Host serum proteins in Taenia saginata metacestode fluid

Taenia saginata cyst fluid was examined for host proteins; IgG1 and IgG2 as well as haemolytic complement activity were detected. Polyacrylamide gel electrophoresis revealed differences in proteinograms among the samples taken from 1-, 4-, and 10-month old cysts. Fluid from older cysts had fewer protein components and showed a weaker antigenic reaction with sera of bovines infected with T. saginata than that of younger cysts. The roles of antibody and complement in initiating degeneration of the parasite are discussed.     

Patterns of silver eel (Anguilla anguilla L.) sex ratio in a catchment

Abstract –  Changes in the numbers and size-class structure of European silver eels, Anguilla anguilla , in the River Frémur (France) were examined over a 9-year period after installation of downstream eel passes. The number of silver eels migrating downstream peaked in 1999, then decreased strongly and steadily after 2000, reaching relatively low levels. At the same time, a gradual shift in the silver eel sex ratio from a dominance of males (size from 270 to 442 mm, age from 3 to 6 years) to females (size from 366 to 1112 mm, age from 4 to 9 years) was recorded. Possible explanations for the escapement patterns observed are environmental sex determination and the installation of eel passes on the main hydraulic engineering structures in 1992 and 1996.     

Effect of canopy cover,seeding depth,and soil moisture on emergence of Centaurea maculosa and C. diffusa*

The effects of canopy cover, seeding depth, and soil moisture on emergence of Centaurea maculosa Lam. and C. diffusa Lam. were studied. Canopy cover had no effect on ermergence rate (seedlings/day/100 seeds) of either species. Seeds of both species emerged faster when placed on the soil surface. Emergence rate decreased as seeding depth increased. Both species required more than 55% initial soil moisture to initiate emergence, with 65–70% being optimum. Percentage emergence followed exactly the same trend as emergence rate. C. maculosa had better emergence characteristics over a wider range of conditions than C. diffusa, possibly being some of the reasons for the former having a wider geographical distribution in the United States and Canada.     

A model of plant virus disease epidemics in asynchronously-planted cropping systems

A mathematical model was developed of the dynamics of a plant virus disease within a spatially-referenced lattice of fields of a host crop. The model can be applied to crops in continuous, contiguous cultivation such as tropical irrigated rice. Disease progress in each field of the host crop was assumed to be logistic and determined by incidence within the field itself as well as incidence in neighbouring fields, depending on the gradient of disease spread. The frequency distribution of planting dates (represented by the proportion of the total number of fields planted in successive months) was assumed to follow a normal distribution and the variance of planting date was used as a measure of cropping asynchrony. Analysis of the model revealed that disease incidence within the lattice (i.e. mean incidence over all fields) depended upon the infection efficiency, the slope of the dispersal gradient, and the variance in planting date. Disease endemicity depended mainly on planting date variance and disease persisted in the lattice if this variance exceeded a certain threshold. Above the threshold for persistence, the response of mean disease incidence to planting date variance was non-linear and the region of greatest sensitivity was closest to the threshold. Thus, disease systems that show moderate rather than high cropping asynchrony are more likely to be influenced by changes in the variance of planting date. Implications for the area-wide management of rice tungro virus disease are discussed.