J. zyxwvutsrqponm Azrst. ent zyxwvutsrqpo Soc., 1987, 26 323-330 323 zyx SEASONAL POPULATIONS IN THE LIFE CYCLE OF MYGALUPSIS MARKZ BAILEY (ORTHOPTERA: TETTIGONIIDAE)’ A. J. LYMBERY~ Department zyxwvutsrqp of zyxwvutsrq Zoology, University of Western Australia, Nedlands, W.A., 6009. Abstract Adult males of Mygalopsis marki Bailey have 2 peak singing periods per year. This results from the emergence of adults in late spring/early summer and in early autumn. Adults emerging in summer were larger than those emerging in autumn. Summer and autumn adults did not represent successive generations. Samples from natural populations and rearing times in the laboratory indicated that summer adults were derived from eggs which hatched in December of the previous year while autumn adults were derived from eggs which hatched in late September or October of the previous year. Insects which emerge as adults in summer and autumn are referred to as different seasonal populations. There is potential for gene flow between the 2 seasonal populations, but the actual extent of gene exchange is not known. Introduction Adult male tettigoniids, or bush crickets, produce species-specific calling songs, and the life history of bush cricket species is often inferred from records of calling activity. Most temperate, Northern Hemisphere species have an annual or biennial life cycle, with at most one discrete singing period each year (Isely 1941 zyx ; Walker 1964; Ragge 1965; Hartley and Warne 1972). Australian species have not been so well studied and published details of life cycles are rare. Of 13 common species around Perth, Western Australia, 1 1 have only one singing period and 2 have 2 singing periods per year (D. Gwynne, pers. comm.). For species with more than one singing period each year, Walker (1 964) pointed out that the development of immature stages must be studied to decide whether successive generations or seasonally separated populations are involved. Mygalopsis marki Bailey is endemic to the coastal plain of Western Australia. Although the calling behaviour of this bush cricket has been studied intensively (Bailey and Stephen 1978; Sandow and Bailey 1978; Thiele and Bailey 1980), little is known of its life cycle. Sandow (1980) reported 2 singing periods per year, but there are no data on the development of immature stages. The taxonomic status of M. marki is uncertain. Dadour and Johnson (1983) found that northern and southern populations are fixed for alternative alleles at one enzyme locus, differ in allele frequencies at another locus and differ in mean number of teeth on the stridulatory file of adult males. In an area of overlap between northern and southern populations the 2 unlinked enzyme loci are in linkage disequilibrium, indicating substantial isolation of northern and southern gene pools. However, taxonomic decisions were suspended pending further studies on morphometric and song characters (I. R. Dadour, pers. comm.). As part of another study (Lymbery 1984), I collected data on the seasonal occurrence of all developmental stages, and on the rate of development of eggs and nymphs, from localities throughout the range of M. marki. This paper presents evidence for the occurrence of seasonally separated populations at both northern and southern localities. Materials and methods Field samples The range of M. marki extends for approximately 500 km along the southwest coast of Western Australia, from near Dongara southwards to Cape Naturalisle. At least every second month from the summer of 1979180 to the autumn of 1982, adults and nymphs were collected from 3 localities; Nicholson Road (32”05’15”S, 1 15”54’45”E), Lake Richmond (32-17’30”S, zyxwv 1 15”43’00”E) and Quindalup Siding (33”37’30”S, 11 5’10’15”E). Dadour and Johnson (1983) found that adult males from Nicholson Road had Communicated by W. J. Bailey Present address: Division zyxwvuts of Veterinary Biology, School of Veterinary Studies, Murdoch University, Murrloch, W.A. 6150