Pierre Silvie

A Brave New World for an Old World Pest: Helicoverpa armigera (Lepidoptera: Noctuidae) in Brazil

The highly polyphagous Old World cotton bollworm Helicoverpa armigera is a quarantine agricultural pest for the American continents. Historically H. armigera is thought to have colonised the American continents around 1.5 to 2 million years ago, leading to the current H. zea populations on the American continents. The relatively recent species divergence history is evident in mating compatibility between H. zea and H. armigera under laboratory conditions. Despite periodic interceptions of H. armigera into North America, this pest species is not believed to have successfully established significant populations on either continent. In this study, we provide molecular evidence via mitochondrial DNA (mtDNA) cytochrome oxidase I (COI) and cytochrome b (Cyt b) partial gene sequences for the successful recent incursion of H. armigera into the New World, with individuals being detected at two sites (Primavera do Leste, Pedra Preta) within the State of Mato Grosso in Brazil. The mtDNA COI and Cyt b haplotypes detected in the Brazilian H. armigera individuals are common throughout the Old World, thus precluding identification of the founder populations. Combining the two partial mtDNA gene sequences showed that at least two matrilines are present in Brazil, while the inclusion of three nuclear DNA Exon-Primed Intron-Crossing (EPIC) markers identified a further two possible matrilines in our samples. The economic, biosecurity, resistance management, ecological and evolutionary implications of this incursion are discussed in relation to the current agricultural practices in the Americas.

Identification and Comparison of Fall Armyworm (Lepidoptera: Noctuidae) Host Strains in Brazil, Texas, and Florida

Abstract Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major economic pest throughout the Western Hemisphere. Studies of populations in the southern United States and the Caribbean demonstrated the existence of two morphologically identical but genetically distinct host strains. These races can be distinguished by using polymorphisms in the mitochondrial cytochrome oxidase I gene that define two distinct maternal lineages that correlate with strain-specific behaviors in Florida populations. Although there is evidence of different biotypes in Brazil, it has not been demonstrated that these biotypes are equivalent to the U.S. strains. Sampling from Brazil indicates that its fall armyworm populations consist of the two strain-specific haplotypes found in Florida and also display the expected biases in plant host distribution. The same genetic markers also were present in samples from Texas, a major source of migrating fall armyworm in North America. These results indicate that the biology and behaviors of Brazilian fall armyworm populations are similar to those found in North America.

Comparison of Haplotype Frequencies Differentiate Fall Armyworm (Lepidoptera: Noctuidae) Corn-Strain Populations from Florida and Brazil

Abstract Fall armyworm,Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major economic pest throughout the Western Hemisphere. Populations can be subdivided into two morphologically identical but genetically distinct strains (corn-strain and rice-strain) that differ in their host plant preferences. These strains can be distinguished by using polymorphisms in the mitochondrialcytochrome oxidase I gene. Additional sequence analysis of this locus identified two sites that were highly polymorphic in the corn-strain population and that produced four different haplotype subgroups. Comparisons of the frequency distribution of these haplotypes found no seasonal or plant host specificities, but they did demonstrate that the Brazil corn-strain population is different from corn-strain fall armyworm found in Florida. The development of a rapid means of distinguishing fall armyworm populations originating from Brazil versus Florida provides an opportunity for investigating and comparing the genetic complexity and long-range movements of this important agricultural pest.

Structure and Distribution of a Strain-Biased Tandem Repeat Element in Fall Armyworm (Lepidoptera: Noctuidae) Populations in Florida, Texas, and Brazil

Abstract Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major economic pest throughout the Western Hemisphere. There exist two morphologically identical but genetically distinct strains (corn-strain and rice-strain) that differ in their host plant preferences. These strains can be distinguished by polymorphisms in the mitochondrial cytochrome oxidase I gene. There is also a tandem-repeat genetic element called FR that is found in large sex-linked clusters primarily in the rice strain, as characterized by sampling of fall armyworm populations in the southeastern United States. It was recently shown that the FR element is also present in Brazil, where it exhibits a similar strain-biased distribution. In this article, the analysis of FR was extended to populations in southern Texas, one of the principle overwintering locations for fall armyworm that infests the continental United States. DNA sequence analysis and an optimized polymerase chain reaction (PCR)-based method demonstrated that FR sequences are present in Texas and show the same distribution pattern as observed in Florida. The distribution of FR in Florida has remained relatively unchanged over a 4-yr period, suggestive of polymorphic equilibrium and the existence of at least partial barriers to the generation of interstrain hybrids. The implications of these findings on our understanding of interstrain mating behavior and the utility of the modified detection method to study fall armyworm populations are discussed.

Fall armyworm migration across the Lesser Antilles and the potential for genetic exchanges between North and South American populations

The fall armyworm, Spodoptera frugiperda (J. E. Smith)(Lepidoptera: Noctuidae), is an important agricultural pest of the Western Hemisphere noted for its broad host range, long distance flight capabilities, and a propensity to develop resistance to pesticides that includes a subset of those used in genetically modified corn varieties. These characteristics exacerbate the threat fall armyworm poses to agriculture, with the potential that a resistance trait arising in one geographical location could rapidly disseminate throughout the hemisphere. A region of particular concern is the Caribbean, where a line of islands that extends from Florida to Venezuela provides a potential migratory pathway between populations from North and South America that could allow for consistent and substantial genetic interactions. In this study, surveys of populations from Peru, Bolivia, Paraguay, and Trinidad & Tobago expand on previous work in South America that indicates a generally homogeneous population with respect to haplotype markers. This population differs from that found in most of the Lesser Antilles where a combination of genetic and meteorological observations is described that indicate fall armyworm migration from Puerto Rico to as far south as Barbados, but does not support significant incursion into Trinidad & Tobago and South America. Air transport projections demonstrate that the wind patterns in the Caribbean region are not conducive to consistent flight along the north-south orientation of the Lesser Antilles, supporting the conclusion that such migration is minor and sporadic, providing few opportunities for genetic exchanges. The implications of these findings on the dissemination of deleterious traits between the two Western Hemisphere continents are discussed.

Evaluation of a virus-insecticide combination for cotton pest control in Togo

Abstract A low dose of cypermethrin combined with Mamestra brassicae virus was applied weekly against the bollworms Helicoverpa armigera (Hubner) and Diparopsis watersi (Rothschild) in smallholder cotton plots in northern Togo in 1989 and 1990. The timing of treatments was based on action thresholds. One or two additional sprays of Bacillus thuringiensis were applied to control Syllepte derogata F., or dimethoate to control aphids. No significant yield differences were observed between the plots treated with the pyrethroid-virus combination and the control plots, treated with the recommended insecticide schedule. However, the latter had a significantly higher percentage of healthy bolls. The virus applied was not reisolated from insects collected in the field.

Knowledge management for a wonderful (computerized) world

Introduction: Knowledge intended to manage pest problems throughout the world is continuously being produced on various topics such as classical or conservation biological control, use of natural pesticide plants and biocontrol agents, trap crops, and conservation agriculture. Traditionally, knowledge is communicated using a diversity of media such as publications, reports, databases, videos and websites. To answer a question such as the potential impacts and outcomes of invasions by alien species on the populations existing in a landscape, the challenge is to extract qualitative and semi-quantitative knowledge from those sources, compile it, and identify conflicts between different items of knowledge. Methods: Building knowledge bases using a semantic network is the modelling approach method used to represent knowledge and manage it. Results: Work carried out using this methodology has enabled the construction of knowledge bases on (a) food webs of cereal stem borers in Africa (RAP), (b) pest control in the sugarcane agrosystem using natural ecological interactions in relation to cultural practices (DECIPESTS), and (c) natural pesticide plants in Sub-Saharan Africa. Initially built to answer specific questions, these knowledge bases can be composed using this modelling approach. For instance, RAP combined with DECIPESTS enables the mapping of wild and cultivated plants that can host sugarcane pests of economic interest. Conclusion: By crossing thematic frontiers in entomology, knowledge management is a key solution for establishing multidisciplinarity. (Texte integral)