BP Singh

184 B.R. Vermaand mites involved is extremely large in plant propagules ascompared to seeds. The vegetatively propagated plant materialharbours eggs, larvae and pupae deep inside the plant_ tissue anddo not bear any external symptoms of their presence till theemergence. Insects and mites belonging to some families arefound hidden inside the plant tissues and need careful examination.(b) Seed 'pests : The seeds may get infested while developing andmaturing on plant, on threshing grounds, during transport or instores. The pests involved can broadly be grouped into twocategories viz; (i) internal feeders including chalcidoids, majorityof bruchids and some other weevils and beetles and (ii) externalfeeders which continue to feed externally and multiply even in thestored seed and cause more serious losses. .The former category includes seed infesting chalcidoids,which except for the adult stage pass their life cycle in the seed.Eggs are deposited through the seed pod into the developing milkystage seeds. The hatching la:r;va feeds, grows and pupates in theseed itself only to emerge as an adult, since such insects can becarried with apparently healthy seed shipments~ they pose aquarantine problem.In the international exchange of seed which can be infestedwith phytophagous chal~idoids, bruchids and some weevils andbeetles, it becomes necessary to either use especial detectionprocedures or SUitably disinfest or reject the imported seeds. Thedetection procedure can be time consuming or seed consuming,whereas the rejection of the planting material would defeat thevery purpose of import.Methods for detection of insects and mitesDetection techniques may be divided hi.to two· broadcategories : active and passive. Active techniques use externalinputs, either physical (flotation or radiograph) or chemical(staining or transparency m.ethod) to derive information in the'form of an output such as film image (X-ray) or colour change (byusing acid fuchsin, genetion violet or berberin sulphate) in anindicator material, or an electronically measurable change inresistance, cOIl).plex ~mpedance, protein spin or the like. Passivetechniques do not use external inputs and depend on naturallyoccurring outputs such as infrared energy radiated by the insect,