Introduction
Cereal crops are a major source of essential nutrients for humans and other animals (Jayas, Reference Jayas2012). Rice, Oryza sativa (Poaceae), is the staple food for over 50% of the global population, providing nearly 20% of the calories consumed by humans. More than 90% of the world’s rice is cultivated in the Asia-Pacific region (Cheng et al., Reference Cheng, Zhu and He2013). In 2011–2012, India produced 2780 kg/ha of rice, ranking second in rice production after China (Ramanjaneyulu et al., Reference Ramanjaneyulu, Shankar, Neelima and Shashibhusahn2014). However, around 200 species of insects and mites act as pests of various stored grains, including rice (Ali et al., Reference Ali, Latif and Ali2009). The stored grain pests (SGPs) causing the most damage to cereal crops during storage and shipment include the granary weevil, the rice weevil, the maize weevil, the lesser grain borer, the rust red flour beetle, and the Angoumois grain moth (AGM; Demis and Yenewa, Reference Demis and Yenewa2022; Hassan et al., Reference Hassan, Hashmi, Sarwar, Mehmood, Saleem and Farooqi2023). AGM, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae), is one of the most serious pests of unhusked rice and can also attack other cereals, such as wheat, barley, maize, and jowar (Basavanjali et al., Reference Basavanjali, Prabhuraj and Basavegowda2020). AGM infestation can damage approximately 76% of total grains and reduce their weight by 13% during an eight-month storage period, equating to an annual loss of 183.2 million tonnes worldwide (Macías-Estrada et al., Reference Macías-Estrada, Orozco-González, Castellanos-Pérez, Castillo-Rosales, Ortega-Ortega, Malvar, Padilla-Chacón and Jiménez-Galindo2023). Chemical treatments are not particularly effective against this pest because the larvae of the moth are internal feeders, preventing direct contact with insecticides (Ma et al., Reference Ma, Chang, Lei and Yang2016). Therefore, it is vital to identify the characteristics linked with susceptibility or resistance of host grains and their influence on the proliferation of S. cerealella (Murad and Batool, Reference Murad and Batool2017). This is an important aspect of integrated pest management and can reduce or eliminate the need for harmful insecticides (Quellhorst et al., Reference Quellhorst, Athanassiou, Zhu and Iiiwr2021). Zote and Shukla (Reference Zote and Shukla2023) observed greater adult emergence, a shorter development period and a higher susceptibility index of AGM on paddy. Based on those parameters, they ranked the host preference of S. cerealella in decreasing order as rice, maize, wheat, sorghum, chickpea, green gram, and Indian bean. Therefore, rice is particularly vulnerable to AGM. Before the Green Revolution, indigenous rice varieties were cultivated, with more than 70 popular aromatic varieties in the agroclimatic zones of West Bengal, India (Chaudhuri and Gharde, Reference Chaudhuri and Gharde2017). Some of these varieties are tolerant to AGM (De and Dey, Reference De and Dey2022).
Host selection by insects depends on chemical cues (Roy, Reference Roy2025; Schoonhoven et al., Reference Schoonhoven, Van Loon and Dicke2005; Scriber and Slansky, Reference Scriber and Slansky1981), and their survival is determined by the primary metabolite (PM) and secondary metabolite (SM) of the hosts (Demissie et al., Reference Demissie, Swaminathan, Ameta, Jain and Saharan2015; Harborne, Reference Harborne1994). Fouad et al. (Reference Fouad, Faroni, Vilela and Lima2013) identified three volatiles associated with host finding and selection by AGM, namely n-nonanal, n-decanal, and geranyl acetone. The PMs affect the vitality, growth and reproduction of herbivores (Mattson, Reference Mattson1980; Turunen, Reference Turunen1990), while the SMs play defensive roles against them (Schoonhoven et al., Reference Schoonhoven, Van Loon and Dicke2005; War et al., Reference War, Paulraj, Ahmad, Buhroo, Hussain, Ignacimuthu and Sharma2012). Development of AGM, from larva to adult emergence, occurs inside grains. Therefore, its phenological features depend on the quantitative and qualitative properties of the nutrition from a single kernel (Aleksandra et al., Reference Aleksandra, Petar, Goran, Marijana, Mihaela and Dušan2018). The adults are strong fliers, enabling the moth to thrive in various habitats and migrate when the conditions change (Trematerra, Reference Trematerra2015). Hansen et al. (Reference Hansen, Skovgård and Hell2004) highlighted that life history data of AGM on maize were available only from India and North America, and none of that allowed the calculation of the intrinsic rate of natural increase (rm). Perez-Mendoza et al. (Reference Perez-Mendoza, Weaver and Throne2004) studied the life history of AGM on maize at different temperatures. They ascertained that the optimal environmental conditions for the development and survivorship of AGM lie between 25–30℃ and 60–75% Relative Humidity (RH). Nevertheless, they have the potential to complete their development at 15 or 35℃ and 43% RH, enabling them to survive in cooler climates as well. Subsequently, more life history studies have been conducted on maize (Boamah et al., Reference Boamah, Osekre and Afun2023), wheat (Borzoui and Naseri, Reference Borzoui and Naseri2016; Khan et al., Reference Khan, Afsheen, Din, Khattak, Khalil, Hayat and Lou2010; Murad and Batool, Reference Murad and Batool2017; Nisar et al., Reference Nisar, Khan, Khan, Saljoqi, Hussain and Muhammad2018), and barley (Karimi-Pormehr et al., Reference Karimi-Pormehr, Borzoui, Naseri, Dastjerdi and Mansouri2018; Zeinalzadeh et al., Reference Zeinalzadeh, Karimi-Malati and Sahragard2016) in different geographic regions. Salim et al. (Reference Salim, Ullah, Saljoqi, Gökçe, Ahmad, Almutairi, Sayed, Aleya, Abdel-Daim and Shah2023) studied age-stage, two-sex life tables of AGM and reported that the value of rm varied significantly across maize, wheat and barley. Based on the initial populations, they also simulated the population sizes at different stages of AGM to project the population growth for a specified period. Life cycle data for AGM on rice have also been reported (Ashamo, Reference Ashamo2010; Basavanjali et al., Reference Basavanjali, Prabhuraj and Basavegowda2020; Chaudhuri and Gharde, Reference Chaudhuri and Gharde2017; Rai et al., Reference Rai, Chaudhuri and Ghosh2011). Several rice cultivars have even been screened to examine their resistance or susceptibility to AGM (De and Dey, Reference De and Dey2022; Kumar et al., Reference Kumar, Pandey, Rout, Singh and Moharana2018; Mathew et al., Reference Mathew, Nelson, Soundararajan, Uma and Jeyaprakash2019; Santos et al., Reference Santos, Agbangla, Chougourou, Missihoun and Ahanhanzo2015). However, there is a dearth of life table studies and population projection data for the moth on rice. The current research was therefore conducted to understand the relationship between the phytoconstituents in five rice cultivars (Miniket [M], Cottondora Sannalu [C], Gobindobhog [G], Swarna [S], and Tulaipanji [T]) and the resulting differences in population growth of AGM. This will augment the comprehensive scheme for the sustainable management of the moth.
Materials and methods
Collection of grains and insects
Uninfested grains and grains infested with S. cerealella of the five rice cultivars (M, C, G, S, and T) were collected from the FCI godown, Chinsurah, Hooghly (22°54′N, 88°23′E), different commercial stores of Burdwan, Purba Bardhaman (23°13′N, 87°51′E) and from farmers of Indas, Bankura (23.1504°N, 87.6318°E), West Bengal, India during their growing seasons of 2023–2025. We selected the uninfested grains after separating the damaged grains by physical investigations. Then we washed the grains properly with distilled water, followed by heat drying (45ºC) for 30 min and UV-treatment (254 nm) for 20 min. After the treatments, the grains were refrigerated (0ºC) in airtight containers and then used for further studies. To ensure disinfestation, a control set (with 50 grains of each rice cultivar in separate containers) was also observed during the course of the population studies. The uninfested grains of the selected rice cultivars, with a moisture content of 8–10%, were divided into two parts. One part of each cultivar served as host for S. cerealella on which the population studies were conducted, and the other part was processed for various phytochemical analyses. The stock culture of AGM was initiated with eggs (F1) from the infested grains in a growth chamber [30 eggs and 50 grains in a glass jar (20 cm diameter × 30 cm height)]. The culture of S. cerealella was maintained from F1 to F4 generations separately on the selected grains, and the F4 generation was used for the population studies with three replicates. All the culture sets were maintained under laboratory conditions (27 ± 1°C, 65 ± 5% RH, 12:12 [L: D] photoperiod and 1500 lux light intensity).
Population studies
Ten pairs of freshly emerged males and females from the stock culture were placed in an oviposition cage of fine nylon net [(25 × 25 × 25) cm3]. The moths were allowed to oviposit separately on each of the selected rice cultivars. Newly laid eggs (n = 30) from F3 females, belonging to a defined cohort, were collected for the population studies. Therefore, the population studies began with the eggs of 3rd generation (F3) females, i.e. the F4 generation. Damaged grains in the oviposition cage were replaced periodically with fresh ones. The larvae were placed in five glass jars [20 cm diameter × 30 cm height] containing fresh grains of the five rice cultivars, and all the larval instars (I–V) were monitored. The mouths of the containers were covered with cotton cloths. Fresh grains were again provided periodically. The pupae were then placed in separate glass jars [6 cm diameter × 10 cm height], covered with cotton cloth, until adult emergence. The males and females were differentiated based on their distinctive physical features. Adult females are larger than the adult males, and males have a more slender abdomen than females. Three replicates were maintained for each rice cultivar, and the experiments were repeated during those years. Survival, mortality, fecundity, and developmental durations from egg to adult were recorded separately for each rice cultivar.
Life table parameters
The data on survival, oviposition and developmental durations of all individuals on the selected grains were subjected to stage-specific, two-sex life tables analyses (Chen et al., Reference Chen, Li, Wang, Ma, Huang and Huang2017; Jaleel et al., Reference Jaleel, Yin, Wang, He, Lu and Shi2018; Yu et al., Reference Yu, Chi and Chen2013). The parameters included probability of survival from birth to age x (lx), proportion dying at each stage (dx), mortality (qx), survival rate (sx) per day per age class from egg to adult stages (Carey, Reference Carey1993, Reference Carey2001; Krebs, Reference Krebs1994; Price, Reference Price1997). Using these parameters the following statistics like total individuals at age x and beyond k (Tx), average population alive at each stage (Lx), life expectancy (ex), exponential mortality or killing power (kx), generation mortality (GM), generation survival (GS), gross reproductive rate (GRR), net reproductive rate (NRR or R0), mean generation time (Tc), doubling time (DT), intrinsic rate of population increase (rm), Euler’s corrected r (rc), finite rate of population increase (λ), weekly multiplication rate (λ7), and increase rate per generation (λTc), which were computed by Carey’s formulae (Carey, Reference Carey1993, Reference Carey2001; Krebs, Reference Krebs1994; Price, Reference Price1997; Ricklefs and Miller, Reference Ricklefs and Miller2000). Some other demographic parameters like potential fecundity (Pf), total fertility rate (TFR), mortality coefficient (MC), population growth rate (PGR), effective population (Ne), population momentum factor of increase (PMF), number of individuals after time t (Nt), expected population size in 2nd generation (PF2), Hypothetical females in 2nd generation (HFF2), general fertility rate (GFR), crude birth rate (CBR), reproductive value (RV), vital index (VI), and trend index (TI) were also analysed using various well-defined formulae (Carey, Reference Carey1993, Reference Carey2001; Krebs, Reference Krebs1994; Roy, Reference Roy2020, Reference Roy2022; Southwood, Reference Southwood1978).
Here, ax: number of survivors at age x; a0: number of survivors at age 0; lx +1: probability of survival from birth to age x + 1; N1: number of larvae in first generation; N2: number of larvae in next generation; N3: number of adults in a generation; kx: exponential mortality or killing power = [−log(sx)]; mx: Age specific fertility or fecundity = [fx/ax], where fx: number of eggs produced at each age; Pf: potential fecundity of a female individual; Nf: number of females in a generation; Nm: number of males in a generation.
Phytochemical estimation of rice cultivars
Uninfested rice grains that had been collected were now dipped in different solvents for the extraction of various PMs (like carbohydrates, proteins, lipids, amino acids, alkanes, and fatty acids) and SMs (like phenols, flavonoids, tannins, saponins, alkaloids phytates, and oxalates). The variability in the metabolites present in the grains were estimated by standard procedures for biochemical analyses, such as carbohydrates (DuBois et al., Reference DuBois, Gilles, Hamilton, Rebers and Smith1956), total proteins (Miller, Reference Miller1959), lipids (Folch et al., Reference Folch, Lees and Sloane Stanley1957), amino acids (Moore and Stein, Reference Moore and Stein1948), nitrogen (Humphries, Reference Humphries1956), moisture (Roy and Barik, Reference Roy and Barik2013), phenols (Bray and Thorpe, Reference Bray and Thorpe1954), flavonoids (Zhishen et al., Reference Zhishen, Mengcheng and Jianming1999), tannins (Trease and Evans, Reference Trease and Evans1983), saponins (Trease and Evans, Reference Trease and Evans1983), alkaloids (Harborne, Reference Harborne1973), phytates (Reddy and Love, Reference Reddy and Love1999), and oxalates (Day and Underwood, Reference Day and Underwood1986). Total alkanes (Roy et al., Reference Roy, Laskar and Barik2013b), free fatty acids (Roy et al., Reference Roy, Laskar and Barik2012), and free and bound amino acids (Roy et al., Reference Roy, Laskar and Barik2013a) were also quantified. Each biochemical analysis was repeated three times and expressed on a dry or fresh weight basis (Roy, Reference Roy2022).
Statistical analysis
Experimental data for different phytoconstituents in the selected rice cultivars and S. cerealella population parameters on the rice cultivars were homogeneous among treatments as confirmed by Levene’s homogeneity test. The data were normally distributed, as determined by Shapiro–Wilk tests, and thus they were compared using one-way analysis of variance (ANOVA). Means associated with the data were separated when they had significant (α = 0.05) differences, using Tukey’s multiple comparison (HSD) test (Zar, Reference Zar1999). All statistical analyses have been performed using Statistical Package for the Social Sciences (SPSS) version 16.0.
Results
Life history and morphology
The moth develops through four distinct stages: egg, larva, pupa, and adult (fig. 1, Supplementary Fig. 1). Newly laid eggs were white and gradually acquired a deep pink or reddish colour. The eggs were oval, with one end curved and the other flat. They were laid singly or in clusters (of up to 64 eggs) near or on the surface of the grain. The freshly hatched first-instar larvae were thread-like and yellowish-white, which then turned pinkish. They began their search for grains immediately after hatching, entered the kernels, fed and soon grew into white second-instar larvae (fig. 1, Supplementary Fig. 1). Multiple larvae were spotted inside a single grain, but typically one larva fully matured. S. cerealella exhibited five larval instars. Except for the larva at the initial stage, all were pure white and became sturdier with each stage. The larva pupated inside a cocoon beneath the bran of the grain (fig. 1, Supplementary Fig. 1). The pupa was initially light brown and darkened with maturation. The adult emerged through a minute pore cut out by the larva (fig. 1, Supplementary Fig. 1). Some larvae developed black marks on their dorsal side, while others did not. Larvae lacking these marks grew into female moths (Supplementary Fig. 1). Males had a blackish, slender abdomen when viewed ventrally, while the female abdomen was shiny white and bulky (fig. 1, Supplementary Fig. 1). The first-instar larvae (1.134 ± 0.191 mm in length, 0.226 ± 0.047 mm in breadth) were slender and longer than the eggs (0.526 ± 0.022 mm in length, 0.387 ± 0.093 mm in breadth). The larvae increased in size gradually until instar-IV, after which they shrank (instar-V larvae: 3.500 ± 0.289 in length, 1.100 ± 0.058 in breadth). Adult females (5.500 ± 0.289 mm in length, 2.000 ± 0.058 mm in breadth) were larger than the adult males (4.500 ± 0.289 mm long, 1.500 ± 0.058 mm wide) (fig. 2, Supplementary Table 1). The total immature period of AGM was more than 40 days on the selected rice cultivars. Female longevity exceeded that of the males (fig. 3).
Complete life cycle of Sitotroga cerealella on the rice cultivars with developmental durations (pooled) on five rice cultivars (Miniket, Cottondora Sannalu, Gobindobhog, Swarna, and Tulaipanji).
Length and breadth (Pooled) of Sitotroga cerealella on five rice cultivars (Miniket, Cottondora Sannalu, Gobindobhog, Swarna, and Tulaipanji). Means (Mean ± SE of three observations) followed by the same alphabet above the error bars are not significantly different (P ≥ 0.05) by Tukey’s HSD test.
Developmental durations of Sitotroga cerealella on five rice cultivars (Miniket, Cottondora Sannalu, Gobindobhog, Swarna, and Tulaipanji). Means (Mean ± SE of three observations) followed by the same alphabet above the error bars are not significantly different (P ≥ 0.05) by Tukey’s HSD test.
Population parameters
The stage-specific life tables of S. cerealella were examined separately for each cultivar. The lx, Lx and Tx gradually decreased with the developmental stages. qx decreased until instar-IV, after which it increased in all the cultivars except in the cultivar T, where it decreased until instar-II. Whereas, ex increased from egg to instar-I, after which it decreased consistently. sx and kx followed a more random pattern across the developmental stages. lx, sx, Lx, Tx, and ex decreased across the rice cultivars in the order as M > C > G > S > T. qx and kx followed the reverse order. Like most other insects, AGM also exhibited a type-III survivorship curve. The population parameters presented in table 1 did not differ significantly (F 4,10 ≥ 2.077; P ≤ 0.176) among different rice cultivars owing to similar metabolic utilities of the phytoconstituents. The population parameters presented in table 2 varied significantly (F 4,10 ≥ 11.162; P ≤ 0.002) among the selected crop cultivars, with few exceptions. The Pf (eggs/female) for AGM was highest on M (121.333 ± 7.513), followed by C (86.000 ± 5.292), G (67.333 ± 3.180), S (55.667 ± 2.028), and T (47.333 ± 3.480). Fx, GRR, Ne, MC, PGR, PF2, RV, VI, and TI followed the same pattern, M > C > G > S > T. The rm (individuals/female/day) followed a similar order with M (0.048 ± 0.002), followed by C (0.033 ± 0.001), G (0.020 ± 0.001), T (0.006 ± 0.003), and S (0.005 ± 0.001). NRR, λ, λ7, λTc, GS, and HFF2 followed the same order as the rm. The values of DT followed the reverse order of rm, while GM followed the reverse order of Pf. The Tc value was lowest on M, followed by C, S, G, and T. The reproductive and population growth parameters of AGM were significantly affected by the respective host phytoconstituents. Thus, the overall population growth of this moth was highest on M, followed by C, G, S, and T.
Population parameters of Sitotroga cerealella on five rice cultivars (Miniket, Cottondora Sannalu, Gobindobhog, Swarna, and Tulaipanji)
Note: Different alphabets within the rows indicate the means (Mean ± SE of three observations) are significantly different (P < 0.05, Tukey’s HSD) while comparing one type of host plant with the other.
Host phytochemicals
Population parameters of Sitotroga cerealella on five rice cultivars (Miniket, Cottondora Sannalu, Gobindobhog, Swarna, and Tulaipanji)
Note: Different alphabets within the rows indicate the means (Mean ± SE of three observations) are significantly different (P < 0.05, Tukey’s HSD) while comparing one type of host plant with the other.
The PMs and SMs varied significantly (F 4,10 ≥ 6.303, P < 0.001) among the rice cultivars (fig. 4 and 5, Supplementary Table 2). C contained the highest amounts of the major PMs, like total carbohydrates, proteins, and lipids (58.173 ± 0.247, 14.404 ± 0.278 and 13.427 ± 0.557 µg/mg dry weight, respectively), closely followed by T. Whereas, M exhibited intermediate levels of these metabolites (57.427 ± 0.878, 13.760 ± 0.767, and 12.063 ± 1.021 µg/mg dry weight, respectively), followed by S and G. Total amino acids and nitrogen (%) also followed a similar order, with the exception that G contained them in higher amounts than M and S (fig. 4, Supplementary Table 2). The content of free fatty acid was lower than that of alkanes, free amino acids and bound amino acids across all the rice cultivars, and they followed the same pattern as the major PMs: C > T > M > S > G (fig. 5, Supplementary Table 2). The highest concentrations of phenols and saponins were present in T (22.680 ± 0.077 and 21.690 ± 0.197 µg/mg dry weight, respectively), followed by C, G, and S and the lowest in M (10.870 ± 0.483 and 8.883 ± 0.463 µg/mg dry weight, respectively). All the other SMs followed the same pattern as T > C > G > S > M (fig. 4, Supplementary Table 2). Ultimately, the ratio of PMs to SMs differed significantly (F 4,10 ≥ 11.275, P < 0.001) among the selected rice cultivars.
Phytochemical variations [Mean ± SE of three observations expressed in dry weight (µg/mg dwt)] in five rice cultivars (Miniket, Cottondora Sannalu, Gobindobhog, Swarna, and Tulaipanji). Means followed by the same alphabet above the error bars are not significantly different (P ≥ 0.05) by Tukey’s HSD test.
Phytochemical variations [Mean ± SE of three observations, expressed in fresh weight (mg/100g fwt)] in five rice cultivars (Miniket, Cottondora Sannalu, Gobindobhog, Swarna, and Tulaipanji). Means followed by the same alphabet above the error bars are not significantly different (P ≥ 0.05) by Tukey’s HSD test.
Discussion
An insect constantly seeks a healthy host that can provide optimal nutrition, a suitable site for mating and oviposition and food for its neonates (Scriber and Slansky, Reference Scriber and Slansky1981). Conversely, herbivore-challenged plants can emit a blend of volatiles and non-volatile compounds that act as feeding and/or oviposition deterrents for the insects, bolstering resistance to future threats. The mixture may also attract insect predators, indirectly defending the hosts (Kessler and Baldwin, Reference Kessler and Baldwin2001; Kost and Heil, Reference Kost and Heil2006). Therefore, insects must employ various mechanisms to acquire a balanced diet with optimum nutritional content, including an appropriate protein-to-digestible carbohydrate ratio (P/C) (Aleksandra et al., Reference Aleksandra, Petar, Goran, Marijana, Mihaela and Dušan2018; Karimi-Pormehr et al., Reference Karimi-Pormehr, Borzoui, Naseri, Dastjerdi and Mansouri2018). Hence, understanding the feeding ecology and population growth of any insect pest is essential before devising a control strategy (Awmack and Leather, Reference Awmack and Leather2002; Roy, Reference Roy2020). We observed the life history, morphology and morphometry of S. cerealella on selected rice cultivars. Our study agreed with El-Sherif et al. (Reference El-Sherif, Hashem and Ahmed2008), who reported that AGM laid eggs singly or in groups of 2–60, with hatchability ranging from 85% to 100%. Aleksandra et al. (Reference Aleksandra, Petar, Goran, Marijana, Mihaela and Dušan2018) proposed that AGM laid eggs when stimulated by mechanical contact of the abdomen with tight interspaces between the kernels. They further stated that two AGM individuals could inhabit the same corn kernel and continue their development. In our study, we noticed that although multiple larvae could enter a single rice kernel and two might develop together, only one reached maturity and emerged as an adult. Our findings on the durations of life stages aligned with previous reports on different grains, except for the larval and pupal periods. The larval period was 24.3 ± 2.25 days on the rice cultivar Gangavati Sona (Basavanjali et al., Reference Basavanjali, Prabhuraj and Basavegowda2020) and 24.78 ± 0.042 days on maize (Sachin et al., Reference Sachin, Kumar, Kumar, Sati, Raj and Thakur2022), while the larval-pupal period was 26.7 ± 1.38 days on wheat (Jena et al., Reference Jena, Moharana, Gosavi and Sahoo2023). Pf was highest on M and lowest on T. The previously recorded data on fecundity of AGM on rice (Rai et al., Reference Rai, Chaudhuri and Ghosh2011), wheat (Borzoui and Naseri, Reference Borzoui and Naseri2016), maize (Demissie et al., Reference Demissie, Rajamanib and Ameta2014) and barley (Karimi-Pormehr et al., Reference Karimi-Pormehr, Borzoui, Naseri, Dastjerdi and Mansouri2018) fall within the range that we recorded. Hansen et al. (Reference Hansen, Skovgård and Hell2004) found that the highest fecundity (124 eggs per female) occurred at 20°C and 80% RH. The differences in immature development period, survivorship and reproductive performance of S. cerealella can be attributed to the differences in physicochemical properties of the host grains (Borzoui and Naseri, Reference Borzoui and Naseri2016; Perez-Mendoza et al., Reference Perez-Mendoza, Weaver and Throne2004). Based on developmental periods and survival of AGM, Ashamo (Reference Ashamo2010) classified the rice cultivar T(N)-1 (which had the longest developmental time of 26.3 days and an egg-to-adult survival of 38%) as most resistant and the cultivar Pusa 44 (which had the shortest developmental time of 23.0 days and an egg-to-adult survival of 68.7%) as least resistant. Borzoui et al. (Reference Borzoui, Naseri and Nouri-Ganbalani2017) obtained the longest developmental time, the highest reproductive performance and the lowest adult weight for AGM on sorghum. In that context, they classified sorghum and rye as unsuitable hosts and triticale and wheat as suitable hosts for the feeding and development of AGM.
Life table parameters offer deep insight into the insect’s fitness and can predict its population growth potential (Karimi-Pormehr et al., Reference Karimi-Pormehr, Borzoui, Naseri, Dastjerdi and Mansouri2018). We based the fitness of AGM on population parameters, such as Tc, R0, rm, etc., as in other studies (Mobarak et al., Reference Mobarak, Roy and Barik2020; Roy, Reference Roy2020, Reference Roy2022). Price (Reference Price1997) demonstrated that the rm is a valuable tool for comparing the population growth of insects. It denotes differences in survival rate and reproduction of the insect (Carey, Reference Carey1993). R0 and GRR represent the reproductive potential, rather than the overall fitness of the insect on different diets (Zeinalzadeh et al., Reference Zeinalzadeh, Karimi-Malati and Sahragard2016). In this study, the Pf, Fx, GRR, R0, rm, λ, GS and PGR and PF2 of AGM were highest on M and lowest on T and/or S. Accordingly, Tc, DT, and GM were lowest on M and highest on T and/or S. Considering these parameters, we classify the susceptibility of rice cultivars to AGM in the order as M > C > G > S > T. This was despite higher concentrations of all the PMs in C and T. The least susceptibility of T and lower susceptibility of C than M can be attributed to their higher levels of SMs. M was highly susceptible due to its lowest SM content and sufficient levels of PM. Now, G and S contained lower amounts of SMs, but they were moderately susceptible because the growth and development of the moth were hindered owing to their lower PM content. Alkaloids, terpenoids, phenols, flavonoids, tannins, saponins, etc., constitute the most widespread group of SMs that provide direct defence to the host plants or grains (Schoonhoven et al., Reference Schoonhoven, Van Loon and Dicke2005; Simmonds, Reference Simmonds2003). Host cultivars that were resistant to AGM contained higher amounts of amylose and phenol and exhibited higher amylase activity compared to susceptible ones (Ashamo, Reference Ashamo2010; Muthukumar et al., Reference Muthukumar, Ragumoorthi, Balasubramani and Vijayakumar2015). Quinones, formed by the oxidation of phenols, covalently bind to leaf proteins and inhibit digestion in herbivores (Applebaum, Reference Applebaum, Kerkot and Gillbert1985; Howe and Jander, Reference Howe and Jander2008). Flavonoids pose threats to various insect pests, such as Helicoverpa armigera and Spodoptera littoralis, by modulating their behaviour, growth and development, and ultimately acting as feeding deterrents (Simmonds and Stevenson, Reference Simmonds and Stevenson2001; Treutter, Reference Treutter2006). Tannins are bitter polyphenols that act as antifeedants by binding to proteins, reducing nutrient absorption efficiency, chelating metal ions and causing midgut lesions (Dadd, Reference Dadd, Kerkot and Gillbert1985). Defensive SMs can even act synergistically against the herbivory of different insects, as seen in maize, tomato, and tobacco against Spodoptera spp. and Helicoverpa spp. (Peng et al., Reference Peng, Deng, Huang, Jia, Miao and Huang2004; Vandenborre et al., Reference Vandenborre, Miersch, Hause, Smagghe, Wasternack and Van Damme2009). Damage and weight loss of gram varieties by Callosobruchus maculatus decreased by 9.11% and 2.08%, respectively, for 1% increase in crude protein, and they increased by 7.12% and 0.34%, respectively, for 1% increase in carbohydrates (Mansha, Reference Mansha and Sc1985). An increase in sugar and starch content in the host also increased the reproduction rate and weights of Sitophilus oryzae (Singh and McCain, Reference Singh and McCain1963). Such correlations may explain the differences in susceptibility of the rice cultivars to AGM. Ashamo (Reference Ashamo2010) observed that mated AGM females lived less than the unmated ones, probably due to the depletion of fats and proteins during egg development. De and Dey (Reference De and Dey2022) reported equal infestations of AGM in aromatic and non-aromatic rice cultivars at low humidity. The present work did not find any preference based on aroma either. Painter (Reference Painter1968) first explained the mechanisms of resistance for plants against insect pests. With advances in biotechnology, it is now possible to instil desirable characteristics and improve the resistance of hosts to S. cerealella or other SGPs. However, care must be taken because this can change the grain’s susceptibility to other pests (Ashamo, Reference Ashamo2010). Despite the efforts, none of the grains or cultivars are completely resistant as of now, and this study found substantial degrees of infestation and damage even in the least susceptible cultivar, T.
It is striking that the population parameters from this study on paddy were lower than those on wheat (Murad and Batool, Reference Murad and Batool2017; Salim et al., Reference Salim, Ullah, Saljoqi, Gökçe, Ahmad, Almutairi, Sayed, Aleya, Abdel-Daim and Shah2023), maize (Salim et al., Reference Salim, Ullah, Saljoqi, Gökçe, Ahmad, Almutairi, Sayed, Aleya, Abdel-Daim and Shah2023), and barley (Karimi-Pormehr et al., Reference Karimi-Pormehr, Borzoui, Naseri, Dastjerdi and Mansouri2018). Hansen et al. (Reference Hansen, Skovgård and Hell2004) obtained a maximum rm value of 0.086 individuals/female/day on maize at 30°C and 80% RH, which declined dramatically at 35°C. The highest value of rm that we obtained was 0.048 ± 0.002 individuals/female/day, on M. The values of rm and λ for AGM on barley cultivars Nik (0.0539 ± 0.004 and 1.055 ± 0.004 individuals/female/day, respectively) and Yousef (0.0542 ± 0.003 and 1.056 ± 0.003 individuals/female/day, respectively) that Zeinalzadeh et al. (Reference Zeinalzadeh, Karimi-Malati and Sahragard2016) recounted are comparable to our findings on M. However, the ranges of R0 (20.500 ± 4.600 to 48.410 ± 8.640 offspring/individual) and GRR (40.558 ± 9.100 to 98.192 ± 14.050 offspring/individual) that they documented vary significantly from our results. Nevertheless, comparing biological parameters or extracting data from separate research can prove to be misleading. Differing experimental conditions, host phytochemicals and genetic variations in the insect populations are responsible for such discrepancies (Chowdhury et al., Reference Chowdhury, Sardar and Roy2025). Similar to our findings, Chaudhuri and Gharde (Reference Chaudhuri and Gharde2017) also found that AGM preferred short and bold varieties, such as Kola Joha (small), Gobindobhog, and Mohanbhog, over long and slender Tulaipanji. Such categorisation can help select the least susceptible crop varieties for cultivation and identify highly susceptible cultivars (like Miniket) that require protection against S. cerealella. Favourability for the growth of AGM on different rice cultivars also varied according to seasonality (Rai et al., Reference Rai, Chaudhuri and Ghosh2011) and location (Santos et al., Reference Santos, Agbangla, Chougourou, Missihoun and Ahanhanzo2015). Future work has to substantiate this with more population data. Population projection models can then encapsulate shifts in the dynamics of the AGM populations in a world with changing climates.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0007485325100552.
Acknowledgements
We wish to express our deepest gratitude to the University Grant Commission (UGC: NTA Ref. No. 211610066466), India, for financial assistance. We must acknowledge the departmental staff members who supported us in every way possible during this work. Finally, we thank the farmers who helped us all through.
Competing interests
The authors declare that there is no conflict of interest other than publication of this paper.
