Survey on insect pests of potato (Solanum tuberosum L.) and their natural enemies in Hassan district of Karnataka state during Kharif and rabi season

Introduction

Potato (Solanum tuberosum L.) is a root vegetable native to America, a starchy tuber of the plant and a perennial in the family of Solanaceae. The potato is an essential food fitting to the tuber and root family. It is one of the top four crops in the world after rice, wheat and maize (Ross, 1986; Douches et al., 2004) [18,8] . Potato is an important food in developing countries claiming fourth place. These countries produce approximately one-third of the worldwide production of potato. It is grown under diverse agro-climatic conditions over an area of 20.85 lakh ha with production of 480.96 lakh metric tonnes and productivity of 23.07 t/ha (Anon., 2016) [2] . In North India, about 85 percent of potatoes are cultivated in Indo-Gangetic plains and 80 percent of the total production is shared by Uttar Pradesh, West Bengal, Punjab, Bihar and Gujarat states. In Karnataka, the potato crop is cultivated over an area of 38,126 hectares with an annual production of 2,25,285 tonnes and a productivity of 6220 kg ha-1 during 2015-16. The major potato growing districts of Karnataka included Hassan (18,671 ha), Belagavi (4802 ha), Kolar (3648 ha), Dharwad (1160 ha) and Bengaluru-Rural (488 ha) (Anon., 2016a) [3] . In Hassan district of Karnataka, about 33 species of insects and a species of mite belonging to 9 orders and 23 families infest potato crop at different stages. Among the insect pests, aphids, thrips, leafhoppers, whiteflies, mites, cutworms, white grubs, epilachna beetles, defoliating caterpillars, tuber moth and stem borers were reported to be economically important causing heavy yield losses (Nandihalli et al., 1996) [13] .

Various lepidopterous caterpillars are known to damage potato crop, viz., Helicoverpa armigera(Hubner), Agrotis lpsilon(Hufnagel), Spodoptera litura(F.), whereas the coleopteran pest Henosepilachna vigintioctopunctata (F.) also known to cause damage. All these pests are known to occur during monsoon (June-September) on 40 to 59 days old crop. The damage is high, where potato has been grown near irrigated channels and coconut areas (Trivedi and Rajagopal, 1999) [20] . The sucking pest's viz., aphids, thrips and leaf hoppers are considered as a major group of sucking pests because of their role as vectors of viral diseases. The specimens were identified as, aphid, Myzus persicae (Sulzer), leaf hopper, Empoasca spp., whitefly, Bemisia tabaci (Gennadius) and thrips, Scirtothrips dorsalis Hood (Natikar et al., 2018) [14,15] . Roving survey on the numerous insect pests documented on potato during roving survey were mole crickets, gross hoppers, termites, green bugs, psyllids, aphids, whiteflies, leaf hoppers, thrips, root grubs, leaf weevils, blister beetles, flea beetles, cutworms, tobacco cut worms, potato tuber moths and black ants. All most all insect pests were found in all the villages. Among those cut worm Spodoptera litura, potato tuber moth Phthoromea operculella and greasy cut worm Agrotis ipsilon were found as major insect pests. Other insect pests namely aphid Myzus persicae, leaf hopper Empoasca Spp., whitefy Bemisia tabaci, thrips Scirtothrips dorsalis, leaf weevil Myllocerus subfasciatus, flea beetle Monolepta signala, termite Odontotermis obesus, green bug Nezara viridula and grasshoppers Chrotogonus Spp, and Cyrtocanthacris rancea were found as moderate insect pests of potato and the remaining were of minor importance in pest status (Bhushan, 2019) [7] . In Karnataka potato is mainly grown in Hassan, Kolar, Dharwad, Bangaluru and Belgaum districts. The farmers of Hassan district grow potato as one of the major vegetable crops especially in Bhageshapura, Chagachagere, Chikkanahallikoppalu, Dasanahalli, Doddamagge, Gandasi, Habbanaghatta, Malalikere, Mokaligrama, Shankarapura and Duddasurrounding villages throughout Hassan district in the transitional zone. The yield of potato is not up to the expected level due to the incidence of different pests and diseases. The major pests of potato are Potato tuber moth, Phthorimaea operculella .Zell., potato cutworm, Agrotis segetum(Hufn) and Spodoptera litura Fab. (Nair, 1970) [12] . Shoot damage due to Leucinodes orbonalis Guen. in potato increased as the level of larval density increased from one larva per 2 plants to 6 larvae in Hassan (Murthy and Nandihalli, 2003) [11] . The insect pests of potato has become the most destructive and ubiquitous pest in the recent years causing heavy yield losses in potato crop. The outbreak of these insect pests causes severe losses in potato crop. Therefore, present investigation was undertaken to study the pest complex of potato during kharif and rabi season in major potato growing villages of Hassan district, Karnataka state.

Material and methods

A roving survey was undertaken during vegetative, reproductive and harvesting stage of the crop to record the incidence of insect pests and their natural enemies prevailing on potato during both kharif and rabiof 2015, 2016 and 2017 at Hassan districts of Karnataka. In a district, eleven villages were selected for the study and from each village 10 farmer's fields were selected for recording the activity of insect pests and their natural enemies. To record the different insect pests of potato and their damage, fortnightly surveys were conducted in Bhageshapura, Chagachagere, Chikkanahallikoppalu, Dasanahalli, Doddamagge, Gandasi, Habbanaghatta, Malalikere, Mokaligrama, Shankarapura and Dudda, of Hassan district. Ten fields were selected in in each village. In each field, 10 plants were randomly selected. The survey was conducted at 15 days intervals. The observation was recorded till 65th day old of the crop. The sucking pests were counted in 100 leaves from randomly selected plants, representing top, middle and bottom portions. The defoliators were recorded from 10 randomly sleeted plants in each field for. The percent damage caused by potato tuber moth, P. operculella were recorded. Observations were pooled and averaged. The methods of selection of parameters were based on the sampling procedures standardised by CPRI, Shimla and adopted by all potato research centres under the All India Co-ordinated Research Project on potato (AICRP on Potato). Incidence of aphids was recorded by selecting 34 plants at random and from each plant three compound leaves from top, middle and bottom portions/canopy of the plant was selected and aphids were counted separately with help of 10 x hand lens and expressed in terms of aphid numbers per compound leaf per plant (Anonymous, 1995) [1] . For leafhoppers, thrips and whiteflies, ten plants were selected randomly and from each plant, three leaves representing top, middle and lower portions were selected. The total number of nymphs and adults on each leaf was counted and expressed in terms of number of insects per three leaves per plant (Bhatnagar, 2007) [6] . For samling mites, ten plants were randomly selected and three leaves covering top, middle and bottom canopy were collected in polythene bags. These leaves were brought to the laboratory and observed under stereo binocular microscope for mites. Number of mites per plant was worked out (Patil, 2005) [19] . Observations on larval population of leaf eating caterpillar, S. liturawas made on ten randomly selected spots of one meter row length. Larval counts were made by shaking the plant gently over a white cloth placed between the rows. Average number of caterpillars found per meter row length was worked out. A total of ten plants were randomly tagged to record the observations on different natural enemies and was expressed in terms of numbers per plant. Root grub incidence was recorded by selecting 10 spots of 1 sq.meter radius area.Observations for leaf miner, ash weevil and mole cricket were recorded from 10 randomly sleeted plants in each field and data was averaged and expressed in Mean standard Error.

Results and Discussion

The Roving survey data revealed the presence of insect pests viz., aphids [Myzus persicae (Sulzer)

Aphid, Myzus persicae

The Roving survey was carried out in selected major potato growing villages of Hassan district and the extent of damage in terms of number aphids per plant were recorded during Kharif surveys of 2015, 2016 and 2017, The highest incidence of Aphids/plant, was recorded at Dudda village 33.54 Aphids/plant followed by Chikkanahalli 31.42 Aphids/plant, Gandasi 30.68 Aphids/plant, Habbanaghatta 27.78 Aphids/plant and least number of aphids were recorded at Mokaligrama 16.58 Aphids/plant (Table 7) whereas in Rabi surveys of 2015, 2016 and 2017 pooled data of 3 yeras indicated that the highest incidence of Aphids/plant, were recorded at Mokaligrama village 43.78Aphids/plant followed by Dudda 41.43 Aphids/plant, Chagachagere 40.40 Aphids/plant, Gandasi 39.34 Aphids/plant and least incidence of aphids were recorded at Shankarapura 32.54 Aphids/plant (Table 8). The present findings are in line with findings of Hegde et al. (2008) [9] who opined that the infestation of aphid in potato increased from 25th day onwards ranging from 2.33 to 176 aphids per 50 leaves, Hassan (4.83 and 4.00 aphids/compound leaf, respectively) (Table 1) and continued upto reproductive stage. Similarly Basavaraju et al. (2009) [4] conducted study in Hassan and revealed that the aphid, M. persicae caused on an average of six percent loss in potato yield. The present findings are in agreement with Natikar and Balikai, (2018) [14,15] recorded highest mean incidence of aphid in Hassan district at vegetative stage was 4.83 aphids/compound leaves and it was continued up to reproductive stage. The incidence was low at harvesting stage which might be due to maturity of the crop and reduction in the succulence of crop.

Thrips (Scirtothrips dorsalis)

The occurrence of thrips was somewhat high at reproductive stage of the crop than vegetative and harvesting stages in all the surveyed villages of Hassan district during kharif and rabi 2015, 2016 and 2017. However during kharif 2015, 2016 and 2017, the incidence of thrips was highest in Malalikere village 15.20 Thrips/plant followed by Dasanahalli 15.03 Thrips/plant, Bhageshapura 14.79 Thrips/plant, Mokaligrama 13.61 Thrips/plant and least incidence of thrips were recorded at Dudda 09.20 Thrips/plant (Table 7) whereas in rabi surveys of 2015, 2016 and 2017 pooled data of 3 years indicated that the highest percent incidence Thrips/plant, was recorded at Doddamagge village 20.92 Thrips/plant followed by Dudda 20.72 Thrips/plant, Habbanaghatta 20.41Thrips/plant, Chagachagere 20.14 Thrips/plant and least incidence of thrips were recorded at Gandasi 14.16 Thrips/plant (Table 8). The present findings are in line with Natikar and Balikai, (2018) [14,15] recorded highest mean incidence of thrips in Hassan district at vegetative stage was 2.01 and reproductive stages with 2.90 thrips/3 leaves. The population of thrips was lower at harvesting stage of the crop because of reduced plant sap. However, literature to support this study of Bhatnagar (2005) [6] reported that, early potato crop is affected by stem necrosis diseases, transmitted by thrips, Thrips palmi (Karny) in Central India.

Leaf eating caterpillar, Spodoptera litura

The incidence of S. liturawas noticed in all the surveyed villages of Hassan district during kharif and rabi 2015, 2016 and 2017. However during kharif 2015, 2016 and 2017, the incidence of S. litura was highest in Bhageshapura village 12.29 S. litura/plant followed by Dudda 11.35 S. litura/plant, Shankarapura 11.18 S. litura/plant and least incidence of S. litura were recorded at Habbanaghatta 6.90 S. litura/plant (Table 7) whereas in rabi surveys of 2015, 2016 and 2017 pooled data of 3 years observed that the highest percent incidence S. litura/plant, was recorded at Chagachagere village 5.64 S. litura/plant followed by Bhageshapura 5.31 S. litura/plant, Mokaligrama 5.18 S. litura/plant and least incidence of S. litura were recorded at Habbanaghatta 2.57 S. litura/plant (Table 8). From the study it is shown that, S. liturais emerging as a another leading pest of potato which might be due to availability of alternate host plants in all the three seasons in the surveyed villages. Trivedi and Rajagopal (1999) [20] observed that the occurrence of S. liturain potato was more in 40 to 59 days old crop. Hegde et al. (2008) [9] witnessed that the foliar damage in potato due to S. litura ranged from 0.4 to 13.9 percent during peak vegetative phase. The present findings are in line with Natikar and Balikai, (2018) [14,15] observed in Hassan, the incidence of S. litura during kharif 2016 and 2017 was (2.95 and 1.30 larvae/meter row length, 2.42 and 1.00 larvae/meter row length at vegetative and reproductive stages, respectively)

Leafminer, Liriomyza trifolii

The infestation of Leafminer was noticed in all the surveyed villages of Hassan district during kharif and rabi 2015, 2016 and 2017. However throughout kharif 2015, 2016 and 2017, the infestation of Leaf miner was highest in Habbanaghatta village 32.72 Leafminer/plant followed by Gandasi 27.74 Leafminer/plant, Chikkanahalli 26.14 Leafminer/plant and least incidence of Leafminer were recorded at Mokaligrama 13.83 Leafminer/plant (Table 7) whereas in Rabi surveys of 2015, 2016 and 2017 pooled data of 3 year's observed that the highest infestation of Leafminer/plant, was recorded at Chikkanahalli village 8.81Leaf miner/plant followed by Dasanahalli 6.75 Leafminer/plant, Doddamagge 5.94 Leaf miner/plant and least incidence of Leaf miner were recorded at Dudda 2.67 Leafminer/plant (Table 8).

Ash weevil, Myllocero spp.

The infestation of Ash weevil was noticed in all the surveyed villages of Hassan district during kharif and Rabi 2015, 2016 and 2017. However in kharif, the infestation of Ash weevil was highest in Doddamagge village 11.20 Ash weevil/plant followed by Shankarapura 9.57 Ash weevil/plant, Malalikere 9.27 Ash weevil/plant and least incidence of Ash weevil were recorded at Chikkanahalli 5.83 Ash weevil/plant (Table 7) but in rabi surveys of 2015, 2016 and 2017 pooled data of 3 years detected that the maximum infestation of Ash weevil/plant, was documented at Habbanaghatta village 6.13Ash weevil/plant followed by Shankarapura 6.03 Ash weevil/plant, Chikkanahalli 5.16 Ash weevil/plant and least incidence of Ash weevil were noted at Dudda 1.86 Ash weevil/plant (Table 8). 8). The incidence of mite was comparatively more in Hassan district which might be due to intermittent rainfall and increased temperature which play an significant role in development of mites population. These observations are in confirmation with those documented by Raj (1990) [17] who opined that, potato grown in rainy season suffers from heavy damage due to P. latus causing upto 60 percent reduction in tuber yield in India. Further, Liu et al. (1991) [10] reported 60 percent reduction in tuber yield due to this pest. The present findings are in agreement with Natikar and Balikai, (2018) [14, 15] [4] reported that, an economic damage by PTM was noticed on the crop of 65 to 70 days old. This report stand as testimony to the present findings. The possible reason for late preference of the crop could be its preference to tuber feeding than the foliage. Natikar and Balikai, (2018) [14, 15] observed that, at reproductive stage, the larval population of potato tuber moth was 0.23 per plant with percent tuber infestation of 3.94 was observed during kharif 2016 while in kharif 2017, the larval population and percent tuber infestation of 0.23 and 4.33, respectively was recorded. At harvesting stage, the infestation was more prevalent in tubers with 5.28 and 7.08 percent tuber infestation during kharif 2016 and 2017, respectively. Similarly, Shahid et al.,. 2022, studied against PTM in Kharif season in 7 taluks of Hassan districts of Karnataka, to understand the extent of foliage damage and leaf mines. Highest mean PTM incidence (6.19%) was witnessed during Kharif season. Number of mined leaves per plant and number of mines per plant were detected during Kharif season (2.62 and 4.32).

Mole cricket,

Natural enemies: Coccinellids (Cheilomenessex maculata), chrysopids (Chrysoperla spp.) and spiders

The occurrence of natural enemies during kharif 2015, 2016 and 2017 was in Hassan district with average mean of all the surveyed village includes 2.66 coccinellids/plant, 1.14 chrysopids/plant and 1.32 spiders per plant were observed. However, during rabi 2015, 2016 and 2017 in an all the surveyed villages of Hassan district with 1.40 coccinellids/plant, 0.88 chrysopids/plant and 1.81 spiders per plant were observed (Table 9). The present findings are in agreement with Natikar and Balikai, (2018) [14,15] observed the maximum incidence of natural enemies at vegetative stage during kharif 2016 and 2017 was in Hassan district with 0.43 and 0.18 coccinellids, 0.22 and 0.06 chrysopids and 0.24 and 0.34 spiders per plant.

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