BP Singh

Methods for Detection of Insects and Mites in Imported Gennplasm 189transmitted through solids, the hydrophone through liquids andthe microphone through gases or air. The vibrations can beconverted into electric signals and could be displayed on a meter /software/printer and recorded (Vick et aI., 1988).5. X~Ray radiographyX-rays are in everyday usage for medical purpose andsomewhat less so in industry. Their use for the analysis of seedquality dates back to the fifties when Simak and Gustafson (1953)and Simak (1953) demonstrated that soft X-ray after passingthrough seeds produce a pattern on X-ray plate. Thus, it is possiblein X-ray picture to recognise the structure, viability and extent ofdevelopment of embryo and endosperm (Swaminathan andKamra, 1961) and also to detect mechanical injuries as well asdamage caused by insects, pathogens and bacteria (Yuasa, 1926;Milner et al., 1950; Wadhi et al., 1967). The insect detection workthrough radiography is fairly common in many countries. Thistechnique has been noted as the lUost accurate method of studyingthe extent of damage, the stage of insect development inside theseed/ stem and the identity of insect could also be ascertainedwithout damaging the seed. Detection of pathogens iscomparatively more difficult since creating contrast between hosttissue and pathogen is so far unsuccessful. Only when the fungalmycelia are in a mass, e.g., in some tea seeds, they become visible.However, the pathological changes accompanied by the pathogenicattack become clea~ at times due to shrivelling.Seeds infested with phytophagous chalcidoids, bruchids andcertain other insects do not present any external evidence for thepresence of infestation on seed. A list of 322 plant genera has beendrawn up, the seeds of which have been known to carry suchinfestation. Whenever seeds of any of the listed plant genera arereceived, these are subjected to X-ray radiogrCij'hy at 22 kv, 3 rnafor 15 seconds at the distance of 30 cm. However, dose-ratedepends on the seed hardness. The infested seeds, if present, arehand picked and only healthy seeds are released to the indentor.The initial cost of X-ray machine and the ongoing cost· of X­ray films and chemicals to develop the X-ray film are high andexamination of each of the individual grain on the X-ray film forinsects is labour intensive. Detection of infestation in very smallseeds (e.g., tobacco and Trifolium spp.) is difficult and cumbersome.