Orientation behavior of predaceous ground beetle species in response to volatile emissions from yellow starthistle damaged by an invasive slug

Authors: OSTER, MARINA - Stanford University; Smith, Lincoln; Beck, John; HOWARD, ABIGAIL - Stanford University; FIELD, CHRISTOPHER - Carnegie Institute - Stanford

Submitted to: Arthropod-Plant Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2014
Publication Date: 8/7/2014
Citation: Oster, M., Smith, L., Beck, J.J., Howard, A., Field, C.B. 2014. Orientation behavior of predaceous ground beetle species in response to volatile emissions from yellow starthistle damaged by an invasive slug. Arthropod-Plant Interactions. 8:429-437.

Interpretive Summary: Yellow starthistle is an alien weed originating from Europe that has invaded about 20 million acres in the western U.S.A. The spiny plant interferes with grazing livestock and outdoors recreation, it is fatally poisonous to horses, and it outcompetes desirable vegetation. The plant is thought to be invasive because few native North American herbivores attack it. The grey garden slug (Deroceras reticulatum), which also originates from Europe, feeds on young plants, often killing them. This slug is known to be attacked by two species of ground beetle, Pterostichus melanarius and Scaphinotus interruptus. It would be interesting to know if these insects are efficient predators of this slug, because such predation would reduce the slug’s ability to control the weed. Furthermore, the slug is also an important pest of many crops. The beetles and slugs are active at night, and it is not known how the beetles find the slugs. We tested the hypothesis that plants attacked by the slug emit an odor that attracts the beetles. The beetle that originated from Europe, P. melanarius, preferred the odor coming from slug-damaged plants, whereas the species native to the U.S.A., S. interruptus, showed no preference. The results suggest that P. melanarius is well-adapted to finding this slug on an alien weed. Further studies should be conducted to determine if crops or native plants can produce odors in response to slug damage that can attract this predator. If they can, then this beetle could be an important biological control agent for controlling this slug.

Technical Abstract: The up-regulation or emission of plant volatiles in response to herbivory may signal to the natural predators and parasitoids that a plant is under attack from herbivores. This is known as an indirect defense within a tritrophic system - where herbivore number is reduced through predation that is stimulated via volatile release. We investigated indirect defense in the yellow starthistle (Centaurea solstitialis)-grey garden slug (Deroceras reticulatum)-ground beetle (Pterostichus melanarius and Scaphinotus interruptus) system, in which beetles are the primary predator of Deroceras reticulatum, which, in turn, is the dominant herbivore of the highly invasive weed, C. solstitialis. The aim of our study was to examine the behavioral responses of two species of ground beetle to olfactory stimuli emitted from yellow starthistle damaged by D. reticulatum. Pterostichus melanarius showed a significant preference for the odor of damaged yellow starthistle relative to the odor of intact plants, while S. interruptus did not. Pterostichus melanarius, D. reticulatum and yellow starthistle originated from Europe, where they may have coevolved, whereas S. interruptus is native to North America. There was no quantitative relationship between the probability of either the beetle’s plant choice or decision time and level of herbivory, suggesting that the presence of leaf damage alone is enough to trigger a volatile release and thus a carabid behavioral response.