EVOLUTION OF BEHAVIORAL RESISTANCE IN GERMAN COCKROACHES (DICTYOPTERA, BLATTELLIDAE) SELECTED WITH A TOXIC BAIT

Two strains of German cockroaches, Blattella germanica (L.), with low- level chlorpyrifos resistance were given a choice between a chlorpyrif os bait and an alternate food source. Survivors were mated, their prog eny tested, and the procedure repeated for 5 generations on 1 strain a nd 7 on the other, Selection caused mortality to drop from 50 to 9.2% in I strain and from 38 to 6.% ill the-other. Percentage bait consumpt ion (amount of bait consumed divided by total food consumption) was >5 0% of that in the parent strains. Physiological resistance tended to i ncrease slightly in I strain but to decrease in the other. Increased a voidance was the major cause of the drop in mortality.