The incidence and abundance of sucking insect pests on groundnut

Transcription

1 The incidence and abundance of sucking insect pests on groundnut Subhash B. Kandakoor, H. Khader Khan, G. Basana Gowda, A. K. Chakravarthy*, C. T. Ashok Kumar and P. Venkataravana 1 Department of Entomology, University of Agricultural Sciences, Bangalore , India * chakravarthyakshay@gmail.com ABSTRACT Twelve species of insect pests were recorded on groundnut crop at Chintamani, (Chikkaballapur). The thrips, leafhoppers and aphids were considered as major sucking insect pests. Planthoppers, eurybrachid bug and pentatomid bug were considered as minor. The population of thrips and leafhoppers were more abundant on the crop during August and September, Results revealed that maximum activity was recorded during September and the correlation studies were made between the incidence of major sucking insect pests and select weather parameters. Thrips, leafhopper and aphids showed negative correlation with rainfall (r= , and , respectively). Thrips showed positive correlation to both maximum (r=0.277) and minimum temperature (r=0.087). But leafhopper showed negative correlation for minimum temperature (r= ) and positive correlation with maximum temperature (r= 0.314). In case of aphids negative correlation were observed with maximum temperature (r= ) and positive correlation with minimum temperature (r= 0.165). With respect to sunshine hours the leafhoppers and aphids showed negative correlation (r= and ). KEY WORDS: Aphids, Groundnut, incidence, leafhoppers, thrips INTRODUCTION Grountnut (Arachis hypogaea L.) is one of the major oilseed crops cultivated in 7.9 million ha, contributing 45% of oilseed production in India. The sucking insect pests complex comprising thrips Thrips dorsalis Hood and Megalurothrips usitatus Bagnall; leaf hoppers Empoasca motti Pruthi, Batracomorphus angustatus Osborn, Cicadulina bipunctata Melichar, Empoascanara prima Distant and Leofa mysorensis Distant and aphids Aphis craccivora Koch are the major pests of importance on groundnut crop specially when raised under rainfed conditions and bunch varieties are severely infested (David and Ramamurthy, 2011). Sucking pests suck the sap from tender plant parts as a result plant or parts of plant dry up. Most of the species of sucking insects are known to be vectors of diseases of groundnut. Thrips mainly feed by lacerating and sucking the sap from leaves and are known to transmit groundnut bud necrosis virus. Aphids suck the sap from tender shoots and twigs and sometimes severely infest the plant and they are vectors of rosette disease. Leafhoppers suck the sap from the leaves and petioles and mainly it prefers the first three terminal leaves and feeding symptoms induce yellowing of foliage that begins at the tip, known as hopper burn (Khan and Hussain, 1965). A heavy infestation on young plants 342

2 cause stunting and leaf tip turn yellow with a typical v-shape marking. On close examination of infected plants, nymphs can be seen on the underside of infected plants. An attempt has been made here to generate information on basic aspects of sucking insect pests complex on groundnut. In this paper data on incidence and abundance of sucking insect pests are furnished and discussed. MATERIAL AND METHODS Studies were conducted to know the thrips incidence on groundnut in 2010 at Agricultural Research Station, Chintamani. The popular groundnut variety JL-24 was sown in m. to record the thrips, leafhopper, aphid and other sucking insect pest incidence. Observations were recorded at weekly intervals on randomly selected ten plants 15 days after germination to the late stage of the cropping season. Thrips population was recorded by counting top three bud leaves of tagged ten plants at each quadrate using 10X magnification lens. Leafhopper population counts were recorded by visual observations on top 3 leaves of tagged ten plants at each quadrate without disturbing the plant. Aphid population was recorded on top 2 cm shoot length of tagged ten plants at each quadrate. There were three replications and size of each quadrate was 1 X 1 m. So, for each species count 30 plants were considered. The data was statistically analysed by correlation analysis between weather parameters and sucking pests viz., thrips and leafhoppers. RESULTS AND DISCUSSION Based on the observations made at sucking insect pests were found feeding and damaging the groundnut crop during the study period. Thrips dorsalis Hood and Megalurothrips usitatus Bagnall were the two thrips found on the top bud leaves as well as inside the flowers. Thrips became severe during September with the average number varying from 3.80 to 7.30 thrips/top bud leaves. They fed on young unopened bud leaves and caused dull yellowish-green patches (Fig. 1) on upper surface and darkbrown necrotic patches on lower leaf surface as well as curling of leaves. This commenced from 15 DAS and continued up to 90 DAS and declined later. The highest thrips population was recorded at 30 DAS and continued till 60 DAS while the minimum numbers were observed before 10 DAS and after 90 DAS (Table 2). The results are in accordance with Wheatley et al., (1989) and Jayanthi et al. (1993) who also observed higher thrips population in wetter end of the season compared to drought stress days Singh and Sachan (1992) recorded the higher thrips population during vegetative stage. Leafhopper Empoasca motti Pruthi was the predominant species in ARS, Chintamani. Other species viz. Batracomorphus angustatus Osborn, Cicadulina bipunctata Melichar, Empoascanara prima Distant and Leofa mysorensis Distant were also recorded. They were found in large numbers on top 3 leaves during August and September in vegetative phase (Fig. 1). Both nymphs and adults suck the sap from the leaves and petioles. A heavy infestation on young plants caused stunting and leaf tips turned yellow with a typical v-shape marking. The crops showed sever yellowing. Leaf hopper damage was on per cent v shaped yellowing or drying and silvery streaks of leaves due to feeding. Similar observations weekly intervals, a total of 13 species of 343

3 have been reported by Wheatley et al., (1989) observed that E. kerri was the most abundant on tender plants. Singh et al. (1990) reported eight insect species (Empoasca kerri, Caliothrips indicus, Toya propinqua, Creontiades pallidifer, Cletus signatus, Frankliniella sulphurea [F. schultzei] and Dorylus orientalis) in considerable numbers on crops. Singh et al. (1991) observed higher incidence of leafhopper, E. kerri during kharif 1987 and The aphids (Aphis craccivora Koch) were present throughout the cropping season and the population was low and did not reached the damaging level. Its peak infestation was observed in September with the highest 4.3 aphids/2 cm top shoot (Fig. 1). Aphids preferred to attack the terminal twigs and tender parts resulting in curling of leaves and stunted growth, also sooty mold was seen to the little extent, but not in severe form. The aphid populations were reduced during rainy days of September. Present results were in confirmation with the observations of Rao et al. (1991). Besides, eurybrachids and pentatomid bugs were also recorded. The population varied from 0.2 to 1 bug per plant. Govindan (1974) mentioned pentatomid bug as pest of green gram, black gram, jowar, maize, bhendi, citrus, tobacco, sunflower, cowpea, groundnut, brinjal and lablab. The results are in accordance Singh et al. (1990) who have mentioned fifty-two species of insect pests. Correlation with weather parameters Correlation was observed between the incidence of major sucking insect pests and few weather parameters like rainfall, temperature, relative humidity (RH) and sunshine hours (Table 3). Thrips, leafhoppers and aphids showed negative correlation with rainfall , and respectively, evening RH showed positive correlation (0.017) for aphids. Thrips showed positive correlation to maximum and minimum temperature with and respectively. But leafhopper showed negative correlation (-0.032) for minimum temperature and positive correlation (0.314) with maximum temperature. In aphids negative correlation was observed (-0.211) with maximum temperature and positive correlation (0.165) with minimum temperature. The results are in accordance with Jayanthi et al. (1993) for evening relative humidity but rainfall and morning relative humidity contrary to this. The results are in accordance with Jayanthi et al. (1993) and Prasad et al. (2008). Leafhoppers and aphids showed negative correlation of and , respectively with sunshine hours. But thrips showed positive correlation (0.072) with sunshine hours. The results of morning relative humidity and maximum temperature match with the study of Jayanthi et al. (1993) and in case of sunshine hours the results are contrary to the Dubey and Thorat (1994) but in accordance with Jena and Kuila (1996). The relative humidity was in accordance with the Jena and Kuila (1996). The rainfall results are contrary to the study of Jayanthi et al. (1993). The maximum temperature has shown positive correlation with leafhopper population (r = 0.314) and results are in accordance with Jayanthi et al. (1993) and Jena and Kuila (1996). For the aphids, significantly negative correlation was observed in rainfall, morning relative humidity, minimum temperature and sunshine hours with aphids incidence (r=-0.134, , , and , respectively). The results of relative humidity and sunshine hours are in accordance with Alegbejo et al. (1999), but 344

4 results of relative humidity contrary to Prasad et al. (2008). The results of rainfall and minimum temperature are in accordance with Prasad et al. (2008). The maximum temperature showed positive correlation with aphid population (0.165) and is in accordance with Nandagopal et al. (2004). The multiple linear regression equation was fitted to the data and the equation arrived for the incidence of aphids, leafhoppers and thrips. The similar work was made by Singh et al. (1990) Environmental factors which affected the abundance of thrips and leafhopper were identified using multiple linear regressions. Y 1 = X X X X X X 6 Y 2 = X X X X X X 6 Y 3 = X X X X X X 6 Where, Y1 = Incidence of aphids (number per top two cm shoot), Y2 = Incidence of leafhoppers (Number per top three leaves), Y3 = Incidence of thrips (Number per top bud leaves), X 1 = Rainfall (mm), X 2 = Maximum temperature ( 0 C), X 3 =Minimum temperature ( 0 C), X 4 = Morning RH (%), X 5 = Evening RH (%), X 6 = Sunshine hours (Hours) According to given regression equation, influence of weather parameters to the aphid, leafhopper and thrips population is up to 67.3, 52.2 and 57.5 per cent (R 2 =0.673, 0.522, 57.5), respectively (Table 4). CONCLUSION The study suggests that peak activity of thrips, leafhoppers and aphids was recorded during August September when plants were 30 days old. Thrips, leafhopper and aphids showed negative correlation with rainfall and thrips showed positive correlation to temperature. Planthoppers, eurybrachid and pentatomid bugs were considered as insects of minor significance on groundnut. ACKNOWLEDGEMENTS I am grateful to Dr. C. A. Viraktamath Emeritus Professor, UAS, GKVK, Bengaluru and Dr. J. Poorani, Senior Scientist, NBAII, Bengaluru for identifying the insect specimens

5 Table 1. Sucking insect pests on groundnut at Chintamani, kharif 2010 Insect pest Scientific name Systematic position (family and order) Thrips Scirtothrips dorsalis Hood Thripidae : Thysanoptera Megalurothrips usitatus Bagnall Thripidae : Thysanoptera Leafhoppers Batracomorphus angustatus Osborn Cicadellidae : Hemiptera Cicadulina bipunctata Melichar Cicadellidae: Hemiptera Empoasca motti Pruthi Cicadellidae: Hemiptera Empoascanara prima Distant Cicadellidae: Hemiptera Leofa mysorensis Distant Cicadellidae: Hemiptera Planthoppers Coronacella sinhalana Kirkaldy Delphacidae: Hemiptera Sogotella kolophon Kirkaldy Delphacidae: Hemiptera Aphid Aphis craccivora Koch Aphididae: Homoptera Eurybrachid bug Eurybrachys tomentosus F. Eurybrachidae : Homoptera Pentatomid bug Nezara viridula Linn. Pentatomidae : Hemiptaera Table 2. Incidence of sucking insect pests * on groundnut, 2010 Date of observation Thrips/ top bud leaves Leafhoppers/ top 3 leaves Aphids/ top 2 cm shoot Eurybrachid bug/plant Pentatomid bugs/plant Mean of 3 quadrates@10 plants/quadrate. Chi square at 1 df (p<0.05) among dates of observation for thrips, leafhoppers and aphids 346

6 Table 3. Correlation of thrips, leafhoppers and aphids incidence with weather Parameters, 2010 Sucking RH (%) Temperature Sunshine Rainfall(mm) insect pests Morning Evening Max. Min. (hrs.) Thrips * Leafhoppers Aphids *significant at 1% Table 4. Linear regression equation for incidence of aphids, leafhoppers and thrips with weather parameters, 2010 Particulars Regression equation R 2 Aphids Ŷ 1 = X X X X X X Leafhoppers Ŷ 2 = X X X X X X Thrips Ŷ 3 = X X X X X X Y1 = Incidence of aphids (number per top two cm shoot); Y2 = Incidence of leafhoppers (Number per top three leaves); Y3 = Incidence of thrips (Number per top bud leaves); X 1 = Rainfall (mm);x 2 = Maximum temperature ( 0 C); X 3 = Minimum temperature ( 0 C); X 4 = Morning RH (%); X 5 = Evening RH (%); X 6 = Sunshine hours (hrs). Fig. 1: Incidence of sucking insect pests on groundnut 347

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