Introduction
Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), commonly known as the fall armyworm (FAW), is a pest native to the tropical and subtropical Americas that has rapidly expanded its global distribution. Its remarkable ability to withstand a broad range of temperature regimes has enabled it to establish across diverse climatic and agricultural landscapes. Fall armyworm has been reported in nearly 76 countries worldwide, including 48 across Africa, 23 in Asia, and 6 in Oceania (Jing et al., Reference Jing, Huang, Li, Zhou, Ren, Li, Xing, Zhang, Xi, Bo and Liu2021). Temperature is a key abiotic factor influencing the development, reproduction, and distribution of arthropods (Haghani et al., Reference Haghani, Fathipour, Talebi and Baniameri2007; Zahiri et al., Reference Zahiri, Fathipour, Khanjani, Moharramipour and Zalucki2010). With ongoing climate change, rising temperatures are expected to accelerate insect pest development, increase generational turnover, and expand their geographic range (Kroschel et al., Reference Kroschel, Sporleder, Tonnang, Juarez, Carhuapoma, Gonzales and Simon2013; Ziska et al., Reference Ziska, Blumenthal, Runion, Hunt and Diaz-Soltero2011). Invasive pests, such as the fall armyworm, due to their high fecundity and ecological plasticity, are particularly well-positioned to exploit changing temperature regimes, potentially leading to more frequent outbreaks and intensified crop damage (FAO, 2008; Nelson et al., Reference Nelson, Bjornstad and Yamanaka2013; Yan et al., Reference Yan, Wang, Feng, Wan and Chang2017; Díaz-Álvarez et al., Reference Díaz-Álvarez, Martínez-Zavaleta, López-Santiz, Barrera, Larsen and Del-Val2021). Therefore, understanding the effects of temperature on insect pest development and reproduction is essential for forecasting their population trajectories and designing effective ecological control strategies.
Fall armyworm (Spodoptera frugiperda) was first reported in India during 2018 from the Southern regions of Chikkaballapur and South Karnataka (Ganiger et al., Reference Ganiger, Yeshwanth, Muralimohan, Vinay, Kumar and Chandrashekara2018; ICAR-NBAIR, 2018). Since its initial detection, the pest has rapidly spread across all major maize-growing zones of the country, which differ significantly in their climatic conditions. As per the Indian Institute of Maize Research (IIMR), these zones include the Northern Hill Zone (NHZ), North West Plain Zone (NWPZ), North East Plain Zone (NEPZ), Central Western Zone (CWZ), and Peninsular Zone (PZ). The temperature regimes in these regions vary widely, ranging from as low as 0 °C in the NHZ (e.g. Himachal Pradesh, Uttarakhand) to as high as 35 °C in the PZ (e.g. Telangana, Karnataka, Tamil Nadu), with intermediate ranges in zones like NWPZ (4–25 °C), NEPZ (7–28 °C), and CWZ (8–30 °C).
Despite these substantial differences in temperature, FAW has successfully established and caused significant damage to maize crops across all zones (Maruthadurai and Ramesh Reference Maruthadurai and Ramesh2019; Ankita et al., Reference Ankita, Sharma and Sharma2020; Desk, Reference Desk2020; Bharadwaj et al., Reference Bharadwaj, Mutkule, Thakre, Ingale and Jadhav2020). In light of FAW’s broad climatic adaptability, a comprehensive understanding of its temperature-dependent biology is essential for anticipating outbreaks and formulating region-specific pest management strategies in India. While previous studies have largely focused on its development under a single constant temperature, little is known about its life-history responses across a wider thermal spectrum. Investigating these responses under controlled laboratory conditions is therefore critical for accurately predicting its population fluctuations and informing effective management practices.
Life table studies, particularly those based on the age-stage, two-sex life table theory utilised in the study, provide a comprehensive assessment of an insect’s population ecology, encompassing development time, survival rate, fecundity, and population growth potential. Traditional life table methods, which focus only on females and age-specific data, fail to account for stage differentiation and male contributions, thereby limiting their utility in pest risk assessments (Chi and Su, Reference Chi and Su2006). Accurate demographic analysis and practical management of S. frugiperda necessitate collecting age-stage, two-sex life table data on its development and survival across a range of temperature regimes.
Given the rapid expansion of fall armyworm across India’s maize-producing regions and the current paucity of comprehensive demographic data under varying thermal conditions, there is a critical need to evaluate its biological performance across a wide temperature spectrum. This study aims to fill that gap by assessing the developmental, reproductive, and demographic traits of S. frugiperda reared on maize under seven constant temperature regimes ranging from 14 ± 1°C to 38 ± 1°C in controlled laboratory conditions. Utilising the age-stage, two-sex life table methodology, we quantify key parameters such as developmental duration, survival rates, fecundity and population growth metrics. The resulting data provide a robust foundation for modelling species development patterns, enhancing forecasting accuracy, and informing temperature-dependent pest management strategies under current and projected climatic scenarios.
Materials and methods
Insects and plants
The larvae of fall armyworm were collected from Maize fields at the Entomological Research Farm and Maize Experimental Area, Department of Plant Breeding and Genetics, PAU, Ludhiana (75˚51′26″E and 30˚54′35″N, 247 meters above sea level). The stock culture was maintained at 26 ± 2 °C, 65 ± 5% RH, and a 14L:10D photoperiod in a controlled environment chamber (Blue Star, New Delhi, India). To standardise physiological condition, the pest was reared on the maize for one generation prior to experimentation.
The host plant used in this study was maize hybrid PMH 13 which was grown following the recommended package and practices as detailed in PAU (2023), Package of Practices for kharif crops of Punjab, in pots as well as under field conditions.
Life table analysis
The effect of temperature on the development and survival of different stages of S. frugiperda was studied at Insect Ecology laboratory, Department of Entomology and Maize Insect Laboratory, Department of Plant Breeding and Genetics, PAU, Ludhiana during March to December, 2021 and March 2022 to May 2023. The development of S. frugiperda was studied under controlled conditions in BOD incubators set at seven constant temperatures: 14 ± 1°C, 18 ± 1°C, 22 ± 1°C, 26 ± 1°C, 30 ± 1°C, 34 ± 1°C, and 38 ± 1°C. The relative humidity (R.H.) of 65 ± 5 percent and photoperiod of 14L:10D was maintained at all temperature treatments. An HTC-18 digital thermometer–hygrometer (HTC, Mumbai, India) was placed inside the incubators to monitor and verify temperature and humidity.
The methodology was followed as per Aggarwal et al. (Reference Aggarwal, Jindal, Singh, Bhargav and Sharma2023) in which one newly laid egg mass was collected from the stock culture and placed in Petri plate (Abdos, New Delhi, India) of 2.5 cm height and 10 cm diameter with moistened cotton swabs at the respective temperature conditions (1 egg mass per replication). Each treatment was replicated five times with five Petri plates per treatment. Soft maize leaf whorls were kept in the Petri plates to ensure availability of food to neonates at the time of hatching. After hatching, 10 newly emerged neonates representing one replication were individually placed into 25-ml plastic cups (Polylab, New Delhi, India) of 3 cm height and 4.5 cm diameter, with one larva per cup (50 larvae per treatment). The food in the plastic cups was changed on regular basis to avoid any contamination in the culture. The progression of larval instars was monitored daily by examining the detached head capsules present in the cups. On cessation of feeding by the sixth instar larvae, the pupae formed were collected and sexed to distinguish between males and females. These pupae were transferred into plastic cups containing a layer of moistened sand with a circular blotting paper on it. The pupae were placed over the blotting paper to avoid direct contact with the sand and the sand was moistened as and when required to maintain favourable humid conditions. One pair was released into a glass chimney kept over 10- to 15-day-old maize seedling in an earthen pot. Cotton swabs containing 10 percent honey solution were hanged with the help of paper clip inside the glass chimney as a source of food for the adults. The observations pertaining to the biological parameters, namely, incubation period, hatchability, larval survival and duration, pupal survival and duration, adult longevity, total life cycle, and sex ratio were recorded at 24-h interval. Egg laying was observed daily and as soon as the egg laying began, the eggs along with the leaf portion on which it was present were cut with the help of scissors. Adult pre-ovipositional period (APOP, the time from adult emergence to first oviposition), total pre-ovipositional period (TPOP, the time from egg hatching to first oviposition), oviposition period and fecundity were recorded on daily basis from the initiation of oviposition till the death of the adults.
Preliminary data for all individuals across different temperatures were organised and analysed using the age-stage, two-sex life table approach using TWOSEX-MS Chart program (Chi, Reference Chi2022b). The following parameters were worked out:
a. Age-specific survival rate (lx): Age-specific survival rate is the probability that a newborn egg will survive to age x and was calculated by the following formula:
\begin{equation*}lx = \sum_m^{j = 1} Sxj,\end{equation*}where lx = proportion of individuals still alive at age X (survival value),
Sxj = probability that a newly laid egg can survive to age x and stage j.
b. Age-specific fecundity (mx): Age-specific fecundity is the number of eggs laid per individual at age x and was calculated by the formula:
\begin{equation*}mx = \frac{{\sum\nolimits_{j = 1}^m {Sxjfxj} }}{{lx}}\end{equation*}where mx = the number of female eggs produced per female in the age interval X (fecundity rate);
Sxj = probability that a newly laid egg can survive to age x and stage j;
fxj = number of hatched eggs produced by female adult at age x;
lx = proportion of individuals still alive at age X (survival value).
c. Net reproductive rate (R 0): The net reproductive rate was calculated as the total of the product of the values of ‘lx’ and ‘mx’ for the entire lifespan of the female. It is the average number of female offspring produced by a female in its lifetime and was calculated by the following formula:
\begin{equation*}{R_o}= \sum {l_x}{m_x},\end{equation*}where R 0 = net reproductive rate;
lx = proportion of individuals still alive at age x;
mx = number of female offspring produced per female at x.
d. Mean generation time (T c): The mean generation time is the approximate value of generation time (T c), i.e. the mean age of the mothers in a cohort at the birth of female offspring. It was calculated by the following formula:
\begin{equation*}T_{c} = \sum x.{l_x}.{m_x}\, / \sum {l_x}.{m_x},\end{equation*}where T c = mean length of generation;
x = age of individual (days);
lx = proportion of individuals still alive at age x;
mx = number of female offspring produced per female at x.
e. Intrinsic rate of increase (r m): To estimate the intrinsic rate of increase, the total number of individuals survived and mean no. of female offsprings birth was recorded at each age interval. It was calculated by the following formula:
\begin{equation*} \sum^{\infty}_{x = 0} {e^{ - rm(x + 1)}}{l_x}{m_x} = 1\end{equation*}where e = base of the natural logarithm;
r = intrinsic rate of increase;
lx = proportion of individuals still alive at age x;
mx = number of female offspring produced per female at x.
f. Finite rate of increase (λ): The finite rate of increase is the number of females per female per day and was calculated by the following formula:
\begin{equation*}{{\lambda }} = {\text{ antilo}}{{\text{g}}_{\text{e}}}{{\text{r}}_{\text{m}}}\end{equation*}where λ = finite rate of increase; r m = intrinsic rate of increase.
g. Doubling time (DT): Doubling time is the time taken in days by a species to double its population and was calculated by the following formula:
\begin{equation*}DT{\text{ }} = {\text{ }}ln{\text{ }}2/{r_m},\end{equation*}where DT = doubling time;
ln = natural log (e = 2.718);
r m = intrinsic rate of increase.
h. Gross Reproductive rate (GRR): Gross reproductive rate is the total number of female eggs laid per female and was calculated by the following formula:
\begin{equation*}GRR = \sum\limits_{x = 0}^\infty {mx} \end{equation*}where GRR = gross reproductive rate;
mx = number of individuals produced per female.
i. Weekly multiplication rate (WMR): The weekly multiplication rate is the no. of times the population increases in a week and was calculated by the following formula:
\begin{equation*}{\text{WMR}} = {\left( {{e^{rm}}} \right)^7},\end{equation*}where WMR = weekly multiplication rate; e = base of the natural logarithm; r m = intrinsic rate of increase.
The data on development and survival of different life stages were analysed using SPSS 20.0 software programme. The significant differences between different treatments were subjected to analysis of variance (ANOVA) with Tukey’s HSD post hoc test at p < 0.05. Using the TWOSEX-MS Chart program (Chi and Liu Reference Chi and Liu1985; Chi, Reference Chi2022b), population parameters were estimated through 100,000 bootstrap iterations to reduce variability in mean and standard error estimates due to random resampling. Statistical differences among the five temperature treatments were determined via the paired bootstrap test, with comparisons made using confidence intervals (Efron and Tibshirani Reference Efron and Tibshirani1993; Huang and Chi Reference Huang and Chi2012).
Population projection of S. frugiperda
Life table data of S. frugiperda generated at five constant temperatures (18 ± 1, 22 ± 1, 26 ± 1, 30 ± 1, and 34 ± 1°C) were utilised to project population growth and associated uncertainty using the TIMING-MS Chart program (Chi, Reference Chi2022a). Projections were conducted over a 350-day period, starting with an initial population of 10 eggs.
Results
Lie history parameters of S. frugiperda
The present study revealed that the developmental period of different life stages of fall armyworm, namely, egg, larvae, pupae, and adult decreased significantly with increase in temperature. In case of egg stage, the incubation period decreased from 7.84 ± 0.13 days at 14 ± 1°C to 1.94 ± 0.04 days at 34 ± 1°C (table 1). The total larval period was longest at 14 ± 1°C, lasting 82.75 ± 0.90 days, and shortest at 34 ± 1°C, with a duration of 8.84 ± 0.24 days. At 14 ± 1°C, the last instar larvae failed to complete their development into the pupal stage. The fastest pupal development was observed at 34 ± 1°C, taking 7.25 ± 0.14 days, while the slowest, 29.89 ± 0.55 days, was recorded at 18 ± 1°C. The longevity of adult males decreased steadily with higher temperatures, lasting 10.71 ± 0.43 days at 18 ± 1°C and 5.35 ± 0.25 days at 34 ± 1°C. A similar trend was observed in case of female longevity. As temperature increased from 18 ± 1°C to 34 ± 1°C led to a steady reduction in female longevity, observed as 12.75 ± 0.25, 13.50 ± 0.50, 10.25 ± 0.25, 11.24 ± 0.49, and 9.55 ± 0.30 days. Female longevity was greater than that of males at all temperatures tested. In case of sex ratio, the females were dominant in the population, with the M:F ratio observed between 1:1.25 and 1:1.76. Total developmental period of S. frugiperda on maize decreased from 83.96 ± 0.90 days at 18 ± 1°C to 24.52 ± 0.41 days at 34 ± 1°C.
Effect of different constant temperatures on developmental stages of Spodoptera frugiperda
CD = critical difference at 5 % level of significance.
* Mean of five replications.
** Development was not completed by S. frugiperda at the respective temperature.
Mean within column followed by different lowercase letters (a-f) are significantly different (at p < 0.05, Tukey’s HSD Post Hoc test).
Reproductive parameters of S. frugiperda
The variations in constant temperature regimes were observed to significantly impact the different reproductive parameters of fall armyworm on maize. The APOP decreased from 5.13 ± 0.08 days at 18 ± 1°C to 2.17 ± 0.09 days as the temperature increased to 34 ± 1°C (table 2). The TPOP significantly varied across all the temperatures. The longest TPOP of 78.13 ± 1.66 days was recorded at 18 ± 1°C and shortest of 20.08 ± 0.83 days at 34 ± 1°C. The oviposition period significantly decreased with increasing temperature. Longest oviposition period of 6.23 ± 1.56 days was recorded at 18 ± 1°C which declined to 3.21 ± 0.80 days at 34 ± 1°C. Fecundity varied significantly in response to the temperatures under study. Maximum fecundity of 1010.19 ± 18.85 eggs/female was recorded at 30 ± 1°C, which was not significantly different from 952.37 ± 27.44 eggs/female at 26 ± 1°C. Minimum fecundity of 466.46 ± 9.89 days was recorded at 18 ± 1°C.
Effect of different constant temperatures on the reproductive parameters of Spodoptera frugiperda on maize
CD = critical difference at 5% level of significance; APOP = adult pre-ovipositional period; TPOP = total pre-ovipositional period (from egg to first oviposition).
* Mean of five replications.
Mean within column followed by different lowercase letters (a-e) are significantly different (at p < 0.05, Tukey’s HSD post hoc test).
The age-stage specific survival rate (Sxj) of S. frugiperda on maize was markedly influenced by temperature as shown in fig. 1. Development at 18 ± 1°C proceeded slowly, with extended durations of immature stages and substantial temporal overlap. The egg stage exhibited the longest duration (9 days) among all tested temperatures, which was associated with lower survival rates and a noticeably flattened survival curve. Higher temperatures, particularly 26 ± 1°C (Pupae: 78%; male: 21%; female: 44%) and 30°C (Pupae: 88%; male: 26%; female: 53%) supported more synchronised development and higher survival rates, as indicated by tall, narrow survival peaks and minimal stage overlap. However, at 34 ± 1°C, elevated thermal stress led to increased mortality in early instars and pupae, resulting in a sharp decline in survival. The age-specific survival rate (lx), fecundity (mx), and maternity (lxmx) curves of S. frugiperda reared on maize at different temperatures are shown in fig. 2. The most optimal survival was observed at 26 ± 1°C, where the lx curve was steep and well-defined, indicating synchronised development and high survival through the immature stages. At 30 ± 1°C, the survival pattern remained favourable but showed a slight increase in early mortality compared to 26°C. Also, highest fecundity was recorded at 26 ± 1°C (157.44 eggs on day 33) followed by 30 ± 1°C (119.42 eggs on day 26). Thermal extremes of 18 ± 1°C and 34 ± 1°C resulted in significant reductions in both survival and fecundity, with 22 ± 1°C yielding intermediate outcomes as depicted in fig. 2.
Age-stage specific survival rate (S xj) of S. frugiperda on maize at a) 18 ± 1oC; b) 22 ± 1oC; c) 26 ± 1oC; d) 30 ± 1oC; e) 34 ± 1oC.
Age-specific survival rate (l x) of S. frugiperda on maize at a) 18 ± 1°C; b) 22 ± 1°C; c) 26 ± 1°C; d) 30 ± 1°C; e) 34 ± 1°C.
The life expectancy (exj), which denotes the average duration an individual of age x and stage j, is expected to live after reaching age x, showed an inverse relationship with temperature in the case of the fall armyworm, decreasing from 51.54 percent at 18 ± 1°C to 17.01 percent at 34 ± 1°C (fig. 3).
Age-stage-specific life expectancy (E xj) of S. frugiperda on maize at a) 18 ± 1°C; b) 22 ± 1°C; c) 26 ± 1°C; d) 30 ± 1°C; e) 34 ± 1°C.
The age-stage reproductive value (vxj) represents the contribution of an individual of age x and stage j to future population growth, and is a key parameter in population forecasting (fig. 4). The age-stage reproductive value (vxj) exhibited a sharp increase following female adult emergence, with a positive trend observed as temperature rose from 18 ± 1 °C to 30 ± 1 °C. A subsequent temperature increase to 34 ± 1 °C led to a noticeable decline in the reproductive value (vxj) of fall armyworm. The maximum value of 604.79 was recorded on day 24 at 30 ± 1 °C, followed by 565.35 on day 31 at 26 ± 1 °C.
Age-stage reproductive value (V xj) of S. frugiperda on maize at a) 18 ± 1°C; b) 22 ± 1°C; c) 26 ± 1°C; d) 30 ± 1°C; e) 34 ± 1°C.
Population parameters of S. frugiperda
The constant temperatures significantly influenced the population parameters. The net reproductive rate (R 0) showed a significant increase as the temperature rose from 18 ± 1°C to 30 ± 1°C but declined when the temperature reached 34 ± 1°C (table 3). The maximum net reproductive rate (R 0) of 499.91 ± 20.71 females/female was recorded at 30 ± 1°C which was not significantly different from 467.32 ± 15.85 females/female at 26 ± 1°C. The mean generation time (T c) varied significantly at all constant temperatures. The maximum mean generation time (T c) of 80.31 ± 1.70 days was recorded at 18 ± 1°C which declined to 46.80 ± 0.83, 33.73 ± 1.14, 26.52 ± 1.10 and 21.77 ± 0.90 days with increase in temperature to 22 ± 1, 26 ± 1, 30 ± 1 and 34 ± 1°C, respectively. The intrinsic rate of increase (r m) was highest at 30 ± 1°C (0.25 ± 0.01 females/female/day), followed closely by 0.24 ± 0.01 females/female/day at 26 ± 1°C. Similarly, the finite rate of increase (λ) increased progressively from 18 ± 1°C, peaking at 1.28 ± 0.05 day−1 at 30 ± 1°C, followed by a slightly lower value of 1.26 ± 0.05 day−1 at 26 ± 1°C, before declining at higher temperature. The shortest doubling time (DT) was observed at 30 ± 1°C (2.84 ± 0.12 days), which was not significantly different from 2.96 ± 0.12 days at 26 ± 1°C. Gross reproductive rate (GRR) and weekly multiplication rate (WRR) followed the same trend, peaking at 30 ± 1°C with values of 858.41 ± 29.11 offspring and 5.64 ± 0.23, respectively, before declining at 34 ± 1°C.
Effect of different constant temperatures on population growth parameters of Spodoptera frugiperda on maize
CD = critical difference at 5% level of significance.
* Mean of five replications.
Mean within column followed by different lowercase letters (a-e) are significantly different (at p < 0.05, Tukey’s HSD post hoc test).
Population projection of S. frugiperda
The stage structure of S. frugiperda, plotted as log(Nt + 1), reflects population dynamics and generational turnover from an initial cohort of 10 eggs under five constant temperatures (fig. 5). Temperature significantly influenced both the rate of population growth and the number of generations completed. At 34 ± 1°C, approximately seven generations were observed over a simulation period of 350 days, suggesting moderate population buildup with signs of thermal stress. Lower temperatures, 22 ± 1°C and 18 ± 1°C, supported seven and four generations, respectively, due to extended development periods. In contrast, rapid growth occurred at 26 ± 1°C and 30 ± 1°C, with nine and eight generations completed annually. The stage-specific growth rates of S. frugiperda over time exhibited cyclical patterns indicative of successive generations (fig. 6). Positive growth rates represent an increase in stage abundance from time t to t + 1, while negative rates reflect stage decline due to progression or mortality. Lower temperatures (18 ± 1°C and 22 ± 1°C) resulted in extended and asynchronous development across stages, whereas intermediate temperatures (26 ± 1°C and 30 ± 1°C) facilitated rapid, and more uniform progression. At 34 ± 1°C, stage peaks were reduced and irregular compared to other temperatures. Among the tested regimes, the intrinsic rate of increase was highest at 30 ± 1°C, followed by 26 ± 1°C.
Population projection of S. frugiperda reared on maize with an initial population of ten eggs at a) 18 ± 1°C; b) 22 ± 1°C; c) 26 ± 1°C; d) 30 ± 1°C; e) 34 ± 1°C.
Stage growth rate of S. frugiperda reared on maize with an initial population of ten eggs at a) 18 ± 1°C; b) 22 ± 1°C; c) 26 ± 1°C; d) 30 ± 1°C; e) 34 ± 1°C.
Discussion
Temperature significantly influences insects’ growth, development, reproduction, distribution, and population dynamics (Li et al., Reference Li, Feng, Huang, Zhong, Tian, Qiu and Huang2017). Within a favourable temperature range, rising temperatures tend to accelerate insect growth and development. However, when temperatures exceed or fall below this optimal range, their growth and development are adversely impacted (Lu et al., Reference Lu, Wu, Wyckhuys and Cuo2009). In the present study, temperature significantly affected the duration of all immature stages of S. frugiperda. A clear inverse relationship was observed between temperature and the duration of egg, larval, and pupal stages. The incubation period decreased from 7.84 days at 14 ± 1°C to 1.94 days at 34 ± 1°C, consistent with the observations of Du Plessis et al. (Reference Du Plessis, Schlemmer and Van den Berg2020), Huang et al. (Reference Huang, Xue, Chen, Guo, Tang, Zhong and He2021), and Ashok et al. (Reference Ashok, Balasubramani, Kennedy, Geethalakshmi, Jeyakumar and Sathiah2021), who reported shortened egg development durations with increasing temperatures in case of fall armyworm. In our study, no egg hatching was observed at 38 ± 1°C. The failure of eggs to hatch at this temperature may be attributed to factors such as desiccation, thermal stress and metabolic disruption (Maharjan et al., Reference Maharjan, Hong, Ahn, Yoon, Jang, Kim and Yi2023). The duration of S. frugiperda larval development sharply decreased with increasing temperature from 82.75 days at 14 ± 1°C to 8.84 days at 34 ± 1°C, supporting earlier reports of temperature-driven developmental acceleration (Busato et al., Reference Busato, Grützmacher, Garcia, Giolo, Zotti and Bandeira2005; Sarkar et al., Reference Sarkar, More, Tamboli, Kulkarni and Nimbalkar2021; Malekera et al., Reference Malekera, Acharya, Mostafiz, Hwang, Bhusal and Lee2022). This is likely due to enhanced metabolic activity of digestive enzymes like invertase, α-amylase, elastase, chymotrypsin, total protease, aminopeptidase, and trypsin at higher temperatures (Bale et al., Reference Bale, Masters, Hodkinson, Awmack, Bezemer, Brown, Butterfield, Buse, Coulson, Farrar and Good2002; Dixon et al., Reference Dixon, Honěk, Keil, Kotela, Šizling and Jarošík2009; Akbar et al., Reference Akbar, Pavani, Nagaraja and Sharma2016; Sharifloo et al., Reference Sharifloo, Zibaee, Sendi and Jahroumi2016; Sharifloo et al., Reference Sharifloo, Zibaee, Sendi and Jahroumi2017; Kamel et al., Reference Kamel, Gamil and Dahi2018; Lazarevic et al., Reference Lazarevic, Milanovic, Seslija Jovanovic and Jankovic-Tomanic2023), while lower temperatures slow development due to reduced feeding efficiency (Amarasekare and Sifuentes, Reference Amarasekare and Sifuentes2012). The consistent observation of six instars across all temperatures (18 to 34 ± 1°C) aligns with previous work (Bailey and Chadha, Reference Bailey and Chadha1968; Pitre and Hogg, Reference Pitre and Hogg1983). Pupal development was also temperature-sensitive, decreasing from 29.89 ± 0.55 days at 18 ± 1°C to 7.25 ± 0.15 days at 34 ± 1°C. Similar trends were observed by Busato et al. (Reference Busato, Grützmacher, Garcia, Giolo, Zotti and Bandeira2005), Savadatti et al. (Reference Savadatti, Ginnu, Mariyanna, Hosamani, Desai, Subbanna and Jalamangala2023) and Ashok et al. (Reference Ashok, Balasubramani, Kennedy, Geethalakshmi, Jeyakumar and Sathiah2021). At low temperatures, such as 14 ± 1°C, larval development often stalled before pupation, indicating a lower thermal boundary for metamorphosis. Adult longevity decreased with increasing temperature, with females consistently outliving males. Maximum longevity occurred at 18 ± 1°C (12.75 ± 0.25 days for females; 10.71 ± 0.43 for males), aligning with findings by Schlemmer (Reference Schlemmer2018) and Praveen and Mallapur (Reference Praveen and Mallapur2019). This trend reflects temperature-dependent metabolic rates, which prolong survival at lower temperatures (Davidowitz & Nijhout, Reference Davidowitz and Nijhout2004). At lower temperatures, insect metabolism slows significantly due to reduced enzymatic activity and decreased overall biochemical reaction rates. This metabolic deceleration minimises the generation of reactive oxygen species (ROS), thereby reducing oxidative damage to critical macromolecules such as nucleic acids, proteins, and lipids. Consequently, cellular integrity is better preserved, contributing to prolonged adult longevity. Recent findings further suggest that this extension of lifespan is not merely a passive thermodynamic outcome but involves active genetic regulation, with certain genotypes exhibiting greater sensitivity to low-temperature-induced longevity (Molon et al., Reference Molon, Dampc, Kula-Maximenko, Zebrowski, Mołoń, Dobler, Durak and Skoczowski2020). Moreover, the pathways involved may partially overlap with those activated by caloric restriction, indicating that multiple molecular mechanisms may contribute to enhanced survival under low thermal conditions (Gribble et al., Reference Gribble, Moran, Jones, Corey and Welch2018). Low temperature induced significant metabolic changes in aphids, enhancing pathways like glycolysis and the pentose phosphate pathway while suppressing the TCA cycle. This shift led to the accumulation of polyols, amino acids (e.g. proline, tyrosine), and fatty acids. Such alterations supported energy conservation and stress tolerance, contributing to prolonged winter survival and longevity (Durak and Durak Reference Durak and Durak2021). The sex-based longevity difference likely arises from divergent life-history strategies, with females prioritising reproductive investment and males favouring competitive traits (Vinogradov Reference Vinogradov1998; Bonduriansky et al., Reference Bonduriansky, Maklakov, Zajitschek and Brooks2008). The sex ratio remained consistently female-biased across temperatures, with moderate variation. Dhaliwal (Reference Dhaliwal2019) reported a similarly female-biased sex ratio in Leucinodes orbonalis Guenée (Lepidoptera: Crambidae), with values of 1:1.38, 1:1.10, 1:1.15, and 1:1.40, which increased with rising temperatures from 20 ± 1°C to 35 ± 1°C. Similar trends were observed by Murua et al. (Reference Murua, Vera, Abraham, Juarçz, Prieto, Head and Willink2008) and Huang et al. (Reference Huang, Xue, Chen, Guo, Tang, Zhong and He2021), suggesting limited thermal influence on sexual differentiation but a potential advantage for population growth under female-dominant ratios. Temperature affects insect sex ratios through various physiological and cytogenetic pathways. Research across arthropods, particularly Lepidoptera, shows that females typically have greater tolerance to heat stress than males, resulting in increased male mortality at higher temperatures and consequently, a female-biased sex ratio (Edmands Reference Edmands2021). Factors such as differential metabolic rates, hormone regulation, and body size may contribute to this sex-specific thermal sensitivity. Additionally, studies in Lepidopteran insects like Talaeporia tubulosa Retzius (Lepidoptera: Psychidae) show that temperature can affect chromosome segregation during meiosis, altering the production of sex-specific gametes which can result in temperature-dependent sex ratio distortion (Seiler Reference Seiler1920).
Reproductive timing and capacity were profoundly temperature-dependent. With an increase in temperature from 18 ± 1°C to 34 ± 1°C, the adult pre-oviposition period (APOP) decreased from 5.13 to 2.17 days, while the total pre-oviposition period (TPOP) declined significantly from 78.13 to 20.08 days. These trends were also observed in studies on Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) (Nitin et al., Reference Nitin, Sridhar and Chakravarthy2018) and Plutella xylostella Linnaeus (Lepidoptera: Plutellidae) (Saeed et al., Reference Saeed, Jaleel, Naqqash, Saeed, Zaka, Sarwar, Ishtiaq, Qayyum, Sial, Batool and Khan2019). Fecundity peaked at 26–30°C (1010.19 ± 18.85 and 952.37 ± 27.44 eggs, respectively), consistent with optimal thermal thresholds observed by Chen et al. (Reference Chen, Chen, Yang and Liu2022) and Islam et al. (Reference Islam, Roknuzzaman, Hassan and Ullah2019). Elevated temperatures above 30 ± 1°C likely suppressed fecundity by compromising gamete development, in contrast to optimal conditions that support robust oogenesis and spermatogenesis as assumed in case of L. orbonalis and Mythimna roseilinea (Walker) (Lepidoptera: Noctuidae) (Leather, Reference Leather2018; Qin et al., Reference Qin, Liu, Zhang, Cheng, Luo and Jiang2018; Islam et al., Reference Islam, Roknuzzaman, Hassan and Ullah2019). Stage-specific survival (lx) showed optimal values at 26–30°C and declined at both thermal extremes. Larval and pupal survival were highest in this range, while early instar mortality increased markedly at 18 ± 1°C and 34 ± 1°C, consistent with Chen et al. (Reference Chen, Li, Wang, Ma, Huang and Huang2017) and Karimi-Malati et al (Reference Karimi-Malati, Fathipour, Talebi and Bazoubandi2014). Life expectancy decreased with rising temperature, from 15.81 days at 18 ± 1°C to 8.26 days at 34 ± 1°C, aligning with reports by Ashok et al. (Reference Ashok, Kennedy, Geethalakshmi, Jeyakumar, Sathiah and Balasubramani2020) and Supriya et al. (Reference Supriya, Sridevi, Uma, Bharati and Srinivasa2022b). Together, these findings suggest that while higher temperatures accelerate development, they also reduce survival across multiple life stages, with early instars being most vulnerable, and cumulative mortality increasing toward pupation and adulthood under heat stress. Reproductive value (vx) peaked during the adult female stage, with the highest values observed at 26 ± 1°C, followed by 30 ± 1°C, consistent with findings by Chen et al. (Reference Chen, Chen, Yang and Liu2022) and Islam et al. (Reference Islam, Roknuzzaman, Hassan and Ullah2019). The sharp decline at 34 ± 1°C suggests increased reproductive senescence and reduced investment per female. Sharma et al. (Reference Sharma, Sharma, Sharma, Verma, Sharma and Sharma2024) also reported higher reproductive value (vx) of fall armyworm as 728.41 eggs on maize at 25 ± 0.5°C. Life table analysis showed the highest net reproductive rates (R 0) at 30 ± 1°C (499.91 females/female) and 26 ± 1°C (467.32 females/female), substantially exceeding values recorded at other temperatures. These results align with those of Prasad et al. (Reference Prasad, Rao, Rao, Bal, Muttapa, Choudhary and Singh2021) and Chen et al. (Reference Chen, Chen, Yang and Liu2022), likely reflecting enhanced survivorship and fecundity under these thermal conditions. Mean generation time (T c) decreased with rising temperature, from 33.73 to 26.52 days between 26 and 30°C, corroborating observations by Ashok et al. (Reference Ashok, Balasubramani, Kennedy, Geethalakshmi, Jeyakumar and Sathiah2021) and Kumara et al. (Reference Kumara, Muhandiram, Ranaweera, Ayeshmanthi, Sarathchandra and Mubarak2022). In the present study, the highest intrinsic rate of increase (r m) and finite rate of increase (λ) were observed at 30 ± 1°C, followed by 26 ± 1°C. This can primarily be attributed to the shorter generation time, higher survivorship of immature stages, and an increased daily progeny production/female of the fall armyworm at the respective temperatures (Osman et al Reference Osman, Mandour, Abd El-Hady and Sarhan2015). Both metrics declined at 34 ± 1°C, indicating a loss of population momentum due to thermal stress, similar to trends reported by Osman et al. (Reference Osman, Mandour, Abd El-Hady and Sarhan2015) and Dalal and Arora (Reference Dalal and Arora2021). The shortest doubling time at 30 ± 1°C, followed by 26 ± 1°C, suggests that S. frugiperda can rapidly increase its population due to its shorter development time and higher net reproduction rate at the particular temperature conditions, enabling it to potentially double its numbers in a short period (Maharani et al., Reference Maharani, Puspitaningrum, Istifadah, Hidayat and Ismail2021). In the present study, the gross reproduction rate (GRR) of S. frugiperda increased from 331.67 ± 7.04 offspring at 18 ± 1°C to a peak of 858.41 ± 29.11 at 30 ± 1°C, before declining to 482.80 ± 20.00 at 34 ± 1°C. This trend aligns with Prasad et al. (Reference Prasad, Rao, Rao, Bal, Muttapa, Choudhary and Singh2021), who reported an increase in GRR from 125.16 at 15°C to 981.08 at 30°C, followed by a drop to 335.62 at 34°C. Similar thermal responses were observed in P. xylostella by Saeed et al. (Reference Saeed, Jaleel, Naqqash, Saeed, Zaka, Sarwar, Ishtiaq, Qayyum, Sial, Batool and Khan2019), though with lower GRR values, likely due to species-specific differences. In the current study, high GRR values were also recorded at 26 ± 1°C (755.77 ± 31.31). In contrast, Adan et al. (Reference Adan, Tonnang, Kassa, Greve, Borgemeister and Goergen2024) reported substantially lower GRRs (378.91 at 28°C and 131.25 at 30°C), possibly due to differences in diet, as their study used sprouted maize and cowpea, while the current study used natural maize leaf whorls. Also, the variations in GRR are likely due to differences in oviposition, egg viability, and adult emergence, all temperature-dependent factors (Khaliq et al., Reference Khaliq, Attique and Sayyed2007). The weekly multiplication rate (WRR) of S. frugiperda increased with rising temperature, peaking at 30 ± 1°C, followed by a decline at 34 ± 1°C. Comparable temperature-dependent patterns related to weekly multiplication rate have been observed in other lepidopteran species (Singh & Yadav, Reference Singh and Yadav2009; Negi et al., Reference Negi, Sharma, Verma and Chandel2020; Supriya et al., Reference Supriya, Sridevi, Uma, Bharati and Srinivasa2022a).
Population projections based on life table parameters effectively illustrate the stage structure and potential impact of pest populations. The present analysis indicates that S. frugiperda exhibits optimal population growth at 26 ± 1°C and 30 ± 1°C, characterised by accelerated development, synchronised stage progression, and increased generational turnover. Conversely, suboptimal temperatures at 18 ± 1°C and 34 ± 1°C restrict population buildup due to prolonged development and thermal stress. These results revealed that under thermally favourable conditions, particularly in warm agroecological zones, enhance the survival, development rate, and fecundity of S. frugiperda, thereby increasing the risk of rapid population growth and significant crop damage. This conclusion is consistent with previous studies that emphasise the pest’s enhanced development and outbreak potential in warmer climates (Early et al., Reference Early, Moreno, Murphy, Murphy and Day2018; Du Plessis et al., Reference Du Plessis, Schlemmer and Van den Berg2020; Hruska, Reference Hruska2019).
The results pertain to maize, a highly favourable host for S. frugiperda that supports rapid development and high reproductive output. On alternative hosts such as sorghum, millets, and legumes, however, the pest generally shows slower growth, lower survival, and reduced fecundity (Chen et al., Reference Chen, Chen, Yang and Liu2022; Ali et al., Reference Ali, Haque, Hossain, Bari, Kabir, Roy, Datta, Howlader, Alam and Krupnik2023; Sharma et al., Reference Sharma, Sharma, Sharma, Verma, Sharma and Sharma2024). Thus, the number of generations and population buildup estimated for maize may be over-projected if extended to these crops. While the optimal thermal range of 26–30°C is likely consistent across hosts, performance will vary with host nutritional quality, local temperature regimes and available dietary resources. Moreover, thermal responses can differ with the geographic origin of invading populations, as strains adapted to distinct climates may perform differently, leading to regional variation in pest dynamics (Phungula et al., Reference Phungula, Kruger, Nofemela and Weldon2023). These factors highlight the need for crop- and region-specific validation to generate reliable risk predictions and management strategies.
The present study conclusively demonstrates that temperature has a significant impact on the development, survival, and reproductive potential of S. frugiperda, with the range of 26 ± 1°C to 30 ± 1°C identified as optimal for its rapid population growth. This temperature range, commonly experienced during the kharif season in Punjab and other parts of Northern India, creates highly favourable conditions for the pest’s proliferation, thereby increasing the risk to maize and other cereal crops. The findings highlight critical thermal thresholds and life table parameters that are essential for understanding the pest’s ecological adaptability. By providing detailed insights into stage-specific survival, reproductive rates, and life expectancy across a broad range of constant temperatures, the study offers a strong foundation for climate-informed, region-specific pest management strategies. These results can aid in developing predictive models and early warning systems tailored to Northern Indian agro-ecologies. Moreover, the interaction between temperature and prevalent biotic stresses such as natural enemies, interspecific competition, and host plant resistance plays a crucial role in shaping pest dynamics under field conditions. Therefore, future research should focus on integrating these laboratory findings with field-based studies under fluctuating temperatures and biotic influences to refine integrated pest management (IPM) approaches and support sustainable crop protection practices across Northern India and similar agro-climatic zones.
Acknowledgements
The authors express their gratitude to the Confederation of Indian Industry, Department of Science and Technology, and FMC Corporation for awarding the Prime Minister’s Fellowship to Oshin Bhargav.
Author contributions
Oshin Bhargav: Data collection and analysis, Investigation, Methodology, Writing-original draft. Naveen Aggarwal: Conceptualisation, Investigation, Methodology, Resources, Supervision, review & editing. Jawala Jindal: Conceptualisation, Supply of seed material, Methodology, Resources, Supervision, review & editing
Competing interests
The authors declare that they have no conflict of interest.
