| dc.description | Two foreign species of weevils have been introduced into North Dakota for the biological control of musk thistle, Carduus nutans L. -Rhinocyllus conicus (Froelich), a seed feeding weevil, and Ceutorrhynchidius horridus (Panzer), an internal root and lower stem inhabiting species. R. conicus has survived for several generations and is showing some promise for thistle suppression in Walsh County, but releases of C. horridus have been unsuccessful. The pigweed flea beetle, Disonycha glabrata (Fab.), which is native in southern United States, has been introduced into experimental sugarbeet plots in the Red River Valley for testing its effects at controlling rough pigweed or redroot, Amaranthus retroflexus L. Although both larvae and adults of these beetles feed heavily on pigweed, damage to the weed occurs too late in the season for them to be effective in suppressing weed growth or seed set. An initial survey for native insects of bindweed has been conducted. Feeding by localized populations of various insects, particularly tortoise beetles, has been observed. Several foreign species of flea beetles and a stem boring beetle are anticipated for release against leafy spurge. | en |
