Spatial resolution and sensitivity of the eyes of the stingless bee, Tetragonula iridipennis

Stingless bees are important pollinators in the tropics. The tremendous variation in body size makes them an excellent group to study how miniaturization affects vision and visual behaviours. Using direct measurements and micro-CT, we reconstructed the eye structure, estimated anatomical spatial resolution and optical sensitivity of the stingless bee Tetragonula iridipennis. T. iridipennis is similar in size to the Australian stingless bee Tetragonula carbonaria and is smaller than honeybees. It has correspondingly small eyes (area = 0.56 mm(2)), few ommatidia (2451 +/- 127), large inter-facet (3.0 +/- 0.6 degrees) and acceptance angles (2.8 degrees). Theoretical estimates suggest that T. iridipennis has poorer spatial resolution (0.17 cycles degree(-1)) than honeybees, bumblebees, and T. carbonaria. Its optical sensitivity (0.08 mu m(2) sr), though higher than expected, is within the range of diurnal bees. This may provide them with greater contrast sensitivity, which is likely more relevant than the absolute sensitivity in this diurnal bee. Behaviourally determined detection thresholds for single targets using y-maze experiments were 11.5 degrees for targets that provide chromatic contrast alone and 9.1 degrees for targets providing chromatic and achromatic contrast. Further studies into microhabitat preferences and behaviour are required to understand how miniaturization influences its visual ecology.

Automated summary

Stingless bee Tetragonula iridipennis was studied to understand its eye structure, spatial resolution, and optical sensitivity. Results showed that it has lower spatial resolution but higher optical sensitivity compared to other bees. Experimental measurements indicated that it has higher contrast sensitivity.