USE OF LIFE TABLES IN INSECT PEST MANAGEMENT

• Submitted to:

Dr. vv Belavadi

Prof. Agril.Entomology

G.K.V.K Bengaluru

• Submitted By:

Chidananda.R

PALB-4098

DEFINITION

• Deevey(1947) “is a concise summary of certain vital statistics of a population, whose members start life together.

Or • A ‘life table’ is a kind of “bookkeeping system”

that ecologists often use to keep track of stage specific mortality in the populations they study.

• A table describes for the successive age intervals the number of deaths, remaining survivors, rate of mortality and expectation of further life.

• To create life table an ecologist follow the life history of many individuals in a population. Keeping a track of how many offspring each female produces, when each one dies and what caused its death.

• After amassing data from different populations, different years and different environment conditions, the ecologist summarizes this data by calculating average mortality within each developmental stages .

ROLE OF LIFE TABLES :

• Study of factors to determine the need to the need to modify the life system of pest with a view to reducing its number below ETL.

• Study of applied ecology which involves application of biological knowledge for achieving desired populations.

• Determining the key mortality factor and predicting the appearance in future.

• Dividing pest control procedures that suits the available technology compatible with the economic and environment quality requirement .

• ETL gives for timing application of need based application of insecticides. Estimation of intensity of pest population.

Importance of life tables:

•  Life tables describes for the successive age intervals the deaths, remaining survivor, rate of mortality and expectation of further life.

• Life table provides an important tool in understanding their life cycles.

• By this technique we can determine the mechanical relationship of various environmental factors and find out the key factor that accounts for large part of the change in population size.

• Especially useful approach in entomology where developmental stage are discrete and mortality rates may vary widely from one life stage to other.

• To know when population suffers high mortality, this is usually the time when it is most vulnerable.

Life tables are two types

•  a) age-specific LT or horizontal LT :

It is based on the fate of a real cohort, the individuals belonging to a single generation. The population may be stationary or fluctuating.

• b) time-specific LT or vertical LT:

It is based on the fate of a imaginary cohort found by determining the age structure, where there is a considerable overlapping generations. Age determination is a pre-requisite for time-specific LT. 

For preparing a life table for the natural population of an insect, the following

columns are required.• B = age interval at which the sample was

taken in units of time (days, weeks etc) • lx = Number surviving at the beginning of

age class ‘x’ (usually out of 1000 born• dx = Number dying during at age interval

stated in the ‘x’ column.• Dfx =The mortality factor responsible for

‘dx’. • 100qx = percentage mortality. Sx = survival

rate within the age interval ‘x’. 

Ex : In a hypothetical insect population, an average female will lay 200 eggs before she dies. Half of the eggs (on average) will be consumed by predators, 90% of the larvae will die from parasitisation and 3/5th of the pupae will freeze to death in winter. :

Developmental stage

Number alive

mortality factor

Number dying

% mortality

Egg 200 Predation 100 50

larva 100 parasitism 90 90

pupa 10 freezing 06 60

Causes of mortality :

• Low vitality (by envi. Factors ). • Ageing. • Accidents. • Physiochemical conditions (temperature). • Natural enemies. (predators, parasitoids,

pathogens) .• Shortage of food. • Shelter.

Applications of life tables:

• The weakest link in the life cycle can be determined and made use of to control pests.

• The effect of most effective biotic factors

causing death of the pest can found out and used effectively. 

• Field life table studies on natural enemies can help in determining the cause of their failure in field information can help to find out the best release techniques.

• Field life table studies predator can help in identifying their natural enemies which can be manipulated to exploit maximum potential of predators.

• Based on survivorship curves one can operate control measures when the mortality factors operating slow and thus can obtain economic results.

• It provides useful information on their mortality factors, information thus obtained can be incorporated in mass production techniques and make it more efficient.

•

• Studies on pest and natural enemies may provide exact time of release of predator and parasitoid and utilize them to their best potential.

• Life table studies on the weeds can yield information on the most effective natural enemies which in turn can help to make decision on import, colonization of weed insects or weed pathogen.

Conclusion•  A ll the ‘lx’ and ‘dx’ values in the life table

indicate the density of individuals per unit of the host or habitat. Life tables have to be prepared for different populations of the same spp throughout its range of occurrence to have a representative view. Measurements have to be made on density, mortality and associated factors in different parts of the habitat.

Thank you