Unit 4: Extractions of biorationals - Subjective Questions

Botanical extracts are preparations obtained by extracting biologically active compounds from plants using water, organic solvents, oils, steam, or other suitable extraction methods.

Biorational biopesticides are pest-management products derived from natural or biologically based materials that are relatively selective, biodegradable, and less harmful to humans, beneficial organisms, and the environment than conventional broad-spectrum pesticides.

Importance in insect pest management:

• They may act as toxicants, repellents, antifeedants, oviposition deterrents, growth regulators, or sterilants.
• They generally leave fewer persistent residues on crops and in soil.
• Their multiple modes of action can help delay insecticide resistance.
• Many botanicals can be prepared from locally available plant materials.
• They are compatible with biological control and integrated pest management when used appropriately.

Examples include neem seed kernel extract, neem oil formulations, pyrethrum, essential oils, and plant-derived alkaloid or terpenoid preparations.

Plant materials should be selected using the following criteria:

• Documented bioactivity: Ethnobotanical knowledge or scientific reports should indicate insecticidal, repellent, antifeedant, or growth-regulating activity.
• Correct botanical identity: The plant must be taxonomically authenticated because related species may differ in chemical composition.
• Active plant part: Leaves, seeds, bark, roots, flowers, fruits, or essential oils should be chosen according to the location of active compounds.
• Growth stage and collection season: Concentrations of secondary metabolites vary with plant age, season, and environmental conditions.
• Availability and sustainability: Materials should be abundant, renewable, and collected without threatening natural populations.
• Safety: Plants with extreme mammalian toxicity or unacceptable effects on non-target organisms should be avoided.
• Stability and extractability: Active compounds should be sufficiently stable and recoverable using practical solvents or extraction methods.
• Economic feasibility: Collection, processing, extraction, and formulation costs should be reasonable.

Representative samples should be cleaned, labelled with collection details, and processed under standardized conditions.

Preprocessing improves extraction efficiency and reproducibility. The major steps are:

1. Collection and authentication: Collect the required plant part and confirm its botanical identity using a taxonomist or authenticated specimen.
2. Cleaning: Remove soil, insects, diseased portions, and foreign matter. Washing should be brief when water-soluble compounds are of interest.
3. Size reduction before drying: Thick plant parts may be sliced to promote uniform drying.
4. Drying: Shade drying or controlled oven drying at a suitable low temperature is preferred for heat-sensitive compounds. Direct sunlight may degrade volatile or light-sensitive constituents.
5. Grinding: Grind the dried material into a uniform powder to increase the surface area available for solvent penetration.
6. Sieving: Use a suitable sieve to obtain consistent particle size.
7. Moisture control: Excess moisture encourages microbial growth and affects extract yield.
8. Storage: Store powdered material in clean, airtight, labelled, light-resistant containers under cool and dry conditions.

Labels should include the plant name, plant part, collection place, date, drying method, and batch number.

A general procedure for preparing an aqueous botanical extract is as follows:

1. Collect, authenticate, clean, and shade-dry the selected plant material.
2. Grind the dried material into a uniform powder.
3. Weigh a known quantity of powder. For a nominal weight-per-volume preparation, use g of powder and make the final volume up to mL with water.
4. Mix the powder with distilled water and soak it for approximately 12–24 hours with occasional stirring.
5. Homogenize or shake the mixture to improve extraction.
6. Filter first through muslin cloth and then through filter paper to remove coarse particles.
7. Add a small amount of a suitable surfactant only when necessary, using the same surfactant concentration in the control.
8. Adjust the filtrate to the required final volume and prepare lower concentrations by dilution.
9. Use the fresh extract promptly because aqueous preparations are often prone to microbial contamination and chemical degradation.

The extract should be protected from heat and light, and its preparation date, concentration, plant-to-water ratio, and extraction time must be recorded.

In solvent extraction, powdered plant material is brought into contact with a solvent capable of dissolving the desired bioactive constituents.

General procedure:

• Dry and grind the authenticated plant material.
• Mix it with a measured volume of solvent by maceration, percolation, or Soxhlet extraction.
• Maintain contact for a standardized period with agitation where appropriate.
• Filter the extract and repeat extraction if necessary.
• Combine the filtrates and remove the solvent under reduced pressure using a rotary evaporator.
• Dry the crude extract to constant mass, calculate its yield, and store it in an airtight amber container at a suitable low temperature.

Influence of solvent polarity:

• Water and methanol extract highly polar substances such as many glycosides, tannins, and phenolic compounds.
• Ethanol extracts a broad range of polar and moderately non-polar compounds and is often preferred for safer formulations.
• Ethyl acetate is suitable for compounds of intermediate polarity.
• Hexane or petroleum ether extracts non-polar substances such as oils, waxes, and some terpenoids.

Solvent selection affects extraction yield, chemical profile, toxicity, cost, and formulation compatibility. Solvent residues must be removed adequately, and appropriate safety precautions should be followed.

Selection of a method depends on the volatility, polarity, and thermal stability of the active compounds, as well as the required purity, available equipment, cost, and intended formulation. Maceration is useful for simple laboratory screening, Soxhlet extraction for exhaustive recovery, and steam distillation for essential-oil-based biopesticides.

Extraction efficiency and biological activity are influenced by several interacting factors:

• Plant species and chemotype: Different genetic types may contain different concentrations of active constituents.
• Plant part and maturity: Seeds, leaves, bark, roots, and flowers differ in metabolite composition.
• Season and location: Temperature, rainfall, soil, and collection season influence secondary metabolites.
• Drying conditions: Excessive heat, sunlight, or prolonged drying can destroy volatile or thermolabile compounds.
• Particle size: Fine particles increase surface area, although excessively fine powder may complicate filtration.
• Solvent polarity: Maximum recovery occurs when the solvent has suitable affinity for the target compounds.
• Plant-to-solvent ratio: Insufficient solvent can reduce mass transfer and extraction yield.
• Extraction time and temperature: Longer time and moderate heating may improve recovery, but excessive conditions can cause degradation.
• Agitation: Stirring, shaking, or sonication improves solvent penetration and diffusion.
• pH and oxygen exposure: Some compounds are sensitive to hydrolysis or oxidation.
• Storage: Light, heat, moisture, and air may reduce the activity of crude extracts.

Therefore, all extraction parameters should be standardized to permit meaningful comparison between treatments and batches.

Extraction yield is calculated from the mass of dry crude extract recovered from a known mass of plant powder:

where is the mass of dried extract and is the mass of dry plant powder.

For example, if g of dry extract is recovered from g of powder:

A weight-per-volume concentration may be calculated as:

Thus, g of extract made up to mL gives a w/v solution.

Dilutions from a stock solution are prepared using:

where and are the stock concentration and required stock volume, while and are the desired concentration and final volume. The same solvent and adjuvant levels should be maintained in the corresponding control.

Phytochemical screening provides preliminary evidence for groups of constituents such as alkaloids, flavonoids, terpenoids, phenolics, saponins, tannins, and glycosides. These groups may contribute to toxicity, repellency, feeding deterrence, or growth disruption.

Chemical profiling may be performed using thin-layer chromatography, high-performance liquid chromatography, gas chromatography, or mass spectrometry. It helps to:

• Identify major active or marker compounds.
• Compare extracts prepared with different solvents.
• Detect degradation or adulteration.
• Relate chemical composition to insecticidal activity.

Standardization ensures that different batches possess reasonably consistent quality and efficacy. Common standardization parameters include:

• Botanical identity and plant part.
• Moisture and foreign-matter content.
• Extraction method and solvent ratio.
• Extractive yield.
• Concentration of a marker or active compound.
• Chromatographic fingerprint.
• Microbial contamination and residual solvent limits.
• Biological potency against a standard test insect.

Because natural products vary with location, season, and processing, standardization is essential for reproducible research and reliable commercial formulations.

A contact-toxicity bioassay can be designed as follows:

1. Test insects: Use healthy insects of the same species, stage, age, and approximate size, preferably from a standardized laboratory culture.
2. Treatments: Prepare a series of at least five concentrations of the botanical extract. Include an untreated control, a solvent or formulation control, and a positive control using a registered insecticide where appropriate.
3. Application: Apply a fixed volume directly to a defined body region using a microapplicator, or expose insects to uniformly treated surfaces. The dose must be consistent among insects.
4. Experimental design: Use randomized treatments with adequate replication and an equal number of insects per replicate.
5. Environmental conditions: Maintain constant temperature, relative humidity, photoperiod, and food supply.
6. Observations: Record knockdown, abnormal behavior, and mortality at predetermined intervals such as 24, 48, and 72 hours. Define death objectively, for example as failure to respond to gentle stimulation.
7. Analysis: Correct treatment mortality when necessary, construct a dose-response relationship, and estimate lethal concentrations or doses with confidence limits.

Any solvent or surfactant used in the treatment must occur at the same level in the control so that observed mortality can be attributed to the botanical extract.

Control insects may die because of handling, age, environmental stress, starvation, or solvent exposure. If raw treatment mortality is used without correction, the insecticidal activity of the test product may be overestimated.

Abbott's formula is:

where is the observed percentage mortality in the treatment and is the percentage mortality in the control.

If treatment mortality is and control mortality is :

Interpretation and precautions:

• The corrected mortality attributed to the treatment is approximately .
• If control mortality is negligible, correction may not materially change the result.
• Excessive control mortality indicates poor experimental conditions, and the bioassay should normally be repeated according to the accepted protocol.
• Abbott's correction does not replace good experimental design, adequate replication, or statistical analysis.

A dose-response analysis relates the concentration or dose of a botanical insecticide to the proportion of insects responding or dying.

• : Concentration expected to kill of the test population under specified conditions.
• : Concentration expected to kill of the population. It is often more relevant to practical control but is estimated with greater uncertainty.
• : Time required to kill of exposed insects at a stated concentration.
• Slope: Describes how rapidly mortality changes with concentration. A steep slope indicates relatively uniform susceptibility, whereas a shallow slope suggests heterogeneous susceptibility or variable exposure.
• Confidence limits: Indicate the precision of the estimated lethal concentration or time. Narrow limits represent greater precision.

Mortality data are commonly analyzed using probit or logit regression after suitable control correction. At least several concentrations spanning low to high mortality should be tested. Comparisons between extracts should consider confidence intervals, slopes, exposure methods, insect stages, and observation periods rather than relying only on raw mortality at one concentration.

Repellency: A choice arena is divided into treated and untreated zones. Insects released at the center are counted in each zone after fixed periods. Repellency may be expressed as:

where and are the numbers in control and treated zones.

Antifeedant activity: In a leaf-disc choice or no-choice test, treated and control leaf discs are offered to insects. The consumed area or mass is measured. A choice-test feeding deterrence index can be calculated as:

where and represent consumption of control and treated food.

Oviposition deterrence: Adult females are offered treated and untreated substrates. Eggs laid on each are counted. A suitable deterrence index is calculated from the difference in egg numbers.

All assays require equal-sized substrates, randomized positions, adequate replication, solvent controls, standardized insect age, and fixed observation periods. Reduced feeding or egg laying should not automatically be interpreted as repellency because toxicity, immobility, or substrate damage may produce similar results.

A biorational biopesticide formulation is a prepared mixture in which a biologically active natural substance is combined with suitable inert ingredients to improve its storage, handling, application, stability, and pest-control performance.

Major components and their functions:

• Active ingredient: Produces toxicity, repellency, antifeedancy, growth regulation, or another biological effect.
• Carrier or diluent: Provides bulk and supports uniform distribution; examples include water, vegetable oil, clay, and starch.
• Solvent: Dissolves the active ingredient and facilitates preparation or application.
• Surfactant: Reduces surface tension and improves spreading and wetting.
• Emulsifier: Enables oil and water phases to form a stable emulsion.
• Dispersant: Prevents particles from aggregating in suspension.
• Sticker: Improves retention of the product on plant surfaces.
• Stabilizer or antioxidant: Protects the active ingredient from oxidation, heat, or chemical degradation.
• Ultraviolet protectant: Reduces decomposition caused by sunlight.
• Preservative: Suppresses microbial contamination, especially in water-based products.

All formulation ingredients should be compatible, effective at low levels, safe to crops, and acceptable for the intended use.

The best formulation depends on the physicochemical properties of the active ingredient, target pest, application equipment, crop, safety, and required persistence.

Preparation:

1. Determine the solubility and stability of the botanical active ingredient in candidate oils or permitted solvents.
2. Dissolve the measured active ingredient in the selected solvent or oil phase.
3. Add a compatible emulsifier or emulsifier blend at an optimized concentration.
4. Incorporate antioxidants, ultraviolet protectants, or other stabilizers if required.
5. Mix until a homogeneous concentrate is obtained.
6. Pack the formulation in clean, compatible, light-resistant containers.

Evaluation:

• Active ingredient content: Confirms the intended concentration.
• Emulsion stability: The diluted product should form a uniform emulsion without rapid oil separation, creaming, or excessive sediment.
• Dilution behavior: Test the formulation in waters of different hardness where relevant.
• pH, viscosity, and density: These affect stability, pouring, and spray application.
• Storage stability: Measure physical appearance, active content, and bioactivity after storage under specified conditions.
• Phytotoxicity: Apply the formulation to the crop at the recommended and higher test rates.
• Bioefficacy: Compare insect mortality or other biological responses with those caused by the unformulated extract, formulation blank, untreated control, and reference product.

The blank formulation must contain all ingredients except the active botanical material.

A wettable powder is a finely divided solid formulation intended to be dispersed in water before spraying.

Preparation steps:

• Dry the botanical extract or adsorb an oily extract onto a suitable porous carrier.
• Select an inert carrier such as clay, silica, starch, or another compatible material.
• Add a wetting agent to allow rapid contact with water.
• Add a dispersing agent to prevent particle aggregation.
• Incorporate stabilizers or ultraviolet protectants if needed.
• Blend the ingredients uniformly and mill the mixture to the required particle size.
• Sieve and package it in moisture-resistant containers.

Quality parameters:

• Active ingredient content and blend uniformity.
• Moisture content and freedom from caking.
• Particle size distribution.
• Wettability or wetting time.
• Suspensibility after dilution.
• Persistent foam and sediment formation.
• Storage stability and retention of biological activity.
• Compatibility with spray equipment and absence of nozzle blockage.

A good wettable powder should wet rapidly, remain uniformly suspended with normal agitation, produce minimal hard sediment, and retain insecticidal efficacy during storage.

Microencapsulation encloses an active botanical substance within a protective wall or matrix of natural or synthetic material. Nanoformulation uses particles, droplets, capsules, or carriers with dimensions in the nanoscale range to improve delivery.

Potential advantages:

• Protection of volatile or light-sensitive compounds from evaporation, oxidation, and ultraviolet degradation.
• Improved dispersion of poorly water-soluble active ingredients.
• Controlled or sustained release of the active compound.
• Better adhesion and coverage on plant or insect surfaces.
• Reduced frequency of application and possible reduction in the quantity of active ingredient required.
• Masking of strong odor and improvement of storage stability.

Evaluation requirements:

• Particle size, size distribution, and surface charge.
• Encapsulation efficiency and active ingredient content.
• Release rate under relevant environmental conditions.
• Physical stability, aggregation, and sedimentation.
• Bioefficacy against the target pest.
• Phytotoxicity and effects on natural enemies, pollinators, aquatic organisms, and soil biota.

These technologies are not automatically safer because of their small particle size. Exposure, persistence, carrier toxicity, environmental fate, production cost, and regulatory requirements must be assessed before field use.

Physical quality tests:

• Appearance, color, odor, homogeneity, and absence of phase separation.
• pH, density, viscosity, particle size, wettability, suspensibility, or emulsion stability as applicable.
• Pourability, sedimentation, caking, persistent foam, and compatibility with packaging.

Chemical quality tests:

• Identity and concentration of the active ingredient or marker compound.
• Chromatographic fingerprint and impurity profile.
• Moisture content, oxidation products, and residual solvents.
• Stability of the active ingredient under normal and accelerated storage conditions.

Biological quality tests:

• Potency against a standard susceptible insect population.
• Dose-response consistency between production batches.
• Phytotoxicity to the intended crop.
• Effects on selected non-target organisms.
• Microbial contamination where water or natural carriers are present.

Storage evaluation:
Samples are tested initially and after storage for changes in active content, appearance, physical properties, and bioefficacy. A formulation is acceptable only if it remains safe, physically usable, chemically stable, and biologically effective within defined specifications.

A field experiment may be organized using a randomized complete block design.

Experimental plan:

1. Select a field with a reasonably uniform crop and natural or standardized pest infestation.
2. Include several formulation rates, an untreated control, a formulation blank when practical, and a registered reference insecticide.
3. Arrange treatments randomly within each block and use at least three or four replications.
4. Maintain adequate plot size, guard rows, and buffer zones to reduce spray drift.
5. Apply all treatments with calibrated equipment using a uniform spray volume and application method.
6. Record pest density or crop damage before treatment and at fixed intervals after treatment.
7. Record natural-enemy abundance, phytotoxicity, weather conditions, and crop yield.

When pretreatment counts differ, population reduction may be calculated with the Henderson–Tilton equation:

where and are treatment counts after and before application, while and are control counts after and before application.

Data should be analyzed using an appropriate analysis of variance or generalized model. Treatment means, variability, economic return, and practical crop protection should all be considered.