal snail, band width polymorphism

Antioviposition and Reduction of Callosobruchus chinensis Pic. 1902 (Coleoptera: Bruchidae) Emergence on Phaseolus vulgaris by Dioscorea sansibarensis Powder and Its Chemical Composition

Callosobruchus chinensis causes damage to the Phaseolus vulgaris seeds. Traditionally, Dioscorea sansibarensis serves as a medicinal plant. Naturally, D. sansibarensis has toxins that protect against herbivores and the surrounding invasive plants in its natural habitat. Phytochemical analysis by thin-layer chromatography (TLC) and laboratory experiments was carried out to determine the activity of D. sansibarensis leaves, bulbils, and yams powders on antioviposition and inhibition of the F1 emergence of C. chinensis. Bioassay data were subjected to nonparametric (Kolmogorov–Smirnov) statistical analysis and a generalized linear model at P≤0.05. Statistically, the powders had an antioviposition activity of 34.3% (R2 = 0.343). A recommendable activity on antioviposition was displayed by the yams powder; treatment by 0.8 g of yams powder had a Wald Chi-Square value of 1.291, P=0.26. Inhibition of F1 emergence was significantly attained by the yams powder; the treatment by 0.6 g of yams powder had a Wald Chi-Square value of 7.72, P=0.01. Statistically, the bulbils powder displayed low antioviposition and inhibition of F1 emergence. Observations on the TLC exposed compounds with similar Rf values; saponin with an Rf value of 0.72 was portrayed in the leaves, bulbils, and yams. A terpenoid and a flavonoid with Rf values of 0.37 and 0.71, respectively, were observed in bulbils and yams but absent in leaves. A terpenoid with an Rf value of 0.49 was visualized in leaves and bulbils but not in the yams powder. The study concluded that the D. sansibarensis yams and leaves powders are viable for application by the farmers in the protection of stored legumes against attack by C. chinensis. However, there may be other diverse interests in other storage insects and other methods of phytochemical analysis that have not been investigated

Chemosensory response of the Phaseolus vulgaris L. (Fabaceae) weevil (Bruchus chinensis Linnaeus, 1758 (Coleoptera: Bruchidae)) to Dioscorea sansibarensis Pax. (Dioscoreaceae) bulbil essential oil

Dioscorea sansibarensis bulbils are well known for their toxicity and medicinal applications. In this study, the attraction and mortality of the Phaseolus vulgaris weevil (Bruchus chinensis) caused by Dioscorea sansibarensis bulbil oil was examined in a Completely Randomized Design experiment using a Y-tube olfactometer on a laboratory bench. Statistical analysis at P < 0.05 showed 10 µL had an attraction of 42.67%. In the case of mortality, the results showed that Phaseolus vulgaris seeds treated with 40 µL of the bulbil oil had a harmonic mean of 55.8% mortality of the weevil population, which was higher than with 10 µL of Actellic 50 EC. GC-MS analysis identified 17 compounds in the bulbil oil, the main constituents of which were 2- pentanone, 4-hydroxy-4-methyl- (17.8%), phenol, 4-ethyl- (11.41%), hexadecanoic acid, methyl ester (11.05%), phenol (7.35%), 9-octadecenoic acid, (E)- (7.2%) and phenol, 4-ethyl-2-methoxy- (7.14%). Attraction by bulbil oil may have been due to the presence of phenolic compounds, and mortality may have been due to hexadecanoic acid, methyl ester and 9-octadecenoic acid, (E)-. Attractants are used for the surveillance and detection of an infestation in stored products. The added advantage of the bulbil oil to cause mortality makes Dioscorea sansibarensis bulbil oil useful in the formulation of a botanical pesticide in stored pest management

Evaluation of the repellent effect of Dioscorea sansibarensis Pax (Dioscoreaceae) leaf essential oil against Bruchus chinensis Linnaeus, 1758 (Coleoptera: Bruchidae)

Laboratory experiments were conducted to determine the repellent activities of the ornamental plant Dioscorea sansibarensis leaf essential oil against the Bruchus chinensis bean weevil in the protection of stored legumes. The leaves exhibited potential repellency in a Y-tube olfactometer. The tabulated data show that 10µL of leaf oil exhibited a repellency of 41.33%, with a grouped median of 53.33%, which was better than 10 µL of Actellic 50 EC, which had a repellency of 36.00% and a grouped median of 40%. Statistically, there was no significant difference in the percentage repellency obtained from the leaf oil and Actellic 50 EC at different concentrations (10, 20, 30 and 40 µL/mL, X2(7, N=200) = 114.93, P< 0.05). The GC-MS analysis identified 16 compounds in the leaf oil. The main compounds and their percentage composition were phytol (19.46%), 1-epi-α-gurjunene (11.71%), palmitic acid (10.48%), ethyl palmitate (8.87%), methyl palmitate (7.72%), isophytol (5.99%), 2-heptadecanone (4.59%) and α-selinene (4.5%). The repellency caused by the by leaf oil may have been due to the presence of α-selinene, also known as naphthalene, 1,2,3,5,6,7,8,8a-octahydro-1,8a-dimethyl-7-(1-methylethenyl)-, [1S- (1.α.,7.α.,8a.α.)]-. Dioscorea sansibarensis may be a good choice for repellent formulations