Contents - Faperta

68 Biotechnological Approaches for Pest Management and Ecological Sustainability
Host plant resistance to insects can be measured in terms of eggs laid or relative preference
for egg laying by the females as in H. virescens on cotton (Lukefahr, Haughtaling, and Graham,
1971; Robinson, Wolfonbarger, and Doday, 1980); H. zea in tomato (Gosenza and Green, 1979)
and maize (Widstrom, McMillian, and Wiseman, 1979); H. armigera in soybean (N. Panda and
Daugherty, 1975), chickpea (Cowgill and Lateef, 1996), pigeonpea (Sharma et al., 2005a), and
cotton (Venugopal Rao, Tirumala Rao, and Reddy, 1991); and A. soccata in sorghum (Sharma
et al., 1992). It is important to record egg laying during the most susceptible stage of the crop
and just before egg hatching, for example, at the fl owering stage in cotton, chickpea, and
pigeonpea for H. armigera, and at the seedling stage for sorghum shoot fl y, A. soccata.
Measurements of Yield and Quality
Yield reduction measures direct insect feeding injury to plants. Measurements of quality of
produce can also be used to measure the effect of insect damage in sorghum, tomato, seed
cotton, etc. For example, head bug, C. angustatus, damage in sorghum during grain development
affects both grain quality and seedling emergence (Sharma, Soman, and Subramanian,
1995). The test entries can be planted under protected and unprotected conditions, and percentage
reduction in grain yield under unprotected conditions can be used as an index of
relative susceptibility or resistance to insects. This method also takes into account the tolerance
or recovery component of resistance, and the stability of resistance across seasons and
locations. Different levels of insect infestation can also be created using different spray
regimes or through artifi cial infestation. Genotypes with high yield and low insect damage
and regression coeffi cients are selected in comparison to the susceptible genotypes.
Measurements of Insect Survival and Development
Effects of antibiosis on insect survival and development are expressed in terms of larval
mortality, decreased larval and pupal weights, prolonged larval and pupal development
period, failure to pupate, and reduced fecundity and egg viability. Insect survival and
development can be measured to assess plant resistance to insects if antibiosis is the principal
component of resistance. Effects of plant resistance on survival and development are
also measured in terms of amount of food consumed per unit of body weight per day and
food utilization (Beck and Reese, 1976). Measurement of feces production (Kasting and
McGinnis, 1962) or honeydew production (Paguia, Pathak, and Heinrichs, 1980; Pathak,
Saxena, and Heinrichs, 1982) can also be used to assess food utilization and antibiosis
mechanism of resistance to insects. Antibiosis effects are also expressed in terms of weight
and size of insects, sex ratio, and proportion of insects entering into diapause. Plant extracts
or specifi c chemicals that confer resistance to insects can also be bioassayed to determine
the levels of resistance to insects in different crops. These can range from simple antifeedant
or phago-stimulant tests to sophisticated behavioral and metabolic effects on insects.
These assays normally include presenting plant fractions or chemicals to the test insects
on host or nonhost tissue or substrates by surface coating or impregnation, inert substrates
such as fi lter paper, glass fi ber discs, or incorporation into artifi cial diets.
Consumption and Utilization of Food
Several indices of consumption and utilization of food can be used to determine the level
of plant resistance to insects (Waldbauer, 1968). Effects of plant resistance on insect feeding
and development are measured in terms of amount of food consumed per unit of body