Pulses are vital food crops globally, providing protein, dietary fiber, vitamins and minerals essential to combat malnutrition (Viguiliouk et al., 2019; Pearce et al., 2021). India is the largest producer, contributing over half of global pulse production, with black gram (Vigna mungo L.) as a key variety (FAOSTAT, 2021; DAC and FW, 2022). Beyond nutrition, black gram forms a symbiotic association with Rhizobium bacteria, enabling it to fix atmospheric nitrogen and thereby improve soil fertility (Sadiq et al., 2023).
       
Post-harvest losses due to storage pests are a major challenge. Among these, the pulse beetle (Callosobruchus chinensis L.) is particularly destructive, often causing 30-40% seed damage in traditional storage and, under severe infestations, complete seed loss (Gbaye et al., 2011). Infestation typically begins in the field and rapidly intensifies during storage, with damage often reaching 60-100% within just two to three months (Ragul and Manivannan, 2024). Of the various bruchid species, C. chinensis and the cowpea weevil (C. maculatus F.) are the most economically significant. Adult females lay eggs on seed surfaces; larvae bore into seeds, reducing weight, quality and germination potential (Sharma, 1984; Hasan et al., 2020).
       
Synthetic insecticides and fumigants are commonly used for storage protection, but their drawbacks include resistance, chemical residues and ecological hazards. Botanical oils offer a safer alternative, providing insecticidal, repellent and oviposition-deterrent effects (Isman, 2006).
       
Oviposition is a key driver of population growth in C. chinensis, yet most studies focus only on adult mortality. Without controlling egg laying, population build-up and long-term seed protection remain uncertain. Botanicals can act via multiple mechanisms, including direct toxicity, repellence, oviposition deterrence and sub lethal effects on progeny (Shivanna et al., 1994; Meghwal et al., 2007; Ravi et al., 2008; Saiful et al., 2013).
       
This study evaluated seven commercially standardized oils-eucalyptus, neem, peppermint, castor, mustard, sesame and sunflower-against C. chinensis in stored black gram. It simultaneously assessed adult mortality and oviposition and analyzed their correlation to determine integrated protective efficacy, with direct practical relevance for pulse storage management.

Experimental site and conditions
 
The research, titled “Comparative Evaluation of Different Botanical Oils against Pulse Beetle (Callosobruchus chinensis) in Stored Black Gram,” was conducted in the Entomology Laboratory at the School of Agriculture, SR University, Warangal, between January and April of the 2024-25 academic year. Experiments were performed under controlled conditions, maintaining a temperature of 27±2^oC and relative humidity of 65±5%.
 
Plant material and treatments
 
Black gram seeds (var. Mash-114) were used to evaluate the efficacy of seven botanical oils: eucalyptus, neem, peppermint, castor, mustard, sesame and sunflower. Oils were applied at a rate of 5/ mL/kg of seeds, while untreated seeds served as the control.
 
Insect culture
 
A continuous laboratory culture of C. chinensis was established using naturally infested black gram seeds collected from the godown at Elkathurthy. Infested seeds containing both eggs and adults were placed in clean plastic containers with healthy black gram seeds (var. Mash-114). Containers were covered with muslin cloth and secured with rubber bands to allow ventilation while preventing insect escape. Newly emerged adults were transferred regularly to fresh containers containing healthy seeds to maintain successive generations. The culture was maintained under standard laboratory conditions (27 ±2^oC, 65±5% RH).Males and females were distinguished based on morphological traits: males have distinctly serrate antennae and a pygidium lacking dark patches, while females have more subtly serrate antennae and a pygidium with two dark midline patches. Females were slightly larger than males, averaging 3.60±0.08 mm in length versus 3.25 ±0.23 mm for males and breadths of 2.02±0.04 mm versus 2.16±0.05 mm, respectively (Devi and Devi, 2013).

Experimental setup
 
High-germination black gram seeds with moisture content below 10% were selected. For each treatment, 1.5 kg of seeds were coated with one of the seven botanical oils. Seeds were thoroughly mixed in high-density polyethylene (HDPE) containers and air-dried for one hour at room temperature. Untreated seeds served as the control. From each batch, 100/ g of seeds were placed in 250/ mL ventilated plastic containers, with three replicates per treatment. Five pairs of 24-48-hour-old adults (5 males + 5 females) were introduced into each container. All containers were maintained under controlled laboratory conditions (27±2^oC, 65±/5% RH, natural light cycles).Adult mortality was recorded after 48 hours of exposure using the formula:

Observations were conducted monthly over four months to assess the residual efficacy of the botanical oils under storage conditions.
 
Number of eggs laid on seeds
 
Each 250/ mL container containing 100/ g of treated seeds was examined using a hand-held magnifying lens. All visible eggs laid by female C. chinensis on the seed coat were counted carefully to avoid damage to seeds or eggs.
 
Statistical analysis
 
Data were analyzed following Gomez and Gomez (1984). Percentage data were transformed using the arc-sine method when necessary. Significant differences between treatments were determined using the critical difference (CD) at a 5% probability level.

Effect of botanicals on adult mortality
 
All seven botanical oils significantly influenced the adult mortality of C. chinensis compared to the untreated control (Table 1 and Fig 1). Among the tested oils, peppermint caused the highest mortality throughout the study period, recording 93.33% in the first month and 80.00% in the fourth month. Eucalyptus oil closely followed, with mortality values ranging from 91.66% to 80.00% over four months. Neem oil also demonstrated high efficacy, producing 83.33% mortality in the first month and maintaining 80.00% by the fourth month. Moderate activity was observed in castor and mustard oils, with mortality decreasing gradually from 73.33% to 56.66% and 71.66% to 50.00%, respectively. Sesame and sunflower oils were comparatively less effective, with mortality declining from 63.33% to 43.33% and 53.33% to 33.33%, respectively. The untreated control consistently recorded the lowest mortality, ranging from 20.00% to 23.33%, confirming that the observed effects were due to the treatments.




       
A general trend observed across all treatments was a gradual decline in adult mortality over the four-month period, which may be attributed to the reduction in residual activity of the oils with storage duration. Nevertheless, the relative efficacy of peppermint, eucalyptus and neem remained superior throughout the experiment.
       
These results are supported by Lalsingh Rathod et al. (2017), who reported that plant-based powders and oils significantly increased adult mortality of C. chinensis in stored legumes, highlighting the effectiveness of botanicals for pulse beetle management.
 
Effect of botanicals on oviposition
 
The application of botanical oils significantly reduced oviposition by C. chinensis on stored black gram seeds compared to the control (Table 2 and Fig 2). Peppermint and eucalyptus oils consistently resulted in the lowest number of eggs laid, indicating strong oviposition-deterrent properties. Peppermint oil reduced egg laying to 40 eggs 100 g seeds in the first month and 80 eggs 100 g seeds by the fourth month, whereas eucalyptus oil allowed 40-70 eggs over the same period. Neem oil also demonstrated substantial suppression of egg laying, ranging from 60-90 eggs 100 g seeds over four months. Moderate oviposition reduction was observed in castor and mustard oils, while sesame and sunflower oils were less effective. Sunflower-treated seeds recorded the highest number of eggs among treated groups (180-230 eggs 100 g seeds), although still lower than the untreated control, which recorded the maximum oviposition (273-330 eggs 100 g seeds).




       
These findings are consistent with earlier reports demonstrating the oviposition-deterrent activity of plant extracts against C. chinensis and related bruchids. In black gram, Azadirachtin-treated seeds exhibited the highest oviposition deterrence (92.18%), followed by Cassia angustifolia (68.56%) and Pongamia (57.01%), whereas Calotropis showed the least effect (40.30%) (Vijayalakshmi et al., 2021). Vanmathi et al., (2010) reported that aqueous extracts of C. gigantea and V. negundo significantly reduced oviposition of C. maculatus in black gram seeds.
       
Similar trends were reported by Sharma et al., (2013), who observed that plant products such as neem, mustard and groundnut oils significantly increased adult mortality and reduced oviposition and seed damage caused by C. chinensis in chickpea.
       
The oviposition-deterrent activity of these botanical oils and extracts is likely due to the presence of repellent compounds or chemicals that interfere with the physiology and behavior of adult bruchids, thereby reducing their egg-laying capacity. The current study reinforces the potential of botanicals as eco-friendly alternatives for the management of C. chinensis in stored pulses, particularly black gram.
 
Overall reduction in egg laying
 
Analysis of cumulative oviposition reduction showed that peppermint oil achieved the maximum suppression (80.71%), followed by eucalyptus (76.65%) and neem (72.58%). Castor and mustard oils provided moderate reduction (56.35% and 50.73%, respectively), while sesame and sunflower were comparatively less effective (41.12% and 35.53%). This pattern mirrors the adult mortality results, highlighting the dual protective role of these oils in reducing both adult populations and reproduction (Table 3).



Correlation between adult mortality and oviposition
 
Correlation analysis revealed a strong negative relationship between mean adult mortality and mean egg laying (r = -0.99, p<0.001) (Fig 3). Treatments causing higher mortality, such as peppermint, eucalyptus and neem oils, also exhibited the strongest oviposition deterrence. Conversely, sunflower and sesame oils, which were less lethal to adults, allowed significantly higher egg deposition. This relationship indicates that botanical oils provide dual protection, reducing both adult populations and reproductive potential, thereby ensuring effective long-term storage management.Peppermint, eucalyptus and neem oils were most effective against C. chinensis, likely due to bioactive compounds such as menthol, eucalyptol and azadirachtin with insecticidal and repellent properties. Castor and mustard oils provided moderate protection; sesame and sunflower were less effective but still better than control.The strong negative correlation (r = -0.99) indicates dual action: direct adult toxicity and oviposition suppression, ensuring immediate and long-term protection. Residual efficacy over four months supports the practical use of these oils for storage protection. Using commercially standardized oils enhances reproducibility and overcomes limitations of crude extracts reported in previous studies.

Peppermint, eucalyptus and neem oils are effective, sustainable protectants against C. chinensis in stored black gram. Their dual action-adult mortality and oviposition inhibition-provides both immediate and long-term protection. Commercially standardized oils ensure reproducibility and practical applicability, offering a safe and eco-friendly alternative to chemical fumigants for integrated pulse storage management.

The authors express sincere gratitude to SR University, School of Agriculture, Warangal, for providing laboratory facilities, materials and guidance essential for the successful completion of this study.

Disclaimers
 
The views expressed in this paper are solely those of the authors and do not necessarily reflect the opinions of their affiliated institutions. The authors are solely responsible for the accuracy of the information provided.
 
Informed consent
 
All experimental procedures involving insects and plant materials were conducted responsibly under laboratory conditions at SR University, School of Agriculture, Warangal. No human participants or vertebrate animals were involved.

The authors declare no competing interests.