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Keywords:

  • Heteronychus arator ;
  • Lolium perenne ;
  • Neotyphodium lolii ;
  • olfactometer;
  • volatile oils

Abstract

Perennial ryegrass (Lolium perenne) is often infected with the fungal-endophyte Neotyphodium lolii. In addition to the ‘wild-type’ strain (EWT), several ‘selected’ strains of N. lolii are now being marketed as AR1 (EAR1) and AR37 (EAR37). Each of these strains impact positively on L. perenne's resistance against many insects, including the African black beetles (Heteronychus arator). The impact of volatile oils produced specifically by each strain in the endophyte–grass association in enhancing the grass's resistance to insects is still largely unknown. Keeping these in view, we determined the volatile oil profiles produced by L. perenne infected with either EWT or EAR1 or EAR37 and determined the impacts of these volatiles on the host-selection behaviour of H. arator adults. In the absence of endophyte infection (E), L. perenne produced 18 different volatile oils. In L. perenne EWT, quantities of 2-ethyl-1-hexanol acetate (Rt = 14.5 min), (Z)-2-octen-1-ol (Rt = 22.2 min), and butylated hydroxyl toluene (Rt = 23.2 min) were 24, 16 and 26%, respectively, greater than L. perenne E. The strains EAR1 and EAR37 affected differently the quantities of the volatile compounds but not their identity. In the four-choice bioassay, males and females of H. arator were equally attracted to each strain. In Y-tube olfactometer, compared against E, H. arator adults were less attracted to L. perenne EWT and EAR1. The attractiveness of EAR37 was similar in effect to E to H. arator. The results indicate that each strain of N. lolii alters the profile of volatile oils in L. perenne differently and that alteration can influence H. arator adult-host selection.