Foreword - CCS HAU, Hisar

Number and size of samples
Factors such as ease of sampling, accessibility, and time and money available for
sampling should be considered. There are formulae for calculating sample size from the
variance, cost, etc. The purpose of the sample is important. Is it descriptive and qualitative,
or quantitative but only preliminary? Is it to give relative results or an exact economic
assessment on a valuable crop?
Type of sampling : Different types of sampling include randum, satisfied randum, vacuum
sequential, etc.
If the basic statistics of the pest or damage population are known, sequential sampling
is useful in deciding whether or not to control. Sample size depends on the population
found. Upper and lower limits are specified and sampling continued until the number of
pests found goes above or below those limits. The method is described by Onsager (1976).
Sampling techniques for some important crop pests
Some commonly used sampling techniques employed for some of the important crop
pests are summarized in Table 1. However, these may be suitably modified keeping in view
the objectives and degree of precision required.
Table 1. Sampling techniques for major insect pests of some crops
Crop Pest Economic threshold Method of sampling
1 2 3 4
Cotton Leaf hopper (jassid) 2 nymphs/leaf or yellowing Count leafhopper nymphs from underside
(Amrasca biguttula biguttula) and curling of 20% leaves of three fully developed leaves in the
from margins. upper canopy of each of 20 random plants
or count leaves showing yellowing
and curling from margins and healthy
leaves of 20 random plants in a field.
Whitefly (Bemisia tabaci) 6-8 adults/leaf Count whitefly adults as above.
Spotted bollworm (Earias spp.) 10% drooping shoots or Count drooping shoots and healthy shoots
5-10% infested fruiting of 25 random plants or examine all green
bodies fruiting bodies of the above plants for spotted
bollworm induced holes or damage.
Pink bollworm 5-10% infested fruiting Count rosetted flowers and examine all
(Pectinophora gossypiella) bodies fruiting bodies for damage by pink
bollworm on 25 random plants.
American bollworm 5-10% infested fruiting Examine all fruiting bodies of 20-25 random
(Helicoverpa armigera) bodies or one larva/2 plants. plants for the pest damage and also count
number of larvae present.
Aphid (Aphis gossypii) 10-15% infested plants Examine presence of aphid or its symptoms
on 20-25 random plants.
Thrips (Thrips tabaci) 10 thrips/leaf or 25% Same as for aphid
infested plants
Paddy a) At earing stage 5-15 insects/hill Select 5 micro-plots of 1m 2 each in a field
Green leafhopper (Nephotettix and shake vigorously plants in 5 hills/plot
nigropictus & N. virescens)/ or shake vigorously 25 random plants
white backed plant hopper and count leafhopper fallen on water.
(Sogatella furcifera)/brown
leafhopper (Nilaparvata lugens)
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