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[Vol. 89 
proportion of “doomed” two-year females was also significantly 
lower than for that of two-year males (Faust 1980, X 2 = 53.2, P < 
0.001; Mendon 1979, X 2 = 9.8, P < 0.005; 1980 X 2 = 30.5, P < 
0 . 001 ). 
Osmia iridis 
Trap-nests were utilized by O. iridis only in 1979 (Table 5). Of the 
83 nests recovered, 54 contained one-year forms exclusively; four 
nests contained two-year forms; and the remaining 25 nests were 
mixed. Although relatively few two-year individuals were produced 
(13.1%), the proportion of two-year females recovered was greater 
than that of one-year females (mixed nests, X 2 = 16.1, P < 0.001, 
total nests, X 2 = 9.0, P < 0.005, both sites combined). 
Unlike other Osmia species studied, the predominant transition 
category of O. iridis in mixed nests was from the two-year form 
(inner cells) to the one-year form (outer cells) 16 of 25 nests). There 
were relatively few nests with either double switches (5) or with 
transitions from one-year (inner) to two-year (outer) forms (4). 
The tabulation of “doomed” individuals in mixed nests demon- 
strated that two-year males were at greater risk than two-year 
females (X 2 = 6.0, P < 0.025). 
Expected and observed sex ratio: 
We calculated the expected equilibrium sex ratio (5/9) for each 
species on the basis of male and female live weights (Table 6) as 
described previously for O. lignaria propinqua (Torchio and Tepe- 
dino 1980). Two interesting points emerged from this analysis. First, 
for each species, the expected sex ratio was the same regardless of 
whether larval or adult weights were used. Second, the expected sex 
ratios of these three species were very similar to each other and to 
0.1 propinqua (Torchio and Tepedino 1980). Apparently the opti- 
mal size ratio between females and males is the same for many 
Osmia species that nest in similar substrates. 
When the expected and observed sex ratios were compared, con- 
sistent biases emerged: For O. montana the observed sex ratio was 
significantly biased towards females for all site-years (P < 0.005 
or less, all tests). In contrast, observed sex ratios for both O. cali- 
fornica and O. iridis were generally biased towards males (P <0.001 
or less, all but O. calif ornica Mendon 1980). In addition, there was 
