I study the behaviour of insects because they are interesting, and particularly because I’m fascinated by the efficient ways in which small-brained insects manage to tackle complex tasks that we currently need supercomputers and the energy budget of a small country to even approximate. But other researchers have a more immediate, practical reason: insects have major effects on the human economy, from pollinators like my bees, who help us out, to insect pests which cause huge losses for farmers worldwide. The more we understand about the physiology and behaviour of pests, the more likely we are to come up with clever and economical ways to beat them.

 

The moth H. vitessoides is a major pest of the important agarwood crop in China.  My colleague Chao Wen and his collaborators used a barrage of microscopy techniques – from traditional light miscroscopes to scanning and transmission electron microscopes, to make a detailed study of their compound eyes.

 

You are probably familiar with the compound eyes typical of insects: they resemble geodesic domes with numerous individual facets, called ommatidia. There are actually two main types of compound eye: apposition eyes are made up of huge numbers of cone-like ommatidia, each of which contains a cluster of light sensitive cells and each of which is isolated from its neighbours so that it only picks up light that directly strikes its own ommatidium. Superposition eyes, by contrast, have an optically clear layer between the facet lenses and the light sensitive cells, allowing each photoreceptor to receive light from several facets on the surface of the eye. Eyes of this type are adapted to gather as much light as possible and so are generally found in species that need good vision under low light conditions. Pan and colleagues demonstrate, here, that H. vitessoides have this second, superposition eye structure.

 

They also found that the eyes are fairly large for a moth of this size, with a high number of facets and an unusually large number of retinal cells to each facet. The surface of each facet is covered with densely packed, microscopic ‘corneal nipples’. These are thought to reduce reflection from the surface of the eye and are probably an adaptation to prevent predators from seeing a reflection from the eyes. The photoreceptive cells themselves have a rare twisting structure which may function to improve colour detection or may improve light sensitivity in low light conditions.

 

The overall picture is that H. vitessoides eyes appear to be adapted for high visual sensitivity in low and variable lighting conditions, suggesting that vision is particularly important for them. Armed with this knowledge, future research can look for ways in which we can disrupt their life-cycle and prevent them from causing so much damage to crops.

 

I acted as a consultant on this study, advising on analysis and presentation and co-writing the manuscript.