Biopesticidal efficacy of Devil’s tree (Alstonia scholaris) on Wheat Weevil (Sitophilus granarius)

V. L. Pawara¹, Y. H. Wasu², S. S. Bhande²

¹Department of Zoology, VVM s S. G. Patil Arts, Science and Commerce College Sakri-424304, India

   ²Department of Zoology, PSGVP Mandals SIP Arts, GBP Science and STKV Sangh Commerce College Shahada-425409, India

Corresponding Author E-mail- bhande.satish@gmail.com

ABSTRACT

            This study highlights the significant biopesticidal potential of Alstonia scholaris against Sitophilus granarius, a major pest of stored wheat. The findings suggest that both crushed fresh leaves and bark of A. scholaris can effectively control pest populations, with mortality rates of 75.66% and 70.66% respectively within 96 hours. The dose and duration-dependent effects indicate the potential for A. scholaris-based bioinsecticides as an eco-friendly alternative to chemical pesticides in grain storage management. Further research on formulation and field application could enhance its practical use in pest control.

KEYWORDS: Alstonia scholaris, Biopesticide, Bioinsecticides, Sitophilus granarius, Stored grain.

INTRODUCTION

            Stored grains are highly susceptible to damage from insect pests, with Sitophilus granarius, commonly known as the wheat weevil, being one of the most destructive pests. This weevil, a member of the family Curculionidae and the order Coleoptera, feeds on a variety of grains, including wheat, corn, rice and many cereals (Padín et. al., 2002; USDA, 2016; Vijay and Bhuvaneswari, 2018; Charles Kasozi et. al., 2018). Its impact on stored grains results in significant economic losses, highlighting the need for effective pest control methods. In general, stored products of agricultural and animal origin are attacked by more than 600 species of Coleopterans, 70 species of Lepidopterans and about 355 species of mites (Tyagi et. al., 2019). Among various storage insect pests Angoumois grain moth (Sitotroga cerealella), maize/ rice weevil (Sitophilus oryzae), lesser grain borer (Rhyzopertha dominica), khapra beetle (Trogoderma granarium), rust-red flour beetle (Tribolium castaneum), legume weevil (Callosobruchus sp.) etc. are most detrimental (Gc, 2006). They are causing both quantitative and qualitative losses (Rajendran and Sriranjini 2008).

            While various pest control methods exist, biopesticides offer a promising alternative due to their environmentally friendly nature. Biopesticides are derived from naturally occurring substances such as living organisms (natural enemies), microbial products, phytochemicals, or their by-products (semiochemicals), which can control pests through nontoxic mechanisms (Salma and Jogen, 2011). One of the key advantages of biopesticides is their minimal impact on the environment, human health, and the quality of stored grains.

            Numerous plant-derived biopesticides, often botanicals, have shown potential in controlling agricultural and stored grain pests. Plants with medicinal properties, such as neem (Azadirachta indica), bach (Acorus calamus), phoolakri (Lantana camara), draik (Melia azadarach), kali mirch (Piper nigrum), and basuti (Adhatoda zeylanica), have been reported to exhibit effective biopesticidal effects. These plants not only help control insect pests without harming the grains or seeds but also contribute to the ecosystem’s overall health (Lal, et. al., 2017). Incorporating plants with biopesticidal properties into Integrated Pest Management (IPM) strategies could be an effective approach to managing stored grain pests. By combining the use of biopesticides with other pest control methods, the reliance on chemical pesticides can be reduced, leading to sustainable and eco-friendly pest management practices.

            In this study, the biopesticidal effects of Alstonia scholaris (Devil’s Tree) on Sitophilus granarius are explored. Alstonia scholaris, a member of the Apocynaceae family, is widely distributed across the dried forests of India, particularly in the Western Himalayas, Western Ghats, and the Southern region (Naik, 1998). Known for its rich array of active compounds, A. scholaris has been utilized in traditional medicine to treat various ailments. The plant’s phytochemical constituents comprise nearly 400 compounds, contributing to its medicinal versatility. It is commonly used as an anti-irritation agent (Goyal and Shinde, 2019; Sharma, et. al., 2016).

                The organic extracts and essential oils of A. scholaris showed strong antioxidant and cytotoxic properties (Siddiqui, et. al., 2015). Larvicidal activity of Alstonia scholaris leaf extract in different solvents against Ae. Albopictus showed 35% mortality in hexane extract at the highest concentration (Yadav, et. al., 2013). Alstonia scholaris leaves column fractions proved to be highly toxic against stored product pests, Rhyzopertha dominica, and mosquito larvae (Kallur and Patil, 2019). The effect of polar and non-polar extract of leaves and stem barks of Alstonia scholaris (L.) R.Br. (Apocynaceae) was evaluated for its repellent activity against T. castaneum. The repellence increased with increasing concentration of the extracts (Pawar, et. al., 2013).

            In this present study, both the leaves and bark of Alstonia scholaris were tested for their biopesticidal effects on Sitophilus granarius, a pest that significantly affects wheat grains.

MATERIALS AND METHOD

• Preparation of leaves and bark tablet
• Collection: Fresh leaves and bark of Alstonia scholaris were collected from the plant.
• Cleaning: The leaves and bark were washed thoroughly under tap water to remove any dirt or impurities.
• Tablet Formation:

      An electronic mixer grinds the washed leaves and bark into a fine consistency. Tablets were made by mixing crushed leaves and bark with wheat flour. First, wheat flour was taken, and its pulp was soaked. Then, freshly crushed leaves and bark were measured in given quantities, mixed with wheat flour, and made into tablets or pellets by hand.

•  Dose Regimens:

        The tablets were prepared in three different dosages: 0.5 gm, 1 gm, and 1.5 gm of crushed fresh leaves and bark.    

        Fig- Alstonia scholaris– Leaves                     Fig- Alstonia scholaris– Bark

      Fig- Crushed fresh leaves and bark                  Fig- Leaves and Bark Tablets

 

Experimental Setup:

Insect Collection and Identification:

• Sitophilus granarius pests were collected from local grocery shops.
• The pests were identified using the Grains Research and Development Corporation (GRDC) user guide.

Fig- Sitophilus granarius- Identify a given insect under the compound microscope.

•  Rearing Conditions:
• The pests were reared in a plastic box with muslin cloth tightly secured with rubber to allow aeration.
• Laboratory conditions were maintained at a room temperature of 27 ± 2°C, with a 14:10 hours light: dark photoperiod.
• Relative humidity was maintained at 65 ± 5%.
• Experimental Groups: The pests were divided into four groups, each containing 100 insects and 100 gm of wheat grains:

Group I: Exposed to tablets containing 0.5 gm of crushed Alstonia scholaris leaves and bark.

Group II: Exposed to tablets containing 1 gm of crushed Alstonia scholaris leaves and bark.

Group III: Exposed to tablets containing 1.5 gm of crushed Alstonia scholaris leaves and bark.

Group IV (Control): Exposed to wheat flour (vehicle control).

• Exposure Duration:

           The exposure was carried out for four different time intervals: 24, 48, 72, and 96 hours.

Experiment No. 1 – Effect of Crushed Fresh Leaves Tablet on Sitophilus granarius Mortality                                   Over Different Exposure Durations 24, 48, 72, and 96 Hours

Experiment No.2 – Effect of Crushed Fresh Bark Tablet on Sitophilus granarius Mortality               Over Different Exposure Durations: 24, 48, 72, and 96 Hours

Mortality Calculation:

            The mean percent mortality was calculated using Abbott’s formula, which is commonly used to adjust for control mortality in bioassays.

• Purpose of Study:

            The purpose of this study seems to be to evaluate the insecticidal or repellent effects of Alstonia scholaris crushed fresh leaves and bark tablets on Sitophilus granarius, a common pest of stored grains and to observe its efficacy at different concentrations (0.5 gm, 1 gm, and 1.5 gm) over time (24, 48, 72, and 96 hours).

RESULT AND DISCUSSION:

            The present study was undertaken to test the biopesticidal effect of crushed leaves and bark of Alstonia scholaris on Sitophilus granarius. Further research on formulation and field application could enhance its practical use in pest control.

            When exposed to crushed fresh leaves in tablet form, Experiment No. 1 shows that the mortality rate increases with the concentration of the crushed fresh leaves, with Group III showing the highest mortality, 75.66%, at 96 hours, compared to the control group, which showed 0% mortality.

Mortality of Sitophilus granarius at 96 Hours of Exposure to Crushed Fresh Leaves Tablets

• Group I: 52.33% mortality
• Group II: 61.66% mortality
• Group III: 75.66% mortality
• Control Group: 0% mortality

This indicates the highest percent mortality of Sitophilus granarius in all three treatment groups at 96 hrs compared to the control group. This data shows a clear trend where increasing the concentration of crushed fresh leaves in tablet form leads to a higher mortality rate of Sitophilus granarius. (Table 1., Graph 1).  Similarly, effects were recorded previously using leaves of Alstonia scholaris against Sitophilus oryzae (Pawara, et, al., 2024) and also effects of leaves from different plants such as Lantana camara (Verbenaceae) (Ogendo, et. al., 2003; Dua, et. al., 2010), Azadiracta indica (Bina, et. al., 2004), Annona squamosa (L.), Moringa oleifera (Lam.), Eucalyptus globulus (Labill.) and datura (Nenaah, et. al., 2011) against a serious pest such as Tribolium castaneum, Trogoderma granarium and Rhyzopertha dominica, Trogoderma granarium and Sitophilus oryzae.

            When exposed to crushed fresh bark in tablet form, Experiment No.2 shows that the mortality rate of Sitophilus granarius increases with the concentration of bark tablet. Group III, with the highest concentration, resulted in 70.66% mortality after 96 hours, compared to 0% in the control group.

 Mortality of Sitophilus granarius at 96 Hours of Exposure to Bark Tablets

• Group I: 48.33% mortality
• Group II: 55.33% mortality
• Group III: 70.66% mortality
• Control Group: 0% mortality

            This is observed that the percent mortality increased with the increase in the concentration of crushed fresh bark in the tablet (Table 2, Graph 2). A similar result bark of Moringa oleifera was reported to be effective against T. castaneum and Scirpophaga incertulus (Ajayi 2007, Deka et al 2006). Hence, crushed fresh bark has been reported to be effective against Sitophilus oryzae (Pawara, et. al., 2024). Thus, it is clear that the biopesticidal effect of crushed leaves as well as bark tablets was increased with the period of drug exposure and also with the concentration of the drug.

Table 1: Biopesticidal effect of leaves tablet of Alstonia scholaris on Sitophilus granarius.

Group	Treatment (gm/100 gm grains)	*Mean % mortality
		24 hrs.	48 hrs.	72 hrs.	96 hrs.
I	0.5	25.33	31.33	38.33	52.33
II	1	29.66	41.66	49.66	61.66
III	1.5	40.66	51.33	57.33	75.66
IV (Control)	Tablet of wheat flour	00.00	00.00	00.00	00.00

Graph 1: Graph for Determination of the biopesticidal effect of leaves tablet of Alstonia scholaris on Sitophilus granarius.

Table 2: Biopesticidal effect of bark tablet of Alstonia scholaris on Sitophilus granarius.

Group	Treatment (gm/100 gm grains)	*Mean % mortality
		24 hrs.	48 hrs.	72 hrs.	96 hrs.
I	0.5	21.33	28.33	37.33	48.33
II	1	27.33	33.33	49.66	55.33
III	1.5	33.66	52.66	61.66	70.66
IV (Control)	Tablet of wheat flour	00.00	00.00	00.00	00.00

Graph 2: Graph for Determination of the biopesticidal effect of bark tablet of Alstonia scholaris          on Sitophilus granarius.

CONCLUSION

            The crushed fresh leaves and bark tablets of Alstonia scholaris exhibit a significant biopesticidal effect against the stored grain pest Sitophilus granarius. at 96 hours, the crushed fresh leaves tablets resulted in 75.66% pest mortality, while the crushed fresh bark tablets showed 70.66% mortality. This study suggests that the biopesticidal effect is dose and duration-dependent. The formulation will be further explored for its potential as an effective natural pesticide against stored product pests.   

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