Feeding preference for and impact on an invasive weed (Crepis tectorum L.) by a native, generalist insect herbivore, Melanoplus borealis (Orthoptera: Acrididae)

Authors: Fielding, Dennis; Conn, Jeffery

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2011
Publication Date: 7/1/2012
Citation: Fielding, D.J., Conn, J.S. 2012. Feeding preference for and impact on an invasive weed (Crepis tectorum L.) by a native, generalist insect herbivore, Melanoplus borealis (Orthoptera: Acrididae). Annals of the Entomological Society of America. 104(6):1303-1308.

Interpretive Summary: Invasive plant species, such as, narrowleaf hawksbeard, can outcompete and displace native flora, and provide a new food resource for insect pests. Narrowleaf hawksbeard in an invasive, exotic weed that was first collected in Alaska in 1974 and by 2004 was common in agricultural fields. Objectives of this study were to determine whether grasshoppers preferentially consume hawksbeard relative to other common plant species, and to determine the potential impact of grasshoppers on this weed. In choice tests, grasshoppers preferred hawksbeard over two native broadleaves (fireweed and dragonhead mint), and a grass species (bromegrass), but dandelion was preferred over hawksbeard. In field cages, in each of three years, grasshoppers reduced biomass of mature plants, flowers, and seedlings of hawksbeard, but not other forbs. We conclude that this weed is a readily accepted new food resource for generalist-feeding grasshoppers, and although grasshoppers could potentially limit seed production of hawksbeard, generally grasshopper densities are not high enough to have significant impact on the weed populations.

Technical Abstract: Crepis tectorum L., narrow leaf hawksbeard, was first collected in Alaska in 1974 and by 2004 was a common weed in agricultural fields. Introduction and establishment of a new plant species in a region represents a potential new resource for herbivores, as well as a new competitor for plant species already present. Objectives of this study were to determine the preference for C. tectorum, relative to other common plant species, by Melanoplus borealis, a generalist herbivore grasshopper common in Alaska, and to determine the potential impact of grasshoppers on this weed. In choice tests, M. borealis preferred C. tectorum over two native forbs, and a grass species, but dandelion, Taraxacum officinale, was preferred over C. tectorum. In field cages, in each of three years, grasshoppers reduced biomass of mature plants, flowers, and seedlings of C. tectorum, but not other forbs. We conclude that this weed is a readily accepted new food resource for generalist-feeding grasshoppers, and although grasshoppers could potentially limit seed production of C. tectorum, generally grasshopper densities are not high enough to have significant impact on the weed populations.