This third type of biological control involves the supplemental release
of natural enemies. Relatively few natural enemies may be released at a
critical time of the season (inoculative release) or literally millions
may be released (inundative release). Additionally, the cropping system
may be modified to favor or augment the natural enemies. This latter practice
is frequently referred to as habitat manipulation. An example of inoculative
release occurs in greenhouse production of several crops. Periodic releases
of the parasitoid, Encarsia formosa, are used to control greenhouse whitefly,
and the predaceous mite, Phytoseiulus persimilis, is used for control of
the two-spotted spider mite.
Lady beetles, lacewings, or parasitoids such as Trichogramma are frequently
released in large numbers (inundative release). Recommended release rates
for Trichogramma in vegetable or field crops range from 5,000 to 200,000
per acre per week depending on level of pest infestation. Similarly, entomopathogenic
nematodes are released at rates of millions and even billions per acre for
control of certain soil-dwelling insect pests. Habitat or environmental
manipulation is another form of augmentation. This tactic involves altering
the cropping system to augment or enhance the effectiveness of a natural
enemy. Many adult parasitoids and predators benefit from sources of nectar
and the protection provided by refuges such as hedgerows, cover crops, and
weedy borders. (Extracted from Cornell University web-site - see below)
Classical Biological Control
In many instances the complex of natural enemies associated with an insect
pest may be inadequate. This is especially evident when an insect pest
is accidentally introduced into a new geographic area without its associated
natural enemies. These introduced pests are referred to as exotics and
comprise about 40% of the insect pests in the United States. Examples
of introduced vegetable pests include the European corn borer, one of
the most destructive insects in North America.
To obtain the needed natural enemies, we turn to classical biological
control. This is the practice of importing, and releasing for establishment,
natural enemies to control an introduced (exotic) pest, although it is
also practiced against native insect pests. The first step in the process
is to determine the origin of the introduced pest and then collect appropriate
natural enemies (from that location or similar locations) associated with
the pest or closely related species. The natural enemy is then passed
through a rigorous quarantine process, to ensure that no unwanted organisms
(such as hyperparasitoids) are introduced, then reared, ideally in large
numbers, and released. Follow-up studies are conducted to determine if
the natural enemy successfully established at the site of release, and
to assess the long-term benefit of its presence.
There are many examples of successful classical biological control programs.
One of the earliest successes was with the cottony cushion scale, a pest
that was devastating the California citrus industry in the late 1800s.
A predatory insect, the vedalia beetle, and a parasitoid fly were introduced
from Australia. Within a few years the cottony cushion scale was completely
controlled by these introduced natural enemies. Damage from the alfalfa
weevil, a serious introduced pest of forage, was substantially reduced
by the introduction of several natural enemies. About 20 years after their
introduction, the alfalfa acreage treated for alfalfa weevil in the northeastern
United States was reduced by 75 percent. A small wasp, Trichogramma ostriniae,
introduced from China to help control the European corn borer, is a recent
example of a long history of classical biological control efforts for
this major pest.
Many classical biological control programs for insect pests and weeds
are under way across the United States and Canada. Classical biological
control is long lasting and inexpensive. Other than the initial costs
of collection, importation, and rearing, little expense is incurred. When
a natural enemy is successfully established it rarely requires additional
input and it continues to kill the pest with no direct help from humans
and at no cost.
Unfortunately, classical biological control does not always work. It is
usually most effective against exotic pests and less so against native
insect pests. The reasons for failure are often not known, but may include
the release of too few individuals, poor adaptation of the natural enemy
to environmental conditions at the release location, and lack of synchrony
between the life cycle of the natural enemy and host pest.
Conservation The conservation of natural enemies is probably the most
important and readily available biological control practice available
to growers. Natural enemies occur in all production systems, from the
backyard garden to the commercial field. They are adapted to the local
environment and to the target pest, and their conservation is generally
simple and cost-effective. With relatively little effort the activity
of these natural enemies can be observed. Lacewings, lady beetles, hover
fly larvae, and parasitized aphid mummies are almost always present in
aphid colonies. Fungus-infected adult flies are often common following
periods of high humidity. These natural controls are important and need
to be conserved and considered when making pest management decisions.
In many instances the importance of natural enemies has not been adequately
studied or does not become apparent until insecticide use is stopped or
reduced. Often the best we can do is to recognize that these factors are
present and minimize negative impacts on them. If an insecticide is needed,
every effort should be made to use a selective material in a selective
(Extracted from Cornell University web-site - see below)
The conservation of natural enemies is probably the most important and
readily available biological control practice available to growers. Natural
enemies occur in all production systems, from the backyard garden to the
commercial field. They are adapted to the local environment and to the
target pest, and their conservation is generally simple and cost-effective.
With relatively little effort the activity of these natural enemies can
be observed. Lacewings, lady beetles, hover fly larvae, and parasitized
aphid mummies are almost always present in aphid colonies. Fungus-infected
adult flies are often common following periods of high humidity. These
natural controls are important and need to be conserved and considered
when making pest management decisions. In many instances the importance
of natural enemies has not been adequately studied or does not become
apparent until insecticide use is stopped or reduced. Often the best we
can do is to recognize that these factors are present and minimize negative
impacts on them. If an insecticide is needed, every effort should be made
to use a selective material in a selective manner.
(Extracted from Cornell University web-site - see below)
Diatomaceous Earth is a desiccant and based on the fossil remains of diatoms,
in the form of a dust. It apparently works on ants, earwigs, woodlice,
and the like. These insects pick up the dust by electrostatic attraction
after it has been sprayed in their vicinity. The dust causes the insects
cuticle to crack so that the insect looses moisture and then dies within
a few days.
Code of Botanical Nomenclature
When I first started to write this section on 'Classification' I had followed
Britton & Rose and Backeberg as far as cactus names were concerned. This
was because that was more stable than the constant changing of names that
seemed to happen. Many nurseries, and even some academics did the same.
But we have to change because the International Code is becoming the standard.
Unfortunately, the 'change of names' previously alluded to is set to continue
because many plants have been wrongly named in the past, and are now rather
publicly changed at plenary sessions of a Congress. The old name, and
the person who got it wrong is recorded, together with the new name, and
All plant names should now be based on the International Code of Botanical
Nomenclature (ICBN) which first declares that botanical nomenclature is
independent of zoological and bacteriological nomenclature which each
have a similar 'International Code' structure of their own.
The purpose of ICBN is to promote standardisation of botanical names in
given plants. In addition, the intention is that each taxonomic group
has only one correct name. The term 'taxon', with the plural 'taxa', applies
throughout. The Code (ICBN) can only be changed by a plenary session of
an International Botanical Congress and the
'Vienna Code (2006)' is the current online one. The 'Vienna Code
(2006)' will supersede that when it is published.
A formal starting date for plant nomenclature has been proposed by ICBN
as 1st May 1753 when Linnaeus published his 'Species Plantarum'. Not as
Linnaeus's book 'Fundamenta Botanica' of 1736 in which he reformed all
the practices that had preceded 1736. In that book he established the
principle of 'genus' and 'species' as a descriptive binomen for not only
plants but all other living things.
To quote from the web-site-
"Every plant is treated as belonging to an indefinite number of taxa of
consecutively subordinate rank, among which species (species) is basic."
It goes on to say that the principal ranks of taxa in descending sequence
kingdom (regnum), division or phylum, class, order, family, genus, and
species (species). Thus each species is assignable to a genus, each genus
to a family etc. When a collector discovers a new plant, he deposits plant
material in a herbarium where it is named and becomes a 'type' or taxon
with that name.
The ICBN is accessable at http://www.bgbm.fu-berlin.de or key in 'ICBN'
Another alternative, on a similar spraying regime, is an insecticidal
soap based on fatty acids. These are not ordinary soaps as they contain
unsaturated, long-chain fatty acids (potassium or alkanolamine salts)
such as oleic acid which comes from animal fats, and also some plant fats.
These soaps work on contact and are only effective when wet. They dissolve
the cuticle of insects yet do not affect the cuticle of most plants. They
are biodegradable and can be used on aphids, mealy bugs, scale, spider
mites, white fly, and many other large and small insects, both indoors
and out. Available on-line and also at some garden centres.
The method takes the apical meristem, which is that translucent tip of
the root of a plant, and divides it, under a microscope, into the smallest
pieces. Actually, the apical dome of the root tip is used, and that is
only about 0.1mm in size.
The pieces are put into a nutrient culture medium and grown on. This they
do quite rapidly until they have grown to a size which can be divided
again. This process is repeated until the required number is reached.
Eventually, these meristemic sections are allowed to grow on in a culture
until first leaves and roots show, at which point they are treated, more
or less, as seedlings.
The prime advantage to commerce and industry is that meristem culture
produces plants which are virus and bacteria free. Another enormous advantage
is that it produces exact clones of the original plant. A exceptional
plant, which has received high awards at the RHS for example, can be mass-produced,
and in far greater quantities, than conventional methods would allow.
Exact copies are produced in terms of flower type, colour, and all the
other characteristics of the original plant. It is what has given the
world cheap, high quality orchids and other plants.
The composts are based on - (parts by volume)
a) good quality sterilised loam = 7
b) peat substitute (or peat) = 3
c) sand = 1
To each cubic metre is added:
d) 594g of limestone
or 1.2Kg of hoof & ho
rn 1.2Kg of superphosphate of lime
e) and 594g of potassium sulphate
All this is based on the original formula which was
f) 1lb of groung limestone
g) 1lb of potassium sulphate
h) 2lb of hoof & horn
i) 2lb of superphosphate of lime.
per cubic yard.
It is said that the original formula was JI-1 and
that JI-2 has twice as much fertiliser, and
that JI-3 has three times as much.
JI Seed Compost
j) 2 parts (by volume) of sterilised loam
k) 1 part of peat
l) 1 part of sand
To each cubic metre is added -
m) 1.2Kg (2lb) of superphosphate of lime
n) 594g (1lb) of ground limestone
The whole mixture has to be quite fine so that seed can make good contact.
First requirement is that it be free-draining and able to function in
without causing damping-off. It may be suitable for some succulents, but
These composts typically comprise -
50% of sand
To each cubic metre is added
4.4Kg of dolomitic lime
1.5Kg of hoof & horn or dried blood, superphosphate of lime, calcium carbonate
148g (4oz) each of potassium nitrate and potassium sulphate.
They say that because cutting composts are low in nutrients, cuttings
need to be fed
CITES - Convention on International Trade in Endangered Species of Wild Flora
IAPT - International Association for Plant Taxonomy
ICBN - International Code of Botanical Nomenclature
IOS - International Organisation for Succulent Plant Study
IPNI - International Plant Names Index
IUCN - International Union for the Conservation of
Nature and Natural Resources
RBGE - Royal Botanic Gardens Edinburgh
WCMC - World Conservation Monitoring Centre
WTMU - Wildlife Trade Monitoring Unit
An over-simplified explanation is that pH is 'potential Hydrogen ions'.
More precisely, it is a measure of the range between high acidity and high
alkalinity in soils. This measure ranges from unity (=1) to 14, with 7 regarded
as neutral. This can be explained as follows.
When hydrogen(H+) and hydroxyl(OH-) ions are in equal
numbers they neutralise each other. This occurs at 0.000,0001 g/litre, or
10-7gH+ from which the figure of 7 comes. By the same
reasoning a pH of 1, or 0.1gH+ is very acid. Conversely, a strongly
alkaline solution at pH=14 is equivalent to 0.000,000.000.0001gH+
or 10-14gH+. It can therefore be seen that an apparently
small change in acidity/alkalinity numerically represents quite a large
Physiologically, pH is important because it affects the availability of
essential elements in the soil, and is critical in the metabolism of plants
on either side of pH7. It (pH) affects how a plant takes up two of the most
important primary nutrients, nitrogen, and phosphorus. Soil pH does not
actually control 'nitrogen' (N), rather it affects the activity level of
the microbes which do the work. High pH causes nitrogen loss in other ways.
The position with phosphorus is more serious. The availability of P is at
a maximum between pH5.5 and 7.5 At pH5.5 and below P gets 'locked up' and
is no longer available. At pH above 7.5 an excess of calcium (lime) can
decrease the availability of P. Below pH6.5 manganese can reach a toxic
level for some sensitive plants. Micronutrients are directly influenced
by pH. In some cases availability increases, in others it decreases.
There is an easy way of testing this outside a plant physiology facility.
A kit seems to be a suitable solution. They are very easy to use. Take a
sample of compost - add some water - add a powder - shake well - then watch
the colour develop. Compare that to a chart and there you have it. They
even tell you how to adjust your pH. Such a test will not give you laboratory
accuracy, which would be to one-tenth of a pH, but it tells you enough.
See illustrations of kits.
There are about seven different types of social wasp in Britain, as well
as a large number of solitary ones. In addition there are the Chalcid
wasps which we employ in the parasitoid mode in Biological Control.
The seven social wasps in Britain are the Common Wasp (Vespula vulgaris),
the German Wasp, (Vespula germanica), the Norwegian Wasp (Vespula norvegica),
the Tree Wasp, ( Vespula sylvestris), the Red Wasp (Vespula rubra), the
Cuckoo Wasp (Vespula austriaca), and the Hornet (Vespa crabra). All of
them may hunt in your garden but telling which is which is difficult because
identification is mainly based on facial patterns. The Hornet is recognisable
as bigger and is a brownish colour.
The one we see most often is the Common Wasp which is reputed to build
nests in holes in the ground, as also does the German Wasp and the Red
Wasp. They use rabbit burrows, mouse holes, or any convenient cavity.
In my experience, nests in the ground are not common because it is usually
too wet. Most 'bikes', as nests are called, are located in buildings,
and most commonly in the eaves of houses. Residents then have to get the
authorities to remove them. The Tree Wasp and the Norwegian Wasp, both
of which may hunt in your garden, build a nest in trees and bushes, and
they can be seen hanging from branches. The Cuckoo Wasp is different in
a number of ways. Firstly, although a social wasp in a sense, it has no
workers, and lays its eggs in the nest of Red Wasps. The Hornet builds
in a hole in a tree.
A young, fertilised Common Wasp queen, who has over-wintered, starts the
nest as a small umbrella-like structure. She lays some 10 to 20 eggs from
which worker larvae hatch. She feeds them until they pupate, after which
they do the bulk of the work of building the colony and feeding future
broods. On one occasion the author found such a structure suspended from
the roof of a shed. This he removed when the wasp was away collecting
more wood shavings, and it was quite comical to see the way the wasp reacted
when it could not find the umbrella. Anyway, it did not come back to try
Wasp nests usually comprise seven horizontal layers like a block of flats.
They are made of wood shavings held together by saliva as wasps cannot
produce wax (and therefore combs) as bees do. Another difference between
bees and wasps is that bees feed their larvae on nectar and pollen, whereas
wasps feed their larvae on protein (other insects, meat, even carrion). Yet
another difference between bees and wasps is that bees are hairy, from whence
their colour comes, and wasps are not.
The other major group of wasps, just as useful to gardeners, are the solitary
wasps. There are two major kinds - the 'digger' wasps, and the 'potter'
wasps. The difference is that diggers dig a hole in a dry sandy place,
place one or two paralysed caterpillars in it, lay an egg, then seal up
the hole. The larva hatches, feeds, pupates, and eventually digs its way
The 'potters' build a small pot, like a Grecian urn, attached to a plant,
shrub, and the like. Otherwise, it does the same as the 'digger', even
sealing up the pot.
There is yet another type of solitary wasp which superficially looks like
a social one. but is actually a spider hunter. It can be recognised because it folds
its wings flat, whereas the other wasps fold their wings along the length
of their bodies.
Chalcid Wasps (some 1,500 known species) are mostly tiny, and less tham
3mm in length. This group includes the parasitoids we employ in Biological
The author cannot resist including another useful insect, also in the
Order Hymenoptera, the Ichneumon Fly; they, too, are parasitoid. They
deposit an egg via an ovipositor, but at least one of them can do this
through wood, after it detects a caterpillar. Others can do the same thing
through the stem of a plant without actually seeing their prey. They must
detect them by the noise they make.
Although wasps are generally not aggressive, unless under threat individually
or collectively, there is always the possibility of being stung. This
is especially so in the autumn. Unfortunately, some people may be allergic
to the proteins which enter the bloodstream on such occasions. As Paisley
University point out in their web-site, this can cause anaphylactic shock
which can be severe and even fatal. They go on to recommend immediate
medical treatment on such occasions.
1 - All American pictures came from http://pdphoto.org and are public domain
- an excellent site worth looking at.
2 - Ladybird on 'Biological Control' courtesy of Henry Doubleday Research
3 - Cryptolaemus larva and Lacewing pictures from Wiki-pedia.org
4 - Augmentation, Classical Biological Control, and Conservation paragraphs
from Biological Control - Cornell University, Weeden, Shelton, Li, Hoffman
NOTE: the webmaster has acknowledged as best he could and consulted where
possible. If anything is unsatisfactory it will be put right - let us know
via the email link on the Contacts page.