Sense organs of the labio-maxillar complex of larvae in tenebrionid beetles: Tenebrio molitor and Zophobas rugipes (Coleoptera, Tenebrionidae)
H. Farazmand, S. Yu. Chaika, E. E. Sinitsina
Moscow State University, Moscow, Russia,
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The aim of the present research was comparison of organization of the sensory apparatus in larvae at two species of the beetles – Tenebrio molitor Linnaeus, 1758 (yellow mealworm beetle) and Zophobas rugipes Kirsch, 1866. The first species is a synanthropic species and harms to food stocks. The beetle Z. rugipes lives in natural biocenosis. The distribution, external morphology and ultrastructure of various types of sensilla on the labio-maxillar complex of tenebrionid beetles larvae T. molitor and Z. rugipes are described based on scanning and transmission electron microscopy. On the labio-maxillar complex of T. molitor and Z. rugipes are placed sensilla of 4 basic morphological types: trichoid, basiconica, styloconica, and ampullaceous.
The labial palp of T. molitor has 69 sensilla: 56 trichoid, 8 styloconic, 4 basiconic and 1 ampullaceous. All trichoid sensilla are placed on the second segment. The sensilla types of styloconica, basiconica and ampullaceous were observed on the distal apex of third segments. The length mean of styloconica and basiconica sensilla were 6,07 and 3,93 micron, respectively. The length and diameter of ampullaceous sensilla were recorded 6,10 and 5,40 micron, respectively.
On the labial palp of Z. rugipes were observed 97 sensilla: 81 basiconic, 11 styloconic and 5 trichoid. All the sensilla types of styloconica and basiconica are placed on the distal apex of third segments and all trichoid sensilla are placed on the second segment. The length of styloconica and basiconica sensilla was 5–8 micron.
The maxilla palp of T. molitor has 35 sensilla: 22 trichoid, 8 styloconic, 4 basiconic and 1 ampullaceous. Sensilla of third segments in maxilla palp are similar on sensilla of third segment in labial palp. In other words, the sensilla types of styloconica, basiconica and ampullaceous are placed on the distal apex of third segments. The length mean of styloconica and basiconica sensilla were 4,2 and 4,3 micron, respectively. The length and diameter of ampullaceous sensilla were recorded 4,3 and 2,1 micron, respectively.
On the maxilla palp of Z. rugipes were observed 110 sensilla: 91 basiconic, 14 styloconic and 5 trichoid. The most of sensilla are placed on the distal apex of third segment. The length of styloconica and basiconica sensilla was 5–7 micron.
It was shown that large basiconica sensilla, diameter up to 3,3 microns and innervated 2–7 receptor cells. The thickness of cuticle layer is equal 0,8 microns. The dendrites are surrounded scolopoid sheath (thickness = 0.05 micron), and one dendrite is completely unbound from others by a septum of scolopoid sheath. This dendrites belongs to mechanoreceptor cells. The dendrites from all receptor cells formed cilia, consisting from 9 pairs microtubules. Basiconica sensilla to a small diameter (1,5 microns) innervated to 6 receptor cells. 10 vertical canals penetrate cuticle layers by a diameter 0,4 microns. Styloconic sensillae also contain a little receptor cells. The diameter cuticle in base of sensilla is equal 2,6 microns, and in papilla 0,8 microns. On the second and third segments of maxilla palps is present 5 mechanoreceptor hair. Each mechanoreceptor hair innervated one receptor cells. The dendrite of mechanoreceptor cell contains a tubular body and terminates at the hair base.
As has shown this research at larvae of the Z. rugipes the number of sensilla on maxillary and labial palps considerably exceeds number of sensilla at T. molitor. It is connected, first of all that environment of larvae of yellow mealworm beetle is rather constant and is submitted by different products of a feed (flour, cereals, dried fruits). The inhabitation of larvae of the beetles Z. rugipes in an open nature and wider spectrum of consumed foodstuff have resulted to formation more advanced of the chemosensory apparatus.
The work was supported by Russian Foundation of Basic Research (grant N 01–04–48526).
Zoocenosis — 2003
Біорізноманіття та роль зооценозу в природних і антропогенних екосистемах: Матеріали ІІ Міжнародної наукової конференції. – Дніпропетровськ: ДНУ, 2003. – С. 182-184.