Zebra stripes, tabanid biting flies and the aperture effect

Area of Science:

• Zoology
• Animal Behavior
• Insect Behavior

Background:

• The function of zebra stripes is debated, with biting fly avoidance being a leading hypothesis.
• The precise visual mechanisms by which stripes deter flies are not fully understood.
• Stripes may disrupt insect optic flow patterns crucial for landing.

Purpose of the Study:

• To investigate the visual mechanisms by which zebra stripes deter biting flies.
• To test the hypotheses that stripes interfere with optic flow via the aperture effect or spatio-temporal aliasing.
• To determine how different visual patterns affect tabanid fly landing behavior.

Main Methods:

• Recorded and reconstructed tabanid fly behavior around horses wearing differently patterned rugs (striped, checked, grey).
• Used realistic target stimuli to simulate natural fly-equid interactions.
• Compared fly landing frequency, flight speed, and approach distance across pattern conditions.

Main Results:

• Flies significantly avoided landing on striped and checked rugs compared to plain grey rugs.
• Flies maintained greater distances and flew faster near striped and checked patterns.
• The avoidance of checked patterns, which lack parallel lines, refutes the aperture effect hypothesis.

Conclusions:

• Zebra stripes likely deter biting flies through visual mechanisms that affect landing.
• The aperture effect is unlikely to be the primary mechanism due to the avoidance of non-parallel patterns.
• These findings narrow down the potential visual interactions driving zebra stripe evolution.