Studies on thysanoptera

The present piece of work deals with the externa morphology of two species of thrips, Aptinothrips rufus and Limothrips cerealium; and the internal anatomy of some of the species representing the two suborders of Thysanopter, Aptinothrips rufus Gmelin, is the common grass inhabiting species and occurs either singly or mixed up with its variety stylifera Trybom. These two varieties are chiefly distinguished by the number of antennal joints. Females are found throughout the year. Males are very rare and only few A4rufus males were collected. No stylifera males were found by me. The larvae also occur on grass and are common. pre_pupae and pupae are found with great difficulty. No male larval, pre-pupal or pupal stages ever came to notice. The other species, Limothrips cerealium Haliday, is the well known corn thrips, which has been believed to cause sterility in oats and wheat. It is found during spring and summer on grasses, wheat and oat plants. The eggs are laid in slits made in leaves and the larvae after hatching go inside the leaf-sheaths or ears of corn. Almost all the stages are found simultaneously on wheat and oat plants in summer. A review of the previous literature shows that except a short description of adult stages, the young forms of A. rufus, and L. cerealium have never been completely described. The female pre-pupae of A. rufus and the male pre-pupae and pupae of Limothrips cerealium are described here for the first time. The collection of Aptinothrips rufus revealed the presence of certain unusual antennal deformities, which are also described here in detail. The mouthparts of L. cerealium were studied, and are described here, establishing the homology as far as possible. A short note on the embryology of L. cerealium is also included. The internal anatomy of Thysanoptera has been very little studied. This is partly due to the minute size of insects. Most of what is known is due to the pioneer work of Jordan (1888), Uzel (1895) and Buffa (1898). In 1915, Peterson made a study of the salivary glands and head-glands in H. femoralis and Cepha.lothrips quccae. In 1926, Klocke published a paper on the anatomy and histology of Thysanoptera. But his work does not present a connected view of the different internal parts. Ten common species were taken for dissection purposes which are :- AEOLOTHRIPIDAE :_ 1. Melanthrips fuscus(Sulzer). THRIPIDA.E :_/ THRIPIDAE : 1. Aptinothrips rufus (Gmelin); 2. Odonto_ thrips ulicis (Haliday); 3, Limothrips cerealïum (Halidayl; 4, Heliothrips haemor.. rhoidalis (Souché); 5. Taeniothrips vulgat.. issimus(Haliday); 6, Taeniothrips atratus Haliday; 7, Thrips tabaci (Lindemann 8. Kakothrips robustus (Uzel) PHLOEOTHRIPIDAE: 1, Haplothrips distinguendus (Uel). The digestive system presents some peculiarities and in order to homologies the parts in the three families of thrips, with the typical digestive system of other insects, certain new nomenclature has been introduced where considered necessary, So far only four rectal glands were known to occur in thrips and I also found usually four in most species; but in Melanthrip fuscus, five rectal glands were found for the first time in Thysanoptera. The salivary glands also show difference of form and attachment, and in the course of anterior ducts, The female reproductive organs are more uniform except the difference in the form of receptaculum seminis; but the male reproductive organs show sometimes great dissimilarity. In Odonto_ thrips ulicis, a third kind of unpaired gland is found and in Taeniothrips atratus, the two testes are con_I netted by a commissure. These structures are not found in other species of thrips examined, Besides other minute details of form, and internal structures or their abnormalities are noted and described. The work was done in the Department of Agricultural Zoology, University of Edinburgh, under the super- vision of Dr 0.B. Williams. I am greatly indebted to him for suggesting this work to me and for placing at my disposal, all his collections and literature on Thysanoptera without which the present paper could not have been written. I am also grateful to Dr G.D. Morison for identifying a few species of thrips for me, and for sending me a specimen of the male of Aptinothrips rufus var stylifera.