Brinjal, also known as eggplant, is a short-lived perennial herb, one of the most commonly produced and low-cost vegetable crops in  Bangladesh  and  other  areas  of  the world. Brinjal (Solanum melongena L.) is a member of the Solanaceae family, which has over 2450 plant species divided into 95 genera (David, 2017). It is a versatile crop that may be grown in a variety of climatic conditions and at any time of the year (Cork et al., 2005). The plant is highly well-suited to both rainy and dry season culture, even though heavy rainfall inhibits both vegetative progress and flower creation. Brinjal has a high nutritional value when compared with other vegetables, containing 89.0 g of water, 1.4 g of protein, 1.0 g of fat, 8.0 g of carbohydrate, 1.5 g of cellulose, 130 mg of calcium, 105 mg of vitamin C, and 1.6 mg of iron (Degri, 2014). Brinjal is a good source of vitamin A (carotene), vitamin B-complex, and vitamin C, all of which are important for optimum health, as well as a decent amount of phosphorus, calcium, and iron ions for the body's bone and blood cell growth (Fayemi, 1999; Natural Resources Institute, 2000).

Brinjal growers in Bangladesh frequently fail to achieve the required output due to excessive damage caused by various insect pests that severely harm brinjal seedlings and plants. At the initial stage, the larvae bore into the shoot choking the movement of plant sap causing shoot drying and at later stages, it enters inside the fruit and demolishes its internal content. This type of interior mode of feeding makes this pest much evasive from the reach of even the most powerful insecticides (Krithika and Ananthanarayana, 2017). A single larva is sufficient to damage 4 to 6 healthy fruits. Alternative pest management strategies are necessary to decrease the misuse of chemical pesticides in vegetables. Here, three plant seed extracts such as ricin (Ricinus communis), devil’s cotton (Abroma augusta), and cotton (Bombax ceiba) seed with a high level of toxicity were used for control of brinjal shoot and fruit borer.

The castor bean or castor oil plant, R. communis L., and its methanolic extracts of the leaves were tested against eight pathogenic bacteria in rats and demonstrated antibacterial activity (Babu et al., 2017). At low doses, the pericarp of Ricinus produced central nervous system responses in mice, while at high levels, animals died rapidly (Sabina et al., 2011). In rats, analgesic efficacy was found in a water extract of the root bark, whereas an ethanolic extract of R. communis root bark showed antihistamine and anti-inflammatory activities (Lomash et al., 2010). The scientific name of Ulat Kambal is A. augusta, a medicinal plant. Steroids, alkaloids, triterpenes, megastigmanes, flavonoids, and phenylethanoid glycosides are found throughout the plant where leaves contain taraxerol and stem bark contains friedelin and beta-sitosterol (Gupta et al., 2011). Diabetes, inflammation, rheumatoid arthritis, migraines, uterine problems, and bleeding are all treated with the leaves (Das et al., 2012; Islam et al., 2013). A. augusta has a long and storied history in the Ayurvedic system, and it is sometimes utilized as a pesticide. The toxin delivers the A. augusta seed with some degree of natural defense from insect pests such as aphids, leafhopper or other insects. Cottonseed oil is a widely used vegetable oil obtained from cotton plant  seeds. The  oil,  vitamin  E, fatty acids, and antioxidants in a whole cottonseed range from 15 to 20%. It is high in polyunsaturated fat, which can help lower LDL and improve HDL, but it is also high in saturated fat, which increases cholesterol and boosts the risk of cardiovascular disease. Unrefined cottonseed oil is used as a pesticide, and this naturally produced toxin helps give the oil its yellow color and protects the plant from insects. It was principally utilized in the manufacture of oil lamps and candles in the 1800s, but it is currently found in pesticides, laundry detergents, and cosmetics.

Sample collection and drying

At first, collected seeds were sliced into small pieces for easy drying. Then the sliced seeds were dried in shade away from the sunlight until they dried. Seed samples required 8 to 14 days to completely dry. 95 g R. communis, 80 g A. augusta, and 100 g B. ceiba seeds were collected and dried in shade away from the sunlight for 8 to 14 days for extract preparation.

Pulverization and powder preparation

Completely dried small pieces of seeds were pulverized into finely powdered substances by using mortar and pestle and finally fine powdered substances were prepared. After drying, 60 g of R. communis, 50 g of A. augusta, and 60 g of B. ceiba seed sample were pulverized and powder prepared, respectively.

Extract preparation

In this work, ethyl acetate and methanol were used, respectively for extraction of R. communis, A. augusta, and B. ceiba seeds as extract solvents. The dried pulverized fine powders of 60 g of R. communis, 50 g of A. augusta, and 60 g of B. ceiba were taken into 3 conical flasks which were previously filled with 200 ml ethyl acetate. After that conical flasks were sealed with foil paper and placed into an automatic electric shaker of 150 rpm for 24 h at room temperature. Seed particles were removed from the ethyl acetate solution after filtration with Whatman No.1 filter paper. The remaining crude extract was taken into another previously washed conical flask for serial extraction of methanol. 200 ml methanol was added to filtrated crude of seed and put into shaker again to prepare methanol extract. After 24 h of shaking in the automatic electric shaker, methanol extract was filtrated using Whatman No.1 filter paper and stored at room temperature after labeling carefully. After filtration, the crude extracts were then condensed to concentrate through a rotatory evaporator. The amount of extract of ethyl acetate is shown in Table 1. Measured extracts were stored at 4°C to use later. 6.52, 6.96, and 9.24 g of R. communis, A. augusta, and B. ceiba extracts were obtained.

The amount of prepared extract in methanol is shown in Table 2. Measured extracts were stored at 4°C to be used later. 8.13, 6.75, and 9.5 g of R. communis, A. augusta, and B. ceiba extracts were obtained.

Larvae collection

Brinjal  shoot  and fruit borer (Leucinodes orbonalis Guenee) larvae were collected from pesticide-free infected brinjal from an experimental field beside the Islamic University area, Kushtia. A sterilized knife was used to chop up infested fruits. With an insect brush, the larvae from the chopped fruits were gathered and released on freshly harvested insecticide-free brinjal fruits from the experimental field. Comparatively particular instar or similar size and shape larvae were selected for this work.

In vitro preparation and growth

Petri dishes were washed and dried for in vitro experiments of botanicals. Pesticide and insect-free, healthy brinjal were collected from the experimental field and sliced into small pieces. 10 larvae were taken in each Petri dish and covered with a muslin cloth to allow aeration. Sliced brinjal fruit was served as food for larvae to allow continued growth.

Efficiency evaluation of seed extract

Ethyl acetate extract was firstly applied, 10 Petri-dishes were washed with detergent and dried afterward, 9 of these Petri-dishes were marked as A1, A2, A3, B1, B2, B3, C1, C2, and C3 for treatment, and one plate was used as control. Exactly 10 larvae were taken into each Petri-dish which was previously selected and sliced brinjal were added as a food source. In A1, A2, and A3 Petri-dishes, sliced brinjal fruit were sprayed with 100, 50, and 25% of R. communis, respectively. In the same manner, 100, 50, and 25% of A. augusta and B. ceiba extracts of ethyl acetate were sprayed in B1, B2, B3, C1, C2, and C3 plates, respectively. One plate was used as a control where no extracts were sprayed on the food source. After each spray, Petri-dishes were wrapped with muslin cloth and make tighten with a rubber band. Every plate was carefully labeled and placed at room temperature. After 24 h, the food supply was changed with fresh pesticide-free brinjal slices. During the change of food source, previously added brinjal were carefully checked and any borer inside, was taken out and placed in a newly supplied food source. Then the food was sprayed again with the same extract and concentration previously used. Secondly, extract solution of methanol was applied in the same manner. 10 Petri-dishes were washed and marked as D1, D2, D3, E1, E2, E3, F1, F2, F3, and control. 100, 50, and 25% solution of R. communis, A. augusta, and B. ceiba extracts of methanol were applied in D1, D2, D3, E1, E2, E3, F1, F2, and F3, respectively. A control plate was also with this preparation. All these plates were kept  in  shade, inspected every 12 h, and counted the live and dead larvae. Food sources were changed after 24 h with fresh pesticide-free healthy sliced brinjal and sprayed with the exact extract which was previously applied. The control plate was maintained as free from any spraying and observed every 12 h.

Effect of plant extracts on larvae

The 100% ethyl acetate extract of R. communis, A. augusta, and B. ceiba control fruit borer and brinjal shoot, L. orbonalis Guenee within 72 to 96 h. R. communis extract controlled earlier than other extract (Figure 1).

The 50% ethyl acetate extract of R. communis, A. augusta, and B. ceiba control fruit borer and brinjal shoot, L. orbonalis Guenee within 72 to 108 h. R. communis extract controlled earlier than other extract (Figure 2).

The 25% ethyl acetate extract of R. communis, A. augusta, and B. ceiba control fruit borer and brinjal shoot, L. orbonalis Guenee within 96 to 108 h. R. communis extract controlled earlier than other extract (Figure 3).

The 100% methanol extract of R. communis, A. augusta, and B. ceiba control fruit borer and brinjal shoot, L. orbonalis Guenee within 72 to 108 h. A. augusta extract controlled earlier than other extract (Figure 4).

The 50% methanol extract of R. communis, A. augusta, and B. ceiba control fruit borer and brinjal shoot, L. orbonalis Guenee within 72 to 108 h. R. communis extract controlled earlier than other extract (Figure 5).

The 25% methanol extract of R. communis, A. augusta, and B. ceiba control fruit borer and brinjal shoot, L. orbonalis Guenee within 72 to 120 h. R. communis extract controlled earlier than other extract (Figure 6).

Brinjal  production  is  one of the major sources of income for rural farmers (Danquah-Jones, 2000). The insect pests are reported to reduced yield and losses of between 75 and 90% of the crop (Onekutu et al., 2013). Plant extracts have been shown to reduce pathogen populations, and they have the potential to be used as an environmentally friendly alternative and as part of integrated pest control strategies (Bowers and Locke, 2004. Insect pests that feed on leaves, flowers, and developing grains, for example, are managed by spraying various extracts of biologically beneficial plant products such as leaves, stems, roots, and whole plants directly on the leaves, flowers, and developing grains. These sprays can control aphids, jassids, and even caterpillars (Prakash et al., 1987, 1990).

In this study, the seed extracts of R. communis, A. augusta, and B. ceiba (ethyl acetate and methanol extracts) were used to in vitro control L. orbonalis Guenee which is the most important insect pest of brinjal. The instar larvae bore into the eggplant, making them unmarketable and unfit for human consumption. Among the three extracts of ethyl acetate, 100% of R. communis and A. augusta extracts controlled 100% borers after 72 h of administration, 50 and 25% of R. communis extract controlled 100% borers after 72 and 96 h of administration. Compare to these three extracts with control, 50% of R. communis displayed a great potential pesticidal activity to controlled L. orbonalis Guenee. Previously, R. communis extract was used to repel Aedes aegypti oviposition behavior. The castor oil plant, which includes the alkaloid ricinine among other things, was used to stop A. aegypti from laying eggs (Leite et al., 2005). The LD50 of castor bean oil against maize weevils was calculated to be 2.04 ml, and 2 ml was shown to be sufficient to kill 50% of the weevils (Wale and Assegie, 2015). In general, R. communis has a larvicidal effect on Plutella xylostella, with 100% mortality recorded in both ingestion and contact toxicity tests on 3rd instar larvae fed with 10% oil emulsion (Kodjo et al., 2011). Castor oil is one of the very few naturally producing triglycerides, with ricinoleic acid accounting for rough nine-tenths of the fatty acid content (Bagali et al., 2010).

In this study, in the case of methanolic extracts, 100% of A. augusta extract controlled 100% borers after 72 h of administration compared to other seed extracts and 50 and 25% of R. communis extract controlled 100% borers after 72 and 84 h of treatment, respectively. From this result, R. communis showed a more effective value than A. augusta extracts because after 72 h of administration, 100% borer were controlled by 50% R. communis where 100% A. augusta extract was used. Previously, chloroform extracts of A. augusta seed, root wood, leaves, and stem bark showed repellent efficacy against adult Tribolium castaneum beetles at dose levels of 314.540, 157.270, 78.635, 39.318, 19.659, and 9.831 g/cm² on filter paper (Mondal et al., 2013). A. augusta is also used for stomachaches, diabetes, dermatitis, and as an abortifacient and anti-fertility agent in  powdered  form.

Leaves are beneficial in the treatment of uterine diseases, diabetes, rheumatic joint discomfort, and sinusitis headaches (Prajapati et al., 2003; Rahmatullah et al., 2010). Singh et al. (2001) conducted antifeedant activity tests on a variety of plants to better understand the repellent potential of various medicinal plant extracts (Singh et al., 2001; Ali et al., 2021). Biopesticides activities of A. augusta extracts are due to the presence of taraxerol, gum, beta-sitosterol, resin, fixed oil, bromine, alkaloids, choline and betaine, stigmasterol, and magnesium salts of hydroxyl acids. In the medical field, they are used to make condiments and products that are intended to treat a variety of diseases and health problems. Rice leaf folder and rice green leafhopper infestations were reduced, and rice trungo virus was controlled, using seed oil (1%) produced from several botanicals sprayed on rice plants (Narasimhan and Mariappan, 1988).

The findings suggest that the seed extracts of R. communis, A. augusta, and B. ceiba possess many active ingredients that showed effective activity against brinjal shoot and fruit borer, L. orbonalis Guenee. 

A potential botanical against L. orbonalis can protect the human, other animals and environment from the toxic effect of chemical pesticides. Out of three botanicals, R. communis, seed extract showed the best performance, whereas A. augusta and B. ceiba seed extract was found to be ineffective to protect the brinjal. Further analysis of the chemical structure of the active ingredients of three botanicals would help to control various insect pests from vegetables. The result concluded that R. communis showed comparatively higher effectivity among the three extracts to the control of the fruit and shoot borer in brinjal, L. orbonalis Guenee.

The authors declared no competing interests.

The research work has been supported by Islamic University research fund (Ref.-141/Edu./IU-2021/17) and Islamic University UGC grant research fund (Ref.-141/Edu./IU-2020/634).