Stefan Fischer

• In spite of the numerous studies on insect compound eyes within the last 100 years, astonishingly the number of investigations specifically dealing with the eyes of species of small body size is near to negligible. Moreover, conclusions by Warrant and McIntyre (1993) and Meyer-Rochow and Gál (2004), based on theoretical optical examinations, suggested that an unlimited eye size reduction was not possible; a suggestion that begged the question as to how the tiniest insects might deal with these restrictions. To demonstrate that optical and structural modifications are widespread, a detailed study of eye miniaturizations involving tiny lepidopteran and hymenopteran species and a quest to determine limiting factors seemed timely and interesting. The main goals of the present work were therefore A) to test through the description of ultrastructural and functional design features of compound eyes of different species of tiny lepidopterans, the prediction of Meyer-Rochow and Gál (2004) that the possession of a superposition type of eye was of no benefit to small eyes B) to describe possible adaptations occurring in these eye of reduced size and C) to carve out through a comparative analysis of eyes of different size, the impacting factors that set the limits for the miniaturization of compound eyes generally. The present work revealed that the conclusions reached by Meyer-Rochow and Gál (2004) based on their theoretical approach holds true and adaptations in small eyes are manifest in form of an intermediate eye type, combining features of apposition and superposition optics. The intermediate eye type is described and discussed in detail as well as the functional consequences resulting from it. Furthermore, adaptations recognizable in the investigated eyes as a consequence of miniaturization are discussed on a functional basis, as is the aspect of limiting factors operating on the smallest possible optics generally.