Seed predation by an Amara species on different weed species prevalent in Pacific Northwest cereal systems

Diversifying wheat production systems include more rotational and cover crops, potentially increasing vulnerability to insect pests and weeds. This presents new challenges as producers simultaneously attempt to sustain or increase yields and maintain soil health while dealing with newly problematic weeds. Incorporation of broadleaf crops constrains herbicide use, making natural suppression of weeds more important in these systems. The effectiveness of invertebrate seed predators in weed control is explored in this study. Anthemis cotula (Mayweed chamomile), Chenopodium album (common lambsquarters), and Bromus tectorum (downy brome) are weeds that are problematic in inland Pacific Northwest (iPNW) cereal systems. Field experiments with sentinel seed stations found that Mayweed chamomile was removed at a lower rate than the other two species. Among the seed predators in the system were Amara spp. (Coleoptera: Carabidae). In laboratory bioassays with live-trapped individuals of an Amara species, seeds of Mayweed chamomile were consumed at a lower rate than the other two species. The apparent defenses of the seeds could not be removed with hexane or methanol rinses, but breaking the seed coat resulting in Mayweed seed consumption at least similar to the other two species, implicating physical defenses. This likely contributes to the invasive nature of Mayweed chamomile and its prevalence as a weed in diversified wheat productions systems.