Seasonal Activity

Although many cockroach species live in relatively stable environments like tropical caves and lowland rainforests, others contend with the annual rhythmicity of seasonal climates. These include the warm-cold cycles of temperate zones and high mountains, and the alteration of wet and dry seasons in various tropical habitats. Cockroaches cope with environmental extremes and fluctuating availability of food in these environs by using varying combinations of movement, habitat choice, physiological mechanisms, and lifecycle strategies. Cockroaches may track food sources, such as those species that move into the canopy or beneath particular trees coincident with new leaf production or the appearance of spent flowers or rotten fruit. In Puerto Rico, for example, branch bagging indicated that cockroaches were more abundant on Manilkara spp. during the wet season, but on Sloanea berteriana during the dry season (Schowalter and Ganio, 2003). Cockroaches in seasonal environments may move into more benign microhabitats during harsh climatic conditions, like burrowing into deeper soil horizons or litter piles. In summer when their open woodlands habitat is excessively dry, Ischnoptera deropeltiformis can be found clustered in the damp area beneath recumbent portions of sedge-like grass clumps in creek beds (Law-son, 1967). Logs lying on the soil surface also serve as refugia for forest-dwelling cockroaches during dry periods (Lloyd, 1963; Horn and Hanula, 2002). Because of surface contact with the soil and the concomitant higher level of fungal invasion, recumbent logs maintain a higher moisture content than standing wood or the top layers of the forest floor (van Lear, 1996). Log refugia may be particularly important in deciduous forests, where 5070% of incident radiation penetrates to the forest floor when trees are in their leafless state, as compared to less than 10% when leaves are fully expanded (Archibold, 1995). Likewise, the spaces beneath stones and logs as well as similarly buffered microhabitats may be seasonally occupied. In the high alpine zone of New Zealand, individuals of Cel. quinquemaculata burrow deep among buried rock fragments in winter, but in summer are found under surface rocks (Sinclair et al., 2001). In the United Kingdom and most of Western Europe, Blatta orientalis can survive normal winters outdoors provided it can avoid short-term extremes of temperature by choosing suitable harborage such as sewers, culverts, and loose soil (le Patourel, 1993). Roth (1995b) noted that cavernicolous Nocticola brooksi leave the more open caves of western Australia as these lose moisture during the dry season.

Using light trap collections in Panama, Wolda and Fisk (1981) demonstrated that cockroaches may show cyclic activity even in habitats lacking obvious climatic cycles. In both a seasonal and an aseasonal site, adults were most common between April and July, corresponding to the rainy season in the seasonal site. In follow-up experiments, Wolda and Wright (1992) regularly watered two plots throughout the dry season on Barro Colorado Island in Panama for 3 yr, with two unwatered plots as controls. Windowpane traps were used to monitor cockroaches and other insects. Forty-six cockroach species were captured, with tremendous variation in numbers between years. Seasonal variation was also common but could not be attributed to the experimental treatment. The author concluded that rainfall was not the proximate cause of cockroach seasonal activity. Staggered seasonal peaks suggested strong interactions among some congeneric species (Fig. 3.5) (Wolda and Fisk, 1981).

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