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Variation in Life-History Pattern in Relation to Worker Mortality in the Bumble-Bee, Bombus lucorum

C. B. Muller and P. Schmid-Hempel
Functional Ecology
Vol. 6, No. 1 (1992), pp. 48-56
DOI: 10.2307/2389770
Stable URL: http://www.jstor.org/stable/2389770
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Variation in Life-History Pattern in Relation to Worker Mortality in the Bumble-Bee, Bombus lucorum
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Abstract

We experimentally varied worker mortality in laboratory colonies of Bombus lucorum to test for the effect of mortality occurring either early or late during the colony cycle on further development and eventual reproductive performance. Ten per cent of the workers were removed each day during 2 weeks immediately after eclosion of the second brood in `early-stressed' colonies. The same percentage was removed for 2 weeks but 15 days after eclosion of the second brood in `late-stressed' colonies. Such variation with respect to colony cycle could result from parasitization of worker bees by endoparasitic larvae of conopid flies (Diptera: Conopidae) at different times of the season. Neither early- nor late-stressed colonies compensated by producing more and/or smaller workers as compared to the controls in which no workers were removed. But stressed colonies invested on average less into male production in terms of biomass and numbers; no differences existed for gynes. Total biomass put into sexuals differed with group and sex ratios were highly skewed towards males. Body sizes of gynes, on the other hand, were somewhat smaller in stressed colonies than those produced by the control colonies. Start of reproduction, i.e. emergence of first sexuals in days after colony initiation and number of workers present at maturity, did not vary among treatments. We conclude that at least for the present experiment, environmental perturbation increasing worker mortality rate affects male numbers while in gynes body sizes decrease. Early stress had more effect on males, late stress more on production of gynes.

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