Contents - Faperta

3
Evaluation of Transgenic Plants and Mapping
Populations for Resistance to Insect Pests
Introduction
Because of the development of insect resistance to insecticides, adverse effects of insecticides
on natural enemies, and environmental pollution, there has been a renewed interest
in the development of insect-resistant cultivars for pest management (N. Panda and Khush,
1995; Sharma and Ortiz, 2002; Smith, 2005). Many crop species possess genetic variation,
which can be exploited to produce varieties that are less susceptible to insect pests.
However, the development of varieties resistant to insects has not been as rapid as for disease
resistance. Slow progress in developing insect-resistant cultivars has been due mainly
to the diffi culties involved in ensuring adequate insect infestation for resistance screening
in addition to low levels of resistance to certain insect species in the cultivated germplasm.
Under natural conditions, the insect infestation is either too low or too high and, as a
result, it becomes diffi cult to make a meaningful selection. Therefore, it is important to
develop techniques to screen for resistance to insect pests under optimum levels of infestation
and under similar environmental conditions. Insects reared on artifi cial diets can be
used to test the material under uniform infestation. However, insect-rearing programs are
expensive, technology development requires several years, and may not produce the
behavioral or metabolic equivalent of an insect population in nature.
Although screening under artifi cial infestation is a necessity for most insect pests, it may
not be an absolute requirement for insects that occur in epidemic proportions over years
or are endemic to particular areas, for example, cotton bollworms, Pectinophora gossypiella
(Saunders), Heliothis virescens (F.), Helicoverpa armigera (Hubner), and Earias vittella (Fab.),
and jassids, Amrasca biguttula biguttula (Ishida) in cotton; aphids, Lipaphis erysimi (Kalt.) and
Brevicoryne brassicae L. in cruciferous crops; pod borer, H. armigera in pigeonpea and chickpea;
corn earworm, Helicoverpa zea (Boddie) in maize; and shoot fl y, Atherigona soccata
(Rondani) and sorghum midge, Stenodiplosis sorghicola (Coquillett) in sorghum. There is
a need to refi ne techniques to screen for resistance to insect pests in several crops, and