Diversity of Stored Grain Insect Pests in the Logone Valley, from Northern Cameroon to Western Chad Republic in Central Africa

Insects are major pests of stored grains. In sub Sahara Africa, stored grain insect pests are mainly Coleoptera or Lepidoptera. In the Logone Valley, area covering the Far North Region of Cameroon and South-West of Chad, to our knowledge, the diversity of insect pests noxious to stored products is not established. These beetles and weevils （Insecta：Coleoptera） during their development depreciate food in storage, were able to destroy a whole stock in a very short period of time if no protection of stored food is made. To achieve the diversity of insect pests, inspections of granaries were done in 209 villages of Logone Valley where insect pests were collected and identified. Secondly, the stored grains were sampled in peasant＇s granaries of Logone Valley and reared in incubators in the Unit of Entomological Research of the University of Ngaound6r6. After their emergence, insects were removed, collected and identified. Their noxious efficiency on stored grains is done by the calculation of the density of each insect pests per gram of grains. This study indicates that 12 species of harmful insects attack cereals and leguminous grains in the Logone Valley during storage. The Bruchids were the main insect pests of legumes. Callosobruchus maculatus was the main pest of legume and attacking mainly cowpeas （34.92 bruchids/g of seed） and peanuts （20.75 bruchids/g of seed）. Seven harmful species destroy the cereals. Sitophilus zeamais is the main pest of maize （15.86 weevils/g of maize） and S. oryzae, for sorghum （36.59 weevils/g of maize）. Tribolium castaneum were the main secondary pest. T. castaneum infests both cereals and leguminous. This work summarizes the importance and the diversification of stored grain pests in Logone Valley. Knowing the pest diversity is an important step in the strategy to develop a friendly and ecological control method of these harmful insects.

A Design of Acoustic Signal Wireless Acquisition System for Stored Grain Pests Based on Compressed Sensing

In order to achieve the acoustic signal distributed acquisition of stored grain pests, a novel acoustic signal acquisition system was presented based on the wireless sensor networks. And the system architecture, hardware configuration, and software were introduced in detail. Considering bandwidth limitation of wireless sensor networks, random sampling algorithm based on the compressed sensing theory was proposed. The developed acoustic signal acquisition system was applied in sampling the crawl acoustic signal of Tribolinm castaneum Herbst adults in granary. Preliminary experimentation indicated the rationality and practicability of the developed system and the proposed algorithm. They can implement the remote, real-time, and reliable wireless transmission for the acoustic signal sampled data of multiple points stored grain pests effectively.

Pest Management of Storage Pests Using Extracts of Afrostyrax lepidophyllus against Sitophilus zeama＇（s, Tribolium castaneum and Rhyzopertha dominica

The use of botanical pesticides in pest management during storage against insects is often encouraged because synthetic insecticides produce multiple side-effects on human health and environment. Insecticidal activity of the hexane, dichloromethane, ethyl acetate and methanol extracts of bark ofAfrostyrax lepidophyllus was tested on Sitophilus zeama~：~, Tribolium castaneum and Rhy-opertha dominica. The mortality rate was measured variable. The results of analysis showed that the mortality rate has a very highly significant variation following extracts, doses, insects and time considered （P 〈 0.001）. Extracts with ethyl acetate and hexane of A. lepidophyllus are effective against S. zeamais at the highest doses （1 g/10 mL and 0.5 g/10 mL of solvent）. These effective extracts werc characterized by gas chromatography coupled with mass spectrometry. Molecules such as thiocyanic acid, ethyl ester： dimetbylditbiophosphinic acid and other were characterizated. These results may consolidate traditional use ofA. lepidophylh^s in pest management.

Chemical Characterization and Insecticidal Activity of Ethyl Acetate and Dichloromethane Extracts of Drypetes gossweileri against Sitophilus zeamais, Tribolium castaneum and Rhyzopertha dominica

The use of botanical pesticides in pest management during storage against insects is often encouraged because synthetic insecticides produce undesired effects. Bark powder ofDrypetes gossweileri is used by farmers in pest management in Central Africa Republic. Hexane, dichloromethane, ethyl acetate and methanol were used for extraction bark powder by maceration. Insecticidal activity of the extracts was tested on Sitophilus zeamais, Tribolium castaneum and Rhy_-opertha dominica. The mortality rate, the number of surviving insects and the number of emerged insects were measured variables. Calculated mortality was obtained by applying Aboth＇s formula. The variables are submitted to variance analysis, model with four factors （plants, insects, doses and time） in Minitab 14. The results of analysis showed that the mortality rate has a very highly significant variation following extracts, doses, insects and time considered （P 〈 0.001）. Extracts with ethyl acetate and dichloromethane of D. gossweileri are effective against S. zeamais and R. dominica at high doses （1, 0.5, 0.250 g/10 mL of solvent）. These effective extracts were characterized by gas chromatography coupled with mass spectrometry. Molecules such as l-isothiocyanatomethyl, thiocyanic acid, phenylmethyl ester and other were characterizated. These results may consolidate traditional use olD. gossweileri in pest management.

Diatomaceous earths as alternatives to chemical insecticides in stored grain

Diatomaceous earth （DE） is a natural inert dust used to control insect pests in stored grain as an alternative to synthetic residual insecticides. Various DE formulations are now registered as a grain protectant or for structural treatment in many different countries throughout the world. The mode of action of DE is through the absorption of cuticular waxes in the insect cuticle, and insect death occurs from desiccation. The main advantages of using DE are its low mammalian toxicity and its stability. The main limitations to widespread commercial use of DE are reduction of the bulk density and flowability of grain, irritant hazards during application and reduction in efficacy at high moisture contents. This paper is an updated review of published results of researches related to the use of DEs and discusses their potential use in large-scale, commercial storage and in small scale applications.

Potential of the neonicotinoid imidacloprid and the oxadiazine indoxacarb for controlling five coleopteran pests of stored grain

The potential for using imidacloprid （a neonicotinoid） and indoxacarb （an oxadiazine） as grain protectants was investigated in bioassays against resistant strains of five stored grain beetles. The species investigated were Rhyzopertha dominica （E） （the lesser grain borer）, Sitophilus oryzae （L.） （the rice weevil）, Tribolium castaneum （Herbst） （the rust-red flour beetle）, Oryzaephilus surinamensis （L.） （the saw tooth flour beetle）, and Cryptolestesferrugineus （Stephens） （the fiat grain beetle）. Each of these species has developed resistance to one or more protectants, including organophosphorus insecticides, synthetic pyrethroids and the juvenile hormone analogue methoprene. Mortality and re- production after a 2-week exposure of adults to treated wheat depended on species, dose and insecticide. Imidacloprid had no effect on S. oryzae at any dose, but none of the other species produced any live progeny at 10 mg/kg. Indoxacarb had no effect on T. castaneum at any dose, but none of the other species produced any live progeny at 5 mg/kg. The results show that although both imidacloprid and indoxacarb can control at least four of the five key pests tested at doses comparable to those used for organophosphorus protectants, more potent neonicotinoid or oxadiazine insecticides would be needed than either of these to provide broad spectrum protection of stored grain .

Point cloud simplification algorithm based on particle swarm optimization for online measurement of stored bulk grain

The simplification of 3D laser scanning point cloud is an important step of surface reconstruction and volume estimation of bulk grain in granary.This study presented an adaptive simplification algorithm based on particle swarm optimization(PSO).It introduced PSO into the average distance method,a conventional simplification method.The basic idea of this algorithm was to adaptively determine the optimal point reducing intervals of scanning lines according to original point cloud density by PSO.By using the 3D point cloud scanned from bulk grain surface in granary,the proposed algorithm was validated.Compared with the average distance method,the proposed algorithm obtained more evenly distributed point set,smaller reduction ratio(6.96%)and higher volume estimation accuracy(relative error was less than 3‰).The 3D laser scanner(GSLS003,Jilin University and SkyViTech Co.,Ltd.,Hangzhou,China)used in this study could scan the complete picture of the grain surface in a granary in one time,so the acquired point cloud data do not have to be jointed.For the good simplification performance and capability of updating the reducing interval at any moment,the proposed algorithm and the 3D laser scanner could be used to realize online real-time measurement of stored bulk grain volume in granary.

Classified denoising method for laser point cloud data of stored grain bulk surface based on discrete wavelet threshold

Surfaces of stored grain bulk are often reconstructed from organized point sets with noise by 3-D laser scanner in an online measuring system.As a result,denoising is an essential procedure in processing point cloud data for more accurate surface reconstruction and grain volume calculation.A classified denoising method was presented in this research for noise removal from point cloud data of the grain bulk surface.Based on the distribution characteristics of cloud point data,the noisy points were divided into three types:The first and second types of the noisy points were either sparse points or small point cloud data deviating and suspending from the main point cloud data,which could be deleted directly by a grid method;the third type of the noisy points was mixed with the main body of point cloud data,which were most difficult to distinguish.The point cloud data with those noisy points were projected into a horizontal plane.An image denoising method,discrete wavelet threshold(DWT)method,was applied to delete the third type of the noisy points.Three kinds of denoising methods including average filtering method,median filtering method and DWT method were applied respectively and compared for denoising the point cloud data.Experimental results show that the proposed method remains the most of the details and obtains the lowest average value of RMSE(Root Mean Square Error,0.219)as well as the lowest relative error of grain volume(0.086%)compared with the other two methods.Furthermore,the proposed denoising method could not only achieve the aim of removing noisy points,but also improve self-adaptive ability according to the characteristics of point cloud data of grain bulk surface.The results from this research also indicate that the proposed method is effective for denoising noisy points and provides more accurate data for calculating grain volume.

Modeling on Heat and Mass Transfer in Stored Wheat during Forced Cooling Ventilation

A mathematical model based on the theory of heat and mass transfer in porous media was developed to simulate the evolution of grain temperature and moisture content in a wheat storage bin during ventilation with cooling air at the constant temperature and humidity.Unlike the previous works on this aspect,the present work was not focused on cooling the stored grain by ventilation with ambient air,but with the refrigerated air.Validation was performed by comparing between predicted and measured grain temperature and grain moisture content for two cases.Predicted data were in reasonable good agreement with measured ones.The model and the parameter values used in the model are applicable for predicting temperature and moisture of stored grains under ventilation conditions.

Does cypermethrin affect enzyme activity, respiration rate and walking behavior of the maize weevil （Sitophilus zeamais）？

Insecticides cause a range of sub-lethal effects on targeted insects, which are frequently detrimental to them. However, targeted insects are able to cope with insecti- cides within sub-lethal ranges, which vary with their susceptibility. Here we assessed the response of three strains of the maize weevil Sitophilus zeamais Motschulsky （Coleoptera.＂ Curculionidae） to sub-lethal exposure to the pyrethoid insecticide cypermethrin. We ex- pected enzyme induction associated with cypermethrin resistance since it would aid the resistant insects in surviving such exposure. Lower respiration rate and lower activity were also expected in insecticide-resistant insects since these traits are also likely to favor survivorship under insecticide exposure. Curiously though, cypermethrin did not affect ac- tivity of digestive and energy metabolism enzymes, and even reduced the activity of some enzymes （particularly for cellulase and cysteine-proteinase activity in this case）. There was strain variation in response, which may be （partially） related to insecticide resistance in some strains. Sub-lethal exposure to cypermethrin depressed proteolytic and mainly cellulolytic activity in the exposed insects, which is likely to impair their fitness. However, such exposure did not affect respiration rate and walking behavior of the insects （except for the susceptible strain where walking activity was reduced）. Walking activity varies with strain and may minimize insecticide exposure, which should be a concern, particularly if associated with （physiological） insecticide resistance.