Classical biological control ofaleurocanthus spiniferus (Hem.: Aleyrodidae), on citrus in Southern Africa

The spiny blackfly,Aleurocanthus spiniferus (Quaintance), is a citrus pest in parts of Mpumalanga, South Africa, and in Swaziland. The leaves, fruit and branches of infested trees are usually covered with sooty mould and a reduction in tree vigour and production is experienced. Classical biological control ofA. spiniferus by the parasitoid,Encarsia cf.Smithi (Silvestri) (Hym.: Aphelinidae) is reported with a significant reduction in numbers ofA. spiniferus. The parasitoid dispersed successfully from isolated trees growing in home gardens andA. spiniferus was virtually eliminated up to 0,8 km from the nearest point of release within 10 months. A mean of 72.9% parasitism was reached. In 8 months,E. cf.smithi statistically reduced theA. spiniferus in parts of a commercial orchard where it was released, reaching 82.4% parasitism.     

Introduction and conclusions for a Discussion entitled Land resources: on the edge of the Malthusian precipice?

Introduction and conclusions for a Discussion hosted by the Ciba Foundation and entitled Land resources: on the edge of the Malthusian precipice? Discussion held on the 4th and 5th December 1996, and organized and edited by D. J. Greenland, P. J. Gregory and P. H. Nye. <br>     

Reducing mean squared error in the analysis of stratified epidemiologic studies

Kalish (1990, Biometrics 46, 493-499) proposed an approximately optimal estimator of a common odds ratio for pair-matched case-control studies. His approach is easily extended to general stratified studies. For unmatched stratified studies, the form of the approximately optimal estimator is very simple, and may often correspond to no more than a small correction to the ordinary stratified estimator.