Foraging Patterns and Water Balance: Problems of Optimization for a Xerophilic Bee, Chalicodoma sicula

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Abstract
(1) The mason bee Chalicodoma sicula made sand nests at an arid and exposed site in Israel, stocking the cells with nectar and pollen from the legume Lotus creticus. Floral resources and sand for construction were collected separately, and each cell was usually completed within a day. (2) Ecological and physiological analyses of foraging patterns and nesting hehaviour showed that collecting adequate amounts of water from flowers was the most vital factor for a bee, overriding energy rewards; and that water requirement depended on ambient temperature (3) Water from the flowers was rapidly assimilated into a bee''s body, where it allowed regulation of blood concentration and control of temperature excess while foraging. Smaller bees were especially susceptible to physiological stresses, and thus made more nectar-only collecting trips. (4) Surplus water and sugar were deposited in the nest cell, and concentration of cell contents were corrected just prior to sealing by rapid nectar-only collection trips to provide a food store suitable for larval growth. (5) Bees preferred the more dilute nectar from patches of Lotus flowers; and at another site where Lotus was unavailable they foraged at a similar legume with more concentrated nectar and to supplement their diet with visits to a relatively dilute labriate nectar source. (6) The application of optimal foraging theory to bees, and especially to monolectic bees where two required sources (water and energy) cannot be selected independently, is considered in the light of these findings and of the physiological constraints are insect foraging in general.