Zoological Studies

Vol. 41 No. 4, 2002

Visual Organization and Spectral Sensitivity of Larval Eyes in the Moth Trabala vishnou Lefebur (Lepidoptera: Lasiocampidae)

Jin-Tun Lin*, Pi-Chi Hwang and Li-Chu Tung

Department of Biology, National Taiwan Normal University, Taipei, Taiwan 116

Jin-Tun Lin, Pi-Chi Hwang and Li-Chu Tung (2002) The caterpillar of the moth, Trabala vishnou Lefebur, has 6 stemmata on each side of its head. The diameter of the lens of each stemma varies. However, the basic structure of a stemma is similar to an ommatidium of a compound eye. Each stemma has a corneal lens, corneagenous cells, a crystalline cone, and retinular cells. The 7 retinular cells in each stemma are organized in 2 tiers, distal and proximal. Stemmata II and V both have 4 distal and 3 proximal retinular cells, while the other stemmata have 3 distal and 4 proximal cells in each stemma. The distal rhabdom is star-shaped radially around the central axis of the stemma, and the proximal one is irregular. The proximal part of each retinular cell narrows forming an axon. The 42 axons from the ipsilateral stemmata join together to form an optic nerve which directly enters into the brain. Axons I-IV project anterodorsally to the optic neuropile of the brain, while axons V and VI project posteroventrally. From the spectral sensitivities of stemmata, it is evident that stemmata I-IV have UV, blue, and green receptors, whereas stemmata V and VI have only blue and green units without UV receptors.

Key words: Lepidoptera, Trabala vishnou Lefebur, Stemmata, Spectral sensitivity.

*Correspondence: Tel: 886-2-29326234 ext. 318. Fax: 886-2-29312904. E-mail: t43004@cc.ntnu.edu.tw