Antixenosis phloem‐based resistance to aphids: is it the rule?

1. The concept of plant defence syndrome states that plant species growing in similar biotic or abiotic constraints should have convergent defensive traits. This article is a first step to test the prediction of this concept, by conducting experiments on wild Solanum species (or accessions) that originated from the Andes. The nature and the tissue localisation of the resistance of five wild Solanum species known to be resistant against the aphids Myzus persicae and Macrosiphum euphorbiae were determined by olfactometry and electrical penetration graph experiments. 2. Volatile organic compounds may contribute to wild Solanum resistance, depending on Solanum accessions and aphid species. Volatiles of S. bukasovii and S. stoloniferum PI 275248 were not attractive to M. persicae, whereas S. bukasovii was repulsive to M. euphorbiae. In contrast, volatiles of S. stoloniferum PI 275248 were attractive for M. euphorbiae. 3. Some wild Solanum species presented a generalised resistance in all plant tissues, so as for S. bukasovii and S. stoloniferum PI 275248 against M. persicae. However, except for S. bukasovii which was susceptible to M. euphorbiae, all tested Solanum species presented a phloem‐based antixenosis resistance against the two aphid species. 4. A review of articles focused on the nature of resistance of wild Solanum species against aphids corroborated with our results, i.e. a phloem‐based antixenosis resistance against aphids is the rule concerning the system aphids–wild Solanum species.     

Short-term variability in physical forcing in temperate reservoirs: effects on phytoplankton dynamics and sedimentary fluxes

1. The effects of wind events on phytoplankton dynamics were investigated in two temperate reservoirs. 2. Meteorological forcing, change in physical and chemical structure of the water column and biological responses of phytoplankton communities were followed for 3 weeks in three seasons. 3. Depending on the season, the phytoplankton response differed in response to nutrient and light conditions, and to the intensity of stratification and mixing. 4. We demonstrated that, on a time scale of a few days, wind events can modify phytoplankton dynamics, in terms of size structure and exported biomass. An increase of mixing favoured the largest size class and disadvantaged the smallest size class, while an increase in stratification had the opposite effects. The short‐term change in size structure was reflected in the sedimentary fluxes but with a time lag.     

Obstacle perception by insect antennae during terrestrial locomotion

Abstract. Insect antennae bear several types of sensilla including chemo-receptors, hygroreceptors, thermoreceptors and mechanoreceptors. A large proportion of sensilla is chemoreceptors, providing olfactory function. Pro-prioreceptors located on the antennae provide information on the position of these organs and are used in flight control. This type of sensillum is present in most insects and might serve other functions. We tested the hypothesis that antennae are used to perceive obstacles in the path of walking beetles. When adult Colorado potato beetles, Leptinotarsa decemlineata (Say), touch an obstacle with their antennae during terrestrial locomotion, they modify the angle of their body to allow the tarsi of one prothoracic leg to reach the top of the obstacle. Our results demonstrate that antennae, by their movements and their position ahead of the beetle, provide information on the presence of the obstacle necessary to initiate step-up behaviour. Furthermore, the change in the body angle needed to increase the reach of the prothoracic leg and step on the obstacle, is proportional to the height of the obstacle. Since the eyes are not involved in the process, normal behaviour can be performed in the dark.