Population dynamics and weather associations of major sucking insect pests on chilli (Capsicum annuum L.) under open-field conditions

Introduction

Chilli (Capsicum annuum L.) is amongst the most economically significant vegetable and spice crops in the world, prized for both for its culinary versatility as well as for its bioactive compounds (capsaicinoids and flavonoids). It supports a global market for chilli and pepper with an estimated value of USD 1.3 billion in 2025 (Ali et al., 2025) [1] . India cultivated 965,612 ha of dry chilli (Capsicum spp. and Pimenta spp.) with a total production of 2,909,844 tonnes and an average productivity of 3,013.5 kg/ha. In contrast, green chilli employed 479,679 hectares, producing 5,317,989.29 tonnes with a significantly higher average productivity of 11,086.6 kg/ha (FAOSTAT, 2024). Millions of smallholder farmers in the tropics and subtropics relies on the chilli production of for their livelihoods, so even slight, recurrent losses in fruit quality or yield leads to significant economic losses at the farm and national levels. Insect pests remain one of the major yield-limiting biotic factors on Chilli (Yadav et al., 2022) [8] . sap-sucking pests, aphids, thrips, and whiteflies, together with boring pests like pod or fruit borer, cause injury to crops, and their populations exhibit seasonal fluctuations in accordance with the abiotic factors (Borgohain et al., 2024; Kumar et al., 2020) [9,10] . Worldwide, a significant amount of potential crop production is already thought to be damaged by insect pests (Oerke, 2006) [5] , and this pressure is anticipated to surge in the coming decades in response to rising temperatures and changing rainfall patterns (Deutsch et al., 2018) [2] . Understanding pest responses to abiotic factors is essential for developing reliable, locally adapted pest forecasting and integrated pest management (IPM) strategies, rather than merely describing pest occurrence. Characterizing pestweather relationships with a systematic approach involves weather-associated population monitoring throughout standard meteorological weeks and correlating pest population with weather data. Research on sucking pests in chilli and related solanaceous crops report that different pest species under the same weather conditions may respond in varied, sometimes in opposite ways (Khatun et al., 2023) [3] . This heterogeneity in response to weather conditions necessitates pest-and location-specific weather correlation investigations to improve forecasting precision, rather than relying on generalized assumptions. Although the observations of the present study were recorded a decade ago, the sustained significance of such systematically documented dataset is evident as it provides a valuable historical baseline for understanding pest and weather relationships. As regional climates continue to change, the temperature and humidity thresholds for pest outbreaks are estimated to change in chilli crop, demanding a strong historical baseline for assessment with future observations (Lawton et al., 2022) [4] . Furthermore, varying pest groups react differently to transient weather changes and prolonged host-plant phenology, suggesting that climate change may enhance certain pest populations higher than others. Consequently, it is vital to retain previously quantified information of pest weather interactions as baseline for future studies. The study analysed the population dynamics of major sucking insect pests viz., aphid, thrips, whitefly affecting chilli (Capsicum annuum L.) cv. Commando under open field conditions during Rabi cropping season. It aims to characterize seasonal population dynamics, evaluate relationships with abiotic factors and identify the key weather predictors for each pest utilizing simple linear regression. This will establish a quantitative reference dataset for weather-based pest advisories on chilli, pliable to changing regional climatic conditions.

Materials and Methods

Experimental site

The experiment was conducted at the Vegetable Research Centre (VRC), G.B. Pant University of Agriculture & Technology, Pantnagar, U. S. Nagar, Uttarakhand, India, during the 2015-16 Rabi season.

Observations on insect pest incidence and meteorological data

Population dynamics of the major sucking insect pest namely aphids (Aphis gossypii), thrips (Scirtothrips dorsalis), and whiteflies (Bemisia tabaci) were recorded at fortnight interval from transplanting until the final harvest of the crop. Counts of insects per five leaves from five randomly selected plants were taken and then expressed as the mean number of insects per leaf. Related meteorological data were procured from the Department of Meteorology, G.B. Pant University of Agriculture and Technology, Pantnagar, U.S. Nagar, Uttarakhand, India, for further correlation and regression analysis.

Statistical analysis

To determine significant differences between Standard Meteorological Weeks (SMWs), the data on the population dynamics of sucking insect pests on chilli were assessed using analysis of variance (ANOVA). The treatment means for each insect species were compared using the critical difference (CD) test at the 5% level of significance. The Pearson's correlation analysis was employed to assess the interaction between seven abiotic weather parameters and pest populations, while simple linear regression analysis was utilised to evaluate the influence of individual weather parameters on the population of sucking insect pests under open field conditions.

Results

Population dynamics of sucking insect pests in chilli under open field conditions

The populations of aphids, thrips, and whiteflies showed noticeable seasonal fluctuations during the study period (Table 1). The population of aphids varied from 0.23 to 1.77 aphids/leaf, with an overall mean of 0.98±0.51 aphids/leaf. The population of aphids was lowest during the 46 th Standard meteorological week (SMW) (0.23 aphids/leaf), then increased gradually through the cropping season, and attained a peak during the 2 nd SMW (1.77 aphids/leaf). Next, the population of aphids declined continuously to 0.63 aphids/leaf by the 10 th SMW.

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A similar pattern was observed for thrips. The population varied from 0.29 to 1.32 thrips/leaf, with a mean population of 0.73±0.38 thrips/leaf. The lowest population was recorded during the 46 th SMW (0.29 thrips/leaf), after which it increased gradually peaking at 1.32 thrips/leaf during the 2 nd SMW. Thereafter, the thrips population declined steadily, reaching 0.43 thrips/leaf by the 10 th SMW. However, whitefly populations were comparatively lower throughout the study period, ranging from 0.04 to 0.69 whiteflies/leaf, with an overall mean of 0.30±0.23 whiteflies/leaf. The minimum population was recorded during the 4 th SMW (0.04 whiteflies/leaf), whereas the maximum population (0.69 whiteflies/leaf) occurred during the 2 nd SMW. Following the peak population, whitefly population declined and remained low during the later observation period, reaching 0.12 whiteflies/leaf by the 10 th SMW. Overall, the populations of all three sucking insect pests exhibited a similar seasonal trend, characterized by a progressive increase from the early observation period to a peak during the 2 nd SMW, followed by a consistent decline towards the end of the observation period. Aphids attained the highest mean population, followed by thrips, whereas whiteflies remained the least abundant pest throughout the study period in chilli under open field conditions.

Prevailing weather conditions during the study period During the experimental period, the maximum temperature ranged from 17.90 to 30.40°C, while the minimum temperature varied between 4.10 to 13.40°C. The morning relative humidity remained consistently high, (86 to 95%), whereas evening relative humidity ranged from 37 to 64%. Additionally, rainfall was negligible throughout the study period, with only 2.50 mm received during 8 th SMW. The sunshine hours ranged between 2.10 to 8.40 hours per day; however, wind velocity ranged from 2.70 to 6.30 km per hour. Overall, the study period was marked by cool to moderately warm temperatures, with high morning relative humidity, negligible rainfall and moderate wind velocity and sunshine (Fig 1).

Relationship between weather parameters and pest populations Pearson's correlation analysis

Pearson's correlation analysis resulted varying relationships between major sucking insect pest populations and the prevailing weather parameters (Fig. 2). The aphid population demonstrated a significant negative correlation with maximum (r=-0.72, P<0.05) and minimum temperature (r=-0.69, P<0.05), whereas showing a significant positive correlation with morning relative humidity (r=0.67, P<0.05). Simultaneously evening relative humidity had a positively influence on aphid abundance (r=0.56), but the relationship was not statistically significant. However, thrips population exhibited marginally significant negative correlations with maximum (r=-0.62, P=0.075) and minimum temperature (r=-0.60, P=0.085), while a significant positive correlation was found with morning relative humidity (r=0.69, P<0.05). In contrast, whitefly population had a weak negative correlation with maximum (r=-0.30) and minimum temperature (r=-0.32), along with weak positive correlations with morning (r=0.54) and evening relative humidity (r=0.28); however, none of these associations were statistically significant. Moreover, Rainfall, sunshine hours, and wind velocity had negative influence on the populations of aphids, thrips, and whiteflies, although none of these correlations were statistically significant (Fig. 2). Overall, aphid and thrips populations had a significant negative influence of temperature and positively relationship with morning relative humidity, however whitefly population showed comparatively weaker and nonsignificant relationship with these weather parameters. Rainfall, sunshine hours, and wind velocity demonstrated negligible, non-significant relationship with on the populations of all three sucking insect pests (Fig. 2).

Simple Linear regression analysis

Simple linear regression analysis revealed that maximum temperature was the strongest predictor of aphid population, explaining 52.1% of the observed variation (R²=0.521, P=0.028). The negative regression coefficient (Y=-0.090x+3.157) suggested a decline in aphid population with increasing maximum temperature. Significant regression models were also obtained for minimum temperature (R²=0.482, P=0.038) and morning relative humidity (R²=0.448, P=0.049), representing negative and positive relationships with aphid population, respectively. In contrast, evening relative humidity, rainfall, sunshine hours, and wind velocity did not yield significant regression models (P>0.05). In case of thrips, morning relative humidity was the only key predictor, explaining 47.2% of the variation in thrips population (R²=0.472, P=0.041). The positive regression coefficient (Y= 0.080x-6.620) suggested a rise in thrips population with increasing morning relative humidity. Regression models for maximum temperature (R²=0.384, P=0.075) and minimum temperature (R²=0.366, P=0.085) displayed marginally significant negative associations, however evening relative humidity, rainfall, sunshine hours, and wind velocity were not significantly associated with thrips population (P>0.05). In contrast, none of the assessed weather parameters significantly predicted whitefly population (P>0.05). However, positive relationships were noted with morning and evening relative humidity and a negative relationships with maximum and minimum temperature, rainfall, sunshine hours, and wind velocity, the ability of the regression models to explain variation was low (R²=0.039 to 0.286), suggesting that these variables explained only a small proportion of the variation in whitefly population. Overall, the regression analysis revealed that maximum temperature was the strongest predictor of aphid population, however morning relative humidity best explained variation in thrips population. In contrast, none of the individual weather parameters significantly predicted whitefly population during the study period.

Discussion

The population dynamics presented in this study are broadly consistent with the general pattern documented for sucking pests of chilli and other related crops, in which aphids and thrips, and to a lesser extent whiteflies increase under the cool, humid environments of the winter (Rabi) season and decrease as temperatures rise toward crop maturity. A comparable pattern was recorded in Bangladesh for sucking insect vectors on chilli, the vectors were active during the cropping period and generally displayed positive relationship with both temperature and relative humidity (Khatun et al., 2023) [3] . In particular, whitefly populations had a negative relationship with temperature and rainfall, which is in accordance with the weak and non-significant relationships between weather parameters and whitefly population documented in the present study.

The strong negative correlation between aphid population and both maximum and minimum temperature, along with a positive correlation with morning relative humidity, aligns with the previously reported sensitivity of aphids to temperature and moisture conditions. A controlled environment study demonstrated that low relative humidity generally enhances heat tolerance in several aphid species, where high relative humidity intensifies mortality under high temperature conditions, and that responses vary between species (Yuan et al., 2026) [6] . These results provide a probable physiological justification for the higher aphid population recorded during the relatively cooler, more humid weeks (50 th to 2 nd SMW) and the following gradual reduction in population throughout the later weeks of the study. The positive association among thrips population and morning relative humidity, coupled with the negative relationship with maximum and minimum temperatures documented in the present study, is in agreement with the findings of Saini et al. (2023) [11] , who also reported negative relationships of thrips population with both maximum and minimum temperatures and a positive correlation with morning relative humidity in chilli, although their associations were comparatively weaker and non-significant. Similarly, Chauhan et al. (2024) [12] revealed a significant negative association between thrips population and maximum temperature and a significant positive relationship with morning relative humidity in non-Bt cotton, suggesting that relatively cooler and more humid weather may favour thrips population across different cropping systems. However, the scale and significance of these associations have been reported to vary among crops, cultivars and agro-climatic circumstances, suggesting that thrips responses to meteorological conditions are influenced by local climate. The whitefly population exhibited weak negative relationships with maximum and minimum temperatures and weak positive associations with morning and evening relative humidity; none of these relationships were statistically significant. A similar pattern was reported in BT cotton (Kataria et al., 2019) [13] and mung bean (Manish et al., 2026) [14] , although the magnitude of the relationship varied among studies. Similar trends have also been reported in bhendi, where incidence of sucking pest was in negative relationship with temperature and in a positive relationship with relative humidity, although again, the magnitude of these relationships varied (Prasad et al., 2026) [15] . However, contrasting associations have also been reported in chilli and other vegetable crops, indicating that crop, season and agro-climatic conditions may differentially influence whitefly population. Therefore, the absence of significant correlations in the present study suggests that abiotic factors alone were insufficient to explain whitefly population dynamics and that additional factors, such as crop phenology, host plant attributes and other biotic factors, may also contribute to its seasonal abundance. Taken together, the current results indicate that the major sucking insect pests of chilli vary in their reaction to prevailing weather parameters. The temperature and morning relative humidity exhibited the strongest influence on aphids, while thrips population had major influence by morning relative humidity. In contrast, whitefly population displayed relatively weak and non-significant associations with the measured abiotic factors, indicating that its population dynamics is likely controlled by additional crop phenology and biotic factors. These results have significant implications for the development of pest forecasting models using weather variables, suggesting that temperature and relative humidity may serve as valuable indicators for forecasting aphid and thrips outbreaks, however, weather variables alone may be insufficient for predicting whitefly incidence. Given the estimated effects of climate change on insect pest dynamics (Deutsch et al., 2018) [2] and the considerable yield losses caused by insect pests worldwide (Oerke, 2006) [5] , long-term field studies will be vital for developing forecasting models and reinforcing integrated pest management approaches in chilli cultivation under open field conditions.

Conclusion

The present study revealed that populations of major sucking insect pests of chilli exhibited distinct seasonal fluctuations under open field conditions. Aphids exhibited significant negative associations with maximum and minimum temperatures and a positive correlation with morning relative humidity, while thrips were primarily associated with morning relative humidity. In contrast, whiteflies showed weak and non-significant relationships with the measured weather parameters, indicating that influences beyond abiotic factors may also influence its seasonal abundance. These results suggest that temperature and relative humidity are valuable predictors for aphid and thrips incidence and may facilitate the developing weatherbased pest forecasting models. Nonetheless, forecasting whitefly incidence may require the integration of additional crop and biotic factors. Further long-term investigations will be effective for validating these associations and reinforcing integrated pest management strategies for chilli cultivation under open field conditions.

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