# Anatomy and Ultrastructural Details of the Compound Eyes of the Pear Psyllid, Cacopsylla chinensis (Yang et Li) (Hemiptera: Psyllidae)

## TL;DR

This study reveals the detailed structure of the compound eye in the pear psyllid, which helps understand its vision and behavior for better pest control.

## Contribution

The paper provides the first ultrastructural analysis of the compound eye in Cacopsylla chinensis.

## Key findings

- The compound eye of C. chinensis is of the apposition type with a two-tiered rhabdom structure.
- The rhabdom is formed by eight retinula cells with distinct distal and proximal regions.
- The microvilli of the rhabdom are arranged in two orthogonal directions.

## Abstract

The pear psyllid Cacopsylla chinensis (Yang et Li) is an oligophagous pest of pear trees in China, causing significant economic losses through both direct feeding and indirect sooty mold damage. In this study, we examined the detailed structure of the compound eye to evaluate its visual acuity. Using a transmission electron microscope, we found that the psyllid possesses apposition eyes, consisting of a plano-convex cornea, a crystalline cone, eight retinula cells forming a fused rhabdom, and both primary and secondary pigment cells. Interestingly, the rhabdom exhibits a distal region formed by R1–R7 and a proximal region including R1–R6 and R8. Understanding the ultrastructural morphology of compound eyes in C. chinensis is essential in understanding its visual capacity and host-seeking behavior, which will inform the development of effective pest management strategies.

The compound eye of the family Psyllidae (Hemiptera: Sternorrhyncha) remains one of the least studied among hemipteran insects. Among the approximately 4000 psyllid species worldwide, the pear psyllid Cacopsylla chinensis (Yang et Li) is a major pest of pear trees in China. The ultrastructure of the compound eye of adult C. chinensis was investigated using a transmission electron microscope (n = 12 adult). The eyes are of the apposition type, lacking a clear zone. Each ommatidium features a laminated corneal lens (about 16.9 ± 1.7 μm in diameter and 7.6 ± 1.7 μm in thickness), a eucone crystalline cone, a centrally fused rhabdom formed by eight retinula cells (R1–R8), and both primary and secondary pigment cells. The 57.0 ± 3.6 μm long rhabdom exhibits a two-tiered structure: a distal region comprising R1-R7 and a proximal region composed of R1-R6 and R8, with R7 withdrawing. Throughout this structure, the rhabdomeres of R1-R6 contribute continuously along the entire length, while R7 and R8 are restricted to the distal and proximal regions, respectively. The microvilli of the rhabdom are arranged in two orthogonal directions. Based on the similarity between the compound eye of C. chinensis and those of other diurnal hemipterans, the evolution and function of eyes are briefly discussed.