Analysis of Sublethal and Lethal Effects of Chlorantraniliprole on Loxostege sticticalis Based on Age-Stage, Two-Sex Life Table

Abstract

Chlorantraniliprole, serving as a substitute for traditional insecticide, has been widely utilized in controlling lepidopteran pests. Loxostege sticticalis (Lepidoptera: Crambidae) is a polyphagous insect and poses a significant threat as a migratory insect. This study investigated the life history traits of a field-collected population in response to chlorantraniliprole exposure based on an age-stage, two-sex life table. After treating the third-instar larvae of L. sticticalis with three different doses of chlorantraniliprole, namely LC₁₀, LC₂₅, and LC₅₀, the survival, development, and fecundity of L. sticticalis were affected significantly in a dose-dependent manner. Chlorantraniliprole at doses of LC₁₀, LC₂₅, and LC₅₀ prolonged the average generation time (T) compared to the control group. The net reproductive rate (R₀) and intrinsic growth rate (r) were significantly higher in the LC₁₀ group but significantly lower in the LC₂₅ and LC₅₀ groups. Chlorantraniliprole used at a dose of LC₁₀ was shown to increase the finite growth rate (λ), while it decreased λ at doses of LC₂₅ and LC₅₀. These results suggested that chlorantraniliprole induces hormetic effects by enhancing fecundity and reproductive potential at lower sublethal concentration (LC₁₀), while reducing the reproductive output at higher doses (LC₂₅ and LC₅₀). Our results provide useful information for developing management strategies for L. sticticalis involving the use of chlorantraniliprole.

1. Introduction

Loxostege sticticalis L., a member of the family Crambidae (Lepidoptera), is a globally distributed migratory pest. Its larvae exhibit high mobility, polyphagous feeding behavior, and sporadic outbreak dynamics, while adults possess strong reproductive capacity and long-distance migratory behavior [1]. This species is a significant agricultural pest worldwide [2], for instance, causing significant damage in China’s North, Northeast, and Northwest agriculture. To date, more than 50 families and over 300 plant species have been reported to be damaged by the larvae of L. sticticalis, including soybeans, corn, sunflowers, and potatoes, among others. During population outbreaks, the larvae can devour plant stems, leaves, and even whole fields of plants, leading to serious destruction to production, and chemical control remains the dominant strategy for control [1,2,3].

Chlorantraniliprole, a diamide insecticide, targets ryanodine receptors (RyRs) and exhibits potent stomach and contact activity with high selectivity against Lepidoptera [4]. The insecticide demonstrates minimal non-target toxicity, prolonged residual efficacy, and rainfastness, making it a key chemical insecticide for lepidopteran pest management [5,6]. However, the application of insecticides in agricultural settings leads to variations in individual pest exposure due to differences in dose and the gradual degradation. This often results in the administration of sublethal doses that do not directly kill the pests but instead induce a range of sublethal effects, including interference with growth, development, and reproduction; alteration of behavioral patterns; and effects on physiological and biochemical characteristics [7]. It has been reported that chlorantraniliprole exhibits sublethal effects against several pests [8,9,10,11,12,13,14,15]. For example, chlorantraniliprole, at doses of LC₁₀ and LC₃₀ against Spodoptera frugiperda (Lepidoptera, Noctuidae), prolonged the development time of the larvae and decreased larval and pupa weight, the pupal rate, adult emergence, and fecundity [14]. Sublethal exposures to chlorantraniliprole significantly reduce the reproduction and flight performance of Agrotis ipsilon and A. segetum, and decrease offspring production. Chlorantraniliprole significantly increased fecundity in the F₁ generation, which could promote population growth and pest resurgence [15].

The age-stage, two-sex life table approach is widely used to investigate the lethal and sublethal effects of insecticides on insects, because it provides a more comprehensive and realistic assessment of insect population dynamics by integrating survival, development, and fecundity between males and females at different life stages (egg, larva, pupa, adult) and ages within each stage [11,12,13,16,17]. Given the growing recognition of the significance of sustainable agriculture and eco-friendly pest management, the life-table studies on key insect pests and their practical application in insect pest control are undoubtedly worth pursuing urgently.

In this study, we used the age-stage, two-sex life-table analysis method to investigate the sublethal and lethal effects of chlorantraniliprole on L. sticticalis after treating the third-instar larvae of the species with three different doses of chlorantraniliprole, viz., LC₁₀, LC₂₅, and LC₅₀. The physiological parameters, including development, fecundity, survival rate, and longevity, were assessed to determine the impact of chlorantraniliprole on L. sticticalis. The findings provide insights for optimizing field applications of chlorantraniliprole in the integrated management of L. sticticalis.

2. Materials and Methods

2.1. Insect and Insecticide

The population of L. sticticalis used in the present study was collected from Kangbao County (41°–42° N, 114°–115° E), Zhangjiakou City, Hebei Province, China, in 2023. It was reared in the laboratory without any pesticide exposure for approximately 30 generations through May 2025 under the standard conditions, 22.5–27.5 °C, 65–75% RH, and a 16:8 L:D photoperiod. The adults were fed with a 10% glucose solution as food by using cotton wicks on the cage lid [3]. Insecticide-free fresh Chenopodium album L. were used to rear L. sticticalis larvae. The mature larvae were collected and transferred to a new jar with 10% water from sterilized soil for pupating. After being reared in the laboratory for three consecutive generations without pesticide exposure, this population was used in the experiment. Chlorantraniliprole (purity, 95.0%) was purchased from Guangzhou Xingyuan Science & Technology Co., Ltd. (Guangzhou, China).

2.2. Bioassays

The laboratory bioassay was conducted in accordance with the “Pesticides guidelines for laboratory bioactivity tests Part 6: The immersion test for insecticide activity” (NY/T 1154.6-2006) [18]. The chlorantraniliprole solution (500 μg/L) was prepared with methanol and diluted to six different concentrations (0.003, 0.010, 0.030, 0.100, 0.300, and 1.00 μg/L) with distilled water, and a solution of 0.2% methanol was prepared as control. The third instar larvae of L. sticticalis were dipped in chlorantraniliprole solution for 15 s, then removed and placed on filter paper to air-dry. After drying, they were transferred to rearing boxes and reared with insecticide-free fresh C. album under the standard conditions (22.5–27.5 °C, 65–75% R.H., 16:8 L:D). Mortality was observed and recorded every 24 h until 72 h. For the bioassays, a minimum of 30 L. sticticalis larvae were used per replicate, and each concentration was tested in triplicate (totaling 90 larvae).

2.3. The Life-Table Study in Loxostege sticticalis

The age-stage, two-sex life table was constructed as described by Cheng et al. [19] to assess the development, survival, and reproduction of L. sticticalis after treating the third-instar larvae with chlorantraniliprole at doses of LC₁₀, LC₂₅, and LC₅₀. The larvae treated with 0.02% (v/v) methanol were used as the control group. For the life-table study, 120 third-instar larvae were selected to dip in the solution for 15s per replicate, and the experiment was repeated three times (totaling 360 larvae for each treatment). After treatment, the larvae were fed with fresh C. album L., which was replaced every day, and larvae were reared under the standard conditions (22.5–27.5 °C, 65–75% R.H., 16:8 L:D). The survival, development, and duration of each larva were observed and recorded every day. When the larvae had completed the fifth instar and ceased feeding, the pupal stage was observed and recorded. Subsequently, a total of 120 pupae were collected from each treatment and divided into three groups [19]. The emergence of adults from each group was recorded, and 30 pairs (female: male, 1:1) were selected and placed individually in a cage and fed with a 10% (w/v) glucose solution as food by using cotton wicks on the cage lid. The longevity of each adult, the number of eggs laid by each female, and the oviposition period were recorded. After oviposition, 120 eggs were collected from each group, and the egg hatching rates were recorded 3 days post-collection.

2.4. Data Analysis

The sublethal concentrations (LC₁₀, LC₂₅) and the median lethal concentration (LC₅₀) along with their confidence intervals were calculated by using IBM SPSS Statistics Grad Pack 29.0 PREMIUM. Based on the age-stage, two-sex life-table theory, the raw life-history data of all L. sticticalis individuals were imported into TWOSEX-MSChart 2022 software for analysis as described in previous studies [20,21,22]. Key parameters were calculated, including the age-stage-specific survival rate (S_xj), age-specific survival rate (l_x), the age-stage-specific fecundity (f_xj), female age-specific fecundity (m_x), and the age-specific net maternity (l_xm_x). Subsequently, these parameters were used to calculate the population parameters R₀ (the net reproductive rate), T (the mean generation time), r (the intrinsic rate of increase), and λ (the finite rate of increase). The means and standard errors (SEs) were estimated through bootstrapping with 100,000 trials, and the statistical significance of the observed difference was determined using the TWOSEX-MSChart program [20,21,22]. The curves related to S_xj, l_x, f_xj, m_x, and l_xm_x were drawn using OriginPro 2018 software. The equations for S_xj, l_x, f_xj, m_x, l_xm_x, R₀, T, r, and λ were as follows, respectively.

The age-stage-specific survival rate (S_xj) refers to the probability of an individual of stage j surviving from age x to the next age (x + 1),

$$S_{xj}={\displaystyle \frac{n_{x+1,j}}{n_{\mathrm{x}\mathrm{j}}}}$$

where n_xj is the number of individuals in stage j at age x.

The age-specific survival rate (l_x) refers to the cumulative survival rate across all stages at age x,

$$l_x={\displaystyle \sum _{j=1}^{\beta }}{s}_{xj}$$

where β is the number of stages.

The age-stage specific fecundity (f_xj) refers to the mean number of hatched eggs laid by female adults in stage j at age x, and j = 7 in this current study,

$$f_{xj}={\displaystyle \frac{E_{xj}}{N_{xj}}}$$

where E_xj refers to the total number of eggs laid by all female adults in stage j at age x, and N_xj refers to the total number of surviving female adults in stage j at age x.

The age-specific fecundity(m_x) refers to the mean number of eggs laid per female individual at stage x,

$$m_x={\displaystyle \frac{{\sum }_{j=1}^{\beta }{s}_{xj}{f}_{xj}}{{\sum }_{j=1}^{\beta }{s}_{xj}}}$$

where β is the number of stages.

The net reproductive rate (R₀;) refers to the mean number of offspring produced by each individual over its lifetime,

$$R_0={\displaystyle \sum _{x=0}^{\mathrm{\infty }}}{l}_x{m}_x$$

The intrinsic rate of increase (r) refers to the maximum instantaneous growth rate of a population under ideal conditions (when time tends toward infinity and the population reaches a stable age-stage distribution), and it was calculated based on the Euler–Lotka equation using the iterative bisection method,

$${\displaystyle \sum _{x=0}^{\mathrm{\infty }}}{l}_x{m}_x{\mathrm{e}}^{-r(x+1)}=1$$

The finite rate of increase (λ) refers to the per-unit time step in discrete-time models,

$$\lambda =e^r$$

where e represents the natural exponential constant (≈2.71828).

The mean generation time (T) refers to the time needed for the population to replace itself under a stable age-stage distribution,

$$T={\displaystyle \frac{l_n{R}_0}{r}}$$

3. Results and Discussion

3.1. Toxicity of Chlorantraniliprole on Loxostege sticticalis Larvae

In this study, the toxicity of chlorantraniliprole on the third-instar larvae of L. sticticalis was detected by using an insect-dip bioassay procedure. The results suggested that chlorantraniliprole had high toxicity against the L. sticticalis larvae following 72 h treatment (

Table 1. Toxicity of chlorantraniliprole against the third-instar larvae of Loxostege sticticalis.

Insecticides	Slope ± SE	LC50 (95% CI) ×10−2 μg/L	LC25 (95% CI) ×10−2 μg/L	LC10 (95% CI) ×10−2 μg/L	χ2	R2
Chlorantraniliprole	0.843 ± 0.154	8.183 (3.418–14.524)	1.297 (2.283–3.172)	0.247 (0.018–0.892)	0.523	0.986

). The lethal concentration that caused 50% mortality (LC₅₀, 72 h) was determined to be 0.08183 (0.03418–0.14524) μg L⁻¹ with a slope ± SE of 0.843 ± 0.154 (χ² = 0.523, df = 14, p = 0.986). The LC₁₀ and LC₂₅ values of chlorantraniliprole against the third-instar larvae of L. sticticalis were 0.00247 (0.00018–0.00892) μg L⁻¹ and 0.01297 (0.02283–0.03172) μg L⁻¹, respectively. The LC₁₀, LC₂₅, and LC₅₀ concentrations were selected to investigate the sublethal and lethal effects of chlorantraniliprole on L. sticticalis. In Spodoptera cosmioides, the ingestion toxicity bioassay showed that chlorantraniliprole was active against larvae of the second instar with an LC₅₀ (48 h) value of 0.054 µg mL⁻¹ [22]. According to reports, the LC₅₀ values of chlorantraniliprole were 7.83 mg/L and 39.00 mg/L (48 h) against the two chironomids larvae, Chironomus javanus and C. kiiensis, respectively [6]. Leaf-dip bioassays showed that chlorantraniliprole had a high level of toxicity against P. xylostella larvae, with a 48 h LC₅₀ value of 0.23 mg L⁻¹ for a susceptible strain [23]. Chlorantraniliprole showed high activity against adults of two major migratory insect pests, namely Agrotis ipsilon and A. segetum, with LC₅₀ values of 0.21 mg L⁻¹ and 0.51 mg L⁻¹, respectively [15]. These LC₅₀ values highlighted the variable toxicity of chlorantraniliprole across different insect species and life stages. The higher toxicity of chlorantraniliprole to L. sticticalis compared to other Lepidoptera (P. xylostella) species might be attributed to a combination of physiological, molecular, and behavioral factors. Specially, L. sticticalis exhibits cyclical population explosions at approximately 20-year intervals, which may correlate with the higher sensitivity to insecticides due to reduced selection pressure during inter-outbreak periods [1,2].

3.2. Sublethal and Lethal Effects of Chlorantraniliprole on Loxostege sticticalis Based on the Life Table

3.2.1. Sublethal and Lethal Doses of Chlorantraniliprole Affect the Development Duration of Loxostege sticticalis

Exposure to sublethal and lethal concentrations of chlorantraniliprole affected the life cycle and development of L. sticticalis. As shown in

Table 2. The sublethal and lethal doses of chlorantraniliprole affect the development duration of Loxostege sticticalis.

Developmental Stage (Days)	Groups
	Control	LC10	LC25	LC50
Egg	2.978 ± 0.051 a	3.000 ± 0.051 a	3.000 ± 0.089 a	2.978 ± 0.033 a
1st instar larvae	2.592 ± 0.087 a	2.592 ± 0.087 a	2.581 ± 0.100 a	2.581 ± 0.100 a
2nd instar larvae	2.570 ± 0.029 a	2.570 ± 0.029 a	2.570 ± 0.029 a	2.570 ± 0.029 a
3rd instar larvae	2.258 ± 0.025 d	2.618 ± 0.038 c	2.818 ± 0.037 b	3.140 ± 0.032 a
4th instar larvae	2.257 ± 0.012 d	2.756 ± 0.029 c	2.861 ± 0.017 b	3.190 ± 0.027 a
5th instar larvae	2.259 ± 0.025 c	2.817 ± 0.037 b	2.861 ± 0.058 b	3.310 ± 0.013 a
Pupa	10.676 ± 0.025 d	12.178 ± 0.051 c	13.056 ± 0.096 b	15.067 ± 0.115 a
Female	9.440 ± 0.577 b	12.222 ± 0.763 a	12.278 ± 1.892 a	12.556 ± 1.528 a
Male	8.778 ± 0.577 b	11.222 ± 0.577 a	11.722 ± 1.041 a	12.333 ± 1.323 a
Egg-adult	35.193 ± 0.333 d	40.276 ± 0.056 c	41.178 ± 0.043 b	44.081 ± 0.028 a

The data are shown as mean ± SE. Means marked with different letters indicate statistically significant differences among groups (p < 0.05) using Turkey’s test in IBM SPSS Statistics Grad Pack 29.0 PREMIUM.

, after treating the third-instar larvae with LC₁₀, LC₂₅, and LC₅₀ doses of chlorantraniliprole, the development duration of larvae from the third instar to the fifth instar was prolonged significantly in all three treated groups compared to the control group (p < 0.05), which resulted in a significant increase in the total larval development duration (p < 0.05). Meanwhile, the treatment with chlorantraniliprole at doses of LC₁₀, LC₂₅, and LC₅₀ increased the mean pupal development time, extending it by 12.32%, 18.22%, and 29.13% compared to the control group, respectively. Furthermore, the longevity of both female and male adult specimens was increased compared to the control group (p < 0.05). Overall, it was found that the time required for L. sticticalis to develop from eggs to adults in the LC₁₀, LC₂₅, and LC₅₀ treatment groups was 44.081, 41.178, and 40.276 days, respectively. These results represented significant extensions of 5.08, 5.99, and 8.89 days in the life cycle compared to the control group (p < 0.001), even though the treatment with chlorantraniliprole began only at the third-instar larval stage of L. sticticalis. It has been widely documented that lethal and/or sublethal doses of chlorantraniliprole can affect the life cycle and development of different insect pests, including Chironomus kiiensis, C. javanus, S. frugiperda, S. cosmioides, and P. xylostella [6,13,22,24]. Similarly, after treating the second-instar S. cosmioides larvae with LC₁₅ and LC₃₀ doses of chlorantraniliprole, the larval development time, pupal development time, and adult longevity were increased, ultimately extending the life cycle [22]. According to previous reports, chlorantraniliprole can prolong the development of insects, possibly due to the disturbances in the normal development of neuronal tissue [7]. The prolonged life cycle, specifically in the larval stage, has implications for the management of insect pests, because a longer development time would mean a longer feeding period, which can lead to greater crop losses or economic impact if not managed properly [25,26].

3.2.2. Sublethal and Lethal Doses of Chlorantraniliprole Affect the Reproduction of Loxostege sticticalis

In this present study, significant effects on the fecundity of L. sticticalis were observed, exhibiting a biphasic response: a low dose (LC₁₀) of the treatment increased reproduction in this species, while higher doses (LC₂₅ and LC₅₀) reduced it. Firstly, the oviposition period of adult females was significantly prolonged in the LC₂₅ and LC₅₀ treatment groups compared to the control group (p < 0.05), whereas the LC₁₀ group exhibited a slight but non-significant increase (p > 0.05) (Figure 1A). The total number of eggs laid by each female in the LC₁₀-treated group increased significantly compared to the control group (p < 0.05), but decreased significantly in the LC₅₀ treated group (Figure 1B). Meanwhile, the hatching rate was significantly reduced in both the LC₂₅ and LC₅₀ treatment groups compared to the control group, but no significant change was observed in the LC₁₀ group (Figure 1C). These results suggested that a low dose (LC₁₀) of chlorantraniliprole may tend to increase L. sticticalis populations and higher doses (LC₂₅ and LC₅₀) can decrease the fecundity of L. sticticalis, highlighting the importance of studying sublethal effects and the need for careful dose selection in control strategies using chlorantraniliprole to manage L. sticticalis.

Other researchers have found that the number of eggs laid per female and the number of viable larvae hatched from eggs decreased in several insect pests after they were treated with chlorantraniliprole during the larval stage [12,27]. Interestingly, according to the report of Zhang et al. (2023), exposure to chlorantraniliprole at LC₁₀ and LC₂₅ concentrations during the larval stage in S. frugiperda significantly reduced the fecundity of the F₀ generation, but increased the fecundity of the F₁ generation [12]. However, the exposure of female Bactrocera dorsalis to 1.30 μg/g of chlorantraniliprole led to increased fecundity compared with the control group. The variations in the reproductive effects of chlorantraniliprole across different insect species have been attributed to dose-dependent and species-specific toxicological responses [27].

3.2.3. The Effect of Chlorantraniliprole on the Survival and Fecundity of Loxostege sticticalis Based on the Age-Stage, Two-Sex Life Table

The age-stage-specific survival rate (S_xj) curves indicated the probability that a newly laid egg will survive to stage j at age x, separately showing survival rate in different life stages. As shown in Figure 2, there was a considerable amount of time overlap between individuals in each group of L. sticticalis, which might be associated with the complexity of individual growth and development. The age-stage-specific survival rate (S_xj) decreased in a dose-dependent pattern after the third-instar larval stage in the LC₁₀, LC₂₅, and LC₅₀ treatment groups, when compared to the control group. Furthermore, the S_xj curves exhibited differences between female and male specimens in the LC₁₀ and LC₂₅ treated groups, characterized by male adults that emerged later but had shorter lives than the females. The age-specific survival rate (l_x) of the population is a simplified version of S_xj, obtained by disregarding stage differentiation [27], and it showed the same tendency as S_xj, with a clear and more straightforward pattern (Figure 3). Furthermore, the values in both S_xj and l_x curves decreased more quickly in the LC₂₅ and LC₅₀ groups at the 10th day than that in the control group. The curve of age-specific fecundity (f_x7) indicated that the fecundity of L. sticticalis increased at the LC₁₀ dose of chlorantraniliprole, but decreased in the LC₂₅ and LC₅₀ dose groups. Meanwhile, the highest peak values of age-specific fecundity (m_x) and age-specific net reproductive value (l_xm_x) in the LC₁₀ group were significantly higher than those in the control group, whereas, those in the LC₂₅ and LC₅₀ groups were lower than that in the control group. Furthermore, the reproductive curves (f_x7, m_x, l_xm_x) started on the 29th, 29th, and 30th day in the LC₁₀, LC₂₅, and LC₅₀ groups, respectively. These data suggested a delay in the oviposition period in exposed females of L. sticticalis compared to that in the control group (on the 26th day), because of the prolonged development of larvae and pupae (Figure 3).

Life-table studies are essential for the study of population ecology. Exposure to chlorantraniliprole significantly altered the life-table parameters and impaired the normal development and reproductive capacity in L. sticticalis populations. According to

Table 3. Life table parameters of Loxostege sticticalis after exposure to chlorantraniliprole at doses of LC₁₀, LC₂₅, and LC₅₀.

Groups	Net Reproductive Rate R0 (Offspring)	Intrinsic Rate of Increase r (d−1)	Finite Rate of Increase λ (d−1)	Mean Generation Time T (d)
Control	82.1950 ± 0.7211 b	0.2532 ± 0.0015 b	1.2881 ± 0.0032 b	17.4135 ± 0.0970 b
LC10	94.6087 ± 1.0504 a	0.2704 ± 0.0006 a	1.3105 ± 0.0021 a	16.8266 ± 0.0470 c
LC25	56.1377 ± 0.9320 c	0.2439 ± 0.0002 c	1.2762 ± 0.0037 c	16.5138 ± 0.0400 d
LC50	18.6342 ± 0.4619 d	0.1030 ± 0.0001 d	1.1085 ± 0.0006 d	28.3953 ± 0.0021 a

The data are shown as mean ± SE. Means marked with different letters indicate statistically significant differences among groups (p < 0.05) using Turkey’s test in IBM SPSS Statistics Grad Pack 29.0 PREMIUM.

, the net reproductive rate (R₀), intrinsic rate of increase (r), and finite rate of increase (λ) were significantly increased in the LC₁₀ group (p < 0.05), while those in the LC₂₅ and LC₅₀ groups were significantly decreased (p < 0.05) compared to the control group. The mean generation time (T) was reduced significantly in both the LC₁₀ and LC₂₅ groups, but increased significantly in the LC₅₀ group compared to the control group. These results confirmed that chlorantraniliprole at the LC₁₀ concentration could stimulate fecundity and increase the resurgence of the L. sticticalis population with higher values of R₀, r, and λ, along with a lower T. However, in the LC₅₀ group, the demographic parameters R₀, r, and λ were significantly reduced, and the mean generation time (T) increased, which suggested that the higher concentration (LC₅₀) of chlorantraniliprole had a detrimental effect on the population dynamics of L. sticticalis by reducing its reproductive potential and prolonging the generation time.

The results obtained from the analysis, which was based on the age-stage, two-sex life table, confirmed the findings observed from the data as described in Section 3.2.1 and Section 3.2.2. Exposure to chlorantraniliprole significantly affected the survival, development, and fecundity of L. sticticalis in a dose-dependent manner. In addition, the stage-specific survival curves (S_xj) revealed sexual dimorphism in L. sticticalis under LC₁₀ and LC₂₅ exposure to chlorantraniliprole. Compared to the control group, the survival rate was reduced and the development duration was prolonged with the increase in the chlorantraniliprole concentration in L. sticticalis. Hormetic effects refer to a biphasic dose–response relationship characterized by beneficial or stimulatory effects at low doses of a pesticide, followed by adverse or inhibitory effects at higher doses [28]. As for the reproductive capacity and fecundity of L. sticticalis, chlorantraniliprole exhibited hormetic effects by enhancing fecundity and reproductive potential at the lower sublethal concentration (LC₁₀), while reducing the reproductive output at higher doses (LC₂₅ and LC₅₀). According to reports, the exposure to chlorantraniliprole at the LC₂₅ and LC₅₀ doses stimulated fecundity in P. xylostella, which increased by 10.28% and 28.02%, respectively [29]. Some studies have found that sublethal doses of some pesticides can stimulate the reproduction of insects [30,31]. Meanwhile, exposure to chlorantraniliprole significantly decreased fecundity in several insect pests, including S. frugiperda. In contrast, the fecundity of the S. frugiperda F₁ generation was increased significantly by 3.75% and 23.0% via sublethal exposure in the S. frugiperda F₀ generation [12,21,25,26]. Interestingly, Wu et al. reported different results, with fecundity in the F₀ and F₁ generations of S. frugiperda decreasing by 67.33% and 27.99%, respectively, after exposure of the third-instar larvae of S. frugiperda to chlorantraniliprole at LC₃₀ [28]. These results highlight the significant differential impact of sublethal and/or lethal doses of insecticides on the development and fertility of insect pests. Consequently, it is essential to thoroughly investigate the effects of widely used insecticides on target insects. Such research is critical for understanding how these insecticides continue to influence pest populations. This knowledge can improve the development of more effective and sustainable pest management strategies.

However, the molecular mechanisms by which sublethal doses of insecticides induce reproductive stimulation or inhibition in pests remain largely unclear. In Aphis gossypii, hormetic effects induced by deltamethrin contributed to the activation of gene expression and protein synthesis associated with sexual reproduction, embryonic development, growth, and reproductive development [32]. The reproductive dysfunctions after insecticide treatment could be due to either physiological or behavioral alterations [8]. According to the report of Meng et al. (2020) [8], the prolonged developmental time and reduced fecundity induced by sublethal concentrations of chlorantraniliprole were associated with increased juvenile hormone levels in Chilo suppressalis [33]. In the present study, the sexual dimorphism illustrated by S_xj curves in both the LC₁₀- and LC₂₅-treated groups may suggest that the underlying mechanisms of hormetic effects induced by chlorantraniliprole in L. sticticalis can be associated partially with the juvenile hormone levels. In the future, further studies should focus on the underlying mechanism influencing the lethal and sublethal effects of chlorantraniliprole on development and fecundity in L. sticticalis.

In this study, we applied the age-stage, two-sex life-table theory to evaluate the effects of chlorantraniliprole on the demographic characteristics of L. sticticalis. Our results provide a comprehensive description of the survival, development, and reproduction of a cohort of individuals after treatment with chlorantraniliprole at doses of LC₁₀, LC_25, and LC₅₀. The results of the present study help us to understand how lethal and sublethal exposure to chlorantraniliprole affected the biological, reproductive, and demographic characteristics of L. sticticalis. Specially, these findings indicated that low levels of chlorantraniliprole may stimulate fecundity and increase the resurgence of insect pests. The increased reproduction and longevity might cause insect pest outbreaks in field contexts that ultimately increase crop damage. Therefore, more attention should be paid to the potential sublethal effects of pesticides on pest population dynamics in integrated pest management strategies [30].

4. Conclusions

In conclusion, our results confirmed that chlorantraniliprole significantly affects the survival, development, and fecundity of L. sticticalis in a dose-dependent manner. Specially, low levels of chlorantraniliprole may stimulate fecundity and increase the resurgence of L. sticticalis, suggesting that more attention should be paid to the potential sublethal effects of pesticides on pest population dynamics in integrated pest management strategies. Based on the findings, it is recommended to avoid low-dose applications of chlorantraniliprole to prevent potential stimulation of fecundity and resurgence in L. sticticalis.