Ryegrass production in Wairarapa, New Zealand: is biological control of Argentine stem weevil important?

Abstract

To investigate the interaction between Argentine stem weevil (Listronotus bonariensis), its parasitoid Microctonus hyperodae, fungal endophyte (Neotyphodium lolii) and its grass host, four endophyte-ryegrass (Lolium perenne) treatments were established on four farms in Wairarapa in autumn 2003. A diploid ryegrass contained either wild-type or AR1 endophyte or was endophytefree, while a tetraploid ryegrass contained AR1 endophyte. Wild-type, AR1 and endophyte-free ryegrasses average 52%, 91% and 2% endophyte-infected tillers for the 3 years of measurement. Moderate increases over time in the proportion of wild-type infected tillers indicated selection pressures favoured endophyte-infected tillers. Endophyte-free tiller populations were 11% lower than AR1 or wild-type but not significantly so. L. bonariensis populations were highest in endophyte-free and wild-type pastures and 80% lower in AR1 pastures. Mean rates of parasitism in L. bonariensis were lower in spring (9%) than autumn (35%), tended to be higher in wild-type than in AR1 diploid ryegrass, and only had a weak relationship with percent endophyte-infection. Keywords: endophyte, Neotyphodium lolii, Lolium perenne, dry matter yields, plant persistence, Listronotus bonariensis, Microctonus hyperodae