130 of selection pressure on the short-lived stages to have a single adult instar. An alternative suggestion is that an adult molt became necessary to complete elongation of the caudal filaments and adult forelegs (Maiorana, 1979). In populations of subtropical and tropical mayflies emergence tends to occur over a considerable length of time, whereas in species from cooler climates it is often highly synchronized, leading to the production of enormous swarms for short periods of the year. On a day-to-day basis, however, emergence may show distinct rhythmicity or require environmental cues such as a minimum water temperature or full moon for its initiation.

Phylogeny and Classification

Although the basic groups within the Ephemeroptera have been recognized since the work of Eaton (1883-1888, cited in Edmunds, 1962), differences of opinion continue to exist with regard to the taxonomic rank that should be assigned these groups, and the relationships among the groups. The primary obstacle to determining these relationships is the high degree of parallel evolution that has occurred among members of different groups. In many insect groups this problem can be overcome usually by comparing a number of different characters from all stages of the life history (Edmunds, 1972). Unfortunately, many mayflies are known only from the juvenile or the adult form.

The scheme used here is based on McCafferty (1991), Wang and McCafferty (1995), Bae and McCafferty (1995), and McCafferty (personal communication). It proposes that the order be arranged in 23 families shared among four suborders. A proposed phylogeny of these groups is depicted in Figure 6.2. According to McCafferty and Edmunds (1979), the ancestor of modern mayflies may have resembled members of the extant family Siphlonuridae

FIGURE 6.2. Proposed phylogenetic relationships within the Ephemeroptera.

that show a large number of primitive features; that is, they have evolved relatively little 131

compared to other mayfly groups. From this siphlonuridlike ancestor, two major lines

Beekeeping for Beginners

Beekeeping for Beginners

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