An eye ultrastructure investigation of a plant pest Acyrthosiphon pisum (Harris) (Insecta: Hemiptera: Aphididae)

Abstract:

The pea aphid Acyrthosiphon pisum (Harris) possess two compound eyes on either side of the head like most other insects. The compound eyes were examined under light and electron microscope to reveal the final structural arrangement. Each eye contains approximately two hundred well separated circular functional units called ommatidia. Each ommatidium has a cornea and eucone type of cone with eight retinula cells, which give rise to a closed rhabdom. The cornea together with the cone form the dioptric apparatus of the ommatidium. The dioptric apparatus focuses the light to the rhabdom which is the light sensing organelle of the eye. There is no space between the distal part of the rhabdom and the cone. The distal rhabdom appears circular in tranverse section. Each rhabdom contains many finger-like projections called microvilli that are packed with the visual pigment opsin. The microvilli are arranged in four different compartments distally. Proximally, the microvilli are arranged in three different directions making an angle of 120° with each other. The arrangement of the cells in the eye shows that it has an apposition type of eye with closed rhabdom pattern.

Keywords::

• aphid vision
• apposition eye
• photoreceptor
• closed rhabdom
• primary pigment granule
• secondary pigment granule