Effects of leaf damage on oviposition choice in an invasive paropsine beetle

In 2007, an invasive paropsine beetle, Paropsisterna nr. gloriosa Blackburn, caused severe defoliation of Eucalyptus in mixed-species foliage plantations in south-west Ireland. At many of the plantations, Eucalyptus parvula L.A.S. Johnson & K.D. Hill was the most heavily damaged species while Eucalyptus pulverulenta Sims was generally resistant to the beetle. However, at the most heavily damaged site beetles moved to feed on E. pulvarulenta presumably during periods when suitable foliage (new leaves) of E. parvula had been severely depleted. The present study examines factors underlying shifts in oviposition from the preferred to non-preferred host. In choice and no-choice experiments, P. nr. gloriosa laid more eggs directly on new E. parvula foliage compared with new E. pulverulenta foliage. However, in choice experiments where new E. parvula foliage was unavailable (but old foliage available), more eggs were laid on new E. pulverulenta foliage. The potential for prior feeding damage to stimulate or deter oviposition on either host was also examined. Prior damage to new and old E. parvula leaves increased egg-laying directly on the damaged foliage; however, prior damage to E. pulverulenta may have inhibited oviposition. The results suggest that in mixed-species plantations, facilitation of oviposition on preferred hosts through prior feeding damage helps maintain the relative resistance of E. pulverulenta against P. nr. gloriosa, even under high beetle densities. However, the vulnerability of E. pulverulenta will increase where suitable age-classes of preferred-host foliage are severely depleted or unavailable. © 2011 Blackwell Verlag, GmbH