Nymph-to-adult Ratio in German Cockroach (Dictyoptera: Blattellidae) Populations After Treatment with Imidacloprid
  Key Words  
  Blattella germanica, gel bait, age structure, population dynamics, nymphs
  Rainer Sonneck, Guenther Nentwig and Volker Gutsmann
  Control of adult roaches is usually not problematic as those life cycle stages are actively exploring the habitat for food sources. Nymphs are less mobile and therefore less likely to access a bait spot directly. Natural occurring populations of German cockroach (Blattella germanica L.) show a relatively constant ratio of nymphs in the total population of 0.6, which is largely unaffected by the size of the population and interference with conventional cockroach baits. Imidacloprid cockroach gel contains a proprietary capsule technology for encapsulating specific feeding stimulants. A detailed analysis of field trial data sets led to the discovery of unique modifications of the nymph ratio in populations treated with the new bait. A reduction of the standard nymph-to-total ratio 0.6 to 0.14 indicated an improved killing of larvae. The preferential elimination of larval stages is caused by the inclusion of the capsules containing a specific blend of feeding stimulants. A predicted consequence of this modulation is a long term inability for populations to recover.