Ultrastructural comparison of the ocelli of Sinopanorpa tincta and Bittacus planus (Mecoptera)

Abstract

On the contrary to compound eyes, dorsal ocelli are poorly investigated for their ultrastructure in many insect groups, including Mecoptera. The ocellar ultrastructure of the scorpionfly Sinopanorpa tincta (Navás) in Panorpidae and the hangingfly Bittacus planus (Cheng) in Bittacidae was examined using transmission electron microscope. Both species possess three ocelli on the vertex of their heads and each ocellus has a corneal lens, some pigment cells at the outer rim of the lens, and fused rhabdoms. Beneath the corneal lens lies a single layer of corneagenous cells, which is very thick with the nuclei located proximally in S. tincta and quite thin in B. planus. A portion of rhabdom is composed of rhabdomeres from two adjacent retinula cells in S. tincta, but from four retinula cells in B. planus. Each rhabdomere comprises parallel microvilli projecting laterally from the apposed retinula cells. In addition, abundant electron-lucent granules are present at the middle part around each retinula in B. planus. Only pigment granules exist around the retinula proximally at the nucleate level in S. tincta.

Hypothesis on monochromatic vision in scorpionflies questioned by new transcriptomic data

“…This is astonishing considering the well-developed compound eyes and ocelli in this genus and the fact that the same study found an opsin with a long- and two opsins with a short wavelength peak absorbance in the mecopteran genus Boreus 21 . While compound eye, ocellar and larval eye ultrastructure has been investigated in some depth 22 – 27 , only two studies so far dealt with opsins in scorpionflies (Mecoptera) 21 , 28 and their closest relative order 29 , the fleas (Siphonaptera) 28 .…”

Ultrastructure of the larval eye of the scorpionfly Panorpa dubia (mecoptera: Panorpidae) with implications for the evolutionary origin of holometabolous larvae

“…The holometabolous larva was thought to be early de‐embryonized, premature hatching, and essentially a free‐living embryo that is caused by a reduction in the amount of yolk stored in the egg (see Truman and Riddiford,1999). Under the control of juvenile hormones, the holometabolous larva was supposed to be derived from a pronymphal stage of hemimetabolous insects before hatching (Truman and Riddiford,1999).…”

“…The evolutionary origin of holometabolous larvae is a long‐standing and controversial issue, which has not been satisfactorily resolved to date (Strathmann,1993; Sly et al,2003). Regarded as an essentially free‐living embryo caused by a reduction in the amount of yolk stored in the egg, the holometabolous larva is thought to be evolved from a hemimetabolous pronymph (see Truman and Riddiford,1999). Recently, Williamson (2009) advocates the hypothesis that caterpillar is acquired by hybridogenesis of a primitive insect with an onychophoran.…”

Fine structure of the ommatidia of the short‐faced scorpionfly Panorpodes kuandianensis (Mecoptera: Panorpodidae)

“…Then they were infiltrated successively through three mixtures of acetone/Epon‐812 resin (3:1 for 2 h, 1:1 for 4 h, and 1:3 for 12 h) and pure Epon‐812 resin for 24 h twice at room temperature. The samples were embedded in pure Epon‐812 resin with nadic methyl anhydride as hardener, dodecenyl succinic anhydride as softener, and 2,4,6‐tri(dimethylaminomethyl)phenol (DMP‐30) as epoxy accelerator, and finally polymerized at the temperatures of 30°C for 24 h and 60°C for 48 h (Wei and Hua, ).…”