B. A. Keddie.                         Biological Control                         March, 2002

- term biological control has been used in a variety of ways.

- many people have tried to expand the definition of the term possibly in an   attempt to add legitimacy (environmental sensitivity) to their own particular  research endeavours.

- some people include in biological control:

1). the development and selection of plants which are more resistant to insects e.g. secondary plant substances - plant resistance.

2). cultural techniques - crop rotation or habitat modification.

3). genetic techniques - sterile male release; sterile insect release.

4). "third and fourth generation pesticides" analogues of insect hormones, or compounds such as pheromones.

5). microbials which are applied in a manner so that the mode of action is different than that of a natural system, e.g. Bt the bacteria is applied like a chemical; the dose/formulation used eliminates any need for the pathogen to replicate in the host or become established in the environment.

6). products of biotechnology are sometimes classified as biological control;

new term(s) has been coined for these products e.g. biorational pesticides.

- may all be useful control techniques, alternatives to the use of chemical insecticides and all that implies while demonstrating a greater awareness of the biology of the system, but they don't fit the original definition of biological control.

- exclude from  biological control, except for comparative  purposes.

- described as part of biological insect pest suppression programs.

- include some as part of natural control.

- coined by Harry S. Smith in 1919 to apply to:

the control or regulation of pest populations by natural enemies, i.e predators, parasites and pathogens, often referred to as

"classical biological control".

Components of natural control of population numbers.

                                                            see HANDOUT 1

definitions:

density-independent factor: any factor causes mortality independent of the population density.  e. g. heavy frost killing plants.

density-dependent factor: a population-regulating factor that changes in intensity with changes in population density.  e. g. Intraspecific competition - how does this operate?

nonreciprocal:  resource doesn't change but interactions of population using the resource change as their populations fluctuate. 

e. g. space - aphids sensing crowding may produce migratory forms before aphid populations impact the plant - "controls" the numbers of users without changing the space available.

reciprocal: vary in numbers (magnitude) in response to changes in host numbers.

e. g.  as the host population increases, predators, parasitoids and pathogens may  increase then decrease as host population decreases.

- original definition restricts the term biological control to predators, parasites and pathogens, among all natural control factors as they relate to the control of insect pests.

- some also argue that biological control must also be simply the reestablishment of interactions that once existed and once reestablished humans need to do very little.

- define more on a case-by-case basis.

- expanded to include biological control of plants using microbes or insects.

HISTORICAL (for you information only)

- the earliest use of one insect species to control another insect species in agroecosystems probably predates the written record. 

- as one might expect, the earliest records (records of 1700 years) come from the Chinese.

 - e.g.  book published in China around 900 A.D. describes the use of predatory ants to control caterpillars and large boring beetles by citrus growers.

ants, Oecophylla smaragdina F weaver ant

- build large paper nests in trees.

- contain large numbers of individuals.

- can be transported from wild to domestic trees.

- can be transported from tree to tree.

- alternatively poles set up between trees to facilitate movement among trees.

- become a source of revenue-farmers bought and sold colonies.

- a current practice as an alternative to chemical control (1987).

- around 1775, a European traveler noted that the Yemenese transported predatory ants from the mountains to oases to feed on insects feeding on date palms.
- the major pest of the date palms were also ants.
- indicated their ability to differentiate between two similar species at least on the basis of their food sources.
- considered to be the first documented case of movement over a substantial distance of natural enemies for the purposes of biological control.

- two early examples of biological control demonstrate the use of one species of predatory insect to control another insect species, however the definition does not exclude other types of predators. 

    e. g. ,the red locust, Nomadacris septemfasciata Serville was a serious pest of sugarcane in Mauritius in the 18th century.

- mynah bird was imported from India in 1762 and by 1770; it was credited with the successful control of this locust.
- first documented case of international movement of a biological control agent.

- birds have been used to help suppress forest insect pests in the Soviet Union; nesting boxes are provided to increase bird populations.

importance of birds often overlooked until birds missing.

e.g.  burrowing owls - suppressed grasshopper populations on Canadian prairies.

- in North America, Amish farmers in Iowa often provide nesting boxes for birds and encourage swallows to nest on their farm buildings.  One farmer estimated that on his farm he could count some hundreds of nesting pairs and a minimum of 2000 fledglings within 300 yards of the centrally located farm building.  He stated that insects were not a problem on any of his crops and thought that the birds were at least partly responsible for this situation.

- in Europe the early observers of natural history began to generate the information which later would be formalized as " biological control".

- why were predators used first?

- readily visible for the reasonably careful observer of animal behaviour. 

                                                    see HANDOUT--Réaumur (1736)

-  understanding of the interactions in the natural history of insects was sufficiently sophisticated that by 1734 Réaumer suggested that the eggs of aphidiverous flies (lacewings) be introduced to greenhouses to keep them free of aphids.

- another student of natural history, De Geer in the 1760's is reported to have said, "we shall never be able to guard ourselves against insects but by means of other insects".

- observation of the phenomena of parasitism and the realization of its potential use in pest control and the use of pathogens for pest insect control are more recent developments.

PARASITISM

- 1602, first person to describe insect parasitism was Ulysses Aldrovandi published a description of the larvae of the braconid, Apanteles glomeratus, emerging from the cabbage butterfly, Pieris rapae (L.) where they spin their external cocoons.  Unfortunately he misinterpreted these structures as the butterfly eggs.

- 1668, Francesco Redi described aphids parasitized by an ichneumonid, again not understanding the actual process however.

                                                        (Note: Redi disproved spontaneous generation).

- 1701-1710 several people, including van Leeuwenhoek (microscopy), described the parasitic nature of the interactions between insect species including Aphidius sp. emerging from aphid.

- once nature of the parasite-host relationship was understood, descriptions of the biology of numerous parasites were published -1750's. 

- One of the first to comment on the use of a parasitic insect to control a pest (1800) was Dr Erasmus Darwin-(grandfather-Charles). 

- noted the destruction of cabbage butterfly larvae infestations after the deposition of eggs by an ichneumonid on the backs of caterpillars.

- also recommended the use of coccinellid beetles to control aphids in greenhouses.

- gathering and storing of parasitized caterpillars for later release of adult parasites was proposed by Hartig in Germany in 1826.

- in 1855 Asa Fitch suggested importation of European parasitoids to use against wheat midge in the U.S.

- first importation into N.A. occurred in 1883 (Cotesia glomerata).

PATHOGENS

Diseases in insects have been noted for a long time, certainly much before the nature of infectious disease was understood.

- early descriptions largely focused on insects that were of economic importance; e.g. diseases of honeybees and other insects were described by:

- Aristotle in his Historia animalium written some 2300 years ago.

- the Roman writer, Virgil, also commented on honeybee diseases some 300 years later.

- descriptions of diseases occurring in the silkworm were published in Japan around 1000 years ago, while the silkworm and related species were reared in China for at least 3000 years--possibly literature exists from these earlier periods.

- silkworms themselves can be considered to play a central role on insect pathology as a discipline, and one may even consider them as central to the development of the whole concept of infectious disease.  With time the rearing of silkworms for the production of silk spread from Asia to Europe and North America.  At various times devastating outbreaks of diseases destroyed large numbers of insects and uninfected stocks from one part of the world were sent to another part for considerable profit.  In addition these diseases created a demand for causes and cures.  One of the first individuals to take up the challenge was a man named Agostino Maria Bassi who examined silkworms with a disease known as calcino (in Italy) or muscardine (in France).  He was able to demonstrate that the disease was caused by a "vegetable parasite" or fungus; and that the growth of the fungus leads to death of the silkworm and the production of an infectious agent which can be transmitted by inoculation, contact or contaminated food.  He was even able to demonstrate that the infectious agent could be destroyed by certain chemicals.  In fact, Bassi demonstrated the GERM THEORY OF DISEASE.

- the date of these discoveries was 1833, although he didn't present his findings until 1834.

Louis Pasteur also was recruited to study the diseases of the silkworm, although not until around 1865.  Pasteur was able to isolate several different microorganisms from silkworms each of which caused diseases.  These included bacteria and protozoa and he also described a disease that we now know to be caused by a small RNA virus, which of course he could not identify.  Certainly one would suspect that the research Pasteur conducted on insect diseases aided in his efforts to understand vertebrate diseases.

 He also suggested using the protozoan against the grape phylloxera and recommended searching for a fungus that could infect these insects and which, once obtained, should be sprayed in infested vineyards.

The first scientific field test of microbial control was conducted by a Russian, Krassilstschik, who used the fungus Metarhizium anisopliae (Metchnikoff) against the sugar beet curculio, Cleonus punctiventris Germar. 

- 50-80% mortality in test plots.

- by 1891 a commercially produced product was available in France, another fungus, Beauveria sp.

- in the 1930's a bacterium, Bacillus thuringiensis, was tested and it became commercially available shortly thereafter.

Each category will be described in more detail:

(1). def'n and description.
(2). some examples of these organisms.
(3). what do you need to know to use successfully.
(4). some examples of introductions, case histories.

The Grape Phylloxera

- in 1863 grape phylloxera,Phylloxera vitifoliae, an insect native to North America, was discovered in Europe, both in England and in France.

Origin in Europe?

- possibly transported to England on ornamental Virginia creeper or possibly on infested American grapestocks which had been imported since1629.
- 1840's, American vines had been imported to France in an effort to combat powdery mildew--may have been the source of phylloxera.
- once the phylloxera was established and devastating native vines, the American vines continued to flourish - unfortunately the American grapes made poor wine -but perhaps pointed to a solution.
- 1873, Riley (Missouri state entomologist) arranged for the shipment of a predatory mite, Tyroglyphus phylloxera, to France - became established - minimal effect.
- on U.S. vines phylloxera has a complex life cycle (has 19 different forms); root and leaf feeding forms; can produce galls both above and below the ground; sexual and asexual reproduction both occur.
- on European vines the infestation is restricted to the root and only parthenogenesis is observed--population dynamics?
- on the U.S. plants galls and other deformities slow growth - increase in root diameter one response of resistant plants - insects tend to stay on the same plant for considerable period of time.
- on European plants the infestation kills the root; phylloxera abandon the deteriorating plant to attack and kill a new plant - increases spread and losses.

- in France a reward of 320,000 francs was offered to anyone who could solve the problem.
solution: initially grafted European vines onto eastern U.S. root stock -- nobody collected the reward.
- Europeans grafted various plants and tested a variety of rootstocks including (AxR #1), not particularily resistant to phylloxera and rejected for widespread use.

comment on current problem in U.S.

- phylloxera not native west of of the Rockies.
- the grape stocks (in California) were not native to U.S. but came from Europe via Mexico with padres of Roman Catholic Church -1524.
- native grapes grew abundantly east of the Rockies and had evolved under constant association with phylloxera.
- when wine industry expanded rapidly in California, a rootstock was selected for its growth characteristics in this location - without due consideration for phylloxera!!!! ---- selected AxR #1.
- eventually phylloxera introduced.
- results - guess.
- requires the replacement of all the rootstock in Napa and Sonoma counties at an estimated cost of 1 billion dollars.

- several excuses have been made including:
 i. people planted the wrong rootstocks - dishonest nurseries.
ii. a new phylloxera biotype, "B" now widespread and has adapted to AxR rootstock.

- French had stopped recommending AxR by the end of WWI; also discount biotypes because phylloxera adapts to feed on all rootstocks, a question of plant resistance.

- during this period one of the earliest chemical pesticides was developed; a mixture of lime and sulphur (Bordeaux mixture) had traditionally applied to grape vines that were accessible to the casual passerby with the intent of discouraging theft of grapes--apparently the insecticidal and antifungal properties of this mixture were observed--this led to the development of a mixture of copper sulphate and arsenic (Paris Green - Colorado Potato Beetle).

Lessons learned from grape phylloxera and other pest species.

- by late 1800's many entomologists were aware that a large proportion of the insect pests in any region were imported and the plea went forth in Canada for:

i. strict quarantine measures.
ii. importation for beneficial insects.