BIOLOGICAL CONTROL

BIOLOGICAL CONTROL

The successful management of a pest by means of another living organism (parasitoids, predators and pathogens) that is encouraged and disseminated by man is called biological control. In such programme the natural enemies are introduced, encouraged, multiplied by artificial means and disseminated by man with his own efforts instead of leaving it to nature. The term biological control was first used by Smith in 1919 to signify the use of natural enemies to control insect pests.

Natural Control: The maintainance of population numbers within certain upper and lower limits by the action of a combination of abiotic and biotic factors as well as the characteristic of the species under consideration is called natural control.

History and development of biological control and classical examples of biological control

First use of insect predators was in 900AD, when Chinese citrus growers used red ant (Oecophylla  smaragdina) on the citrus trees to control citrus leaf chewing insects.

Year 1762 - ‘Mynah’ bird (Gracula religiosa) imported from India to Mauritius to control red locust (Nomadacris septemfasciata).

1770 - Bamboo runways between citrus trees for ants to control caterpillars.

1888 - First well planned and successful biological control attempt made

During 1888 citrus industry in California (USA) seriously threatened by cottony cushion scale, Icerya purdian. Chemical treatments not known at that time. Mr. C.V. Riley, a prominent entomologist suggested that the scale inset originated from Australia and natural enemy for the scale from Australia should be introduced into USA.Mr. Albert Koebele was sent to Australia. He found a beetle called Vedalia (Rodolia cardinalis) attacking and feeding on seeds. Vedalia beetle (Rodolia cardinalis) was imported in November 1888 into USA and allowed on scale infested trees. Within a year spectacular control of scale insect achieved. Even till date this beetle controls the scale insect. 

1898 - First introduction of natural enemy into India

1898 - A coccinellid beetle, Cryptolaemus montrouzieri was imported into India from Australia and released against coffee green scale, Cocus viridis. Even today it is effective against mealybugs in South India.

1920 - A parasitoid Aphelinus mali introduced from England into India to control Woolly aphid on Apple, Eriosoma lanigerum.

In 1960, a tachinid, Spogossia bezziana was introduced from Srilanka into India for control of Coconut black headed caterpillar.

Techniques in biological control:

Biological control practices involve three techniques viz., Introduction, Augmentation and Conservation.

1. Introduction or classical biological control: It is the deliberate introduction and establishment of natural enemies to a new locality where they did not occur or originate naturally. When natural enemies are successfully established, it usually continues to control the pest population.

      Pest – Cotton cushion scale, Icerya purchesi

      Predator-nVedalia beetle, Rodolia cardinalis

2. Augmentation: It is defined as the effort to increase population of natural enemies either by propagation and release or by environmental manipulation. It is the rearing and releasing of natural enemies to supplement the numbers of naturally occurring natural enemies. There are two approaches to augmentation.

a. Inoculative releases: Large number of individuals are released only once during  the season and natural enemies are expected to reproduce and increase its population for that growing season. Hence control is expected from the progeny and subsequent generations and not from the release itself.

b. Inundative releases: It involves mass multiplication and periodic release of natural enemies when pest populations approach damaging levels. Natural enemies are not expected to reproduce and increase in numbers. Control is achieved through the released individuals and additional releases are only made when pest populations approach damaging levels. In this case large numbrs of natural enemies are released to obtain rapid pest suppressions.

3. Conservation: It is defined as the actions to preserve and release of natural enemies by environmental manipulations or alter production practices to protect natural enemies that are already present in an area or non use of those pest control measures that destroy natural enemies.

Important conservation measures are

• Use selective insecticide which is safe to natural enemies.
• Avoidance of cultural practices which are harmful to natural enemies and use fauorable cultural practices
• Cultivation of varieties that favour colonization of natural enemies
• Providing alternate hosts for natural enemies.
• Preservation of inactive stages of natural enemies.
• Provide pollen and nectar for adult natural enemies

Parasite: A parasiteis an organism which is usually much smaller than its host and a single individual usually doesn’t kill the host. Parasite may complete their entire life cycle (eg. Lice) or may involve several host species. Or Parasite is one, which attaches itself to the body of the other living organism either externally or internally and gets nourishment and shelter at least for a shorter period if not for the entire life cycle. The organism, which is attacked by the parasites, is called hosts.

Parasitism: Is the phenomena of obtaining nourishment at the expense of the host to which the parasite is attached.

Parasitoid: is an insect parasite of an arthopod, parasitic only in immature stages,destroys its host in the process of development and free living as an adult.

      Eg: Braconid wasps

Qualities of a Successful Parasitoid in Biological Control Programme

A parasitoid should have the following qualities for its successful performance.

§              Should be adaptable to environmental conditions in the new locally

§              Should be able to survive in all habitats of the host

§    Should be specific to a particulars sp. of host or at least a narrowly limited range of hosts.

§              Should be able to multiply faster than the host

§              Should be having more fecundity

§              Life cycle must be shorter than that of the host

§              Should have high sex ratio

§              Should have good searching capacity for host

§              Should be amendable for mass multiplication in the labs

§              Should bring down host population within 3 years

§              There should be quick dispersal of the parasitoid in the locality

§              It Should be free from hyperparasitoids

SUCCESSFUL / CLASSICAL EXAMPLES OF BIOLOGICAL CONTROL

1.      1929-1930 - Rodolia cardinalis was obtained from California and Egypt and used for successful control of Icerya purchasi at Nilgris

2.      1940- Specific parasite Aphelinus mali was obtained from Punjab and used effectively against Erisoma lanigerum.

3.      1960 - Parasites Bracon brevicornis, Parasierola nephantidis, Trichospilus                 pupivora were used at 10:10:20adults/tree against coconut black head                  caterpillar.

4.      Egg parasitoid Trichogramma australicum against early shoot borer of       sugarcane.

5.      Cryptolaemus montrouzieri against grapevine mealy bug

6.      Chrysoperla carnea against aphids

7.      Gambusia fish against  mosquitoes

8.      Ichneumonid parasitoid Isotima javensis against top shoot borer of sugarcane.

9.      Ducks against army worm and striped bug in rice

Parasites can be grouped as furnished below

1. Depending upon the nature of host,

                                                              i.      Zoophagous - that attack animals (cattle pests)

                                                            ii.      Phytophagous - that attack plants (crop pests)

                                                          iii.      Entomophagous - that attack insects (parasites)

                                                          iv.      Entomophagous insects - parasitoids

II. Based on the specialization of the site of parasitisation

1.                  Ectoparasites: they attack its host from the outside of the body of the host. The mother parasite lays its eggs on the body of the host and after the eggs are hatched the larvae feed on the host by remaining outside only. Head louse; Epiricania melanolenca, Epipyrops sp. Sugarcane fly.

2.                  Endoparasites :they enters the body of the host and feeds from inside. The mother parasite either lays its eggs inside the tissues of the host or on the food material of the host to gain entry inside.

                     Eg. Braconids & Icheneumonids, Apanteles flavipes on jowar stemborer larvae.

III. Specialization based on the stage of the host

Eg.Host: Coconut black headed caterpillar, Opisina arenosella

TAMGESTT

                          i.      Egg parasite : Trichogramma australicum

                        ii.      Early larval parasite – Apanteles taragama

                      iii.      Mid larval parasite – (Micro) Bracon hebtor

                       iv.      Prepupal parasite – Gonizus nephantidis

                         v.      Prepupal parasite – Elasmus nephantidis

                       vi.      Pupal parasite –Stomatoceros sulcatiscutellum

Trichospilus pupivora, Testrastichus israeli,

IV. Depending upon the duration of attack

1. Transitory parasite :It is not permanent but transitory parasite which spends a few stages of its life in one host and other stages on some other species of hosts or as a free living organism.Eg. Braconids and Ichneumonids

2. Permanent parasite :

Which spends all the stages of its life on the same host.Eg. Head louse

V. Depending upon degree of parasitization

1. Obligatory parasites: Parasite, which can live only as a parasite and cannot live away from the host even for shorter period. Eg. Bird lice, Head louse.

2. Facultative parasite:Parasite, which can live away from the host at least for a shorter period Eg. Fleas.

VI. Depending upon the food habits

1. Polyphagous: develops on number of widely different host species Eg. Bracon sp. Apanteles sp on lepidopteran caterpillars

2. Oligophagous: which has very few hosts (more than one host) but all the hosts are closely related. Eg. Isotema javensis on sugarcane and sorghum borers.

3. Monophagous:which has only one host sp. and can’t survive in another sp. i.e. host specific. Eg. Gonizus nephantidis on Opisina aresosella

Kinds of Parasitism

1. Simple parasitism :Irrespective of number of eggs laid the parasitoid attacks the host only once. Eg. Apanteles taragamae on the larvae of Opisina arenosella, Goniozus nephantids

2. Super parasitism :phenomenon of parasitization of an individual host by more larvae of single species that can mature in the host. Eg. Apanteles glomeratus on Pieris brassica, Trichospilus pupivora on Opisina arenosella.

3. Multiple parasitism :Phenomenon of simultaneous parasitization of host individual by two or more different species of primary parasites at the same time. Eg:Trichogramma, Telenomous and Tetrastichus attack eggs of paddy stem borer Scirpophaga incertulas.

Super parasitism and multiple parasitisms are generally regarded as undesirable situations since much reproductive capacity is wasted

4. Hyper parasitism: When a parasite itself is parasitized by another parasite. Eg. Goniozus nephantidis is parasitized by Tetrastichus israeli, Most of the Bethylids and Braconids are hyper parasites.

Primary parasite:A parasite attacking an insect which itself is not a parasite (Beneficial

      to man.)

Secondary parasite:A hyperparasite attacking a primary parasite (Harmful to man )

Tertiary parasite: A hyperparasite attacking a secondary parasite ( Beneficial to man )

Quaternary parasite :A hyperparasite attacking tertiary parasite ( Harmful to man)

      A primary parasitoid becomes harmful in case of productive insects like silkworms, Bombyx mori and lac insect Kerria lacca.

Predators and Predatism

A predator is one which catches and devours smaller or more helpless creatures by killing them in getting a single meal. It is a free living organism through out its life, normally larger than prey and requires more than one prey to develop.

Insect predator qualities

i.                  A predator generally feeds on many different species of prey , thus being a generalist or polyphagous nature

ii.                  A predator is relatively large compared to its prey , which it seizes and devours quickly

iii.                  Typically individual predator consumes large number of prey in its life time

                                       Eg: A single coccinellid predator larva may consume hundreds of aphids

iv.                  Predators kill and consume their prey quickly , usually via extra oral digestion

v.                  Predators are very efficient in search of their prey and capacity for swift movements

vi.                  Predators develop separately from their prey and may live in the same habitat or adjacent habitats

vii.                  Structural adaptation with well developed sense organs to locate the prey

viii.                  Predator is carnivorous in both its immature and adult stages and feeds on the same  kind of prey in both the stages

ix.                  May have cryptic colourations and deceptive markings

                                      Eg. Preying mantids and Robber flies

                       

   Predatism

Based on the degree of use fullness to man, the predators are classified as on

  i.      Entirely predatory, Eg. lace wings, tiger beetles lady bird beetles except Henosepilachna genus

ii.      Mainly predator but occasionally harmful. Eg. Odonata and mantids occasionally attack honey bees

iii.      Mainly harmful but partly predatory. Eg. Cockroach feeds on termites. Adult blister beetles feed on flowers while the grubs predate on grass hopper eggs.

iv.      Mainly scavenging and partly predatory. Eg. Earwigs feed on dead decaying organic matter and also fly maggots. Both ways, it is helpful

v.      Variable feeding habits of predator, eg: Tettigonidae: omnivorous and carnivorous but damage crop by lying eggs.

vi.      Stinging predators. In this case, nests are constructed and stocked with prey, which have been stung and paralyzed by the mother insect on which the eggs are laid and then scaled up. Larvae emerging from the egg feed on paralyzed but not yet died prey. Eg. Spider wasps and wasps.

Differences Between predator and a parasite

Predator	Parasite
Mostly a generalized feeder excepting lady bird beetles and hover flies which show some specificity to pray	Exhibits host specialization and in many cases the range of host species attacked is very much limited
Very active in habits	Usually sluggish one the host is secured
Organs of low common sense organs and mouth parts are well develop	Not very well developed and some times reduced even, Ovipositor well developed and oviposition specialized
Stronger, larger and usually more intelligent than the prey	Smaller and not markedly more intelligent than the host
Habitat is in dependent of that of its prey	Habitat and environment is made and determined by that of the host
Life cycle long	Short
Attack on the prey is casual and not well planned	Planning is more evident
Seizes and devours the prey rapidly	Lives on or in the body of the host killing it slowly
Attack on prey is for obtaining food for the attacking predator itself, excepting in wasps which sting the caterpillars to paralyze the and provide them as food in the nest for the young	It is for provision of food for the off spring
A single predatory may attack several hosts in a short period	A parasite usually completes development in a single host in most cases

Predators

            Predators are bigger in size, kill the prey, free living throughout their life, and require more than one prey to complete development and adults and larvae feed upon similar insects.

Non-insect predators

Arachnids        - Spiders, Scorpions, mites

Fishes              - Gambusia affinis on mosquito larvae

Amphibians     - Frogs and toads (insectivorous)

Birds               - Ducks, owls (on rats), king crow, mynah (on larvae of    Helicoverpa)

Reptiles           - Lizards, snakes (rats)

Biological control of weeds with insects

Many insects feed upon unwanted weeds, just the same manner they do with cultivated plants. As they damage the noxious and menacing weeds, these insects are considered to be beneficial to man and called as weed killers. Successful eradication of certain weeds due to specific insects is achieved. Later certain insects are specifically employed against deleterious weeds and got rid of them. The classical example being prickly pear control with cochineal insect, Dactylopius tomentosusLantana, a troublesome weed was kept in check by the coccid, Orthezia insignis. Water hyacinth was controlled by bruchids, Neochetina eichhorniae and Neochetina bruchi

A successful weed killer

  i.            Should not itself be a pest of cultivated plants or later turn into a pest of cultivated crops.

ii.            Should be effective in damaging and controlling the weed

iii.            Should preferably be a borer or internal feeder of the weed and

iv.            Should be able to multiply in good numbers without being affected by parasitoids and predators.

In South Indian, Opuntia dilleni was wrongly introduced in 1780 in place O.  coccinellifera for cultivating commercial cochineal insect Dactylopius cocci, valued for its dye. For controllingOpuntia dilleni, the insect D. tomentosus was introduced from Srilanka in 1926 and within 2 years it gave effective control of O. dillenii. The prickly pear Opuntia inermis in Australia was kept under check by the moth borer Cactoblastis cactorum.

Control of water-hyacinth: Water-hyacinth is a free-floating fresh water plant. It impedes flow of irrigation water, interferes with pisciculture etc. and can be effectively controlled by two weevils namely Neochetina eichhorniae and N. bruchi andmite Orthogalumna terebrantis. Control of Parthenium hysterophorus by beetle Zygogramma bicolorata

Biotic agents used for control of weeds

Weed	Sc. Name	Biotic agent	Origin
Terrestrial weed
Prickly pear	Opuntia dillent	Dactylopius opuntiae(Dactylopidae: Hemiptera)	USA
Congress grass or carrot weed	Parthenium hysterophorus	Zygogramma bicolorata(Chrysomelidae:  Coleoptera)	Maxico
Lantana Weed	Lantana camera	Ophiomyia lantanae (Tortricidae: Lepidoptera) Teleonemia scrupulosa(Tingidae, Hemiptera)	Mexico
Siam weed	Chromolaena odorata	Pareuchaetes pseudoinsulata (Arctiidae: Lepidoptera)	West Indies
Crofton weed	Eupatorium adenophorum	Procecidochares utilis (Trypetidae;Diptera)	Mexico
Aquatic weed
Water fern	Salvinia molesta	Crylobagus singularis (Curculionidae: Coleoptera)	Australia
Water hyacinth	Eucharnia crassipes	Neochetina eichorniae (Curculionidae: Coleoptera)	USA

Advantages of Biological control

1.            Control of the insect is achieved in a wide area.

2.            The pest is hunted out and thus complete control over a large area is possible.

3.            Biological agent survives as long as the pest is prevalent and hence control is effective over longer periods.

4.            Though the initial cost is more it will be cheaper in a long run since after, few years of field, release, when it got established there may not be any necessity to propagate it further.

5.            Compatible with other methods

Disadvantages:

• It is a slow process and takes a long time.
• Natural enemies can not be restricted to particular pest, crop or areas.
• Presence alternate hosts delays the biological control
• If hyper parasites are there the effect of parasites is adversely affected.
• Expensive to develop and supply bioagents