Genetic hitchhiking and resistance evolution to transgenic Bt toxins: insights from the African stalk borer Busseola fusca (Noctuidae)

Since transgenic crops expressing Bacillus thuringiensis (Bt) toxins were first released, resistance evolution leading to failure in control of pests populations has been observed in a number of species. Field resistance of the moth Busseola fusca was acknowledged 8 years after Bt maize was introduced in South Africa. Since then, field resistance of this corn borer has been observed at several locations, raising questions about the nature, distribution and dynamics of the resistance trait. Using genetic markers, our study identified four outlier loci clearly associated with resistance. In addition, genetic structure at neutral loci reflected extensive gene flow among populations. A realistically parameterised model suggests that resistance could travel in space at speed of several kilometres a year. Markers at outlier loci delineated a geographic region associated with resistance spread. This was an area of approximately 100 km radius, including the location where resistance was first reported. Controlled crosses corroborated these findings and showed significant differences of progeny survival on Bt plants depending on the origin of the resistant parent. Last, our study suggests diverse resistance mutations, which would explain the widespread occurrence of resistant larvae in Bt fields across the main area of maize production in South Africa

La cochenille du manioc et sa biocoenose au Congo 1979-84

Uniquement connue au Sud des Etats-Unis d'Amérique, l'Entomophthorale #Neozygites fumosa (Speare) Remaudière et Keller a été retrouvée en République Populaire du Congo, où elle attaque la cochenille du manioc, #Phenacoccus manihoti Matile-Ferrero (Hom. : #Coccoidea Pseudococcidae). De légères variations d'ordre biométrique sont mises en évidence au sein de l'espèce fongique. A ce jour, parmi les Entomophthorales mentionnées dans la littérature comme pathogènes de cochenilles, seules deux espèces peuvent être retenues avec certitude : #Neozygites fumosa et #Conidiobolus pseudococci Speare (Tyrrell and MacLeod), toutes deux pathogènes de #Pseudococcidae. (Résumé d'auteur

Response of maize stemborers and associated parasitoids to the spread of grasses in the rainforest zone of Kisangani, DR Congo : effect on stemborers biological control

The challenge with respect to nourishing the human population should be met in the context of global environmental change. Land-use change has the potential to affect insect pest-natural enemy interactions. In the Democratic Republic of Congo, the rainforest zone is subjected to intense anthropogenic disturbances that lead to the spread of habitats with a higher proportion of grasses in the landscape. Such a land-use change raises the question of its effects on the biological control of insect pests. The proximity of varying vegetation types around agroecosystems is expected to influence species fitting differently and hence the population dynamics of insect pests and their biological control. Thus, the response of maize stemborers and their parasitoids to the spread of habitats with a higher proportion of grasses was assessed along an anthropogenic disturbance gradient in the rainforest zone of Kisangani, Democratic Republic of Congo. The present study identified a decreased density of stemborers and infestation rates on maize as a result of an increased larval/pupal parasitism in wild habitats as the amount of grasses increased in the landscape. This effect was attributed to an increased parasitoid diversity subsequent to the settlement of an abundant and diverse stemborer community in wild habitats

Comportement de sélection de la plante hôte par la cochenille farineuse du manioc M. Manihoti : rôle dse composés biochimiques

Le manioc, Manihot esculenta Cratz (Euphorbiaceae), originaire d'Amérique latine, représente à l'heure actuelle un aliment de base dans les zones forestières de l'Afrique centrale. Depuis les années 1960-1970, à la suite de l'introduction en Afrique de boutures contaminées, le manioc subit de graves dommages dus à la cochenille farineuse Phenacoccus manihoti Matile-ferrero (Hom., Pseudococcidae). cet insecte piqueur-suceur, phloémophage et oligophage, inféodé au genre Manihot, est en effet doté d'un important pouvoir de multiplication

Disturbance of the rainforest has the potential to enhance egg parasitism of lepidopteran noctuid stemborers in Kisangani, DR Congo

Landscape context influences population dynamics of insects and impacts biological processes within communities. It was expected that anthropogenic disturbances of the rainforest landscape in DR Congo would lead to a decreased level of noctuid stemborer egg parasitism as a consequence of a decoupling between stemborers and their naturally occurring parasitoids through dispersal. To test this hypothesis, noctuid egg batches were collected in maize fields along an anthropogenic disturbance gradient to assess change in the rates of eggs parasitism and maize plant infestation with noctuid egg batches. Our results showed that, in contrast to what was initially expected, egg parasitism increased from less to highly disturbed landscape whereas maize infestation had an inverse tendency. Discovery efficiency and mean egg parasitism were 1.416 and 1.392 times higher, respectively, in the most than in the less disturbed landscape. The numbers of eggs and egg batches per 100 maize plants were 0.55 times and 0.532 times the value in the less disturbed landscape, suggesting a dilution of the stemborer population within a large habitat patch encompassing cultivated fields and the surrounding wild host plants. It was concluded that the presence of suitable host plants enhances noctuid stemborers egg parasitism in adjacent maize fields