Surveying for Oregonian slugs in Hawai’i with the goal of removing their quarantine status
Slugs are one of the most important pests of Christmas trees grown in the Pacific Northwest relative to load rejections in Pacific Rim destinations. For example, when a shipment of trees contaminated with an Arion slug is discovered at a port of entry in Hawai’i officials reject the load, and either ship it back to Oregon/Washington or have it cleaned up in Hawai’i at the shipper’s expense. Current strategies for managing slugs focus on a combination of chemical and cultural measures but even with these approaches, slugs continue to pose a significant economic problem for Christmas tree growers. An alternative approach would be to survey for these quarantine slug species throughout the Hawaiian Archipelago. Slugs in this genus have successfully invaded many regions of the U.S. and they could be present on one or more islands. If these slugs are in fact established in Hawai’i then it is likely that they would no longer be considered a quarantine pest and their discovery on a shipment of trees should not lead to shipment rejection. Thus, we surveyed for these invasive slugs on 20 sites on Oahu, Maui, Hawai’i and Kauai. Slugs in the genus Arion are temperate species and to help select survey sites, occurrence records of other invasive temperate gastropods on the Hawai’i Islands were mined from slug databases e.g. iNaturalist. In addition, we also surveyed in anthropogenic areas (e.g. garden centers) where Arion slugs have been found by us in other U.S. states. In total, we collected 22 different slug and snail species across the four islands. Slugs in the genus Arion can be difficult to identify using only morphological traits and as a result the identity of all of the Arion specimens that we collected were confirmed using DNA analysis. This analysis showed that we collected two species, Arion intermedius on Maui, Hawai’i and Kauai and Arion distinctus on Hawai’i only. All of these specimens were found in forest habitat indicating that both species have established beyond highly anthropogenic habitats and also occur in more natural areas. Given that A. intermedius and A. distintus are temperate gastropods perhaps then it is no surprise that we only collected these slugs at altitudes greater than 2,700ft where cooler and likely damper conditions prevail. For future surveys, we recommend focusing on such higher altitude locations. The fact that we did not collect any Arion slugs, which are largely associated with humans and trade, on Oahu is surprising especially since it is the most populous island in the archipelago and is also home to the principal seaport for the State. In addition, given that Oahu is the most visited island in the archipelago it would be surprising that the species has not been reported if it does in fact occur there. Consequently, for now we should assume that A. intermedius is not present on Oahu. The occurrence of A. intermedius on Maui, Hawai’i and Kauai and the presence of A. distinctus on Hawai’i will be reported to the Hawai’i Department of Agriculture and we will encourage them to use these data to review the quarantine status of Arion slugs in shipments of Christmas trees.
- Project ID19-05-OSU
- CategoriesPost Harvest
- Growing Region(s)Pacific Northwest
- Tree SpeciesFir
- Investigator(s)McDonnell
- Institution(s)Oregon State University
- Research Year2019
- Publication Year2024
- ReportDownload 📁