Recent Developments in Plant-Derived Compounds for Pest Management

Nicholas Panella
Colorado State University
Fort Collins, Colorado 80523
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 

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.
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 
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.
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Heartwood, Bark/Sapwood and Leaves of Juniperus Species From the United States.а 
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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.
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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.
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Reproduction in the Cowpea Aphid Aphis craccivora Koch.а J. Appl. Ent. 119: 67-71.
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in Mature Females of Rhodnius prolixus.а Z. Naturforsch.а 43c:908-913.
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Responses to Some Neem Compounds by Pieris brassicae Larvae.а Physiol. Entomol. 
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in Locusta migratoria.а Physiol. Entomol. 10:431-437.
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Extracts and Oils as Oviposition Deterrents of Noctuid Moths.а Entomologia 
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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.
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