ABUNDANCE AND RELATIVE COMPOSITION OF PARASITOIDS AND PREDATORS OF APHIDS INFESTING WHEAT
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Date
2018-07-24
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CSKHPKV, Palampur
Abstract
The present investigations entitled “Abundance and relative composition of parasitoids and predators of aphids infesting wheat” were undertaken at Experimental Farm of Department of Entomology, CSK HPKV, Palampur during Rabi 2017-18. The activity of two species of aphids viz., Rhopalosiphum padi (Linnaeus) and Sitobion avenae Fabricius commenced from 1st week of January and reached to their peak (30.40 aphids/shoot) during 3rd week of March. Seven different species of coccinellid beetles were recorded, among which Coccinella septempunctata (Linnaeus), Hippodamia variegata (Goeze) and Coccinella transversalis Fabricius were observed to be predominant. Maximum population of coccinellids (8.10 beetles/m2) as well as peak population of grubs and pupae of coccinellids were observed during 1st week of April. Six different species of syrphids viz., Episyrphus balteatus (De Geer), Episyrphus viridaureus (Wiedemann), Ischiodon scutellaris (Fabricius), Sphaerophoria sp. and Melanostoma spp. were recorded in wheat during Rabi 2017-18 and their peak population (13.00 adults/5 sweeps) was recorded during 3rd week of April. Maggots and pupae of syrphids reached to peak levels during 1st week of April. Lacewing, Micromus sp. started appearing on wheat from 1st week of March and peak population (2.65 adults/5 sweeps) was recorded during 3rd week of March. The activity of parasitoid of aphids i.e. Diaeretiella sp. commenced from 3rd week of February and peaked during 1st week of April with 16.60 per cent parasitization. Natural enemies of aphids viz., coccinellids, syrphids, lacewings and parasitoids showed a significant positive correlation with aphid population. Aphids, lacewings and Diaeretiella sp. had positive but non-significant correlation with maximum and minimum temperature whereas, it was negative and non-significant with rainfall and relative humidity. Coccinellids and syrphids showed a significant positive correlation with maximum and minimum temperature. Duration of third instar grub and adult of C. septempunctata varied from 4.40±0.16 to 4.67±0.33 and 30.30±1.05 to 32.00±1.10 days, respectively. Third instar grub of C. septempunctata with 1, 3, 5 and 7 number of grubs consumed 78.54±0.59, 204.53±1.62, 307.03±1.80 and 406.64±1.60 aphids, respectively. Adult of C. septempunctata with 1, 3, 5 and 7 number of beetles fed 625.46±0.18, 1491.12±0.36, 2261.80±0.39 and 2853.21±0.99 aphids, respectively. The order of efficacy of insecticides and biopesticides against aphids on wheat was cypermethrin > thiamethoxam > dichlorvos > azadirachtin > darekastra. Higher population of coccinellids was recorded in the treatments of darekastra (6.83 coccinellids/10m2) and azadirachtin (6.54 coccinellids/10m2) as compared to synthetic insecticidal treatments ranging between 2.91 to 5.62 coccinellids/10m2. Maximum parasitization was observed in the treatments of darekastra (10.88%) and azadirachtin (10.54%) as compared to the synthetic insecticidal treatments rendering them relatively safer to the parasitoid.
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