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The impact of mirid true bugs on cocoa production is widely assessed for Sahlbergella singularis and Distantiella theobroma species in the cocoa growing area in Africa. No study has been focused on the impact of another common mirid species in cocoa farming, such as Helopeltis sp., on the cocoa productivity. Thus, the main objective of this work was to assess the effect of Helopeltis sp. attacks on cocoa productivity of ten genotypes. Observations were made on infested fruits (cherelles, immature and mature fruits) under a randomized experimental field design. A control assay was also used in our investigations. The overall results revealed that only fruits infected by mirids aborted: 80.0% for cherelles and 0.4% for immature fruits. The numbers of aborted fruits were statistically comparable between cocoa genotypes and their rates varied from 60 to 96%. In contrast, ANOVA showed that the feeding lethal punctures of Helopeltis sp. were significantly (p

The impact of mirid true bugs on cocoa production is widely assessed for Sahlbergella singularis and Distantiella theobroma species in the cocoa growing area in Africa. No study has been focused on the impact of another common mirid species in cocoa farming, such as Helopeltis sp., on the cocoa productivity. Thus, the main objective of this work was to assess the effect of Helopeltis sp. attacks on cocoa productivity of ten genotypes. Observations were made on infested fruits (cherelles, immature and mature fruits) under a randomized experimental field design. A control assay was also used in our investigations. The overall results revealed that only fruits infected by mirids aborted: 80.0% for cherelles and 0.4% for immature fruits. The numbers of aborted fruits were statistically comparable between cocoa genotypes and their rates varied from 60 to 96%. In contrast, ANOVA showed that the feeding lethal punctures of Helopeltis sp. were significantly (p

Mirid populations and their damages on cacao production have been widely studied in farms found under shaded conditions worldwide. The recent establishment of unshaded cacao plantations in Cameroon provided us the opportunity to assess the mirid abundance and damage in nine farms in three locations, from savannah to forest zones, in two consecutive years. Mirid abundance was assessed by visual counts of individuals and damage by scoring dry leaves on branches and cankers on twigs and trunks of trees. All mirids observed belonged to the species Sahlbergella singularis (Hemiptera Miridae). Generally, mirid numbers were low (0.26 ± mirid tree-1 for year 1 and 0.35 ± mirid tree-1 for year 2) and significantly lower in the Savannah zone (0.24 mirid cacao tree-1) than the transition zone (0.51 mirid cacao tree-1) and the forest zone (0.60 mirid cacao tree- 1). The Mirid damages was varied significantly (p

The population dynamics of African cacao mirids have been widely studied in shaded cacao systems, which are predominant in most of the cocoa producing countries. The current establishment of new cacao systems in Cameroon enables us to study mirids and the spatial distribution of their damage in six unshaded cacao plantations that are down on savannah and forest regions. We assessed mirids density through visual counts of individuals and damage by scoring dry leaves on branches and cankers on branches and trunks. Our results showed that the mirid populations were low and aggregated on few cacao trees. Mirid spatial distribution was structured in half of the plots and trees with mirids were grouped in distinct areas and/or scattered throughout the plots. Dry leaves damage was low but more widely spread with a spatial distribution less structured than mirid populations. Canker damage was high and their spatial distribution was structured, with some areas more infested. Since cankers accumulated on branches during the 4-years period following plot establishment, our results provide information about the history of mirid infestation in the plots. Despite the aggregation of mirid populations in the plots, infestation areas vary over space and time. However, the presence of higher infestations in some areas in the plots could indicate that there are zones that offer better ecological conditions to mirids. Our study contributed to a better knowledge of population dynamics for cacao mirids in sunny habitats as well as their damage; and these should be taken into consideration for integrated pest management strategies against S. singularis.

The aim of this study was to analyze the spatial distribution of S. singularis populations and associated damage in young not yet shaded cocoa-based agroforestry systems. The study was carried out in six 4 years-old cocoa plantations located in the Centre region of Cameroon. Three different specialized models were used for analysis: the Taylor's power law, the binomial negative distribution and semi-variograms. The populations of S. singularis were strongly aggregated in the studied plantations. Recent damage, namely feeding lesions on flushes and pods, was also relatively aggregated yet less clearly than mirid populations. In contrast, older damage, namely cankers on trunks and branches, was more regularly distributed, although some zones of the cacao plantations were more damaged than others. These results provide information about the history of mirid infestations in these young and unshaded plantations, and suggest that, if mirid populations are usually aggregated, infestation areas vary over space and time, leading to relatively uniform cumulated damage. However, the presence of higher infestations in some areas of the cocoa plantations could indicate that there are zones that offer better ecological conditions (in the form of habitat and/or food) to mirids. Our study contributes to the understanding of the spatial distribution of S. singularis populations and its damage in young cocoa plantations, and these should be taken into consideration for integrated pest management (IPM) strategies against S. singularis, especially in unshaded cocoa plantations.

The study aims to identify the explanatory factors of the commercial cocoa yield farmer's fields in 9 villages located in 4 agro-ecological zones of Cameroon. The method of analysis statistical of segmentation CART was used to explain the variables of the output according to all the explanatory variables available. The test was carried out starting from the data of two years diagnosis, in 36 farmer's plots where the observations related to 30 cocoa trees, that is a total of 1080 trees. The genetic Type, the vigour off the tree (section), flowering (flowers cushion), the bios attackers (stings pods rate and rotted pods rate) and the climate factors (the monthly average temperature and monthly rainfall) were the parameters measured to try to explain the variables of production (the number and the weight of harvested cocoa pods). The results obtained show that the hybrid genetic type have rate of trees in farmer's field is more than 33%, predicted 250% increase production in pods number and weight. Moreover, it was observed that the rate of stings and rotted pods was reduced by 2% when the temperature lied between 24 and 27°C and the mean annual rainfall equal gold less than 1775mm. Moreover the rate of things pods fruits was reduced by 2/3 (two thirds) the number of flowering when this one is lower than 2066. The rate rotted pods was reduced by 40% when the section of the cacao-trees is higher than 138 mm ².

Background: Field trapping experiments were conducted to evaluate the attractiveness of five different pheromone blends as well as the impact of trap design on attractiveness towards cocoa mirids, Sahlbergella singularis Hagl. and Distantiella theobroma (Dist.), in Cameroon. Results: A total of 361 adults of S. singularis (359 males and two females) were caught. The highest numbers of mirids were found in traps with pheromone blends that combined a monoester and a diester, compared with traps with the diester or the monoester individually and control traps with no pheromone. Rectangular traps caught significantly more mirids compared with delta traps. The mean number of 5.1mirids trap-1 year-1 caught in rectangular traps was significantly higher compared with the 1.8 mirids trap-1 year-1 for the delta traps. Conclusion: The data revealed that rectangular traps containing pheromone blends combining both themonoester and the diester have a good potential to lure and trap adult males of S. singularis on cocoa farms. The pheromone blends used were specific for S. singularis, and the use of pheromone traps appears to be a promising strategy for incorporation into integrated pest management strategies for the monitoring or even the control of S. singularis in cocoa plantations.

Les mirides du cacaoyer, et plus particulièrement l'espèce #Sahlbergella singularis#, causent au Cameroun des pertes de production considérables. Une enquête récente estime que 25 % des arbres du verger cacaoyer camerounais ont disparu du fait des attaques de mirides, depuis le début des années 90, et la fin des traitements en régie organisés par l'état. La plupart des planteurs se trouvent en effet fort démunis face à ce fléau, n'ayant ni les moyens financiers, ni les connaissances techniques nécessaires à une lutte efficace. La lutte intégrée est une voie prometteuse, car elle s'adapte aux contraintes techniques et socio-économiques des planteurs. Mais sa mise en oeuvre nécessite une connaissance approfondie de la biologie et de l'écologie du ravageur cible, connaissance qui est encore lacunaire chez #S. singularis# au Cameroun. C'est pour cette raison qu'une étude de la distribution spatiale de #S. singularis# a été engagée il y a 3 ans, dans le cadre du projet FSP Régional " Systèmes de Cacaoculture Compétitifs et Durables ". Cette étude a été menée au sein de 36 plantations paysannes réparties dans 4 zones de production de la province du Centre au Cameroun, présentant des caractéristiques agro-écologiques variables. Des parcelles de 30 arbres ont été délimitées dans ces plantations et des comptages de mirides ont été réalisés sur chaque arbre, de façon hebdomadaire, pendant deux années consécutives. Des cartes de distribution des mirides ont été réalisées témoignant d'une répartition agrégée des mirides au sein des parcelles sélectionnées. Des semivariogrammes ont été élaborés pour chaque parcelle dans le but d'analyser la dépendance des données de comptage dans l'espace. Les semi-variogrammes ont généralement présenté une allure propre au modèle " gaussien ", traduisant l'existence de gradients d'infestation au sein des parcelles. Enfin, la méthode d'interpolation spatiale de " krigeage " a été appliquée de manière à matérialiser, dans les parcelles représentées en trois dimensions, les foyers d'infestation de mirides et leur amplitude. Les résultats sont discutés et leurs conséquences sur l'efficacité des méthodes de lutte actuelles et les stratégies de lutte intégrée à développer dans l'avenir sont analysées.

Mirid bugs are regarded as the most damaging pests of cocoa in Africa. In Cameroon, Sahlbergella singularis is by far the most common mirid species on cocoa. In nature, S. singularis populations display sharp seasonal fluctuations. Yet, in absence of integrated studies, including cocoa tree growth and physiology, chemical ecology, as well as mirid life history, the origin of these seasonal variations has not been clarified. Therefore, we studied the impact of cocoa tree phenology and canopy microclimatic conditions on survival and fecundity of S. singularis, with the aim of contributing to a better understanding of the seasonal variations of S. singularis. Ten to 25 newly moulted females were sampled from ten successive generations of a rearing population, i.e. generations G1 to G5 in 2006 and generations G8 to G12 in 2007. After a premating period of 5 days, females were mated for 24 hours and transferred on sleeved pods, in an on-station plot. Because they were embedded in the plant tissues, eggs were difficult to detect. Therefore, we assessed fecundity by a daily monitoring of nymph emergence. Cocoa phenology was characterized by weekly counting of flowers, growing pods, adult pods and ripe pods, of one branch of the ten cocoa trees used for experimentation. Vegetative growth was assessed by grading the flush abundance on a notation scale. Temperature and relative humidity were recorded within the cocoa canopy with a Testo humidity/temperature logger. Fecundity displayed great variations both within and between generations. Mean fecundity per generation decreased significantly from G1 to G5 and from G8 to G12. In 2006, mean fecundity dropped from 49.3 ± 41.4 nymphs/female to 4.6 ± 12.1 nymphs/female. In 2007, mean fecundity dropped from 89.2 ± 94.0 nymphs/female to 16.7 ± 21.1 nymphs/female. The maximum fecundity was obtained for a female of the generation G8, with 236 nymphs. Fecundity was correlated with the abundance of the fruiting organs and especially with the abundance of growing pods. In the other hand, individual fecundity was negatively correlated with the mean flushing score and the maximum daily temperature. Since mean fecundity varied according to natural populations, we hypothesize that the drop of fecundity is an important parameter of the decrease in mirid densities in nature. The use of such results in pest management strategies against cocoa mirids is discussed. (Texte intégral)

Termites play a prominent role in the decomposer food web as ‘ecosystem engineers’. However, the effect of spatial scales on termite assemblages has, to date, been poorly studied. Here, we evaluate the contribution of two spatial levels [transects (100 m · 2 m) and sections within transects (5 m · 2 m)] on the local termite assemblage of a continuous mixed secondary lowland rainforest in southeast Cameroon. Standardized 100 m · 2 m transects were run in five vegetation types to cover more of the heterogeneity of this forest. The additive partitioning of the species richness of all species, soil- and wood-feeder species was statistically tested with sample-based randomization. The average species richness per transect (61) was the highest ever recorded. The section scale significantly influenced the observed species richness of all groups. This suggests that physical complexity and heterogeneity exist on a small scale within each transect and create a variety of microhabitats for different termites. Still, soil-feeder species were less influenced by this scale than wood-feeder species. Although different vegetation types were sampled, transect scale did not enhance observed termite species diversity. Overall, as a wide variety and high density of microhabitats is inherent to large primary or regenerating forests, conservation programmes should focus on interconnecting large tropical rainforest blocks in Central Africa to maintain biodiversity hot spots of termites and optimal ecosystem functioning.

Field and laboratory tests were conducted for different components of the resistance of cocoa to mirids (Sahlbergella singularis) at the Nkoemvone and Nkolbisson research stations of IRAD as part of the CFC/ICCO/IPGRI project activities in Cameroon. Almost 40 local or international genotypes were tested for one or for several components of resistance. Laboratory micro-tests were used to assess attractiveness. Antixenosis was measured by enclosing mirid nymphs in sleeve cages on young flushes. Attractiveness and antixenosis were estimated in the same set-up by counting the feeding points after 24 hours. Ability to recover from mirid damage (tolerance) was assessed by observing degradation of twigs with time. Finally, antibiosis tests were conducted with the aphid Toxoptera aurantii, with the aim of evaluating whether this aphid could be used as an indicator for cocoa antibiosis towards mirids. Statistical analysis generally revealed a strong effect of genotypes on the different components of the resistance. However, there was no significant difference between the genetic groups studied (Upper Amazon and Lower Amazon Forasteros, Trinitarios and hybrids), which appears to be in contrast with field observations on mirid damage in Côte d'Ivoire. We also failed to identify genotypes that combine favourable responses to several resistance components. As an important result, the activities have made it possible to improve and standardize the evaluation methods. Mechanisms involved in attractiveness and antixenosis appeared to be similar, therefore one test should be enough to evaluate these components. We propose to standardize the methods for antixenosis (under no-choice conditions) and tolerance. We suggest that a new assessment method be developed for the effect of genotype on antibiosis (female mirid fecundity and nymph survival), using cocoa pods on the tree as the feeding and egg-laying environment. Finally, we propose to include in our future activities studies on resistance of cocoa to fungal pathogens that may be associated with mirid damage, with the aim of achieving a better understanding of tolerance and dieback.

Le scolyte des cerises de caféier, Hypothenemus hampei (Ferrari) (Coleoptera, Scolytidae), est l'un des plus sérieux ravageurs du café robusta commercialisé; une étude de lutte biologique a été menée dans deux sites au Cameroun: Nkoemvone dans la province du Sud du pays et Nkolbisson près de Yaoundé, dans la province du centre. Pendant six mois, 500 baies étaient mensuellement prélévées au hassard dans chaque site. Les observations sur le champignon entomopathogènes étaient réalisées au laboratoire sur les baies attaquées par les scolytes. Le nombre de Baies portant le champignon entomopathogène Bauveria bassiana (Bals.). s'est révélé plus significativement élevé à Nkolbisson qu'à Nkoemvone. Les observations sur les scolytes morts ont été aussi significativement plus élevés à Nkolbisson, par contre celles sur les scolytes vivants étaient significativement très faible dans ce même site. Dans les 2 sites, le taux de mortalité du scolyte due à Bauveria bassiana était plus élevé en période humide (Septembre et Octobre) qu'en période sèche (Décembre à Février). Ces deux sites ont besoin d'un apport par infection artificielle du B. bassiana pour une stratégie de lutte biologique conte for H. hampei. (Texte intégral)

Des tests d'antixénose et de tolérance du cacaoyer aux attaques de mirides ont été menés sur 10 génotypes, dans une parcelle expérimentale d'une station de recherche au Cameroun. Une larve de Sahlbergella singularis, affamée pendant une nuit, était maintenue sur un jeune rameau de cacaoyer, à l'intérieur d'un manchon de tulle, afin qu'elle si alimente pendant 24 heures. L'antixénose était mesurée par le comptage du nombre de piqûres d'alimentation après 24 heures. La tolérance était estimée par des observations régulières de l'évolution des dégâts dus aux piqûres et de la reprise du bourgeonnement des jeunes rameaux. L'analyse des résultats a montré d'une part un effet hautement significatif du génotype sur le nombre de piqûres et sur les capacités de l'arbre à contenir l'évolution des dégâts et à reprendre une croissance normale après l'attaque, et d'autre part que ces deux dernières composantes doivent être considérées comme deux facteurs distincts de la résistance génétique du cacaoyer aux mirides.

Laboratory tests were performed in Cameroon in order to assess the level of attractiveness of eleven cocoa genotypes towards mirids. Clones were ranked according to their attractiveness score and from a distance to a mean value. An analysis of variance was performed and showed significant differences between cocoa clones (F=3.15, p

Field tests for antixenosis (feeding non-preference) and tolerance of cocoa trees to mirid damage were conducted as part of the CFC/ICCO/IPGRI Project, in the budwood garden of IRAD Nkolbisson Station. Antixenosis was assessed by counting the number of mirid bites on the flush after 24 hours, while assessment of tolerance was based on regular observations of the evolution of mirid damage and of the ability of twigs to recover from it. An analysis of covariance, with the surface area of the flush leaves as a covariable, revealed a highly significant effect of the clone on the number of mirid bites, and SIC 5 and CATONGO showed a stronger effect of antixenosis than the other clones. The results obtained by observing the evolution of mirid damage and the sprouting of twigs revealed that the ability of clones to contain the extent of damage, and their ability to recover from it must be considered as two distinct components of genetic resistance to mirid attack. The analysis of covariance also revealed a highly significant effect of clones for these two components. UF 676 and IMC 60 showed the best ability to contain the degree of damage, while PLAYA ALTA 2, ICS 1 and UF 676 were the best clones in terms of ability to recover from mirid damage.