Insect Pests of Vegetable, Ornamental and Spice Crops (2+1)

Sampling Techniques

Lecture 5: Sampling Techniques

COMMON SAMPLING TECHNIQUES:

• Insitu count
• Knock down (By jarring, by chemicals, by heating)
• Netting
• Sweep netting
• Vacuum netting
• Aerial netting
• Trapping
• Light trap
• Bait trap
• Pheromone trap
• Malaise trap
• Suction trap
• Window trap
• Water trap
• Sticky trap
• Pitfall trap
• Mark, release and recapture technique
• Sequential sampling

Population estimates:

• Absolute estimates
• Absolute estimates (number per ground surface area e.g. per hectare or acre or 1 m²)
• Population intensity (per habitat unit e.g. leaf, plant, etc)
• Basic population estimates (intermediate between above two e.g. per 5 cm of stem)
• Relative estimates (don’t give definite number per unit area )
• Population indices (insects themselves are not counted but their products)

Criteria of estimates:

• The estimates must be evaluated for:

• Fidelity: accuracy with which estimates follow the actual number in the population.
• Precision: It is the reproducibility of the results and measures the degree of error
• Cost: Cost is very important. Any estimates having great fidelity and precision will be of no use until and unless it is cost effective.

Parameters of sampling programme:

• Insect stage to be sampled
• Number of sampling units
• Time of sample
• Pattern of sampling
• Types of sampling

Sampling unit:

• The size should be such that every unit of the universe should have the chance of selection.
• Sampling unit must be easily delineated in the field
• Sampling unit should be of such that it provides a reasonable balance between precision and cost

Number of samples:

N = [(t x s)/ (d x m)] ²

Where
N = no. of sampling units required,
t = student ‘t’ value
s = standard deviation
d = precision (RV) expressed as decimal
m = mean density

Pattern of sampling:

Random, diagonal, double diagonal, zigzag diamond, ‘W’ pattern, micro plot, ‘U’ pattern etc.

Types of sampling:

• Random sampling
• Stratified random sampling
• Systematic sampling
• Sequential sampling