Cocoon Heat Tolerance of Pheretimoid Earthworms Amynthas tokioensis and Amynthas agrestis
Research Summary by Abby Bezrutczyk
Summary
Asian earthworms (Amynthas tokioensis and A. agrestis) are invading the northern United States through soil, potted plants, mulch and compost– along the way changing soil structure, nutrient cycles, and soil communities. There are no current established methods for removing these earthworms from invaded sites, but Johnston & Herrick (2019) studied ways to disrupt their reproductive cycle, and potentially limit their spread. Mating worms form cocoons from which their offspring will hatch– and at this cocoon stage, worms are easily introduced to new locations. But can heating the soil to 55C (131˚F) kill the earthworm cocoons? By rearing cocoons and testing their heat tolerance at different temperatures and treatment lengths, they found that the cocoons indeed have a temperature threshold consistent for all treatment lengths. When soil was heated to higher than 40C (104 ˚F), none of the cocoons survived. Knowing the temperature tolerance for these invaders can help curb their spread – there is potential in simply treating composts and soils with sustained heat.
Take-home points
- Asian earthworms are invading through gardening materials across the northern U.S., causing negative ecosystem impacts.
- The Asian earthworms’ cocoons did not survive when the soil temperature was raised above 40C.
Management implications
- Producers of compost and organic garden products should follow recommendations to heat soil to 55C, with earthworm cocoons as a target.
- Managers can consider experimenting with heat to control invasive earthworms (via prescribed fire or solarization). However, more research is needed on how heat affects the worms in different materials (compost vs. soil vs. mulch) before heat application can be a management practice.