Farms,pastures and woodlands: the fine‐scale distribution of Palearctic Culicoides spp. biting midges along an agro‐ecological gradient

The spatial epidemiology of Bluetongue virus (BTV) at the landscape level relates to the fine‐scale distribution and dispersal capacities of its vectors, midges belonging to the genus Culicoides Latreille (Diptera: Ceratopogonidae). Although many previous researches have carried out Culicoides sampling on farms, little is known of the fine‐scale distribution of Culicoides in the landscape immediately surrounding farms. The aim of this study was to gain a better understanding of Culicoides populations at increasing distances from typical dairy farms in north‐west Europe, through the use of eight Onderstepoort‐type black‐light traps positioned along linear transects departing from farms, going through pastures and entering woodlands. A total of 16 902 Culicoides were collected in autumn 2008 and spring 2009. The majority were females, of which more than 97% were recognized as potential vectors. In pastures, we found decreasing numbers of female Culicoides as a function of the distance to the farm. This pattern was modelled by leptokurtic models, with parameters depending on season and species. By contrast, the low number of male Culicoides caught were homogeneously distributed along the transects. When transects entered woodlands, we found a higher abundance of Culicoides than expected considering the distance of the sampling sites to the farm, although this varied according to species.     

Egg formation and the pre-laying period of the Common guillemot Una aalge

The patterns of colony attendance of male and female Common guillemots, relative to calendar date and relative to the female's laying date during the three weeks prior to egg laying, are presented. The probability of a male being at the colony was consistently higher than that for females. Male attendance peaked in the three days before his mate laid: female attendance was lowest at this time. Examination of the yolk showed that the egg was formed over 14–15 days, with yolk deposition (of first eggs) taking 11–5 days, and a lag period (between the end of yolk deposition and laying) of 3–4 days. Yolk deposition occurred over a shorter period (9–3 days) in replacement eggs, and followed a different pattern from first eggs.     

The action of alpha chymotrypsin upon mixtures of esters and proteins at enzyme-saturating concentrations

The behavior of α-chymotrypsin has been studied in the simultaneous presence of two different substrates, each present in the reaction mixture at its saturation level. Mixtures of two esters were hydrolyzed at rates intermediate between the rates of hydrolysis of each ester when present alone, suggesting, in this case, competitive hydrolysis. In contrast, the rates of hydrolysis in mixtures of casein with gelatin or of either protein with an ester were equal to the sum of the rates of hydrolysis of the separate substrates, indicating in these cases independent hydrolysis. The activity of the α-chymotrypsin preparation used could not be attributed to contamination with other enzymes. Studies of the effect of soy bean inhibitor on chymotrypsin indicate that the mechanism of inhibition with protein substrates differs from that when esters are used, providing further evidence that α-chymotrypsin reacts differently with esters and proteins. These results indicate that if chymotrypsin forms specific complexes with its substrates, it must possess at least three distinct active sites. However there is independent chemical evidence that the proteolytic and esterolytic activities of this enzyme reside in the same active center. If this is true, the experimental observations reported here cannot be explained unless it is supposed that this enzyme does not form specific Michaelis complexes with its substrates.