Abstract:

Surveys in northern Uganda showed that the bruchid Callosobruchus chinensis L. was the
most serious and predominant storage pest of pigeonpea (Cajanus cajan (L.) Millsp.),
infesting both pods in the field and stored seeds. Because of the high damage the bruchid
causes, farmers practice a number of cultural management techniques with varying degrees
of success.
In the field, various factors affected C. chinensis infestation, including infestation by
Helicoverpa armigera (HOb.), pod splitting, and pod developmental stage, pod surface
hair density, and pod wall thickness. Two polymorphic forms of C. chinensis were
identified, the flight and flightless forms, which are adaptively suited for survival and for
successful propagation under field and storage conditions, respectively. The predominance
of emerged adults of the flightless forms in dry seed and the flight forms in green pods
were triggered by low moisture content in seed and high moisture content in green pods,
respectively.
To reduce the transfer of C. chinensis infestation to storage, field application of
cypermethrin (0.5% at 1 1/ha) and pod (cf. seed) storage were found effective. In storage,
the physical methods found effective were hermetic storage of seed in the traditional mudstraw
silo "tua", solar disinfestation and seed splitting. Plant and plant products found to
be effective in reducing damage in storage were admixture with Tephrosia vogelli Pers,
fire-cured tobacco (Nicotiana tabacum L.), wood ash, Tagetes sp. and Eichhornia
crassipes Solms.
Resistance screening was conducted on 262 pigeonpea genotypes against C. chinensis
infestation both on pods (immature and mature) and in stored seed. Significant negative
correlations were found between pod surface hair density and pod wall thickness on the
one hand and field resistance, in terms of both resistance to oviposilion and to adult
emergence. In the seeds, significant negative correlations were found between seed coat
thickness and infestation. Sixteen pigeonpea genotypes were identified with high
resistance to C. chinensis in both field and store; two of these showed exceptional
resistance to damage in store.
A provisional IPM strategy for reducing pigeonpea seed damage is presented.