Indian bean Lablab purpureus (L.) is an important pulse cum vegetable crop in India and it is also used as cattle feed. The protein content of field bean is quite high varying from 20.0 to 28.0% (Reddy et al., 2017). Insect pests are the major constraints for the productivity of Indian bean, as it is attacked by a number of insect pests viz. aphid Aphis craccivora Koch.; jassids Empoasca fabae (Harris); E. krameri Ross & Moore and E. kerri Pruthi; pod borers Etiella zinckenella (Treit.), Maruca vitrata Geyer and Helicoverpa armigera (Hubner); whitefly Bemisia tabaci (Genn.); stem fly Ophiomyia phaseoli (Tryon); Bihar hairy caterpillar Spilosoma obliqua (Wlk.) (Jakhar et al., 2017; Reddy et al., 2017). For development of successful IPM strategies, detailed information on the population buildup in particular the influence of weather factors is of great significance. This information will be helpful in preferring predictive models in forecasting the pest outbreaks. Hence, this study on the population dynamics of major pests of Indian bean.

Study was carried out at the College Farm, N M College of Agriculture, Navsari Agricultural University, Navsari, Gujarat during 2019-20. The Indian bean variety GNIB-22 was sown on 22^nd October 2019 in 400 m² area. All the recommended post-sowing agronomical practices were followed except the plant protection. Observations were recorded at an interval of seven days starting from one week after germination till harvesting from five randomly selected plants from each of five quadrates. Aphid population was recorded on three randomly selected twigs (about 10 cm long) from each tagged plant and mean number of aphids/ twig were counted. Jassid and whitefly were counted from three leaves (from top, middle and bottom), while that of thrips was assessed by shaking flowers with twigs over a white paper and counting thrips fallen on the paper piece. Number of pod borer H. armigera and M vitrata larvae were recorded and mean number of larvae/ plants was calculated. The data on weather parameters obtained from the Agricultural Meteorological observatory, Department of Meteorology, Navsari Agricultural University, Navsari were utilized for computing correlation coefficients.

The results obtained revealed that the incidence of aphid Aphis craccivora commenced from 2^ndweek after sowing (WAS) i.e. 2^nd week of November (46^th SMW) and persisted till 1^st week of February (6^th SMW, 14^th WAS); and ranged from 1.94 to 25.27 aphids/ twig of 10 cm, and their incidence increased from 8^th WAS to reach its peak during 10^th WAS (2^nd SMW- 25.27 aphids/ twig) (Fig. 1). The relationship with weather factors revealed that maximum temperature (r=-0.782**), minimum temperature (r=-0.726**), morning vapour pressure (r=-0.775**) and evening vapour pressure (r=-0.738**) exhibited highly significant negative correlation; while, wind speed (0.546*) had a significant positive correlation and morning relative humidity- RH (-0.539*) had a significant negative correlation (Table 1). These results agree with those of Chaudhary et al. (2016) on the seasonal incidence. Dalwadi et al. (2007) stated that minimum and mean temperature and vapour pressure showed significant negative association with aphids, while RH, sunshine hours and wind speed correlated positively.

The activity of jassid E. kerri started from of 2^nd WAS i.e. 2^nd week of November (46^th SMW) and persisted till 1^st week of February (6^th SMW, 14^th WAS) with peak (8.20 jassids/ leaf) during 4^thweek of December (52^nd SMW, 8^th WAS). There was a significant negative correlation with maximum temperature (r= -0.632*), minimum temperature (r=-0.556*) and morning RH (r=-0.537*) (Fig. 1; Table 1). Dalwadi et al. (2007) reported that RH had significant negative correlation with jassids. Singh et al. (2019) revealed that jassid, Empoasca motti incidence had a negative correlation with maximum and minimum temperature, RH and rainfall. With whitefly B. tabaci, the incidence was found to commence from of 2^nd WAS i.e., 2^nd week of November (46^th SMW) and persisted till 1^st week of February (6^th SMW, 14^th WAS) with peak (7.12 whiteflies/ leaf) during 4^th week of December (52^nd SMW, 8^th WAS). Correlation coefficients with weather parameters showed significant negative correlation with maximum temperature (r= -0.594*) and morning RH (r=-0.541*) (Fig. 1; Table 1). Marabi et al. (2017) observed that whitefly exhibited significant positive correlation with maximum and minimum temperature, morning and evening vapour pressure and evaporation in soybean; whereas, negative correlation was observed with morning RH % during rabi season. The activity of thrips M. distalis started from of 4^th WAS i.e. 4^th week of November (48^th SMW) and persisted till 2^nd week of February (6^th SMW, 14^th WAS) with peak (10.35 thrips/ flower) during 1^st SMW (9^th WAS). Its incidence exhibited a highly significant negative correlation with the maximum temperature (r=-0.830**), minimum temperature (r=-0.727*) and morning vapour pressure (r=-0.669*), ehile, evening vapour pressure (r=-0.565*) showed significant negative correlation (Fig. 1, Table 1).

The larvae of H. armigera appeared starting 2^nd week of November (46^th SMW, 2^nd WAS) with 0.83 larva/ plant and remained on the crop till 1^st week of February (6^th SMW, 14^th WAS); maximum counts were during 2^nd week of January (2^nd SMW) i.e. 5.80 larvae/ plant. Maximum temperature (r= -0.644*), minimum temperature (r= -553*), morning RH (r=-0.535*) and morning vapour pressure (r=- 543*) were found to exhibit a significantly negative correlation with H. armigera (Fig. 1; Table 1). These results are in agreement with those of Rashmi et al. (2019), who reported that the highest infestation of this pest was found during the month of December and January and reported a significant negative association with maximum temperature. Chavan et al. (2020) and Dindor et al. (2020) revealed that H. armigera exhibited significant negative correlation with RH. Maruca vitrata incidence was observed from 2^nd week of November (46^th SMW, 2^nd WAS) with 0.63 larva/ plant and remained till 1^st week of February (6^th SMW, 14^th WAS); maximum counts were observed during 2^nd week of January (2^nd SMW- 7.21/ plant; the incidence was showing a highly significant negative correlation with maximum temperature (r= -0.701**), while, minimum temperature (r=-570*), morning RH (r=-0.534*) and morning vapour pressure (r=-593*) exhibited a significantly negative correlation (Fig. 1, Table 1). These results are in agreement with those of Rashmi et al. (2019), who observed that M. vitrata was found in large numbers during December and January; and maximum temperature, minimum temperature and evaporation showed significant negative correlation.

Significant at p=0.01 (r=± 0.66);

Significant at p=0.05 (r=± 0.53)

References