Seasonal incidence of major insect pests of pigeonpea in relation to weather parameters

Introduction

Pigeonpea scientifically recognized as Cajanus cajan (L.) Mill sp., is an agriculturally significant leguminous crop known by various regional names, including "red gram," "tur," or "arhar." It stands as one of India's paramount pulse crops. This versatile crop has garnered attention for its multifaceted contributions and nutritional richness. Pigeonpea stands as a nutritionally formidable crop, boasting an impressive protein content that ranges from 16.2% to 35%. It not only provides a substantial protein source but also excels in its amino acid profile, contributing substantially to dietary diversity. Its dried seeds serve as a staple food source, while both pods and immature seeds are celebrated as delectable green vegetables. The leaves and stems find their purpose as valuable fodder for livestock, and even the dry stems contribute to the provision of fuel. Beyond its immediate nutritional and culinary significance, pigeonpea exhibits its worth in sustainable agriculture. This is achieved through its exceptional capability to enhance soil fertility via nitrogen fixation. The leaf fall and the natural recycling of nutrients also play pivotal roles in this context (Sreekanth et al. 2019) [15] . Pigeonpea holds a unique position as a protein-rich staple, offering a substantial 22% protein contribution to the human diet, nearly tripling that of cereals. It also distinguishes itself with a lower fat content compared to other pulses. Commonly consumed in the form of split pulses or "Dal," pigeon pea complements cereal-based vegetarian diets in an indispensable manner. India takes the lead in pigeon pea cultivation, boasting a vast expanse of 44.29 lakh hectares, yielding a remarkable 35.69 lakh tonnes, and registering a productivity rate of 806 kg per hectare. Within India, the state of Maharashtra emerges as a focal point for pigeon pea cultivation.

The pigeon pea crop flourishes across 12.61 lakh hectares in Maharashtra, yielding an annual harvest of 8.34 lakh tonnes, with an average productivity of 800 kg per hectare. Notably, the markets of Akola, Jalgaon, Latur, and Nagpur in Maharashtra play pivotal roles in the trade and distribution of this crop, further emphasizing its regional importance. The Marathwada region within Maharashtra significantly contributes to the overall pigeon pea landscape. Covering approximately 4.56 lakh hectares, this region yields an annual production of 3.80 lakh tonnes and maintains an average productivity rate of 789 kg per hectare, as of the 2017-18 agricultural season (Anonymous 2018) [1] . Several insect pests are known to infest pigeon pea, with some posing particularly severe threats to its cultivation. Notable among these are gram Pod Borer (Helicoverpa armigera), Pod fly (Melanagromyza obtuse), Plume Moth (Exelastis atomosa) Spotted Pod Borer (Maruca vitrata) Blue Butterfly (Lampides boeticus), is among the most serious pests, causing substantial harm to both crop yield and quality. According to research by Lal et al. (1992) [8] , pigeon pea crops can suffer substantial yield losses, ranging from 60% to 90% under favorable conditions. Moreover, the damage caused by the pod fly can vary from 14.3% to 46.6%. Notably, a significant portion of this damage, around 60%, is attributed to the combined impact of Helicoverpa armigera (Hubner) and Melanagromyza obtusa (Malloch), collectively referred to as the "borer complex" (Wadasker et al. 2013) [19] . This complex of pests has posed a persistent challenge to pigeon pea cultivation. One of the prevailing issues in pigeonpea cultivation is the stagnation in yields over the past three to four decades. This stagnation can be primarily attributed to the substantial damage inflicted by insect pests, which has impeded the crop's potential for increased productivity and improved agricultural outcomes. Due to significant variations in agro-climatic conditions across different regions, pests exhibit diverse patterns in their distribution, occurrence, behavior, and the severity of crop damage they cause. Additionally, certain known and unknown factors may play a crucial role in influencing the prevalence and dominance of specific pests or pest complexes (Meena & Kanwat, 2010; Patel et al., 2009) [10,11] . Understanding the peak periods of pest infestations is essential for implementing effective pest management strategies while minimizing the use of highly toxic chemicals in agricultural fields. Considering these aspects, the current study was conducted to examine the seasonal occurrence of major insect pests of pigeonpea and their relationship with weather parameters such as rainfall, temperature, and relative humidity.

Materials and Methods

The present investigation was carried out within the premises of the experimental farm at the Department of Entomology, VNMKV, Parbhani, during the kharif seasons of 2021-22 and 2022-23. The pigeonpea variety BDN 13-41 (Godavari) was grown on an area of 100 m 2 by adopting the spacing of 90 x 30 cm following the recommended package of practices. The whole plots were exposed to natural infestation and no insecticides applied. The recording observations on population dynamics of pod borer complex and other pod bugs on plot was divided into four quadrates from each quadrate, five plants were selected randomly and tagged. The larvae of the leaf roller, Grapholita critica were recorded from vegetative to flowering stage at weekly intervals. Larval population of Helicoverpa armigera, Exelastis atomosa and M. vitrata was recorded from tagged plants in each plot at weakly intervals. For this, each tagged plant was critically examined and larval stages of the pest were counted right from flowering to harvesting stage of the pigeonpea crop. The incidence of pod fly, Melanagromyza obtuse in pigeonpea was recorded based on, 25 green pods were collected periodically from pod formation stage to till harvesting of the crop. Damaged pods were stored out by detecting the presence of maggot or pupa, tunnelled grains inside the pod and small pin hole window were recorded. The data pertaining to seasonal incidence were correlated with weather using WASP 2.0 software.

Results and Discussion

Seasonal incidence of Grapholita critica during kharif 2021-22 and 2022-23 is graphically presented in Fig. 1. During the 2021-22 season, initial observations noted larval presence during the 36 th Standard Meteorological Week (SMW) in September, with an average density of 0.88 larvae per plant. Subsequently, there was a consistent rise in larval numbers until the last SMW in October. The peak density of larvae, reaching 2.72 per plant, was observed in the last week of October (44 th SMW). During 2022-23 season, Initially, at the onset during the 36 th Standard Meteorological Week (SMW) in September, an average of 0.82 larvae per plant was observed. Following this, there was a steady increase in larval counts until the third SMW in October. The highest density of larvae, peaking at 1.98 per plant, was recorded in the third week of October (42 nd SMW). These result inline with results of Chakryavarty et al. (2017) [2] found that the activity of G.critica started during 37 th SMW and it attained peak during 41 st standard week. Ugale et al. (2020) [18] observed that population of G. critica to the extent of 1.98 larvae/plant was noticed during 42 nd SMW, respectively. Seasonal incidence of Helicoverpa armigera during kharif 2021-22 and 2022-23 is graphically presented in Fig. 1. During season 2021-22, initial observations recorded the presence of larvae at 42 nd (SMW) in October, with an average density of 0.16 larvae per plant. Subsequently, the larval population exhibited a steady increase until the fourth SMW of December. The peak larval density, reaching 4.36 larvae per plant, was observed in the third week of December (51 st SMW). In 2022-23 season, larval presence noted during the 40 th SMW in October, with an average density of 0.33 larvae per plant. The peak larval density of 4.10 larvae per plant occurred during the 52 nd SMW in December. These findings align closely with previously documented data by Keval et al. (2017) [6] and Chavan et al. (2018) [3] , who also reported a similar onset and continuation of H. armigera infestation from the 40 th to the 52 nd SMW. Chopde et al. (2020) [4] reported that the maximum infestation of H. armigera (Hubner) (18.78%) was observed in 52 nd SMW. The trends in M. vitrata larval population on pigeonpea fields during 2021-22 and 2022-23 graphically presented in Figure 02. The initial sighting of larvae occurred during the 39 th SMW in September, registering an average density of 0.18 larvae per plant. The pinnacle of larval density, at 4.12 larvae per plant, manifested during the initial week of December (49 th SMW). During 2023-24 season, initial observations recorded the presence of larvae during the 39 th SMW in September, with an average density of 0.13 larvae per plant. The peak larval density, reaching 3.80 larvae per plant, occurred during the concluding week of December (52 nd SMW). These observations are notably congruent with the findings of Rodge et al. (2019) [13] , who reported the presence of M. vitrata during the flowering stage (47 th to 48 th SMW), maintaining activity until crop maturity, with a pinnacle in population density occurring between December (49 th SMW) and January (2 nd SMW). Similarly, Sreekanth et al. (2019) [15] documented the incidence of M. vitrata during the 45 th SMW, reaching its zenith during the 50 th SMW (December 10-16), aligning with the peak flowering stage of the crop. Moreover, Ugale et al. (2020) [18] [16] , which documented the activity of the pod fly starting around the 44 th Standard Meteorological Week (SMW), reaching its peak during the 8 th SMW, with observed larval counts of 36.00 and 30.96 maggot per 50 pods. Rodge et al. (2019) [13] similarly reported the presence of the pod fly, M. obtusa, on crops during the flowering stage (47 th to 48 th SMW), persisting until maturity, and peaking between December (49 th SMW) and January (2 nd SMW). Additionally, Chopde et al. (2020) [4] observed the highest percentage infestation of M. obtusa (Malloch) at 18.38 during the 1 st SMW. The data regarding correlation coefficients between weather parameters and the leaf webber population during the 2021-22 and 2022-23 seasons are displayed in Table No. 01. The correlations between the leaf webber population on pigeonpea and various weather parameters during 2021-22, namely rainfall (r= 0.240), maximum temperature (r= 0.275), minimum temperature (r= 0.094), morning relative humidity (r= 0.301), evening relative humidity (r= 0.057), evaporation (r= 0.201), bright sunshine per day (r= 0.246), and wind velocity (r= 0.113), exhibited positive nonsignificant correlations. During the 2022-23 season, rainfall (r= 0.140), minimum temperature (r= 0.165), and morning relative humidity (r= 0.036) showed positive non-significant correlations with the leaf webber population. Conversely, evening relative humidity (r= -0.134) and wind velocity (r= -0.227) displayed negative non-significant correlations. In contrast, maximum temperature (r= 0.534), evaporation (r= 0.402), and bright sunshine per day (r= 0.500) manifested positive and significant correlations with the leaf webber population The present findings closely align with Kumar et al. (2010) [7] observations, which highlighted a positive and significant impact of water evaporation on the increase in leaf webber population. In case of H. armigera, during season 2021-22, correlation with weather parameters was like, rainfall (r = -0.513), minimum temperature (r = -0.827), evening relative humidity (r = -0.761) and wind velocity (r = -0.574) exhibited statistically significant negative correlations. Conversely, maximum temperature (r = -0.283) and morning relative humidity (r = -0.235) displayed negative correlations that were not statistically significant in relation to the H. armigera population. Additionally, evaporation (r = 0.176) demonstrated a statistically non-significant positive correlation, while bright sunshine per day (r = 0.484) displayed a significant positive correlation. During season 2022-23, the population of H. armigera on pigeonpea showed diverse correlations with distinct weather parameters. Notably, rainfall (r = -0.424), maximum temperature (r = -0.468), minimum temperature (r = -0.639) and evening relative humidity (r = -0.575) displayed statistically significant negative correlations. However, morning relative humidity (r = -0.192), bright sunshine per day (r = -0.016) and wind velocity (r = -0.194) exhibited negative correlations that were not statistically significant concerning the H. armigera population. Additionally, evaporation (r = 0.085) indicated a statistically nonsignificant positive correlation. The findings derived from this experiment align closely with previous studies conducted by Jakhar (2016) [5] , Keval et al. (2017) [6] and Chavan et al (2018) [3] . These earlier works also observed a significant negative correlation between the minimum temperature and evening relative humidity, mirroring the results obtained in the present investigation. Additionally, Shinde et al. (2017) [14] corroborated this research by noting that the larval population of H. armigera showed a negatively significant correlation with rainfall. The correlations between weather parameters and the E. atomosa population during the 2021-22 season showed, rainfall (r = -0.458), minimum temperature (r = -0.731), evening relative humidity (r = -0.641) and wind velocity (r = -0.496) exhibited statistically significant negative correlations. Conversely, maximum temperature (r = -0.354) and morning relative humidity (r = -0.142) displayed negative correlations that were not statistically significant in relation to the E. atomosa population. Additionally, evaporation (r = 0.125) and bright sunshine per day (r = 0.365) demonstrated a statistically non-significant positive correlation. During season 2022-23, it was rainfall (r = -0.476), minimum temperature (r = -0.574) and evening relative humidity (r = -0.699), exhibited statistically significant negative correlations. Conversely, maximum temperature (r = -0.205), morning relative humidity (r = -0.267) and wind velocity (r = -0.271) displayed negative correlations that were not statistically significant in relation to the E. atomosa population. Additionally, evaporation (r = 0.326) and bright sunshine per day (r = 0.193) demonstrated a statistically non-significant positive correlation. Consistent results were documented by Landge (2009) [9] , who noted that maximum temperature, sunshine, and evaporation had an adverse impact on the larval population. Similarly, Rawat et al. (2017) [12] arrived at the same conclusion. However, contrasting findings were observed by Shinde et al. (2017) [14] , who found a non-significant correlation between rainfall and the larval population of E. atomosa.

Correlations between weather parameters and the population of spotted pod borer during the 2021-22 season revealed that rainfall (r = -0.472), minimum temperature (r = -0.699), evening relative humidity (r = -0.600) and wind velocity (r = -0.492). Conversely, negative correlations were found for maximum temperature (r = -0.339) and morning relative humidity (r = -0.137), although these correlations were not statistically significant concerning the Spotted pod borer population. Furthermore, both evaporation (r = 0.085) and bright sunshine per day (r = 0.308) displayed statistically non-significant positive correlations. During season 2022-23, statistically significant negative correlations were observed for rainfall (r = -0.423), maximum temperature (r = -0.470), minimum temperature (r = -0.750) and evening relative humidity (r = -0.603). Conversely, negative correlations were found for and morning relative humidity (r = -0.184) and wind velocity (r = -0.260) although these correlations were not statistically significant concerning the Spotted pod borer population. Furthermore, both evaporation (r = 0.095) and bright sunshine per day (r = 0.111) displayed statistically non-significant positive correlations. The current study aligns with Sreekanth et al, (2019) [15] findings, highlighting a notable correlation between M. vitrata and both minimum temperature and evening relative humidity. Additionally, Tagger et al. (2019) [17] documented a positive influence of maximum temperature on the larval population. The correlations between weather parameters and the pod fly population during the 2021-22 season revealed that rainfall (r = -0.611), minimum temperature (r = -0.945), evening relative humidity (r = -0.869) and wind velocity (r = -0.571) exhibited statistically significant negative correlations. Conversely, maximum temperature (r = -0.293), morning relative humidity (r = -0.296) and evaporation (r = 0.316) displayed negative correlations that were not statistically significant in relation to the pod fly population. Additionally, bright sunshine per day (r = 0.571) demonstrated a statistically significant positive correlation. During season 2022-23, statistically significant negative correlations were observed for rainfall (r = -0.438), maximum temperature (r = -0.673), minimum temperature (r = -0.741) and evening relative humidity (r = -0.522). Conversely, morning relative humidity (r = -0.203), evaporation (r = 0.039), bright sunshine per day (r = 0.028) and wind velocity (r = -0.126) exhibited negative correlations that did not reach statistical significance concerning the pod fly population. The present findings align with earlier studies such as Keval et al. (2017) [6] , who noted a significant negative correlation between the maximum incidence of M. obtusa and relative humidity. Similarly, Shinde et al. (2017) [14] found a negative correlation between maggot population and maximum temperature, a result echoed by Srinivas et al. (2019) [16] who observed significant negative correlations between pest population and various temperature and humidity variables minimum and average temperature, morning, evening, and average relative humidity.

Acknowledgement

AcknowledgementsThe authors thank Department of Entomology, College of Agriculture, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani, Maharashtra for providing facilities.

References

1. Anonymous. Annual report of research work on pulses 2017-2018. VNMKV ARS, Badnapur; 2018. p.VI.
2. Chakravarty S, Agnihotri M. Seasonal incidence and natural parasitization of leaf webber, G. critica Meyrick (Lepidoptera: Tortricidae) on pigeonpea. J Environ Ecol. 2017;35(1):128-133.
3. Chavan AP, Chavan KA, Latake SB, Kute NS, Mhase LB, Rangari PS. Incidence and damage severity of pod borer complex in pigeonpea. Int J Agric Sci. 2018;10(18):7141-7144.
4. Chopade BJ, Mehendale SK, Narangalkar AL, Desai VS, Sapkal SD. Seasonal incidence of pod borer complex of pigeonpea, Cajanus cajan (L.) Millsp. J Entomol Zool Stud. 2020;8(5):1041-1047.
5. Jakhar BL. Influence of climate change on Helicoverpa armigera (Hubner) in pigeonpea. J Agric Ecol. 2016;2:25-31.
6. Keval R, Khamoriya J, Chakravarty S, Ganguly S. Seasonal incidence of gram pod borer, Helicoverpa armigera (Hubner) and tur pod fly, Melanagromyza obtusa (Malloch) on late maturing pigeonpea in Varanasi region of Indo-Gangetic plain. J Exp Agric Int. 2017;19(1):1-8.
7. Kumar A, Nath P, Ram S, Keval R. Effect of weather factors on the population dynamics of some insect pests of pigeonpea. J Environ Ecol. 2010;28(4):2318-2320.
8. Lal C, Sharma SK, Chahota RK. Oviposition response of pod fly (Melanagromyza obtusa) on resistant pigeonpea (Cajanus cajan) selections. Indian J Agric Sci. 1992;64:658-660.
9. Landge SS, Das SB, Veda OP, Sharma HL. Study on bioefficacy of newer chemicals against pigeonpea pest complex under late sown conditions. In: National Symposium on Climate Change, Plant Protection and Food Security Interface, Bidhan Chandra Krishi Vishwavidyalaya, Kalyani, Nadia, W. Bengal; 2009. p. 59.
10. Meena NK, Kanwat PM. Studies on seasonal incidence and relative safety of pesticides against Coccinellids in okra ecosystem. J Biol Control. 2010;24(2):116-122.
11. Patel BH, Koshiya DJ, Korat DM. Population dynamics of chilli thrips, Scirtothrips dorsalis Hood in relation to weather parameters. Karnataka J Agric Sci. 2009;22(1):108-110.
12. Rawat RK, Ram K, Ganguly S, Chakravarty S. Seasonal incidence of plume moth, Exelastis atomosa (Lepidoptera: Pterophoridae) on long duration pigeonpea, Cajanus cajan; 2017.
13. Rodge VJ, Patel PS, Deb S. Seasonal abundance of pigeonpea pod borer in relation to meteorological International Journal of Advanced Biochemistry Research https://www.biochemjournal.com parameters in North Gujarat. J Agromet. 2019;21(2):224-226.
14. Shinde SV, Kadam DR, Sonkamble MM, Kadam BS. Seasonal incidence of pigeonpea pod borer in relation to weather parameters. Agric Update. 2017;12(T3):648652.
15. Sreekanth M, Ratnam M, Ramana MV. Influence of weather parameters on pod borer of pigeonpea (Cajanus cajan (L.) Millsp.). J Entomol Zool Stud. 2019;7(5):821-825.
16. Srinivas G, Kumar S, Patel NM. Seasonal abundance of pod fly, M. obtusa and seed damage on pigeonpea in relation to weather factors and cropping systems. J Entomol Zool Stud. 2019;7(1):1404-1408.
17. Taggar GK, Singh R, Cheema HK, Singh P. Relative abundance, population dynamics, and damage potential of spotted pod borer, Maruca vitrata (Fabricius) on early pigeonpea in Punjab. Int J Trop Insect Sci. 2019;39:229-234.
18. Ugale MV, Bantewad SD, Suradkar AL, Shaikh AB. Studies on population dynamics of pigeonpea (Cajanus cajan L.) pod bugs, green stink bugs & leaf webber. J Pharmacogn Phytochem. 2020;10(1):1114-1116.
19. Wadaskar RM, Bhalkare SK, Patil AN. Field efficacy of newer insecticides against pod borer complex of pigeonpea. J Food Legume. 2013;26(1&2):62-66.