RA 00015.pdf - OAR@ICRISAT

3000
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A. M i l d Stress
r = . 9 4 * * *
2500
2000
B. Severe Stress
r = . 5 7 * * *
1500
1500
1000
1000
1000 1500 2000 2500 3000 3 500 4000
1000 1500 2000 2 500 3000 3500
Yield in control ( k g / h a )
Yield in control ( k g / h a )
Figure 9. Relationships of sorghum yields under stress with yields in absence of stress.
filling. There is also a much better possibility to
improve yields via improvements in harvest
index (converting a greater percentage of the
total dry matter produced into grain) in the long
GS 2 types.
Entomology
Pest Assessment and Pest Populations
For the third season three standard sorghum
cultivars-CSH-1, "Swarna," and Local
(Pachajonna)-were planted at the break of the
rainy season on a pesticide-free Vertisol area and
detailed insect observations recorded throughout
the season. Shoot-fly infestation was low in
the early sown crop and 95 percent of the males
bred from the crop were Atherigona soccata. A
potentially important predatory mite, identified
as Abrolophus sp., was discovered feeding on
eggs and first-instar larvae of this pest. Attack by
stem borer, Chilo partellus, was heavier than
usual, and also earlier; however, little difference
in damage was recorded between cultivars. At
harvest time more larvae were present in CSH-1
than in the other cultivars, and larvae tended to
be more numerous in harvested stalks, to persist
longer, and to survive better in this cultivar.
Midge attack was low.
We prepared a detailed list of insects and their
parasites recorded from sorghum at ICRISAT
Center; the list will be published.
Shoot-fly Taxonomy and Biology
Of seven species of shoot fly bred from sorghum,
only A. soccata is important as a pest. Three
additional alternative grass hosts of shoot fly
were identified - Cymbopogon caesius (Nees)
Stapf, Echinocloa crusgalli (Linn.) P. Beauv., and
Eragrostis japonica (Thunb) Trin. Three other
grass hosts, one of which appears to be of
significance, remain unidentified. Shoot flies
were also bred from wheat and Sorghum halepense
(Linn.) Pers.; the latter is a potentially
important carry-over host. In a study to determine
if diapause occurs in the pupal stage,
most pupae emerged at the expected time - but
one took 10 weeks, indicating that extended
development is possible.
Studies on the various shoot-fly species and
alternative hosts confirmed prior observations
that flies are highly discriminative in selection of
a host plant. Although A. oryzae and A.falcata
were dominant on grasses, the former clearly
preferred E. japonica and Digitaria adscendens
(H.B.K.) Henr. and the latter Echinocloa colonum
(Linn.) Link and E. crusgalli (Reddy &
Davies 1977). A total of 18 different species of
shoot fly has been recovered from fields at
ICRISAT Center-four of which are new to
science.
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