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 ar.e 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 Ariki' (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.

Field resistance to Argentine stem weevil(Listronotus bonariensis)in different ryegrass cultivars infected with an endophyte deficient in lolitrem B

“…Infection of the host grass with fungal endophytes adds another dimension to this relationship, with the endophyte interacting with the plant genotype to influence the levels of alkaloids which are produced. The greater susceptibility of the tetraploid ryegrasses to ASW attack compared with the perennial ryegrasses is apparent in these trials and has been demonstrated before (e.g., Goldson 1982). Endophyte infection reduced the level of ASW attack considerably but the amount of damage inflicted on E+ Greenstone and Moata in our trials was in some instances similar to that on E-Nui and Pacific.…”

Observations on Argentine stem weevil mortalities in Volcanic Plateau pastures

“…comm. ) and reports from Canterbury (Pottinger 1961;Goldson 1982). Identification of the factor Downloaded by [York University Libraries] at 03:43 18 November 2014 responsible for density dependent population regulation would increase our understanding of Argentine stem weevil population fluctuations and may lead to a new approach to control if the causal agent can be manipulated by farm management practices.…”

Multitrophic interaction between the ryegrassLolium perenne,its endophyteNeotyphodium lolii,the weevil pestListronotus bonariensis,and its parasitoidMicroctonus hyperodae

“…For example, Prestidge et al (1982) cited weevil densities of c. 220 nr 2 in their nil endophyte ryegrass pastures. It can be conjectured that in all plots in this study there were sufficient volunteer non-endophyte ryegrass plants and other host grass species (e.g., Goldson 1982) to support the low numbers of weevils present, irrespective of the sown L. perenne. It is notable that significant inverse endophyte/peramine effects on adult weevil densities have been recorded in the same plots when the populations ranged downwards from 80 m~2 (L. R. Fletcher unpubl.…”