Measuring spatial displacement of Blattella germanica (Blattaria: Blattellidae) populations pressured by repellent-treated harborages

Spatial statistical analysis was used to compare and quantify the distribution of German cockroaches among harborages before and after application of a repellent solution to those encompassing at least 85% of the cumulative distribution. Trials consisted of 16 yellow laminated Plexiglas harborages (7.5 by 7.5 cm) in (1.2 by 1.2 m) arenas, and concurrent studies involving 49 harborages in a room 6 by 8 m. Results in arena and room trials were similar. In rooms under a photoperiod or continuous lighting conditions, harborages cumulatively encompassing 89-95% of the population (18 or 19 of 49 harborages) each were treated with a formulation containing 2% n-methyl neodecanamide (MNDA) repellent. All other harborages received an equal volume of water. Subsequent spatial analysis revealed a dramatic shift of 96-98% of the reintroduced cockroach populations to nonrepellent treated harborages; patterns persisted for the duration of the study (28 d (12:12) and 20 days (continuous)). Spatial analysis also was used to quantify the areas of emigration and immigration in experimental rooms resulting from the repellent; 89% of the population was redistributed into harborages occupying 16.7 m2 of the room, leaving 11% of the population in harborages within the remaining 28.5 m2. Only 2-4% of the population remained in the 16.1 m2 that originally contained 89% of the cockroach population. This approach allows researchers to quantify the impact of an intervention that changes distribution rather than survivorship. These studies indicated that this formulation clearly precluded populations from re-establishing in previously inhabited harborages under either lighting condition Implications of these spatial measuring procedures, and the repellent, to a reduced-risk integrated management strategy are discussed, including the concept of herding cockroaches toward areas strategically baited with toxicants