Feeding Appropriate Nutrients during the Adult Stage to Promote the Growth and Development of Carposina sasakii Offspring

Simple Summary

The peach fruit moth, Carposina sasakii Matsumura, is a significant fruit-boring pest that negatively impacts the East Asian agricultural economy. To aid the development of pest control strategies, peach fruit moths are raised and studied for multiple generations in laboratory. It is important when maintaining a laboratory moth colony to consider the effects of nutrition on the colony’s growth, survival, and reproduction. In this study, adult peach fruit moths (F₀) were divided into separate groups, and each group was fed one of seven different nutrient solutions under laboratory conditions. The development and fitness of the moths’ offspring (F₁) were then analyzed. The results showed that F₀ adult peach fruit moths fed with 10 grams per liter sucrose had F₁ offspring with significantly higher fitness and reproductive parameters, suggesting that this concentration of sucrose is more suitable for raising laboratory peach fruit moths. Thus, appropriate nutrition during the adult stage of the peach fruit moth’s life cycle could play an important role in the development of future offspring in laboratory studies and in turn influence the future of East Asian agriculture.

Abstract

Nutrients consumed during the adult stage are a key factor affecting the growth, development, and reproduction of insect offspring and thus could play an important role in insect population research. However, there is absence of conclusive evidence regarding the direct effects of parental (F₀) nutritional status on offspring (F₁) fitness in insects. Carposina sasakii Matsumura is a serious, widespread fruit-boring pest that negatively impacts orchards and the agricultural economy across East Asia. In this study, life history data of F₁ directly descended from F₀ C. sasakii fed with seven different nutrients (water as control, 5 g·L⁻¹ honey solution, 10 g·L⁻¹ honey solution, 5 g·L⁻¹ sucrose solution, 10 g·L⁻¹ sucrose solution, 15 g·L⁻¹ sucrose solution, and 20 g·L⁻¹ sucrose solution) were collected under laboratory conditions. The growth and development indices, age-stage specific survival rate, age-stage specific fecundity, age-stage specific life expectancy, age-stage specific reproductive value, and population parameters of these offspring were analyzed according to the age-stage, two-sex life table theory. The results showed that the nutritional status of F₀ differentially affects the growth, development, and reproduction of F₁. The F₁ offspring of F₀ adult C. sasakii fed with 10 g·L⁻¹ sucrose had significantly higher life table parameters than those of other treatments (intrinsic rate of increase, r = 0.0615 ± 0.0076; finite rate of increase, λ = 1.0634 ± 0.0081; net reproductive rate, R₀ = 12.61 ± 3.57); thus, 10 g·L⁻¹ sucrose was more suitable for raising C. sasakii in the laboratory than other treatments. This study not only provides clear evidence for the implications of altering F₀ nutritional conditions on the fitness of F₁ in insects, but also lays the foundation for the implementation of feeding technologies within the context of a well-conceived laboratory rearing strategy for C. sasakii.

1. Introduction

Nutritional consumption in the adult stage plays a vital role in the development, growth, and reproduction of insects [1,2]. Many species of Coleoptera, Hymenoptera, and Lepidoptera require supplementary nutrition during the adult stage to improve sexual maturity and reproduction [2]. Nutrition in the adult stage can also prolong longevity and improve the fecundity of insects [3,4]. However, previous studies have not provided conclusive evidence regarding the direct effects of adult parent (F₀) nutritional status on the population parameters, such as rates of increase, of first-generation offspring (F₁).

While nutritional requirements become more crucial to F₁ after birth, minor variations during prenatal development can have significant impacts on the phenotype and adaptability of the individual [5,6]. The nutritional status of F₀ may affect the fecundity of F₁, as well as gamete quality and epigenetic inheritance during gametogenesis, causing transgenerational effects [7,8]. Previous research is composed of a large number of vertebrate studies. There is an absence of conclusive evidence on the direct effects of F₀ nutritional status on F₁ fitness in insects, though some studies speculate that the accumulation of metabolic resources in F₀ insects can affect the fitness of F₁ [9]. For example, adequate nutrition can significantly prolong the lifespan of F₀ Dolichogenidea tasmanica, but may affect the sex ratio of its F₁ offspring [10].

The majority of Lepidoptera species rely on carbohydrate-rich food, such as plant nectar, dew, sweat, fruit juice, or animal excrement [11], as external nutrition. Various concentrations of sucrose and honey solution are often used to study the effects of nutrition on the development and reproduction of lepidopteran F₀ individuals [12,13]. Plutella xylostella adults fed with carbohydrates exhibited significantly greater longevity than those fed with water, and honey markedly increased fecundity [14]. On the other hand, Diglyphus isaea fed high concentrations of sugar solution showed significantly reduced adult longevity compared with those fed low concentrations of sugar solution in the same generation [15]. An absence or excess of caloric consumption seems to negatively affect insect F₀ fitness.

Carposina sasakii Matsumura (Lepidoptera: Carposinidae), a species of fruit-boring moth, also named peach fruit moth, is a widespread and serious pest mainly infesting orchards in China, Japan, Korea, Southeast Asia, and the Russian Far East [16,17]. C. sasakii has a wide range of host plants, and its larvae can damage many kinds of fruit, including apple, jujube, hawthorn, peach, plum, apricot, and pomegranate [18,19]. The damage from C. sasakii larvae renders fruit inedible and in turn, negatively affects the economic income derived from fruit production. The fruit infestation rate can exceed 80% in some cases [19], even reaching 100% in poorly managed apple orchards [20]. Current research regarding C. sasakii focuses on life cycle, diapause, and integrated pest control. The laboratory rearing and obtaining of a substantial quantity of uniformly developed individuals is a prerequisite for population ecology, pest management, toxicity, and behavioral studies of C. sasakii. The caloric intake of these individuals has obvious effects on the survival of the laboratory colony. Although honey solution is often used to feed C. sasakii adults during laboratory rearing [21], it has been reported that adult C. sasakii do not feed in the field [22].

To determine which source and amount of calories are best-suited for the laboratory rearing of C. sasakii, varying concentrations of sucrose solution and honey solution were fed to F₀ C. sasakii adults in different treatment groups in the present study. An age-stage, two-sex life table for C. sasakii was constructed to investigate the effects of feeding different nutrients to F₀ on the survival rate, duration of development stages, fecundity, and life cycle of F₁. The data collection and analysis enabled precise predictions of C. sasakii population growth, thereby aiding in the selection of the timing for integrated pest management strategies [23,24,25]. This study not only provides clear evidence regarding the implications of F₀ nutritional conditions on F₁ fitness in insects, but also lays the foundation for the implementation of feeding technologies, within the context of a well-conceived insect laboratory rearing strategy for C. sasakii.

2. Materials and Methods

2.1. Insects

The colony of C. sasakii was established from infested apples collected from a pesticide-free orchard in Taigu County, Shanxi Province, China, in the fall of 2012. Fresh, unscathed, mature Fuji apples (70–80 mm in diameter, 200–220 g in weight) were selected to raise C. sasakii in a laboratory incubator (MGC-250BP-2, Shanghai Yiheng Scientific Instruments, Shanghai, China) at 25.5 ± 0.5 °C, 75.0 ± 5.0% RH, with a photoperiod of 15:9 (L:D). This C. sasakii colony has been continuously raised in the laboratory for over 30 generations. Field individuals from pesticide-free orchards were added to the rearing colony annually to minimize inbreeding depression.

2.2. Methods

Newly emerged adult C. sasakii, with a sex ratio of 1 female:3 males [26], serving as experimental parents or the initial generation (F₀), were placed in adult feeding containers within an incubator. Each transparent plastic adult feeding container was 7.5 cm diameter × 9.5 cm height and included an inverted vial (with a downward-facing opening plugged with a cotton ball) filled with a different nutritional solution. The bottom of the container was lined with an egg card (a sheet of filter paper roughened by a razor blade) for egg deposition. One of seven different solutions were fed to each F₀ group, including double-distilled H₂O (W) as the control, 5 g·L⁻¹ honey solution (5H), 10 g·L⁻¹ honey solution (10H), 5 g·L⁻¹ sucrose solution (5S), 10 g·L⁻¹ sucrose solution (10S), 15 g·L⁻¹ sucrose solution (15S), and 20 g·L⁻¹ sucrose solution (20S). Each treatment and control group underwent 10 replications.

Egg cards containing first filial generation (F₁) eggs laid within the previous 24 h were collected daily and placed into an incubated plastic container (800 mL) with a layer of cotton (5.5 g), humidified with 19.5-mL double-distilled H₂O (ddH₂O) at the bottom [21]. The eggs were kept in the incubation chamber for 3 d until the blackhead stage. The eggs were then separated onto smaller pieces of filter paper and placed directly on the calyx of clean apples [27], with 20 eggs per apple [21], in a transparent plastic larval feeding container (800 mL). All larval stages (first to fifth instars) were grouped into a single category, since they fed exclusively inside of the apple during the entire larval stage. ddH₂O was sprayed daily onto the filter paper pieces containing eggs, and the paper was then covered with plastic wrap to preserve the humidity until the eggs hatched into larvae and bored into the apples.

The emergence of mature fifth-instar larvae was checked at 19:00 every day, and these mature larvae were placed individually into transparent plastic pupation containers (11 cm diameter × 5 cm height, containing 90 g autoclaved sand and 10 g ddH₂O), where they developed into pupae. The egg–larva period of each individual was determined based on its larval emergence date. The development of each individual was checked daily, and the dates of mature larva emergence, pupation, and adult emergence were recorded. Newly emerged F₁ adult moths were paired by the same sex ratio as their parents of 1:3 in adult feeding containers. Because the number of male F₁ offspring obtained from experimentally treated F₀ adults was often insufficient for pairing, young male adults were recruited from the greater mass-rearing colony when necessary; these males, however, were excluded from life table analysis. The F₁ generation laid eggs on egg cards that were replaced every day, and the fecundity and longevity of these adults were recorded daily at 20:00 until all F₁ adults died. There were limitations in regards to accurately recording the exact duration time of individuals when they died in the egg, larval, and pupal stages. Thus, the duration time of eggs that did not hatch was recorded as the average egg duration time of each treatment. Similarly, the duration time of larvae that did not mature/emerge was recorded as the average larva duration of each treatment, and the duration time of pupae that did not survive to adulthood was recorded as the average duration time of pupae of each treatment.

2.3. Data Analysis

Raw experimental data were analyzed using TWOSEX-MSChart [28], based on the age-stage, two-sex life table theory [29,30]. A bootstrap procedure with 100,000 iterations was used to estimate the mean and standard errors of the population parameters for the offspring of each nutritional group [31]. The significant difference between each nutritional group was analyzed using the paired bootstrap test embedded in TWOSEX-MSChart software [28]. Age-stage specific survival rate (s_xj), age-stage specific survival rate (l_x), age-specific fecundity (f_xj), age-specific fecundity (m_x), age-specific maternity (l_xm_x), life expectancy (e_xj), net reproductive rate (R₀), intrinsic growth rate (r), finite rate of increase (λ), mean generation time (T), and age-stage specific reproductive values (v_xj) were calculated. The parameters obtained from the life table of the age-stage, two-sex population and the TIMING-MAchart program were used to predict the population dynamics of C. sasakii after 90 days. Graphs were prepared with SigmaPlot 14.0 software, according to the results of the life table analysis.

2.4. Life Table Analysis

The calculation formulas for age-stage specific survival rate (s_xj, where x = age and j = stage), age-stage specific fecundity (f_xj), age-specific fecundity (m_x), and age-stage specific survival rate (l_x) are as follows [29]:

$$s_{xj}=\frac{n_{xj}}{n_{01}}$$

$$f_{x_j}=\frac{E_{xj}}{n_{xj}}$$

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

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

where n_xj represents the number of individuals who survive to age x and stage j; n₀₁ represents the number of individuals at the beginning of the study as obtained from the life table; E_xj is the total number of eggs laid by n_xj; and k represents the number of stages.

The life expectancy e_xj is calculated according to Chi and Su [32]:

$$e_{xj}=\sum _{i=x}^{\infty }\sum _{r=j}^k{s}_{iy}^{\prime }$$

where $s_{iy}^{\prime }$ is the probability that individuals of age x and stage j will survive to age i and stage y, under the assumption that $s_{iy}^{\prime }$ = 1.

2.5. Population Parameters

The net reproductive rate (R₀) represents the total number of offspring that an individual can produce in its lifetime:

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

The intrinsic rate of increase (r) is calculated by iterative dichotomy with the Euler–Lotka formula [33]:

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

The finite rate of increase (λ):

$$\lambda =e^r$$

The mean generation time (T) indicates the length of time required for the population to increase by R₀ times when the age distribution is stable.

$$T=\frac{ln{R}_0}{r}$$

The reproductive value (v_xj) refers to the contribution of individuals in age x and stage j to the future population. According to the theory of Tuan et al. [34,35], the calculation formula is as follows:

$$v_{xj}=\frac{e^{r(x+1)}}{s_{xj}}\sum _{i=x}^{\infty }{e}^{-r(i+1)}\sum _{y=j}^k{s}_{iy}^{\prime }{f}_{iy}$$

3. Results

3.1. Developmental Duration and Longevity

Differences in the effects of feeding different nutrients to adult stage F₀ C. sasakii on their F₁ offspring were observed at all stages of F₁ development (Figure 1,

Table A1. Mean (±SE) egg–larva duration (d), pupa duration (d), pupa mortality (%), preadult survival rate (%), preadult duration (d), proportion of female adults (N_f/N, %), the proportion of reproductive female adults (N_fr/N, %), and female and male adult longevity of F₁ C. sasakii produced from F₀ adults fed with 7 different nutrient solutions.

Parameter	Treatments
	N	W	N	5H	N	10H	N	5S	N	10S	N	15S	N	20S
Egg–larva duration (d)	44	30.36 ± 0.66 a	57	26.49 ± 0.57 c	73	28.37 ± 0.45 bc	46	26.83 ± 0.78 c	48	26.02 ± 0.83 c	69	30.33 ± 0.68 a	64	28.72 ± 0.51 ab
Egg–larva survival rate (%)	300	14.67 ± 2.05 c	300	19.00 ± 2.27 abc	300	24.33 ± 2.47 a	300	15.33 ± 2.09 bc	300	16.00 ± 2.11 bc	300	23.00 ± 2.42 a	300	21.33 ± 2.36 ab
Pupa duration (d)	36	11.83 ± 0.38 c	43	11.88 ± 0.46 bc	60	14.42 ± 0.44 a	31	12.55 ± 0.33 bc	35	13.03 ± 0.41 b	52	13.02 ± 0.50 bc	45	12.40 ± 0.28 bc
Pupa survival rate (%)	36	81.82 ± 5.88 a	43	75.44 ± 5.75 a	60	82.19 ± 4.52 a	31	67.39 ± 6.98 a	35	72.92 ± 6.48 a	52	75.36 ± 5.22 a	45	70.31 ± 5.74 a
Preadult survival rate sa (%)	300	12.00 ± 1.87 bc	300	14.33 ± 2.02 abc	300	20.00 ± 2.31 a	300	10.33 ± 1.76 c	300	11.67 ± 1.85 c	300	17.33 ± 2.17 ab	300	15.00 ± 2.06 abc
Preadult duration (d)	36	41.81 ± 0.58 a	43	38.00 ± 0.60 c	60	42.28 ± 0.62 a	31	38.32 ± 0.80 bc	35	38.34 ± 1.06 bc	52	42.25 ± 0.82 a	45	39.82 ± 0.57 b
Nf/N (%)	300	6.00 ± 1.37 bc	300	6.67 ± 1.43 abc	300	10.67 ± 1.78 a	300	3.67 ± 1.09 c	300	5.67 ± 1.34 bc	300	8.67 ± 1.62 ab	300	7.33 ± 1.50 ab
Nfr/N (%)	300	6.00 ± 1.37 ab	300	6.33 ± 1.40 ab	300	9.67 ± 1.70 a	300	3.67 ± 1.09 b	300	5.67 ± 1.34 ab	300	8.00 ± 1.56 a	300	6.33 ± 1.40 ab
Female adult longevity (d)	18	7.33 ± 0.74 bc	20	7.50 ± 0.67 bc	32	5.91 ± 0.51 cd	11	10.55 ± 0.97 a	17	8.94 ± 0.78 ab	26	5.11 ± 0.34 d	22	5.14 ± 0.41 d
Male adult longevity (d)	18	6.00 ± 0.45 bc	23	6.74 ± 0.68 abc	28	6.86 ± 0.47 ab	20	8.00 ± 0.74 a	18	8.17 ± 0.77 a	26	5.23 ± 0.43 cd	23	4.26 ± 0.31 d
Mean longevity of all (d)	300	24.53 ± 0.88 c	300	18.99 ± 0.92 d	300	24.36 ± 1.00 c	300	27.03 ± 0.64 b	300	22.48 ± 0.81 c	300	31.50 ± 0.72 a	300	28.66 ± 0.70 b

Means with different letters in the same row indicate significant differences between treatments (paired bootstrap test, p < 0.05). Standard errors were estimated by using 100,000 bootstraps. W.—double-distilled water; 5H.—5 g·L⁻¹ honey solution; 10H.—10 g·L⁻¹ honey solution; 5S.—5 g·L⁻¹ sucrose solution; 10S.—10 g·L⁻¹ sucrose solution; 15S.—15 g·L⁻¹ sucrose solution; 20S.—20 g·L⁻¹ sucrose solution.

). Compared to the double-distilled water control (W) treatment, F₀ adults fed with honey or sucrose solution produced F₁ offspring with significantly shorter egg–larva durations, accelerated egg–larva growth rates (Figure 1A), and improved egg–larva survival rates (Figure 1B). The shortest F₁ egg–larva duration was observed in the 10 g·L⁻¹ sucrose solution (10S) treatment (26.02 d), whereas the longest F₁ egg–larva duration was observed in the W treatment (30.36 d) (Figure 1A). Treatment groups fed with sucrose or honey exhibited a significantly prolonged F₁ pupa duration compared to that of the control (Figure 1C). However, feeding carbohydrate nutrients can significantly shorten F₁ preadult duration compared to that of the W treatment. The F₁ preadult duration was shorter in the 5 g·L⁻¹ honey solution (5H) and 5 g·L⁻¹ sucrose solution (5S) treatments (38.00 d and 38.32 d, respectively) (Figure 1E) than in the other treatments. The F₁ preadult survival rate (s_a) in the 10 g·L⁻¹ honey solution (10H) treatment was higher than that of the W treatment (Figure 1F). Female F₁ adult longevity was greater than that of males in all treatments except for the 10H and 15 g·L⁻¹ sucrose solution (15S) treatments (Figure 1G,H). Moreover, F₁ female and male adult longevities were greater in the 5S (10.55 d, 8.00 d) and 10S treatments (8.94 d, 8.17 d) (Figure 1G,H).

3.2. Age-Stage Specific Survival Rate

The age-stage specific survival rate (s_xj) not only provides a detailed description of the survival probability of newly laid eggs at age x and stage j, but also gives a comprehensive account of stage differentiation. Differences in the age-stage specific F₁ survival rates were observed (Figure 2). A clear overlapping phenomenon between different stages was observed due to the variation in developmental rates among F₁ individuals. The s_xj of the F₁ pupa stage in the 10S treatment peaked (0.13) the earliest amongst treatment groups at age 31 d (Figure 2B). The peak values of s_xj for the pupa stage and for F₁ female and male adults in the 10H treatment were significantly higher compared to those of other groups (Figure 2B–D).

3.3. Age-Stage Specific Fecundity and Fertility

Both the proportion of female adults (N_f/N) and the proportion of reproductive female adults (N_fr/N) were high among the F₁ offspring derived from non-control F₀ adults. The 10H treatment showed the highest N_f/N (10.67%) and N_fr/N (9.67%) in the F₁ among the seven treatments (Figure 3A,B). The female adult fecundity and oviposition days (O_d) of F₁ were significantly different between treatments (

Table 1. Mean (±SE) adult preoviposition period (APOP), total preoviposition period (TPOP), oviposition days (O_d), and female adult fecundity (offspring) of F₁ C. sasakii produced from F₀ adults fed with seven different nutrient solutions.

Parameter	Treatment
	W	5H	10H	5S	10S	15S	20S
F1 Female Adult Fecundity (eggs/female)	185.89 ± 30.33 a	176.55 ± 26.25 a	77.63 ± 16.08 b	202.18 ± 40.52 a	222.53 ± 35.80 a	88.23 ± 13.35 b	110.64 ± 18.67 b
Od (days)	5.44 ± 0.75 ab	5.89 ± 0.75 a	4.03 ± 0.57 bc	7.64 ± 1.12 a	6.71 ± 0.87 a	3.13 ± 0.26 c	4.16 ± 0.44 b
APOP (days)	1.28 ± 0.25 ab	1.00 ± 0.15 bc	1.62 ± 0.24 a	1.09 ± 0.09 b	1.18 ± 0.26 ab	1.38 ± 0.18 ab	0.63 ± 0.14 c
TPOP (days)	43.72 ± 0.86 ab	39.42 ± 1.07 c	45.10 ± 0.93 a	39.91 ± 1.47 c	39.53 ± 1.87 c	44.96 ± 1.29 a	41.05 ± 1.07 bc

Means with different letters in the same row indicate significant differences between treatments (paired bootstrap test, p < 0.05). Standard errors were estimated by using 100,000 bootstraps. W.—double-distilled water; 5H.—5 g·L⁻¹ honey solution; 10H.—10 g·L⁻¹ honey solution; 5S.—5 g·L⁻¹ sucrose solution; 10S.—10 g·L⁻¹ sucrose solution; 15S.—15 g·L⁻¹ sucrose solution; 20S.—20 g·L⁻¹ sucrose solution.

). Interestingly, F₁ female adult fecundity was significantly higher in the 10S treatment (222.53) than in the other treatments, whereas F₁ female adult fecundity was the lowest in the 10H treatment (77.63). Surprisingly, F₁ female adult fecundity in the control treatment was higher than that of some honey and sucrose fed insects. The number of F₁ oviposition days (O_d) was significantly greater in the 5S and 10S treatments (7.64 d and 6.71 d, respectively) compared to other treatments as well. In terms of the F₁ total pre-oviposition period (TPOP) and the adult pre-oviposition period (APOP), significant differences were observed among the seven treatments. F₁ APOP was significantly longer in the 10H treatment (1.62 d). F₁ APOP in the 10S treatment (1.18 d) was shorter than that in the control treatment (1.28 d), and the 10S F₁ TPOP (39.53 d) was significantly shorter than that of the control (43.72 d).

The age-specific survival rate (l_x) represents the cumulative survival probability of an individual from birth to age x, calculated as the sum of age-specific survival rates across all life stages (s_xj). It denotes the likelihood that a newborn individual will survive to age x (Figure 4) [36]. The l_x of F₁ began to decline as early as age 4 d in 10S, then gradually decreased to zero by age 68 d (Figure 4A). Generally, as the insects matured, there was a clear initial increase, followed by a subsequent decrease to zero in the age-stage specific fecundity (f_x3, adult female is the third life stage), age-specific fecundity (m_x), and age-specific net maternity (l_xm_x) across the seven C. sasakii colonies (Figure 4). The maximum F₁ f_x3 (105.00) occurred at age 30 d, and the maximum F₁ m_x (77.00 eggs) occurred at age 61 d in 10S (Figure 4B). F₁ m_x shows that C. sasakii reproduction began at age 30 d in the 10S treatment, while that of the W treatment began at age 39 d (Figure 4C). The maximum value of F₁ age-specific net maternity (l_xm_x) was lower in 10S (0.88 eggs) compared to that of the control (1.29 eggs) (Figure 4D). Furthermore, fluctuations in the fecundity curve suggested that the emergence and oviposition of F₁ individuals did not occur at a specific age.

3.4. Age-Stage Life Expectancy

The age-stage life expectancy (e_xj) values for all F₁ offspring gradually decreased to zero as age increased (Figure 5). Notably, the life expectancy curve of the seven treatments showed that F₀ diets had varied effects on the growth and development of F₁ at different stages. The initial e_xj values of F₁ for 5H and 10S treatments (18.99 days and 22.48 days, respectively) were significantly lower than those of the other treatments (Figure 5A). Furthermore, this result is consistent with the trends of mean longevity in the corresponding treatments. In addition, the e_xj values of female F₁ adults were typically higher than those of males (Figure 5C,D). The e_xj curve exhibited varying degrees of fluctuation at different stages in different treatments, with higher levels of fluctuation indicating higher mortality rates.

3.5. Age-Stage Specific Reproduction Values

The age-stage specific reproductive value (v_xj) indicates the magnitude that an individual at a particular age (x) and stage (j) contributes to the future population (Figure 6). v_xj values increased significantly when F₁ began to lay eggs. The v_xj of female F₁ adults had two peaks, observed at age 30 d (295.04) and 61 d (239.64) in the 10S treatment. The peak values of F₁ v_xj in 10S were higher than that of other treatments except 5H (319.19). A single F₁ v_xj peak was observed in all treatments except 10S. Additionally, amongst these 7 treatments, the longest reproductive period of female F₁ was observed in 10S (32 d), which far exceeded that of W (19 d) (Figure 6C).

3.6. Population Dynamics Parameters

There were significant differences in the intrinsic rate of increase (r), finite rate of increase (λ), net reproductive rate (R₀), and mean generation time (T) of F₁ among the seven treatments (

Table 2. The population parameters of F₁ C. sasakii produced from F₀ adults fed with seven different nutrient solutions.

Parameter	Treatment
	W	5H	10H	5S	10S	15S	20S
r (d−1)	0.0531 ± 0.0067 a	0.0606 ± 0.0069 a	0.0457 ± 0.0065 a	0.0476 ± 0.0099 a	0.0615 ± 0.0076 a	0.0449 ± 0.0058 a	0.0467 ± 0.0061 a
λ (d−1)	1.0546 ± 0.0071 a	1.0624 ± 0.0073 a	1.0467 ± 0.0068 a	1.0488 ± 0.0103 a	1.0634 ± 0.0081 a	1.0459 ± 0.0060 a	1.0478 ± 0.0064 a
R0 (offspring/individual)	11.15 ± 3.11 a	11.77 ± 3.05 a	8.28 ± 2.18 a	7.41 ± 2.62 a	12.61 ± 3.57 a	7.65 ± 1.82 a	8.11 ± 2.12 a
T (days)	45.40 ± 0.88 a	40.71 ± 0.74 c	46.29 ± 1.56 a	42.05 ± 1.60 abc	41.21 ± 1.61 bc	45.36 ± 1.40 ab	44.83 ± 1.03 ab

Means with different letters in the same row indicate significant differences between treatments (paired bootstrap test, p < 0.05). Standard errors were estimated by using 100,000 bootstraps. W.—double-distilled water; 5H.—5 g·L⁻¹ honey solution; 10H.—10 g·L⁻¹ honey solution; 5S.—5 g·L⁻¹ sucrose solution; 10S.—10 g·L⁻¹ sucrose solution; 15S.—15 g·L⁻¹ sucrose solution; 20S.—20 g·L⁻¹ sucrose solution.

). The finite rate of increase (λ) of F₁ for each treatment group exceeded 1, indicating that the F₁ colony in all treatments experienced quantifiable growth. The highest F₁ values of r, λ, and R₀ were observed in 10S (r = 0.0615, λ = 1.0634, R₀ = 12.61), indicating that F₁ could achieve the highest colony growth with the 10S treatment. The lowest F₁ values of r (0.0449) and λ (1.0459) were observed in 15S. The lowest F₁ R₀ (7.41) was observed in 5S (Figure 7). The F₁ mean generation time (T) was significantly longer in the 10H treatments. However, the F₁ mean generation times (T) in 10S (41.21 d) and 5H (40.71 d) were relatively short.

3.7. Simulation of Population Growth Dynamics

The population dynamics of F₁ C. sasakii derived from F₀ adults treated with seven different nutrients were predicted over a 90-day period using TIMING-MSChart (Figure 8). The colonies in all treatments showed numerical growth. Each treatment group started with 10 eggs, and the fastest-growing colony was produced from 10S F₀ adults. At 90 days, the third-generation filial pupae (F₂) appeared in the 10S treatment, with overlapping generations, while the F₂ individuals in all other treatments were still in the egg–larva stage. After 90 days, the 10S treatment colony was expected to reach a total of 915.63 offspring individuals (906.02 egg–larvae, 5.67 pupae, and 3.93 adults), which was nearly twice that of predicted total of 506.55 W offspring individuals (496.27 egg–larvae, 4.44 pupae, and 5.84 adults).

4. Discussion

In the results of this study, the longevity, egg–larva duration, pupa duration, adult duration, and fertility of F₁ C. sasakii offspring were significantly affected by both the type and concentration of nutrient solutions fed to F₀ parents. When F₀ adults were fed sucrose and honey solutions, the F₁ egg–larva duration was significantly shortened, and the F₁ egg–larva survival rate was significantly increased. A similar effect was also found in Plodia interpunctella, where a high-quality F₀ larval diet accelerated F₁ development [37]. Previous research has found that supplementation with multiple forms of carbohydrates, such as fructose, glucose, and sucrose, was sufficient in increasing Cnaphalocrosis medinalis F₀ adult longevity and fecundity [12]. Spodoptera exempta F₀ adult longevity and fecundity were also significantly reduced when females were fed diets lacking carbohydrates [4]. Greater longevity in adult insects may benefit mating and the oviposition period. However, these studies do not provide conclusive evidence regarding the potential effects of F₀ adult nutrition on F₁ adult longevity. Through this study, we noted that feeding suitable concentrations of sucrose or honey solutions can prolong the adult duration of F₁ C. sasakii offspring. Our results indicate that the nutritional condition of F₀ parents can improve F₁ egg quality and shorten F₁ preadult duration. Improved nutritional conditions of F₀ can accelerate the development of F₁ and thus benefit overall insect population growth.

It is important to note that not only does insufficient caloric consumption seem to negatively affect C. sasakii colonies, but excessive caloric consumption does so as well. Compared to the control group fed exclusively with distilled water, higher concentrations of carbohydrate solutions shortened the adult longevity of both female and male F₁ C. sasakii and reduced F₁ female adult fecundity. A previous study of Diglyphus isaea [15] observed similar phenomena, with higher concentrations of sugar solution fed to F₀ significantly shortening adult longevity of the same generation. Therefore, we speculate that these results are related to the structure of the adult mouthparts of C. sasakii [22]. Nutrient solutions with higher carbohydrate concentrations, which are more adherent to surfaces and therefore more difficult to consume, may lead to an increase in internal osmotic pressure within the body of an insect and thereby affect physiological processes. Conversely, clear water and lower concentrations of carbohydrates seem to be more beneficial to C. sasakii growth and development. In other words, only the appropriate amount of parental caloric consumption is beneficial to producing the next generation of C. sasakii.

Nutrition is important for the reproductive capacity of female adults. Feeding on nutrients during the adult stage plays a major role in converting potential fecundity into actual fecundity [38]. However, there is an absence of conclusive evidence on the direct effects of F₀ parental nutritional status on F₁ offspring in insects. Our results show that nutrition at an appropriate concentration of honey or sucrose during the adult stage of F₀ C. sasakii can increase female adult fecundity and prolong the O_d of F₁ offspring. In a previous study that fed only 10 g·L⁻¹ honey solution to F₀ adults saw improved F₁ adult fecundity, to a certain extent [21]. A higher nutritional status of F₀ Chironomus tepperi also significantly increased the fecundity of F₁ [9]. We speculate that the adequate nutritional status of C. sasakii parents will enhance the reproductive potential of their offspring.

Previous research has shown that some insect species are capable of mating and laying eggs immediately after adult emergence, while other species require additional nutrients and time for reproduction [39,40,41,42]. In the present study, the APOP for newly emerged individuals across seven treatments was 0.63 to 1.62 days, indicating that C. sasakii adults require additional time for reproduction after emergence. This phenomenon may be associated with further post-emergence ovariole development to facilitate reproduction [43]. The APOP and TPOP of F₁ C. sasakii during the adult stage were significantly shorter in suitable honey and sucrose treatments than in the control. On the contrary, it has been shown that the APOP of Spodoptera exigua fed with water is shorter than that with honey solution [38]. Insects may have different nutrient requirements at different life stages, and different nutrients may have varying effects on insect life activities. Further research is needed.

Both F₀ and F₁ adult C. sasakii in this study were able to successfully mate and spawn, and their eggs hatched normally when provided with only distilled water. This evidence indicates that the nutrition required for reproductive development before adult emergence was sufficient. This may also be a contributing factor to the widespread agricultural damage caused by C. sasakii. The results of previous studies on other moths, including Athetis lepigone [44], Spodoptera exigua [38], Spodoptera frugiperda [45], and Stenoma catenifer [46], were consistent with this phenomenon. Nutrition is considered inessential to the mating behavior of C. sasakii, but significantly higher adult fecundity of F₁ female C. sasakii was derived from F₀ adults that underwent nutritional treatment. Therefore, adult nutrition still influences future offspring’s fecundity and thereby, affects colony growth.

The quality of the parental insect diet has been previously demonstrated to impact the colony structure of the offspring. Ant colonies that consumed carbohydrate-rich diets showed higher numbers of worker and brood production compared to those on carbohydrate-deficient diets [47,48]. Life table analysis revealed that the C. sasakii colony raised on 10 g·L⁻¹ sucrose solution exhibited the highest r, λ, and R₀ values. Life table parameters r, λ, and R₀ are used to estimate the growth and reproductive potential of insect populations [49]. Our analysis indicates that the experimental colony displayed either higher fecundity or a faster rate of development [50].

Population projection based on the age-stage, two-sex life table can reveal changes in stage structure during population growth. Understanding stage structure and colony growth predictions is crucial for pest management and laboratory colony rearing because the colony growth of C. sasakii varies with different external environments. In previous studies, C. sasakii exhibited faster colony growth with lower larval density [21]. Suboptimal nutrient concentrations lead to weakened colony growth of C. sasakii. The source and concentration of nutrients consumed by C. sasakii adults can have significant positive effects on the population growth of future generations. Understanding how F₀ nutritional conditions affect the fitness of F₁ is important for the development and implementation of pest control against C. sasakii based on feeding technologies.