. Bulletin. Science; Natural history; Natural history. MONARCH BUTTERFLY. Fig. 1. North American monarch butterfly winter and summer geographic ranges. Overwintering areas are primarily Hmited to coastal California between San Francisco and Los Angeles, and a small region in the Transvolcanic Mountain Range of central Mexico (striped). Small relicts of summer populations survive in southern Florida and the low deserts of Arizona in some years, but represent insignificant numbers in terms of the population biology of the monarch butterfly. Each spring the geographic range expands from the overw
. Bulletin. Science; Natural history; Natural history. MONARCH BUTTERFLY. Fig. 1. North American monarch butterfly winter and summer geographic ranges. Overwintering areas are primarily Hmited to coastal California between San Francisco and Los Angeles, and a small region in the Transvolcanic Mountain Range of central Mexico (striped). Small relicts of summer populations survive in southern Florida and the low deserts of Arizona in some years, but represent insignificant numbers in terms of the population biology of the monarch butterfly. Each spring the geographic range expands from the overwintering areas as depicted by the stippled bands. Monarch populations normally decline in the gulf states in mid summer. Range contraction occurs each fall. cremaster (Urquhart 1960, 1970). Eclosion occurs 9 to 15 days after pupation, depending upon temperature and other environmental conditions (Urquhart 1960; Petersen 1964a). Pupae are green except for a row of gold spots, whose function remains speculative (Taylor 1964; Petersen 1964a; Urquhart 1960, 1972a, b, c, d, 1973; Ackery and Vane-Wright 1984). Imago emergence from the pupa is described in detail by Urquhart (1960). Danaus plexippus in California appear to be limited to plants of the genus Asclepias plus Apocynum androsaemifolium (taxonomy of Munz and Keck 1970). Asclepias are perennial herbs, which under normal west coast conditions, annually die back to their deep-seated roots. West coast milkweeds reappear each spring (primarily from underground rootstock), first in California southern coastal regions, followed by Asclepias populations at progressively higher elevations and more northerly latitudes (Munz and Keck 1970). Monarch butterflies are sequentially abundant at these seasonal oviposition sites (Urquhart 1966). The result is a displacement of the population annually, with the population center following a geographically cyclic pattern each year (Williams 1958; Urquhart 1960; Johnson 1969; Orr 1970; Nagano et
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