THE EFFECT OF FLOWER OCCUPANCY ON THE 
FORAGING OF FLOWER-VISITING INSECTS* 
By V. J. Tepedino and F. D. Parker 
Bee Biology & Systematics Laboratory, Agricultural Research, 
Science & Education Admin., 
USDA 
Utah State University, UMC 53 
Logan, Utah 
Introduction 
To locate flowers, insects use a variety of visual and olfactory cues 
such as flower color, shape, movement and scent (Faegri and van 
der Pijl 1971). In addition, other insects on the flowers may also 
serve as cues that either attract or repel prospective foragers. First, 
foragers might avoid occupied inflorescences because: 1) there is a 
high probability that other flowers on the inflorescence have been 
recently exploited (Pleasants and Zimmerman 1979, Zimmerman 
1981); 2) of the potential loss of time and energy due to aggressive 
encounter with the occupant (Kikuchi 1963, Decelles and Laroca 
1979); 3) the occupant might be an enemy (e.g., thomisids, phyma- 
tids, etc.). Thus, when flowers are abundant, unoccupied inflor- 
escences may yield a greater quantity of energy and/or nutrients per 
unit effort. If so, the distribution of foragers across inflorescences 
should be regular or underdispersed, i.e., there should be more 
inflorescences with only one insect than expected on the assumption 
of a random distribution. 
Existing evidence also suggests that a second hypothesis is 
tenable. Prospective foragers may be attracted by floral occupants 
because: 1) the presence of other foragers indicates that resources 
are available on the inflorescence; 2) the occupants themselves are 
sources of pollen to some foragers (Laroca and Winston 1978, 
Thorp and Briggs 1980). If insects are attracted to occupied 
inflorescences, then their distribution across inflorescences should 
be over-dispersed. 
* Manuscript received by the editor October 20, 1981 
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