ROLE OF AVIAN PREDATORS IN HELIOTHIS ARMIGERA (HUBNER) MANAGEMENT AND BREEDING BIOLOGY OF THE BANK MYNA ACRIDOTHERES GINGINIANUS LATHAM
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Date
1989
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AAU, Anand
Abstract
Studies on role of avian predators in the management H. armiKera. assessment of depredation, other mortality factors and breeding biology of one of the chief predatory species Acridotheres ginginianus Latham were carried out at Anand Campus of Gujarat Agricultural University, during 1988 and 1989. The net installed at 2 m height above the crop facilitated- movement of Heliothis moths across the net. The birds activity started as soon as the medium and large larvae appeared in the field. During both the years, mean number of small larvae was equal in T1 and T2 while medium and large differed significantly, mainly due to the bird predation in open area. Two sprays of endosulfan - 0.07 % significantly reduced larval number but the yield was higher only in the area grown at 60 cm distance. Slightly more inter-row distance (60 cm) improved efficiency of predatory birds. In bird free area (netted) pod damage was always high and hence the yield was very poor compared to the open area where birds controlled the pest. The Heliothis eggs were totally free from parasites whereas the small larvae were parasitised by Campoletis cl-qorideae to the tune of 23 per cent and 15.33 per cent during 1988 and 1989 respectively. Very poor pupal recovery was attributed to the inability of larvae to pupate in very hard soil, and predation by squirrel. The activity of predatory birds was comparatively less during morning hours (0730 to 1030) compared to evening (1430 to 1830) hours and no activity was observed inbetween., Due to the birds preference to forage in wider spaced crop, larval population was significantly less compared to closer spaced area. The breeding season of the Bank Myna A. ginginianus. extended from the 1st week of May to last week of the August, with peak period during dry weather of May and ijune. Average egg size was 2.68 x 1.88 cm; weight 5.600 gm and average volume was 5.22 cc. The mean clutch size varied between 3.78 to 3.88. Average incubation period ranged between 12,73 - 12,80 days whereas nestling period ranged between 22.47 to 23.45 days. Hatching success was higher in dry period as compared to wet period. The entry of rainywater. Black ants and ectoparasitic mites were chief mortality causing factors in wet period. Nestling food studies show that the Bank Myna feed their youngs mainly on animal matter (95.59 per cent) of which insects contributed 84.73 per cent. Bank Myna used very wide range of nesting material which included plant, Animal and synthetic materials. Key words : Gram, Bird predation, Heliothis armigera. larval parasitism, Campoletis chlorideae. Bank Myna Acridotheres ginginianus. breeding biology
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