Pest Forecasting, Biology tutorial


In agriculture, substantial losses in crop produce take place due to the infestation of different pests and diseases. These losses can be decreased to a great extent when their occurrence is recognized in advance so that timely remedial measures can be taken. Therefore, there is as well a requirement to build up forewarning systems that can give advance information for outbreak of pests/diseases attack so that protection evaluates can be implemented prior to the actual onset of the damage.

Pest Monitoring:

Monitoring phytophagous insects and their natural enemies is a basic tool in IPM - for taking the management decision.  


  • Estimation of changes in the insect distribution and plenty. 
  • Information regarding insects, life-history 
  • Affect of biotic and abiotic factors on the pest population 

Pest Surveillance:

Signifies to the constant watch on the population dynamics of pests, its incidence and damage on each and every crop at fixed intervals to forewarn the farmers to take up timely crop protection measures. 

Three fundamental components of pest surveillance are as follows:

Determination of: 

  • The level of incidence of pest species.
  • The loss caused due to the incidence 
  • The economic remuneration, the control will offer 

Objectives of Pest Surveillance: 

  • To identify existing and latest pest species.
  • To evaluate pest population and damage at various growth phase of crop. 
  • To study the affect of weather parameters on pest 
  • To study the changing pest status (that is, Minor to major) 
  • To evaluate natural enemies and their affect on pests 
  • Effect of latest cropping pattern and varieties on the pest.

Pest Forecasting:  

Forecasting of pest incidence or outbreak based on the information attained from the pest surveillance. 


  • Predicting the pest outbreak that requires control measure.
  • Appropriate phase at which control measure provides maximum protection.   

Two kinds of pest forecasting:

a) Short term forecasting: Mainly based on 1 or 2 seasons. 

b) Long term forecasting: Mainly based on the influence of weather parameters on the pest.

Precise forecasting of pest attacks helps control program to be efficient. It mainly based on the established relationship between the given factors:

  • Phase of growth of the crop.
  • Phase of the growth of the pest.
  • Ecological factors.

Survey of pest species:  

It is basically conducted to study the profusion of the pest species. There are two kinds of survey:

1) Roving survey:

  • Evaluation of pest population or damage from arbitrarily chosen spots representing bigger region. 
  • Big area surveyed in a short time period.
  • Gives information on pest level over big area   

2) Fixed plot survey:

Evaluation of the pest population or damage from a fixed plot chosen in a field. The data on pest population or damage recorded periodic from sowing till harvest. Example: 1 sq.m. plots arbitrarily chosen from 5 spots in one acre of crop area in case of rice. From each plot 10 plants chosen at arbitrary. Net tillers and tillers influenced by stem borer in such 10 plants counted. Total leaves and number influenced through leaf folder noticed. Damage expressed as percent damaged tillers or leaves. The population of BPH from all tillers in 10 plants noticed and deduced as number or tiller.   

Sampling Techniques:

Absolute sampling: Mainly used to count all the pests taking place in a plot. 

Relative sampling: To calculate pest in terms of certain values that can be compared over time and space example: Light trap catch and Pheromone trap.

Methods of sampling

a) In situ counts: Visual observation on the number of insects on plant canopy (that is, either whole plot or arbitrarily chosen plot)  

b) Knock down (Sudden trap): Gathering insects from a region through eliminating from crop and counting.

c) Netting: Utilization of sweep net for hoppers, odonates and grasshopper.

d) Narcotized collection: Quick moving insect's anaesthetized and counter.

e) Trapping:

  • Light trap: Phototropic insects 
  • Pheromone trap: Species specific 
  • Sticky trap: Sucking insects 
  • Bait trap - Sorghum shoot fly - Fishmeal trap 
  • Emergence trap: For soil insects  

f) Crop samples: Parts of plant eliminated and pest counted example: Bollworms 

Stage of Sampling:

  • Generally most injurious phase counted. 
  • At times egg masses counted-Practical considerations.
  • Hoppers-Nymphs and adult counted 

Sample Size

  • Distinct by nature of pest and crop 
  • Bigger sample size provides accurate outcomes 

Decision Making:

  • Population or damage evaluated from the crop. 
  • Compared by means of ETL and EIL 
  • If pest level crosses ETL, control measure has to be taken to save pest from the reducing EIL. 

Economic Injury Level

  • Stated as the lowest population density which will cause the economic damage. 
  • As well stated as a critical density where the loss caused due to the pest equivalents the cost of the control measure.

EIL = C / (V x I x D x K)



EIL = Economic injury level in insects or production (or) insects/ha 

C = Cost of the management activity per unit of production (Rs./ha) 

V = Market value per unit of yield or product (Rs./tonne) 

I = Crop injury per insect (Per cent defoliation/insect) 

D = Damage or yield loss per unit of injury (Tonne loss/percent defoliation) 

K = Proportionate reduction in the injury from pesticide use Economic threshold level (ETL) or Action threshold 

  • ETL is stated as the pest density at which control measures must be applied to prevent the rising pest population from reaching the Economic Injury Level (EIL).
  • ETL shows pest density lower than EIL to let time for initiation of the control measure.

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