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1 April 2013 Effectiveness of Erythrina gall wasp biocontrol and implications for the recovery of threatened Wiliwili trees (Fabaceae: Erythrina sandwicensis)
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Abstract

Wiliwili (Erythrina sandwicensis), an endemic Hawaiian dry forest tree species, is threatened by an invasive gall-forming wasp (Quadrastichus erythrinae) first detected in Hawai‘i in 2005. Eurytoma erythrinae, a predator of Q. erythrinae from Tanzania, was selected as a biological control agent and was released at sites throughout the Hawaiian Islands. To assess the effectiveness of this biocontrol release, we measured the extent of damage attributable to Q. erythrinae wasps in 124 E. sandwicensis trees at the Waikoloa Village Dry Forest Recovery Project before (January, 2009) and after (January, 2011) the release of the parasitoid wasp at this site. Because host spatial distribution has important consequences for the establishment and success of natural enemies such as parasitoids, we took a spatially explicit approach to account for the potential spatial heterogeneity in E. sandwicensis. We observed an increase in galling damage across the population and 21 trees became completely defoliated between the two survey years. The distribution of E. sandwicensis across the landscape was highly clumped and tree-level change in galling damage showed a strong spatial signal. Erythrina sandwicensis recovery was non-random with respect to landscape indicating that individual response to the biocontrol agent and exogenous factors (e.g., drought) may have strong interactions with the invasion and persistence of the pest Q. erythrinae.

Torrey Botanical Club
Rayna C. Bell, Amos Belmaker, Courtney S. Couch, Katherine M. Marchetto, Joseph L. Simonis, R. Quinn Thomas, Jed P. Sparks, Julia M. Brown, Kainana S. Francisco, and Mark E. Manuel "Effectiveness of Erythrina gall wasp biocontrol and implications for the recovery of threatened Wiliwili trees (Fabaceae: Erythrina sandwicensis)," The Journal of the Torrey Botanical Society 140(2), (1 April 2013). https://doi.org/10.3159/TORREY-D-12-00069.1
Received: 22 October 2012; Published: 1 April 2013
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