Indian Journal of Entomology 83(2021) Online published Ref. No. e20202 DoI No.: 10.5958/0974-8172.2020.00232.1

POPULATION DYNAMICS OF PESTS IN ECOSYSTEM

S V S Raju, Kamal Ravi Sharma*, Ramesh Babu S and Pankaj Kumar Mohanta

Department of Entomology and Agricultural Zoology, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi 221005 *Email: [email protected] (corresponding author)

ABSTRACT

Investigations on major insect pests in rice was carried out at the Agricultural Research Farm, Banaras Hindu University, Varanasi during kharif 2017-18 and 2018-19. Observations on incertulas incidence revealed that deadhearts and white ears were observed to be maximum during 1st week of October (40thSMW) and 3rd week of November (47th SMW), respectively. Likewise, medinalis was observed during 1st week of August (31st SMW) with maximum incidence being in the 1st week of October (40th SMW) with 11.39% damaged leaves/ 10 hills. Nilapravata lugens appeared from 2nd week of August (33rd SMW) and attained its peak in 1st week of October (40th SMW) as 17.33/ 10 hills. The maximum incidence of Nephotettix virescens was observed in the 4th week of October (43rd SMW)- 15.67 / 10 hills. The activity of Leptocorisa acuta commenced from 3rd week of October (42nd SMW) and reached its peak during 3rd week of November (47th SMW- 14.67/ 10 sweeps in nets). Correlation analysis revealed that the rainfall and evening RH exhibited a negative impact on S. incertulas, C. medinalis, N. lugens, N. virescens and L. acuta; minimum and maximum temperature, and morning RH, showed both positive and a negative impact on these insect pests of rice.

Key words: Rice, pests, population dynamics, Scirpophaga incertulas, Cnaphalocrocis medinalis, Nilaparvata lugens, Nephotettix virescens, Leptocorisa acuta, temperature, relative humidity, rainfall, correlation coefficients

Rice ( L.) is the most important staple Farm, Banaras Hindu University, Varanasi. Rice variety food of over half of the world’s population (Khush, Swarna was transplanted during 2nd fortnight of July 1997). Among the several limiting factors for improved in plot of 10x 10 m with the spacing of 20x 15 cm, yields in rice, insect pests are the most important. and the crop was grown following the recommended More than 100 insects attack rice, and of these 20 practices except plant protection measures. The pests cause economic damage, resulting in >30% yield observations on insect pests were recorded at weekly loss (Athwal and Dhaliwal, 2005). Among these, the intervals starting from one week after transplanting till yellow stem borer (Scirpophaga incertulas Walker), harvest. Observations on the incidence of yellow stem leaf folder (Cnaphalocrocis medinalis Guenee), borer (YSB) was done based on the % of deadhearts/ brown plant hopper (Nilaparvata lugens Stål), green white ear head; leaf folder by % damaged leaves; leafhopper (Nephotettix virescens Distant) and gundhi and brown planthoppers as well as green leafhoppers bug (Leptocorisa acuta Thunberg) heavily infest the rice with counts of nymph and adults/ hill. These were crop in the Varanasi region (Sharma et al., 2018; 2018; made from ten randomly selected hills. For gundhi 2019). Weather factors such as temperature, relative bug, nymphs and adults were counted from ten sweep humidity and rainfall are known to have a significant net catches made during panicle formation stage. influence on insect population dynamics. Knowledge Weather data were obtained from the meteorological of the seasonal incidence and population buildup trend observatory, Agricultural Research Farm, Institute of is essential to ensure effective IPM, especially in Agricultural Sciences, BHU, Varanasi. The data on developing forecasting models (Kumar et al., 2019). weather parameters and the incidence of the insect This study explores the population dynamics of some pests were analyzed by correlation analysis using the major pests of rice in the agroecosystems of Varanasi. SPSS software.

MATERIALS AND METHODS RESULTS AND DISCUSSION

The field experiment was carried out during the The data on the incidence of YSB (deadhearts/ kharif 2017-18 and 2018-19 at the Agricultural Research white earhead- DH/ WEH), leaf folder damaged leaves, 2 Indian Journal of Entomology 83(2021) Online published Ref. No. e20202 and counts of brown planthopper and green leafhopper negatively correlated with rainfall; and WE incidence (nymph and adults)/ hill and gundhi bug (no./ 10 sweep was significantly and negatively correlated with all the net catches) obtained during the kharif 2017 and 2018 weather factors. Somashekara and Javaregowda (2015) were pooled and plotted in relation to weather factors reported that stem borer incidence (DH and WE) had (Fig. 1). These reveal that in case of YSB, initial a negative correlation with evening RH and rainfall incidence (DH) was observed from 4th week of August (Fig. 2). (34th SMW), and thereafter increased during subsequent weeks with a peak during first week of October (40th The incidence of C. medinalis started from first SMW- 10.56%); white earheads (WE) were observed week of August (31st SMW- 1.11%) attaining its peak first time during fourth week of October i.e. 43rd SMW (5.59%) during first week October (40th SMW) (Fig. (0.83%), and this increased with peak being during third 1). Kakde and Patel (2015) was also observed its first week of November (47th SMW- 6.94% WE). These appearance on the 3rd week of August (34 SMW). Kakde results agree with those of Kakde and Patel (2014). and Patel (2014) and Sharma et al. (2018) also observed Similar results were also reported by Kalitha et al. that its attained peak during 4th week of September. The (2015). Singh et al. (2018) also observed maximum correlation coefficients between % leaf damage with DH in the first week of October, and maximum WE in weather factors showed significant negative correlation the first week of November. with morning RH (r = - 0.558**), evening RH (r = - 0.525**) and rainfall (r= - 0.474*); it was a negative Correlation coefficients revealed a significant non-significant correlation with minimum temperature positive correlation of DH with minimum temperature (r = - 0.103). A positive significant correlation was (r =0.559**), positive non-significant correlation with observed with maximum temperature (r = 0.434*) maximum temperature (r = 0.410) and a significant (Fig. 2). These results are in accordance with Rai et negative correlation with morning RH (r= - 0.474*), al. (2000). Sawai and Kothikar (2019) also observed evening RH (r = - 0.554**) and rainfall (r= - 0.440*); a positive correlation with temperature and a negative with WE, there was a significant negative correlation one with RH and rainfall. with maximum temperature (r = - 0.663**), minimum temperature (r= - 0.861**), rainfall (r = - 0.425*), The initial occurrence of N. lugens was during and evening RH (r = - 0.621**); and it was a positive second week of August (33rd SMW- as 1 hopper/ 10 non-significant one with morning RH (r = 0.285). hills (Fig. 1); this increased to a peak (17.33) during These results agree with those of Sharma et al. (2018) first week of October (40th SMW). Similar results were on DH that was observed to be significantly and obtained by Khan and Misra (2003) and Firake et al.

20 Yellow stem stem borer borer (dead (dead heart heart%)/ %)/ 10 10 hills hills Yellow stem stem borer borer (white (white earhead earhaed%)/ %)/ 10 10hills hills Leaf folder (% damage leaves/ 10 hills) Brown plant hopper (no. of insects/ 10 hills) 18 Green leaf hopper (no. of insects/ 10 hills) Gundhi bug (no. of insects/ 10 sweeping nets)

16

14

12 Pest incidence 10

8

6

4

2

0 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 Standard Meteorological Weeks

Fig. 1. Seasonal incidence of insect pests in rice (kharif 2017, 2018 pooled) Population dynamics of insect pests in rice ecosystem 3 SVS Raju et al.

Rainfall (mm) Temperature (maximum) Temperature (minimum) Relative Humidity (morning) Relative Humidity (evening) 0.8

0.6

0.4

0.2

0

-0.2

Correlation coefficient (r) -0.4

-0.6

-0.8

-1 Pests infestation/ incidence (*Correlation is significant at 0.05 level, **Correlation is significant at 0.01 level

Fig. 2. Correlation coefficient (r) of insect pest incidence with weather factors (kharif 2017, 2018 pooled)

(2010). Correlation coefficients with weather factors with minimum temperature (r = - 0.278) and morning revealed that the incidence was significantly and relative humidity (r = - 0.121), and there existed a negatively correlated with morning RH (r = - 0.439), and positive non-significant correlation with maximum significantly and positively with maximum temperature temperature (r = 0.135) (Fig. 2). Kakde et al. (2015) (r =0.568**); a non-significant positive correlation also reported that minimum temperature and relative was observed with minimum temperature (r = 0.299), humidity had a significant negative correlation; while whereas a non-significant negative one was obtained Firake et al. (2010) observed a positive correlation with with rainfall (r = -0.207) and evening relative humidity the minimum temperature and negative correlation with (r= -0.113) (Fig. 2). Sharma et al. (2018) also reported morning RH, evening RH and rainfall. that mean temperature had a positive relationship. th Khan and Misra (2003) obtained a positive correlation The occurrence of L. acuta commenced from 4 nd between minimum and maximum temperature. week of September (42 SMW- 0.67/ 10 sweep nets) and attained its peak on 47th SMW (14.67/ 10 sweep The incidence of N. virescens started on fourth nets) (Fig. 1). Girish et al. (2012) observed that it week of August (35th SMW- 2/ 10 hills), which reached appeared during the reproductive stage, while Parwez maximum of 15.67/ 10 hills during fourth week of et al. (2012) reported it from 15th week crop stage and October (43rd SMW); this decreased later to 2.67/ 10 remaining throughout. Kalita et al. (2015) also reported hills on 47th SW. These results corroborate with those its maximum incidence during the milking stage. Fig. of Kakde et al. (2015) who observed it from the first 2 reveals that its incidence had a significant negative week of September up to the fourth week of October. correlation with evening relative humidity (r = - Sawai and Kothikar (2019) observed its peak during 0.642**), rainfall (r = - 0.428), maximum temperature (r fourth week of October. The correlation coefficients of = - 0.613**) and minimum temperature (r = - 0.850**); the incidence revealed a significant negative correlation and it was a positive non-significant one with morning with rainfall (r = - 0.457) and evening relative humidity relative humidity (r = 0.217). These results agree with (r = - 0.540); and it was a non-significant negative one those of Parwez et al. (2012) who reported a negative 4 Indian Journal of Entomology 83(2021) Online published Ref. No. e20202 correlation of maximum temperature and wind velocity. dorsalis (Hood) and aphid, Aphis gossypii (Glover). Journal of Gupta et al. (2018) and Sharma et al. 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(Manuscript Received: July, 2020; Revised: September, 2020; Accepted: September, 2020; Online Published: December, 2020) Online published (Preview) in www.entosocindia.org Ref. No. 20202