Key Words  
  Blattella, oxypurinol, resistance
  H. N. WREN
  A new type of bait has been developed, aimed at control of pest insects, and tested successfully on the model insect Blattella germanica (L.) - the German cockroach. The active ingredient, termed a nutritional metabolism disrupter (NMD), is a non-toxic composition of the compounds oxypurinol and xanthine, and exploits a new mode of action with very effective results. The insects are not killed by an immediate toxic reaction, but die when their reserves of uric acid are not restored after mating, egg-case development, or moulting. The composition acts by inhibiting the enzyme xanthine oxidase while simultaneously increasing its substrate. This causes a block in the purine metabolic pathway which, in cockroaches, is the synthetic pathway for uric acid. This latter compound is normally stored in the cockroach fat body cells, and is used as a resource during periods of high nitrogen demand. Whole-body uric acid levels in dead, treated insects were measured by spectrophotometric assay and were found to be extremely low, confirming this as the mechanism of action. Laboratory colonies treated with NMD declined to total extinction within four to six weeks. About six days of feeding proved sufficient to ensure population control, and the test insects made no distinction between treated and untreated diets when given a choice. In further tests, both insecticide-resistant and susceptible cockroach strains were equally affected, indicating that there is no cross-resistance from other mechanisms Nymphs also died when they were fed feces from treated colonies, which implies good residual effects. The bait's inert matrix was carefully designed to enhance the effects of the active ingredient, as well as to attract the target pests for multiple feedings. Early field-trial results confirmed that the bait was effective against large populations of German cockroaches, and that it compared well with known toxic baits. The product, named EcologixTM, is being developed in the USA, and patented world-wide, by Dominion BioSciences Inc., Blacksburg, Virginia, USA.