Listronotus bonariensis (Kuschel) is a pest of agriculturally important graminaceous species, with mining larvae that kill the stems of the host plants. In this study, larval populations were measured in spring and summer in irrigated dairy grassland comprising Lolium perenne L. (cv. Nui) and Poa annua L. with and without the endophyte Epichloë festucae var. lolii Latch, M.J. Chr. and Samuels. Larvae were extracted from tillers taken from the swards of these two grass species as well as extracted from turfs. Tiller population densities were used to estimate larval populations on a m^-2 basis. Mean larval population densities extracted from the turfs were significantly higher than those from the tillers, but there was no correlation between tiller and turf larval densities. Head capsule -widths of larvae emerging from turf samples  showed seasonal effects. The widths of 2^nd, 3^rd and 4^th instar larvae were significantly wider in the spring than the summer, while for the 1^st instars the converse was found. Mean head-capsule widths for all instars were significantly greater when extracted from the tillers than the turf ( P <0.001). There was a significant endophyte effect on head-capsule widths of larvae collected in summer, but the effect was not consistent across instars or source. No significant endophyte effect on head capsule width was found in spring populations from either tillers or turfs. This study shows that in irrigated dairy pasture, a high proportion of L. bonariensis larvae can live externally of tillers, presumably amongst the organic matter around the base of grasses in irrigated dairy pasture, and that density estimates based only on tiller populations will have significantly underestimated actual numbers. Having a precise indication of larval population densities is essential when developing life tables or determining economic damage threshold levels.

Collection of field samples. Host grasses (Lolium perenne, Poa annua), Collection of tillers or turfs (taken as cores) for weevil larvae, Cores of known diameter, with the number of grass tillers counted to determine grass species density. Heat extraction of larvae from samples. Measurement of larval head capsule widths under a binocular scope and eyepiece graticule. 

No missing values