Abstract
Many insects have triplets of camera type eyes, called ocelli, whose function remains unclear for most species. Here, we investigate the ocelli of the bumblebee, Bombus terrestris, using reconstructed 3D data from X-ray microtomography scans combined with computational ray-tracing simulations. This method enables us, not only to predict the visual fields of the ocelli, but to explore for the first time the effect that hair has on them as well as the difference between worker female and male ocelli.We find that bumblebee ocellar fields of view are directed forward and dorsally, incorporating the horizon as well as the sky. There is substantial binocular overlap between the median and lateral ocelli, but no overlap between the two lateral ocelli. Hairs in both workers and males occlude the ocellar field of view, mostly laterally in the worker median ocellus and dorsally in the lateral ocelli. There is little to no sexual dimorphism in the ocellar visual field, suggesting that in B. terrestris they confer no advantage to mating strategies.We compare our results with published observations for the visual fields of compound eyes in the same species as well as with the ocellar vision of other bee and insect species.
Highlights
Many insects have two parallel visual systems: a pair of compound eyes that provide spatially-resolved imaging and simple camera-type eyes, known as ocelli
We investigate the ocelli of the bumblebee, Bombus terrestris, using reconstructed 3D data from X-ray micro computed-tomography scans combined with computational ray-tracing simulations
There is little to no sexual dimorphism in the ocellar visual field, suggesting that in B. terrestristhey confer no advantage to mating strategies
Summary
Many insects have two parallel visual systems: a pair of compound eyes that provide spatially-resolved imaging and simple camera-type eyes, known as ocelli. Ocellar morphology varies tremendously both within species (worker and male honeybees, for example; Ribi et al 2011) and between even closely-related species (Ribi and Zeil, 2018) These differences are likely to be driven by selection pressure caused by variation in environment, behaviour and mating strategies as well as potentially reflecting differences in function. It was assumed for a long time that ocelli were incapable of receiving focused images of the world, as the focal plane of their lenses was generally thought to lie completely behind their retinae (Mizunami, 1994). The results argued against the notion that the ocelli only received under-focused light, and implied intricate, trinocular navigational functionality that went beyond what had previously been hypothesised
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