RIPPLE COMMUNICATION IN AQUATIC AND SEMIAQUATIC INSECTS

Among insects, ripple communication has been described in water stride rs (Gerridae) and giant water bugs (Belostomatidae), although it also seems likely to occur in whirligig beetles (Gyrinidae). In water strid ers, signals are usually produced by vertical oscillations of the legs which remain in contact with the water. Giant water bugs make ripple signals with vertical oscillations of their entire bodies. Various sig nals described to date are sinusoidal wave trains varying in frequency from 2-3 Hz up to around 100 Hz, with most signals being in the 20-50 Hz range. Lower-frequency signals have been observed to communicate o ver distances of at least 60 cm. Signals vary in duration from 0.2 sec ond pulses to several seconds, and different signals may intergrade ov er several seconds from one signal type to another. One species of wat er strider, Aquarius remigis, appears to be able to sense ripple ampli tudes of only 0.002 mu m, and another species, Rhagadotarsus anomalus, can distinguish a frequency difference in signals of 1.5 Hz or less. In water striders as a whole, ripple signals occur in the contexts of calling and courtship (precopulation), copulation, postcopulation, sex discrimination, mate-guarding, induction of oviposition, individual s pacing, territoriality, and food defense. In various species, experime ntal playbacks of signals have demonstrated functions of attraction of females by males, induction of oviposition, sex discrimination, mate- guarding, enhancement of female foraging, nonterritorial individual sp acing, and intra- and interspecific territoriality. In giant water bug s, ripple signals occur in the contexts of male courtship and aggressi ve displays and may be involved in induction of oviposition. Ripple si gnal playbacks have demonstrated that males which signal longer obtain more copulations than males which signal more briefly. Ripple signals could have evolved through ritualization from virtually any body moti ons. For example, in belostomatids, male ripple signals may have evolv ed from the aeration motions of males incubating eggs on their backs.