Francis Fleurat-Lessard

The effect of cold acclimation and deacclimation on cold tolerance, trehalose and free amino acid levels in Sitophilus granarius and Cryptolestes ferrugineus (Coleoptera)

Canadian and French laboratory strains of Sitophilus granarius (L.) and Cryptolestes ferrugineus (Stephens) were cold acclimated by placing adults at 15, 10 and 5 degrees C successively for 2wk at each temperature before deacclimating them for 1wk at 30 degrees C. Unacclimated S. granarius had an LT(50) (lethal time for 50% of the population) of 12days at 0 degrees C compared with 40days after the full cold acclimation. At -10 degrees C, unacclimated C. ferrugineus had an LT(50) of 1.4days compared with 24days after the full acclimation. Cold acclimation was lost within a week after returning insects to 30 degrees C. Trehalose, as well as the amino acids proline, asparagine, glutamic acid and lysine were higher in cold acclimated insects for both species. For S. granarius, glutamine was higher in cold acclimated insects and isoleucine, ethanolamine and phosphoethanolamine, a precursor of phospholipids, were lower in cold acclimated insects. For C. ferrugineus, alanine, aspartic acid, threonine, valine, isoleucine, leucine, phenylalanine and phosphoethanolamine were higher in cold acclimated insects. For both species tyrosine was lower in cold acclimated insects. There were small but significant differences between Canadian and French strains of S. granarius, with the Canadian strain being more cold hardy and having higher levels of trehalose. There were small but significant differences between male and female S. granarius, with males being more cold hardy and having higher levels of proline, asparagine and glutamic acid. In conclusion, high levels of trehalose and proline were correlated with cold tolerance, as seen in several other insects. However, correlation does not prove that these compounds are responsible for cold tolerance, and we outline further tests that could demonstrate a causal relationship between trehalose and proline and cold tolerance.

Cytotoxicity of fumonisin B1: implication of lipid peroxidation and inhibition of protein and DNA syntheses

Abstract The effects of fumonisin B1 (FB1) from Fusarium moniliforme on lipid peroxidation and protein and DNA syntheses were studied in monkey kidney cells (Vero cells). FB1 was found to be a potent inducer of malondialdehyde (MDA), one of the secondary products formed during lipid peroxidation. At 0.14 μM (0.1 μg/ml), FB1 induced 0.496 ± 0.1 nmoles of MDA/mg protein, compared to the control level 0.134 ± 0.01 nmoles of MDA/mg protein (P < 0.005). No inhibition of protein or DNA synthesis was observed at this concentration of FB1. Inhibition of protein and DNA syntheses was observed at FB1 concentrations >14 μM (10 μg/ml) with an IC50 of 33 μM for both protein synthesis and DNA synthesis. These results indicate that lipid peroxidation is a very sensitive cellular response to the mycotoxin fumonisin B1 observed at concentrations lower than that required to inhibit cellular synthesis of macromolecules, protein and DNA. This oxidative damage induced by FB1 concentrations encountered in naturally contaminated foodstuffs and feed might lead to mutagenicity and genotoxicity.

Qualitative reasoning and integrated management of the quality of stored grain: a promising new approach

Abstract Grain quality maintenance has traditionally been the responsibility of grain storekeepers who rely on measurements of grain or its milled products and on implicit knowledge gained through scientific results, common sense and job experience. Thus, managers of grain stores must comprehend the ecological, economic and technical consequences of their actions. Practical application of available knowledge by a grain-store manager may be greatly enhanced by the combination of fundamental concepts from stored-grain ecosystems with principles of expert systems (ES). The ES are computer programs with the capacity to mimic the reasoning logic of human experts when solving complex problems. They have been available as aids for stored-grain management for about a decade. The existing systems that focus mainly on pest management issues are briefly reviewed in the introductory part. Today, there is increasing pressure on the grain-handling industry to manage not only pests but also a broader range of parameters involved in grain quality maintenance. The implementation of a new type of ES to manage grain quality parameters during storage through an integrated qualitative approach is presented. In practice, most of the existing basic knowledge on progressive changes in grain quality attributes can be approximated by the statement of an initial state of quality and predictive models using only three variables: storage duration, grain temperature and water activity (or related moisture content). Combinations of qualitative variables through a logical decision network, predicting changes in different aspects of quality, may enable the prediction of quality from the initial diagnosis. Such a rule-based reasoning approach called “qualitative reasoning” has recently been developed as a decision support tool, starting from the diagnosis of quality attributes of a grain batch upon delivery at a grain store and anticipating the changes that will occur during the storage period. The new approach, based on high level reasoning methods and using a knowledge base (KB) of interactive rules about grain quality changes, is briefly presented. The implementation of this KB has focused on attributes that change very early in unsafe storage conditions such as germination capacity, micro-organism respiration, dry matter loss, visible moulding appearance, pest dynamics, cooling aeration effects and efficacy of residual protectants. Available models that may be introduced into the KB of the system have been reviewed. Most of the parameters of predictive models can be obtained by computation of existing experimental data. The prototype testing indicates that the system may give reliable quality diagnosis and prediction of optimal storage with a level of expertise and advice comparable to human experts. The additional work needed to extend the scope and domain of applicability of this new generation of ES is discussed. The procedure of qualitative reasoning applied to the whole grain ecosystem is shown to be a promising tool for detecting the weaknesses of basic knowledge about changes in cereal quality during storage.

Effects of fumonisin B1 on growth and metabolism of larvae of the yellow mealworm, Tenebrio molitor

The chronic and acute toxicity of fumonisin B1 (FB1), a mycotoxin from Fusarium moniliforme, to the larvae of the yellow mealworm, Tenebrio molitor, was assessed. The toxin was administered via the diet or injected directly into the larvae. Young T. molitor larvae fed on a diet containing 450 μg FB1 per g diet exhibited reduced growth performance but only after consuming the fumonisin‐contaminated diet for several weeks. FB1‐contaminated diet also reduced the rate of carbon dioxide production, food consumption and protein metabolism. The concentrations of FB1 in the diet did not increase mortality, even when tested at the highest dose of 450 μg FB1 per g of diet. Injection of 25 ng FB1 per larva decreased the CO2 production, but became significant only 11 days after the injection and was reversible with time. A parallel analysis of the retention of FB1 by the larvae indicated that about 40% of the ingested FB1 was excreted in the faeces.

Assessment of dry matter loss and frass production in cereal grain due to successive attack by sitophilus oryzae (L.) and tribolium castaneum (herbst)

Local West African strains of Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) were placed in 200 g of wheat samples, one species after the other, during 6 weeks. The rate of infestation for S. oryzae was 6,12,24 or 48 pairs of adults, while it was fixed to 20 for T. castaneum. The generation of S. oryzae was killed by fumigation before T. castaneum infestation of the grain samples. The loss in dry weight and the frass production were recorded at the end of each rearing period of time for each species.The dry matter loss caused by S. oryzae was highly correlated with the rate of adult infestation and measured as high as 600 mg per infesting pair of weevils. The frass production for both S. oryzae and T. castaneum was highly correlated with the rate of infestation by weevils only. For S. oryzae, the average frass production was about 60 mg per adult pair, while for T. castaneum it was variable from 27 to 44 mg per pair of the primary infestation level by the weevils.The importance of these results is discussed in relation to standard loss assessment methods when there are several infesting species and particularly when there is a preponderance of secondary species over primary species.RésuméPour comparer les pertes causées par deux ravageurs d’importance très différente, des souches ivoiriennes de Sitophilus oryzae (L.) et Tribolium castaneum (Herbst) ont été placées sur des échantillons de 200 g de blé tendre, l’une après l’autre, pendant 6 semaines. Les taux d’infestation par le ravageur primaire S. oryzae ont été de 6, 12, 24 ou 48 couples tandis que pour Tribolium, un taux d’infestation fixe de 20 couples d’adultes par échantillon a été retenu.Après la période de développement du charançon, S. oryzae, les lots de blé ont été désinsectisés par fumigation pour détruire l’infestation initiale avant d’y introduire le ravageur secondaire, T. castaneum. On a mesuré, à la fin de chaque période de l’essai, ia perte en matière sèche et la production de “frass”.Pour le charançon, la perte de matière sèche est déjà élevée et elle est bien corrélée avec le taux d’infestation initial, en étant légèrement supérieure à 600 mg par couple de parents. La production de frass est réduite à environ 60 mg par couple pour S. oryzae.Dans le cas de T. castaneum, il existe une bonne correlation entre la production de frass et le taux d’infestation par le ravageur primaire (S. oryzae). La production moyenne de frass sur la période de 6 semaines varie seulement de 27 à 44 mg par couple de ravageur primaire (S. oryzae).L’importance des résultats est discutée en relation avec les méthodes conventionnelles d’évaluation des pertes dans le système post-récolte des climats tropicaux. Il est proposé d’utiliser la mesure de la quantité de “poussière” produite par les insectes en tant que paramètre d’estimation de la perte causée, que ce soit par des ravageurs primaires ou par des espèces secondaires.

Diagnosis and Grading of Grain Initial Quality

Abstract Building up an expert system enabling initial grading of cereal grain quality is presented. The system, easily changeable, is reasoning from experts knowldege about quality deterioration during grain storage. Knowledge was represented as asbtract objects. These objects were inter-related by abstract operations, and scaled into a common space of qualities.A certitude coefficient was affected to each scaled objects and operations in relation to error risk given by experts. These coefficients were then propagated accross the whole process. The separation between the knowledge base, inference engine, and user interface renders the system fully evolutive.

Control of Insects in Post-Harvest: Inert Dusts and Mechanical Means

Residual chemicals are currently used to control stored-product insects pests that are found in granaries and food-processing facilities. Long-term use of these chemicals has resulted in the development of insect populations that are resistant to the common insecticides (e.g. malathion, chlorpyrifos-methyl, pirimiphos-methyl, fenitrothion or deltamethrin) (White and Leesch 1995). Inert dusts are used in a fashion similar to the residual chemicals, and hence offer a convenient alternative for the control of insect pests in grain-and food-processing industry installations such as flour mills, food warehouses and retail outlets.

Planning and Monitoring of Stored Malting Barley Quality Maintenance

Abstract Representing the stored grain ecosystem for quality maintenance implies the representation of all its characteristics that take part in the grain quality degradation process. A mixed qualitative and quantitative modelling is used to represent the stored grain ecosystem. The temperature, moisture content and presence of insects are used as control variables. The quality maintenance operations are represented as actions to be executed in time requiring available equipment and consumable. Our planning approach involves three consecutive stages: treatment to obtain a safe grain storage condition, storage to maintain the storage condition and dispatch to respond to the market requirements.