Activity 6: Wiliwili Gall Wasp Invasion
Materials & Setup
Class Period One: Exploring the Gall Wasp Invasion on Google Earth
- This exercise requires access to Google Earth (free software available for download at www.earth.google.com) and the Wiliwili Gall Wasp Hoike.kmz file (included with this curriculum). It’s best to pre-load computers with the program and file, rather than use class time to do so.
- Ideally students will work in small groups at their own computers as you lead them through the lesson, using a projector and screen. If that’s not possible, a single computer and projector will suffice.
- Prior to teaching the lesson, open Google Earth. If you’re using the software for the first time, take a few moments to learn how zoom, pan, search, etc. using the “Navigating Google Earth” tutorial available at www.earth.google.com. It is best, though not necessary, to use Google Earth while connected to the Internet.
- Explore the Wiliwili Gall Wasp Hoike.kmz file.
Provided Map Layers:
- Initial infestations (8 sites documented by Hawai‘i state entomologist, Mach Fukada)
- Pu‘u o Kali (best example of native wiliwili forest in Hawai‘i and the Erytoma erythrinae biological
control release site)
- Wiliwili habitat (area on Maui where native wiliwili trees can be found)
- Wind lines (Maui’s prevailing wind directions)
- Major roads
- Ports of entry
- Agricultural land (where nonnative wiliwili trees were used as windbreaks)
- Erythrina Gall Wasp Survey (50 infected tree sites documented by the Maui Invasive Species Committee)
- Tanzania (country where state entomologist Mohsen Ramadan located the gall wasp’s natural enemy: Eurytoma erythrinae.)
- Computer (s)
- Wiliwili PowerPoint.ppt file (included as media below)
- “Wiliwili PowerPoint Script” (Teacher background, pages 152-158)
- Google Earth software (available for free download at www.earth.google.com)*
- Wiliwili Gall Wasp Hoike.kmz file (included as media below)*
*loaded onto each computer
Students will trace the path of the 2005 wiliwili gall wasp invasion on Maui and respond to the challenge of controlling the pest using real-life data: wind patterns, roads, ports of entry, presence of nonnative host trees, and life cycle of the native wiliwili. Their task is to control the vectors to stop the gall wasp’s spread.
1) Present the “Wiliwili PowerPoint” to class, using the Teacher Background “Wiliwili PowerPoint Script.”
2) Homework assignment: Have students strategize how to assist the spread of Eurytoma erythrinae, taking the new environmental factors into account. Things to consider:
- Non-native erythrina trees are gone and no longer serve as a breeding ground. How will this affect the speed of the spread?
- A: It will likely be slower, and not cover as much ground in residential and farming areas.
- Which season would be best for encouraging spread?
- A: Late winter or spring, when the trees have new leaves. The period of dormancy, when there are few leaves, would not be a good choice.
- How might heavy rain or drought affect the new wasp’s spread?
- A: Rain would encourage new plant growth, which would in turn encourage gall wasp reproduction. The predatory wasp would find plenty to prey on. Drought would have the opposite effect; spread would be slower.
- Where is the best location to release the wasp?
- A: Wherever there is still a large population of Erythrina species showing signs of infection— in particular, Pu‘u o Kali.
- How can each vector be incorporated into the release plan?
- Cars can be used to intentionally transport the wasp to other areas across the island.
- Planes and boats can be used to intentionally transport the wasp to other islands, such as Moloka’i and Lāna’i.
- Wind can be taken into consideration. Biologists might choose to release wasps in a breezy area where the insects are likely to be blown to the next grove of trees.
- Change the elements of the gall wasp invasion; have students devise control strategies for a hypothetical insect that crawls, or is a foot long, or burrows underground.
- Have students predict the success of the introduced biological control, Eurytoma erythrinae, based on new factors: the elimination of the nonnative wiliwili trees as hosts, the longer lifespan of the predatory wasp, rainfall, wind direction, etc.
- When the gall wasp invasion started on Maui, some people suggested eliminating the thousands of nonnative wiliwili trees to prevent them from acting as a host for the wasp. Others thought that destroying the trees was too extreme. What are your thoughts? Do you think people would have been willing to cut down their trees? Why or why not?
- Do you think eliminating the false wiliwili trees would have ultimately changed the progression of the invasion? Why or why not?
- What could Maui County or the State of Hawai‘i do to protect itself from similar invasions in the future?
- Which elements of the wiliwili gall wasp’s journey can we predict? Which elements do we have no control over?
- Answers from brainstorming session
- Participation in group discussion
- Homework assignment