Parasitism of Lepidopterous Stem Borers in Cultivated and Natural Habitats

Plant infestation, stem borer density, parasitism, and parasitoid abundance were assessed during two years in two host plants, Zea mays (L.) (Cyperales: Poaceae) and Sorghum bicolor (L.) (Cyperales: Poaceae), in cultivated habitats. The four major host plants (Cyperus spp., Panicum spp., Pennisetum spp., and Sorghum spp.) found in natural habitats were also assessed, and both the cultivated and natural habitat species occurred in four agroecological zones in Kenya. Across habitats, plant infestation (23.2%), stem borer density (2.2 per plant), and larval parasitism (15.0%) were highest in maize in cultivated habitats. Pupal parasitism was not higher than 4.7% in both habitats, and did not vary with locality during each season or with host plant between each season. Cotesia sesamiae (Cameron) and C. flavipes Cameron (Hymenoptera: Braconidae) were the key parasitoids in cultivated habitats (both species accounted for 76.4% of parasitized stem borers in cereal crops), but not in natural habitats (the two Cotesia species accounted for 14.5% of parasitized stem borers in wild host plants). No single parasitoid species exerted high parasitism rates on stem borer populations in wild host plants. Low stem borer densities across seasons in natural habitats indicate that cereal stem borer pests do not necessarily survive the non-cropping season feeding actively in wild host plants. Although natural habitats provided refuges for some parasitoid species, stem borer parasitism was generally low in wild host plants. Overall, because parasitoids contribute little in reducing cereal stem borer pest populations in cultivated habitats, there is need to further enhance their effectiveness in the field to regulate these pests

Selection on Alleles Affecting Human Longevity and Late-Life Disease: The Example of Apolipoprotein E

It is often claimed that genes affecting health in old age, such as cardiovascular and Alzheimer diseases, are beyond the reach of natural selection. We show in a simulation study based on known genetic (apolipoprotein E) and non-genetic risk factors (gender, diet, smoking, alcohol, exercise) that, because there is a statistical distribution of ages at which these genes exert their influence on morbidity and mortality, the effects of selection are in fact non-negligible. A gradual increase with each generation of the ε2 and ε3 alleles of the gene at the expense of the ε4 allele was predicted from the model. The ε2 allele frequency was found to increase slightly more rapidly than that for ε3, although there was no statistically significant difference between the two. Our result may explain the recent evolutionary history of the epsilon 2, 3 and 4 alleles of the apolipoprotein E gene and has wider relevance for genes affecting human longevity

Cereal stemborder species complex and establishment of Cotesia flavpipes Cameron in eastern Uganda

Studies were conducted in two districts of eastern Uganda from 1997 to 1999 to introduce and monitor the establishment of an exotic parasitoid, Cotesia flavipes Cameron (Hymenoptera: Braconidae), for the control of the stemborer Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), and also to determine the stemborer species complex in maize and sorghum. The study confirmed the presence of four important stemborers, two pyralids Ch. partellus and Eldana saccharina Walker and two noctuids, Busseola fusca Fuller and Sesamia calamistis Hampson. Chilo partellus was dominant, constituting 53-88% of stemborers found followed by B. fusca at 8-37 %. The most abundant local parasitoid was the larval parasitoid Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae). The pupal parasitoids Pediobius furvus Gahan (Hymenoptera: Eulophidae) and Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae) were also recorded. Parasitism of Co. sesamiae on Ch. partellus ranged between 0 and 13.1 %. The introduced Co. flavipes was recovered from all sites in four consecutive seasons (between 1998 and 1999) causing parasitism of between 4 and 32.9 % on Ch. partellus. Cotesia flavipes was also recovered from the indigenous stemborers B. fusca and S. calamistis. This study indicates that Co. flavipes has established in eastern Uganda. RÉSUMÉ Des études ont été menées dans deux départements en Ouganda entre 1997 et 1999 infin d'introduire et de suivre l'aclimatation d'un parasitoïde exotique, Cotesia flavipes Cameron (Hymenoptera: Braconidae), dans le cadre de la lutte contre le foreur, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), et de determiner le complexe d'espèces de foreurs sur maïs et sorgho dans cette région. Cette étude a confirmé la présence de 4 espèces importantes de foreurs; deux pyrales, Ch. partellus et Eldana saccharina Walker et deux noctuidés Busseola fusca Fuller et Sesamia calamistis Hampson. Chilo partellus était l'espèce dominante formant près de 53-88% des borers collectés, suivit par B. fusca à 8-37 %. Le parasitoïde local le plus abundant a été le parasitoïde larvaire Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae). Les parasitoïdes des pupes Pediobius furvus Gahan (Hymenoptera: Eulophidae) et Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae) ont aussi été trouvés. Le parasitisme par Co. sesamiae sur Ch. partellus a varié entre 0 et 13.1%. Le parasitoïde introduit Co. flavipes a été collecté sur tous les sites pendant quatres saisons consecutives (entre 1998 et 1999) avec un taux de parasitisme entre 4 et 32.9 % sur Ch. partellus. Cotesia flavipes a aussi été collecté sur des foreurs locaux , B. fusca et S. calamistis. Cette étude a montré que Co. flavipes s'est acclimaté dans l'est de l'Ouganda