Integrating multiple criteria for the characterization of Psammotettix populations in European cereal fields.

The wheat dwarf disease is among the most damaging diseases in cereals. Its aetiological agent is the Wheat dwarf virus (WDV), which is exclusively transmitted from plant to plant by leafhoppers from the genus Psammotettix (Hemiptera, Cicadellidae). The parameters linked to the WDV/Psammotettix pathosystem are still poorly understood. We studied Psammotettix individuals collected in wheat and barley fields in France and, as a comparison, from grassland at agroecological interface in West Slovenia. Species identity of males and females has been determined using multiple criteria. In the first step, the characterization of the collected individuals included recordings of vibrational signals used in mating behaviour and morphometric analyses. In addition, a 442 nt sequence of the mitochondrial cytochrome oxydase I (COI) gene was obtained for some individuals and compared to COI sequences of the Psammotettix leafhoppers available in public databases. In the cereal fields in France, P sammotettix alienus was the most numerous species; however, it sometimes occurred together with Psammotettix confinis, while in the grasslands in Slovenia, the third syntopic species in Psammotettix community was Psammotettix helvolus. The temporal parameters of the P. alienus male calling song that were measured in this study were very similar to those measured in a previous study. The local biotic and/or abiotic parameters most likely influence the life history of Psammotettix leafhoppers, and the proportion of viruliferous individuals collected in cereal fields was 14.9%, while leafhoppers collected in Slovenia were virus-free. Taken together, results show that more detailed information on population structure of Psammotettix leafhoppers is crucial for providing an insight into the epidemiology of wheat dwarf disease.

Limits for the central production of Theta+ and Xi(--)pentaquarks in 920-GeV pA collisions.

We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).