Angsumarn Chandrapatya Department of Entomology

Kasetsart University Bangkok, Thailand

Plants produce a high diversity of secondary metabolites for defense and survival in the ecosystem

generally secondary metabolite presents at 1-3% of dry plant weight

Secondary metabolite presents in specialized cells at distinct developmental stages

have highly complex structures

cell culture techniques facilitates large-scale continuous production of secondary metabolites

Secondary metabolites

Secondary plant metabolites, currently exceeding 100,000 identified substances, belong to three major chemical classes:

terpenes (a group of lipids)

phenolics (derived from carbohydrates)

alkaloids (derived from amino acids)

secondary metabolites

A pesticide whose active ingredient is a plant-produced chemical such as nicotine or strychnine.

Also called a plant-derived pesticide.

Being 'natural' pesticides, as distinct from synthetic ones, they are typically acceptable to organic farmers.

Botanical pesticide

Hyperactivity: restlessness, active movement, locomotion Ataxia: uncoordinated movement, stumbling, insect can right itself Prostration: rolling on side or back, cannot right itself (knockdown) Convulsion: lying on side or back, rapid movement of mouthparts and legs, tremor Paralysis: slow or no movement, cannot right itself Death: no movement, does not respond to stimuli

Insecticide Symptomology

EPA Web site for downloading a Log Probit Computer Program for mortality calculations: URL = http://www.epa.gov/ncea/bnchmrk/versions.htm

Log Probit Calculation of Mortality

ABBOTT'S FORMULA

Corrected % Mortality = (% alive control - % alive treated) x 100%

(% alive control)

Toxicity is the capacity to cause injury. It must be present at its site of action at an effective dose. For most accurate comparison of toxicity, topical application or injection is the method of choice because a measured dose is applied to each insect.

median lethal dose or LD50 is the generally accepted standard for defining toxicity expressed as a ratio of toxin to body weight (e.g. mg/kg)

LT50 is the time required to kill 50 % of a population at a given dose or concentration.

When insects are not killed, as with hormone analogs, the effective dose 50 (ED50) and effective concentration 50 (EC50) are used.

Toxicity test

Toxicity is Condition Dependent

Affected by environment and physiology Age

Sex

physiological condition

Diet

Temperature

Humidity

route of administration

length of exposure

species used.

The simplest extraction of secondary metabolites can be achieved by the use of three solvents,

based on increasing polarity to solubilize the sample

Extraction of secondary metabolite

hexane dichloromethane and ethanol

The extracts are then separated on silica gel

(TLC, thin layer chromatography) plates with three solvents of

increasing polarity.

Extraction of secondary metabolite

Prep TLC can be applied for high throughput purification of up to

95% purity of compounds.

This is a 24-hour test to detect the lethality of the extract to shrimp larvae

Brine Shrimp Bioassay (BSB)

One plant species may possess substances with a wide range of activities.

antifeedant antioviposition repellent growth-regulating

Over 2000 species of plants are known to possess some insecticidal activity

Extracts from the neem tree are:

The low toxicity of botanical insecticides makes the processing and application of the product inexpensive.

Thematerials are locally available and affordable.

Botanicals are a promising source of pest control compounds.

Fumigation

Fumigation

(Topical application)

Microapplicator

Microapplicator

(Topical application)

Topical application

Spray tower

Antifeedant (choice test)

Repellent

Attractant

Antifeedant

Growth inhibition

Toxicity & Repellent

A substances which, when tasted by insects, result in either temporarily or permanently, depending on potency, in the cessation of feeding.

antifeedants

Chronic larval growth bioassay

incorporated into artificial diet at different concentrations.

Control diets were prepared with the carrier solvent alone

Two freshly enclosed neonate larvae (

After 10 days, all larvae were individually weighed and mean weights determined.

Mean weights for each treatment group were expressed as a percentage of the controls.

EC50 (effective concentration causing 50% inhibition of larval growth relative to the control)

Chronic larval growth bioassay

Antifeedant choice bioassay

Control leaf discs were painted on each side with the carrier solvent. Test leaf discs were painted with the same amount of the test substance in solution.

One treated and one control disc were placed in each compartment.

One starved larva was introduced gently into the centre of each compartment.

Areas of control and treated leaf discs eaten were measured.

feeding deterrence index (FDI) was calculated using the formula FDI = (C-T/ C+T) x 100

where, C and T are the control and treated leaf areas consumed by the insect DC50 values (concentration causing 50% feeding deterrence compared with the control) were calculated by using regression from the line of best fit.

Antifeedant choice bioassay

toxicity

growth retardation

feeding inhibition

oviposition deterrent

suppression of calling behaviors

reduction of fecundity and fertility

Effect of secondary metabolite on insect

Rapid degradation -- less persistence in environment and reduced risks to non-target organisms. Rapid action -- act very quickly to stop feeding by pest insects. They may not cause death for hours or days, but they often cause immediate paralysis or cessation of feeding. Low mammalian toxicity -- most botanicals have low to moderate mammalian toxicity. Selectivity -- more selective for plant-feeding pest insects and less harmful to beneficial insects. Low toxicity to plants -- most botanicals are not phytotoxic.

Advantages

Rapid degradation -- creates a need for more precise timing or more frequent applications. Toxicity -- all toxins used in pest control pose some hazard to the user and to the environment. Cost and availability -- botanicals tend to be more expensive than synthetics, and some are not as widely available. Lack of test data -- data on effectiveness and long-term (chronic) toxicity are unavailable for some botanicals, and tolerances for some have not been established.

Disadvantages

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