Introduction
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Chapter 1 INTRODUCTION The class insecta is the largest group among all Animal Kingdom. It includes 29 orders and 8, 00,000 known species of insects. The expected numbers of insect species on earth are around 50,000,000 but a majority of them have not been identified nor discovered (Angel fire, 2013). The typical insect has distinct body regions viz; head, thorax and abdomen. The head is anterior most segment that bear pair of antennae, pair of compound eyes and ocelli at frontal region and mouthparts at terminal portion. The thorax is middle region and usually three segmented viz. prothorax, mesothorax and metathorax. The abdomen is terminal region of the body, usually distinctly segmented, but number of segments greatly varies amongst different groups of insects and terminal few segments are modified into genital organs. Usually each abdominal segment bears a pair of spiracles as respiratory structure, although the number of segments that bears spiracles again varies amongst different groups (Snodgrass, 1935). Hemiptera, the word hemi means half + pteron means wings; from the character of the partly thickened and partly membranous wing or hemelytra. Hemiptera is a large order of insects which is cosmopolitan in distribution. The order was established by Linnaeus in 1735; it includes around 150 families, 1,000 genera and 48,000 species. Latreeille in 1810 divided the order hemiptera into two suborders viz Heteroptera and Homoptera. (Essig, 1942). 1 The name Heteroptera consequent from the Greek “hetero” means different and “ptera” meaning wings, having the texture of the forewing is hard and the hindwing is membranous. The term hemelytra refer to the members of the suborder heteroptera, due to distinctive forewing. Dorsally the wing crosses one over another while resting. The characteristic feature of the heteropteran insects are having elongated, piercing-sucking mouth parts which originates from the head capsule. The mandibles and maxillae are modified to form long thread like uniform structure of feeding tube also known as proboscis. It contains both food channel and salivary channel. The proboscis in general specific to suck the plant juice from the various parts and also to suck the cell sap of seed. Some species of hemiptera are predators which suck the blood of mammals, small animals and arthropods. The heteropteran insects are adapted to various habitats like aquatic, semi-aquatic and terrestrial. Aquatic heteropterans are predators of aquatic organism usually found in both fresh water as well as salt water for example Waterstrider genus Halobates (Mayer, 2009). The terrestrial heteropterans are habitual to plants. They found both on cultivated and wild plants. They cause injury to plants by feeding on its vascular tissue; they deprived the quality of seeds by feeding on its stored food material. They spread plant pathogenic diseases to different plants as well as human. The bed bug of family cimicidae is pathogenic to human, animals and birds (Mayer, 2009). Family pentatomidae (Leach, 1815) comprises stink bugs and shield bugs. The Greek meaning of “pente” meaning five and “tomos” means section. The shield bug are green to brown in colour with scutellum is half an inch long and 2 three tarsal segments. There are near about 5000 species of stinkbug, which varies from size, color and shape. They are brown, green to metallic in colour and oval, convex or broad in shape. They measures between 5-12 mm in size. The stink bugs have hemielytra with presence of scent gland at thoracic region which produce disagreeable odour to external stimulus. Chemically the substance releases from scent gland is aldehyde or in some of the species the substance is cyanide compound. They are true bugs and shows incomplete metamorphosis. The female lays about 100, barrel shaped eggs on surface of plant leaves, bark, stem, etc. The bugs hibernate during winter season and in favorable conditions the eggs hatched out into pronymphs, the developmental stages are egg, nymph and adult (Encyclopedia Britannica, 2010). These bugs are also pests of agriculture, mostly of cultivated crops like soyabean, sorghum, corn, cotton, etc. in large numbers. But some pentatomid bugs are also useful like the anchor bug which is predator of Japanese beetles, Mexican bean beetle and other insects (Encyclopedia Britannica, 2010). Genus Halys is revised by Ghauri in 1988 where he described four Asian species. H. serricollis (Westwood, 1837), H. serigerra (Westwood, 1837), H. sulcatus (Thunberg, 1783) and H. shaista (Ghauri, 1988) where H. shaista is described as new species (David Rider, 2011). Halys dentatus is distributed in North West Africa, China, Japan, India, Pakistan and Iran and commonly found on trees like Samania saman, Millingtonia 3 hortensis, Spathodea companulata, Acacia moniliformis under loose bark of trees where they suck the cell sap by inserting their stylets into plant tissue. H. dentatus is fuscous brown in coloured, the head is long with five segmented antennae, pair of compound eyes; thorax (pronotum) is broad with the scutellum forms triangular plate. The forewings modified into hemielytra and hind wings are membranous. The thorax ventrally bears three pairs of legs. The scent gland is present at metathoracic region. The abdomen is seven segmented. At each abdominal segment bears open type of spiracle. The H. dentatus undergoes incomplete metamorphosis. The life cycle stages are egg, nymph and adult. The female deposit 14-20 eggs in two batches on the surface of bark or leaves of plants. The eggs are rounded in shape with presence of micropyle projections. At the time of hatching they appear grey white in colour but after hatching the colour turn towards the brown. The bug is univoltine with obligatory diapauses in winter (Dhiman et al, 2008). The nymphs are similar to adults but sexually immature. The wings are functional at adult stage only. There are five nymphal instars. At each nymphal instar the nymph moults and cast off the old cuticle. The excretory system maintains the stable internal environment for the tissue of the body along the regulatory procedures such as removal of the nitrogenous waste products of protein metabolism and the control of electrolyte composition of the haemolymph. The malphigian tubules are the most important excretory organ of insect. They are derivatives of ectodermal proctodeaum. Malphigian tubules of H. dentatus are long highly convoluted lobulated tubule 4 arising at the junction of midgut and hindgut, and compactly arranged over posterior of abdominal cavity. The nervous system acts as a connecting link between the sense organs which react with various exterior as well as interior stimulus while the effector organs such as muscles, glands and radiating structures through which the insect give response to stimuli by showing the change in its behaviour. The nervous system of H. dentatus constitute a brain and two ventral compound ganglia located in the thoracic region. Dichlorovos (2,2-dichlorovinyl dimethyl phosphate) is an organophosphorus compound widely used against crawling and flying insects. The oral application is rapid and effective as compared to dermal and fumigation, as it is absorbed quickly through gastro-intestinal tract. (Advisory Committee on Pesticides, Food and Environment Protection Act 1985, part III). Morphometric study of Lygus hesperus (Miridae) using scanning electron microscopy by Shrestha et al. (2007) wherein discussed the advantages of SEM morphometry for identification of species. They have reported measurements of fifty different body parts. Shrestha et al. (2007) have discussed that critical point drying and use of fresh sample was critical for better imaging. In there further statement they reported that use of alcohol stored sample for SEM had problem of shrinkage so that measurement could not be done accurately. There is no significant effect of use of secondary fixative such as 2% OSO4 on morphometry, it may not be necessary. But sputter coating is needed for imaging and 15KV 5 accelerating current gives better results than higher voltage as they may damage the sample while higher magnification. Dan et al. (1980) studied anatomy of alimentary canal of pentatomid bug Brachymena quadripustulata wherein reported that oesophagus consists of long semi-transferent tube that extends from anterior of head passing through circumoesophageal connectives and posteriorly opens into ventriculus. Ventriculus divided into thin four regions, first ventriculus appears as a large empty elongate thin walled sac bearing dorsal raphe; second ventriculus is long slender tube deflecting dorsally and then anteriorly to pass ventrally beneath the posterior region of first ventriculus; third ventriculus is shortest among alimentary canal and bulbous structure while fourth ventriculus consists of tubular structure surrounded by four rows of gastric caecae. Pylorous serves for attachment of fourth ventriculus and insertion of malphigian tubules. Rectum is posteriormost part of alimentary canal terminating into anal opening. There are two principal salivary glands with unequal bilobed located on dorsum of ventriculus in thoracic region. Harris (1938) studied anatomy and histology of alimentary system of Murgantia histrionica and reported nine distinct regions in alimentary canal viz. three stomodeal, three ventricular and three proctodeal of which stomodium comprises of functional mouth, cibarium and oesophagus while ventriculus divided into anterior, mesial and posterior ventriculus respectively;