Asian earthworms Amynthas agrestis and A. tokioensis present an ongoing challenge for ecologists and professionals in natural resources conservation, first throughout the Eastern and Southeastern US and now in the Upper Midwest. These invasive earthworms are competitive in diet, grow rapidly to transform soil to unconsolidated casts, and presumably overwinter as cocoons. No effective controls are known to manage these earthworms, but compost operations that maintain 55°C may kill cocoons in addition to soil pathogens. Research is underway at the UW Arboretum to investigate (1) cocoons abundance when reared in the laboratory and (2) cocoon temperature tolerance. We hypothesize that Amynthas cocoons will be of the greatest abundance in soil which had been previously worked by the earthworms, and that cocoons will become inviable when exposed to heat (55C), but will remain viable when exposed to cold (–20°C). An incubation study was designed to house adult Amynthas earthworms in soil from two sources. Soil was sieved in five 20-d periods to collect cocoons of known species and age, which were later exposed to heat (3 or 15 d at each 40, 45, 50, 55, and 60°C) and cold (e.g., flash freeze: 24 h at –20°C).
Amynthas earthworms housed in the laboratory produced >3000 cocoons, and the selected heat temperature treatments affected cocoon viability (cold treatments are in progress). Earthworms produced ~200 cocoons in 20 days at their peak, with an average rate of 3.8 cocoons produced per earthworm over a 20-d period. Soil source did not significantly alter cocoon production rate (P = 0.32) to suggest that newly invaded areas could have a similar cocoon abundance as previously invaded areas. Upon dissection, cocoons showed evidence of embryonic development prior to heat exposure. These tissues were dead following all heat treatments, whereas the control cocoons (those held at room temperature) contained live earthworms. Live young were pigmented and 4 to 11 mm in length. Thus exposing cocoons of A. tokioensis and A. agrestis to 40°C for 3 d was sufficient for 100% cocoon mortality. In Wisconsin among many states, licensed compost operations are required to maintain compost temperature at 55°C for either 3 or 15 days (depending on the type of pile) in order to kill the majority of pathogens. These results therefore support the use of compost operations as a means for helping manage the spread of Amynthas earthworms.