Author
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Lee, Jana |
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SEYBOLD, STEVEN - USDA FOREST SERVICE |
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Submitted to: Journal of Insect Behavior
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/26/2009 Publication Date: 7/16/2009 Citation: Lee, J.C., Seybold, S.J. 2009. Host acceptance and larval competition between the invasive banded and European elm bark beetles, Scolytus schevyrewi and S. multistriatus (Coleoptera: Scolytidae):potential mechanisms for competitive displacement. Journal of Insect Behavior. Available: http://www.springerlink.com/content/wx128537661662pn/fulltext.pdf Interpretive Summary: The newly invasive Asian banded elm bark beetle is more common in areas of Colorado and Wyoming than the long-established European elm bark beetle. Both beetles feed on the phloem of elm trees. Laboratory studies were initiated to determine how these two species would interact in close proximity and explain why the banded elm bark beetle appeared to be replacing the European elm bark beetle. First, the likelihood that unmated females of either species would tunnel into an elm host was mostly similar when the host was uninfested or when the host was infested with earlier colonizers of the same or different species. Secondly, the number of eggs laid by females when introduced onto elms in medium and high numbers was not substantially different when only one species was present or both species were present. Thirdly, differences in competitive ability appeared when the eggs hatched and larvae of both species developed. When both species were introduced alone (one species) to an elm host, the size of offspring were smaller when parents were introduced at high densities than medium densities. When both species were introduced onto the same elm host, the banded elm bark beetle was a superior competitor, it produced four-fold more offspring than the European elm bark beetle. Technical Abstract: A recent survey revealed that the newly invasive banded elm bark beetle, Scolytus schevyrewi, was much more abundant than the long-established European elm bark beetle, S. multistriatus, in areas of Colorado and Wyoming, USA. This study sought to determine whether competitive displacement of S. multistriatus by S. schevyrewi may be mediated by a sequence of interactions between the species on and below the bark surface. At the first step in the sequence, host acceptance behavior (i.e., time to tunnel into the host) was monitored among female S. schevyrewi and S. multistriatus. There was no substantial difference in host acceptance behavior when females were offered small cut logs (bolts) of Ulmus pumila infested with con- or heterospecific females. At the second step, mating and oviposition usually follow after a female has excavated a gallery. Mean oviposition per parental female in 1 wk was not significantly different among treatments: S. schevyrewi at medium density of 2.86 parental females per dm2, at high density of 5.71 per dm2; S. multistriatus at medium density, at high density; and mixed species (i.e., S. schevyrewi and S. multistriatus combined, with each at medium density). At the third step, progeny production and progeny size were monitored among the same density treatments, but the number of parental beetles and size of bolts were doubled. Differences in progeny production would reflect larval competition, since the number of eggs initially laid was not different. Both S. schevyrewi and S. multistriatus were sensitive to intraspecific competition, size of progeny was smaller in high than medium density treatments, but total progeny production was similar at both densities. Scolytus schevyrewi was a stronger interspecific competitor than S. multistriatus. Smaller S. multistriatus progeny, and four-fold more S. schevyrewi progeny were produced when both species developed on the same host. |
