Studies were conducted in farmer's field, Lambwe School of the Deaf, and Mbita Point Field Station of ICIPE (ICIPE-Mbita) in western Kenya during the long rains of 2001 and 2002 to assess the impact of a diversionary stemborer management strategy on the pest's predators. Treatments consisted of a maize monocrop (control) and an intercrop of maize and desmodium, Desmodium uncinatum Jacq., with Napier grass, Pennisetum purpureum (Schumach), as trap crop around the field (‘push-pull’) in the farmer's field and Lambwe School of the Deaf. Sudan grass, Sorghum vulgare sudanense (Pers.), was used in place of Napier on the station. A combination of sticky traps, direct observation and hand-collection methods were employed. Predator groups encountered included 12 families from 7 insect orders and 4 families from one arachnid order, with most of the foregoing represented in both maize monocrop and ‘push-pull’ plots. A Cheilomenes sp. and Chrysopa sp. were, however, recovered from ‘push-pull’ plots only. Ants, earwigs and spiders were the main predators encountered. Both overall and individual group populations of these predators as well as ant diversity were significantly higher in ‘push-pull’ than monocrop plots in all the sites during the vegetative, flowering and mature maize growth stages (P < 0.05, t-test). The results thus indicate a numerical enhancement of stemborer predators by use of this habitat management system.

In West and Central Africa, panicle-feeding mirid bugs, particularly Eurystylus oldi Poppius (Hemiptera: Miridae), are major pests of improved sorghum cultivars. Population dynamics of panicle-feeding bugs were studied on the sorghum cultivar ICSV 197, sown on eight dates each year from 1992 to 1994 at Samanko, Mali. Relationships between weather factors and abundance of paniclefeeding bugs were examined for the three most commonly found mirids, E. oldi, Campylomma spp. and Creontiades pallidus Rambur (representing on average respectively 58, 39 and 2% of all mirid species). Although only one generation of E. oldi could develop between flowering and grain maturity on a particular panicle, there were three successive generations each year during the extended grainmaturing period in the experiment with eight sowing dates, with a major peak in abundance in early October, followed by a gradual decrease until late November. Abundance of Cr. pallidus peaked in late October, while that of Campylomma spp. showed no relationship with date of sowing.

An increase in abundance of E. oldi nymphs (y1) was favoured by high precipitation, reduced maximum temperature and high minimum relative humidity during and 2–3 weeks before the grainfilling period [a strong negative relationship was found with the number consecutive days without precipitation from 78–88 days after sowing (das) (x1): y1 = −11.7x1 + 149.3 (r2 = 0.67)]. The abundance of Cr. pallidus (y2) was correlated with wide temperature ranges and low precipitation during the same periods (notably precipitation frequency from 75–91 das: x2): y2 = −2.28x2 + 24.6 (r2 = 0.65). The abundance of Campylomma spp. (y3) was negatively correlated with amount of rainfall between 19–32 das (x3): y3 = −3.82x3 + 705.9 (r2 = 0.49). Reasons for these trends are suggested and their possible application for management of panicle-feeding bugs discussed.

L'étude présente une application de la méthode géostatistique transitive à une dimension (1D) pour estimer la précision des évaluations de biomasse effectuées au Sénégal par écho-intégration. Le problème majeur rencontré dans cette étude a été la prise en compte de la variabilité temporelle dans l'estimation de la variance d'échantillonnage. Lors des campagnes acoustiques, l'écho-intégration se fait en continu le long de la route du navire. Lorsque le plan d'échantillonnage est constitué de transects parallèles, cette caractéristique permet de considérer chaque transect comme une unité d'échantillonnage. En faisant la somme des valeurs mesurées le long des transects, l'estimation à 2D est simplement ramenée à une estimation à 1D. Si de plus les transects sont équidistants, la méthode géostatistique transitive à 1D offre une solution correcte et simple au calcul de la variance d'estimation. La méthode a été appliquée à la série des campagnes acoustiques sénégalaises qui ont toutes été effectuées selon le même réseau de transects équidistants et parallèles d'orientation Est-Ouest. Les densités sont sommées le long des transects. Les variations latitudinales de la biomasse par transect sont présentées sous forme de profils à 1D. La biomasse, la répartition spatiale et l'autocorrélation sur ces profils présentent des différences importantes d'une campagne à l'autre. Les profils ont été regroupés en 4 catégories présentant des caractéristiques différentes. L'autocorrélation moyenne (structure) par catégorie a été estimée et modélisée. Une valeur moyenne de l'erreur relative d'estimation est fournie pour chaque catégorie. L'erreur relative d'estimation varie en fonction des différences de structures entre catégories et aussi en fonction de différentes hypothèses pour la modélisation de la structure aux petites distances. Deux cas ont été considérés : continuité de la distribution (absence d'un effet pépite) ou discontinuité (présence d'un effet pépite). L'erreur relative maximale estimée est d'environ 31 %. Le problème majeur rencontré à la modélisation de la structure 1D des biomasses par transect a été de choisir de prendre en compte ou non un effet de pépite. L'interprétation de cette pépite serait la variabilité temporelle à l'échelle de la radiale.

An analysis of statistical data available in eight glass eel fisheries distnbuted over the French Atlantic coastline is used to define the upstream migration dynamics of Anguilla anguilla in estuaries. The CPUE (Catch Per Unit of Effort) data reveal three different types of seasonal trends that reflect different migration kinetics. The recruitment abundance is studied compared to the salinity of the estuary. The first two types of trends correspond to years of high recruitment andor of reduced fishing effort. In brackish estuarine zones, the abundances then follow a symmetrical curve, with a peak in JanuaryFebruary. This time course is due to the passage of a wave of migrants. Further upstream, in tidal freshwater zones, the abundances follow an asymmetrical curve which may describe the progressive accumulation of eels between November and March/April. When recruitment is low andlor the fishing effort is high, CPUEs vary during the season following a plateau curve, with values staying more or less constant between November and March. This latter trend represents a balance status between immigration and capture. In this case, abundance indicescan only be established with total catches. The curves are explained by the migration behaviour of glass eel which exhibit a resting phase in brackish zones and an accumulation in tidal oligohaline zones. These results have direct consequences particularly for the determination of recruitment abundance indices.

The occurrence and distribution of Cerataphis palmae (Ghesquierei) on Raphia palms in six Southern States of Nigeria, were studied. The percentage infestation of palms in the States were 24.9% (Bendel), 41.23% (Cross River), 37.17% (Imo), 34.73% (Lagos), 11.55% (Oyo) and 28.0% (Rivers). C. palmae is found in places in Southern Nigeria where Raphia palms, particularly R. hookeri Mann & Wendl. and R. vinifera Beauv. occur. There was no significant difference in percentage aphid coverage among the six States (F = 2.013; 0.01 < P > 0.05).

Schooling fish may aggregate in very high densities covering very small areas. Thus the probabilityof hitting such high-density spots during a large-scale sampling is very low. The sampling fluctuations of the tail of the histogram are thought to be very significant. The stock biomass estimate and its precision rely greatly on how precisely the tail of the histogram can be sampled. In order to acquire elements for improving survey designs and abundance estimators wc study here the relation in space that the high values have with the other values. A disjunctive kriging approach is used. Different quantiles of the histogram are coded by indicators. The spatial structure of each indicator and its spatial covariation with the others are studied by computing experimental indicator variograms and cross-variograms. Such analysis is applied to dissect finely the spatial structure of a Norwegian herring stock sampled acoustically. It is shown that when going from low-density areas to high-density ones, intermediate values are not necessarily crossed. Thus a particular disjunctive kriging model with no transition in space is well adapted to the herring data. The model is based on the regressions of each indicator on the one immediately below it. In the model one can estimate the probability for the fish density to trespass a given cut-off at a given location when knowing that the density trespasses lower cut-offs at surrounding points. It is shown on the data that the high densities are structured and show small aggregations. Then it is shown that having trespassed a certain cut-off, i.e. inside the corresponding areas in space, the high-density aggregations can be considered to be positioned independently from the other values. These areas, where the structuring of the high values is not correlated to the structuring of the other values, are mapped using the fitted disjunctive kriging model. The implications for survey designing of the existence of such areas and of their geometry are discussed. Also discussed is the possibility of stratifying the data in spatially uncorrelated boxes when deriving the biomass estimate and its precision, on the basis of an observed spatial non-correlation property between the spatial distribution of different quantiles.

The Boreoatlantic gonate squid Gonatus fabricii is the most abundant squid in the offshore arctic and subarctic waters of the northern Atlantic. Adults are common in midwater while juveniles occur in surface waters close to the continents. As part of a research project focussing on the interactions among fish stocks off West Greenland we examined squid collections sampled with small pelagic nets in summer 1989 and in summer and autumn 1990 off Southwest Greenland. G. fabricii was by far the most abundant cephalopod species caught. We recorded a total of 698 juvenile specimens. During the summer cruise in 1989 the mantle lengths varied from 6 to 35 mm (n = 84); in summer 1990 they ranged from 10 to 48 mm (n = 542) with significantly larger body sizes in the southern part of the region. In autumn 1990 the mantle lengths ranged from 19 to 64 mm (n = 72) with largest animals again at the southern sampling sites. The data suggest growth rates for juvenile G. fabricii off West Greenland of 4 to 5.5 mm per month between July and November 1990.

Light and scanning electron microscopy investigations were carried out to identify and count the chemoreceptors on the legs of the tsetse, Gbssina tachinoides Westwood, and topographical maps, considered of value in electrophysiological and behavioural research are presented. The candidate chemoreceptors are located on the femorae, the tibiae and the tarsi and are more abundant on the ventral zone of each segment. The study demonstrates that the prothoracic, mesothoracic and metathoracic legs have a similar number of chemoreceptors and male flies possess more than female (1033 and 570, respectively). The variability of the number of chemoreceptors on the prothoracic legs has been estimated in both sexes.

Zooplankton samples were collected over a 21-month period in five floodplain lakes of the Orinoco River in orderto establish zooplankton species composition, abundance patterns, and biomass and their relationships with the patterns of inundations and lake morphometry. 60 rotifer taxa were identified. This group was generally more abundant thancopepods and cladocerans (mean : 73,4 % of total zooplankton). Common and abundant rotifer species included K. americana, K. cochlearis, B. mirus, B. gessneri, P. vulgaris and F. longiseta. Copepods were dominated by nauplii (mean : 73,8 % of total copepod stages). Cladocerans were scarce and dominated by M. minuta, C. cornuta and D. spinulosum.Most frequent and abundant zooplankton species were euplanktonic with a dominance of filter feeders and microphagous detritivores. Mean zooplankton density in all lakes ranged from 340 ind./l to 3 486 ind./l. Biomass ranged from 71,1 µg.l (dw) to 432,8 µg/l. Rotifers accounted for 64,7 % of the total mean zooplankton biomass in three lakes whilecopepods accounted for 57,8 % of the biomass in two lakes. Both density and biomass were markedly seasonal withhighest mean values at low waters. Mean density in the lakes was 100 times higher than in the Orinoco main stem. Lakeswith highest variabilities in surface area and water depths showed highest zooplankton densities. The type of connection (direct or indirect) established between the lakes and the major source of the water also seemed important to interpret the productivity of floodplain lakes.

The compositon, abundance and biomass of the benthic fish fauna were studied along a 6 km stretch of the GuariticoRiver. This water course is located in the western plains of Venezuela and belongs to the Apure River floodplain system.Monthly collections from June, 1990 to January, 1991 were made by means of a small trawling apparatus rigged todugout canoes according to the design of López-Rojas et al. (1984). 42 fish species were identified with a dominanceof species from the orders Siluriformes and Gymnotiformes. The fish assemblage differed markedly from other Venezuelan river systems. Seasonally, higher diversity and evenness were observed at the high water phase while the abundance, relative biomass and CPUE were higher at low water.

Zooplankton samples collected at low and high water in 14 and 21 stations respectively along some 900 km of the Orinoco and its Delta, revealed the presence of 100 rotifer and 48 cladoceran taxa. Of these, only 13 rotifer and 8 cladoceran species were frequent and numerically important, mainly Keratella americana, Lecane proiecta, Ploesoma lenticulare, Polyarthra vulgaris, Bosmina tubicen, Bosminopsis deitersi, Diaphanosoma birgei and Moina minuta. Nauplii were dominant among the copepods. At low water, rotifers were by far the most abundant group (mean 49 org./l ) followed by cladocerans (mean 2.8 org/l) and copepods (1.5 org/l). At high water, rotifer densities declined to a mean of 3,5 org/l, followed by copepods (mean 3.4 org/l) and cladocerans (1.2 org/l). Mean zooplankton densities at low water were eight times higher than at high water. At low water, longitudinal zooplankton densities seemed to be influenced by tributary river waters. At high water, densities were generally low up to the Delta where a longitudinal increase was observed. A high proportion of egg carrying cladocerans, particularly B. tubicen, B. deitersi and M. minuta, were observed at low water along the sampling sites, suggesting an ability of the species for growth and reproduction in the river.

From early March 1981 to late May 1982, the aphid population trend on 2-year-old Raphia hookeri palm plantation in Nigerian Institute for Oil Palm Research Benin, was studied in relation to ambient weather conditions. The population, taken from the central ‘spear’ and leaflets of Raphia, where it is most abundant, was high from March to April 1981. This declined to a low level in July and August 1981 following a heavy rainfall. Another peak was observed in September, but this however declined gradually to a very low level at the end of March 1982. However, in mid-April, there was an incipient peak which was quickly lowered again in early May by larvae of the ladybird, Platynaspis sp. The number of adult alatae correlated positively with the total aphid population on spear and leaflets (r = 0.68). There was no direct relationship between the measured environmental factors and the aphid population fluctuation.

Competition between Corcyra cephalonica (Stainton) and Ephestia cautella (Walker) was studied in broken cocoa beans using the two species alone, introduced one before the other and together. Both species of moths cannot co-exist for an extended period and in competition E. cautella becomes extinct. The results offer an explanation of recent evidence that C. cephalonica is rapidly becoming the most important pest of stored cocoa beans in Ghana today.