2 
Psyche 
[March 
nounced fluctuations during this period. One of the most dramatic, 
and one whose behavior can be rationalized at a mechanistic (proxi¬ 
mate) level, is Pieris napi microstriata Comstock. 
Seasonality of P. n. microstriata 
The Pieris napi (L.) complex, which probably includes several 
genetic species, is circumpolar in distribution and largely restricted 
to cool-temperate to subarctic climates. In California about four 
subspecies occur, only two of which are well-known biologically: P. 
n. venosa Scudder, confined to the coastal fog belt, and P. n. 
microstriata which occurs farther east in the Inner Coast Ranges 
and on the west slope of the Sierra Nevada. These populations, now 
disjunct, were probably connected in riparian forest in the Central 
Valley as recently as the mid-19th century (Shapiro, 1978). P. n. 
venosa is normally double- to partially triple-brooded, with two 
seasonal phenotypes (Shapiro, 1975, 1977) under photoperiod and 
temperature control. P. n. microstriata is normally univoltine, with 
only a spring phenotype (Shapiro, 1975, 1976a, 1977). It is capable 
of producing a summer phenotype and may have a partial second 
brood in some localities in some years. This most often occurs in 
Coast Range localities subject to occasional maritime influence, as 
around the Napa Valley. 
Populations of P. n. microstriata occur at two of the regular 
sampling stations along 1-80: Gates Canyon, an east-facing canyon 
on the east slope of the Vaca Hills (Inner Coast Range) near Vaca¬ 
ville, Solano Co. (50-600 m), and Lang Crossing of the South Yuba 
River in the mixed-conifer belt of the Sierran west slope, Nevada 
Co. (1350-1500 m). These are matched with nearby U.S. Weather 
Bureau stations of record at Vacaville and Blue Canyon Airport, 
respectively. Some aspects of the host-plant relations of the butter¬ 
flies are described in Shapiro, 1974 and 1976b. Both populations 
fluctuated during the most anomalous year (1977), but in opposite 
directions. Both were quantified by direct census of both adults and 
immatures. 
Gates Canyon 
The history of this population since 1972 is given in Table 1. The 
1972 estimate is unreliable because only one sampling day is 
involved, but all of the others are based on weekly to biweekly visits 
through the flight season. 
