Population Growth and Behavior of Blattella germanica (L.) (Orthoptera: Blattellidae) in Experimentally Established Shipboard Infestations

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Abstract
Groups of German cockroaches were established in known harborages (shelters) onboard an inactive ship. They were allowed to grow for ca. 3 months. Growth and movement were monitored by traps placed near infested harborages and at various locations between them. Three types of collection were made at the termination of the experiment: (1) the final (fifth) set of traps; (2) cartons that housed a major portion of the cockroaches making up the various groups; and (3) a “cleanout” collection from an insecticide treatment of the area around and including each of the infested harborages. Catch in traps immediately adjacent to spot infestations gave reasonably good indications of relative densities of cockroaches in the resident groups and the immediate vicinity. Age class distributions in these traps resembled those of within-harborage groups only in the relative frequencies of adult males and middle to late instars. Trap catch for the total shipboard population increased exponentially throughout the summer, whereas that of individual groups varied. Underlying changes in age class distribution distinguished the development of large from that of small groups. The results can be explained if small groups were limited by harborage, that group response to this limitation was dispersal of middle to late instars, and that much of the movement was from small to large groups, at least until the large groups reached the carrying capacity of nearby harborages. Trapping data are discussed with respect to factors that influence the amount of movement, skewed adult sex ratios, the significance of a preponderance of early instars, and the effects of removing water and food from a nearby harborage.

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