Concept of Pest & Pest Outbreak
Dr. Jamba Gyeltshen
19/8/2011
Content
1.1. Definition of pest
1.2. Types of pest
1.3. Pest outbreak
1.1. Definition of pest:
• Pest is a general term used to describe any
organism (usually insect or animal) that is
harmful to our health and properties including
crop and livestock. The term, in its broader
sense also includes micro-organisms, parasitic
plants and weeds.
1.2.1 Classification based on
morphological difference
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Insect pests
Mite pests
Micro-organisms (pathogens)
Nematodes
Vertebrate pests
Molluscs
Weeds & parasitic plants
1.2.2 Classification based on nature,
intensity or frequency of occurrence
• Regular pest: A pest that occurs every crop
season and causes yield losses.
• Sporadic pest/Occasional pest: A pest that is
irregular, occurs here and there or at random but
occasionally causes problems.
• Potential pest: A pest that could cause significant
economic loss if allowed to establish.
• Major pest: A more common and important pest
• Minor pest: A pest that is not causing huge
damage
1.3. Pest outbreak
• 1.3.1. Factors affecting natural insect
population
• The way that the numbers of an insect species
change represents the balance of birth and
deaths over a given time period.
Birth rate is influenced by
1. Weather and climate
2. the food quality received by the adults
3. the degree of crowding of the individuals.
Crowding affects birth rate partly through
affecting the quality of the food but also by
more direct influences such as stimulating
restlessness of individuals.
Death rate is influenced by
1. climate
2. natural enemies
3. diseases
4. crowding
• Crowding may lead to cannibalism or
starvation. Moreover, crowding may also lead
to emigration which, like death, leads to a
reduction in the number of individuals in an
area.
Mortality e.g. Frost,
storms
Directly
Natality
e.g. Fecundity,
development rate
CLIMATE
Indirectly
Growth and
condition of food
plant
Differential effect
on organism and
natural enemies
FACTORS
AFFECTING
INSECT
POPULATION
With natural
enemies
for own survival
COMPETITION
Within the species
e.g. Overcrowding,
starvation
With other species
e.g. For food,
oviposition sites
1.3.2. Causes of pest outbreak
1.
2.
3.
4.
5.
6.
7.
Favourable weather
Intensive cultivation and monoculture
Destruction of natural enemies
Destruction of natural habitat
Introduction of new crops
Accidental introduction of foreign pests
Use of pesticides
Favorable weather condition
• Direct effect: under favourable weather
conditions, birth rate is high and death rate
low.
• Indirect effect: a) through the improvement in
the growth and condition of food plants. b)
the differential effect. If the good weather and
climate favors the pest more than it favours
the natural enemies, it will increase the rate of
growth of the pest population
Intensive cultivation and monoculture
• Intensive cultivation means making rigorous
use of the cultivable land. Both intensive
cultivation and monoculture favour insect
pests. When land is intensively cultivated,
pests get a continuously supply of food and
natural enemies of pests are low or absent.
In an uncultivated land,
• individual plants of any one kind are often few
and scattered. Arriving insects are met by a
bewildering mixture of odour cues which
makes it much harder for them to locate their
host plants, and it is hard for overcrowded
population on one plant to spread to another;
large mortalities are likely to occur in the
process.
In a monoculture system
• plants have been specially selected and
managed so as to emerge, grow and mature in
synchrony.
• Provided that the pest arrives at the right
time, it will find a very large population of the
plants at a high level of suitability.
In a monoculture system
• Fertilizers and thinning are among the
management practices which maintain a high
plant quality suitable also for the rapid
development of pest infestations.
• Infestation spreads much more evenly, and
average densities can be very high before
emigration or other competition effects of
crowding cause significant reductions.
Destruction of natural habitat
• Agriculture generally involves destruction of
the natural areas including forests that are the
natural habitat of insects and natural enemies.
When the natural areas including forests are
encroached upon for cultivation, habitation or
industrial development, insects migrate to
fields.
Accidental introduction of pests
• When planting materials are brought into the
country, new pests may be accidentally
introduced. These new pests may have been
under suppression in its native place but in
the new place where natural enemies are
absent, it can multiply and buildup
population.
Use of insecticides
• When insecticides are used excessively, not only the
pests are killed but also the natural enemies of the
pests are wiped out. In the absence of natural enemies,
the surviving population of insect pests multiply rapidly
and reach epidemic proportions. Indiscriminate use of
pesticides also leads to development of resistance in
pests. This occurs as a result of killing the susceptible
genotypes and selecting the more resistant genotypes
at every pesticide application event. After several years
of using the same pesticide, there would come a time
when that particular pesticide will have no effect on
the pest because they have developed resistance to the
pesticide.