Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2009
Publication Date: 4/1/2009
Citation: Clement, S.L., Smith, L.J., Prena, J., Kleene, M.D., Johnson, R.C. 2009. Non-Target Plant Use by a Weed Biocontrol Agent in Idaho: Host Expansion or Opportunistic Behavior? Biocontrol Science and Technology 19:455-461.
Interpretive Summary: Safflower is mainly grown as a spring crop for its high seed oil content, with major production ares in eastern Montana and the Sacramento Valley in California. Although safflower is not widely grown in the Palouse region of eastern Washington and northern Idaho, it might become a new crop for farmers in this region if suitable cultivars were available. An unexpected outcome of 2007 and 2008 field evaluations of safflower cultivars in northern Idaho was the colonization of experimental plants by a seed-eating weevil from Greece. This weevil was first introduced in the western U.S. in 1992 to biologically control yellow starthistle. Yellow starthistle, an invasive thistle from Europe and western Asia that infests several million hectares in the U.S., is taxonomically related to safflower. This research by a team of USDA-ARS entomologists and University crop scientists showed this weevil with the scientific name of Larinus curtus did not inflict serious feeding damage to the flowers of safflower plants. None of the pollen-feeding female weevils in safflower flowerheads developed eggs. Additionally, no eggs, larvae, or evidence of larval feeding on developing seeds were detected in dissected flowerheads. The collective results show this weevil has not expanded its host plant range from yellow starthstle to safflower, and thus is unlikely to pose a risk to safflower production as a new seed pest in the western U.S.
Technical Abstract: The weevil Larinus curtus Hochhuth (Coleoptera: Curculionidae) was first introduced into western United States from Greece for the biological control of yellow starthistle (YST), Centaurea solstitialis L. in 1992. Adults feed on YST pollen and flowers, laying eggs among flowers of YST capitula. The discovery of L. curtus adults on flowering safflower (SF), Carthamus tinctorius L., near Lewiston, Idaho in 2007 suggested this weevil might be expanding its host range to include a non-target crop species closely related to YST. Eighty-eight adults were found in yellow and yellow/orange SF flowers in 2008 near Lewiston, Idaho, and fed (‘minor feeding’) on pollen and flowers of these SF capitula. The sex ratio of 30 adults was 19':11'; however, no eggs were found in the ovarioles of these pollen-feeding females. No eggs, larvae, or evidence of larval feeding were detected in 39 tagged and dissected SF capitula, and no adults emerged from approximately 7,135 mature SF capitula. These collective results are not indicative of an expanding physiological host-range of L. curtus. However, the opportunistic feeding of adult L. curtus in northern Idaho is consistent with observations that adults fed on SF pollen and flowers in pre-release no-choice tests and that a few adults colonized SF flowers in an open-field host-specificity test in Greece in 1988.