IP Excretiony

Physiological and behavioral strategies used by cockroaches to reduce water loss: an overview

Dept. of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849-5413, USA

Cockroaches are among the oldest groups of insects and are found in a variety of habitats ranging from aquatic to desert. Cockroaches have evolved behavioral and physiological strategies to limit cuticular, respiratory, and fecal water loss in stressful environments. In addition, at least one species, Arenivaga investigata, has evolved the ability to absorb water vapor to aid total water balance. Cuticular water loss can be reduced by acclimation to low humidity environments by increased synthesis or secretion of high molecular weight epicuticular hydrocarbons, dehydration of the endocuticle, and physical layering of fat body on the basal lamina of the epidermis. Increased concentration of melanin in Blattella germanica also reduces cutaneous water loss. Cockroaches can rapidly lower their cuticular permeability in response to changes in humidity and physical stress. This hormone-mediated reduction in permeability can occur in <10 min and presumably is caused by changes in cuticle water content and ion concentration. Resting cockroaches reduce respiratory water loss by initiating discontinuous gas exchange cycles (DGC). Spiracles are closed during most of the DGC reducing respiratory water loss. However, only fully-hydrated cockroaches (such as Diploptera punctata and Periplaneta americana) in their resting posture exhibit DGC. Because of the surface area to volume relationship, and strategies that reduce the relative amount of surface area exposed to the environment will reduce cutaneous water loss. Cockroaches alter their posture by closely pressing the body against a substrate. Cockroaches are also highly aggregative and will rest next to or on other individuals resulting in a significant reduction of exposed surface area and water conservation. The relative importance of each strategy and combined strategies in reducing water loss by cockroaches will be discussed.

Index terms: Blattella germanica, Diploptera punctata, Periplaneta americana, cuticular permeability.