Biocontrol of invasive pheretimoid earthworms using Beauveria bassiana

Abstract

Background Invasive species cause enormous costs of over $120 billion to the U.S. economy. Among biological invasions, the invasion by pheretimoid earthworms has gone relatively unnoticed and their invasion imposes yet unknown damage on USA agriculture and horticulture. The main dispersal is with horticultural goods such as plant material and composts. Pheretimoids affect commercially important hardwood forest. With no chemical agents currently certified for earthworm control nor any best horticultural practices, slowing the invasion is difficult. Methods In this study we measured the efficacy of a commercial entomopathogenic fungal isolate of B. bassiana (BotaniGard®) to kill pheretimoid earthworms under greenhouse conditions. Four treatments of B. bassiana were applied: The commercial product as per label, re-cultured commercial B. bassiana, 15 g and 25 g millet grains mycotized with recultured product. In all, three bioassays were conducted in 2 consecutive years with two batches of BotaniGard®. Results With fresh batches, all B. bassiana treatments with re-cultured product resulted in greater than 70% mortality within 4 weeks. Mortality was less than 60% when BotaniGard® was used as prescribed by the label. When using 1-year old spores (refrigerated at 4 °C), mortality rates for B. bassiana treatments were less than 20% and not significantly different from the controls. However, B. bassiana still affected the earthworms by slowing their development from juvenile to adult stage. Conclusion B. bassiana was effective against pheretimoid earthworms. Overall, mycotized millet grains did not significantly increase mortality over the re-cultured, directly applied B. bassiana spores. More experimentation is needed to find the mode of action of the re-cultured B. bassiana before investigating ways to improve the efficacy of B. bassiana when applied as prescribed on the label.

Genetic population structure and reproductive system of two invasive Asian earthworms,Amynthas tokioensisandAmynthas agrestis

“…First, the largest number of genotypes for A. agrestis was found at a nursery (CRN) and a site adjacent to a tree farm (HF), so these may result in other sites being seeded with the earthworm eggs (resistant cocoons). Control measures like with entomopathogenic fungi ( Nouri-Aiin & Görres, 2021 ) should be centered on horticultural nurseries. Second, if there are indeed all-purpose phenotypes among clones, then we would expect that the earthworms would be tolerant of any environmental threat.…”

“…Briefly, a panel of ∼100 individuals were sequenced for the mitochondrial COI barcoding gene ( Hebert, Ratnasingham & De Waard, 2003 ) that revealed only the two species were present at the sites, then another group of 40 individuals that could be unambiguously identified by morphology were sequenced for the COI gene, and species-specific primers that produced different sized amplicons were designed. This method was then tested and gave clear unambiguous identification for the two species (details in Nouri-Aiin & Görres, 2021 ). The adult earthworms could often be identified by morphology ( Chang, Snyder & Szlavecz, 2016 ), but sometimes, due to various degree of degradation in external and internal characteristics associated with their reproductive organs, identification required the barcoding method.…”

“…Identifying these species morphologically requires examination of the male parts, i.e. , characters often missing, so rapid molecular methods have recently been developed ( Nouri-Aiin & Görres, 2021 ).…”