Sap or picnic beetles are pests of fruit. The picnic beetle--the most frequent pest of raspberries--is about 1/4 inch long and has four orange spots on its back. Other species of sap beetles also are found occasionally in raspberries.
As the fruit begins to ripen, the adult beetles are attracted, especially to overripe or decaying fruit. Moreover, anything damaging fruit during harvest can stimulate sap beetle attacks. Sap beetles bore into the fruit, devour a portion, and lay eggs. If disturbed, the adults fall to the ground and seek cover. These beetles also are implicated in the transmission of rot organisms. Damage to the fruit by larvae is inconsequential because it does not take place until the fruit begins decomposing and is unmarketable.
Field control is best accomplished by prevention. Remove damaged, overripe, or diseased fruit from the planting at regular intervals. Other decomposing fruit also should be removed from the area. An insecticide application 3 to 5 days before the first picking also might be necessary.