. The Canadian field-naturalist. 1989 Young and Owen: Foraging of Bumble Bee Workers 343 uniformly distributed. The total number of plants (racemes) in each of the three study plots was 2011, 2220 and 3024, representing a density of , and per m2, respectively. Each raceme had from six to ten flowers in bloom. Nectar production Sugar concentration in nectar varied from 22% to 95% sucrose equivalents during the study period. Fluctuations over this range occurred on a diel basis on some occasions. Figure 1 shows nectar production in relation to ambient humidity and temperature on
. The Canadian field-naturalist. 1989 Young and Owen: Foraging of Bumble Bee Workers 343 uniformly distributed. The total number of plants (racemes) in each of the three study plots was 2011, 2220 and 3024, representing a density of , and per m2, respectively. Each raceme had from six to ten flowers in bloom. Nectar production Sugar concentration in nectar varied from 22% to 95% sucrose equivalents during the study period. Fluctuations over this range occurred on a diel basis on some occasions. Figure 1 shows nectar production in relation to ambient humidity and temperature on 19 July. Sugar concentration increased during the day as humidity decreased; a similar though less pronounced trend was also apparent for volume and total sugar. Both showed considerable fluctuation, no doubt reflecting intrinsic variation between flowers as well as measurement error. The amount of sugar per flower did not show any overall trend during the study period (Table 1) and, given a high density of plants, resources were apparently abundant. The correlations between environmental variables and nectar production for the data pooled over all study days are given in Table 2. Both sugar concentration in nectar and total sugar/flower are influenced by humidity and temperature. We can postulate a causal pathway connecting temperature, humidity and sugar concentration; humidity is inversely related to temperature, and in turn sugar concentration is inversely related to humidity, thus leading to a positive correlation between temperature and concentration (Table 2). Bombus species composition Workers of seven Bombus species {occidentalis, bifarius, flavifrons, frigidus, melanopygus, mixtus, sylvicola) occurred in the meadow during the study period. The last three accounted for more than 80% of the total abundance (Table 3). Workers of B. melanopygus and B. sylvicola are of similar size (see below) and can be distinguished only by the amount of yellow pile on the scutum anteri
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Keywords: ., bookauthorottawafi, bookcentury1900, bookdecade1910, bookyear1919
