Nathan Rank Sonoma State University Natural enemies and host plant use Effects of host plant variation on natural enemies (Page 5 of 5) Introduction & Collaborators Chemical Ecology Predictions & Study Systems Host Preference & Performance Natural Enemies Research Home See also Research summary. Previous studies found that the secretion repels ants & generalist ladybird beetles. However many natural enemies of salicylate-using leaf beetles are specialists. Specialist syrphid flies (Parasyrphus spp.) are not repelled by the secretion. Rather, it acts as an olfactory attractant and a feeding stimulant. Generalist bug predators that feed on leaf beetles in nature were not repelled by P. vitellinae secretions. See also research summary at the bottom of the page. Ant on a poplar leaf where beetle larvae fed. Role of Ants Other researchers have shown that the beetle secretion repels ants and ladybird predators in laboratory choice tests. It is also effective against ants under field conditions where ants are abundant on leaves with aphids (studies by Thomas Whitham and coworkers). However, ants were not important predators on C. aeneicollis or on P. vitellinae. Ants were also not recorded as predators in several studies of the natural enemies of leaf beetles. Specialist predators of beetles An important natural predator on C. aeneicollis is the trap nesting wasp Symmorphus cristatus. This wasp feeds exclusively on beetle larvae across North America. Other Symmorphus species also specialize on leaf beetles in Europe and Asia. These wasps must have evolved a way to overcome the larval secretion of the beetles. Wasp feeding on a beetle larva Artificial traps that determined that wasps feed only on beetle larvae. Above: Whitish Parasyrphus eggs laid between beetle eggs Right: Parasyrphus larva attacking and consuming a third instar beetle larva.   The other important natural predator on C. aeneicollis is the syrphid fly Parasyrphus melanderi. Female flies lay their eggs on the beetle egg clutch and hatchlings consume beetle eggs.. Fly larvae then consume beetle larvae until they pupate. These flies feed only on beetle larvae. A close relative, Parasyrphus nigritarsis, feeds on several beetle species, including P. vitellinae, in Europe. Syrphid feeding on beetles feeding on salicylate-rich and salicylate-poor willows.   Effects of host plant on Parasyrphus The beetle secretion does not repel the specialist Parasyrphus fly. Feeding tests with Californian and Finnish Parasyrphus larvae show that flies eat beetle larvae from salicylate-rich willows just as readily as from salicylate-poor willows Parasyrphus eggs are most abundant on beetle eggs that were laid on salicylate-rich willows in nature. Beetle secretions as an attractant & feeding stimulant The beetle secretion attracts Parasyrphus larvae and stimulates them to feed. Thus the beetles' host derived chemical defense seems to have backfired. Effects on generalist bugs Anthocorus nemorum and Rhacognathus punctatus are two generalist bug predators that feed on beetle larvae throughout Europe and Scandinavia. These bugs feed as readily on P. vitellinae larvae on salicylate-rich plants as on larvae on salicylate-poor plants. Thus the beetle secretion is not very effective against some important natural generalist predators.   Previous Page Research Home|Nathan Rank's Homepage |Department of Biology | Sonoma State University January 23, 1999 NER