RA 00110.pdf - OAR@ICRISAT

Host-Plant Resistance to Insect Pests in Pearl Millet
(Resistance des plantes-hotes aux insectes ravageurs du mil)
H.C. Sharma
Entomologist, Sorghum Group, ICRISAT, Patancheru, Andhra Pradesh 502 324, India
Nearly 500 insect and other animal pests have been reported to feed on pearl millet, of which a few are serious
or potential pests on a global or regional scale. Host-plant resistance is the most appropriate tool to keep insect
populations below economic threshold levels. Resistance screening and breeding programs may be undertaken
against pearl millet insects such as shoot fly (Atherigona approximata Malloch), stem borers {Acigona
ignefusalis Hmps., Chilo partellus Swin., and Sesamia inferens Wlk.), armyworms (Mythimna separata Wlk.,
Spodoptera exempta Wlk., and S. frugiperda J.E. Smith), midge (Geromyia penniseti, Raghuva albipunctella
de Joanis, and Eublema spp). A few other insects may be locally important.
A strategy to screen for host-plant resistance involving planting dates, use of infester rows, split plantings,
hot-spots, controlling other insects interfering in resistance screening, and artificial or no-choice screening has
been suggested and discussed. Rearing insects on artificial diets or collecting and carrying diapausing larvae in
2% agar-agar has been suggested to augment natural populations. Sources of insect resistance identified under
natural conditions have been listed, and need to be confirmed in multilocational trials. Oviposition nonpreference,
and slower rates of development because of morphological barriers or antibiotic factors in the food
source may contribute towards host-plant resistance to most insects. Early- and late-maturing cultivars escape
Raghuva damage, while compact panicled cultivars tend to be damaged less. Cultivars with a thick cover of
anthers suffer higher damage by Heliothis armigera. Presence of awns may be helpful in reducing oviposition
and feeding by panicle feeding insects.
Discussion
The presentations and discussions indicated that the most important insect pests of pearl millet are grey weevil
and white grub in Rajasthan; shoot fly, stem borer, and white grub in peninsular India; and spike worm
(Raghuva albipunctella) and stem borer (Acigona ignefusalis) in West Africa. Midges, headbugs, blister
beetles, and army worms are considered minor pests.
Population monitoring of various insects has been conducted using light and pheromone traps, counting
insect numbers (eggs, larvae, and pupae), as well as through damage surveys of crops. Peak activity of millet
shoot fly (Atherigona approximata) has been recorded during Jul-Sep in peninsular India.
A number of alternate host plants have been report-ed for off-season carryover of insect pests. Paragrass is
an alternate host of the leaf roller, and a number of grasses are hosts for grey weevils in India and stem borers in
West Africa during the off season.
Among the various control measures, cultural techniques are advocated to reduce pest populations.
Destruction of stems before the rainy season reduces the population carryover of stem borers. Early planting
escapes shoot fly damage. A well-fertilized crop is generally attacked less by spikeworm, while the reverse is
true for stem borer. Other cultural practices such as intercropping, mixed cropping, and crop rotation help
reduce pest infestations.
Although a number of predators, parasites, and pathogens have been reported to attack millet pests, their
role in reducing pest populations is limited. Bacillus thuringiensis was suggested as an alternative to synthetic
insecticides.
Use of insecticides is a costly way to control insect pests of millet. Although granular application of
carbofuran has shown promising results in controlling shoot fly and stem borers, the cost-benefit ratio is yet to
be determined. Foliar applications of endosulfan and phosalone are also promising. Drilling BHC with
farmyard manure (2:3) in the furrows before planting helps control white grubs. It was suggested that since a
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