Psyche 
[March 
at Davis, Yolo County, since 1871. For both only the 1975/76 and 
76/77 water years stand as consecutive severe doughts. At both 
stations 1930/31 and 32/33 were dry, separated by an average year, 
and at Davis 1917/18 and 1919/20 were dry, separated by a wet 
year. Is the long-run rainfall variance in central California adequate 
to select for a carryover response, or is it a preadaptive property of 
Pierids generally? Data on populations from other climates are 
needed. 
It is dangerous to argue that because an aspect of the biology of 
an animal is adaptive in a particular situation, it evolved as a 
response to that situation in evolutionary time. In the case of P. n. 
microstriata at Gates it is not clear that a tenfold reduction in host 
biomass would have adversely affected fitness, had the insect 
attempted to reproduce. (Compare Murdoch, 1966 for a Carabid 
beetle case.) We simply do not know if intra- or interspecific compe¬ 
tition for food would have occurred. Because P. n. microstriata is 
usually out of phase with Dentaria at Gates, it uses that plant 
mainly at the beginning of the flight and in early years, and most of 
its eggs are placed on the phenologically better-matched Barharea, 
even though Dentaria is more abundant. Its eggs are strongly conta¬ 
giously distributed, and it does not. assess egg load on individual 
hosts, so that single plants sited such that females find them easily 
may receive overloads of eggs. It can thus be argued that with fewer 
and smaller plants intraspecific competition would have been 
aggravated—but we do not know if oviposition behavior might have 
been modified. P. n. microstriata is also positively associated with 
A. sara on individual hosts. This butterfly seems to assess its own 
egg load but not that of P. n. microstriata. The Pieris is a leaf-, the 
Anthocaris a silique-feeder. In 1977 there was no conspicuous 
reduction in numbers of A. sara adults or eggs at Gates, even though 
it is able to carry over (indeed, most captive pupae do);'its 1978 
performance was outstanding. A major reduction in host biomass, 
then, failed to adversely affect it, perhaps because it distributes eggs 
more evenly. 
We do not know where the 1978 butterflies at Lang came from. 
Some may have been carryovers, but here the destruction of the 
1977 egg crop may have been more apparent than real. Many hosts 
at Lang are inaccessible for censusing, and precisely these—on 
steep, wooded slopes- may have afforded more benign microcli¬ 
mates to eggs and larvae than those at and near canyon bottoms. In 
