Summary1. Sound production by aquatic insects is found in four orders — Trichoptera, Odonata, Heteroptera and Coleoptera.2. Immature aquatic insects that produce sound are rare, stridulation being present in one family of Trichoptera (Hydropsychidae) and one genus and species in a relic suborder of Odonata (Anisozygoptera) ‐ Epiophlebia superstes. Hydropsychid larvae produce sound with a head/fore femur mechanism and use sound as part of aggressive behaviour for defence of feeding nets. Larval E. superstes use a hind femur/abdominal mechanism to dissuade predators.3. Sound production has been documented in adults of all families of aquatic Heteroptera except Helotrephidae. In corixids and notonectids, acoustic signals play a role in mating. Members of the genus Buenoa (Notonectidae) are unique in having two stridulatory mechanisms in the same individual. Sound production has been most intensively studied in the Corixidae. Although sounds are used in mating by all singing corixids, their use seems to be facultative in some species and obligatory in others. Recent experiments by Theiss (1982) have shown that the air stores carried by corixids are used for both sound radiation and reception.4. The adephagan beetle families Hygrobiidae, Dytiscidae and Haliplidae have all been shown to produce sound. Mechanisms of sound production have been established for haliplids and hygrobiids but have yet to be for most dytiscids. Sound production is used by beetles as part of sequences of aggressive/defensive and reproductive behaviour.5. Sound production is especially well documented in the Hydrophilidae (Polyphaga). Hydrophilids use an abdominal/elytral mechanism and sound appears to be used in the same contexts as in adephagans.6. Insects that produce sound under water must contend with the physical problems of sound transmission in a relatively dense, viscous medium with sharp boundaries. Because of potential distortion of the frequency components in a signal by reflection from the air/water interface in very shallow water, frequency is unreliable for encoding information. Aquatic insects use instead amplitude modulation and temporal patterning of signals.7. For aquatic invertebrates, sound fields are different than those in air because the extent of the near field is approximately four times greater in water. This near field, a region in which displacement waves are predominant over pressure waves, extends to a greater distance than most aquatic insects communicate over. Such displacement waves could have important but as yet unconsidered effects.8. The mass and viscosity of the water dictates that sound producing structures of aquatic insects should be heavier and more massive than those of terrestrial insects. A survey of stridulatory organs of aquatic insects reveals this to be true and reveals that the relatively fragile, membranous stridulatory organs of some terrestrial insects (especially Orthoptera) are absent.9. The elaboration of sound producing structures in aquatic insects probably occurred at the family or subfamily level and for Heteroptera, Trichoptera and Odonata evolved after the invasion of the water. Acoustic signals used reproductively would probably be more closely associated with the emergence of new taxa.10. Stridulatory structures have been derived from either structures devoted to some other function or from structures involved in the behaviour currently enhanced by sound production.

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The adhesive strength of specialized setae on the palettes of male Dytiscus alaskanus was investigated by recording the mass that palettes were able to lift. Large primary and secondary adhesive setae were removed and the adhesive strength of the palette was tested. The primary and secondary adhesive setae accounted for 59.5% of the adhesive strength of the palette. The ability of the palette to hold nearly 4 times the mass of a female may be needed to overcome the force generated by an accelerating female.

There are few studies of life history and population growth of large dytiscid beetles in North America. We sampled populations of Dytiscus alaskanus in a eutrophic lake in north central Alberta weekly in the summers of 1982 and 1983. Like many other temperate zone dytiscids, D. alaskanus has a univoltine life cycle. Dytiscus alaskanus prefers the area at the limit of emergent vegetation in the lake and is most often associated with shoreline vegetation of cattail and sedge. Populations of adult D. alaskanus are at a peak in the late spring and decline throughout the summer. Mark–recapture experiments allowed determination of total population size and monitoring of movement patterns in the lake. Data are discussed with reference to the relatively short summer with which these beetles must cope.

1. Equal numbers of the sibling species Drosophila melanogaster and D. simulans were allowed to compete in population cages. Two sets of 5 cages each-A & B-took 20 and 26 weeks respectively until D. simulans comprised less than 15% of the population for 2 successive generations. 2. At the beginning of each cage set, the fecundity of stock females of each species in the presence of con-& heterospecific females, con- and heterospecific larvae, distilled water and a water soluble extract from larvainfested media were determined. Fecundities of daughters of the last generation to be in competition were tested under the same conditions. 3. In all conditions, D. melanogaster stock females had a higher fecundity than D. simulans females at the beginning of each cage set. After competition, the fecundity of both species changes (generally increased) although that of D. simulans increased to a greater degree. 4. In test of the water-soluble extract of previously used media, females of both species showed decreased fecundity. This indicates that females can determine whether a food source has been used by larvae even when no larvae are immediately observable.