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The success of biological bontrol (BC) introductions can be enhanced by considering theory and knowledge of biological systems. The gregarious braconid parasitoid Cotesia sesamiae (Cameroon) is one of the best studied biological control agent from the perspective of molecular ecology. Its evolutionary adaptation to the target host involves symbiotic partners. Polydnaviruses are responsible for immune and developmental adaptations whereas Wolbachia bacteria may reinforce this local adaptation though genetic isolation mechanisms. The noctuid Busseola fusca is a major stemborer pest of maize in sub-Saharan Africa. In contrast to eastern Africa, C. sesamiae is rarely found on B. fusca in western Africa. It is however often obtained from other stemborer species feeding on wild grasses. A biological control project was launched in 2006–2007 by introducing to Cameroon seven crosses of Kenyan populations of C. sesamiae collected in different ecozones. They included populations adapted to B. fusca that develop on maize as well as populations adapted to other hosts feeding on wild plants to allow carryover between cropping seasons. Wolbachia strains responsible for cytoplasmic reproductive incompatibilities with endemic strains were included in the crosses to limit genetic exchanges between introduced and endemic C. sesamiae and preserve genetic adaptation to B. fusca of the introduced populations, while at the same time preserving their ability to survive on wild plants. Six post release surveys were carried out on maize from 2007 to 2013, and on wild grasses in 2013. A total of 393 C. sesamiae individuals, each from one cocoon mass, were genotyped for 11 microsatellite loci. Multidimensional scaling analysis, STRUCTURE and GENECLASS analyses assigned almost all the parasitoids recovered from maize to those introduced from Kenya. The introduced strains were also recovered from wild host plants with little genetic exchanges with endemics. Each population remained strongly associated with its original Wolbachia component, suggesting that Wolbachia may contribute to genetic isolation between endemics and introduced populations in wild host plants when maize is absent, thereby conciliating biological control success and safety.

Abstract: 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. [ABSTRACT FROM AUTHOR]

Abstract: The African parasitoid wasp Cotesia sesamiae is a generalist species structured in locally adapted populations showing differences in host range. The recent discovery of Cotesia typhae, a specialist, sister species to C. sesamiae, provides a good framework to study the genetic determinants of parasitoid host range. To investigate the genomic bases of divergence between these populations and species, we used a targeted sequencing approach on 24 samples. We targeted the bracovirus genomic region encoding virulence genes involved in the interaction with the lepidopteran hosts of the wasps. High sequencing coverage was obtained for all samples, allowing the study of genetic variation between wasp populations and species. By combining population genetic estimations, such as nucleotide diversity (π), relative differentiation (FST) and absolute divergence (dxy), with branch‐site dN/dS measures, we identified six of 98 bracovirus genes showing significant divergence and evidence of positive selection. These genes, belonging to different gene families, are potentially involved in host adaptation and in the specialization process. Fine‐scale analyses of genetic variation also revealed mutations and large deletions in certain genes inducing pseudogenization and loss of function. The image emerging from these results is that adaptation mediated by bracovirus genes happens through selection of particularly adaptive alleles and loss of nonadaptive genes. These results highlight the central role of the bracovirus in the molecular interactions between the wasps and their hosts and in the evolutionary processes of specialization. [ABSTRACT FROM AUTHOR]

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Interactions within and between species sharing the same resources are characterised by competition or facilitation, and can be influenced by factors such as larval numbers and phenotypic plasticity of the interactions. The effect of larval density on the survival and relative growth rate of the stemborers Busseola fusca ( Fuller) and Sesamia calamistis Hampson (both Lepidoptera: Noctuidae), and Chilo partellus ( Swinhoe) ( Lepidoptera: Crambidae) were studied, as well as the temporal plasticity of their competitive interactions. These stemborers attack maize crops ( Zea mays L.) ( Poaceae) in sub-Saharan Africa. Experiments were conducted in the laboratory under controlled conditions at the optimum development temperature (25 °C) for the three species. Surrogate stems filled with artificial diet were intra- and interspecifically infested with larvae of each species. The effect of larval density on competition was studied at low (six larvae) and high (12 larvae) levels of infestation, whereas the temporal plasticity of competition was evaluated at 7, 14, 21, or 28 days after infestation. The two experiments involved single- and multi-species infestation treatments. Larval numbers and wet mass in each artificial stem were recorded in each experiment. Survival and relative growth rate of the three species were significantly higher at low-infestation levels when facing either intra- or interspecific competition. The intensity of competition was also temporally plastic among the species and increased as the duration of competition increased. These results are discussed in terms of general infestations of cereal crops by borers. [ABSTRACT FROM AUTHOR]

The geographic mosaic of coevolution predicts parasite virulence should be locally adapted to the host community. Cotesia parasitoid wasps adapt to local lepidopteran species possibly through their symbiotic bracovirus. The virus, essential for the parasitism success, is at the heart of the complex coevolutionary relationship linking the wasps and their hosts. The large segmented genome contained in the virus particles encodes virulence genes involved in host immune and developmental suppression. Coevolutionary arms race should result in the positive selection of particular beneficial alleles. To understand the global role of bracoviruses in the local adaptation or specialization of parasitoid wasps to their hosts, we studied the molecular evolution of four bracoviruses associated with wasps of the genus Cotesia, including C congregata, C vestalis and new data and annotation on two ecologically differentiated populations of C sesamie, Kitale and Mombasa. Paired orthologs analyses revealed more genes under positive selection when comparing the two C sesamiae bracoviruses belonging to the same species, and more genes under strong evolutionary constraint between species. Furthermore branch-site evolutionary models showed that 17 genes, out of the 54 currently available shared by the four bracoviruses, harboured sites under positive selection including: the histone H4-like, a C-type lectin, two ep1-like, ep2, a viral ankyrin, CrV1, a ben-domain, a Serine-rich, and eight unknown genes. Lastly the phylogenetic analyses of the histone, ep2 and CrV1 genes in different African C sesamiae populations showed that each gene described differently the individual relationships. In particular we found recombination had happened between the ep2 and CrV1 genes, which are localized 37.5 kb apart on the wasp chromosomes. Involved in multidirectional coevolutionary interactions, C sesamiae wasps rely on different bracovirus mediated molecular pathways to overcome local host resistance. [ABSTRACT FROM AUTHOR]

Sesamia nonagrioides (Lefèbvre) (Lepidoptera: Noctuidae), is a widespread insect pest in Africa, the Middle East, and Europe. However, its pest status varies across its distribution range. It is a major pest of maize in Europe and of sugarcane in Iran. In Africa, it is a major pest of maize in West Africa but not considered as a pest in East Africa. Recent surveys conducted in 2015 recorded S. nonagrioides to be a major pest of sugarcane in Ethiopia and reported the species for the first time in Botswana, outside its known geographic range. The genetic relationship of these records with the previously recorded population of S. nonagrioides was investigated using the cytochrome oxidase subunit I region of the mitochondrial genome. In total, 113 individuals across the geographic range of the species were analyzed and 63 haplotypes were identified. Phylogenetic analysis separated the populations into two clades with no distinct geographic distribution pattern. The genetic differentiation was also not associated with host plants and geographic distances. Results of the molecular analysis revealed the long-time establishment of S. nonagrioides population in Botswana and identified the newly recorded sugarcane population from Ethiopia as part of the wild host population in the country. The phylogeographic patterns observed among population of S. nonagrioides have probably been shaped by Pleistocene's climatic oscillations and geographic range expansions from different refugia with secondary contact and admixture. Possible reasons for the host-plant expansion by the Ethiopian population are discussed.

As a result of an intense host-parasite evolutionary arms race, parasitic wasps frequently display high levels of specialization on very few host species. For instance, in braconid wasps very few generalist species have been described. However, within this family, Cotesia sesamiae is a generalist species that is widespread in sub-Saharan Africa and develops on several lepidopteran hosts. In this study, we tested the hypothesis that C. sesamiae may be a cryptic specialist when examined at the intraspecific level. We sequenced exon 2 of CrV1, a gene of the symbiotic polyDNAvirus that is integrated into the wasp genome and is associated with host immune suppression. We found that CrV1 genotype was more closely associated with the host in which the parasitoid developed than any abiotic environmental factor tested. We also tested a correlation between CrV1 genotype and an infection with Wolbachia bacteria, which are known for their ability to induce reproductive isolation. The Wolbachia bacteria infection polymorphism was also found as a major factor explaining the genetic structure of CrV1, and, in addition, the best model explaining CrV1 genetic structure involved an interaction between Wolbachia infection and host species. We suggest that Wolbachia could act as an agent capable of maintaining advantageous alleles for host specialization in different populations of C. sesamiae. This mechanism could be applicable to other insect models because of the high prevalence of Wolbachia in insects., (© 2011 Blackwell Publishing Ltd.)