Department of Entomology, College of Agriculture, G.B. Pant University of Agriculture & Technology, Pantnagar-263145
Coccinella septempunctata was appeared variably late in March during the studies of three consecutive years, 1993, 1994 and 1995 in rapeseed mustard at Pantnagar, Tarai of Uttar Pradesh. The arrival of mustard aphid was recorded in January (Ist, 2nd, Ist Standard Week) and reaching its peak (273, 211, 230 aphids per 10 cm terminal shoot length) in February (8th, 7th and 7th standard week) during the respective years. The population of the predator was recorded zero when the alate population of the aphid was at its peak. Whereas, the appearance of C.septempunctata (1.2, 2.0 and 1.0 grubs and adults/ plant) were observed in 9th, 10th and 10th (Standard week) during the consecutive years of investigations, when the population of alate aphids started to migrate from the mustard fields. The beetle could not multiply due to low population of the aphid on mustard during March and onward. So it was concluded that there was no proper synchronization between populations of the prey and predator.
KEY WORDS : Coccinella septempunctata, Lipaphis erysimi, Mustard aphid, Synchronization
The aphidophoguous lady bird beetle, Coccinella septempunctata L. is one of the potential predator of the mustard aphid, Lipaphis erysimi (Kult), a key pest of the rapeseed and mustard. The beetle occupy quite a remarkable place among the naturally occurring biocontrol agents of mustard aphid (Mathur, 1983). The researchers have studied the behaviour and efficiency of its predation and abiotic factor influencing its population in field as well as laboratory conditions (Singh and Sing, 1986; Verma and Chaudhary, 1975) with varying results and no work has been reported from tarai of Uttar Pradesh, India. Therefore, the present investigation was undertaken in rabi season of three consecutive years, 1993, 1994 and 1995 to find out lag time between population of the mustard aphid (economic threshold bred to peak) and its predator, C.septumpunctata.
The experiments were conducted at the Crop Research Centre, G.B. Pant University of Agriculture and Technology, Pantnagar, Nainital (U.P.) India. It is situated in the tarai region of Uttar Pradesh, south of foothils of Himalayas (Shivalik range). Pantnagar falls under subhumid and subtropical climatic zone. Geographically, it is located 20°N latitude, 79.3°E longitude and at an altitude of 243.84 meters above the mean sea level. The soil type of experimental plot was patharchatta sandy loam. This region is characterized by hot dry summer and cold winter. The summer temperature rises upto 44°C while it falls to 1°C in winter. The plot size of 5 x 4 m was taken and replicated 10 times. The crop variety was Varuna (Brassica juncea). All the agronomic packages of practices were followed to raise the crop except the application of pesticides.
As the aphid arrival was observed in the last or first standard week the observations were taken on aphid as well as predator population count, per 10 cm terminal shoot length, at weekly interval started from first standard week. The corresponding meteorological data were also recorded. The statistical interpretation were undertaken to correlate the meteorological observation, aphid and predator population.
The mustard aphid L. erysimi were started to appear in Ist, 2nd and 3rd standard weeks during the years of investigation, 1993, 1994 and 1995, respectively. The population of the aphid went on increasing steadily and reached at its peak (273, 211 and 230 aphids per 10 cm terminal shoot length) in 8th, 7th and 7th standard weeks (Fig. 1 (i), (ii), (iii)) during all three consecutive years. The temperatures, maximum and minimum, the relative humidity maximum and minimum rainfall and sunshine hours were 23.3°C and 7.9°C, 89°C and 39°C, 1.8 mm and 5.5 hours during 1993 which were highly conducive for its multiplication at which the population of the aphid reached at its peak (Fig. (1(i)). Similarly almost same pattern were observed for 1994 and 1995 (Fig 1(ii) and 1 (iii)) whereas the population of C. septempunctata were found zero from appearance of the aphid and till it reached at its peak. The predator started to appear in 9th, 10th and 10th standard weeks during 1993, 1994, 19955, respectively. This lag time varied from 5 to 6 weeks (Fig. 1(i), (ii), (iii)) in all the years. This gap may only be filled up by the use of botanicals, non-toxic to predators.
It gained its maximum population in 12th, 11th and 12th during all three consecutive years. The population of the predator were composed of 4-5 different species which were affected by environmental factors (Kumar et al., 1996 and Yadav and Singh, 1994). So it was observed that the population could not synchronized with the economic threshold level and peak of the population of L.erysimi and hence were found unable to control the aphid. However, the lag time may be bridged up by the application of ecoenvironmentally insecticides (botanicals), once or twice sprays (unpublished work).
The predator, though an efficient predator could not control the aphid population naturally due to low predator population and a lag time (5 - 6 weeks) between the pest population peak and that of its natural enemy and the gap may be minimize by application of botanicals.
The authors are grateful to the Director, Experiment Station, G.B. Pant University of Agriculture & Technology, Pantnagar for providing research facilities.
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