Two-Sex Life Table Analysis of Frankliniella intonsa Reared on Nine Different Vegetable Crops in Guangxi, China

Abstract

Frankliniella intonsa (Thysanoptera: Thripidae) is a polyphagous pest that causes significant economic agricultural losses by damaging flowers, vegetables, and fruit trees. We performed an age-stage two-sex life table analysis to evaluate the performance and adaptability of F. intonsa against nine common vegetable crops cultivated in Guangxi: cowpea (Vigna unguiculata) (Fabales: Leguminosae), green beans (Phaseolus vulgaris) (Fabales: Leguminosae), soybean (Glycine max) (Fabales: Leguminosae), catjang cowpea (Vigna cylindrica) (Fabales: Leguminosae), courgette (Cucurbita pepo) (Cucurbitales: Cucurbitaceae), wax gourd (Benincasa hispida) (Cucurbitales: Cucurbitaceae), bitter gourd (Momordica charantia) (Cucurbitales: Cucurbitaceae), cucumber (Cucumis sativus) (Cucurbitales: Cucurbitaceae), and chieh-qua (Benincasa hispida) (Cucurbitales: Cucurbitaceae). Among the tested host crops, green beans, cowpea, and courgette significantly accelerated the growth rate and favored the reproductive success of F. intonsa. Green beans, cowpea, and courgette facilitated rapid growth and reproductive success. The mean generation times (T) and net reproductive rates (R₀) were as follows: 14.90 d, 17.09 d, 21.03 d, and 104.04, 45.51, 32.61. Bitter gourd and chieh-qua significantly suppressed population growth (T: 49.49 d, 0 d; R₀: 0.73, 0). Wax gourd, catjang cowpea, cucumber, and soybean exhibited moderate effects characterized by delayed development and lower reproductive output (T: 22.30 d, 20.30 d, 19.51 d, 32.73 d; R₀: 7.17, 25.22, 13.74, and 12.54). These findings highlight the critical role of crop type in F. intonsa population dynamics. Therefore, the agricultural production of green beans, cowpea, and courgette crops necessitates improved control measures and monitoring. Similar measures are needed for cucumber, catjang cowpea, soybeans, and wax gourds because they pose risks as potential hosts.

1. Introduction

The thrips (Frankliniella intonsa) belongs to the order Thysanoptera and family Thripidae [1]. It is a polyphagous pest notably with a broad host range that encompasses 106 species of host crops from 48 families. F. intonsa (Thysanoptera: Thripidae) primarily infects crops such as sunflower, cotton, cowpea, goji berry, rose, and tea [2,3]. Moreover, it is a major pest that affects leguminous crops such as green beans and soybean [4,5,6,7]. It feeds on plant tissues by rasping and sucking nutrients from the stems, leaves, flowers, and fruits. This leads to symptoms such as leaf curling, shrinkage, drying, and abscission. In severe cases, the photosynthetic processes is disrupted, which stunts plant growth and development. Moreover, F. intonsa is a major vector of Tospovirus infections, which trigger multiple plant viral diseases that exacerbate crop loss. Additionally, it exhibits high reproductive capacity and broad adaptability, which leads to substantial agricultural economic losses [8,9]. Recent developments such as climate change and shifts in agricultural planting structures have significantly intensified the F. intonsa impacts on agricultural crops. Currently, it is considered a key pest and threat to China’s agricultural yield. In 2023, the Ministry of Agriculture and Rural Affairs of the People’s Republic of China issued the Announcement No. 654, in which F. intonsa was designated as a Class I crop disease or pest. This highlights its destructive potential and the urgent need for control measures [10].

Life table analyses are crucial tools that aid in insect population ecology and pest management because they precisely capture the effects of various factors on key population parameters such as survival, development, and reproduction under diverse environmental conditions [11]. However, traditional life table methods emphasize the reproductive capacity of females and often overlook the contributions of males to population growth. The age-stage two-sex life table addresses this limitation by offering a more precise description of the influence of various insect developmental stages and sex ratios on population growth. Hence, this method has been widely applied in recent years in insect ecology and pest management [12,13]. Zhang et al. used an age-stage two-sex life table to investigate the effect of different corn varieties on the growth, development, and reproduction of the Spodoptera frugiperda (Lepidoptera: Noctuidae) [14]. Khan used a two-sex life table to explore the lethal and sublethal effects of cyromazine on several biological traits and population parameters of Musca domestica (Diptera: Muscidae) [15]. Li et al. used the two-sex life table to determine the optimal temperature range for maximizing the population growth of Bradysia odoriphaga (Diptera: Sciaridae). They found that temperatures < 25 °C yielded the highest intrinsic rate of increase, net reproductive rate, and finite rate of increase and the shortest generation time [16]. Thus, the age-stage two-sex life table method is more impactful than traditional life tables in population ecology and pest management. Consequently, it has been extensively applied in constructing insect life tables.

As a polyphagous pest, F. intonsa shows substantial variation in its growth, development, and reproduction depending on the host plant. During preliminary field investigations, our research team observed varying infestation levels of F. intonsa on nine economically important crops: cowpeas, green beans, soybeans, catjang cowpea, courgette, wax gourds, bitter gourd, cucumbers, and chieh-qua. To systematically examine the developmental, reproductive, and population dynamics of F. intonsa across these host crops, we conducted age-stage, two-sex life table analyses to elucidate host-specific population growth patterns, thereby providing a scientific basis for targeted pest management strategies.

2. Materials and Methods

2.1. Samples

2.1.1. Insects

Natural colony of F. intonsa was collected from vegetable fields at the Guangxi Academy of Agricultural Sciences and reared on cowpea pods until the F1 generation was obtained. Approximately 5000 F1-generation adult thrips (both male and female) were transferred to cowpea pods and allowed to lay eggs for 12 h. The eggs hatched into first-instar nymphs after 2.5 days. The rearing conditions were maintained at temperature of 25 ± 2 °C, relative humidity of 65 ± 5%, and a photoperiod of 14 L:10 D.

2.1.2. Crops

The following nine vegetable crops cultivated in Guangxi were selected for this study: cowpea (V. unguiculata L. Walp.), green beans (Phaseolus vulgaris L.), soybean (Glycine max L. Merr.), catjang cowpea (V. unguiculata subsp. cylindrica (L.) Verdc.), courgette (Cucurbita pepo L.), wax gourd (Benincasa hispida Thunb. Cogn.), bitter gourd (Momordica charantia L.), cucumber (Cucumis sativus L.), and chieh-qua (Benincasa hispida (Thunb.) Cogn. var. chieh-qua How). The seeds were sown in seedling trays, which were filled with nutrient soil without additional fertilizer application and irrigated with 300 mL of water every three days. The seedlings were used for the experiment after developing 4–6 true leaves. The nutrient soil was purchased from Hekang Agricultural Technology Co., Ltd. (Nanning, China), with the following specifications: pH 5.0–6.5, EC value ≤ 0.1 mS/cm, and humic acid content ≥ 10%.

2.1.3. Test Set-Up

In the experiment, polypropylene 5 mL centrifuge tubes (Beijing Labgic Technology Co., Ltd. Beijing, China) were used as rearing containers for Frankliniella intonsa. Specifically, a hole with a diameter of 1 cm was drilled in the center of each tube cap, which was subsequently covered with a piece of 250-mesh gauze to ensure adequate ventilation.

2.2. Method

The experimental procedure described by Wang et al. was modified for this study [17]. Centrifuge tubes were filled with 1 mL of 2.5% agar solution, which was allowed to solidify to form flat surfaces. Healthy young leaves were obtained from the nine experimental crops. These were used to prepare 1 cm in diameter leaf disks that were tightly attached to the agar surfaces. Individual first instars were selected and reared on the leaf disks. Each group was allocated 50 larvae per crop. The leaf disks were replaced with fresher one twice a day (at 8:00 and 20:00 h). The changes in insect stages and survival rate from larvae to pre-adult stages were recorded. After the larvae developed into adults, male and female adults were paired and transferred to centrifuge tubes without agar. These tubes were provisioned with 2 cm long fresh fruits from the respective crops. The fruits were replaced twice daily at 08:00 and 20:00 h. The survival status of the adults was monitored. If the female failed to pair successfully, an additional male was introduced. If the paired male died, it was replaced with a new male until the female died. Furthermore, the insects were transferred to new centrifuge tubes each time that the fruits were replaced until all eggs hatched. The first instar of the F2 generation was used as an indicator of the reproductive capacity of the adults in the F1 generation. Temperature and humidity were strictly controlled (25 ± 2 °C, 65 ± 5% relative humidity) for the entire duration of the experiment, and external disturbances were minimized.

2.3. Data Processing

The IBM SPSS Statistics 26 software was used to perform a one-way analysis of variance (ANOVA) on the duration of each developmental stage, survival rate, and fecundity of thrips, followed by multiple comparisons using the Least Significant Difference (LSD) method. Significance level was set at 0.05. TWOSEX-MSChart 2024 software [18,19] was used to construct the life table for thrips and analyze the following core parameters:

Age-stage-specific survival rate (S_xj): The probability that an initial population survives to age x and reaches stage j.

Age-specific survival rate (l_x, $l_x=\sum _{j=1}^k{s}_{xj}$): The probability that the population progresses from the egg stage (j = 1) to age x.

Age-stage-specific fecundity of females (f_xj): The number of eggs laid by female adults at age x.

Age-specific fecundity (m_x, $m_x={\displaystyle \frac{\sum _{j=1}^k{s}_{xj}{f}_{xj}}{\sum _{j=1}^k{s}_{xj}}}$): The average number of eggs laid per individual at age x.

Age-specific reproductive capacity of the population (l_xm_x): The net reproductive capacity of the population at age x.

Intrinsic rate of increase (r, $\sum _{x=0}^{\infty }{e}^{-r(x+1)}{l}_x{m}_x=1$): This represents the maximum instantaneous growth rate of a population with a stable age distribution.

Finite rate of increase (λ, λ = er): This represents the population growth rate.

Net reproductive rate (R₀, $R_0=\sum _{x=0}^{\infty }{l}_x{m}_x$): This represents the expected number of offsprings produced by an individual during its lifetime.

Mean generation time (T, $T={\displaystyle \frac{\left(ln{R}_0\right)}{r}}$): This represents the average time required for a population to progress from one generation to the next.

The means and standard errors of various group parameters were calculated using the bootstrap method in the TWOSEX-MS chart (bootstrapping with 100,000 replicates). OriginPro 2021 software was used for mapping.

3. Results

3.1. F. intonsa Growth and Development on Nine Crop Species

The developmental duration of F. intonsa during the pre-adult stage varied significantly depending on the host crop (

Table 1. Developmental status of Frankliniella intonsa feeding on different crops.

Hostplant	Developmental Duration/Days
	Egg	1st Instar	2nd Instar	Prepupa	Pupa	Egg-Adult
Cowpea	2.5 ± 0.00 a (50)	1.00 ± 0.00 d (50)	2.92 ± 0.06 e (49)	1.01 ± 0.03 a (48)	2.15 ± 0.08 a (47)	9.65 ± 0.08 d (47)
Green bean	2.5 ± 0.00 a (50)	0.53 ± 0.01 f (50)	2.85 ± 0.07 e (47)	0.73 ± 0.04 bc (47)	1.60 ± 0.03 cd (44)	8.22 ± 0.07 e (44)
Soybean	2.5 ± 0.00 a (50)	1.04 ± 0.02 d (50)	3.67 ± 0.08 d (46)	0.67 ± 0.03 c (45)	1.75 ± 0.04 bc (43)	9.65 ± 0.08 d (43)
Catjang cowpea	2.5 ± 0.00 a (50)	1.96 ± 0.04 b (50)	4.26 ± 0.17 c (39)	0.80 ± 0.03 bc (39)	1.74 ± 0.05 bc (35)	11.28 ± 0.19 b (35)
Courgette	2.5 ± 0.00 a (50)	0.73 ± 0.05 e (50)	4.83 ± 0.23 b (33)	0.84 ± 0.05 b (32)	1.73 ± 0.07 bc (30)	10.65 ± 0.28 c (30)
Wax gourd	2.5 ± 0.00 a (50)	1.23 ± 0.07 c (50)	6.08 ± 0.23 a (37)	0.83 ± 0.04 b (34)	1.77 ± 0.05 bc (31)	12.32 ± 0.26 a (31)
Bitter gourd	2.5 ± 0.00 a (50)	1.24 ± 0.04 c (49)	3.43 ± 0.21 de (39)	0.76 ± 0.04 bc (38)	1.50 ± 0.04 d (35)	9.15 ± 0.15 d (35)
Cucumber	2.5 ± 0.00 a (50)	2.05 ± 0.09 b (49)	5.11 ± 0.39 b (39)	0.77 ± 0.06 bc (33)	1.85 ± 0.07 b (28)	11.76 ± 0.40 b (28)
Chieh-qua	2.5 ± 0.00 a (50)	2.37 ± 0.16 a (12)	-	-	-	-
F	-	104.646	32.609	9.871	13.249	5.508
df (n1,n2)	-	8400	7321	7308	7285	7285
p	-	0.000	0.000	0.000	0.000	0.000

Note: Data in the table are mean ± SE. Values in the same column followed by different letters are significantly different (LSD test, p < 0.05). “()” is the number of thrips that survived during that period.

). The first-instar development duration was observed to be fastest (<1 day) for green beans (0.53 days) and courgette (0.73 days) crops. Intermediate durations were observed for soybean (1.04 days), wax gourd (1.23 days), bitter gourd (1.24 days), and catjang cowpea (1.96 days). Longer durations were recorded for cucumber (2.05 days) and chieh-qua (2.37 days). The second-instar development duration was observed to be fastest for green beans (2.85 days) and slowest for wax gourd (6.08 days), which was a 3.23-day difference. Notably, none of the second instars survived on chieh-qua as all 12 first instars died before reaching the next stage. The prepupal stage duration was observed to be the longest for cowpea (1.01 days); intermediate for catjang cowpea (0.80 days), courgette (0.84 days), and wax gourd (0.83 days); and short for green beans (0.73 days), soybean (0.67 days), bitter gourd (0.76 days), and cucumber (0.77 days). The pupal stage development duration was observed to be the longest for cowpea (2.15 days) and shortest for bitter gourd (1.50 days). Comparable durations ranging from 1.60 to 1.80 days were observed for green beans, soybean, cucumber, catjang cowpea, courgette, and wax gourd. Overall, the complete developmental cycle from egg to adult emergence was the shortest for green beans (8.22 days), followed by bitter gourd, cowpea, and soybean (<10 days). Longer cycles were observed for catjang cowpea, courgette, wax gourd, and cucumber (>10 days), and the longest cycle was recorded for wax gourd (12.32 days).

3.2. Adult Longevity and Fecundity of F. intonsa on Nine Plant Species

As shown in

Table 2. Effect of host feeding on longevity and fecundity of Frankliniella intonsa.

Hostplant	Longevity/Days		Sex Ratio (F/M)	Fecundity
	Female Adult	Male Adult
Cowpea	29.03 ± 2.70 ab (26)	21.95 ± 2.58 b (21)	26:21	87.50 ± 6.84 b (26)
Green bean	25.74 ± 1.87 bc (35)	14.00 ± 2.54 bcd (9)	35:9	148.68 ± 14.88 a (35)
Soybean	18.07 ± 2.06 c (27)	11.12 ± 1.86 cd (16)	27:16	23.22 ± 6.89 de (27)
Catjang cowpea	30.65 ± 2.71 ab (26)	13.22 ± 4.06 bcd (9)	26:9	48.46 ± 5.45 cd (26)
Courgette	32.90 ± 4.13 ab (22)	37.81 ± 5.98 a (8)	22:8	73.86 ± 10.44 bc (22)
Wax gourd	35.94 ± 5.09 a (17)	20.53 ± 3.89 bc (14)	17:14	21.06 ± 3.01 de (17)
Bitter gourd	29.84 ± 3.75 ab (19)	13.03 ± 1.92 bcd (16)	19:16	1.89 ± 1.02 e (19)
Cucumber	27.78 ± 3.11 ab (14)	9.67 ± 2.65 d (14)	14:14	49.50 ± 9.46 cd (14)
Chieh-qua	-	-	-	-
F	3.128	6.838	-	26.049
df (n1,n2)	7178	7.99	-	7178
p	0.004	0.000	-	0.000

Note: Data in the table are presented as mean ± SE. Values in the same column followed by different letters are significantly different (LSD test, p < 0.05). The number in the parenthesis “()” is the number of thrips.

, the lifespan and fecundity of adult thrips varied significantly depending on the crop that they fed on. Female adults exhibited the longest lifespan on wax gourd (35.94 days), which significantly exceeded the lifespan on other crops. In contrast, females lived the shortest on soybean (18.07 days), which is 17.87 days shorter than the lifespan on wax gourd. Male adults showed the longest lifespan on courgette (37.81 days), which was the highest among all the crops, whereas the shortest lifespan was observed on cucumber (9.67 days). Overall, the average lifespan of female thrips was significantly longer than that of male thrips for all crops. Females that fed on cowpea, green beans, soybean, catjang cowpea, wax gourd, bitter gourd, and cucumber lived significantly longer than the males. The smallest lifespan difference between sexes occurred for soybean, where females showed a 1.63-fold longer lifespan than that of males. The largest difference occurred for cucumber with a 2.87-fold longer lifespan for females than for males. However, male adults that fed on courgette lived significantly 1.15-fold longer than females. Additionally, the fecundity of female thrips differed among crops. Females laid the most eggs on green beans (148.68), followed by cowpea (87.50) and courgette (73.86). Egg production was significantly lower on cucumber (49.50), catjang cowpea (48.46), soybean (23.22), and wax gourd (21.06) crops. Of the nine crops, thrips failed to develop or reproduce on chieh-qua. Thus, the lifespan and fecundity data of adult thrips indicate that this species exhibits a reproductive strategy that favors females as the dominant sex in most crops. Consistent egg-laying patterns were observed on cowpea, green beans, catjang cowpea, courgette, and cucumber, which suggests that these crops effectively supported population growth. However, egg production was relatively low (<25 eggs) on soybean and wax gourds, which indicates slower population growth despite successful development and reproduction. Moreover, thrips failed to achieve intergenerational reproduction on bitter gourd or chieh-qua.

3.3. Age-Stage-Specific Survival Rate of F. intonsa

The graphs in Figure 1 illustrate the differences in the survival and developmental rates of F. intonsa at various stages when feeding on different crops. All nine growth curves, each of which correspond to thrip feeding on a different crop, showed significant overlap with an initial increase followed by a decrease at each developmental stage. As shown in Figure 1, first-instar larvae showed a peak on day 2.5 for all nine crops. For the second-instar larval stage, the earliest peak was observed on day 3.5 for cowpea and green beans, followed by wax gourd and courgette (day 4). The peak occurred on day 4.5 for bitter gourd and soybean, whereas it occurred on day 5 for cucumber. The last peak was observed on day 5.5 for catjang cowpea and chieh-qua. During the prepupal stage, the earliest peak occurred for green beans on day 6, whereas the last peak was observed for catjang cowpea and wax gourd on day 8.5 with a difference of 2.5 days. For the pupal stage, pupae feeding on green beans, bitter gourd, soybean, cowpea, and courgette exhibited peak development within a similar timeframe (days 7.5–8.5), whereas those feeding on catjang cowpea, wax gourd, and cucumber exhibited the peaks from days 10–10.5. At the adult stage, female thrips feeding on green beans reached peak development fastest (11 days), whereas those feeding on wax gourds took the longest (16 days). Male thrips showed a similar pattern with the shortest peak time observed for green bean (8.5 days) and longest for wax gourd (14 days). Adults feeding on cowpea reached peak development at the same time for both sexes (day 11.5). Male adults that fed on cucumber reached their peak 0.5 days later than the females. In contrast, males that fed on green beans, bitter gourd, catjang cowpea, soybean, wax gourd, and courgette reached their peak body weights earlier than the respective females.

This study has shown that larvae that consumed green beans and cowpea reached their peak earlier than those that consumed catjang cowpea and cucumber. During the prepupal stage, the peak occurred fastest for green beans and slowest for catjang cowpea and wax gourd; the difference in the rates was 2.5 days. This suggests that green beans offered superior growth conditions and nutrients for the thrips than the other crops. Additionally, pupae that fed on green beans, bitter gourd, soybean, cowpea, and courgette exhibited peak development at a similar timeframe (7.5–8.5 days). This indicates that these crops offered comparable growth conditions and nutritional resources for thrip development.

3.4. F. intonsa Age-Specific Survival and Fecundity

As shown in Figure 2, all nine age-specific survival rate (l_x) curves of thrips feeding showed declining trends. The longest survival time was recorded for thrips feeding on wax gourd (88 days), followed by bitter gourd (76.5 days) and courgette (73 days). The survival duration for thrips feeding on cowpea, green beans, catjang cowpea, cucumber, and soybean ranged from 50 to 66 days. In contrast, F. intonsa that fed on chieh-qua showed the shortest survival time, and survival rate reached 0 on day 11.5. The f_xj curves of female thrips feeding on cowpea, green beans, soybean, courgette, and cucumber initially showed an increasing trend, followed by a decreasing trend and another increase before a final decrease; the peaks were observed at 16.8, 21.9, 10.7, 5.2, and 8.6, respectively. The thrips that fed on wax gourd and catjang cowpea showed curves with an initial increasing trend, followed by a decreasing trend and peak values of 1.8 and 5.1, respectively. The m_x curves for all crops except chieh-qua generally exceeded the l_xm_x curves after day 30. Notably, the m_x curves for green beans and soybeans were significantly higher than those for the other crops. Additionally, Figure 2 indicates that the m_x and l_xm_x curves for thrips feeding on cowpea, green beans, soybean, catjang cowpea, and courgette overlapped significantly before day 30.

The l_x curves for all nine crops declined. This indicates a gradual decrease in survival over time. The age-stage fecundity curves of females indicate that the reproductive capacity of thrips fluctuated over time as multiple peaks were observed rather than a simple continuous increase or decrease.

3.5. F. intonsa Population Life Table Parameters

Table 3. Population parameters of Frankliniella intonsa fed on nine host crops.

Hostplant	Net Reproductive Rate	Intrinsic Rate of Increase/d−1	Finite Rate of Increase/d−1	Mean Generation Time/d
Cowpea	45.5100 ± 0.0224 b	0.2228 ± 0.0000 b	1.2496 ± 0.0000 b	17.0896 ± 0.0012 g
Green bean	104.0416 ± 0.0444 a	0.3112 ± 0.0000 a	1.3652 ± 0.0000 a	14.8967 ± 0.0007 h
Soybean	12.5365 ± 0.0127 f	0.0756 ± 0.0000 g	1.0786 ± 0.0000 g	32.7307 ± 0.0050 b
Catjang cowpea	25.2152 ± 0.0140 d	0.1585 ± 0.0000 d	1.1718 ± 0.0000 d	20.2962 ± 0.0022 e
Courgette	32.6065 ± 0.0216 c	0.1650 ± 0.0000 c	1.1796 ± 0.0001 c	21.0293 ± 0.0033 d
Wax gourd	7.1653 ± 0.0055 g	0.0871 ± 0.0000 f	1.0911 ± 0.0000 f	22.2977 ± 0.0018 c
Bitter gourd	0.7300 ± 0.0012 h	−0.0101 ± 0.0000 h	0.9900 ± 0.0000 h	49.4894 ± 0.0398 a
Cucumber	13.7354 ± 0.0126 e	0.1320 ± 0.0001 e	1.1413 ± 0.0001 e	19.5130 ± 0.0020 f
Chieh-qua	-	-	-	-

Note: Data in the table are presented as mean ± SE. Values in the same column followed by different letters are significantly different (LSD test, p < 0.05).

shows the effects of feeding on nine different crops on population parameters of F. intonsa. Significant differences were observed in the R₀ of thrips between crop types. The highest net reproductive rate (104.0416) was observed for green beans, followed by cowpea (45.5100), courgette (32.6065), catjang cowpea (25.2152), cucumber (13.7354), and soybean (12.5365). In contrast, the lowest net reproductive rate (0.7300) was observed for bitter gourd. Significant differences were also observed in the r between the nine crops. The highest intrinsic rate of increase (0.3112) was observed for green beans, followed by cowpea (0.2228), courgette (0.1650), catjang cowpea (0.1585), and cucumber (0.1320). Feeding on soybean, wax gourd, and bitter gourd produced an intrinsic rate of increase that was significantly lower than that of the other crops. Notably, the intrinsic rate of increase (−0.0101) observed for bitter gourd-fed thrips indicated a negative growth rate. The finite rate of increase (λ) was highest for green bean-fed F. intonsa (1.3652), followed by those that fed cowpea (1.2496). The remaining crops showed values in the range of 1.1796–0.9900 with the lowest value observed for bitter gourd-fed thrips (0.9900). The mean generation time (T) of thrips varied significantly among the crops with the longest mean generation time observed for bitter gourd (49.4894 days), followed by soybean (32.7307 days). In contrast, the shortest mean generation time was observed for green beans (14.8967 days), whereas the remaining crops showed values in the range of 17.0896–22.2977 days with no significant differences.

4. Discussion

The two-sex life table is a critical tool in insect population ecology and pest management because it offers valuable insights into pest survival, developmental time, and fecundity. This information is useful for the enhancement of control strategies [20,21]. In the present study, life table analyses were performed on F. intonsa populations with respect to nine crops. This analysis elucidated the developmental duration, survival rate curves, and population parameters of the pest at various stages in different crops. Based on the developmental time of F. intonsa on different crops, the first-instar nymph develops fastest on green bean and slowest on chieh-qua. The second-instar nymph develops fastest on green bean and slowest on wax gourd, and it cannot develop normally on chieh-qua. The prepupal and pupal stages have the longest developmental time on cowpea and the shortest on bitter gourd. The total developmental cycle of F. intonsa is shorter on green beans, bitter gourd, cowpea, and soybeans, while it is longer on wax gourd, cucumber, catjang cowpea, and courgette. This indicates that the nutrients and energy provided by different crops can affect the developmental time of F. intonsa at each stage. Green beans, bitter gourd, cowpea, and soybeans offer more suitable growing conditions for F. intonsa, whereas the other four crops are less conducive to its rapid development. Notably, the second-instar larvae of F. intonsa failed to complete their development on chieh-qua, suggesting that chieh-qua may contain resistance factors or lack the nutrients required by F. intonsa, which prevents F. intonsa from completing its life cycle. Additionally, chieh-qua possesses a notably thicker epicuticular wax layer compared to cowpeas, green beans, and courgette. This physical barrier significantly reduces feeding activity in F. intonsa, resulting in inadequate nutrient uptake to support normal growth and development. The reproductive capacity of F. intonsa differed significantly among different crops. The highest egg production was observed for the insect group that fed on green beans, followed by those that fed on cowpea, courgette, cucumber, and catjang cowpea, whereas egg production was lower for those that fed on soybean and wax gourds. This indicates that green beans, cowpea, and courgette are highly suitable for the reproduction of F. intonsa, whereas feeding on cucumber, catjang cowpea, soybean, and wax gourd resulted in slower population growth, which is unfavorable for expansion. Moreover, F. intonsa that fed on bitter gourd and chieh-qua exhibited an extremely low reproductive capacity and failed to achieve intergenerational reproduction. This leads to the conclusion that these two crops significantly suppress the reproduction of F. intonsa. In terms of population parameters, green bean-fed F. intonsa exhibited the highest intrinsic rate of increase (0.31) and net reproductive rate (104.04), indicating that green beans were the most suitable host crops for population growth. In contrast, the intrinsic rate of increase was negative (−0.01) for bitter gourd-fed F. intonsa, which suggests that bitter gourd strongly suppresses the population growth of F. intonsa. This finding is consistent with numerous studies on the influence of host plants on insect growth and development. Wang et al. discovered that the Phthorimaea operculella (Lepidoptera: Gelechiidae) exhibits a stronger preference for potato plants over tobacco, demonstrating both a higher intrinsic rate of increase and net reproductive rate when feeding on potatoes [22]. Similarly, Tok et al. revealed that the Phenacoccus madeirensis (Hemiptera: Pseudococcidae) utilizes various host plants, including Phenaconium zonale (Lamiales: Acanthaceae), Hibiscus rosa-sinensis (Malvales: Malvaceae), Hibiscus syriacus (Malvales: Malvaceae), and Cestrum nocturnum (Solanales: Solanaceae). However, when feeding on Cestrum nocturnum, the P. madeirensis showed accelerated larval development and achieved the highest reproductive rate among these four host plants [23]. These findings highlight the significant effect that crop selection exerts on the population dynamics of F. intonsa. Factors such as plant pigmentation, secondary metabolite profiles, and nutrient composition play pivotal roles in the mutual adaptability of pests and their hosts [24,25,26]. The rapid population growth of F. intonsa on green beans, cowpea, and courgette may be attributed to the fact that these crops meet the feeding and survival requirements of F. intonsa. For example, green beans and cowpea are rich in proteins and amino acids, and courgette sap contains high levels of sugars. Additionally, since F. intonsa prefer to feed on tender tissues, which include crops such as green beans, cowpeas, and courgette—with their smooth surfaces and thin waxy layers [27]. Moreover, F. intonsa favor feeding and laying eggs inside blossoms. Green beans, cowpeas, and courgette typically exhibit long flowering periods with abundant flowers, providing excellent hiding spots to evade natural predators. This is one of the reasons for the host preference differences observed in courgette. Courgette exhibits lower levels of secondary metabolites (e.g., alkaloids) [28] and emits distinct volatile organic compounds [29] that strongly attract F. intonsa, which further promotes its feeding and reproductive behaviors. Additionally, the warm and humid growing environments of these crops are highly suitable for the survival and reproduction of F. intonsa. In contrast, feeding on cucumber, catjang cowpea, soybean, and wax gourd was less conducive to the population growth of F. intonsa. This may be attributed to insufficient nutrients in cucumber and catjang cowpea to meet the nutritional needs of F. intonsa. Soybean contains high levels of protease inhibitors that interfere with the digestive system of the insect and reduce its feeding efficiency. Furthermore, the rough surfaces of soybean and wax gourd leaves and fruits and the presence of a thick wax layer on wax gourd impede both the feeding and oviposition by F. intonsa. Thus, bitter gourd and chieh-qua may suppress the reproduction of F. intonsa because of their chemical defense mechanisms, surface structures, nutrient composition, and growth environments. Similarly, the dense plant structure of bitter gourd leads to poor ventilation, which results in excessive humidity or temperature. This may have suppressed the reproduction of F. intonsa on bitter gourd.

Furthermore, the discrepancies between the conditions in the laboratory and field environments in conjunction with the feeding preferences of F. intonsa may have influenced the experimental outcomes. Often during agricultural production, F. intonsa is found to be the dominant pest of cucumber, bitter gourd, and chieh-qua crops, which sustain relatively large populations of F. intonsa. However, this contradicts the findings of the present study. A number of key factors may have contributed to this discrepancy. Firstly, the field and laboratory environments show disparities. In the field, F. intonsa selectively feeds on different crop parts and migrates between various crops to optimize its food sources. Furthermore, the volatile compounds released by the flowers of cucurbit crops attract F. intonsa, and the extended flowering periods of cucumbers, bitter gourds, and chieh-qua (which bloom continuously throughout the growing season) ensure the availability of food sources and oviposition sites for F. intonsa. In contrast, this study was conducted under controlled laboratory conditions, which restricted F. intonsa from consuming tender leaves and fruits. This may have resulted in a difference in the nutritional intake compared with that under field conditions. The fruits and tender leaves of cucumber, bitter gourd, and chieh-qua exhibit antixenotic properties that suppress the growth and development of F. intonsa. Secondly, the composition of the pest species varied across different crop developmental stages. F. intonsa prefers to feed on floral organs. Under laboratory conditions, the tender leaves and fruits of cucumber and bitter gourd may not supply sufficient nutrition to F. intonsa, leading to prolonged developmental cycles and reduced egg production. Furthermore, the tender leaves of chieh-qua only supported F. intonsa development up to the second-instar larval stage. In natural ecosystems, F. intonsa exhibits behavioral plasticity in response to suboptimal host crops such as cucumber, bitter gourd, and chieh-qua by migrating to other hosts or selecting alternative food sources. However, in the laboratory, this adaptive behavior was restricted.

The lifespan of male and female F. intonsa shows significant differences. Based on the adult lifespan and oviposition data of F. intonsa, their survival strategy on most crops favors females as the dominant sex. The average lifespan of female F. intonsa is significantly longer than that of males after feeding on different crops (e.g., 29:21 days on cowpeas, 25:14 days on green bean, 29:13 days on bitter gourd, etc.). Female thrips can rapidly increase the population size through oviposition, reflecting the typical characteristics of an r-selection reproductive strategy. This gender difference may stem from the fact that females extend their lifespan to gain multiple oviposition opportunities, while males experience rapid physiological decline after mating.

According to this study, green beans, cowpea, and courgette acted as the primary host crops that supported the rapid population growth of F. intonsa. Therefore, the implement surveillance and integrated pest management (IPM) strategies need to be strengthened for these crops during agricultural production. Green beans are particularly prone to pest population surges because of the short developmental cycle and high reproductive capacity of F. intonsa. Hence, we recommend early intervention strategies such as biological and chemical control to effectively manage the F. intonsa population. Despite the fact that cucumber, catjang cowpea, soybean, and wax gourd are less favorable for the rapid reproduction of F. intonsa, their potential as secondary hosts should not be overlooked. This is particularly relevant in crop rotation and intercropping systems, where these crops can act as transitional hosts for F. intonsa. Additionally, this information is valuable because insect population dynamics and developmental growth are influenced by both host plants and biotic and abiotic factors such as natural enemies and environmental conditions [30,31]. This study has some limitations. Firstly, the experiments were performed under controlled indoor conditions, which potentially differ from the field conditions. Hence, future studies are needed to confirm these findings under field conditions. Secondly, this study primarily examined the growth, development, and reproduction of F. intonsa but did not explore the antibiosis and antixenosis mechanisms of crops. Hence, future studies should further investigate the mechanisms of antibiosis and antixenosis in the tested crops against F. intonsa and examine how these mechanisms interact with environmental factors, natural enemies, and insecticides to collectively influence thrips population dynamics. Field studies can optimize crop layout to reduce the population base of thrips. In areas with a high F. intonsa incidence, the concentrated planting of snap beans, cowpeas, and zucchini should be reduced to lower the initial pest source. In thrips-prone areas, rotating or intercropping with bitter melon and chieh-qua can leverage their natural resistance to suppress population growth. Additionally, integrating chemical control is essential. Strengthen monitoring on cowpeas, green beans, and courgettes, and prioritize pesticide application before the rapid population growth of F. intonsa (e.g., during flowering). On cucumbers, catjang cowpea, soybeans, and wax gourds, where thrips populations grow more slowly, the intensity of chemical control can be appropriately reduced to minimize pesticide residues and resistance risks. For bitter gourd and chieh-qua, their natural resistance mechanisms can be explored, and low-toxicity biopesticides (such as spinosad and azadirachtin) can be used for supplementary control.

Such investigations would provide a scientific basis for developing more comprehensive integrated pest management (IPM) strategies.

5. Conclusions

This study systematically assessed the growth, development, and reproductive traits of F. intonsa in nine different crops using an age-stage two-sex life-table approach. F. intonsa showed significant variations in the growth, development, and reproduction among these crops. Green beans, cowpea, and courgette were the most suitable host crops for population growth. In contrast, cucumber, catjang cowpea, soybean, and wax gourd were less favorable for the population establishment of F. intonsa, whereas bitter gourd and chieh-qua significantly suppressed population growth. These findings are critical for devising targeted control measures against F. intonsa as they provide valuable guidance for optimizing crop arrangements and pest management during agricultural production.