Maize weevil

Abstract: The maize weevil (MW), Sitophilus zeamais (Motsch.), is a storage pest that causes serious losses in maize (Zea mays L.) in developing countries. This study was conducted to investigate the role of pericarp cell wall components as factors that contribute to MW resistance in nine genotypes of tropical maize. Six susceptibility parameters to MW were measured and related to cell wall components such as simple phenolic acids, diferulic acids (DiFAs), hydroxyproline-rich glycoproteins (HRGPs), and nutritional and physical traits. Weevil susceptibility was negatively correlated (P < 0.001) with total DiFAs (r = -0.77), HRGPs (r = -0.82), grain hardness (r = -0.87), pericarp/whole kernel (P/K) ratio (r = -0.68), and pericarp thickness (r = -0.86). A detailed analysis of phenolics indicated the presence of trans-ferulic acid (FA), p-conmaric acid (CA), and four isomers of DiFA. The most prominent were 5,5'-DiFA, 8-O-4-DiFA, and 8,5'-DiFA benzofuran form (DiFAb). On the basis of regression models, 5,5'-DiFA, 8-O-4-DiFA, trans-FA, and p-CA were the most important phenolic components of resistance. Grain hardness was correlated (P < 0.001) with cell wall bound HRGPs (r = 0.61) and DiFAs (r = 0.75). Cell wall cross-linking components could contribute to MW resistance by fortification of the pericarp cell wall as well as increase grain hardness. This structurally based mechanism should be considered in the development of hybrids and varieties where storage pests are prevalent.

Abstract: In the period 2007 to 2010, at localities Backi Maglic and Krivaja studies of weed seedbank were performed under soybean crop. Results showed that weed seed separated at Backi Maglic in all years dominated in the top soil layer, while the lowest quantities were separated from the deepest layer, and that number of weeds declined annually. At Krivaja, the lowest weed seed stocks were found in the top layer, and the highest in the deepest layer. At this locality, number of weed seeds kept rising from season to season, which was the consequence of application of different cultural practices. Key words: Soybean, weed seedbank, Amaranthus retroflexus L., Chenopodium album L.,Datura stramonium L.

Abstract: BACKGROUND: In a screening programme for new agrochemicals from Chinese medicinal herbs, Chenopodium ambrosioides L. was found to possess strong fumigant activity against the maize weevil Sitophilus zeamais (Motsch.). Essential oil of C. ambrosioides was obtained by hydrodistillation, and the constituents were determined by GC-MS analysis. The active compounds were isolated and identified by bioassay-directed fractionation. RESULTS: Five active compounds [(Z)-ascaridole, 2-carene, ρ-cymene, isoascaridole and α-terpinene] were isolated and identified from the essential oil from Chinese C. ambrosioides. The LC50 values (fumigation) of the crude essential oils and the active compound (Z)-ascaridole against S. zeamais adults were 3.08 and 0.84 mg L−1 air respectively. The LD50 values (contact toxicity) of the crude essential oil and (Z)-ascaridole against S. zeamais adults were 2.12 and 0.86 µg g−1 body weight respectively. CONCLUSION: The findings suggested that the essential oil of Chenopodium ambrosioides and its main active constituent, (Z)-ascaridole, may be explored as a natural potential fumigant. Copyright © 2011 Society of Chemical Industry

Abstract: Accessions representing twenty eight landraces of maize were assessed for susceptibility to the maize weevil, Sitophilus zeamais in standardized resistance tests. Susceptibility parameters such as weight loss of grain, number of insect progeny produced, the Dobie index of susceptibility, and oviposition on grain were found to vary significantly by genotype, with exceptional resistance found in accessions representing the Naltel, Chapalote and Palomero landraces. As in improved genotypes, susceptibility was negatively correlated to phenolic and protein content of the variety tested but positively correlated to moisture content. A detailed analysis of the phenolics revealed the presence of diferulate which may contribute to mechanical resistance of the seed by cross-linking of cell wall hemicelluloses. A canonical discriminant analysis of the resistance data suggests that most of the five landrace groupings are significantly different. The ancient indigenous and prehistoric mestisos groupings are sources of resistant genotypes.