Miniature brain encodes optomotor response behavior in tiny thrips

Miniaturization of insects requires a reduction and simplification of morphological and physiological systems. An extreme example is the visual system of tiny thrips that has only 120 ommatidia and a tiny brain for image processing. To investigate the significance of this reduction, our study combines measurements of optical properties of ommatidia using micro-tomography with a behavioral assay on optomotor response and numerical analyses on the movement detector. We found large interommatidial and photoreceptor acceptance angles of ∼18°. During stimulation by a rotating stripe pattern, thrips walk on circular paths to compensate for retinal slip. We estimated ∼3.5 Hz stimulus temporal frequency for maximum optomotor response and ∼41 ms time constant for the low-pass filter of the movement detector. Our study suggests that even animals with an extreme miniaturization of their sensory systems maintain optomotor behaviors and possibly neural coding strategies of visual information that are typical for larger insects.