Leaf-galling insects on naio tree reproduction (TCBES Defens - Event Details

This event has concluded and is no longer current.

This event has concluded and is no longer current.

Leaf-galling insects on naio tree reproduction (TCBES Defens

Location: STB 226

Corie Yanger

TITLE: Impacts of introduced leaf-galling insects on reproduction and seedling survival of Myoporum sandwicense, a native Hawaiian tree



ABSTRACT:

Insect herbivores released from biotic and abiotic controls of their native environment can have severe negative impacts on plant reproduction and survival in their introduced range. On Hawaiʻi Island, a recently introduced leaf-galling thrips species (Klambothrips myopori) has infested populations of naio (Myoporum sandwicense), an abundant native tree, causing widespread dieback. While mature trees show signs of infestation and have disappeared in some areas,the extent to which infestation affects naio reproduction has been unknown.Within two naio populations recently invaded by thrips, one mesic and one dry, I counted flowers and fruits and assessed gall damage and foliage dieback for naio trees with different levels of initial gall damage monthly for one year. At these same sites, gall damage, foliage dieback and height were recorded for naio seedlings. I found that naio reproduction decreased for trees with moderate and high initial gall damage regardless of site. Reproduction also declined drastically for trees with zero to low initial gall damage at the dry site. Results from analyses indicated that tree foliage dieback, branch foliage dieback and branch death were the most significant variables for explaining naio reproductive decline over time. Damage increased for trees with zero to low initial gall damage at the mesic site, while gall damage remained extremely low and foliage dieback was mostly low for trees with zero to low initial foliage dieback at the dry site. Gall damage and foliage dieback increased for trees with moderate initial gall damage at both mesic and dry sites, while gall damage and foliage dieback were high and then declined for trees with high initial gall damage at both mesic and dry sites. Seedling survival was 35% at the mesic site and 89% at the dry site, and did not appear to be strongly related to thrips damage. At a third site, I used pesticide to remove thrips and evaluated reproductive differences in treated versus untreated naio trees. Reproduction decreased for all trees at the experimental site. Thrips-removal trees showed slightly less gall damage and foliage dieback in the last months of monitoring. These results indicate that introduced thrips have a notable negative impact on naio reproduction and that without management action, naio populations will decline.

For more information, contact: ostertag@hawaii.edu (808) 932-7573

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Tags: thesis defense seminar

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