Influence of farmscaping on the diversity of major insect pests of cowpea [Vigna unguiculata (L.) Walp] and the associated natural enemies
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Date
2015
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MPUAT, Udaipur
Abstract
Investigations on “Influence of farmscaping on the diversity of major insect pests of cowpea [Vigna unguiculata (L) Walp] and the associated natural enemies” were carried out in the Department of Entomology, Rajasthan College of Agriculture, MPUAT, Udaipur, during the kharif seasons from 2012 to 2013 with a view to record the population dynamics and species diversity of major insect pests of cowpea and associated natural enemies in the sole and different crop combinations under farmscaping; and evaluate the impact of plant oils on the major insect pests of cowpea and the associated natural enemy complex.
With regard to the pestiferous insects, during both the crop seasons (kharif 2012 and 2013), under the plant oil treated and untreated conditions, the mean density of all the major insect pests was relatively more in sole cowpea and less in cowpea + marigold farmscape treatment. Comparison between treated and untreated conditions evinced blister beetles to be significantly more when cowpea was not treated with plant oil spray (3%). The mean pest numbers per plant were significantly the maximum in sole cowpea and the minimum in cowpea + marigold farmscape treatment. The mean atmospheric temperature had a significant positive correlation with the population of aphid, whitefly and blister beetle; whereas, the mean atmospheric temperature showed significant negative correlation with the population of jassid. The mean relative humidity and total rainfall had a significant positive correlation with the populations of pod sucking bugs and pod borer while, the population of leaf miner showed significant positive correlation only with the mean relatively humidity during both years of study. The relative abundance of aphids (A. craccivora) was more in 2012; while that of jassids (E. kerri) was more than the other insect pests in 2013.
Under both untreated and plant oil treated conditions during kharif 2012 and 2013, significantly maximum mean per cent pod damage was recorded in sole cowpea while significantly minimum per cent pod damage was recorded in cowpea + marigold farmscape treatment.
During both the crop seasons (kharif 2012 and 2013) under unprotected and protected conditions, Relative Plant Effect (RPE) values of dominant natural enemies were the maximum under farmscape treatments than sole cowpea.
Among the natural enemies, the mean density values for coccinellids were maximum in cowpea + niger and for syrphid fly, wasps, spiders and carabids in cowpea + marigold as farmscape treatment; whereas, the mean density values for natural enemies were the lowest in sole cowpea. Based on the relative abundance, carabids dominated in kharif 2012 under both plant oil treated and untreated conditions; whereas, during kharif 2013, under untreated conditions spiders dominated and under plant oil treated conditions carabids dominated.
Bio-efficacy of plant oils (3%) on the major insect pests in different farmscapings resulted in significant maximum mean per cent population reduction of aphids, jassids, whiteflies, thrips, blister beetles and pod bugs when marigold was intercropped with cowpea rather than when cowpea was cultivated sole. Likewise, with respect to the side effects of plant oils on natural enemies, the minimum mean per cent population reduction of coccinellids was recorded in cowpea + niger farmscape treatment and that for syrphid fly, wasps and spider was observed in cowpea + marigold farmscape treatment; whereas, maximum per cent reduction of all the natural enemies was in sole cowpea. Under laboratory conditions, the numbers of deformed pupae and mortality of coccinellids were not more in both the treatments (karanj and neem oil 3.0%) when fed treated aphids as compared to that in control; thus, indicating both plant oils to be safe to the coccinellids grubs.
The insect pest diversity index was relatively lower in sole cowpea (both protected and unprotected) during both years of study; while, the indices were higher in different farmscape treatments when unprotected or protected that varied in both the years. For natural enemies, the diversity index was lower in sole cowpea under both unprotected and protected conditions; whereas, their diversity varied in the different farmscape treatments under treated and untreated conditions.
Both plant oil (A. indica and P. pinnata 3%) treated aphids when fed to the coccinellids grub did not show a significant effect on egg laying and hatchability by the adults of the coccinellids species (C. septempunctata).
During both the years (kharif, 2012 and 2013) under unprotected and protected conditions, the average yield of cowpea per plot was recorded significantly the maximum in cowpea + marigold, while it was significantly minimum in sole cowpea plots.
Description
Influence of farmscaping on the diversity of major insect pests of cowpea [Vigna unguiculata (L.) Walp] and the associated natural enemies
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Citation
Meena and Swaminathan, 2015