Food searching behaviour of a Lepidoptera pest species is modulated by the foraging gene polymorphism.

The extent of damage to crop plants from pest insects depends on the foraging behaviour of the insect's feeding stage. Little is known, however, about the genetic and molecular bases of foraging behaviour in phytophagous pest insects. The foraging gene (for), a candidate gene encoding a PKG-I, has an evolutionarily conserved function in feeding strategies. Until now, for had never been studied in Lepidoptera, which includes major pest species. The cereal stem borer Sesamia nonagrioides is therefore a relevant species within this order with which to study conservation of and polymorphism in the for gene, and its role in foraging - a behavioural trait that is directly associated with plant injuries. Full sequencing of for cDNA in S. nonagrioides revealed a high degree of conservation with other insect taxa. Activation of PKG by a cGMP analogue increased larval foraging activity, measured by how frequently larvae moved between food patches in an actimeter. We found one non-synonymous allelic variation in a natural population that defined two allelic variants. These variants presented significantly different levels of foraging activity, and the behaviour was positively correlated to gene expression levels. Our results show that for gene function is conserved in this species of Lepidoptera, and describe an original case of a single nucleotide polymorphism associated with foraging behaviour variation in a pest insect. By illustrating how variation in this single gene can predict phenotype, this work opens new perspectives into the evolutionary context of insect adaptation to plants, as well as pest management.

Molecular characterization of a phospholipase C beta potentially involved in moth olfactory transduction.

To clarify the role of phospholipase C (PLC) in insect olfactory transduction, we have undertaken its molecular identification in the moth Spodoptera littoralis. From the analysis of a male antennal expressed sequence tag library, we succeeded in cloning a full-length cDNA encoding a PLC that belongs to the cluster of PLC-beta subtypes. In adult males, the PLC-beta transcript was located predominantly in brain and antennae where its presence was detected in the olfactory sensilla trichodea. Moreover, PLC-beta was expressed in antennae at the beginning of the pupal stage, then reached a maximum at the end of this stage and was maintained at this level during the adult period. Taken together, these results provided molecular evidence for the putative participation of a PLC-beta in signaling pathways responsible for the establishment and the functioning of insect olfactory system.

Tidal height influences the levels of enzymatic antioxidant defences in Mytilus edulis.

We investigated the potential variability of enzymatic antioxidant activities in blue mussels Mytilus edulis from a single intertidal population but living at different tidal heights. Activity levels of antioxidant enzymes (Cu/Zn superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione transferase) were measured in the gills and digestive gland of mussels sampled at high shore (HS, air-exposure>6h/12h) and low shore (LS, air-exposure<2h/12h) of an intertidal zone (Yport, Normandie, France) for two consecutive autumns. In both tissues, levels of each enzymatic activity (except GST) were clearly higher in HS mussels than in LS for the two years. These results suggest an ability to acclimate the enzymatic antioxidant defences to the degree of undergone stress, confirming the importance of environmental conditions in the antioxidant responses. Therefore, the location of organisms on the shore should be taken into account in sampling for ecotoxicological studies.

Differential pattern of Cu/Zn superoxide dismutase isoforms in relation to tidal spatio-temporal changes in the blue mussel Mytilus edulis.

Inducible antioxidant defences in marine organisms such as mussel bivalves are commonly used as biomarkers of pollutant-induced oxidative stress and their variations proposed as one of the biological effect measurements for assessment of contamination impact in aquatic environments. Among them, the copper/zinc superoxide dismutases (Cu/Zn-SODs) are metalloenzymes which play a key role in the protection of cells in case of oxidative stress. In order to observe possible variations of an antioxidant response in relation to tidal oscillations, the copper/zinc superoxide dismutase activity (Cu/Zn-SOD) was characterized in the digestive gland and gills of blue mussels sampled at high and low shore throughout the tidal cycle. Determination of SOD activity was performed on gels after isoelectro-focusing, allowing the revelation of three isoforms. In both tissues, high-shore mussels exhibited a higher level of total SOD activity than low-shore mussels. During emersion, a decrease of total SOD activity appeared in digestive gland for both groups. In high-shore mussels, the less acidic form contributed to 75% of the total activity, the second one to 20% and the more acidic one to 5% in both tissues before air exposure. During emersion, the relative contribution of the three isoforms to the total activity was markedly changed with a significant decrease in intensity of the first isoform and parallel increases in the two other ones. After re-immersion a progressive recovery of proportions of SOD isoforms was observed. In low-shore mussels, the relative contribution of the three isoforms to the total SOD activity showed similar changes. The observed variations could correspond to changes in the redox status of the mussels during tidal oscillations.