Interactions between endophyte (Neotyphodium spp.) and ploidy in hybrid and perennial ryegrass cultivars and their effects on Argentine stem weevil (Listronotus bonariensis)

Argentine stem weevil damage was assessed in 1998 and 1999 on two diploid perennial ryegrasses (cvs. 'Yatsyn' and 'Samson'), a diploid long-rotation hybrid ryegrass (cv. 'Marsden'), a tetraploid perennial ryegrass selection ('4N') and in a tetraploid hybrid (cv. 'Greenstone') in a field trial in Taranaki. 'Greenstone' was infected with a selected Neotyphodium endophyte that produces peramine and ergovaline but not lolitrem B. All other cultivars were naturally infected with endophytes that produce all three alkaloids. In the first year, percent endophyte infection levels were low in 'Greenstone' (61%), 'Marsden' (70%) and '4N' (71%) relative to 'Yatsyn' (85%) and 'Samson' (86%), but increased in the second year to greater than 88% in all cultivars. Argentine stem weevil adult feeding and larval damage were greatest on 'Greenstone' and least on 'Yatsyn' and 'Samson' in both years. 'Greenstone' tillers damaged by larvae were more severely affected than tillers of other cultivars. Individually and in combination, percent endophyte and peramine and lolitrem B levels in the leaf lamina were correlated with adult activity which in turn was the main factor affecting larval damage. Overall, the tetraploid and hybrid species sustained more damage than the diploids and perennials. This was attributed mainly to lower leaf lamina peramine concentrations in the hybrid and tetraploid combinations which affected adult feeding, but additional attractiveness factors in these cultivars may also play a role in their susceptibility to Argentine stem weevil. The absence of lolitrem B was not a major factor in the number of tillers damaged by larvae in 'Greenstone', but may have resulted in more severe damage to those tillers.