The raspberry crown borer, Pennisetia marginata (Harris), has been observed as a serious pest of blackberries in Arkansas causing loss of vigor, loss in yield and destruction of plants. Only one insecticide formulation remains labeled for this pest, Guthion Solupak (Azinphos methyl) and it may be cancelled in the near future. An efficacy trial was conducted in October 2003 and May 2004 to compare timing and efficacy of 7 treatments: Novaluron, Azinphos methyl, Bifenthrin, Chlorpyrifos, Steinernema feltiae, S. feltiae infected M. galleria cadavers and untreated check. The treatments were applied to 5-plant plots (5 replicates). The plants were removed and the crowns dissected in June 2004 to determine differences in treatment mean numbers of larvae per crown. In the cooler northern states, the raspberry crown borer takes two years to complete its lifecycle but is expected to be only one year in the warmer southern states such as Arkansas. To test this, 10 infested blackberry plants were dissected at two week intervals from May to October, larvae were removed and measured (head capsule width, length, and weight). From May through June, the larvae found were similar in size suggesting a 1-year lifecycle.