Zhong Du, Tianhao Zhang, Fengming Wu, Zulong Liang, Xiaokun Liu, Muinde Jacob, Weili Fan, Lei Jiang, Lijie Zhang, Siqin Ge, Guohong Wang
Callosobruchus maculatus (Fabricius, 1775) (Coleoptera: Bruchinae) is a destructive agricultural pest that is harmful to beans worldwide and an important quarantine pest in China. It was divided into two phenotypes based on polyphenism: normal and flight forms. In this study, we first compared the morphological structures of the compound eyes of the two forms. According to the results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), microcomputed tomography (micro-CT), and computer three-dimensional reconstruction, there are no differences in the structures of the compound eyes between the normal and flight forms except for the number of ommatidia. From the internal structure, the compound eyes have a biconvex cornea with open rhabdom and acone eye, crystalline cone directly connected with rhabdom, and no clear zone. It is a kind of apposition eye. Ommatidia facets range in shape from quadrilateral to hexagonal and some irregular shapes. On electroretinograms (ERGs), the normal and flight forms showed different spectral sensitivities: the normal form had the strongest response to ultraviolet light, whereas the flight form had the strongest response to white light. Behavioral assays revealed that the normal and flight forms showed completely opposite phototaxis behaviors; the flight form exhibited positive phototaxis, whereas the normal form exhibited negative phototaxis. This study not only enriches our knowledge on coleopteran compound eyes but also provides a foundation for in-depth research on the photoreceptor mechanisms of compound eyes, which may be useful in pest control management.
