Independent and interactive effects of eCO2 and eTemp. on Spodoptera frugiperda (J E Smith) on Maize-A major input for prediction of future pest scenario

Climate change is now unequivocal and influences crops and the incidence of insect pests. Understanding the spatially variable, species-specific, and complex effects of climate change is essential in developing an appropriate pest management strategy. The two dimensions of climate change i.e., elevated temperature (eTemp.) and elevated CO2 (eCO2) influence insect herbivores. In the present study, the growth and development of an invasive insect pest, fall armyworm, Spodoptera frugiperda (J E Smith) (Lepidoptera: Noctuidae) on maize at eCO2 and eTemp conditions using CO2 and temperature Gradient Chambers (CTGC) was estimated. Dilution of bio-chemical constituents was noted with lower leaf nitrogen (9%–14%), higher carbon (3%–11%), higher C : N (18%–26%), and higher tannins (13%) in maize foliage at eCO2+eTemp levels. A significant influence on primary parameters of insect viz., higher total consumption by larvae (38%), extended larval duration (13%) with increased larval weights (17%), and differential pupal weights (14%) in successive generations was recorded at eCO2 + eTemp compared to ambient. Their effect was continued on various insect performance indices also, with higher relative consumption rate, RCR (40%), lower relative growth rate, RGR (11%), and varied approximate digestibility (AD), the efficiency of conversion of ingested food (ECI) and digested food (ECD) of S frugiperda larvae. The interactive effect of eCO2 and eTemp led to a higher Potential Population Increase Index (PPII) (19%) due to higher fecund adults. The effect of eCO2 offsets the impact of eTemp when interacting together on some of the insect parameters. The present results indicate that eCO2 and eTemp play a key role in influencing the growth and development of S frugiperda indicating higher pest incidence in future climate change periods.


Introduction
Climate change is a reality and is evident with elevated temperature and elevated atmospheric carbon dioxide (CO 2 ) concentration, the prime facets influencing crop growth (Hunter 2001), and the nutritional quality of crop plants. The global mean surface temperature is predicted to increase by 1.1°C to 4.8°C by the end of the 21st century (2081-2100) compared to 1986-2005, across representative concentration pathway (RCP) based emission scenarios, and the CO 2 concentration will reach up to 500 to 1000 ppm (IPCC 2021). The impact of elevated temperature on insect pests is evident and divergent (Bale et al 2002). Feeding on plants grown in elevated CO 2 conditions affects insect herbivores' survival, growth, development, and reproduction (Wu et al 2006).
Among the cereal crops, maize (Zea mays L) is the most important crop and largely grown after wheat and rice, and is used extensively as feed, fodder, and raw material for many industrial purposes. Among the maizegrowing countries, India ranked 4th in area and 7th in production representing around 4% of the world maize area and 2% of total production in 2020. Maize was grown throughout the year in all states of the country for various purposes. In the triennium of 2017-2020, maize was grown on an area of 9325 thousand hectares with a production of 28 411 thousand tonnes and with a productivity of 3047 Kg per hectare (DES 2021) and the incidence of various biotic and abiotic factors often affected the potential yield of maize crop.
The fall armyworm (FAW), Spodoptera frugiperda (J E Smith) (Lepidoptera: Noctuidae), is a polyphagous and highly destructive insect pest of economically important crops such as maize, rice, sorghum, cotton, and vegetables (Bueno et al 2010). The larvae have the potential to consume 353 different plant species belonging to 76 botanical families (Montezano et al 2018), including crops, weeds, and ornamental plants. In recent times, it has been identified as a major insect pest of maize causing substantial yield losses in India. FAW, native to tropical and subtropical regions of the Americas is now noticed in India. For the first time, the incidence of fall armyworm in Asia was reported by Sharanabasappa et al (2018), Ganiger et al (2018), and Shylesha et al (2018) from the Southern part of India 2018. In the subsequent crop seasons, it caused severe damage in various districts of south Indian states. Later, it was reported from different districts of Northern India (Mahadeva Swamy et al 2018, Rakshit et al 2019). Since then, the area of infestation escalated (Suby et al 2020) rapidly in the maize crop within the country. Cruz and Turpin (1983) reported that fall armyworm caused up to 34% loss in maize yield.
The temperature has a direct influence on changes in the phenological events of the insects (Bale et al 2002) while the influence of elevated CO 2 on insect pest performance is indirect and host-mediated (Hunter 2001, Manimanjari andRao 2022). The impact of temperature and CO 2 on the phenology of insects is documented individually or independently whereas the information on their interactive effects is very scarce or poorly known. Climate change-driven variations in eTemp and eCO 2 levels would impact the growth and development of new invasive insect pests like S frugiperda and the primary data obtained will be useful for pest model development and refining pest management tactfully and strategically. With this background, experiments were designed to study the individual and concurrent effects of eTemp and eCO 2 on the growth, development, and performance of S frugiperda on maize using a first-of-its-kind facility in India i.e., CTGC facility.

Materials and methods
2.1. Carbon dioxide and temperature gradient chambers (CTGC) CTGC chambers were commissioned at ICAR-CRIDA for quantifying the influence of eTemp and eCO 2 on the phenology of crop and insect pests. The future climate is simulated in the CTGC chambers by regulating CO 2 and temperature levels. The concept, philosophy, and details of the facility are documented (Srinivasa Rao et al 2018). We considered two levels of CO 2 concentration, i.e., 400 ± 25 ppm (ambient CO 2 ) and 550 ± 25 ppm (elevated CO 2 ). Myers et al (2014) and Sui et al (2015) predicted that the future atmospheric CO 2 concentration would be up to 550 ± 25 ppm in RCP 8.5 by 2050 period and a similar eCO2 concentration was adopted here. The facility has eight chambers and the following conditions were maintained.
i. Two chambers with ambient conditions of Temp and CO 2 will serve as-'Reference' (aTemp + aCO 2 ); ii.
Two Chambers with a temperature increment/gradient of 5 ± 0.5°C (28, 30, 33 ± 0.5°C) than the reference are considered as elevated Temperature, -'eTemp'; iii. Two Chambers with a temperature increment of 5 ± 0.5°C compared to the reference and an increase in CO 2 concentration of 550 ± 50 ppm-'eTemp + eCO 2 '; iv. Two Chambers with reference temperature and an increase in CO 2 concentration of 550 ± 50 ppm-'eCO 2 '.

Maize crop growing conditions
Line sowing of maize seeds (DHM 117) in all the CTGC chambers was done in the second fortnight of June during the monsoon season, 2020-2021 and the crop was grown under eight set conditions i.e., the reference (27 ± 0.5°C; 400 ppm CO 2 , aTemp + aCO 2 ), eTemp (28, 30, 33 ± 0.5°C with 400 ppm CO 2 ), eCO 2 (27 ± 0.5°C; 550 ppm CO 2 ) and eTemp + eCO 2 (28, 30, 33 ± 0.5°C with 550 ppm CO 2 ) conditions. Consequent simulation of the set conditions was done for the studies. 30-day-old leaves of the maize crop were used for conducting the phenology experiments of Spodoptera frugiperda with respective set-conditions. Insecticide-free conditions were maintained in the chambers to quantify the influence of eCO 2 and eTemp on the crop and pests.

Biochemical analysis of maize foliage
Leaf tissues from leaves of maize plants used in the feeding experiments were collected at 30 and 60 days after sowing (DAS) and their carbon, nitrogen, C : N ratio, protein, amino acid, and tannin contents were analyzed. Biochemical constituents are estimated from the dried (at 80°C) and powdered leaves. Organic carbon in the leaf tissues of maize was analyzed using the Walkley and Black (1934) method. Nitrogen concentration was estimated using the CHN analyzer by the method proposed by Jackson (1973). After the estimation of Carbon and Nitrogen, C : N was arrived at. Protein content analysis was done according to the procedure given by Lowry et al (1951). Estimation of free amino acids was done by taking Ninhydrin as a powerful oxidizing agent as suggested by Moore and Stein (1948). Further, the dried leaf samples (at 40°C for 48 h) were powdered and the tannins were extracted using methyl alcohol. Estimation of tannin content was done by Folin-Denis method as suggested by Anderson and Ingram (1993). Tannic acid standard was used to determine the tannin concentration in the leaf extract using a spectrophotometer.

Insect stocks
Insectary of ICAR-CRIDA has an insect culture of S frugiperda comprising all four stages of the life cycle. A controlled chamber with a light intensity of 550 μ mol m −2 s −1 during the day and a 10 h night cycle set at 20°C, was used to maintain the stock cultures of fall armyworm. 60% RH during the day and 70% during the night were maintained.

Feeding experiments
During the second fortnight of July 2020, the first-generation experiments were initiated. Each petri dish with a neonate larva of S frugiperda cultured in the laboratory formed a replication. A filter paper was placed in the petri dish and moistened to maintain the turgidity of the leaf disc. Ten replications per each of the eight set conditions were maintained. Standard procedure (Srinivasa Rao et al 2014) was followed to conduct the feeding experiments. The treatment associations were maintained in conducting the feeding experiments by collecting the leaves from the respective CO 2 and temperature conditions for the two successive generations. About 5-6 gm of leaf disc of known quantity was offered to the larvae in each petri dish and these were placed inside the CO 2 growth chambers akin to CTGC at the eight set conditions. The weights of the larva, its leaf consumption, and the frass excreted were recorded from each petridish around 10 AM on the next day. After recording the weight, each larva was again kept in the same petridish and offered with a pre-weighed fresh leaf from the respective conditions. Larval life span was calculated as the period between the emergence of the larva from the egg till its pupation was considered as larval duration. The weight of the Pupa was recorded at 24 h after pupation. The pupal duration as well as adult emergence per treatment were noted. The number of male and female adults emerged was counted and the sex ratio was recorded. After the emergence, the adults were kept in a wooden cage of size (30 cm × 30 cm × 30 cm) for two days. Later, they were paired 1:1 (Male: Female) and released in to the plastic jars (15 × 15 × 15 cm) tied with muslin cloth. Egg laying began within 48 h of the adult release in to the jars. Treatment-wise counting of the eggs laid was done every day. The muslin cloth cover was replaced daily. Daily record of the egg hatching percentage per female was maintained. Second generation feeding experiments of S frugiperda were initiated using the first instar larvae hatched from the eggs laid by the first-generation female adults. There larvae were reared individually and separately to conduct the experiment as per the set conditions explained above. The data on primary parameters viz., weights of larvae, leaf consumption, and frass excreted were measured for both generations.

Potential population increase index (PPII) & potential population consumption (PPC)
By adopting the methodology proposed by Wu et al (2006), Srinivasa Rao et al (2013), PPII and PPC were computed.
(i) Total eggs laid by all females were obtained by multiplying the initial larval individuals number, survival rate of the larvae, rate of pupation, adult emergence rate, the ratio of females, and the eggs laid per female KKKKKKKKK (A) (ii) The second generation potential initial no. of larval individuals has arrived as a product between (A) of the first generation and rate of hatchingKK (B) (iii) Potential total larval consumption was obtained by multiplying (B) with survival rate of the larvae and per larva consumption.
(iv) The second generation potential population increase index was the ratio between the total number of eggs laid by all second generation females and the total number of eggs laid by all first generation females

Data analysis
The effect of the set temperature and CO 2 conditions on the primary parameters, performance indices, PPII, and PPC of S frugiperda was analysed by using Two-way ANOVA test. By adopting Tukey's test, the treatment means were compared and separated. The data on primary parameters were analyzed with temperature and CO 2 as the sources of variability By considering CO 2 level as a main factor and temperature as a sub-factor of variability, the data on primary parameters was analyzed in a split-plot design.
To evaluate the ratio-based insect performance indices, we adopted the analysis of covariance (ANCOVA) to evaluate the effect of covariates on the response of various variables as proposed by Raubenheimer and Simpson (1992).
The model of Analysis of covariance (ANCOVA) is as follows: Where: Y ij , is a dependent variable (index) of i treatment in j block; X ij , an observation of covariate X in the plot receiving i treatment in j block; X¯K., the overall average for each covariate m, T i , b j, and β are parameters, uncorrelated and ∑ ij the experimental error with N.
ANCOVA was adopted for these ratio-based indices. Initial larval weight was taken as a covariate for RCR and RGR. For ECI and ECD, total consumption and food assimilated were considered as covariates respectively (Hagele and Martin 1999) to correct for the effect of variation in the growth and food assimilated on intake and growth. The growth and consumption of larvae in the different treatments were obtained respectively, by cosidering the final weight of the larvae and food consumption for the covariate feeding time. SPSS version 16.0 was used for conducting all statistical analyses.
The findings of ANCOVA conducted on ratio-based variables of Generation I indicated that eCO 2 (P 0.048) and eTemp (P 0.001) affected RCR when the initial weight of the larva was taken as a covariate. Using a covariate caused the reduction of the residual mean sum of squares. In the case of RGR, the interactive outcome (P 0.001), eCO 2 (P 0.001), and eTemp (P 0.001) also influenced the RGR of larvae, when the initial weight of larva was taken as a covariate for both RCR and RGR. The ECI and ECD were significantly affected by eCO 2 (P 0.001), eTemp (P 0.001), and their interactive outcome (P 0.001) when total consumption and food assimilated were taken as covariates respectively. The larval weight of S frugiperda was significantly affected only by eTemp (P 0.001) when the initial weight is taken as a covariate (table 6(a)). A similar trend was reflected in the second generation also with more significance concerning eCO 2 and eTemp and interactive levels. The significant association is more evident with RGR, ECI, and ECD indices (table 6(b)).

Discussion
The two major dimensions of climate change viz., eTemp and eCO 2 influence the crops and herbivore insects, and their effects were studied separately and independently by various research workers.  (Weigel 2014) that in turn influence the insect pest indirectly, popularly known as 'host-mediated effect' (Hunter 2001, Manimanjari andRao 2022). However, studies on the interactive effects of eTemp and eCO 2 on herbivore insects are scarce and have not been studied. In the present study, it was hypothesized that eTemp and eCO 2 impact the growth and development of Fall armyworm, S frugiperda on maize crop and in turn estimated population development in the form of PPII.

Dilution of the biochemical composition of maize foliage
The findings of the present study showed that the percent variation of biochemical constituents was considerable at eCO 2 and eTemp than ambient. The percent reduction of nitrogen content (9%-14%) and increased percentage of carbon (3%-11%) and C : N ratio (18%-26%) under eCO 2 + eTemp over ambient was more evident at 60 DAS than at 30 DAS. Earlier it was reported that both eCO 2 (Stitt and Krapp 1999) and eTemp (Tjoelker et al 1999) decrease foliar N content and lead to a reallocation of nitrogen within a plant. Present findings of interactive effect also confirm a similar trend. The present findings indicated that increased carbon intake led to higher carbon and C : N ratio of the leaf tissues as reported by Hughes and Bazzaz (1997). An increase in carbon (Gutierrez et al 2008) and a decrease in nitrogen (Xin et al 2013) and in turn increased C : N ratio due to eCO 2 led to the dilution of the biochemical composition in various crops (Srinivasa Rao et al 2012 and. Concurrent elevation of CO 2 and temperature resulted in a distinct increase in the growth and development of potato crops and eCO 2 caused reduced nitrogen and increased C : N ratio (Lee et al 2020). The positive outcome of eCO 2 could offset the negative impact of warming on the C : N ratio (Wang et al 2019).
Nitrogen is the key element required for protein and amino acid synthesis and thus plants grown under eCO 2 have lower protein and amino acids in their tissues due to a reduction in the nitrogen content. In the present study, there was a decrease in the protein content by 13% at 30 DAS and 16% at 60DAS at eCO 2 + eTemp compared to the ambient. Similar results were with amino acids where the reduction was about 15% at 30 DAS and 11% at 60 DAS at eCO 2 + eTemp than the ambient (figure 1).
Bezemer and Jones 1998 reported that a higher percentage (80%) of condensed tannins in crop foliage under eCO 2 conditions and tannins offer a defense mechanism in crop plants against insect pests. Under eCO 2 + eTemp, similar increased tannin content (13.43%) was found in the maize leaves. It is understood that Carbon Nutrient Balance (CNB) hypothesis indicates that excess carbon accumulating in plant tissues due to eCO 2 is probably allocated to more carbon-based secondary metabolites viz., phenolics, condensed tannins, and terpenoids (Sun et al 2009).

Variation in insect primary parameters
Our results showed that eCO 2 , eTemp and eCO 2 + eTemp had a substantial effect on insect primary parameters (mean of two generations) of S frugiperda. Total consumption of foliage by the larvae was higher at 33 ± 1°C at eCO 2 and was 38% more than the ambient (figure 2). These findings are in tune with Awmack ane Leather (2002) AD/ECI/ECD expressed in % & RCR/RGR expressed in mg. mg −1 day −1 . aCO 2 −400 ± 25 ppm; eCO 2 −550 ± 25ppm. All values are mean ±Standard deviation. * Significant 5% level of significance.

**
Significant 1% level of significance. Same upper-case alphabets across CO 2 levels and lower-case alphabets across temperatures indicate that means are not statistically significant, at P < 0.05.   Total eggs laid by all females = Initial numbers of larval individuals X larval survival rate X pupation rate X rate of adult's emergence X ratio of female X eggs laid per female. b Potential initial numbers of larval individuals for the second generation = (potential) Total eggs laid by all females in first generation X hatch rate. c Potential population increase index for the second generation = total eggs laid by all females in second generation / total eggs laid by all females in first generation. d Potential total larval consumption (g) for the second generation = Potential initial numbers of larval individuals for the second-generation X larval survival rate X consumption per larvae. Same upper-case alphabets across CO2 levels and lower-case alphabets across temperatures indicate that means are not statistically significant, at P < 0.05. Means within a row indicated by different letters are significantly different (LSD test, P < 0.05) who reported that lepidopteran larvae would exhibit compensatory feeding on plants grown under eCO 2 and we observed a similar trend at interactive levels of eCO 2 + eTemp.
The eCO 2 + eTemp affected larval weight (17%) and fecal weight (32%). Chen et al (2004) reported that the larvae of H. armigera fed more on spring wheat grains grown under eCO 2 conditions and produced 37.8% more frass. Increased larval duration of S frugiperda by 3%-13% in the mean of two subsequent generations was at eCO 2 + eTemp over the ambient. Goverde and Erhardt (2003) found that elevated CO 2 extended the larval duration of lepidopteran C pamphilus when fed on grass species grown in higher CO 2 .
Hence, alterations in plant chemistry due to changes in eCO 2 level have been shown to have lower growth rates, slow larval developmental time, and higher compensatory feeding for herbivore insects, which were in close agreement with the reports of Lincoln et al (1993), Hattenschwiler and Schafellner (2004), Wu et al (2007), Srinivasa Rao et al (2009), Srinivasa Rao et al (2012, Srinivasa Rao et al (2014).
Larvae fed on maize foliage grown under the eCO 2 +eTemp condition had higher food intake, and larval weight gain, and excreted more feces than those fed on maize grown at the reference condition. Thus, the feed utilization of the insect herbivore is influenced majorly by its quality (Hodar et al 2002) because host plant components directly affect the plant feeder's intake (Awmack and Leather 2002). A significant outcome (9%-14%) of eCO 2 + eTemp on pupal weights (mean of two generations) was detected in the case of S frugiperda also.  Additionally, the energy storage ability of the insect expressed in terms of pupal weight, altered significantly depending on the quality of food. Body weight is an important fitness parameter of insect population dynamics (Liu et al 2004) and pupal weight is an indirect and easy indicator of lepidopteran fitness.
The significant response of insect herbivores to the effects of elevated CO 2 through multiple generations was reported in the case of H armigera (Yin et al 2010) and such a phenomenon holds valid for S frugiperda too. An intensive simultaneous increase of CO 2 and temperature as experimented here, may decrease the leaf's metabolic ability and decrease proteins accordingly. Proteins are the basic nutrients for insects (Qin 1987) and in the present experiment, a reduction of nitrogen, amino acids, and proteins was noted. The variation of the biochemical composition of maize leaves led to the variation of the primary parameters of S frugiperda at eCO 2 +eTemp conditions.

Variation in food conversion efficiency indices
The present results for the mean values of two generations revealed that insect performance indices varied when the larvae of S frugiperda allowed to feed on maize foliage grown under eCO 2 +eTemp than the ambient. The values of AD were diverse at eCO 2 +eTemp when compared to the ambient. An increase in RCR by 40% was recorded at eCO 2 +eTemp than ambient. Decreased ECI and ECD were at eCO 2 compared to aCO 2 across four temperatures tested and were more evident at 28 ± 1°C. Mixed values of RGR were at eCO 2 +eTemp when compared to the reference.
The foliage consumption by larvae was more under eCO 2 +eTemp condition and the increase in the RCR values indicate higher consumption despite slower growth rate (lower RGR) and longer larval duration (0.4-1.9 days more than ambient). Earlier workers (Wu et al 2006, Srinivasa Rao et al 2012 reported similar findings under eCO 2 condition only. We obtained similar findings which were more evident at interactive eCO 2 and eTemp conditions. The bioavailability of metal ions to the herbivores will be reduced as tannins have a tendency to chelate them. Protein digestion is also reduced by tannins indicating a reduction in the availability of nutrition to the herbivores from the plants and plant parts. Barbehenn and Peter Constabel 2011 studied the role of tannins in defense mechanism of plants against various stresses including the response induction by the plants to the damage caused by the insect. In the paper birch trees (Betula papyrifera) grown under elevated CO 2 conditions, two-fold increase in the tannin concentration was reported (Lindroth et al 1995). Our studies also recorded increased tannin content at the climate change treatments of eCO 2 and eTemp as compared to the ambient.
Studies by Masters et al 1998 revealed that the nitrogen content reduction in the foliage decrease the efficiency of feed conversion in to body mass resulting in a reduced growth rate, decline in the rate of survival of larvae and density of the insect herbivore. eCO 2 can promote plant growth with consequent reallocation of resources and dilution of foliar nitrogen, which influence the rate of consumption by the insects (Yin et al 2010). Elevated CO 2 can affect plant quality by inducing changes in the allocation of carbon and nitrogen to primary and secondary metabolites, which affects the growth and development of the insect herbivore. Under higher CO 2 levels, H. armigera was found to have an increased RCR from the first to the third generation (Wu et al 2006). Srinivasa Rao et al (2014) reported an increased AD (about 9%) and RCR (7%), decreased levels of ECI (13%), ECD (19%), and RGR (9%) in lepidopteran larvae fed eCO 2 foliage as against aCO 2 (figure 3). A similar variation in insect performance indices was reported earlier by Chen et al 2007 andWu et al 2007. In the present study, these trends were more evident at eCO 2 and eTemp conditions. The effects of eCO 2 and eTemp on the insects are independent and interactive. The direct effects are by altering the growth and consumption of insects and the indirect effects are by diluting the biochemical constituents of the leaf (Williams et al 2000). The phytochemistry of the crop plants changes with eTemp and eCO 2 and at interactive levels also. Most of the earlier studies were conducted either on eCO 2 or eTemp separately, not concurrently. Our studies were carried out to capture the concurrent effects of both the dimensions of climate change which are found significant.
At concurrent levels of eCO 2 and eTemp, the outcome of these two factors is complex and confounding in nature indicating their interdependency.
eTemp is found as a dominant factor in some cases while in other cases eCO 2 is significant showing their species-specificity (Sun et al 2009). The present findings reflected that the effect of eCO 2 balances the influences of eTemp when interacting together on most of the insect parameters (RCR, AD here). It was inferred that increased fecundity or production of offspring was higher at interactive levels of eCO 2 and eTemp referring that proliferation will be higher during future climate change periods. This might be due to the dilution in phytochemistry of the crop plants under eCO 2 and eTemp levels implying that maize may experience a higher incidence of S frugiperda in future. The impacts of eCO 2 and eTemp on life history parameters are found significant albeit the incidence of insect pest is a function of nature of host and its susceptibility to these dimensions.

Potential population increase index (PPII)
Percent potential population increase index (PPII) of S frugiperda fed on maize increased by (19%) under 33 ± 1°C at eCO 2 than ambient. The potential total number of eggs laid by all females was significantly higher at eCO 2 + eTemp at the ambient (figure 4). Wu et al (2006) reported lower PPII in cotton bollworms on wheat, and in our present experimentation, higher PPII of S frugiperda was noted and ascribed due to the integrative result of longer larval period with increased fecundity. The potential larval consumption of maize foliage was higher (56.11%) at eCO 2 + eTemp conditions. The findings on PPII indicate that the proliferation of the fall army worm would be higher during climate change periods leading to increased population build-up.

Conclusion
In general, host plant quality declines in eCO 2 and eTemp conditions with lower nitrogen and higher carbon content in the foliage. The food intake pattern and its digestibility were associated with biochemical constituents  of maize leaves. This assumption holds good with other lepidopteran insect pests, and the current study was aimed at S frugiperda on maize. Current study revealed increased feed uptake levels (38%) of larvae under eCO 2 +eTemp conditions in two generations than in the ambient. eCO 2 caused the extension of larval duration and elevated temperature from 27°C to 33°C led to the reduction of duration. However, at interactive levels, the impact of etemp offsets the effect of CO 2 . The significant variation in the primary parameters of S frugiperda was more evident at interactive levels of eCO 2 and eTemp across two generations and reflected on insect performance indices also. The higher potential population increase index at interactive levels of eCO 2 and eTemp indicate the higher incidence of insect pest during future climate change. Probably, S frugiperda is likely to be much prevalent resulting higher crop losses and thus affect maize production. The data generated from the present experimentation will contribute to the development of pest models and their refinement and forecasting the pest scenario of S frugiperda on maize during future climate change periods.