Effects of resources, environmental conditions, and conspecifics on harborage site selection and movement in the...

German cockroaches (Blattella germanica L.) remain one of the most challenging indoor pests to manage. Most common management tactics rely on cockroaches contacting/interacting with treatments. As such, it is critical to understand what factors drive aggregation and movement decisions, such that treatments can be optimally placed to result in maximal efficacy. In this study, we explored the effects of multiple harborage factors (width, materials, heat, resource distance) on initial site selection. Further, we explored how environmental modifications and infestation density impact harborage site switching. When evaluating initial harborage site preference, adult male German cockroaches preferred to harbor in 3 and 5 mm widths and at temperatures between 31-40°C. In horizontal harborages (parallel to the floor), cockroaches were willing to harbor within all materials tested (cardboard, wood, metal, plastic) and no strong preferences could be detected; however, within vertical harborages, they showed significant preferences for cardboard and wood over metal and plastic. Furthermore, cockroaches rapidly found and harbored near resources regardless of the resource-harborage distance. When evaluating the effects of environmental modifications on site switching, eliminating original resources and providing new ones resulted in the greatest movement shifts. In addition, as they became crowded (more cockroaches per harborage area), they became more likely to switch to new harborage sites. Adult male German cockroaches display clear patterns of harborage site preference and predictable patterns of movement based on habitat modification. These results highlight how environmental modifications, like sanitation, can increase movement between harborages, likely leading to increased contact with traps and treatments.