Contents - Faperta

50 Biotechnological Approaches for Pest Management and Ecological Sustainability
FIGURE 3.4 Screening for resistance to spotted stem borer, Chilo partellus in sorghum. (A) Rearing stem borer
larvae on artifi cial diet, and (B) infestation of sorghum seedlings using Bazooka applicator.
(CIMMYT) for infesting the maize plants with the neonate larvae (Mihm, 1982). This technique
has been used effectively with several insect species (Mihm, 1982, 1983, 1985; Smith,
Khan, and Pathak, 1994). The Bazooka applicator has been modifi ed at the International
Crop Reseach Institute for the Semi-Arid Tropics (ICRISAT) to infest a large number of
sorghum genotypes with neonate larvae of spotted stem borer, C. partellus (Sharma et al.,
1992) (Figure 3.4). The larvae can be mixed with a carrier (corn cob grits, poppy seed, or any
other lightweight material, such as foxtail and fi nger millet seed) in such a manner that
each stroke of the Bazooka applicator releases known numbers of larvae on each plant
(generally 5 to 10 larvae per plant). The larval density can be manipulated by changing the
ratio between the numbers of larvae and the amount of carrier used.
The Bazooka applicator is quite effi cient for infesting a large number of plants under
fi eld conditions. The applicator should be standardized to deliver a uniform number of
larvae to distinguish between the resistant and susceptible plants. While infesting the
plants, the Bazooka should be rotated constantly to ensure that the larvae are distributed
uniformly in the carrier. Care should be taken that the neonate larvae are not killed due
to abrasive action of the carrier. Infestations should be carried out early in the morning or
late in the evenings. If there is heavy rainfall immediately after infestation, it is important
to repeat the infestation or check the plants for feeding symptoms, and re-infest the plants
that do not show any signs of insect feeding. Field infestation should be carried out at the
most susceptible stage of the crop. In cereal crops, it may be necessary to infest the crop
when there is no excess water in the leaf whorls. However, in cotton, grain legumes, and
vegetable crops, which do not have leaf whorls or distinct sites where the larvae can be
released, it may be useful to infest the crop after the rain or when there is enough morning
dew. The crop can also be sprayed with water before infestation. The larvae should be
dispensed into the leaf whorls of cereals, into the ears of sorghum, silks in corn, and the
infl orescence in food legumes and cotton. The following protocol may be followed for
evaluation of the test material under artifi cial infestation.
• Raise the crop in the fi eld, and do not apply any insecticides, except to control nontarget
insects with selective insecticides. Space the insect infestation and insecticide
application so that there is no effect of the insecticide on the target insect.