Effects of pasture establishment and renovation techniques on the hymenopterous parasitoids of Oscinella frit L. and other stem-boring Diptera in ryegrass.
Abstract
In field trials in the UK, different levels of attack by hymenopterous parasitoids occurred in stem-boring larval Diptera (including Oscinella frit) in swards which had been re-seeded after conventional cultivation or by direct drilling or which had been improved by the addition of nitrogen fertilizer. The numbers of the major parasitoid of established grass, Chasmodon apterus (a wingless braconid), were greatly reduced by ploughing and re-seeding but were reduced to a lesser extent by chemical desiccation with the herbicide glyphosate and direct drilling. Other (alate) parasitoids showed greater prevalence in seeding grass than established grass. Four months after sowing, over 40% of stem-boring larvae were parasitized. Changes in host population numbers were correlated with the initial level of parasitoid attack.