Nathan Rank

Sonoma State University

Natural enemies and host plant use

Effects of host plant variation on natural enemies (Page 5 of 5)

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Chemical Ecology

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Host Preference & Performance

Natural Enemies

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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.

 


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January 23, 1999 NER