Competition of Urophora Stylata F. and Terellia Serratulae L. (Dipt., Tephritidae) in the Flowerheads of Cirsium Vulgare

Abstract

Fruit flies infesting the floverheads of thistles are not generally regarded as being of any economic importance. There are two reasons, however, to include some notes on their biology in this place. There have been attempts to use them as biocontrol agents against thistles that pose a weed problem (Peschken 1979, Schröder 1980). The use of Urophora stylata, especially, against its host-plant Cirsium vulgare in Canada has lead to encouraging results. More important, the “ecosystem in a nutshell” of insects in the flowerhaeds of thistles lends itself well to the study of small, compartmented food-webs. This type of trophic systems has been estimated to contain roughly half of the terrestrial species on earth (Price 1980). A close comparative study of some compartmented systems could well lead to a better understanding of the basic principles underlying the population dynamics of species that are part of plant-phytophage-entomophage-type food-webs. For an example, the review of Prokopy (1983) and the theoretical considerations of Pimm (1982) are mentioned. These more generalizing considerations could inspire the more practical and methodological discussions of people concerned with weed or pest control.