The natural appearance of mustard aphid on Brassica germplasm was observed on 11th January (60 DAS) and disappeared after 2nd March (110 DAS). The peak aphid population was found at a maximum, minimum and average temperature of 23.37°, 6.87° and 15.76°C, respectively and mean relative humidity of 54.75% on 10th February at 90 DAS. Then, decline in aphid population and simultaneously increase of Coccinella was at 100 and 110 DAS, respectively. Maximum and average temperature showed as positively non-significant effect while minimum temperature caused negatively non-significant on the population of aphid. However, relative humidity had a negative effect. Late appearance of Coccinella too could not have any regulatory effect on the incidence of this pest.
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Rapeseed and mustard are one of the most important oilseed crops in Jammu and Kashmir as they rank second to cereals. Mustard aphid, Lipaphis erysimi (Kalt.) has been found to be great hindrance and cause severe reduction to rapeseed and mustard. The losses in yield by mustard aphid were 66-96% (Singh and Sachan, 1997). Weather conditions play the most favorable role for its rapid multiplication (Sinha et al., 1989; Rana et al., 1993; Singh and Malik, 1998). Therefore, the present research was undertaken to study the population dynamics of mustard aphid in relation to weather conditions with the following objective to study the population build-up of mustard aphid in relation environmental fluctuations on Brassica sp. So, that a pest management module may be devised with minimum input and maximum benefit to farmers.
MATERIALS AND METHODS
Seeds of 25 Brassica germplasm were obtained from NRCRM, Sewar, Bharatpur and sown in RBD as a rabi crop during 2000-2001 at the R.A.K Institute of Agricultural Sciences, A.M.U. Aligarh in the plot size of 3x3 m2 and replicated thrice. In each plot the row to row distance was 40 cm and plant to plant 15 cm which was maintained by thinning. For all test germplasms, 10 plants were tagged randomly from each plot and the population count of mustard aphid/10 cm twig was measured at 10 days interval from initial stage of appearance to final disappearance by method adopted by Bakhetia and Sandhu (1973). Further, population of Coccinella/plant (immature and adult) was also monitored from tagged plants. The crop was not protected by any insecticide during the course of experiment.
Meteorological records: The data on weather parameters viz., maximum, minimum and average temperature and also mean relative humidity were collected from the Department of Physics, A.M.U. Aligarh. Ten days mean data were collected from daily data record and daily data taken into account 10 days ahead of infestation because this data was correlated and regressed against aphid numbers.
RESULTS AND DISCUSSION
Initial level of infestation of mustard aphid was observed on 11th of January at 60 DAS at maximum, minimum and average temperature of 15.78, 6.96 and 11.37°C and also mean relative humidity of 79.70% (Table 1) with the aphid population varies from 0-17.25 aphids/10 cm twig on different germplasms (Table 2). The present findings is in confirmation of Sinha et al. (1989) and Jitendra et al. (2000) who reported that during end of January if it appeared with its intial intensity of 2.8 aphids/plant on 66 days old crop and increase upto the seventh standard week in February with 403.00 and 264.33 aphids/plant and then decrease and elimination of aphid by the end of March.
|Meteorological data during the period of infestation at 10 days interval at Aligarh
|*DAS-Days After Sowing
|Mean aphid and Coccinella population on Brassica germplasm
|Mean aphid population/10 cm twig, -Mean Coccinella population/plant
While Varuna and Pusa Bold escaped from the colonization of mustard aphid. On 21st January at 70 DAS all germplasms even Varuna and Pusa Bold were infested by the aphid and its population varies from 13.25- 45 aphids/10 cm twig on different germplasms in relation to weather conditions.
At 80 DAS on 31st of January population increases rapidly between 175.56-340.50 aphids/10 cm twig on all germplasms with the increase of 3°C in maximum, minimum and average temperature and also 11% reduction in mean relative humidity as compared to 70 DAS. The present findings are in agreement with the reports of Singh and Malik (1998) that the increase in temperature was significantly conducive for aphid multiplication but relative humidity has shown negative response on its intensity. On 10th of February at 90 DAS the peak was obtained ranging from 245.20-425.25 aphids/10 cm twig at maximum, minimum and average temperature at 23.37, 6.87 and 15.12°C, respectively and mean relative humidity of 54.75%. At this stage Coccinella appeared in the field but its population was almost negligible.
On 20th of February at 100 DAS aphid population declines many fold irrespective of germplasms due to increase of 3°C temperature and 8% mean relative humidity as compared to 90 DAS. Population of Coccinella was ranged from 2.53-3.73 individuals/plant because of increase was obtained in temperature and relative humidity. Further decrease in population was obtained ranging from 79.90-180.30 aphids/10 cm twig at 110 DAS with maximum, minimum and average temperature of 26.87, 12.42 and 19.64°C and mean relative humidity of 62.85% and peak period of Coccinella was obtained which is ranged between 3.00-3.40 individuals/plant.
|Analyzed data showing correlation co-efficient (r), regression co-efficient (b) and co-efficient of determination (R2)
|*Significant at 5% level
After that neither aphids nor Coccinella were present in the field. In the present findings, the aphids disappeared after 110 DAS on the first week of March. It is due to the maturation of crop and onset of summer season. Identical reports are obtained by Singh and Malik (1998). It was further explained by Singh and Singh (1994) that maturation of crop has created net deficit in water content in plant tissues leading to food scarcity and alate formation in aphid colonies.
The appearance of Coccinella in the later half of February might have played an important role but it was too late to fetch potential importance as the harm to the crop has already been done (Hodek, 1967).
Correlation (r) and regression coefficient (b) showed a positive effect with maximum temperature and average temperature (Table 3). However, minimum temperature caused negative effect on the population of mustard aphid. Whereas mean relative humidity showed significantly negative effect. While, the combined effect of all the environmental factors expressed as the coefficient of determination (R2) ranged between 78.4-97.3%. This showed much variability among the test Brassica germplasm but Lal et al. (1997) concluded that different germplasm different significantly in relation to infestation. The same results are obtained to the present study and none of the germplasm was found immune or escaped by mustard aphid but differed significantly in their level of infestation.
Infestation of mustard aphid on different germplasm is largely governed by the average temperature and negatively by mean relative humidity. Whereas, minimum temperature influenced negatively on the infestation of aphid. The same reports have been reported by Sing and Singh (1994). It is in confirmation of earlier reports of Atwal et al. (1971) and Sinha et al. (1989). Contrary results have been found by Chandra and Kushwaha (1986) that temperature had negative effect whereas relative humidity is positively correlated with the abundance of aphid. Devi et al. (1995) suggested that due to increase in mean relative humidity during third week of February favoured the multiplication or mustard aphid. Moreover, Sing and Singh (1994) concluded that abiotic factors Shares 77.69% impact on aphid population.
Therefore, it was finally concluded that germplasms differed significantly in the rate of infestation and age of crop as well but weather factors play an important role in the abundance of mustard aphid. So, the weather factors are an important tool in forecasting the aphid multiplication and the farmers are forewarned for the management of mustard aphid by various pest management strategies at proper time or mustard crop.
- Atwal, A.S., J.P. Chaudhary and M. Ramzan, 1971. Mortality factors in the natural population of cabbage-aphid, Lipaphis erysimi (Kalt.) (Aphididae: Homoptera), in relation to parasites, predators and weather conditions. Ind. J. Agric. Sci., 41: 507-510.