B. Delobel’s research while affiliated with INSA and other places

Host plant resistance to pests is an important component of integrated control strategies. Due to the specialised phloem-feeding of aphids and many other hemipteran insect pests, which necessitates specific chemical treatments and control of virus transmission, this genetic strategy seems particularly attractive for this insect group. In the melon Cucumis melo L., a gene labelled vat, for virus aphid transmission (Pitrat & Lecoq, 1982), brings both a resistance to the melon aphid Aphis gossypii Glover and a resistance to the transmission by this vector of many non-persistent viruses. This gene induces both an antixenotic response to adults and an apparent antibiosis towards A. gossypii larvae. The purpose of the experiments reported here was to investigate the mechanisms of this resistance (mechanical, chemical, tissue localisation...) and to characterize any chemical difference between genotypes differing by the presence/absence of the vat gene.

Pea albumin 1b (PA1b) is a small sulphur-rich peptide from pea seeds, also named leginsulin because of the binding characteristics of its soybean orthologue. Its insecticidal properties were discovered more recently. By using a combination of molecular, biochemical and specific insect bioassays on seed extracts, we characterised genes from numerous Papilionoideae, but not from Caesalpinioideae or Mimosoideae, although the last group harboured species with partially positive cues (homologous biological activities). The A1b defence peptide family, therefore, appears to have evolved relatively late in the legume lineage, maybe from the sophoroid group (e.g. Styphnolobium japonicum). However, unambiguous sequence information is restricted to a group of tribes within the subfamily Papilionoideae (Psoraleae, Millettieae, Desmodieae, Hedysareae, Phaseoleae, Vicieae, and the now clearly polyphyletic "Trifolieae" and "Galegeae"). Recent diversification by gene duplications has occurred in many species, or longer ago in some lineages (Medicago truncatula), as well as probable gene or expression losses at different taxonomic levels (Loteae, Vigna subterranea).

Because of their particular biology, seed beetles exhibit a strong relationship with their larval host plants. In Europe, however, field data have long been scarce and unreliable. The results of Legume seed collections of nearly 1,000 samples belonging to 292 species from various locations in Europe are summarized. The status of current Bruchidius species groups is amended on morphological and phylogenetic bases. Recent advances in the knowledge of phylogenetic structures of both Fabaceae and Bruchinae provide a new picture of Bruchinae-Fabaceae interactions. It reveals a certain level of host conservatism. The hypothesis of radiative adaptation seems the most compatible with observed data.

constituents were identified. The major components are found to be aliphatic acids and identified as hexanoic acid (27%), butyric acid (10.4%) and valeric acid (6.3%) with lesser amounts of p-ethylphenol (17.2%) and p-methylphenol (13%). Examination of the protein fraction from leaves indicated 20.2% in the crude leaves and 12.9% in the fermented leaves. The participation of 10 g of fermented C. obtusifolia leaves to the daily requirements in essential amino acids of an adult is from 13 to 25% of needed amount. Moreover this traditional food had a high content of potassium and calcium.

Improvement of an existing meat-based diet has been obtained for rearing the generalist predator Dicyphus tamaninii (Heteroptera: Miridae). The approach followed, different from the classical addition/deletion method, was performing biochemical analysis of adult carcasses in order to have information about the nutritional status of the predator. Comparison of total, free amino acids and lipid composition of meat-reared and conventionally reared females allowed detecting some nutritional deficiencies. A reformulated diet with new sources of proteins and lipids was tested again with the predator. Some biological parameters of bugs that were inferior in the initial meat diet when compared with those of the conventionally reared insects, such as nymphal development time and fresh weight, have been improved with the reformulated diet.

The authors complete and modify results published in 2003 on trophic relationships between seed-beetles of the French fauna and their larval host plants. New data are given for France, Italy and Greece. Forty-four new host plants were identified, which constitutes for several beetle species the very first biological data available. The diet of 86 % of the seed-beetles in the three countries is now more or less precisely known. The previously expressed hypothesis, according to which any given beetle species will feed on a single plant species, genus or tribe, is confirmed in most cases.

Pea albumin 1b (PA1b) is a small sulphur-rich peptide from pea seeds, also called leginsulin due to the binding properties of its soybean orthologue. Its insecticidal properties were discovered more recently. By using a combination of molecular, biochemical and specific insect bioassays, we characterised new genes and their products from the seeds of four legume species. Two species (Glycine max and Phaseolus vulgaris) display most of the characteristics of the Pisum sativum type: homologous genes and predicted toxic hydrophobic peptides with similar post-translational processing. The third species (Medicago truncatula) possesses homologous genes and high insecticidal activity, but no specific biochemical detection of the peptide products was obtained, indicating possible variant post-translational processing. Our combined approach appears to be efficient for a broad study of A1b within legumes.

Intracellular symbiosis is widespread in the insect world where it plays an important role in evolution and adaptation. The weevil family Dryophthoridae (Curculionoidea) is of particular interest in intracellular symbiosis evolution with regard to the great economical and ecological features of these invasive insects, and the potential for comparative studies across a wide range of host plants and environments. Here, we have analyzed the intracellular symbiotic bacteria of 19 Dryophthoridae species collected worldwide, representing a wide range of plant species and tissues. All except one (Sitophilus linearis) harbor symbiotic bacteria within specialized cells (the bacteriocytes) assembled as an organ, the bacteriome. Phylogenetic analysis of the 16S rDNA gene sequence of the Dryophthoridae endosymbionts revealed three endosymbiotic clades belonging to gamma3-Proteobacteria and characterized by different GC contents and evolutionary rate. The genus name Candidatus Nardonella was proposed for the ancestral clade infesting Dryophthoridae 100 MYA and represented by five of nine bacterial genera studied. For this clade showing low GC content (40.5% GC) and high evolutionary rate (0.128 substitutions/site per 100 Myr), a single infection and subsequent cospeciation of the host and the endosymbionts was observed. In the two other insect lineage endosymbionts, with relatively high GC content (53.4% and 53.8% GC), competition with ancestral pathogenic bacteria might have occurred, leading to endosymbiont replacement in present-day last insects.