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ThesisItem Open Access Population dynamics of major insect-pests of pigeonpea (Cajanus cajan (L.) Millsp.) and assessment of avoidable yield losses due to them(CCSHAU, 2017) Balwan Kumar; Verma, TarunField studies on “Population dynamics of major insect-pests of pigeonpea (Cajanus cajan (L.) Millsp.) and assessment of avoidable yield losses due to them” was carried out during kharif 2016. Population dynamics of major insect-pests (E. kerri, M. vitrata, H. armigera, C. gibbosa and M. obtusa) of pigeonpea was studied on four varieties of pigeonpea viz., Paras, AL 201, Manak and PAU 881. The incidence of E. kerri started from 29th SMW to 44th SMW with a peak during 33rd SMW (3.83 nymphs/three leaves/plant). Population of M. vitrata larvae, H. armigera larvae, C. gibbosa nymphs and C. gibbosa adults first appeared in 38th SMW (flowering) with peak activity during 40th SMW (0.50 larvae/plant), 44th SMW (0.39 larvae/plant), 47th SMW (0.36 nymphs/plant) and 40th SMW (4.08 adults/plant), respectively. Maximum number of web formed by M. vitrata larvae and egg masses laid by C. gibbosa was found 2.29 webs/plant (40th SMW) and 0.59 egg masses/plant (38th SMW), respectively. Incidence of M. obtusa first appeared during 41st SMW with a peak in 45th SMW (3.08 % pod damage). Population of M. vitrata larvae disappeared in 42nd SMW while that of H. armigera, C. gibbosa and M. obtusa prolonged to harvesting of the crop (48th SMW). Non-significant impact of all weather parameters was observed on incidence of E. kerri and H. armigera. Significant and negative correlation found between M. vitrata and sunshine hours; M. obtusa and sunshine hours; C. gibbosa nymphs and temperature. Significant and positive correlation found between C. gibbosa adult and temperature, rainfall; C. gibbosa egg masses and temperature; M. obtusa and morning relative humidity. Total pod damage caused by different insect-pests studied ranged from 27.78 to 39.50 per cent. The grain yield of different varieties ranged from 7.94 to 10.52 q/ha. For the assessment of yield losses, variety Manak was sown on paired plots. Spraying was done in protected plots with dimethoate 30 EC (first spray) and deltamethrin 2.8 EC (second and third spray) when the insect-pests crossed economic threshold (ET). The avoidable loss in grain yield was 28.37 per cent, while the reduction in pod damage in protected plots over unprotected plots was 45.91 per cent.