Summary• Substantial evidence has been published in recent years demonstrating that postphotosynthetic fractionations occur in plants, leading to 13 C-enrichment in heterotrophic (as compared with autotrophic) organs. However, less is known about the mechanism responsible for changes in these responses during plant development.• The isotopic signature of both organic matter and respired CO 2 for different organs of French bean ( Phaseolus vulgaris ) was investigated during early ontogeny, in order to identify the developmental stage at which isotopic changes occur. Isotopic analyses of metabolites and mass balance calculations helped to constrain the metabolic processes involved.• At the plant scale, apparent respiratory fractionation was constantly positive in the heterotrophic phase ( c . 1‰) and turned negative with autotrophy acquisition (down to -3.08‰). Initially very close to that of the dry seed (-26.83 ± 0.69‰), isotopic signatures of organic matter and respired CO 2 diverged (in opposite directions) in leaves and roots after onset of photosynthesis. Respired CO 2 reached values up to -20‰ in leaves and became 13 C-depleted down to -29‰ in roots.• It was concluded that isotopic differences between organs occurred subsequent to metabolic changes in the seedling during the transition from heterotrophy to autotrophy. They were especially related to respiration and respiratory fractionation.

Climate warming is expected to impact the response of species to insecticides. Recent studies show that this interaction between insecticides and temperature can depend on other factors.Here, we tested for the influence of transgenerational effects on the Insecticide x Temperature interaction in the crop pest moth Spodoptera littoralis. Specifically, we analysed reaction norms among experimental clutches based on a split-plot design crossing the factors temperature, insecticide and clutch. The study was performed on 2280 larvae reared at four temperatures (23, 25, 27 and 29°C), and their response to the insecticide deltamethrin (three concentrations and a control group) was tested. Temperature had a global influence with effects on larval survival, duration of development, pupal body mass, and significant reaction norms of the clutches for temperature variations of only 2°C. In addition to the expected effect of deltamethrin on mortality, the insecticide slightly delayed the development of S. littoralis, and the effects on mortality and development differed among the clutches.Projection models integrating all the observed responses illustrated the additive effects of deltamethrin and temperature on the population multiplication rate. Variation in the response of the clutches showed that transgenerational effects influenced the impact of insecticide and temperature. Although no evidence indicated that the Insecticide x Temperature interaction depended on transgenerational effects, the studies on the dependence of the Insecticide x Temperature interaction on other factors continue to be crucial to confidently predict the combined effects of insecticides and climate warming.

Adult moths need energy and nutrients for reproducing and obtain them mainly by consuming flower nectar (a solution of sugars and other compounds). Gustatory perception gives them information on the plants they feed on. Feeding and food perception are integrated in the proboscis extension response, which occurs when their antennae touch a sugar solution. We took advantage of this reflex to explore moth sugar responsiveness depending on different parameters (i.e., sex, age, satiety, site of presentation, and composition of the solution). We observed that starvation but not age induced higher response rates to sucrose. Presentation of sucrose solutions in a randomized order confirmed that repeated sugar stimulations did not affect the response rate; however, animals were sometimes sensitized to water, indicating sucrose presentation might induce non-associative plasticity. Leg stimulation was much less efficient than antennal stimulation to elicit a response. Quinine prevented and terminated sucrose-elicited proboscis extension. Males but not females responded slightly more to sucrose than to fructose. Animals of either sex rarely reacted to glucose, but curiously, mixtures in which half sucrose or fructose were replaced by glucose elicited the same response rate than sucrose or fructose alone. Fructose synergized the response when mixed with sucrose in male but not female moths. This is consistent with the fact that nectars consumed by moths in nature are mixtures of these three sugars, which suggests an adaptation to nectar perception.

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