Biology, population dynamics and management of spotted pod borer, Maruca vitrata G. on yam bean (Pachyrrhizus erosus L.) in Bihar
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Date
2012
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Rajendra Agricultural University
Abstract
Biology and population fluctuation of spotted pod borer (Maruca vitrata G.) in relation to abiotic factors on yam bean were studied. In order to develop strategies for its management through crop resistance/host evasion, effective synthetic insecticides, schedules of spray and certain eco-friendly pest control tactics, a series of field as well as laboratory experiments were conducted during two successive crop seasons viz; 2009-10 and 2010-11. The field trials were conducted at the research farm and laboratory experiment in the Departmental laboratory of Entomology, Tirhut College of Agriculture, Dholi, Muzaffarpur (Bihar). Results pertaining to different aspects of the present study viz; determination of the effects of different genotypes on growth and development aspects of this insects, trend of population buildup in relation to meteorological parameters, management of M. vitrata on yam bean through plant resistance, host evasion, adjustment in sowing time, foliar spray of synthetic as well as botanical insecticides and spray schedules of common insecticide against M. vitrata on yam bean have bean abstracted below.
Among the eight yam bean genotypes the shortest (1.44 day) and longest (1.82 day) preoviposition period were recorded on R.M-1 and DPH-2, respectively. The oviposition period of M. vitrata varied from 3.82 to 3.95 days with minimum and maximum on DPH-2 and R.M-1, respectively. Its fecundity on DPH-2, DPH-11, DPH-17, DL-14, DPH-18, DPH-45, Nepali and R.M-1 (C) was recorded to be 65.40, 68.30, 69.30, 70.60, 71.70, 72.30, 74.60 and 80.00 egg per female, respectively. The shortest (2.50 days) and longest (4.00 days) incubation period were recorded on R.M-1 and DPH-2, respectively. The mean viability of eggs ranged from 51.83 to 72.39 per cent, the minimum and maximum being on DPH-2 and R.M-1, respectively. Of the remaining genotypes Nepali, DPH-45, DPH-18 and DL-14 occupied second, third, fourth and fifth position from egg viability point of view i.e. 70.25, 64.06, 62.22, 59.91 per cent, respectively. The length of larvae of M. vitrata got influenced by yam bean genotypes used as larval food, the longest (1.40 to 16.72 mm) and heaviest (1.80 to 17.39 mm) being on DPH-2 and R.M-1, respectively. Larval duration and larval weight was shortest and heaviest (10.80 days and 75.00 mg) on R.M-1 while longest and highest duration and weight (13.00 days and 56.30 mg) were recorded on DPH-2, respectively. The shortest (1.32 and 6.50 days) and longest (1.66 and 7.90 days) pre pupal and pupal period were recorded on R.M-1 and DPH-2, respectively. The weight of male and female pupae so developed were heaviest on the genotype R.M-1 (33.34, 35.50 mg) and lightest (27.86, 28.67 mg) on DPH-2. The weight of male and female pupae obtained from larvae reared on remaining genotypes occupied intermediate position. As regards the pupal survival of M. vitrata, the highest adult emergence (81.67%) was recorded in case of larvae reared on R.M-1 which was statistically at par to Nepali (78.33%), DPH-45 (76.67%), DPH-18 (76.67%) and DL-14 (73.33%). Thus, it became obvious that the yam bean genotypes viz; R.M-1 and DPH-2 proved most and least favourable larval foods in terms of adult emergence. The sex ratio male to female were recorded to be 1:1.3, 1:1.3, 1:1.3, 1:1.3, 1:1.4, 1:1.4, 1:1.4 and 1:1.5 on DL-14, DPH-2, DPH-11, DPH-17, DPH-18, DPH-45, Nepali and R.M-1 (C), respectively. Longevity of male and female adults was comparatively shorter (3.40, 4.70 days) on DPH-2 than on other seven test yam bean genotypes between two sexes. Female adults invariably lived longer on corresponding yam bean genotypes. Thus, both male and female adults of M. vitrata lived for shorter period (3.40, 4.70 days) on DPH-2, while longevity of both the sexes was more on R.M-1 (4.30, 5.80 days). On the basis of overall performance, the total life cycle of M. vitrata was 29.36, 29.62, 30.86, 30.90, 31.41, 32.08, 32.45 and 33.29 days in case of male while 30.86, 31.21, 31.76, 32.40, 32.91, 33.28, 34.05 and 34.69 days in case of female on R.M-1, Nepali, DPH-45, DPH-18, DL-14, DPH-17, DPH-11 and DPH-2, respectively. Among the genotypes tested the total life cycle of M. vitrata was shortest on R.M-1 (29.36, 30.86 days) while it was longer on DPH-11 and DPH-2 (32.45, 34.05 and 33.39, 34.69 days) both in case of male and female. The growth index value was worked out to be 7.17, 6.12, 5.24, 4.28, 4.21, 3.81, 3.41 and 3.11 on R.M-1 (C), Nepali, DPH-45, DPH-18, DPH-14, DPH-17, DPH-11 and DL-2 genotypes of yam bean, respectively. Of the test genotypes R.M-1 and DPH-2 proved to be the best and poor most food plants, respectively for the larvae of M. vitrata as reflected by the highest (7.17) and shortest (3.11) growth index value.
The mean number of larvae, number of webs per flower shoot and extent of flower damage gradually increased from 41st standard week with maximum larval population (22.00 larvae/flower shoot) and mean number of webs (3.34/flower shoot) was recorded during 47th standard week when the mean maximum temperature, minimum temperature, average relative humidity at 7 A.M and 2 P.M prevailed around 27.200C, 13.500C, 95.45 and 44.75 per cent, respectively. On the other hand maximum flower infestation (47.67%) was recorded during 48th standard week when mean maximum temperature, minimum temperature, average relative humidity at 7 A.M and 2 P.M prevailed around 26.550C, 12.100C, 94.70 and 54.40 per cent, respectively. The pod infestation by M. vitrata commenced from 43rd standard week (8.64%) and reached its peak (36.53%) during 49th standard week when mean maximum and, minimum temperatures were fluctuating between 31.55-26.450C and 17.70-10.950C, respectively and average relative humidity at 7 A.M and 2 P.M were between 94.30-98.35 and 46.95-51.50 per cent, respectively. The larval population, flower infestation and pod damage started declining gradually from 48th standard week, 49th standard week and 50th standard week, respectively and became almost untraceable after 52nd standard week.
Among the relationship between larval population, number of webs per flower shoot, per cent flower, pod damage and weather factors like maximum temperature, minimum temperature, relative humidity at 7 A.M, 2 P.M and rainfall (mm) were taken in to account for computing correlation and regression analyses. It could be inferred that except relative humidity at 2 PM, almost all the abiotic factors under study showed negative but non-significant effect on larval population, number of webs per flower shoot and flower infestation, while relative humidity at 2 P.M exerted negative but significant effect on larval population and flower infestation. However, maximum and minimum temperature as well as relative humidity at 2 P.M showed negative but highly significant effect on pod infestation whereas, relative humidity at 7 A.M and rainfall exerted significant positive and non-significant negative effects on pod infestation, respectively. However, regression equation or analysis clearly indicated that the maximum and minimum temperature, relative humidity at 7 A.M, 2 P.M and rainfall together contributed 51.70 and 52.00 per cent towards the changes in larval population and number of webs on flower shoot while the same weather parameters together shared 53.50 and 85.80 per cent towards the fluctuation of flower and pod infestation caused by M. vitrata on yam bean crop.
Among the thirty yam bean genotypes evaluated under natural field condition and compared on the basis of per cent flower infestation, DPH-72 suffered least due to flower infestation (18.00%) while three genotypes viz; DPH-71, DPH-82 and DPH-2 recorded 23.33, 22.67 and 23.33 per cent flower infestation, respectively which were statistically at par to DPH-72. On the other hand DL-6 suffered most by recording highest flower infestation (82.67%) followed by DL-17 (80.00%), DL-8 (77.33%) and majority of them were intermediate in their reaction by registering mean flower infestation ranging between 25.33 to 74.00 per cent including the local check i.e. R.M-1 (64.00%). Only nine genotypes viz; DL-5, DPH-45, DPH-46, DPH-11, DPH-18, DPH-3, DL-20, DPH-48 and Nepali showed low level of flower infestation (25.33-35.33%) than local check R.M-1. Among them only one genotypes viz; DPH-72 was identified as highly resistant while DL-6 showed highly susceptible reaction to M. vitrata.
On the basis of level of pod damage caused by M. vitrata among thirty yam bean genotypes the level of pod infestation varied widely from 12.77 to 43.27 percent with minimum and maximum being in DPH-11 and R.M-1, respectively. Among the remaining genotypes under test four genotypes viz; DPH-45, DPH-46, DPH-89 and DPH-18 recorded significantly less pod infestation (13.26-14.80%) which were statistically at par with DPH-11. Seven genotypes viz; DL-1, DPH-33, DPH-71, DL-18, DPH-2, DL-12 and DPH-72 occupied position next to DPH-18 with respect to pod infestation varying between 16.69-20.40 per cent. Thirteen genotypes occupied intermediate position with mean per cent pod infestation ranging from 21.39 to 30.57 while four genotypes viz; DL-20, DPH-3, DL-2 and Nepali had relatively high pod infestation level (31.10-38.64%) but significantly less than local check. On the basis of overall tolerance value twenty seven genotypes posses higher level of tolerance than standard check i.e. R.M-1, while two genotypes viz; DL-8 (1.03) and DL-6 (1.07) recorded over all tolerance values of less than R.M-1 (1.00).
The yam bean crop sown earlier till first week of August suffered most and delayed sowing afterwards ensured better plant stand against M. vitrata. The crop sown on first date (18th June), second date (3rd July) and third date (18th July) recorded mean larval population ranging from 11.92 to 17.77 per flower shoot while the same declined drastically with delay in sowing beyond the third date which ranged from 1.04 to 4.67 larvae per flower shoot. The crop sown on sixth date of sowing was found free from pest attack. On the other hand, number of webs per flower shoot, percent flower and pod damage also declined with delay in sowing, while the sixth dates of sowing was found free from pest attack. From yield point of view second date (3rd July) proved to be the most suitable date of sowing followed by 18th June, among all date of sowing.
Among the foliar spray of synthetic insecticides profenofos 50 EC (750g a.i./ha) when applied thrice at fortnightly interval starting at 50 per cent flower initiation stage afforded maximum protection to yam bean crop. There were reduction in larval and webs population, per cent flower and pod damage with highest seed yield (15.33 q/ha) and cost-benefit ratio (1:2.49) as compared to individual insecticides. The treatment was followed by indoxacarb 14.5 SC (60g a.i./ha) and spinosad 45 SC (73g a.i./ha) while remaining synthetic insecticides novaluran (10 EC), dimethoate (30 EC), DDVP (76 EC), acephate (75 SP), and cartap hydrochloride (50 SP) were found to be less effective than profenofos (50 EC) but significantly superior than untreated control.
Foliar spray with plant products ultimately resulted into reduction of larval and webs population of the test crop i.e. yam bean cv. R.M-1 in varying degree. Among the plant products, NSKE (5%) and Neem oil (0.2%) showed their superiority in reducing larval and webs population with minimizing flower and pod infestation, highest seed yield (11.26 q/ha) with highest cost-benefit ratio (1:3.44) and proved statistically at par to the synthetic insecticide i.e. dimethoate (0.03%) but significantly superior to other plant products viz; Karanj oil (0.2%), Neem gold (0.25%), Rakshak gold (0.2%), Neemta (0.5%), and Multineem (0.2%) at their respective dose, regardless of the number of spraying besides untreated control.
Among the different spray schedules of profenofos 50 EC (750g a.i./ha) three round spraying at bud stage + flowering stage + podding stage of yam bean cv. R.M-1 recorded lowest larval and webs population per flower shoot (1.40 and 1.14/flower shoot, respectively) by minimising flower (7.67%) and pod (5.77%) damage as well as enchancing yield (15.91 q/ha) and yield attributing parameters simultaneously, which was statistically at par with two rounds spraying of the same insecticide when applied at flowering + podding stage or bud + flowering stage. On the other hand, single spraying of profenofos (50 EC) at its test dose when applied at flowering stage was proved as good as two spraying of the same insecticides at bud + podding stage inrespect of minimizing pest infestation. But on the basis of cost benefit ratio among the various treatments, the highest cost-benefit ratio (1:3.89) was recorded in case of two rounds of insecticidal spray one each at flowering + podding stage followed by the same at bud + podding stage (1:3.52) while three rounds spraying at bud stage + flowering stage + podding stage occupied the third position (1:3.08) in this regard while remaining treatments occupied intermediate positions.
Description
Keywords
Yam bean, Pod borer, Management, Bihar