Understanding the physical and biological effects of dust-induced insect death

Background Quality and quantity of stored grain is constantly changing due to insect and fungal activity. The efficacy of storage method dictates the quality of grain. Traditional chemical pesticides, though effective, were often criticised for issues like increasing insect resistance, chemical residue, environmental contamination and human health risk. The diatomaceous earth based formulations could reduce chemical pesticides usage at some extent. But the slow insect killing and being non-food grade limited wide application. The high recommended dosage (500 to 3500 ppm) results in several adverse effects on grain, including reduce in the flow ability and bulk density, visible residue, extra dust generation during processing. Synthetic amorphous silica (SAS) consists three types: pyrogenic, precipitated, surface-treated SAS. These dusts can be distinguished from natural amorphous silica such as diatomaceous earth by its high chemical purity, the finely particulate nature and characteristics of particles. All types of SAS have been widely used in topical and oral medicines, food and cosmetics for many decades without evidence of adverse human health risks. Based on extensive physico-chemical, ecotoxicology, human health and epidemiology data, SAS as non-chemical method for pest management is revolutionary and advantageous compared to traditional approaches. However, their insecticidal mechanism is poorly understood. The optimal application protocol is not developed. This study described a comprehensive investigation of insecticidal mechanism of SAS particles and their application as an alternative practical stored grain pest control method. Results The first study was aimed to investigate the efficacy of different synthetic amorphous silica (SAS) powders against different insect species at multiple developmental stages compared with diatomaceous earth (DE). The stationary stages, egg and pupa, were more tolerant than that of the mobile stages, larva and adult, upon SAS and DE exposure. The insect infestation cannot be completely control by all the SAS and DE. A 100% of hatching rate was observed and more than 32% of pupa emerged in all the dust treated groups. Larva stage was most susceptible to the SAS and DE. Newly emerged adults were more susceptible to SASs and DE than older adults. The outcome for larvae was opposite. Among the three insect species adults, when treated by SAS and DE, T. castaneum was the most tolerant species and C. ferrugineus was the most susceptible. The efficacy of SAS against insects was higher than that of DE. Among of SASs, precipitated SAS performed better than pyrogenic SAS in term of mortality. Hydrophobic SAS powders were more effective against T. castaneum adult, while hydrophilic SAS powders were more effective against T. castaneum larvae, pupae and Sitophilus oryzae adults. We evaluated the physical property of aforementioned SAS and DE in relation to efficacy. SAS powders have higher specific surface area, total pore volume, oil sorption capacity and smaller particle size than DE. In term of the SAS powders produced by different methods, pyrogenic SAS powders had higher oil sorption capacity but lower total pore volume and specific surface area, and larger particle size than precipitated SAS. Comparing with hydrophilic SAS, the particle size of hydrophobic SAS was smaller while has lower oil sorption capacity. There was a significant relationship between physical property of powder and insecticidal efficacy in SAS without a specific index. We developed and evaluated a rapid screening protocol to identify electrostatic charge dictates attachment processes during initial contact between SAS and insects. The charge ability of three major stored grain insects, Sitophilus oryzae, Tribolium castaneum and Cryptolestes ferrugineus and four hydrophilic precipitated SAS and one DE was assessed on two insulated surfaces filter paper and glass. After contact with insulation surfaces, synthetic amorphous silica (SAS) and DE carry negative charges due to attaining electrons from insulation surfaces, while stored product insects carry charges of opposite polarity from electron loss. According to Coulomb’s law, the SAS particles would then be passively attracted by insect via the mere effect of electrostatic forces. A linear correlation was observed between electrostatic charge and bioactivity of dust. After exposure to SAS, the changes in water content and other physiological components of insects led to changes in coloration and gross appearance. The heterogeneous distribution made visual comparisons difficult. Hyperspectral imaging systems with optically tuneable filters can record images at hundreds of contiguous wavelengths (narrow spectral resolution) in the form of a hypercube (three-dimensional hyperspectral data). Hyperspectral imaging coupled with back propagation neural network models was employed to quantify differences in parameters which reflected the response of T. castaneum and S. oryzae to hydrophobic and hydrophilic precipitated SAS. The presence of SAS on ventral and dorsal cuticle of two insect species caused differential values of relative reflectance in visible and short-wave near-infrared ranges. The control samples of all groups were correctly classified by BPNN model and misclassification occurred only with the two SAS treated. These results suggested that the differences in absorption characteristics of cuticular fat and protein contributed to the varied performance. The recognition rate between two SAS treated was within the acceptable identification range. This suggested that both SASs have similar effect on insect with varied degree. We investigated how these two hydrophobic and hydrophilic precipitated SASs physically influenced insect in intersegmental membrane and their biological effects. Both SASs rapidly reduced insect locomotion to the limiting value within 3.5 hours and 12 hours for S. oryzae and T. castaneum, respectively. In addition, we found that there was significant differential decrease in straightness and upward length which were used as parameters to evaluate insect behaviours. Environmental scanning electron microscope (ESEM) images and data of stride length directly exhibited SAS eroded insect intersegmental membrane and absorbed the vital body fluid, eventually caused irreversible structural damage. The hydrophilic SAS was more effective in changing these parameters in S. oryzae, while hydrophobic SAS was more effective in T. castaneum. Male population was more susceptible than female. We further evaluated the efficacy of SAS structural treatment combined with a new integrated trap as insect control in the field trial. Insect infestation was monitored by integrated trap utilising insect behaviours. Prior to SAS treatment, five integrated traps captured 1722 g insect inside a warehouse in seven day. Synthetic amorphous silica was aerogelize and dispersed uniformly in different locations of the warehouse. The mortality of five major species of stored grain insect adults reached 100% within three days post exposure. Conclusion SAS powders are food-grade, quick, effective, low cost and easy to apply as an insect control method. They don’t have the disadvantages of traditional chemical pesticide regarding to occupational health, environmental and safety concern. Detecting the electrostatic charge is an effective protocol for SAS efficacy evaluation. As an emerging non-destructive and reagent-less analytical technique, hyperspectral imaging proved to be highly efficient in pesticidal effect evaluation. Intersegmental membrane is a promising target site for new inert dust pesticide products

Empowering Smallholder Farmers in Markets: Changing agricultural marketing systems and innovative responses by producer organizations

Though some producer organizations have enabled developing country farmers to exploit new opportunities and/or cope with emerging challenges through developing and/or taking advantage of innovative mechanisms and institutions, there are many farmers who lack sustainable access to inputs and services as well as to remunerative output markets. This paper is intended to generate a better understanding of the conditions which make producer organizations capable vehicles by which farmers, especially small-scale farmers in developing countries, can reach markets in a dynamic and demanding trading environment, and respond to the needs of their clients and members. It aims at identifying lessons on the forms of organizations as well as the innovative mechanisms and institutions that producer organizations can adopt and/or help promote in response to challenges in the changing agricultural marketing systems, in particular, to strengthen the bargaining position of farmers.agricultural marketing systems; producer organizations; innovative rural finance

Rural institutions and producer organizations in imperfect markets: experiences from producer marketing groups in semi-arid eastern Kenya

"Many countries in sub-Saharan Africa have liberalized markets to improve efficiency and enhance market linkages for smallholder farmers. The expected positive response by the private sector in areas with limited market infrastructure has however been disappointing. The functioning of markets is constrained by high transaction costs and coordination problems along the production-to-consumption value chain. New kinds of institutional arrangements are needed to reduce these costs and fill the vacuum left when governments withdrew from markets in the era of structural adjustments. One of these institutional innovations has been the strengthening of producer organizations and formation of collective marketing groups as instruments to remedy pervasive market failures in rural economies. The analysis presented here with a case study from eastern Kenya has shown that while collective action – embodied in Producer Marketing Groups (PMGs) – is feasible and useful, external shocks and structural constraints that limit the volume of trade and access to capital and information require investments in complementary institutions and coordination mechanisms to exploit scale economies. The effectiveness of PMGs was determined by the level of collective action in the form of increased participatory decision making, member contributions and initial start-up capital. Failure to pay on delivery, resulting from lack of capital credit, is a major constraint that stifles PMG competitiveness relative to other buyers. These findings call for interventions that improve governance and participation; mechanisms for improving access to operating capital; and effective strategies for risk management and enhancing the business skills of the PMGs." Author's AbstractMarket imperfections, Transaction costs, Farmer organizations, Institutions, Collective action, Semi-arid tropics, Kenya, East Africa,

The Federal Child Nutrition Commodity Program: A Report on Nutritional Quality

Examines the types of food California schools order through the USDA Child Nutrition Commodity Program and how they affect the nutritional value of school meals. Includes policy recommendations for ensuring that meals meet nutritional guidelines

Expert Consultation on Market Information Systems and Agricultural Commodity: Exchanges: Strengthening Market Signals and Institutions. Proceedings of an expert meeting held in Amsterdam, The Netherlands, 28–30 November 2005

The Expert Consultation on Market Information Systems and Agricultural Commodity Exchanges: Strengthening Market Signals and Institutions was convened to review CTA’s investments in MIS and ACEs within a broad perspective to determine which are the more successful systems, what conditions have enabled them to function well, and how they are being used by farmers’ organisations, traders and other development partners..