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E. F. Legner
Professor of Biological Control
University of California
eflbio@outlook.com
Biological
pest control might have been recognized circa 400 BCE in China with the
correct interpretation of behavior and development of predators, but F. Redi
in 1668 observed that arthropods do not arise by spontaneous generation
(DeBach & Rosen 1991). Van
Leeuwenhoek in 1700 proposed that parasitoids and pathogens might be
essential to the natural control of pests.
However, it was R. Réaumur in 1734 that suggested such organisms be
used as a direct pest control tactic.
He advised the release of lacewings in greenhouses for the control of
aphids.
Earlier observations by ordinary farmers certainly led to
an appreciation of the action of predators, as predation is obvious and easily
viewed. Indeed, pest control was
attained in Egypt by 2,000 BCE when humans kept cats to protect stored grain
from rodents. In China citrus growers
used Oecophylla smaragdina Fab. for the control of
lepidopteran and coleopteran pests in 324 BCE. The ants build nests in
trees and these were collected and sold to growers. In order to aid the foraging of ants, bamboo bridges were built
between the citrus trees. DeBach
(1974) observed this practice still being used in North Burma in the 1950s,
and it continues to be used in China.
Other efforts deployed general predators such as the mongoose, owls
and other birds, toads, ants, etc.
Linnaeus also considered the use of predators for pest
control (Höestadius 1974). The first
successful importation of an organism from one country to another for
biological pest control took place in 1762 with the introduction of the mynah
bird from India to the island of Mauritius for control of the red locust Nomadacris septemfasciata (Serv.) (DeBach & Rosen 1991).
Insect parasitism was not recognized until the 17th
Century when the Italian U. Aldrovandi in1602 observed the cocoons of Apanteles glomeratus (L.) being attached to larvae of Pieris brassicae L. (Bodenheimer 1931). He incorrectly believed that the cocoons
were insect eggs, as he stated, "Twice have I also observed the cabbage
caterpillar laying yellow eggs covered with delicate wool, and afterwards
transforming itself into a yellowish pupa, marked with green and black. What appeared peculiar to me was that from
these eggs emerged small winged animalcules, so small that they could barely
be seen..."
Illustrations of parasitoids appeared in Holland by
Johannes Goedaert (1662) in his book Metamorphosis et Historia Naturalis Insectorum. He noted, "Out of one caterpillar,
which had pupated on June 12, emerged on the 30th the butterfly
species.... But out of another
caterpillar of the same species, which had pupated on July 13, emerged after pupation
82 small flies, as the reader can see in the figure added. Thus from one caterpillar a butterfly
emerged and from the other 82 small flies."
The British physician Martin Lister suggested in letters
published in the 1670-71 issue of the Philosophical Transactions
of the Royal Society of London, that some insects
lay their eggs in the bodies of living caterpillars and in 1685 he correctly
interpreted Goedaert's observations, "The 82 flies that emerged from the
pupa are the progeny of an ichneumon fly, which had gotten into the
caterpillar in a manner that is still not entirely clear to me..."
Another 25 years was required before the cycle of
parasitism was fully analyzed and described.
The Dutch microscopist Antoni van Leeuwenhoek in a letter of 26
October 1700 to the Royal Society fully noted that some of the berry plants
in his garden in Delft had more flowers than usual. He also observed that the "black flies" on these
plants were more numerous than in other years. He dismayed that the offspring of so many blackflies would
completely devastate his berry plants.
After studying the mouthparts of the "blackflies" he
concluded that they would not be able to eat the leaves, "These last flies
that I caught were all females, and had their eggs in them; from whence I
more strongly concluded that the black flies did the trees no harm; for if
they had laid their eggs on the trees, and that all their eggs had produced
so many living insects, there would not, I am positive, be one leaf or any
fruit remaining on the trees."
Leeuwenhoek strongly denied the theory of spontaneous generation, a
hotly debated topic during his time.
He continued with, "I shifted these flies into another glass
tube, where I had before put six green lice [aphids], which I had taken from
the leaf of a currant-tree... These
flies, as soon as ever they came near the said lice, brought the hinder part
of their body, which was pretty long, between all their feet, and stretched
their body far out, and their tail making a kind of semicircle with the rest
of the body, stood out beyond their head, and in this manner they insinuated
their tail into the bodies of the worms, and this the flies did in a short
time to all the worms they came near to; but that which was most remarkable
in this action was that in this conjunction they never touched the lice,
either with their feet or bodies, so that they often essa'd to approach the
creatures, in order to thrust in their tails into their bodies, and could not
effect it; nay, one would say they were so afraid of these lice as if they
would have devoured them; and as they entered the bodies of the lice they
made a trillende [shivering] motion of shaking with their tail, which came to
be done so that they might thrust it in further."
"Now, as
the flies remained but two days alive without copulation, as ever I observed,
whereas the green lice lived seven or eight days, I though not otherwise but
that the flies by that insinuation of their tails into the bodies of those
lice, did withal convey their eggs in the same time, and that from those eggs
young worms should have been produced, which having received their
nourishment and increase from the bodies of the lice, should be changed again
into a fly, but the green lice died, and for the most part dried away. Not content with this observation I got
together again 25 dead lice, all of which in their bellies a worm, or else a
fly newly changed, for I saw through the skin of some of the lice, living
flies, which flies I took out alive from the bodies of some of those green
lice which I opened on purpose... Now
if we observe the wonderful formation of such a small creature, and how such
a fly is produced, and then consider that the worm which is changed into the
fly, and we imagine that such a thing will not happen, unless the worm that
comes out of the egg of the fly makes use of another creature for its food,
we must remain perfectly amazed."
From this description it can be concluded that what van
Leeuwenhoek very exactly described the behavior of a parasitoid of
aphids. The illustration, which was
published with the letter, is of such good quality that the insect could
easily be determined to be Aphidius
ribis Haliday, a parasitoid of the
aphid Cryptomyzus ribis (L.). Thereafter in the 18th Century, knowledge of parasitoids
rapidly increased.
Silkworm diseases were recognized as early as the 18th
Century, although earlier the Greeks and Romans were aware of diseases of
bees. Many publications in the 16th,
17th and 18th Centuries dealt with diseases of silkworms, silk being a very
important industry at the time.
Vallisnieri was the first to mention the muscardine disease of
silkworm. De Reamur (1726) described
and was the first to illustrate a fungus, Cordyceps,
infecting a noctuid larva. The
microbial nature of these diseases was not yet realized. From William Kirby’s chapter on "Diseases of
Insects" (Kirby & Spence 1815) we learn that it was recognized that
true fungi grew in the bodies of insects as saprophytes and possibly as
parasites. Agustino Bassi (1835)
first experimentally demonstrated that a microorganism, Beauveria bassiana(Bal. Vuill) caused an animal
disease, namely the muscardine disease of silkworms, and he suggested that
microorganisms be used for insect pest control. Later in 1874, Louis Pasteur advised the use of microorganisms
against the grape phylloxera in France.
These suggestions did not result in practical application. Elie Metchnikoff tried to develop
biological pest control for the wheat cockchafer, Anisopilia austriaca Herbst, a serious pest of cereal
crops in the area of Odessa, Russia.
In 1879 he published a paper on Metarrhizium
anisopliae (Metsch) Sorok., and his experiments led to the conclusion
that the fungus, when mass-produced and properly introduced in the field,
might result in effective control.
Based on Metchnikoff's work, Metarrhizium
was mass-produced in 1884 in the Ukraine, and the spores were tested in the
field against a curculionid, Cleonus
punctiventris Germ. in sugar beets.
Biological weed control did not begin until after 1850
(Goede 1978). The American Asa Fitch was the first to suggest biological control of weeds around
1855, when he observed that a European weed in New York pastures did not have
American insects feeding on it. He
suggested that importation of European insects feeding on this weed might
solve the problem. The first
practical attempt dates from 1863, when Dactylopius
ceylonicus (Green), was distributed for cactus control in southern India
after they had been observed to decimate cultivated plantings of the prickly
pear cactus, Opuntia vulgaris Miller, in northern India (Goeden 1978). In 1865, the first successful
international importation for weed control took place, when this same insect
was transferred from India to Sri Lanka, where in a few years widespread
populations of the same cactus, O. vulgaris, was effectively controlled.
During the 19th Century taxonomy rapidly developed and
many biological studies of natural enemies were made. Practical ideas and tests about
application of biological pest control gradually advanced. Erasmus Darwin, the grandfather of Charles
Darwin, published Phytologia, a book on agriculture and
gardening in 1800, in it stressing the role of natural enemies in reducing
pests. Moreover, he advised that
aphids in hothouses be controlled by artificial use of predaceous syrphid fly
larvae. Augmentation of ladybird
beetles for control of hop aphids in the field and aphids in greenhouses was
also recommended by Kirby & Spence (1815).
By 1850 with the westward expansion of agriculture
biological pest control obtained full attention in the United States, where
imported pests were taking a large toll of both domestic and imported
crops. Entomologists, such as Asa
Fitch, C. V. Riley and Benjamin D. Walsh, suggested the importation of
natural enemies from their homeland.
It was C. V. Riley (1893) who organized the first intra-state
parasitoid transport when he sent parasitoids of the plum curculio, Conotrachelus nenuphar (Herbst),
to different localities in Missouri [probably a wasted effort]. Riley was also the first to propose
conservation of parasitoids of the rascal leafcrumpler of fruit trees, Acrobasis indigenella, by collecting larvae in their cases in mid-winter and
then placing them away from the tree far enough that the larvae could not
reach the trees anymore, but the parasitoids emerging from parasitized
individuals in springtime could easily do so. Also, in 1873, Riley stimulated the first international transfer
of an arthropod predator by sending the predatory mite Tyroglyphus phylloxerae Riley to France for control of the
grape phylloxera, Daktulosphaira vitifolii Fitch. It established
but did not result in effective control.
The first international shipment of a predatory insect took place in
1874, when aphid predators, among which Coccinella
undecimpunctata L., were shipped from England to
New Zealand and became established.
The first international transfer of parasitic insects was Trichogramma from the United States to
Canada in 1882. The first
intercontinental parasitoid shipment took place in 1883, when Riley organized
the shipment of Apanteles glomeratus (L.) from England to the United States for control of cabbage
white butterflies. It was just another
six years before the spectacular success with Rodolia cardinalis Muls. against the citrus cottony-cushion
scale, Icerya purchasi Mask., took place, again under the direction of
Riley.
Biological control expanded in the 20th Century
when Harry S. Smith of the University of California redefined the host
relationships of entomophagous insects (Smith 1916). This was followed by a half century of
numerous successes worldwide (Bellows & Fisher 1999).
Integrated
Pest Control
Integrated Control's future is very bright, especially
with its new title "Integrated Pest Management," that is more
generally understood by scientists and the public alike. There is no doubt
expressed concerning the importance and value of the integrated control
concept. But, much work remains in order to implement integrated control on a
wider scale. A broad interdisciplinary approach is needed, pooling talents of
research teams. This also means incorporating economic considerations.
There are
special difficulties of establishing integrated control in crops where
excessive demands for eye appeal as a measure of quality, are great. There
are also great difficulties in grower and extension personnel education.
Integrated control programs are complicated and in some instances require
trained supervisors. Governments can
take a more active role in stimulating development of integrated control by
instituting advisory services for promoting its merits, supporting intensified
research in ecology, systematics, population dynamics, and in the development
of selective insecticides, attractants, repellents, etc. Governments would be
wise to take over from the chemical industry the cost of the non-paying part
of selective insecticide development. The conclusion is that we have a long
way to go before integrated control gains widespread effective application
(Pimentel et al 1991.
Particular
problems exist for the integration of Insect Pathology. Ways must be found to better use
microorganisms to control insect pests: mass production, dissemination, and
in combination with insecticides and with entomophagous insects. However, Biological Weed Control's future
is extremely optimistic if environmental groups concerned with endangered
species can weigh the gains and detriments accurately. As there are over 1,000 introduced weed
species in America, and only ca. two percent of weeds are presently targets
for the technique, there are still relatively unlimited opportunities for
future efforts. Great possibilities
exist for the Biological Control of Medically Important Pests, especially
where chemicals are not practical to apply (Legner & Sjogren 1984, Garcia
& Legner 1999) The prospects of importation of natural enemies has just
begun to be explored. Where importation has been done, results were often
spectacular. The problem of financing this research is great since economic
losses are not neatly tied to the problem. Local financing is available, but
rarely is this adequate for importing exotic beneficial organisms.
ACKNOWLEDGEMENTS
I
would like to acknowledge the assistance of Dr. Joop Van Lenteren with the
Leeuwenhoek translation.
REFERENCES:
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T. S., Jr. & T. W. Fisher, (eds)
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