Studies on the Anatomy of the Sugarcane Moth Borers
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STUDIES ON THE ANATOMY OF THE SUGARCANE MOTH BORERS V. ComparativeAnatomy of the Adult Thorax BY V. D. PURl, M.Sc. (HoNS.), F.R.E.S. (Sugarcane Research Institute, Pusa, Bihar) Received October 22, 1957 (Communicated by Shri K. L. Khanna, F.A.SC.) CONTENTS PAGE ° INTRODUCTION ...... • O .... 65 2. MATERIAL AND METHODS .. • O .... 66 3. DESCRIPTION OF DIFFERENT PARTSm (i) Cervix ...... 67 (ii) Thorax: (a) Prothorax .... • • .... 67 (b) Mesothorax .. • • .... 68 (c) Metathorax .. • • .... 7t , LEGS .... .... 73 5. DIAGNOSTIC CHARACTERS ..... 76 6. SUMMARY AND CONCLUSIONS .... 76 7. ACKNOWLEDGMENTS .. .... 76 8. REFERENCES .... ..... 76 9. EXPLANATION OF PLATES .. .... 77 1. INTRODUCTION ALTHOUGH the anatomy of the different sugarcane moth borers of India has been a subject of study for quite a few workers in the past, no serious attempt appears to have been made to elucidate on a comparative basis the complete anatomy of these insects in detail. In particular, the thorax of these insects has received very little attention and no absolute descriptions of the same are available. Gupta (1940) studied and described the anatomy of four different species of striped moth borers of sugarcane found in North ~l 65 66 V.D. Pure Bihar and WesternUttar Pradesh, viz., Chilotma infuscatellus, C. auricilia, Pro- ceras indicus Kapur and Chilo zonellus but his descriptions pertaining to the thorax of these insects are too brief. He has recorded only three species out of seven recorded in the State of Bihar as serious pests of sugarcane. Kapur (1950) dealt with the revision of taxonomy of different crambinid moths of sugarcane but did not describe the detailed anatomy of their tho- raX. Imms (1951) is of the opinion that the imagines of Lepidoptera exhibit a remarkable constancy as regards their fundamental structure in the order. This appears to be true of the insects under study but for the few useful and interesting differences being presented below which have not been noticed and described before. Cheema (1951) reproduced a very brief description of the adult moth of Emmalocera depressella with little differences of colour, etc.; already described by Hampson (1896). Krishnamurti and Usman (1952) gave a brief description of the anatomy of thorax in case of Sesamia inferens without any illustration of the parts thereof. Purl (1957) worked out in detail the external anatomy of Chilo tumidicostalis, a stem borer of sugarcane in Bihar. The object of the present contribution is to discuss the comparative anatomy of the thorax of eight different species of sugarcane moth borers, viz., Scirpophaga nivella, Chilo tumidicostalis, C. zonellus, Chilotrtea infus- catellus, C. auricilia, Bissetia steniellus, Sesamia inferens and Emmalocera depressella and to provide a basis for further studies needed to bridge existing gaps in the knowledge of anatomy of thorax in these insects. Important in this connection may be mentioned the study of characters that might be helpful in the identification of different species as also in tracing out their phylogenetic relationships with one another. 2. MATERIALAND METHODS The moths of seven different species, viz., Scirpophaga nivella, Chilo tumidicostalis, C. zonellus, Chilotram infuscatellus, C. auricilia, Sesamia inferens and Emmalocera depressella were reared in the laboratory at Pusa. Those of Bissetia steniellus were supplied by the Cane Commissioner and the Entomologist to Punjab Government and also by the Sugarcane Entomolo- gist, Sh ahjahanpur. The study of the thorax was carried on after soaking the specimens in 1070 KOH solution, for about 24 hours, washing under a current of water for about 8 hours, dehydrating, staining with eosin in 9070 alcohol, clearing in carbo-turpentine, turpentine, cedar wood oil and finally mounting them in canada balsam as suggested by Puri (1954). It has been observed that the complete internal tissues could not be squeezed out completely in order Studies on the Anatomy of the Sugarcane Moth Borers--V 67 to make the specimens clear and transparent in case of Bissetia steniellus as the specimens were old and completely dried up. The photographs repro- duced in the present paper are direct microphotographs from the permanent slides of various structures. 3. DESCRIPTION OF DIFFERENT PARTS (i) Cervix The intersegmental region which is almost entirely membranous forms the neck or the cervix. The two sclerotized lateral cervical sclerites, in the form of V (laterally placed), are quite prominent. Each lateral cervical sclerite (Plate VIII, Fig. 1-9) appears to be composed of two pieces or arms arranged in such a way so as to form a V-shaped lateral cervical sclerite. The two arms of each sclerite are hinged together externally at a point that forms the apex of the letter V which articulates with the anterior margin of the prothoracic episternum and is prolonged beyond the point of articulation as a short thick free stem. The distal ends of the anterior or dorsal ends of each sclerite are produced into peg-like projections to fit into the concavities of the occipital condyles of their respective sides, thus affording an articulation between the head and the neck at the points on which the former can move freely. The posterior or the ventral arms of these sclerites articulate with the prothoracic episternum laterally and appear to be united by a narrow bridge. (ii) Thorax The general structure of the thorax of all the eight species of these moths is almost of similar type but for the minor differences in the shape and form of the convergent ridges in the metathorax, the presence or the absence of the median carina in the mesoscutum. These are the only characters which can be said to be useful in the proper identification of these species so far the thorax is concerned. The convergent ridges are comparatively well developed in the Pyralidce than in the Noctuidce. This is probably due to the fact that the formers are swift fliers. The observation that the length of the convergent sutures is more in the swift fliers in the order Lepidoptera needs further investigations before it can be established as a fact. (a) Prothorax.--The prothorax (Plate VIII, Figs. 4 and 5; Plate IX, Fig. 11)may be composed of three pronotal plates which are arranged in such a way that mesally these give rise to a Y-shaped structure in between the two lateral lobes formed by these plates and their lateral outgrowths or the patagia. The free stem or the posterior elongation of the letter Y is produced into a vertical peg-like projection articulating posteriorly with 68 V.D. Ptmi a concavity on the mesothoracic pre-scutum and appears to be partially fused with the episternal sclerites. The pronotal plates are comparatively much reduced and fused together in Sesamia inferens. The patagia in all these species are somewhat similar structures but for little differences in their length and breadth in these species. There are no larger lobes referred to as parapatagia by Madden (1944) behind the patagia in these insects. The ventral margins of the pronotum are fused with the episternum which is somewhat a convex sclerite. A distinct pleural suture is quite obvious and forms a prominent pleural ridge which in turn gives rise to a long slender pleural arm. The two pleural arms of both the sides join the sternal furca near the sternal pits (Plate VIII, Fig. 3). The anterior portion of the sternum is fused with the episternum by a faint and narrow pre-coxale and the post- coxales attain their separate entity and connect the epimeron with the sternum, behind the coxal cavity on both the sides. The presternum is also well developed and runs horizontally as an inter- nal apodeme. It is partially fused with the episternum and also connected with the basisternum and sternellum by the so-called strap-like spinasternum. At its sides it also receives the post-coxale and the inturned ventral edge of the trochantin. The edges of a deep median fold of the transverse internal ridge or the sternacosta represent the reduced basisternum. It is separated from the sternellum by a well-marked sternacostal suture which extends right up to the sternal pits in the form of a broad U. The spinasternum is represented by a vertical median strap-like process which forks into two lateral arms posteriorly which almost touch the anterior margin of the mesothoracic basisternum. The troehantin is a large plate bounded by the pleural arms, its own in- turned ventral edge and the post-coxale. (b) Mesothorax.--The largest and the most prominent of the three segments of the thorax in these insects is the mesothorax (Plate IX, Figs. 1-11). The pre-scutum lies anterior to the scutum, directed ventrad and is almost invisible from the dorsal aspect. A narrow bowl-shaped cavity occurs near its anterior margin almost in the centre. Laterally its margins are produced into two lateral prealares which form the prealare bridge. The pre-scutal ridge formed by the pre-scutal suture sets off the pre-scutum from the scutum. Studies on the Anatomy of the Sugarcane Moth Borers--V 69 The scutum (Plate IX, Figs. 1-11) as usual is very prominent, being the largest of the thoracic tergites in all these species. Its anterior margin is cleft and the lateral margins caudad to the prealares, providing for the in- cision of the notal sub-tegular wing processes or arms. A little beyond this point, each lateral margin is produced or flattened into a suralare which serves as an anterior pivotal point for the wings. The median suture which forms the median earina is well developed in Scirpophaga nivella, Chilotrtea infuscatellus and Emmalocera depressella while in other species it is either very feebly developed or completely obliterated as is the case in Sesamia inferens (Plate IX, Fig.