This document discusses screening techniques for legume pod borer resistance in cowpea. It describes two main techniques: field screening and bioassay screening. Field screening relies on natural pest infestation but has biases due to varying environmental conditions between experimental units. Bioassay screening uses controlled rearing of the pest and artificial infestation of cowpea plants to overcome the limitations of field screening. It allows for equal pest pressure and control of environmental factors. The document outlines methods for rearing the pest and artificially infesting plants, and recommends using dual choice arena tests and intact pod tests in bioassays to study different resistance mechanisms.

1. SCREENING FOR LEGUME POD
BORER RESISTANCE IN COWPEA

2. Introduction
• Africa’s economy is driven by agriculture, the sector generates one-
third of the national income
• Agriculture accounts for 70-80% of the labor force in the continent
• Cowpea is an important legume crop in sub-Saharan Africa
• It’s a good source of proteins, energy micro and macro nutrients
• There is low production due to so biotic and abiotic challenges like
pests, diseases, low soil fertility and climate change
• This causes high cost of production and low profits to the farmer

3. Introduction
• Legume pod borer (Maruca vitrata) is the most devastating insect of
cowpea
• It feeds on over 70 species in Fabaceae
• The pest is known to damage cowpea flowers, pods and tender leaves
• This damages have a direct implication on the yield and quality of the
cowpea and can cause total crop failure
• There have been efforts made by researchers to control the borer
• Research in legume pod borer resistant cowpea is geared more towards
breeding and selection of resistant cowpea

4. SCREENING TECHNIQUES
a) Field Screening
This method relies on natural infestation
Susceptible cowpea variety is planted two weeks before test cowpea
variety to increase pest pressure
Apply selective pesticide to reduce interference from other pests like
flower thrips that feed on same plant parts as LPB (Sodedji et al, 2020)
Recommended agronomic practices carried out except plant protection
measures (Mohammed B.S., 2013)
Assessment requires accuracy of measurements taken
Measurement of damage is taken on flowers, pods and seeds, they
provide most important assessment

5. Field screening
• This method has been adopted widely
• It has some biases. For instance, it is very hard to ensure equal
pressure in all experimental units.
• some of environmental conditions are not under control of the
researcher,
• Using this method one may fail to know truly resistant or susceptible
varieties due to escape

6. SCREENING TECHNIQUES
b) Bioassay method
It is used to overcome shortcomings in field screening method due to
low or unknown infestation levels
The pest are reared in controlled environment
Both cowpea and composite diets are used for this purpose
A cowpea wheat flour diet can be used (50g of flour as the main
ingredient)
Wang et al. (2013) developed artificial diet based on soybean flour and
wheat germ for rearing LPB
Traore et al. (2017) modified a commonly used diet to rear stem borer
by supplementing cowpea flour for rapid multiplication of LPB

7. SCREENING TECHNIQUES
Artificial infestation
One has to think of how to perform the inoculation of insect on the plant
and how many insects to use
10 eggs/plant were used on young plants which were at 5-7 shoot stage
and resistance was checked based on larval survival and level of damage
on flowers, flower buds and pods(Odekola et al, 2008)

8. SCREENING TECHNIQUES
b) Use of bioassay
Jackai (1991) proposed two complimentary bioassays to screen for LPB
resistance:
Dual choice arena test(DCAT) where fresh pods segments of both test
and control cowpea were exposed to LPB larvae. It provides feeding
index and preference ratio
DCAT helps study antixenosis mechanism of resistance
Intact pod test provides information on about insect response in a no-
choice situation

9. THANK YOU