Seasonal fluctuations of the Simulium damnosum Theobald complex and the prevalence of Onchocerca volvulus Bickel in blackflies caught in river systems bordering the Nigeria–Benin border were assessed for their direct impact on the epidemiology of onchocerciasis in South-western Nigeria. Entomological evaluation and heteroduplex assay (HDA) techniques were performed on flies caught in the eight capture points in the Ogun and Yewa river systems between October and December 2007, July and December 2008 and May and December 2009. A total of 5789 blackflies were caught on human bait, of which 727 (12.6%) flies were captured in 2007, 1723 (29.8%) in 2008 and 3339 (57.6%) in 2009. The majority of flies caught during the study were forest flies representing 90.3% of the total catch while savanna flies constituted 9.7%. Proportions of parous to nulliparous flies were low in all the catching points (31.1 and 68.9%, respectively). Of the 5789 flies dissected, 11 (0.2%) flies were infected with Onchocerca parasites with nine of the infected flies having L3 head parasites. The HDA results revealed that the Beffa form of S. soubrense was the dominant cytospecies present (87.1%) in all the capture sites when compared with 12.9% of S. damnosum s.s. The low level of infectivity of flies may therefore indicate a low transmission level of onchocerciasis in the communities along the Ogun and Yewa river systems. However, there is a need for constant surveillance on species composition and fly infectivity in the river systems along the borders of Nigeria–Benin Republic.

The effects of wet and dry seasons on soil termites within a humid tropical West African forest are examined. Samples were taken monthly, over a 14-mo period, and termite abundances and species richness were estimated. These estimates were compared with the total cumulative rainfall for 30-d, 7-d and 2-d periods before each sampling. For all these time periods abundances and species richness of termites were significantly negatively correlated with rainfall. However, the strongest correlations were generally found with the 2-d period, suggesting that short-term movement of termites up and down the soil profile may be the most important factor in the observed differences, rather than longer term changes in overall abundance or species composition. This conclusion was supported by a detrended correspondence analysis which showed no significant changes in species composition between dry and wet months.

Les effets de saisons sèches ou humides, sur des termites souterrains d'une forêt tropicale humide Ouest-Africaine sont examinés. Les échantillons étaient prélevés mensuellement, sur une période de 14 mois. L'abondance en termites ainsi que leur richesse spécifique sont estimées. Ces estimations sont mises en relation avec un total cumulé des pluies d'une période de 30, 7 et 2 jours avant chaque échantillonage. Pour toutes ces durées, l'abondance et la richesse spécifique sont significativement négativement corrélées avec la pluviométrie. Toutefois, les corrélations les plus fortes sont généralement trouvées avec des pluies des 2 jours précédants, suggérant que les mouvements à court terme des termites au sein du profil du sol, seraient le facteur le plus important des differences observées, plutôt que des changements à long terme de leur abondance ou composition spécifique. Cette conclusion est confortée par une analyse des correspondances, qui ne montrent pas de changements significatifs dans la composition spécifique entre mois secs et pluvieux.

Occurrence, abundance and seasonal fluctuations of Culicoides peliliouensis in the mud and sand flats of Hooghly estuary were studied in relation to some important environmental parameters (air temperature, soil temperature, soil moisture, rainfall, salinity, dissolved oxygen and pH of interstitial water, organic carbon, available phosphorus, percentage of sand, silt and clay of soil) at three stations in and around Sagar Island during July 1982 to June 1984. They were more or less found throughout the year, withmaximum abundance during postmonsoon and minimum during premonsoon. Several statistical analyses have been computed to study the relation between population of C. peliliouensis and all ecological parameters. Results of ANOVA indicate that almost all ecological parameters varied significantly over months, stations and years, whereas the population of C. peliliouensis varied significantly only over months and stations. Soil temperature, rainfall, organic carbon and available phosphorus appear to be the major factors controlling their distribution in the intertidal habitat as evident from correlation coefficient analysis. Multiple regression analysis shows that the combined effect of all parameters is positively significant at all the stations.

Population studies of the whitefly, Bemisia tabaci, carried out in the field indicated that whiteflies were present in cassava all year round and that there were marked seasonal fluctuations in the population levels. Possible explanations for these fluctuations are discussed. It was found that the interaction of atmospheric temperature and relative humidity was highly correlated (r = 0.924) with the development of the whitefly. Results of the studies suggested that rainfall has an indirect effect on whitefly population. Whether B. tabaci behaves in the same way in mixed cropping system has not yet been established.