BIOLOGY, POPULATION DYNAMICS AND MANAGEMENT OF SORGHUM APHID, Rhopalosiphum maidis Fitch AND SUCCESSION OF DIFFERENT PESTS OF FORAGE SORGHUM
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Date
2003
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AAU, Anand
Abstract
Present investigations were made on biology, population dynamics and management of sorghum aphid, R. maidis and succession of different pests of forage sorghum at the Gujarat Agricultural University, Anand campus, Anand during the year 2001. Study on biology of R. maidis on sorghum was carried out at fluctuating temperature ranging from 28.0 to 31.9°C (Av. 29.82 ± 1.16°C) and average relative humidity of 68.42 percent, while biology of R. maidis on maize was carried out at fluctuating temperature ranging from 28.0 to 31.9°c (Av. 29.68 ± 1.16°C) and relative humidity of 69.49%. The aphid passed through four distinct nymphal instars. The average duration of first, second, third and fourth instar nymph on sorghum was found to be 1.20 ± 0.08, 1.48 ± 0.10, 1.72 ± 0.12 and 1.16 ± 0.07 days with body length of 0.68 ± 0.06, 0.82 ± 0.03, 0.95 ± 0.05 and 1.47 ± 0.03 mm and breadth of 0.30 ± 0.040, 0.36 ± 0.03, 0.45 ± 0.06 and 0.66 ± 0.07 mm, respectively. On maize, duration of first, second, third and fourth instar nymph was found to be 1.08 ± 0.05, 1.24 ± 0.09, 1.12 ± 0.07 0.07 and 1.04 ± 0.04 days with an average body length of 0.70 ± 0.07, 0.86 ± 0.04, 0.99 ± 0.06 and 1.50 ± 0.07 and breadth 0.33 ± 0.07, 0.38 ± 0.03, 0.47 ± 0.08 and 0.69 ± 0.08 mm, respectively. On sorghum, the average body length of adults was recorded 1.77 ± 0.06 mm and breadth of 0.90 ± 0.04 mm. Whereas, on maize the average length and breadth were 1.78 ± 0.13 and 0.93 ± 0.06 mm. The pre- reproduction, reproduction and post reproduction periods were recorded to be 0.52 + 0.14, 22.84 + 0.53 and 4.96 ± 0.21 days, respectively, on sorghum, whereas on maize it was 0.28 ± 0.10, 18.92 ± 0.69 and 4.44 ± 0.26 days, respectively. The average longevity of R. maidis on sorghum and maize was 28.22 ± 0.62 and 23.40 ± 0.72 days. Whereas, average fecundity was 54.48 ± 2.66 and 64.44 ± 2.51 nymphs per female on sorghum and maize. The average life span was recorded to be 33.88 ± 7.0 days on sorghum and 28.16 ± 7.7 days on maize. The study on persistent residual toxicity of different insecticides against sorghum aphid revealed that imidacloprid persisted for longer period (16 days) than rest of the insecticides. It was followed by monocrotophos (13 days), phosalone (12 days) and lufenuron (11 days). Karenj oil persisted for shorter period (7 days). On the basis of PT value, the order of relative efficacy was imidacloprid (1077.44) followed by monocrotophos (795.51), lufenuron (683.32), phosalone (673.83), endosulfan (633.63), dimethoate (584.46), thiamethoxam (582.17), azadirachtine (553.70), neem oil (541.08), karenj oil (413.14) and NSKS (405.44). Different insecticides can be ananged as Imidacloprid (1.00), monocrotophos (0.7383), lufenuron (0.6341), phosalone (0.6253), endosulfan (0.5880), dimethoate (0.5424), thiamethoxam (0.5021), azadirachtine (0.5139), neem oil (0.3834), karenj oil (0.3834) and NSKS (0.3762) on the basis of RPT value. The result on the comparative bio-efficacy of different insecticides against aphid on sorghum crop showed that dimethoate 0.03%, imidacloprid 0.06% and monocrotophos 0.036% found to be most effective insecticides for the control of the pest. The percent reduction in aphid population was maximum in dimethoate treated plot followed by imidacloprid and monocrotophos. Maximum yield was recorded in plot treated with monocrotophos 0.036% followed by dimethoate 0.03%) and imidacloprid 0.06%. Dimethoate 0.03% was observed to be the most effective and economical insecticide giving net incremental cost benefit ratio (1: 24.50) followed by monocrotophos 0.036% (1: 14.57) and imidacloprid 0.06% (1: 7.61). Study on the activity ofR. maidis on sorghum revealed that the activity of pest commenced from the third week of July which reached to its peak during last week of September and was present up to harvesting. Activity of natural enemies of aphid viz., coccinellid beetle; syrphid larvae and the larvae of chrysopid were found to be positively correlated with the pest population. Among different weather parameters, minimum temperature, mean temperature and sunshine hours exhibited positive effect, whereas, relative humidity, vapour pressure, rainfall and wind speed were negatively correlated with the pest population. The effect of weather parameters on the activity of coccinellids indicated that minimum temperature, mean temperature and sunshine hours were significantly positively correlated, whereas, relative humidity, vapour pressure and rainfall had significant negative correlation. Chrysopid population was found to be positively correlated with minimum temperature, mean positively correlated with minimum temperature, mean temperature and sunshine hours, whereas, relative humidity was found to be negatively correlated. Minimum temperature, mean temperature and sunshine hours were significantly positively correlated in case of syrpbid fly population. Whereas, relative humidity, vapour pressure and rainfall were significantly negatively correlated. The activity of shoot fly was found up to one month after sowing. The maximum numbers of dead hearts were found during the fourth week of July. Among different abiotic factors minimum temperature and sunshine hours were negatively correlated with the dead heart formation. Whereas, relative humidity, vapour pressure and maximum temperature were positively correlated with dead heart formation. Occurrence of stemborer was first observed during the last week of July and was found active up to harvesting. The pest population increased and reached to its peak in the second week of September. Parasitism of Chilo partellus Swinhoe by Apentelus flavipes L. was found positively correlated with the pest. Different abiotic factors such as maximum temperature, mean temperature, vapour pressure and sunshine hours were found to be positively correlated with the pest population. Relative humidity showed negative correlation with the pest activity. The effect of different weather parameters on the activity of A. flavipes indicated that maximum temperature and sunshine hours exhibited significantly positive effect, whereas relative humidity, vapour pressure and wind speed showed significantly negative effect. Appearance of nymphs and adults of Pyrilla perpusilla Wlk. on sorghum started from the first week of August. The population reached to its peak during first week of October and was present up to harvesting. The pest activity was found positively correlated with percent parasitism by Epericania melanoleuca Fletcher. Among the different weather parameters maximum temperature, minimum temperature, mean temperature and sunshine hours were found to be significantly positively correlated with the pest population. Whereas, relative humidity was found to be negatively correlated with the pest population. The activity of Myllocerous maculocus Desbroachers was started after one week of sowing and was present up to harvesting. The pest reached to its peak during first week of September. Among the different weather parameters vapour pressure was found significantly negatively correlated with the pest population. The activity of thrips commenced fi-om third week of July, reached to its peak during second week of September and was found up to harvesting. Among different weather parameters minimum temperature, mean temperature and sunshine hours exhibited significant and positive correlation with pest population. Whereas, relative humidity showed negative correlation. The activity of jassid was first observed in the second week of July, reached to its peak in the last week of August and was present up to harvesting. Among the different weather parameters maximum temperature, minimum temperature, mean temperature, sunshine hours and wind speed were found to be positively correlated with the pest population. Whereas, relative humidity, vapour pressure and rainfall were found to be negatively correlated with the pest population. However, no any weather parameters produced significant effect on population fluctuation of the pest.
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AGRICULTURAL ENTOMOLOGY, AGRICULTURE, A STUDY