Canadian Forest Service Publications

Evidence for mate-encounter Allee effect in an invasive longhorn beetle (Coleoptera: Cerambycidae). 2015. Rhainds, M.; Heard, S.B.; Hughes, C.C.; MacKinnon, W.E.; Porter, K.B.; Sweeney, J.D.; Silk, P.J.; DeMerchant, I.; MacLean, S.; Broderson, G. Ecological Entomology 40: 829–832.

Year: 2015

Issued by: Atlantic Forestry Centre

Catalog ID: 36394

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1111/een.12255

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  1. Limited empirical support is available for mate-encounter Allee effects in invasive insects due to the logistical challenges of studying demographic trends in low-density populations.
  2. Traps baited with pheromone and spruce volatiles were used to monitor the abundance of female Tetropium fuscum F. (Coleoptera: Cerambycidae) at multiple sites in Nova Scotia in 2011 and 2012. Each female was dissected to determine the presence or absence of sperm in its spermatheca (mated or virgin female, respectively).
  3. Both male and total T. fuscum abundance declined with increasing distance to the focal point of T. fuscum’s invasion. Female mating probability declined with male abundance and with distance from the invasion focus, and mating probabilities were very low at the most peripheral sites. Difficulty in encountering mates may thus contribute to limiting the spread of T. fuscum.
  4. The approach outlined here could be integrated into existing surveys of wood borers using traps baited with semiochemicals to improve our understanding of the role of the mate-encounter Allee effect in invasion dynamics.

Plain Language Summary

The brown spruce longhorn beetle (BSLB) was introduced near Halifax more than 25 years ago and it has since been a threat to spruces across the Maritimes region and beyond. Previous studies indicated that the range of distribution of BSLB is ‘pinned’ geographically, i.e., the abundance of BSLB is very low at sites more than 80 km from its point of distribution. In this study, females BSLB captured at semiochemical-baited traps at multiple sites in 2011-2012 were dissected to determine their mating status. In the core range distribution of BSLB near the site of introduction, the proportion of mated females (relative to virgin, as yet unmated females) varied between 30 and 80%. The proportion of mated females declined with the distance to the site of BSLB introduction, and no mated females (0%) were sampled at sites more than 80 km from the site of introduction. This finding suggests that difficulty in encountering males at low density populations (mate-encounter Allee effect) restricts the spatial spread of invasive BSLB.