Some fruit flies are used as agents of biological control, thereby reducing the populations of pest species. Several species of the genus "Urophora" are used as control agents against rangeland-destroying noxious weeds such as starthistles and knapweeds, but their effectiveness is questionable. "Urophora sirunaseva" produces larvae that pupate within a woody gall within the flower and disrupt seed production. "Chaetorellia acrolophi" is an effective biocontrol agent against knapweeds "Chaetorellia australis" and "Chaetorellia succinea", deposit eggs into the starthistle seedheads, where their larvae consume the seeds and flower ovaries.