Temporal Patterns of Emergence in Aquatic Insects

Abstract

In aquatic insects, emergence (ecdysis to the adult or subimaginal stage) varies widely in temporal pattern. The comparative study of this pattern is feasible and informative in orders such as Plecoptera, Ephemeroptera, Odonata, Diptera and Trichoptera in which all members of a population pass through the water-surface when emerging. Methods by which emergence rate can be measured are discussed. Four basic temporal patterns of emergence exist. Emergence may be (1) continuous with irregular fluctuations in rate; (2) rhythmic, with a lunar period; (3) sporadic, occurring at irregular intervals of a few days; or (4) seasonal. Examples of each of these patterns are given, and reference is made to the proximate and ultimate environmental factors which may be maintaining the patterns observed. Diurnal rhythms of emergence are excluded from consideration. When emergence is restricted seasonally in temperate latitudes, the degree of its synchronization within the emergence period varies widely but is usually constant and typical for a given species. This has provided the basis for an ecological classification of British Odonata, the validity of which is examined in the light of recent research.

Population Synchrony in Mayflies: A Predator Satiation Hypothesis

“…Others have noted that mass emergence of aquatic insects along a river bank attracts large numbers of non-territorial birds (Martin, 1895 andLyon, 1915 as cited in Corbet, 1964). As Corbet (1964) points out, this is probably one of several potential drawbacks that might occur from synchronous emergence.…”

“…As Corbet (1964) points out, this is probably one of several potential drawbacks that might occur from synchronous emergence. Thus, the selective value of mass emergence may in certain situations hang in a fine balance.…”

“…For parthenogenetic mayflies, the selective disadvantage of emerging early and late would theoretically be lower relative to bisexual populations if a mating success hypothesis were valid. The possibilities that parthenogenesis could lead to a breakdown of synchronized emergence patterns was proposed initially by Corbet andTjonneland (1955) andTjonneland (1960) who reported evidence of a temporal dispersal or "decay" in the diel flight activity pattern in certain tropical parthenogenetic species of mayflies. No differences in the degree of adult synchrony for bisexual versus unisexual species were reported for time frames exceeding 24 h. Gibbs (1977), however, suggested that the unusually long (June to November) emergence period of Cloeon triangulifer McDunnough is due to its parthenogenetic mode of reproduction.…”

“…Adults of many species appear in flight in large numbers during a brief period each year and form vast mating swarms over the water surface. Both the size and periodicity of mayfly swarms have been conspicuous enough to stimulate detailed descriptions by early naturalists (see Needham et al, 1935 for review) as well as more recent speculation concerning the ecological and evolutionary significance of swarm periodicity (Corbet, 1964;Edmunds and Edmunds, 1980).. Population synchronization in aquatic insects, especially mayflies, refers to a tendency for the adult reproductive stage of individuals in a given population to be active in the environment during a short, well defined period of the year (i.e., seasonal synchronization within a time frame >24 h but usually less than 2-4 wk) and/or the day (i.e., time frame <24 hand usually about 1-2 hin duration). For our purpose here, each 24-h period represents a unit of observation and the sum of such units describes the emergence period for each species under consideration.…”

Environmental drivers influencing stonefly assemblages along a longitudinal gradient in karst lotic habitats

“…emergence (Davies, 1984). Stoneflies are one of the most important components of benthic macroinvertebrate communities in the lotic habitats which also undergo emergence (Corbet, 1964;Brittain, 1990). These hemimetabolous insects generally have very specific life cycles and flight periods with a tendency to emerge at specific time every year.…”