Aggregations as Nurseries

Because the costs and benefits of grouping behavior vary with species, stage, sex, and environment, there is no simple answer to the question of why cockroaches aggregate. However, a persistent thread that runs through the previous sections relates to gregarious behavior in connection to benefits conferred on young nymphs. Regardless of the advantages other group members enjoy, affiliative aggregations may provide juveniles with all the necessities of early cockroach life. The benefits of aggregation behavior are often most pronounced in the young, which typically suffer the greatest mortality due to desiccation, starvation, predators, and cannibals (Eickwort, 1981). The more humid environment that surrounds an aggregate of cockroaches may be crucial for young nymphs, as their higher respiratory rate and smaller radius of action increases their dependence on local sources of moisture (Gunn, 1935). The company of conspecifics assures the rapid development of nymphs via group effects, and the presence of older developmental stages assures a supply of conspecific food and an inoculum of digestive micro-biota (Chapter 5) within the harborage (Nalepa and Bell, 1997). Away from the harborage, it is possible that trail following and local enhancement allow young cockroaches access to better food sites than they would find by searching on their own. Young nymphs may also pick up adaptive patterns of behavior by living in social groups. Cockroaches can learn, retain, and recall information; this ability is a thorn in the side of urban entomologists attempting to develop effective baits for cockroach control (Rierson, 1995).

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