An examination of the relationship between Argentine stem weevilListronotus bonariensis(Kuschel)) and several of its host grasses

Abstract

The susceptibilities of several New Zealand pasture grasses to Argentine stem weevil oviposition and larval attack were investigated. Short rotation cultivars of ryegrass showed higher susceptibility to both forms of attack than perennial ryegrass cultivars. It is possible that the latter are resistant to weevil attack because of their comparatively high cellulose levels and consequent toughness. Of the other grasses, tall fescue was found to be highly resistant to egg-laying whereas Timothy was found to be tolerant to larval mining. Larval survival of 30%–40% was estimated to occur between the egg and first instar stage in most grasses compared with the more variable and lower survival levels of 7%–23% between the first and second instars. These levels of survival were again proportional to relative cellulose levels. From the second instar onwards there was little or no larval mortality. The resistance to adult weevil feeding in the young seedlings of‘low cellulose’ (‘L.C.’) selection of ‘Grasslands Arikï’ (N889) ryegrass is not expressed as ovipositional or larval resistance in mature plants. It is hypothesised that the seedling ‘L.C.’ Ariki plants initially have high levels of the alkaloid perloline which confer resistance but this rapidly dissipates as the plants develop.