Genetic differentiation at the inter- and intra-specific level of stored grain insects using a simple molecular approach (RAPD).

Population diversity in stored grain insects linked with geographical origin of the infesting strains may be an issue in international trade. It may be that some imported strains exhibit phenotypes that may negatively impact control strategies available in the country at the destination of imported grain lots. However, several molecular methods are routinely used to assess genetic diversity among insect species or strains in the same species. Therefore, the potential of RAPD technique for the identification of different strains based on polymorphic DNA revealing was investigated with grain insect species. The banding patterns observed from DNA extracts with six different primers were compared between several grain insect species: Sitophilus spp., Oryzaephilus surinamensis, Rhyzopertha dominica, Tribolium castaneum, Ephestia kuehniella, Plodia interpunctella, and three bruchid beetles. Then a particular study with the same molecular tools was performed for the differentiation between geographical strains in the Sitophilus spp. complex, with a special attention paid to S. zeamais strains originating from different continents (Africa, South America and Europe). The repeatability of the banding patterns was tested on: i/ extracted DNA from pool samples of different stages and generations in the same strains; ii/ Extracted DNA from individuals of the same species and strain. The differences observed in band profiles of the different species were highly significant and enabled the easy differentiation between them. It was shown frequent dissimilarities between the band profiles of geographical strains of S. zeamais. The potential for RAPD-PCR technique to provide useful genetic data for the discrimination up to the population level of insects found in stored products in international trade is discussed.