Behavioral responses of German cockroaches (Blattella germanica L.) to gel baits under varying environmental conditions

BACKGROUND: Gel baits are one of the most effective tools for managing German cockroaches (Blattella germanica L.); even so, it remains unclear how German cockroaches locate baits. To investigate bait perception by German cockroaches, we evaluated differences in trap catch after applying cockroach gel baits onto glue traps and placing these baited traps at various distances away from both harborages and arena walls in large (110 cm) diameter still-air arenas. In addition, we modified various environmental factors (access to food/water, harborage size) and evaluated the impacts of these modifications on trap catch. Mortality assays were also conducted under a similar design, with baits placed directly into arenas rather than on glue traps. RESULTS: German cockroaches were unable to detect baits placed 8 cm or farther from the harborage and arena walls, as indicated by a lack of difference in trap catch in traps with and without baits. However, trap catch increased significantly when traps were placed closer to the harborage, when German cockroaches were deprived of food and water, and when harborage size was reduced. In mortality assays, German cockroaches died at a faster rate when baits were placed near the harborages, when cockroaches were starved, and when harborage size was reduced. CONCLUSIONS: Given the addition of baits had no effect on trap catch while other environmental modifications did, cockroaches do not appear capable of locating baits when more than 8 cm away. Further, increased mortality in arenas with baits placed closer to harborages (8 cm vs. 30 cm) supports a lack of attraction over distances >8 cm. When considering current pest management practices, it is critical that cockroach bait programs focus on placing baits near harborages and foraging paths, increasing the number of bait applications points, and removing competing food and water.