Effects of an early-season folivorous moth on the success of a later-season species, mediated by a change in the quality of the shared host, Lupinus arboreus Sims.

Larvae of Platyprepia virginalis (Lep.: Arctiidae) and Orgyia vetusta (Lep.: Lymantriidae) feed on the foliage of bush lupine (Lupinus arboreus Sims) at Bodega Bay, California, USA, in February-April and May-July, respectively. Female O. vetusta attained lower pupal weights and produced fewer eggs on branches of L. arboreus which had experimentally received P. virginalis damage earlier in the same year, compared to those reared on control branches.Growth rates of first-instar O. vetusta were lower on undamaged leaves of previously damaged L. arboreus than on leaves of undamaged controls. This was true for lupine bushes damaged by P. virginalis in the field; and also for greenhouse-grown lupine plants damaged by Estigmene acrea (Lep.: Arctiidae) when excised foliage was used in the assay. However, fifth (last) instar female O. vetusta larvae showed no preference for damaged versus undamaged greenhouse-grown L. arboreus in their feeding or choice of a site for pupation.These experiments demonstrate the potential for competition-like interactions between herbivores mediated by changes in quality of the shared host.