Insect Fauna Associated With Anacardium occidentale (Sapindales: Anacardiaceae) in Benin, West Africa
ABSTRACT. Cashew, Anacardium occidentale L. (Sapindales: Anacardiaceae), is an important cash crop in Benin. However, its production is threatened by several biotic factors, especially insects. In Benin, very few studies have focused on insects and just listed species commonly found on cashew worldwide. The present investigation fills this gap by presenting an exhaustive inventory of insect species associated with this crop in the country. The survey was carried out from September 2009 to August 2010 in 22 cashew orchards (5 young and 17 mature) distributed over three major agroecological zones where cashew is most produced in the country. Insects were collected using chemical knock-down technique and visual observation followed by capture with sweep net. In addition, infested plant organs were sampled and incubated to collect emerging insects. In total, 262 insect species were recorded and identified. Among them, the wood borer Apate terebrans Pallas, the leafminer Eteoryctis gemoniella Stainton, and the mirid bugs Helopeltis schoutedeni Reuter., and Helopeltis anacardii Miller., appeared as the most important insect species attacking cashew in Benin. Beneficial insects encountered included some predators, parasitoids, and pollinators. Few vertebrate predators were also recorded on the trees. Differences in agroecological conditions or in field cleanliness did not affect the number of insect species encountered in the cashew orchards. The results of this study represent an important baseline data for the design and implementation of strategies for cashew protection in Benin.
Spatial and Temporal Infestation Rates of Apate terebrans (Coleoptera: Bostrichidae) in Cashew Orchards in Benin, West Africa
Cashew, Anacardium occidentale L. is an important export crop in Benin, but incurs serious damage from the cashew wood borer Apate terebrans Pallas. In spite of its economic importance, the population dynamics of this beetle have never been studied, thus precluding any science-based development and implementation of control strategies. The spatial and temporal abundance pattern of A. terebrans was therefore monitored in 17 mature cashew orchards distributed across three agro-ecological zones in Benin. In each orchard, 30 cashew trees were chosen at random and inspected monthly for two consecutive years. As this insect feeds inside branches and trunks by boring holes, direct observations of adults inside the tree are not possible. Therefore infestations of trees were estimated by the occurrence and number of fresh entry holes. Over the two-year observation period, infestations in the cashew trees by A. terebrans started in September, peaked in January–February and sharply declined thereafter, reaching zero by July–August. Whereas the infestation rates were statistically similar between sampling years or among agro-ecological zones, they differed significantly among sampling months. Aggregation indices calculated using Taylor's power law indicated that A. terebrans has an aggregated spatial distribution. Values of the Spatial Analysis by Distance IndicEs (SADIE) index indicated that the spatial pattern of the infestation in a given year does not depend on the pattern observed in the previous years, suggesting that A. terebrans generally prefers to infest new trees. Implications of our findings for the development, implementation and monitoring of effective control strategies against A. terebrans are discussed.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.