When host-plant resistance to a pest leads to higher plant damage

2017

English

The effects of the association between grasses and fungal endophytes on orthopterans are very poorly studied although they are important grassland pests. Here, the endemic New Zealand weta, Hemiandrus sp. ‘promontorius’, and Festulolium loliaceum infected with Epichloë uncinata, were used to study the effect of endophyte-mediated resistance in grasses on this large orthopteran insect in the laboratory, and the effects of this interaction on the grass. The insect was presented with F. loliaceum with and without E. uncinata infection in no-choice and paired choice experiments. Other controls were Epichloë festucae-infected Festuca rubra and endophyte-free Lolium perenne. In no-choice experiments, persistent attempts by the insect to graze the endophyte-infected grasses (but promptly abandoning them) resulted in a significantly higher number of plants lost due to excision at their stems after the first bite (P = 0.004). The inability of affected grasses to compensate for the lost biomass resulted in a lack of significant difference between the dry biomass of endophyte-infected and endophyte-free controls (P = 0.206). However, in choice experiments, there was a preference for the endophyte-free controls when they were paired with the endophyte-infected grasses (P < 0.05). The current work shows that endophyte-infected grasses can sustain high plant losses when attacked by an orthopteran insect in the absence of an alternative food source. This contrasts other endophyte/herbivory experiments in which high herbivory occurs because chemical plant defences are at a low concentration or the endophytes have other non-toxin roles in the plant.

Nboyine, J. A.; Saville, D.; Boyer, S.; Cruickshank, R. H.; Wratten, S. D.