Population dynamics of aphid, Aphis craccivora Koch and their natural enemies in Indian bean

Introduction

Indian bean, Lablab purpureus (L.) Sweet, belongs to the Fabaceae family of pulse crops (Deka & Sarker, 1990) [4] . The cultivation of Indian beans originated in India and subsequently spread to other regions of South Asia, Southeast Asia, Africa and various tropical countries (Raghu et al., 2018) [8] . It is a twining plant with trifoliate, alternating leaves and widely variable pods and seeds in size and colour (Guretzki & Papenbrock, 2014) [5] . Indian beans are mostly grown for their delicate pods but are also grown as fodder or green manure crops (Morris, 1999) [7] . The crop offers a dense green cover which serves a dual purpose it protects the soil against desiccation and acts as a source of natural manure (Kimani et al., 2012) [6] . In Gujarat, the crop is invaded by several insect pests viz., pod borer, Ettiella zinckenella (Treitschke), Bihar hairy caterpillar, Spilosoma oblique Walker, Maruca vitrata (Fabricius) and Helicoverpa armigera (Hubner), aphid, Aphis craccivora Koch, jassids, Empoasca fabae (Harris) and Empoasca kerri Singh-Pruthi, whitefly, Bemisia tabaci (Gennadius) (Vaidik et. al., 2021) [11] . Aphid, A. craccivora causes 20 to 40 per cent yield loss in cowpea (Singh & Allen, 1980) [9] . Due to their fast multiplication, within a few days, aphids usually cover the entire surface of apical shoots and with the result of continuous feeding by such a large population yellowing, curling and subsequent drying of leaves take place, which ultimately leads to the formation of weak pods and undersized grain in the pods and decreased yield (David & Kumaraswami, 1982) [3] . Hence, the present investigation of population dynamics in Indian bean is crucial for predicting outbreaks and assessing the impact of environmental factors, natural predators, and human interventions on pest behavior and reproduction. Through this analysis, researchers can develop targeted pest control IPM strategies that minimize crop losses, reduce reliance on chemical pesticides, and promote ecological balance and sustainable farming practices.

Materials and Methods

The present experiment was conducted at the research farm of the Anand Agricultural University, Anand, Gujarat during kharif-rabi 2023-24. The Indian bean variety Gujarat Navsari Indian Bean 22 (GNIB 22) was sown at 60 × 30 cm spacing. The crop was sown on September 05, 2023. The experimental plot was kept free from the application of any insecticides. The entire plot was divided into four equal size (6.0 × 6.0 m) sectors. To record observations on population of aphid, five plants were randomly selected from each sector. From each selected plant, three 10 cm long twigs were selected and the number of aphids were counted. Based on this, number of aphids/10 cm long twig were worked out. The observations on aphid population were recorded at weekly intervals starting from one week after the germination of the crop and continued up to the termination of the crop. While recording observations of aphids, observation on the population of natural enemies Coccinellids and chrysopids were also recorded. Based on this, the mean population of natural enemies per plant was worked out. A simple correlation was worked out between population of aphid as well as natural enemies and weather parameters. The data on weather parameters were obtained from the meteorological observatory located at Anand Agricultural University, Anand, Gujarat.

Results and Discussion Population Dynamics of Aphid

The data on the aphid population are presented in Table 1, which indicate that the infestation initiated in the second week after sowing i.e., the third week of September (39 th SMW) and continued up to the termination of the crop in the second week of January i.e., 17 th week after sowing (2 nd SMW). Overall, the population ranged from 5.9 to 26.8 aphids per 10 cm twig. The population exhibited an increasing trend from the second week after sowing i.e., the third week of September (39 th SMW) to the eighth week after sowing i.e., the first week of November (45 th SMW). The highest population of aphid (41.8 aphids/twig) was recorded during the eighth week after sowing i.e., the first week of November (45 th SMW). Thereafter, the population declined to 29.5 aphids/twig in the ninth week after sowing i.e., the second week of November (46 th SMW). During the third week of November (47 th SMW), the aphid population increased to 34.90 aphids/twig. During the fourth week of November (48 th SMW), the population declined to 13.39 aphids/twig. Thereafter, there was a gradual increase in the population till the 13 th week after sowing i.e., the second week of December (50 th SMW) i.e., 22.80 aphids/twig. In the subsequent week (51 st SMW) there was slight decline in the population (20.67 aphids/twig). After this week, the aphid population again increased in the 15 th week after sowing i.e., the 4 th week of December (52 nd SMW) and reached 31.60 aphids per twig. In the following two weeks, the aphid population exhibited a declining trend. The aphid population showed four distinct peaks i.e., 45 th SMW (41.80 aphids/twig), 47 th SMW (34.90 aphids/twig), 50 th SMW (22.80 aphids/twig) and 52 nd SMW (31.60 aphids/twig). The above results are in agreement with Dalwadi et al. (2007) [2] , who reported that A. craccivora remained active from mid-November to the end of March. Bhagora (2019) [1] also reported that the population of aphid was at its peak during the first week of November. Thus, the present findings are more or less in agreement with the reports of above workers.

Correlation with weather parameters

The correlation coefficient values between the population of A. craccivora and weather parameters were computed to ascertain their influence on the population build-up. The correlation coefficient values are presented in Table 2, which indicated that the aphid population had a highly significant negative correlation with minimum temperature (r = -0.667), morning vapour pressure (r = -0.693) and evening vapour pressure (r = -0.820). Morning relative humidity (r = -0.561), evening relative humidity (r = -0.605) and rainfall (r = -0.560) showed a significant negative correlation, whereas maximum temperature (r = -0.068) and wind speed (r = -0.226) showed a non-significant negative correlation with aphid population. Bright sunshine hours (r = 0.455) exhibited a non-significant positive correlation with the aphid population in Indian bean. [2] reported that minimum temperature and vapour pressure showed a significant negative association with the aphid population, whereas sunshine hours exhibited positive correlation with the aphid population. Bhagora (2019) [1] also reported negative correlation between aphid population and maximum temperature, minimum temperature, morning vapour pressure and evening vapour pressure, while the bright sunshine had a non-significant positive correlation with aphid population. Vaidik and Patel (2022) [10] found that minimum temperature, morning and evening vapour pressure had a highly significant negative correlation with aphid population, whereas maximum temperature, morning and evening relative humidity had a negative correlation with aphid population. Thus, the above reports are in conformity with the present findings. rainfall (r = -0.021). Additionally, there existed a nonsignificant positive correlation between Chrysopids population and bright sunshine (r = 0.274) as well as maximum temperature (r = 0.248). According to Bhagora (2019) [1] , minimum temperature, morning vapour pressure, morning relative humidity and evening vapour pressure exhibited negative correlation with the population of chrysopids.

Correlation between Population of Aphids and Natural Enemies

The aphid population showed positive correlation with the population of Coccinellids (r = 0.533) and Chrysopids (r = 0.515), as indicated by the values given in Table 3. Very few workers have studied the correlation between population of aphids and natural enemies in Indian bean. Bhagora (2019) [1] reported a positive correlation between the aphid population and the population of coccinellids and chrysopids.

Conclusion

The infestation of aphid, A. craccivora commenced in the third week of September (39 th SMW) and persisted up to the termination of the crop in the second week of January (2 nd SMW). The population fluctuated from 5.90 to 41.80 aphids/twig with four distinct peaks. The highest population was observed i.e., 41.80 aphids per twig during the first week of November (45 th SMW). The aphid population showed a highly significant negative correlation with minimum temperature and morning and evening vapour pressures. It also had a significant negative correlation with morning relative humidity, evening relative humidity and rainfall. Coccinellid population was observed from the fourth week of September (40 th SMW) to the termination crop. The highest population was observed during the second week of December (50 th SMW). The Coccinellid population exhibited a significant negative correlation with morning vapour pressure and evening vapour pressure. The Chrysopids emerged in the first week of October (41 st SMW) and persisted till the second week of January (2 nd SMW). The Chrysopids population was highest during the first week of November (45 th SMW). There was significant negative correlation between the population of Chrysopids and evening vapour pressure.

Acknowledgement

AcknowledgmentsThe authors thank the Director of Research and the Dean of Post Graduate Studies at Anand Agricultural University, Anand for their support, resources and encouragement throughout this investigation.

References

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