The relationship between populations of stem‐boring Dipterous larvae in leys and damage to subsequent winter wheat crops

SUMMARY During September of each year from 1978-82, dipterous stem-boring larval populations were assessed in 28–35 grass fields in northern England before they were ploughed and sown with winter wheat. Larvae were mainly Oscinella spp. and their populations ranged from <60–3100/m2 (mean 300/m2). Subsequent damage to winter wheat assessed during December of each year from 1978-81 was positively related to the larval population in the grass. Regressions of plant damage on larval numbers indicated that 500, 1000 and 2000 larvae/m2 resulted in respectively 10, 19 and 36% damaged wheat plants. Mean populations were greatest (558/m2) in 2-yr-old leys containing Lolium multijlorum. Three-yr-old leys had a mean of 319/m2 and leys of 4 yr and older had 168 larvae/m2. Soil type and management of leys had little consistent effect on larval populations. Populations tended, however, to be larger on silty or silty-clay loams than sandy loams and where leys were grazed in late summer after earlier silage cuts compared with those continuously grazed.