Host preferences of Palaearctic Culicoides biting midges: implications for transmission of orbiviruses

Feeding success depends on host availability, host defensive reactions and host preferences. Host choice is a critical determinant of the intensity at which pathogens are transmitted. The aim of the current study was to describe host preferences of Palaearctic Culicoides species (Diptera: Ceratopogonidae) Latreille using traps baited with the five different host species of poultry, horse, cattle, sheep and goat. Collections were carried out nightly in July and August 2009 in western France with three replicates of a 5 × 5 randomized Latin square (five sites, five hosts). Moreover, an ultraviolet (UV) light/suction trap was operated during host‐baited collections to correlate Culicoides biting rates and UV light/suction trap catches. A total of 660 Culicoides belonging to 12 species, but comprised mainly of Culicoides scoticus Downes and Kettle, Culicoides dewulfi Goetghebuer and Culicoides obsoletus Meigen, were collected on animal baits. Abundance was highest for the horse, which accounted for 95% of all Culicoides caught, representing 10 species. The horse, the largest bait, was the most attractive host, even when abundance data were corrected by weight, body surface or Kleiber's scaling factor. Culicoides obsoletus was the only dominant species attracted by birds. Both C. scoticus and C. dewulfi were collected mainly from the upper body of the horse. Finally, the quantification of host preferences allows for discussion of implications for the transmission of Culicoides‐borne pathogens such as bluetongue virus.     

Dynamics of Architectural Development of Isolated Plants of Maize (Zea mays L.), in a Non-limiting Environment: The Branching Potential of Modern Maize

The maximal architectural development of a modern maize cultivar(Zea mays L. ‘Dea’) was studied in fully isolatedand carefully irrigated plants. Under these favourable conditions,this (usually) non-tillering and non-prolific cultivar displayeda large amount of branching (down to the third order), includinglarge basal tillers and prolific ear shoots. This developmentwas analysed by combining: (1) architectural analysis, initiallydeveloped for trees; and (2) quantitative analysis of tilleringkinetics, designed for other grass species. The architecturalunit of maize included a main long axis (A1) and lateral shortshoots bearing a terminal spike (A2). The basal tillers (notedA1') resulted from a complete and sylleptic reiteration. Itskinetics were consistent with tillering models, but with a particularlylong delay in branch emergence (seven phyllochrons), comparedto other grass species. This delay is likely to enhance regulationby leaf (or root) density in stands and explains the inhibitionof branch development, as usually observed in field conditions,even at low density. Similarly, the suppression of the basalreiteration in secondary branches observed in isolated plantsprobably results from increased intra-tussock density. In isolatedplants, androgenous axes combining A1' and A2 morphologies werealso produced in intermediate positions. It is shown that theycan result from a basipetal sequence of A2 differentiation reachingbuds in the course of their A1' development. The consequencesof these unexpected results are discussed in terms of maizedevelopment and architectural analysis of grasses. Copyright1999 Annals of Botany Company Plant architecture, development, maize (Zea mays L.), tillering, branching, shoot, prolificacy, phyllochron.