Comparative study of spiracular structure in some selected Blattidae (Dictyoptera)
The differences in structure and function of tracheal system of different species of cockroaches may give some clue to the differences in the action of different insecticides in gaseous and powder form. Hence the present study on the comparative structure of spiracles and their function was undertaken in Blattella germanica (L), Periplaneta americana (L), Blatta orientalis (Stoll) and Supella longipalpa (Serv.) belonging to family Blattidae of Order Dictyoptera. All the cockroach species studied possess 10 pairs of spiracles which is a full complement in the present day insects. The average spiracular aperture areas (mm2) of 1st thoracic spiracle in the four cockroach species studied was 0.5, 0.28, 0.14 and 0.1 in Periplaneta americana (pa), Blatta orientalis (bo), Supella longipalpa (sl) and Blattella germanica (bg), respectively. The second thoracic spiracle measured 0.2, 0.08, 0.045 and 0.049 mm2 in size in pa, bo, sl and bg, respectively. The first abdominal spiracle measured 0.08, 0.049, 0.03 and 0.019 mm2 in size in pa, bo, sl and bg, respectively. Whereas average spiracular aperture areas (mm2) of last abdominal spiracle was found to be 0.0295, 0.0275, 0.0053 and 0.0058 mm2 in pa, bo, sl and bg, respectively. In the present study both the lids of the 1st thoracic spiracle are equally developed in Blattella germanica (L), whereas the immovable lid gets reduced in Periplaneta americana (L), Blatta orientalis (Stoll) and Supella lonqipalpa (Serv.). Maximum reduction is observed in immovable lid of 1st thoracic spiracle of Blatta orientalis (Stoll). In cockroach species studied, the external type of spiracular regulatory mechanism is noticed in the thoracic and internal in the abdominal ones. But the fan shaped muscle found in both the thoracic as well as abdominal spiracles, whereas parallel cylindrical muscle has been observed in the abdominal ones. The position of all the spiracles in other 3 Blattids is the same just as described in P. americana (L). The first and second thoracic spiracles show very little deviation from the basic plan as seen in P. americana. The structural differences are mainly conspicuous in the abdominal spiracles of different species.