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The presence of so-called secondary compounds, which have no known function in photosynthesis, growth or other aspects of plant physiology, give plant materials or their extracts their anti-insect activity. Secondary compounds include alkaloids, terpenoids, phenolics, flavonoids, chromenes and other minor chemicals. They can affect insects in several different ways: they may disrupt major metabolic pathways and cause rapid death, act as attractants, deterrents, phagostimulants, antifeedants or modify oviposition. They may retard or accelerate development or interfere with the life cycle of the insect in other ways (Bell , et al. 1990).

Table 1 lists the secondary metabolites most commonly found in the plant species examined. It is noteworthy that many compounds are common to the plant species tested. Plants, which provide large or economic yields of these key chemicals, may offer the best scope for using as botanicals in the future. Details of the mammalian toxicology of these compounds are listed in Table 2.

Table 1: List of commonly found secondary metabolites.

Nitrogen-containing compounds
Acetic Allicin Caffeine
Hydrocyanic acid Azadirachtin Hydrogen cyanide
Iso-butyric acid Butyric Methyl isothiocyanate
Malic acid Caprylic Nicotine
Oxalic acid Formic Sanguinarine
Succinic acid Iso-valeric a -Tomatine
Salicylic acid Methyl salicylate
Sebacic acid Pyrethrins I/II


Valeric Pyrogallol




Acetaldehyde Rutin


Citral Ergosterol


Fatty acids


Benzyl alcohol Ricinoleic acid Ascaridole
Carvacrol Saturated fatty acids Azadirachtin
1,8 –Cineol Capric acid 1-Borneol
Citronellol Lauric acid Camphor
Eugenol Myristic acid Carene
Geraniol Palmitic acid Carvone
Gossypol Stearic acid 1,8-Cineol
Linalool Unsaturated fatty acids Cinnameldehyde
Menthol Linoleic acid Citral
Pentanol Oleic acid Citronellol
Pyrogallol Cumene




Oleandrin Eugenol
Anabasine Solamine Geraniol
Capsaicin Limonene


Methyl anthranilate Camphene Menthol
Methyl salicylate Limonene b -Ohellandrene
Nicotine a -Pinene a -Pinene
Nornicotine Pulegone


Ryania Coumarin Terpinen-4-ol
Vinblastine Thujone

Sources: Southon and Buckingham, 1988; Glasby, 1982; Norris, 1990; Rauffauf, 1970.

Table 2: Toxicity data for some chemical components of different plant genera
(list of abbreviations given at end of table).

Chemical Toxicity Plant genera
Acetaldehyde oral rat LD50 1930 mg Carum, Cinnamomum, Citrus, Lycopersicon,
Mentha, Nicotiana, Pimpinella, Rosmarinus
Acetic acid oral hmn TDLo 1470 mg
oral rat LD50 3310 mg
Widespread, including Gossypium
Acetone oral rbt LD50 5300 mg Coriandrum, Lycopersicon, Pogostemon
Allicin mice LD50 60 mg Allium
Amyl alcohol oral rat LD50 3030 mg Mentha, Origanum
Anabasine oral rat LDLo 10 mg Nicotiana
Anethole oral rat LD50 2090 mgADI 0-0.6 mg Anethum, Ocimum, Pimpinella, Piper
Apiole scumus LDLo 1000 mg Apium, Piper
Asarone ipr gpg LD50 275 mgEC recommended hmits:
0.1 mg/kg in food and beverages
Acorus, Piper
Ascaridole oral LDLo 250 mg Chenopodium
Azadirachta lethal dose pig 6000 mg Melia
Benzyl alcohol oral rat LD50 1230 mg
ADI 0 5 mg
Canaga, Canangium, Eugenia
Borneol oral rbt LDLo 2000 mg Angelica, Blumea, Cinnamomum,
Citrus, Coriandrum, Cymbopogon,
Eucalyptus, Lavendula, Myristica,
Ocimum, Rosmarinus, Salvia, Thymus,
Valeriana, Zingiber
Butyraldehyde ihl hmn TCLo 580 mg/m2

Artemisia, Eucalyptus, Lavendula, Raphanus

Butyric acid  oral rat LD50 2940 mg Eucalyptus, Gossypium, Sapindus
iso-Butyric acid oral rat LD50 280 mg Artemisia, Cinnamomum, Croton, Eucalyptus,
Laurus, Lavendula
Calamus oil   oral rat LD50 777mg Acorus
d-Camphene   Rosmarinus, Zingiber
Camphor ipr rat LDLo 900 mg Acorus, Alpina, Artemisia, Chenopodium,
Chrysanthemum, Cinnamomum, Curcuma,
Lavendula, Lippia, Ocimum, Rosmarinus,
Caproic acid 
oral rat LDLo 3000 mg Chrysanthemum, Cinnamomum, Cocos,
Laurus, Lavendula, Mentha
Caprylic acid ivn mus LD50 600 mg Cinnamomum, Citrus, Cocos, Cymbopogon,
Mentha, Myristica
Capsaicin ivn cat LDLo 1600 mg Capsicum
Caraway oil  oral rat LD50 3500 mg Carum
Carene  oral rat LD50 4800 mg Chenopodium, Citrus, Eucalpyrus, Piper
Carvacrol oral LD50 810 mg Anabasis, Carum, Cinnamomum, Mentha, Ocimum, Origanum, Thymus, Zea
Carvone oral LD50 1640 mg Anethum, Carum, Chrysanthemum, Citrus, Cymbppogon, Eucalpyrus, Lavendula, Lippia,
Mentha, Syzygium
Cassia oil oral rat LD50 2800 mg Cinnamomum
Choline ipr rat LD50 400 mg Acorus, Artemisia, Eupatorium, Glycine,
Gossypium, Helianthus, Linum, Olea,
Pimpinella, Trigonella, Valeriana
Cineole (1-8) oral rat LD50 2480 mg Alpina, Artemisia, Blumea, Cinnamomum,
Curcuma, Eucalyptus, Eugenia, Laurus,
Lavendula, Lippia, Mentha, Ocimum, Piper,
Psidium, Rosmarinus, Salvia, Syzygium
Cinnamaldehyde oral gpg LD50 1160 mg Cassia, Cinnamomum, Lavendula, Pogostemon
Citral oral rat LD50 4960 mg ADI 0-0.5 mg Citrus, Cymbopogon, Eucalyptus, Lavendula, Lippia, Ocimum, Piper, Thymus, Zingiber
Citronella oil  oral mam LDLo 1000 mg Cymbopogon
Citronellol   ims mus LD50 4000 mg Cinnamomum, Citrus, Cymbopogon, Lippia
Clove oil oral rat LD50 3720 mg Syzygium
Coriander oil    oral rat LD50 4130 mg Coriandrum
Coumarin oral rat LD50 293 mg Ageratum, Cinnamomum, Lavendula
Cumene oral rat LD501400 mg Cuminum
Cumin oil  oral rat LD50 2500 mg Cuminum
Cuminic alcohol oral rat LD50 1020 mg Cinnamomum, Cuminum, Eucalyptus,
Cuminic aldehyde oral rat LD50 1390 mg Aegele, Artemisia, Cinnamomum, Cuminum,
ADI 0-0.1 mg Lavendula, Zanthoxylum
Curcumin Curcuma
p-Cymene oral hmn TDLo 86 mg CNS
oral rat LD50 4750 mg
Aegele, Chenopodium, Cinnamomum, Citrus,
Coriandrum, Croton, Cuminum, Cupressus,
Eucalyptus, Eupatorium, Myristica, Origanum,
Pimpinella, Salvia, Thymus
Decanal oral rat LD50 3730 mg Cassia, Cinnamomum, Citrus, Coriandrum,
Ergosterol oral dog LDLo 4 mg Citrus, Nicotiana
Esdragole (estragole) oral rat LD501820 mg Antemisia, Ocimum, Pimpinella
Ethyl alcohol  

oral man LDLo 50 mg

Citrus, Eucalyptus, Lycopersicon, Mentha, Nicotiana

Eucalyptus oil
oral rat LD50 4440 mg
oral rat LDLo 500 mg
Acorus, Ageratum, Alpina, ADI 0.1-2.5 mg/kg Cinnamomum, Citrus, Cymbopogon, Eugenia, Lantana, Laurus, Lavendula, Myristica, Nicotiana, Ocimum, Pimpinella, Piper, Pogostemon, Syzygium
oral LD50 1560 mg
Canaga, Canangium, Cinnamomum, Myristica
Formic acid
oral rat LD50 1210 mg
Artemisia, Cinnamomum, Citrus, Mentha,
ADI 0-3 mg
Myristica, Nicotiana, Ricinus, Valeriana
oral rat LD50 127 mg
Angelica, Carum, Cinnamomum, Citrus,
Cupressus, Cymbopogon, Gossypium,
Lavendula, Mentha, Myristica, Syzygium, Zea
Gaultheria oil
oral hmn TDLo 170 mg
oral rat LD,o 887 mg
oral LD50 3600 mg
Cinnamomum, Citrus, Eucalyptus, Eugenia, Laurus, Lavendula, Lippia, Myristica, Thymus, Zingiber
oral rat LD50 2315 mg
ivn dog LDLo 50 mg
Chenopodium, Citrus, Lycopersicon
Hydrocyanic acid oral hmn LDLo 570 mg
ADI not to be used
Ageratum, Allium, Annona, Boscia, Cassia, Chenopodium, Cinnamomum, Citrus,
Combretum, Crotalaria, Cymbopogon,
Erythrophleum, Eucalyptus, Euphorbia,
Gliricidia, Glycine, Ipomaea, Jatropha,
Lantana, Linum, Nerium, Nicotiana, Ocimum, Piper, Psidium, Ricinus, Tagetes, Tephrosia
Isovaleraldehyde   Cinnamomum, Citrus, Cymbopogon,Eucalyptus, Glycine, Lavendula, Mentha, Raphanus
Lauric acid ivn mus LD50 131 mg Cinnamomum, Citrus, Cocos, Elaois, Laurus
Limonene oral rat LDLo 4600 mg
ADI not specified
Anethum, Apium, Carum, Chenopodium, Cinnamomum, Citrus, Coriandrum, Croton, Cuminum, Cymbopogon, Eucalyptus, Hyptis, Lavendula, Lippia, Mentha, Myristica, Nicotiana, Ocimum, Origanum, Pimpinella, Piper, Rosmarinus, Salvia, Syzygium, Valeriana
Linalool oral rat LD50 2790 mg
ADI 0-0.5 m
Artemisia, Cinnamomum, Citrus, Coriandrum, g Cymbopogon, Eucalyptus, Laurus, Lavendula, Mentha, Myristica, Ocimum, Origanum, Rosmarinus, Salvia, Syzygium, Thymus, Zingiber
Linoleic acid   Helianthus, Ricinus
Malic acid oral rat LDLo 1600 mg
ADI not specified
Artemisia, Capsicum, Coriandrum, Helianthus, Juniperus, Lycopersicon, Nicotiana, Ricinus
Menthol oral rat LD50 3180 mg
ADI 0-0.2 mg
  Mentha, Thymus
Methanol oral hmn LDLo 340 mg Carum, Gossypium, Lycospericon, Mentha, Syzygium
Methyl anthranilate oral rat LD50 2910 mg
ADI 0-1.5 mg
Cananga, Canangium, Citrus
Methyl chavicol oral rat LD50 1820 mg Artemisia, Ocimum, Pimpinella
Methyl eugenol   Syzygium
Methyl salicylate oral hmn LDLo 170 mg
oral rat LD50 887 mg
ADI 0-0.5 mg
Chenopodium, Erythroxylum, Eugenia,
Gaultheria, Myristica, Syzygium,
Myristic acid ivn mus LD50 43 mg Cinnamomum, Citrus, Cocos, Croton, Elaeis, Helianthus, Myristica, Pimpinella
Myristicin oral cat LDLo 570 mg Anethum, Carum, Cinnamomum, Myristica
Nicotine oral hmn LDLo 1 mg Erythroxylum, Nicotiana
(D and L)
ipr rat 6-23.5 mg Nicotiana
Noscapine ivn mus LD50 83 mg Lycopersicon
Nutmeg oil
oral rat LD50 3640 mg Myristica
Nutmeg oil
oral rat LD50 2620 mg Myristica
Oleic acid i vn mus LD50 230 mg Major component of oilseeds
Origanum oil oral rat LD50 1850 mg Origanum
Oxalic acid oral hmn LDLo 700 mg Allium, Anacardium, Capsicum, Chenopodium, Citrus, Coriandrum, Glycine, Ipomaea, Juniperus, Lycopersicon, Mentha, Momordica, Nicotiana, Raphanus
Palmitic acid ivn mus LD50 57 mg Common in oilseeds, Apium, Gossypium, Ricinus
Pennyroyal oil oral rat LD50 400 mg Mentha
Peppermint oil oral rat LD50 4441 mg Mentha
Phellandrene   Aegele, Anethum, Angelica, Artemisia, Cinnamomum, Citrus, Coriandrum, Cuminum, Curcuma, Cymbopogon, Eucalyptus, Lantana, Laurus, Lavendula, Mentha, Pimpinella, Piper, Zingiber
a-Pinene   Coriandrum, Cuminum, Eucalyptus, Laurus, Myristica, Origanum, Pimpinella, Piper, Rosmarinus, Syzygium
Pipericide   Piper
Propionic acid oral rat LD50 1510 mg Widespread, including Cinnamomum, Lavendula, Pimpinella
Pulegone ipr mus LD50 150 mg Bystropogon, Mentha, Origanum
Pyrethrin I oral rat LD50 1200 mg Chrysanthemum
Pyrethrin II oral rat LD50 1200 mg Chrysanthemum
Pyrethrum oral rat LD50 200 mg Chrysanthemum
Pyrocatechol oral rat LD50 3890 mg Allium, Citrus, Eucalyptus, Psidium, Raphanus
Pyrogallol unk man LDLo 120 mg
oral rat LD50 787 mg
Quercitin    oral rat LD50 161 mg Allium, Euphoria, Euphorbia, Gossypium, Psidium, Shorea, Zea
Ricinoleic acid scu rbt TDLo 3120 mg Cassia, Ricinus
Rotenone oral rat LD50 132 mg Derris, Lonchocarpus, Tephrosia
ivn mus LD50 950 mg Widespread, including Artemisia, Calotropis,
(sophorin)   Eucalyptus, Gossypium, Lycopersicon, Nerium,(vitamin P), Nicotiana, Tephrosia,
oral rat LD50 1950 mg
Chenopodium, Cinnamomum, Myristica,
(shikimol) No ADI allocated Ocimum, Pimpinella, Piper
Sage oil oral rat LD50 2600 mg Salvia
Salicylic acid oral rat LD50 891 mg
No ADI allocated
Cinnamomum, Gaultheria, Gossypium,
Sanguinarine ipr rat LD50 18 mg Sapindus, Zanthoxylum
Saponin oral mus LDLo 3000 mg Very widespread, including Acorus, Aegele, Allium, Anabasis, Bassia, Cassia, Chenopodium, Citrus, Eucalyptus, Eugenia, Euphorbia, Glycine, Helianthus, Lippia, Momordica, Nicotiana, Ocimum, Olea, Raphanus, Ricinus, Salvia, Sapindus, Thymus
Sebacic acid ipr mus LD50 500 mg Ipomaea
Solanine ipr mus LD50 32 mg Capsicum, Lycopersicon
Stearic acid (Octadecanoic acid) ivn rat LD50 22 mg Citrus, Croton
Succinic acid scu frg LDLo 2000 mg Artemisia, Gossypium, Helianthus
Tannic acid oral mus LDLo 2000 mg Widespread, including Acorus, Artemisia, Catharanthus, Cinnamomum, Coriandrum, Cuminum, Eucalyptus, Eugenia, Eupatorium, Euphoria, Helianthus, Ipomaea, Lavendula, Melia, Myristica, Pimpinella, Rosmarinus, Salvia, Syzygium
Terpinen-4-ol oral rat LD50 4300 mg Artemisia, Cinnamomum, Citrus, Cuminum, Cupressus, Cymbopogon, Lantana, Laurus, Lippia, Myrisfica, Origanum, Pimpinella, Rosmarinus, Salvia, Thymus
Thujone ipr rat LDLo 120 mg Artemisia, Lavendula, Lippia, Salvia
Thyme oil oral rat LD50 2840 mg Thymus
Thymol oral LD50 980 mg Anabasis, Carum, Lavendu/a, Ocimum, Origanum, Thymus
Tomatine oral rat LDLo 800 mg Lycopersicon
Trimethylamine ipr mus LDLo 75 mg Acorus, Chenopodium, Gossypium, Nicotiana
Tryptothane oral rat TDLo 1100
Glycine, Helianthus, Ipomaea, Linum, Lycopersicon, Nicotiana
Turmurone   Curcuma
Undecanoic acid ivn mus LD50 140 mg Artemisia, Cocos, Thymus
Valeric acid ivn mus LD50 1290 mg Cananga, Canangium, Croton, Laurus Lavendula, Mentha, Valeriana
iso-Valeric acid oral rat LDLo 3200 mg Artemisia, Calotropis, Cinnamomum, Citrus, Croton, Eucalyptus, Lavendula, Lippia, Mentha, Nicotiana, Rosmarinus, Valeriana

Note: Toxicity data quoted in Duke, 1985. Derived from NIOSH, 1975. Unless otherwise indicated all g, mg and m g entries are expressed as per kg body weight. ADI quoted from JECFA, 1994.

Abbreviations used: 

acceptable daily intake
central nervous system
Economic Community
gastrointestinal tract effects
guinea pig
lowest published lethal concentration
lethal dosage 50 percent kill
lowest published lethal dose
neoplastic effects
lowest published toxic concentration
lowest published toxic dose

The six plant genera most frequently investigated, namely Acorus, Chenopodium, Eucalyptus, Mentha, Ocimum and Piper possess many chemical constituents in common and these are listed below in Table 3. Eight constituents are found in at least three of the six listed. These include five terpenoids: carene, cineole, citral, eugenol and phellandrene; the alcohol, linalool and the phenol, safrole. The terpenoid, limonene, is found in five of the plants, whilst hydrocyanic acid is found in four. Acorus, which is not reported to possess either toxicant, contains the phenyl propene, asarone (Lander and Schreier, 1990).

It is often assumed that ‘natural’ plant extracts are safer than synthetic chemicals, but this is not always true. Plant fragments or extracts should not be recommended for admixture with stored foodstuffs until appropriate tests have shown them to be safe.


Table 3: Toxins found in frequently examined plant genera

Plant species Toxins
Acorus asarone, calamus oil, camphor, choline, eugenol, eugenol ethyl ether, heptanoic acid, methylamine, saponin, tannic acid, trimethylamine.
Chenopodium Ascaridole, carene, cymene, histamine, hydrocyanic acid, limonene, methyl salicylate, oxalic acid, safrole, saponin, trimethylamine.
Eucalyptus Benzaldehyde, borneol, butyraldehyde, butyric acid, carene, carvone, cineole, citral, cuminic acid, cymene, ethyl alcohol, eucalyptus oil, gallic acid, geraniol, hydrocyanic acid, isoamyl alcohol, isobutyric acid, isoprene, isovaleraldehyde, isovaleric acid, limonene, linalool, mandelonitirle, phellandrene, pyrocetechol, quercitrin, quinic acid, rutin, saponin, shikimic acid, tannic acid, valeraldehyde.
Mentha Acetaldehyde, amyl alcohol, caproic acid, caprylic acid, carvacrol, carvone, cineole, ethyl alcohol, formic acid, furfural, isoamyl alcohol, isovaleraldehyde, isovaleric acid, limonene, linalool, menthol, methanol, methylamine, nonanoic acid, oxalic acid, pennyroyal oil, peppermint oil, phellandrene, pulegone, salicylic acid, valeric acid.
Ocimum Anethole, camphor, carvacrol, cineole, citral, esdragole, eugenol, hydrocyanic acid, limonene, linalool, safrole, saponin, thymol.
Piper Anethole, apiole, asarone, carene, cineole, citral, dihyrokawain, eugenol, eugenol methyl ether, hydrocyanic acid, limonene, phellandrene, piperidine, piperonal, safrole, stearyl alchol.

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