Stem‐boring Diptera in perennial ryegrass in relation to fertiliser.

SUMMARY Two levels of fertiliser were applied to perennial ryegrass in four equal doses according to two different time schedules. Stem‐borer larvae were more frequent in plots treated with the higher rate and the relative incidence of the species varied according to fertiliser level. At the high fertiliser level the later applications resulted in an earlier increase in larval numbers and a higher larval population in the winter. At the low fertiliser level the total number of larvae was greater in the plots receiving earlier fertiliser applications due to an increase in the number of Oscinella vastator larvae. Populations of larvae were related to the tillering of the grass but not to the nitrogen content of the host plants.