ИСТИНА

Miniaturization is one of the main trends of the insect evolution; as a result of this process some insects become comparable in size to protozoa. An extremely small body size has profound effect upon morphology, physiology, and biology in each minute species. The decrease in size of the insect body is associated with the transformation of all organ systems, including the sense organs, such as vision system. Compound eyes are known for their impressive evolutionary preservation which determines its value for higher taxonomy in arthropods. Information on morphology of minute compound eyes is still scarce. We investigated eye morphology in two of the smallest known insects from two orders. The families Trichogrammatidae and Ptiliidae contain the tiniest parasitoid wasps and free living coleopterans, respectively. With body size of only 200-300 microns, such insects demonstrate all the structures of the optical apparatus specific to the insect compound eyes. Nevertheless, some size-related adaptations were detected, among them one should mention the reduction of number and size of facets, extreme reduction of space in each ommatidia, a decrease in the radius of curvature of the cornea, the interlocking arrangement of the retinula cell nuclei in neighboring ommatidia, the shape of the pigment granules, an increase of the rhabdom diameter. Our study highlights the basic features of minute eyes organization as well as special adaptations or reductions. The adaptations are discussed with respect to compound eye miniaturization as well as functional consequences.