Invasive pest species may strongly affect biotic interactions in agro-ecosystems. The ability of generalist predators to prey on new invasive pests may result in drastic changes in the population dynamics of local pest species owing to predator-mediated indirect interactions among prey. On a short time scale, the nature and strength of such indirect interactions depend largely on preferences between prey and on predator behavior patterns. Under laboratory conditions we evaluated the prey preference of the generalist predator Macrolophus pygmaeus Rambur (Heteroptera: Miridae) when it encounters simultaneously the local tomato pest Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) and the invasive alien pest Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). We tested various ratios of local vs. alien prey numbers, measuring switching by the predator from one prey to the other, and assessing what conditions (e.g. prey species abundance and prey development stage) may favor such prey switching. The total predation activity of M. pygmaeus was affected by the presence of T. absoluta in the prey complex with an opposite effect when comparing adult and juvenile predators. The predator showed similar preference toward T. absoluta eggs and B. tabaci nymphs, but T. absoluta larvae were clearly less attacked. However, prey preference strongly depended on prey relative abundance with a disproportionately high predation on the most abundant prey and disproportionately low predation on the rarest prey. Together with the findings of a recent companion study (Bompard et al. 2013, Population Ecology), the insight obtained on M. pygmaeus prey switching may be useful for Integrated Pest Management in tomato crops, notably for optimal simultaneous management of B. tabaci and T. absoluta, which very frequently co-occur on tomato.

Early studies have shown that cesium (Cs + ) competes with the macronutrient potassium (K + ) for uptake by plants. The present study investigates the effect of K + supply on Cs + uptake and translocation in Arabidopsis thaliana. Taking advantage of the frequent use of this model plant in + concentration above 100 µM. We propose that non-selective cation channels, likely involved in Cs + uptake under K + -sufficient conditions according to previous studies, could also mediate Cs + uptake under K + -starvation and high Cs + concentrations. Finally, evidences for Cs + translocation mediated by K + channels are discussed.

Understanding the molecular mechanisms that underlie cesium (Cs + ) transport in plants is important to limit the entry of its radioisotopes from contaminated areas into the food chain. The potentially toxic element Cs + , which is not involved in any biological process, is chemically closed to the macronutrient potassium (K + ). Among the multiple K + carriers, the high-affinity K + transporters family HAK/KT/KUP is thought to be relevant in mediating opportunistic Cs + transport. Of the 13 KUP identified in A. thaliana, only HAK5, the major contributor to root K + acquisition under low K + supply, has been functionally demonstrated to be involved in Cs + uptake in planta. In the present study, we showed that accumulation of Cs + increased by up to 30% in two A. thaliana mutant lines lacking KUP9 and grown under low K + supply.Since further experiments revealed that Cs + release from contaminated plants to the external medium is proportionally lower in the two kup9 mutant alleles, we proposed that KUP9 disruption could impair Cs + efflux. By contrast, K + status in kup9 mutants is not affected, suggesting that KUP9 disruption does not alter substantially K + transport in experimental conditions used. The putative primary role of KUP9 in plants is further discussed. | INTRODUCTIONCesium is an alkali metal generally occurring at low concentrations in soil solution, predominantly as the monovalent cation Cs + (Greenwood & Earnshaw 1997). Although it has not been implicated in any biological process to date, Cs + is taken up by plants and can even be toxic (Hampton et al. 2004). Due to its low environmental concentration, the chemical toxicity of stable Cs + is rarely relevant in