Recent Developments in Plant-Derived Compounds for Pest Management

Nicholas Panella

Colorado State University

Fort Collins, Colorado 80523

nap4@CIDVBI1.EM.CDC.GOV

Introduction

Although the use of plant species to control insect pests has been in practice for 

centuries to a limited extent, it has been only recently that interest has renewed 

in the pest management potential of natural products.а Theseа 



products



аare the 

compounds that have evolved in plants for defense against phytophagous insects.а 

Interestingly, a quite convincing case has been proposed suggesting that these 

secondary plant products have actually co-╪evolved with insects that would 

potentially exploit them as a food resource (Berenbaum 1982).а One can imagine the 

plant kingdom striving to slow down the attack of the herbivores over evolutionary 

time by formulating novel compound after novel compound and tirelessly conducting 

bioassays in order to find out what works and what does not.а The herbivores in 

return develop new strategies over evolutionary time to break down some of these 

chemical defenses to exploit the plants if they can.а It is because of this never 

ending back and forth struggle that these vast number of chemical compounds have 

evolved in the plant kingdom. The modern researcher now has the technology to 

exploit the toxic properties of some of these compounds and use them against 

organisms that were never originally intended.а Namely, the pests of modern man.

One group of compounds that has demonstrated significant toxic effects on some pests 

of modern man have been discovered in the neem tree (Azadiricta indica) (A. Juss.).а 

The most active constituent, azadiractin (AZA), a triterpenoid, has been shown to 

have properties including feeding and ovipositional deterrence, repellency, growth 

disruption, reduced fitness, and sterility in a number of species of hemimetabolous 

and holometabolous insects (Ascher and Meisner 1989; Shmutterer 1990).а Research has 

been focused on controlling agricultural pests as well as medically important 

arthropods with products derived from neem.

Perhaps the most medically important arthropod world wide is the mosquito which 

transmits diseases such as the malarias, dengue, and yellow fever to name but a few.а 

Because mosquitoes and many other insects have become resistant to pesticides, heavy 

and frequent applications are required leading to problems of toxic residues 

contaminating the environment and adversely affecting non-╪target organisms.а This 

dictates the need to develop safe, less expensive, and preferably locally available 

materials for pest control.а In this vain, NeemAzal, a product derived from the neem 

seed kernel, was evaluated as a potential means of control for Aedes aegypti 

(Boschitz and Grunewald 1994).а Boschitz and Grunewald used the larval stage of the 

mosquito to measure mortality rates depending on concentration and then looked at 

the effects of sub-lethal doses on the fecundity of the surviving larvae.а They 

hypothesized that if sterility could be proven, then the advantage of sub-lethal 

doses would be the obvious reduction of risk of damage to non-target flora and 

fauna.а Other control projects that have been conducted with neem tree products have 

also targeted other medically important mosquito vectors such as Anopholes 

stephensi, Culex quinqefasciatus, Culex pipiens, Aedes togoi and Aedes aegypti 

(Attri & Pradas 1980; Chavan & Nikam 1988; Zebitz 1984).а These studies reported 

strong variations in susceptibility of a muito species towards neem tree products.

Neem and its products have also been the focus of agricultural pest control research 

as well.а Dimetry et al. (1995) have been working with neem azal-F to inhibit the 

growth and reproduction in the cowpea aphid (Aphis craccivora).а This particular 

product contains 5% azadiractin and produced an antifeedent effect which hindered 

larviposition of the adults and decreased the reproductive period as well as the 

longevity of the adults.а In addition they were able to show an aphicidal effect as 

the concentration increased.а In another application, Naumann and Isman (1995) used 

three concentrations of an oil-free neem seed extract to deter oviposition in 

noctuid moths.а They found that most commercial neem-based products are not 

effective noctuid oviposition deterrents.а Their studies suggest that the results 

demonstrated in other research using neem-based deterrents were effective because 

the compounds were removed by a higher level of processing and thus not found in 

commercial products.а Another approach using neem products has involved integrating 

neem with endomychorrhiza to control root knot nematodes onа tomato plants (Rao et 

al. 1995).а In this effort researchers planted mychorrizal seedlings of tomato into 

soil that was treated with neem cake.а Vesicular arbuscular mycorrhizal fungi (VAM) 

has been established as a reducer of nematode parasites of many plant species.а By 

combining neem cake in the soil with the VAM the investigators sought to elevate the 

level of protection for the seedlings.а Yet another application for this product has 

been tested by a group of researchers in Winnipeg, Canada on three stored-product 

beetles (Xie et al. 1995).а The beetles in question; the rusty grain beetle 

(Cryptolestes ferrugineus) (Stephens), the red flour beetle (Tribolium casteneum) 

(L.), and the rice weevil (Sitophilus oryzae were exposed in the laboratory to 

several extracts of neem.а In this case the researchers were looking for repellency 

effects as well as toxic effects.а The variance in susceptibility between the 

species was expected as several investigators working with mosquitoes observed 

similar phenomena.

Neem is not the only plant derived chemical that has demonstrated arthropocidal and 

toxic effects however.а Several species of Juniper have also been studied and the 

active constituents isolated.а A broad spectrum study was conducted using extracts 

from twelve different species of Juniper to look for termiticidal activity and then 

to isolate the active components (Adams et al. 1988).а Oda et al. 1977 conducted a 

systematic survey of Juniper species across the United States and reported the 

isolation of two sesquiterpene alcohols, cedrol and widdrol, as the most active 

ingredients.а Other research, involving Lyme disease vectoring ticks (Ixodes 

scapularis) (Acari: Ixodidae) (Say) hasdemonstrated that two species of Juniper; 

western and eastern, (J. occidentalis) and (J. virginiana) respectively, had 

considerable acaricidal activity (Panella et al.а submitted).а Moreover it was shown 

that these two species had toxic effects on the Oriental rat flea (Xenopsylla 

cheopis) (Insecta: Syphonaptera) an important vector of the plague bacterium 

Yersinia pestis, in laboratory (Panella et al. submitted).а In addition to species 

of Juniper, Panella et al. (submitted) demonstrated significant biological activity 

in several different plant extracts against ticks and fleas.

Discussion

It is clear by the review of recent research listed above that there is an unlimited 

number of applications for secondary plant compounds and their derivatives and many 

different methods have been used to study their biological activity.а Boshitz and 

Gruwenwald (1994) placed larval Ae. aegypti mosquitoes in beakers containing 

deionized water with differing concentrations of NeemAzal.а This bioassay technique 

sought to simulate real ecological parameters that exist in nature to a certain 

extent.а Probably the best bioassys are conducted in the field under real life 

circumstances, but when that is not possible the researcher must use creativity and 

resourcefulness to obtain a high quality bioassay.а Perhaps the most interesting 

observation made by Boschitz and Grunewald was that the toxic effect of the product 

decreased as the larval stage increased.а That is 1st instar larvae were more 

susceptible to the NeemAzal than were 3rd and 4th instar.а Boschitz and Grunewald 

also reported that there was not a significant reduction in fecundity among the 

mosquitos that were exposed to sub-lethal concentrations and allowed to molt into 

adults.а These results were inconsistent with results published by other researchers 

that claimed a significant reduction in fecundity after neem exposure (Mordue 1985; 

Schmidt 1986;Feder et al. 1988; and Schmutterer 1986).а This variation could be due 

to the difference in bioassay techniques.а Boschitz and Grunewald put the NeemAzal 

directly into water allowing the larvae to come into contact with it by normal 

locomotion whereas the other studies mentioned above administered the toxin by 

either blood meal or direct injection into the hemocoel.а It was clear in either 

case though that NeemAzal inhibited growth of the early instar larvae.

Detrimental physiological effects have also been observed in insect agricultural 

pests such as aphids.а Dimetry et al. (1995) tested various concentrations of Neem 

Azal-F (a commercial product of the neem seed kernel extract containing 5% 

azadiractin) on the cowpea aphid (Aphis craccivora) to measure inhibition in growth 

and reproduction.а Lowery and Isman (1994) also tested neem seed oil on several 

species of aphids to measure the same effects.а The results obtained by Dimetry and 

Hawary (1995) demonstrate that Neem Azal-F was effective at reducing fecundity in 

the adults and inhibiting successful molting.а They also determined that the 

aphicidal effect is concentration dependent, which is consistent with the published 

results of other studies done with aphids (Schmutterer 1985; Rembold 1989; Koul et 

al. 1990).а Lowery and Isman (1994) in an earlier study also found similar results 

among the species they tested, but also reported that susceptibility varied among 

the life stages.а Both studies employed bioassays that required the larval aphids to 

ingest treated plant materials.а It is still unclear whether or not direct contact 

with neem will induce the same results (Lowery & Isman 1994).а Another interesting 

observation made by Dimetry and Hawary (1995) was that when the Neem Azal-F was not 

in lethal concentration it caused the surviving larval aphids to increasingly molt 

into the winged form as concentrations increased.а This suggests that the Neem Azal-

F even in non-lethal doses can trick the aphids physiology into thinking that 

conditions at its present location are unfavorable and develop the winged form to 

perhaps leave and look for a more suitable host plant.а 

In contrast to the fecundity reducing effect neem has on aphids, Naumann and Isman 

(1995) found that their same neem seed oil extract had little or no effect on three 

species of noctuid moths: Trichoplusia ni, Peidroma saucia, and Spodoptera litura.а 

In this experiment captive moths were given cabbage plants treated with the three 

extracts of varying concentrations (10,50 and 100ppm of azadiractin) and then 

oviposition was measured for the life span of the female which is 8-13 days.а There 

was no significant difference in the amount of eggs laid by the female on the plants 

of varying treatments.а When the researchers presented the female moths with a 

choice of treated and non-treated cabbage plants to oviposit on there were no 

differences observed in the number of eggs laid.а According to Naumann and Isman 

(1995) this is in contrast to what has been suggested in many reports, including 

those for S. litura.а Again the question of processing and formulations of both the 

products and extracts is raised.а The pesticidal power of neem is not just limited 

to phytophagous insects.а Roa et al. (1995) were able to achieve control of the root 

knot nematode on tomato plants by integrating a known nematocide, vesicular 

arbuscular mychorrhiza, with neem cake.а The bioassay used in this study could 

easily be applied in the real world because plants don'



t move much so changes are 

usually easily observable to the trained eye.а Rao et al. (1995) placed tomato 

seedlings with the (VAM) already growing on the roots into soil amended with neem 

cake.а They then removed a sample of five plants at pre-determined time intervals to 

look for infestations of nematodes.а What they found was quite remarkable.а Not only 

were the root knot nematodes virtually wiped out, but the soils amended with neem 

cake caused an increase in plant growth parameters and an increase in the 

mychorrizal population on the roots, thus affording the plants even greater 

protection.а 

The other class of plant-derived chemicals that have been shown to demonstrate 

biological activity in arthropods are those found several plant species in North 

America (Forlines et al. 1992).а Research conducted with extracts from Juniper 

species have proved to be effective in controlling termites.а Termites were exposed 

to the heartwood, bark/sapwood, and leaves initially and then to a methanol and 

hexane extract of twelve different species of Juniper found throughout the United 

States (Adams et al. 1988).а Adams et al. (1988) found that the bioassay they used 

for the raw materials was 100 percent effective for all species after 4 weeks of 

exposure heartwood.а This bioassay consisted of placing 1.5g of raw materials in a 

zipper case with 50g of sand, 7ml of distilled water and 100 termites.а Mortality 

was checked every 7 days and in all instances 100 percent mortality was achieved 

noted after 4 weeks.а Adams et al. (1988) fail to mention what kind of control they 

ran so it is hard to be sure that it was the plant material that was exhibiting all 

the activity.а With the Hexane and Methanol extracts, the investigators treated 

filter paper with a 1mg/ml solution and placed 25 termites on it.а These bioassay 

trials yielded mixed results.а The Hexane extracts only produced 100 percent 

mortality after the 4 weeks in 5 species, while the Methanol extracts were 100 

percent effective in only 4 species.а From these results Adams et al. (1988) 

concluded that perhaps the Hexane and Methanol extracts were not extracting all the 

antitermitic properties of the compounds found in the heartwood.

Other research using the extracts of Juniper as well as other plant species has been 

focusing attention on two medically important arthropods: ticks and fleas (Panella 

et al. submitted).а In these studies several extracts of heartwood, bark/sapwood and 

leaves have been evaluated as to their biological effectiveness against the afore 

mentioned arthropods.а The bioassay technique used for this research is known as the 

disposable pipet method first developed by Barnard et al. (1982).а This method 

consists of serially diluting the extract in acetone solvent into as many 

concentrations as desired.а Once the formulations are complete the solutions are 

sucked into the pipet a number of times to ensure complete coating.а The pipets are 

left for 24 hours to dry and then the ticks or fleas are introduced via a vacuum 

pump.а After 24 hrs the arthropods are checked for mortality.а Thus far, it appears 

that two of the crude extracts show a lot of promise.а Those extracts being from 

Alaska yellow cedar (Chamaecyparis nootkatensis) and Eastern red cedar (Juniperus 

virginiana).а Both of these extracts have exhibited impressive values and could 

potentially be commercially important.а It is worth noting that these extracts are 

much more toxic to the larval stage of ticks than the nymphal stage, which is 

current with what other researchers have encountered while testing other compounds 

such as neem on different stages of insects.а The active chemical compounds in these 

extracts has yet to be elucidated, but that is the focus of current research.

To understand how these compounds are working on the physiological level, 

investigations into the behavioral and sensory effects have been carried out on some 

neem based products.а Three extracts; toosendanin, salanin, and azadirachtin, from 

plants of the genus Melia were compared in their ability to deter feeding and evoke 

neurophysiological responses with Maragosan-OR, a commercial product based on an 

ethanolic extract of seeds from Azadirichta indica (Lin-er et al. 1995).а The anti-

feedant bioassay consisted of placing treated and untreated cabbage discs in a petri 

dish and then introducing caterpillars of the species Pieris brassicae.а The discs 

were checked at intervals to measure the amount the larvae consumed of each disc 

over a 4 hour period.а The degree of material consumed was then converted to an 

anti-feedant index established by the authors.а They found that Margosan was the 

best anti-feedant, but the other extracts were not significantly worse.а To measure 

sensory responses in the insects the investigators used the tip technique which 

recorded the action potentials of the two sensilla styloconica when stimulated with 

various concentrations of the 4 compounds mentioned above.а By doing this the 

authors were able to get a picture of what was happening on the cellular level in 

specific sensory cells.а They noted that some of the compounds were causing a change 

in the insects'



аsensory code.а They were able to observe if the compounds were 

inhibiting the sugar cell, glucosinalate cell or the amino acid cell.а At higher 

concentrations the responses were greater for all compounds.а In conclusion the 

authors determined that toosendanin was the strongest neem-derived compound tested.а 

Moreover, their tests indicated a good correlation between the action potential 

frequency in the caterpillar'



s medial deterrent receptor and the anti-feedant 

bioassays conducted with the compounds.ааа 

As research continues in the rapidly growing field of plant derived chemicals, many 

more applications will arise that have not been discussed in this review.а As 

researchers gain more understanding as to how these compounds affect organisms on 

the behavioral and physiological level the potential for eco-friendly products to 

control pests is enormous.а Future research in this field should expand out of the 

laboratory and into the real world.а In this way these novel products can be 

evaluated as viable alternatives to the persistent, less environmentally friendly 

products on the market currently.

References

Adams, R.P.; C.A. McDaniel & F.L. Carter.а 1988.а Termiticidal Activities in the 

Heartwood, Bark/Sapwood and Leaves of Juniperus Species From the United States.а 

Biochemical Sytematics and Ecology.а 16(5): 453-456.

Ascher, K.R.S. & J. Meisner.а 1989.а The Effects of Neem on Insects Affecting Man 

and Animals.а In: The Neem Tree.а Ed. M. Jacobsen.а Boca Raton (CRS Press) 113pp.

Attri, B.S. & R. Prasad.а 1980.а Neem Oil Extractive - An Effective Mosquito 

Larvicide.а Indian Journal of Entomology.а 42(3): 371-374.

Barnard, D.R.; B.G. Jones, G.D. Rodgers & G.A. Mount. а1981. Acaricide 

Susceptibility in the Lone Star Tick: Assay Techniques and Baseline Data.а J. Econ. 

Entomol.а 74:466-469.

Berenbaum, M. 1982. Coumarins and Caterpillars: A Case for Coevolution.а Evolution 

20: 163-173.

Boschitz, C. & J. Grunewald 1994.а The Effect of NeemAzal on Aedes aegypti (Diptera: 

Culicidae).а J. of App. Parisitol.а 35:251-256.

Chavan, S.R. & S. Nikam.а 1988.а Investigation of Alkanes From Neem Leaves and Neem 

Larvicidal Activity.а Pesticides.а pp 32.

Dimetry, N.Z. & F.M.A. El-Hawary.а 1995.а Neem Azal-F as an Inhibitor of Growth and 

Reproduction in the Cowpea Aphid Aphis craccivora Koch.а J. Appl. Ent. 119: 67-71.

Feder, D.; D. Valle, H. Rembold, E.S. Garcia.а 1988.а Azadirachtin Induced Sterility 

in Mature Females of Rhodnius prolixus.а Z. Naturforsch.а 43c:908-913.

Lou Lin-Er; J.J.A. Van Loon & L.M. Schoonhoven.а 1995.а Behavioural and Sensory 

Responses to Some Neem Compounds by Pieris brassicae Larvae.а Physiol. Entomol. 

20:134-140.

Lowery, D.T. & M.B. Isman.а 1994.а Insect Growth Regulating Effects of Neem and 

Azadirachtin on Aphids.а Entomol. Exp. Appl. 72:77-84.

Mordue, A.J. 1985.а Azadirachtin: Its Effects on Gut Motility, Growth and Moulting 

in Locusta migratoria.а Physiol. Entomol. 10:431-437.

Naumann, K. & M.B. Isman.а 1995.а Evaluation of Neem Azadirichta indica Seed 

Extracts and Oils as Oviposition Deterrents of Noctuid Moths.а Entomologia 

Experimentalis et Applicata.а 76: 115-120.

Oda, J., N. Anado, Y. Nakajima & Y. Inouye.а 1977.а Studies on Insecticidal 

Constituents of Juniperus recurva Buch.а Agric. Biol. Chem. 41(1)201-204.

Panella, N.A.; J. Karchesy, G.O. Maupin, J.C.S. Malan & J. Piesman. 1995.а 

Susceptibility of Immature Ixodes scapularis (Acari: Ixodidae) to Plant-Derived 

Acaricides.а Submitted to J. of Med. Entomol. 4/96.

Rao, M.S.; P. Reddy, & S. Mohandas.а 1995.а Effect of Intergration of Endomycorrhiza 

(Glomus mossae) and Neem Cake on the Control of Root-Knot Nematode on Tomato.а J. of 

Plant Diseases and Protection.а 102(5): 526-529.

Schmidt, G.H. 1986.а Studies of the Sterilization Effect of Neem Extracts in Ants.а 

Progr. 3rd Int. Neem Conf. Nairobi. p361

Schmutterer, H. 1986.а Fecundity Reducing and Sterilizing Effects of Neem Seed 

Kernel Extracts in the Colorado Potato Beetle,а Leptinotarsa decemlineata.а Proc. 

3rd Int. Neem Conf. Nairobi. p.351.

(1990).а Properties and Potential of Natural Pesticides From the Neem Tree, 

Azadirichta indica.а Ann. Rev. Entomol. 35:271-289.

Xie, Y.S.; P.G. Fields & M.B. Isman.а 1995.а Repellency and Toxicity of Azadirachtin 

and Neem Concentrates to Three Stored-Product Beetles.а J. of Econ. Entonol.а 20(2): 

134-140.

Zebitz, C.P.W. 1984.а Effect of Some Crude and Azadirachtin-Enriched Neem 

(Azadirichta indica) Seed Kernel Extracts on Larvae of Different Mosquito Species.а 

J. of Appl. Entomol. 102: 455-463.аааааааааааааааааааааааааааааааааааааааааа