Fifteen years of field tests were conducted in California on 1200 plots infested with the annual puncturevine (Tribulus terrestris L.) in order to examine the effect of 2 introduced weevilsMicrolarinus lareynii (Jacquelin du Val) andM. lypriformis Wollaston (Col.: Curculionidae) on puncturevine. Since 5 of the 6 series of plots marked a substantial reduction in viable seed production and puncturevine coverage it is suggested that the 2 introduced weevils curtailed the pucturevine population\s capacity to compensate in the natural situation and significantly contributed to the decline in puncturevine density.