FORAGING BEHAVIOR OF BEE POLLINATORS ON THE TROPICAL WEED TRIUMFETTA-SEMITRILOBA - DEPARTURE RULES FROM FLOWER PATCHES

We studied the departure rules from flower patches used by bee pollina tors of the tropical shrub weed Triumfetta semitriloba Jacq. (Tiliacea e). Flowering plants were distributed in well delimited clumps, in eac h of two pasture areas (A1 and A2) and one area of forest gap (A3), in Vicosa, southeastern Brazil. Five solitary bee species, Augochlorella michaelis, Augochloropsis cupreola, Pseudocentron paulistana, Ceratin ula sp., Melissodes sexcincta, and one social bee, Plebeia droryana, w ere observed. Three departure rules were examined: (1) ''residence tim e'' (time spent per patch); (2) ''giving-up time'' (time spent in the patch between the last successful resource encounter and departure); ( 3) ''probabilistic rule''. Three log-linear models were delineated to analyze the ''probabilistic rule'' of departure: (1) DPTLF*TPF*TTP; ( 2) DPTLF*TPF*ALF; (3) DP*TLF*TPF*NFV, where DP is departure from the patch; TLF is time spent in the last visited flower; TPF is time spent in penultimate visited flower;TTP is total time spent in the current patch; ALF is activity in the last visited flower; NVF is total number of visited flowers on the current patch. Flowering plants were consid ered as flower patches. The results showed that the departure from pat ches of flowers was influenced by intrinsic factors, such as body size , energetic requirements and pollen load size, and by extrinsic factor s, such as resource availability and distribution, and density of reso urce patches. Small bodied bees, with lower energetic requirements and smaller pollen loads (Ceratinula sp. and P. droryana) or bees which o ccurred in A3, the area with fewer flowers per patch and lower density of flower patches (Ceratinula sp. and A. michaelis), used a ''residen ce time'' departure rule. Species with larger body size or which occur red on areas of higher density of newer patches and with more flowers per patch, A1 and A2 (II paulistana, M. sexcincta, A. cupreola), used a ''probabilistic'' role of departure.