Eggplant (Solanum melongena L.) is one of the most widely cultivated vegetable crops in India and belongs to the family Solanaceae. It is valued for its nutritional richness, adaptability to diverse agro-climatic conditions and year-round cultivation. However, eggplant production is severely constrained by infestation from a complex of insect pests, among which the brinjal shoot and fruit borer, Leucinodes orbonalis Guenée, is considered the most destructive. Other important pests include Henosepilachna vigintioctopunctata, Euzophera perticella, Myllocerus subfasciatus, Cestius phycitis and Aphis gossypii (Srinivasan, 2009; Ambethgar et al., 2025).
       
The larvae of L. orbonalis cause damage throughout the crop growth stages. During the vegetative phase, larvae bore into tender shoots, leaf midribs and petioles, leading to drooping and drying of plant parts (Siam et al., 2024). As the crop enters the reproductive stage, larvae penetrate developing fruits, where the entry hole is often plugged with frass, making early detection difficult (Gautam et al., 2019). Infestation during the fruiting stage directly reduces marketable yield and quality. Because of its concealed feeding habit and rapid life cycle, this pest is difficult to manage under field conditions.
       
Integrated pest management (IPM) strategies in brinjal recommend initiating control measures when shoot damage reaches approximately 5% and fruit damage reaches about 10% to prevent economic yield loss (Meena et al., 2012; Singh et al., 2000). Accurate knowledge of the pest’s biology, developmental pattern and stage-specific morphology is therefore essential for timely monitoring, mass rearing and effective implementation of IPM strategies (Ambhure et al., 2016; Jat et al., 2003; Senapati and Senapati 2006). Life table studies provide valuable information on stage-specific survival, mortality and population dynamics of insect pests and their natural enemies. Similar approaches have been successfully used to understand the population ecology of Acerophagus papayae associated with Paracoccus marginatus, highlighting the importance of life table analysis in developing effective biological and ecological management strategies (Nisha et al., 2026).
       
Although several studies have described the general biology of L. orbonalis on brinjal under field conditions, limited information is available on its comparative biological performance and morphometric variation when reared on different natural and artificial diets under controlled laboratory conditions. Detailed morphometric benchmarks across developmental stages in response to diet are also scarce.  Host-associated variation in developmental traits and life-history parameters has been reported in other insect species, demonstrating that differences in host quality can drive adaptive responses and influence population performance (Nisha et al., 2026). Therefore, the present study was undertaken to evaluate the influence of different diets on the biology, life table parameters and morphometric characteristics of L. orbonalis under laboratory conditions.

Experimental site
 
The study was carried out during 2025 at the Entomology Laboratory, SRM College of Agricultural Sciences, Baburayanpettai, Chengalpattu district, Tamil Nadu, India.
 
Mass rearing of brinjal shoot and fruit borer
 
Infested brinjal fruits containing larvae of Leucinodes orbonalis were collected from fields and markets. Larvae were reared in ventilated plastic containers and fed fresh brinjal pieces daily until pupation on muslin cloth and adult emergence. Newly emerged adults were paired in containers with a potted brinjal plant for oviposition. A 10% sugar solution was provided as food and eggs were laid on leaves, container surfaces and the muslin cloth.
       
Eggs laid on the same day were collected and reared individually on three diets-brinjal fruit, potato tuber and an artificial diet (Table 1) to avoid cannibalism. Rearing was continued for one generation to minimize field variability. Eggs from the next generation were then used for detailed biological and morphometric studies of Leucinodes orbonalis across diets.


       
Healthy brinjal fruits were chopped into small pieces and finely ground with a small quantity of water to obtain a uniform pulp. After that, the pulp was cooked in 150 ml of water until it became slightly darker and reached the required consistency. In a separate glass jar, 150 ml of water was used to dissolve black gram flour, sorbic acid, ascorbic acid, methyl-p-hydroxybenzoate, vitamin solution and formaldehyde and the mixture was thoroughly mixed (Table 1).
       
In another container, yeast was combined with 200 ml of water and boiled together with agar-agar for about 10 minutes. This mixture was allowed to cool for about five minutes before the other two preparations were gradually added with constant stirring. After pouring the prepared mixture into plastic trays and letting them cool, the trays were refrigerated at 4°C for further studies Hegde et al. (2018).
 
Life table analysis
 
A cohort of 100 freshly deposited eggs was used to conduct life table analysis in a laboratory setting. The number of individuals who survived and died at each developmental stage and age interval was recorded on a daily basis until the life cycle was completed.
 
Age-specific life table
 
• x: Age in days.
• l_x: Number surviving at age x.
• d_x: Number dying during age interval x.
• 100q_x: Percentage mortality = (d_x/l_x) × 100.
 
Life expectancy (e_x) was calculated as:
 

 
Where:

These parameters describe survival, mortality and life expectancy across age intervals.
 
Stage-specific life table
 
The parameters observed were apparent mortality, stage-specific survival fraction (S_X), generation survival fraction (S_G), Mortality Survival Ratio, indispensable mortality (IM) and k-values and the total generation mortality (K). The total generation mortality (K) was calculated following the key factor analysis concept described by Varley and Gradwell (1960).
       
Apparent mortality (%) at each stage was calculated as:

 
Where,
I_x= Number entering the stage.
d_x= Number dying.
       
Stage survival fraction (S_x) was computed as:

Generation survival (S_G) from egg to adult was obtained by multiplying survival fractions of successive stages:
 

S_G = S_E × S_L × S_P

 
Mortality-survivor ratio (MSR) was estimated as:

Indispensable mortality (IM) for each stage was calculated as:
 

IM = N_a × MSR

 
Where,
N_a= Total number of adults emerged.
 
K-value analysis
 
K-value analysis was done for the identification of the key mortality stages that influence the population. The difference between successive logarithmic values of lx was estimated to find the k value for each developmental stage:
 

K_x = logix - logix + 1

 
The total generation mortality (K) was obtained by summing the stage-wise k-values:
 

k = k₀ + k₁ + k₂ + k₃

 
Where,
k₀= Egg stage.
k₁= Larval stage.
k₂= Pre-pupal stage.
k₃= Pupal stage.
       
The total K-value represents overall generational mortality by giving information on population growth or decline between generations. For analysing the stage- specific mortality, larvae were collected weekly and raised in a lab setting on bhendi till adult emergence.
 
Experimental design
 
The experiment was conducted with three treatments (diets), namely brinjal fruit, potato tuber and artificial diet, arranged in a completely randomised design (CRD) with eight replications under laboratory room-temperature conditions (27±2°C; 70±5% RH; 12:12 h L:D photoperiod). Data were subjected to analysis of variance (ANOVA) and treatment means were compared using LSD at 5% significance level.
       
For each replication, ten freshly laid eggs of Leucinodes orbonalis were placed in separate plastic containers. Upon hatching, newly emerged first instar larvae were reared individually in plastic containers (20 × 15 cm) and provided with the respective diets to avoid cannibalism. Larvae were maintained on the same diet throughout their development.
       
Morphometric characterisation from egg to adult stage was carried out using a Leica stereo zoom microscope at 0.5× magnification, fitted with an ocular micrometre calibrated with a stage micrometre for accurate measurements.

The experiment evaluated two natural diets and one artificial diet for rearing L. orbonalis larvae under laboratory conditions. Diet performance was assessed based on larval survival at different instars, pupation percentage, adult emergence, duration of larval and pupal stages and fecundity of emerged females. Larval survival exceeded 90% on natural diets, particularly brinjal and potato and was consistently higher than that recorded on the artificial diet across all larval stages. This higher survival on the natural host agrees with Rahman et al., (2011) and Sethi et al., (2016), who reported that host suitability directly influences survival and population build-up of Leucinodes orbonalis.
 
Developmental time of Brinjal Shoot and Fruit Borer L. orbonalis on different diets
 
The development of Leucinodes orbonalis comprised egg, five larval instars, prepupa and pupa, with significant variation among diets (Table 2). The egg period was shortest on brinjal fruit and potato tuber (3.51±0.28 and 3.51±0.25 days) and longest on artificial diet (4.00±0.19 days), with brinjal and potato statistically on par. For all larval instars (I–V), prepupa and pupa, the longest duration consistently occurred on artificial diet (2.44, 2.71, 2.70, 3.30, 3.68, 1.41 and 7.45 days, respectively), whereas the shortest duration was recorded on brinjal fruit (1.33, 2.19, 2.21, 2.68, 3.19, 1.16 and 7.10 days, respectively). Consequently, the total developmental period was minimum on brinjal fruit (20.18±0.43 days) and maximum on artificial diet (24.01±0.16 days). These findings are consistent with reports of faster development in the natural host (Rahman et al., 2011; Sethi et al., 2016; Laichattiwar et al., 2017; Harit et al., 2005). The prolonged development on artificial diet may be attributed to the lack of essential phytochemicals and nutrients present in brinjal tissues.


 
Adult longevity of L. orbonalis on different diets
 
The statistically significant differences among the different diets in terms of male adult longevity are higher in brinjal fruit (5.50±0.22) and the least from potato tuber and artificial diet (4.95±0.19 days and 4.94±0.16 days, respectively) and they were on par with each other. The female adult longevity was higher in brinjal fruit and potato tuber (6.88±0.57 and 6.76±0.40 days) and lower in artificial diet (6.15±0.36 days). The brinjal fruit and the potato tuber were on par with each other. The preoviposition period was significantly higher in artificial diet (1.55±0.28 days) and lower in brinjal fruit and potato tuber (2.81±0.17 and 2.53±0.23 days, respectively) and they were on par with each other. The oviposition period was highest in brinjal fruit (2.81±0.17 days) and the least from artificial diet (2.14±0.19 days). The post-oviposition period was highest in the artificial diet (2.85±0.17 days) and the least from brinjal fruit (2.16±0.15 days) (Table 3). These findings agree with (Rahman et al., 2011 and Sethi et al., 2016), who reported enhanced adult fitness and fecundity when larvae were fed on brinjal. The delayed reproductive parameters observed in artificial diet-reared adults may be due to suboptimal larval nutrition affecting physiological maturity (Ambhure et al., 2016).


 
Morphometric characters of L. orbonalis eggs and larvae length on different diets
 
Significant dietary effects were observed on the morphometric length of immature stages of Leucinodes orbonalis. Egg length was greater and statistically similar on brinjal fruit and potato tuber (0.52±0.02 and 0.51±0.01 mm) than on the artificial diet (0.43±0.02 mm). Across larval instars I-V, the maximum lengths were consistently recorded on brinjal fruit (0.74, 4.27, 8.46, 9.84 and 12.43 mm), followed by potato tuber (0.69, 4.15, 8.49, 9.97 and 12.55 mm), while the minimum lengths occurred on artificial diet (0.63, 3.17, 6.48, 8.60 and 10.15 mm). Morphometric growth increased progressively from first to fifth instar on all diets, conforming to Dyar’s rule. The reduced body dimensions on artificial diet indicate nutritionally constrained growth, in agreement with earlier reports (Hegde et al., 2018; Haldhar et al., 2023; Chaudhary and Sharma, 2000).
 
Morphometric characters of L. orbonalis eggs and larval width on different diets
 
Egg width was higher and on par with brinjal fruit and potato tuber (0.35±0.02 mm) and lower on artificial diet (0.31±0.01 mm). A similar trend was observed for larval width. For instars I-V, widths were greatest on brinjal fruit (0.12, 0.80, 1.66, 1.99 and 2.76 mm), followed closely by potato tuber (0.12, 0.78, 1.64, 1.99 and 2.56 mm) and lowest on artificial diet (0.10, 0.77, 1.61, 1.85 and 2.39 mm). The gradual increase in width across instars further supports Dyar’s rule and confirms head capsule and body width as reliable parameters for instar determination, while reduced values on artificial diet reflect sub-optimal nutrition. (Bindu et al., 2015; Jat et al., 2003) (Table 4).


 
Morphometric characters of L. orbonalis pupa on different diets
 
The statistically significant differences among the different diets in terms of pupal morphometry indicated that the pupa without cocoon length was significantly higher in brinjal fruit (9.36±0.18 mm), followed by potato tuber (9.10±0.30 mm). In contrast, it was significantly lower in the artificial diet (7.43±0.28 mm). The pupa with cocoon length was significantly higher in brinjal fruit and potato tuber and they were on par with each other (12.02±0.54 and 11.90±0.33 mm, respectively). The lowest length was recorded in the artificial diet (11.29±0.52 mm). The pupa without cocoon width was significantly higher in brinjal fruit (2.63±0.07 mm), which was on par with potato tuber (2.61±0.06 mm). The lowest width was observed in the artificial diet (2.55±0.03 mm). The pupa with cocoon width was significantly higher in brinjal fruit (5.24±0.15 mm), followed by potato tuber (5.08±0.19 mm), while the lowest width was recorded in the artificial diet (4.87±0.10 mm) (Table 5).


 
Morphometric characters of L. orbonalis  adults on different diets
 
Adult morphometry also varied significantly with diet. Female length was highest on brinjal fruit (9.49±0.30 mm), followed by potato tuber (9.20±0.12 mm) and lowest on artificial diet (8.54±0.10 mm). Male length was similar on brinjal fruit and potato tuber (8.15±0.26 and 8.01±0.12 mm) and least on artificial diet (7.25±0.10 mm). Female width was greater and on par on brinjal fruit and potato tuber (18.90±0.87 and 19.21±0.26 mm) than on artificial diet (17.31±0.51 mm), while male width was highest on brinjal fruit (18.49±0.45 mm), followed by potato tuber (18.04±0.05 mm) and lowest on artificial diet (15.97±0.19 mm). Larger pupae and adults from brinjal-reared larvae and consistently larger females across diets indicate clear sexual dimorphism, corroborating earlier observations (Hegde et al., 2018) (Table 5).
 
Morphometric characters of L. orbonalis  of head capsule width on different diets
 
The statistically significant differences among the different diets in terms of head capsule width of the larvae revealed that the first instar head capsule width was significantly higher in brinjal fruit (0.104±0.003 mm), followed by potato tuber (0.098±0.003 mm), whereas it was significantly lower in the artificial diet (0.093±0.005 mm). The second instar head capsule width was significantly higher in brinjal fruit (0.610±0.008 mm), followed by potato tuber (0.568±0.025 mm) and the lowest width was recorded in the artificial diet (0.404±0.020 mm). The third instar head capsule width was significantly higher in brinjal fruit (1.117±0.002 mm), followed by potato tuber (1.095± 0.006 mm), whereas it was significantly lower in the artificial diet (0.897±0.034 mm). The fourth instar head capsule width was significantly higher in brinjal fruit (1.217±0.008 mm), followed by potato tuber (1.117±nb0.018 mm) and the lowest width was observed in the artificial diet (1.040±0.022 mm). The fifth instar head capsule width was significantly higher in potato tuber and brinjal fruit and they were on par with each other (1.244±0.013 and 1.236±0.018 mm, respectively), whereas it was significantly lower in the artificial diet (1.124±0.014 mm). The progressive increase in body size and head capsule width across instars confirms Dyar’s rule (Table 6). The developmental stages of L. orbonalis, including egg, larval, pupa, and adult (male and female), are illustrated in Fig 1.




 
Life table for L. orbonalis  on brinjal diet
 
The life table was developed specifically for the brinjal diet since brinjal is the primary and preferred natural host of Leucinodes orbonalis, providing accurate insights into its survival and population dynamics. Studying the pest on its natural host makes it easier to predict field-level infestation and to design effective pest management strategies. The life table constructed for L. orbonalis showed higher mortality during egg and early larval stages, followed by greater survival in later instars and the pupal stage. This survivorship trend agrees with Rahman et al., (2022), who reported that early instars are more vulnerable to environmental stress, while later stages exhibit greater tolerance. The gradual decline in life expectancy with advancing age observed in the present study represents the normal survivorship pattern of lepidopteran borers.
 
Age-specific life table
 
The survivorship pattern derived from the present data depicts a Type III survivorship curve, where higher mortality occurs in the early stages of life, followed by greater survival in later stages. This pattern is typical for many lepidopteran insects, including L. orbonalis, as observed in laboratory life table analyses by Rahman et al., (2022) and Khan et al., (2019).
       
From the age-specific life table, it is evident that the early developmental stages play a major role in determining the population dynamics of L. orbonalis. Hence, management practices targeting eggs and early larval stages would be more effective in regulating population buildup (Table 7).


 
Stage-specific life table
 
The stage-specific life table of Leucinodes orbonalis on brinjal under laboratory conditions (Table 8) showed the highest mortality at the egg (12.00%) and first instar (13.64%) stages, indicating greater vulnerability of early immature stages. The survival fraction (S“ ) increased from 0.880 in the egg stage to 0.964 in later stages, reflecting improved stability with development, in line with reports by Rahman et al. (2022).


       
Mortality-survivor ratio and indispensable mortality were also highest in the egg and first instar, confirming their major contribution to generational mortality, as similarly observed by Khan et al., (2019).

The present study documented the biology and morphometric characteristics of Leucinodes orbonalis under laboratory conditions on different diets. The host diet significantly influenced development, survival and reproduction. Brinjal fruit and potato tuber proved more suitable than the artificial diet, supporting higher larval survival, shorter development and better fecundity. The life cycle ranged from 28 to 36 days, indicating multivoltine potential. Morphometric traits, particularly the progressive increase in head capsule width across instars, provided reliable criteria for stage identification. Females were consistently larger than males, confirming sexual dimorphism.
       
Overall, the baseline biological, morphometric and life table data generated on the brinjal diet offer useful reference information for accurate stage identification, laboratory rearing and development of effective management strategies for this pest.

The authors declare that there is no conflict of interest regarding the publication of this manuscript.