Deer mouse predation on the biological control agent, Urophora spp., introduced to control spotted knapweed

Abstract

Field observations made in 1993 suggested that rodents were preying on spotted knapweed (Centaurea maculosa) seedheads, possibly targeting the gall fly larvae (Urophora spp.) which overwinter within them. I conducted a brief study to determine the cause of seedhead predation and quantify gall fly predation. Stomachs were examined from 19 deer mice (Peromyscus maniculatus) captured in the fall of 1993 and winter of 1997. All individuals had preyed upon gall fly larvae. The mean number of gall fly larvae found in 10 deer mouse stomachs in the winter of 1997 was 212.8. The minimum number of larvae consumed by these 10 animals for 1 night of foraging was 2686. Availability of a concentrated protein that is a readily accessible and abundant resource during winter may elevate deer mouse populations in knapweed-infested habitats. Increases in densities of deer mice due to gall fly presence could bring about shifts in composition of small mammal communities.

Keywords

Peromyscus maniculatus, Urophora, Centaurea maculosa, deer mouse, gall fly, spotted knapweed, predation, biological control

Citation

Pearson, D. E. 1999. Deer mouse predation on the biological control agent, Urophora spp., introduced to control spotted knapweed. Northwestern Naturalist. 80(1): 26-29.