Screening method is important in agriculture for the measurement of resistance.

1. Screening
Techniques for
Different Insect
Pests in Crop
Plants
SHWETA PATEL
Id no. 42537

2. Procedures in screening program
• Development of screening methods
• Sources of seeds for screening,
• Selection of seeds to begin the screening program,
• Multiplication of seeds for screening,
• Selecting a screening site,
• Sources of insects for screening,
• Sowing seed and maintaining plants,
• Management of field plots,
• Screening techniques.

3. Screening techniques for insects
(Based on plant damage)
1. Field screening :
• Using field populations- used in early stage of a plant
resistance program.
Problems-
• Populations may be either too low or too high or unevenly
distributed in space or time
• Year-to-year variation in population levels
• field population may be contaminated with non target pest
insect

4. Solutions –
• Trap crop
• Selective insecticides to eliminate the insect pest’s predators
and parasites
• Higher dose of nitrogenous fertilizer, closer spacing
• Placing light traps, pheromone traps, or kairomone traps
• Mass collection and release of indigenous insect population
• “Spreader rows”
using artificial infestation
• Mass rearing of test insects on natural host plants or artificial
diets.

5. 2. Field cage screening
• Limits emigration of the test insect
• Protection from predation and parasitism
Disadvantages-
• May cause abnormal environmental conditions
• Can alter plant growth, insect behavior
• Can cause foliar disease outbreak

6. 3. Greenhouse screening
Standard seedbox screening test-
• test cultivars are sown in wooden or metal flats filled with soil
• Test insects are uniformly distributed onto the seedlings
Modified seedbox screening test-
• plants are older at the time of infestation and the infestation rate is
lowered.
No-choice screening test
• extremely useful in the preliminary evaluation of resistance

7. 4. Laboratory screening
• A reliable and rapid method for confirming insect
resistance
• Only excised leaves and leaf disks are utilized
• It can be forced or free choice

8. 5. Bioassay techniques
• Used for Heliothis spp and pink boll worm in cotton
• Lyophilized square powder is incorporated in an
artificial diet
• By periodic observations, larval survival, larval
growth and percent pupation are recorded

9. Screening techniques for insects
(Based on insect responses to plants)
• Orientation
• Contact
• Settling
• Feeding
• Metabolism of ingested food, growth, adult longevity
• Fecundity and oviposition

10. 2. Feeding
Piercing and sucking insects- Damage by loss of sap from vascular
tissue, particularly phloem.
Screening techniques-
• Parafilm sachet technique- it is used for collection and
quantitative determination of honeydew
• Filter paper technique- the relative amount of feeding can be
assessed by measuring the area of honeydew excreted by them on
a filter paper disk.

11. Direct Measurement of Resistance
• Direct-feeding injury- tissue necrosis, fruit abscission, and stem
damage, quality of produce and defoliation
• Indirect feeding injury- plant growth, photosynthetic rates,
transpiration rates, ethylene production and respiratory rates
• Simulated feeding injury- feeding injury simulated by
mechanical defoliation
• Correlation of plant factors with insect resistance- e.g.,
concentrations of allelochemicals or density and size of
morphological structures

12. Indirect Measurements of Resistance
• Sampling insect populations- Shaking the plants, use of
sampling nets, use of traps, or actual counts
• Measurements of insect feeding and development- it is
measured in terms of amount of food consumed per unit body
weight day-1 or leaf area consumed, duration of larval/pupal
development, fecundity and insect survival.
• Measurements of insect behavior. by olfactrometers

13. Rice
Yellow stem borer: freshly hatched first instar larvae are
released @ one larva/tiller forty and Eighty days after
seedling to screen at vegetative and reproductive phase, resp.
Scale % dead hearts (D)
0 No damage (HR)
1 1-10% (R)
3 11-20% (MR)
5 21-30% (MS)
7 31-60% (MS)
9 ≥61% (HS)
Scale % White heads (D)
0 No damage (HR)
1 1-5% (R)
3 6-10% (MR)
5 11-15% (MS)
7 (16-25% (S)
9 ≥25% (HS)

14. Leaf folder (Cnaphalocrocis medinalis) :
Standard evaluation system has been developed for
screening for resistance to leaf folders are
Scale % leaf damage category
0 No damage Highly resistant
1 1-10 Resistant
3 11-30 Moderately resistant
5 31-50 Moderately susceptible
7 51-75 Susceptible
9 > 75 Highly susceptible
[IRRI,1998]

15. Gall midge(Orseolia oryzae )
Scale Plants with galls
0 More
1 < %
3 1-5 %
5 6-15 %
7 16-50 %
9 51-100 %
% of infested plants converted to 0-9 scale using SES

16. Sorghum
Shoot fly(Atherigona soccata):
Screening is done under natural field
condition and in cage
Seedling resistance is evaluated by counting
number of dead hearts.
Formation of deadhearts in
sorghum due to shootfly
damage.

17. Cotton :
Pink bollworm(Pectinophora gossypiella) : the resistance is determined based on
carryover population in leftover green bolls (Agarwal et al., 1973 and Sukhija et al.
,1983)
Jassid( Amrasca biguttula biguttula): The screening is being done on the basis of
injury grades. Under natural conditions, the population level is increased by
growing an infested row of an okra between the two cotton rows (Batra and Gupta,
1970)
Whitefly: screening is done under greenhouse conditions as free choice test. The
sampling of adults and eggs is done from three leaves of the upper and middle
canopy (Butter and Vir, 1990)

18. Sugarcane
Top borer(Scirpophaga excerptalis) : Evaluation is done by randomly
selected stalks of each of healthy and damaged canes and examined for
length, number of internodes, girth, weight and sugar concentration.
Shoot borer (Chilo infuscatellus) : based on the economic threshold
level of 15% incidence, the varieties may be graded as being less
susceptible (0-15%), moderately susceptible (15.1-30%) and highly
susceptible (above 30%).
Incidence (%) Category
00.0-10 Highly resistant
10.1-15 resistant
15.1-20 moderately resistant
20.1-25 moderately susceptible
25.1-50 susceptible
50.1 and above highly susceptible
Yadav (1985)

19. Sunflower
Leaf hopper : 5 random plants/row were selected and the
nymphal population on two leaves each from top, middle and
bottom of each plant were recorded.
Screening of leaf hopper injury (visual estimation scale)
0 Free from leaf hopper injury
1 Slight yellowing on edges of leaves upto 30%
2 Yellowing and curling upto 40% of leaves
3 Yellowing and curling upto 60% of leaves
4 Yellowing and curling upto 80% of leaves
5 Maximum yellowing, ‘cupping and curling of leaves
upto 100%

20. Head borer: Randomly 5 plants were selected, % seed damage head and the larval
number flower bud and flower head were recorded.
Damage by defoliators: Defoliation by ash weevil were recorded by 5 randomly
selected plants, counting the total and affected leaves.
Mean scale index
0 Highly resistant
0.1-1 resistant
1.1-2.5 Moderately resistant/tolerant
2.6-3.5 Susceptible
3.6-5.0 Highly susceptible

21. Rapeseed and mustard
Mustard aphid screening: Screening is done at the
flowering stage on the basis of the number of aphids
Number of aphids on
Grade Designation Stem Leaf Inflorescence
0 No aphid 0 0 0
I Very low >10 >10 >10
II Medium 10-20 10-50 10-20 flowering
normal
III High 20-100 50-200 20-100, sickly
inflorescence
IV Very high >100 >200 >100,
inflorescence
drying or dried
up

22. Pest
Susceptibility
(%)
Susceptibilit
y
rating
Category (1-9 scale)
100 1 Highly Resistant (HR)
75 to 99.9 2 Highly Resistant (HR)
50 to 74.9 3 Least Susceptible (LS)
25 to 49.9 4 Least Susceptible (LS)
10 to 24.9 5 Least Susceptible (LS)
–10 to 9.9 6 Moderately Susceptible (MS)
–25 to –9.9 7 Moderately Susceptible (MS)
–50 to –24.9 8 Highly Susceptible (HS)
–50 or less 9 Highly Susceptible (HS)

23. Pulses
Pigeon pea
Pod borer and pod fly: It will be desirable to conduct separate trails with a narrow
range of maturity for screening the lines against the pod borer and pod fly because
the time of flowering and maturity of cultivars may influence the levels of damage
caused by the insect pests.
(Lateef and Reed, 1980)

24. Scale (1-9) Description Category
1 No visible leaf feeding damage Highly resistant
2 Few pin holes on older leaves Resistant
3 Several shot-holes injury on a few leaves Resistant
4 Several shot-hole injuries common on several
leaves or small lesions
Moderately
resistant
5 Elongated lesions (> 2 cm long) on a few
leaves
Moderately
resistant
6 Elongated lesions on several leaves Susceptible
7 Several leaves with elongated lesions or
tattering
Susceptible
8 Most leaves with elongated lesions or
severe tattering
Highly
susceptible
Maize
Stem borer (Chilo partellus) : The most commonly used stem borer leaf
damage assessment is the 1−9 visual rating scale.

25. .
Development and standardization of screening
techniques is pre-requisite for effective resistance
breeding programme
Among several techniques, majority of screening is
carried out in field condition
Under field condition, resistance is measured
based on both plant damage and insect responses.

26. Thanks