Introduction

Medicinal plants have emerged as some of the most widely studied plants and significant interest has been shown in their chemistry because of their potential application in medicine [₁,₂,₃]. Many of these medicinal plants contain chemical constituents that could cause harmful effects to human if taken in large quantities. Alkaloids occurring in a large amount make these plants poisonous [₄]. Large quantity of oxalic acid, a proto plasmic poison in the form of oxalates of calcium, sodium and potassium also produces poisoning [₅,₆,₇].

Some of these plants are poisonous to insects and pests [₈,₉,₁₀]. There is a necessity to find cheap insecticides for the diverse needs of agriculture, destruction of house holds pests and prevention of vectors of diseases such as malaria in developing countries such as Sri Lanka and India. Plant based insecticides [₁₁,₁₂] are preferred to chemical insecticide as they have little or no negative effect on the agricultural environment [₁₃]. At present, there is not much knowledge of these plant based insecticides in the literature. The evidence suggests that plants containing a high percentage of rotenone [₁₄], powdered young leaves and twigs of Javanica (Blume) and nepalenis (Benn) are used to kill mosquito Larvae [₁₅].

In a quest to identify a plant based insecticide in this study we investigate the toxic effects of Datura alba, an indigenous medical plant used in ancient Indian medical system. Datura alba, which is under the family of solanaceae, is one of the most useful medicinal plant used in treating asthma, muscle spasm, whooping cough, skin ulcers etc [₁₆]. This plant grows in warmer parts of the world particularly in South and Southeast Asia including India and Sri Lanka. This annual herb is bushy, smooth, fetid, 0.5 to 1.2 m in height also attaining 6 feet or more in rich soils. The leaves are 18 cm long and the flowers are white in colour (Figure 1). Various parts of the plant (leaves, seeds, roots and fruits) are used for different purposes in medicine [₁₇].

Figure 1

Figure 1:

The aim of this study was to determine the inorganic contents quantitatively and organic contents qualitatively in the leaves of Datura alba and test its toxic activity in common agricultural insects such as aphids and black ants.

Materials and methods

Inorganic analysis

Qualitative organic analysis

Extraction

Preparation of different concentrations

Toxicity of Datura alba on Aphids

Toxicity of Datura alba on Ants

Statistical Analysis

Results

Inorganic analysis

The moisture content of Datura alba was 86.23 ± 0.15. The carbon content as a measure of ash was 8.73 ± 0.30. The mean organic matter was 10.06 ± 0.11. (Table 1)

Figure 2

Table 1: Quantitative measure of moisture, ash and organic matter of

Calcium, magnesium, ferric and phosphate contents were (3.17 ± 0.02) × 10 ⁴ , (3.37 ± 0.01) × 10 ⁴ , (1.38 ± 0.004) × 10 ⁴ and (4.20 ± 0.03) × 10 ⁴ ppm respectively (Table 2).

Figure 3

Table 2: Quantitative measure of inorganic cations and anions.

Qualitative organic analysis

In the chloroform extract, five organic constituents were tested for out of which only two were present (Table 3). Analysis of alkaloids and steroids was positive.

Key: - Absence; + Presence.

Figure 4

Table 3: Organic constituents of

Toxicity of Datura alba on Ants and Aphids

There was a significant dose dependent effect of Datura alba on the number of living Ants (P<0.001) and Aphids (P<0.01) (figure 2). This indicates that high doses of leaf extracts are toxic.

Figure 5

Figure 2: Scatter plot of dose dependent effect of on the number of live (a) ants or (b) aphids in the experimental chamber. ANOVA ; *=P

The results showed the Effective Concentration 50% survival rate (EC₅₀) was 12000 ppm for aphids and 11600 ppm for ants.

Discussion

Datura alba is a commonly used medicinal plant for inflammatory diseases such as asthma, rheumatism, muscle spasm and whooping cough and also used in wound healing as a disinfectant [₁₆] among indigenous doctors in the Indian subcontinent. In the northern part of Sri Lanka, local farmers found that aphids feed young leaves of beans. Also, various size ants were found in valuable vegetable plants (ladies finger, aubergine) before they were ready for harvest damaging its stem that attached to the vegetable. In addition, at homes ants feed on variety of substances including sweets, starch and fats. Commonly available chemical insecticides are inorganic substances that are toxic to human and could dissolve in water and pollute the environment. Since water is often obtained from underground wells in these parts of the world, farmers are greatly interested in natural insecticides as they are organic compounds that cannot dissolve completely in water and hence pollute the environment to a lesser degree. These are also easily available and cheap. People are reluctant to use chemical insecticides at home as they can be toxic to the human body. In this regard, Datura alba was suggested to be an ideal candidate by the local farmers that lead to this project.

In this study for the first time, we have isolated and confirmed the presence of chemical constituents in the leaf of this plant and tested its toxicity on aphids and ants. Inorganic cations, anions, moisture, ash and organic matter were also determined quantitatively. The concentration of Ca ²⁺ , Mg ²⁺ , Fe ³⁺ and PO₄ ^3? were found to be (3.17 ± 0.02) × 10 ⁴ , (3.37 ± 0.01) × 10 ⁴ , (1.38 ± 0.004) × 10 ⁴ and (4.20 ± 0.03) × 10 ⁴ ppm respectively. The Initial screening test in this study confirmed the presence of alkaloids in the leaf extracts. Alkaloids in excessive amount could be poisonous. Hence we investigated the toxicity of this plant on aphids and ants. Experiments suggest a statistically significant dose dependent decrease in the survival rate and an increase in the percentage mortality of ants and aphids in the presence of Datura alba. These experiments suggest that extract of Datura alba at suitable concentration could potentially be useful to local farmers.

Acknowledgement