| dc.description.abstract | The interactions between the bean bruchid
Acanthoscelides obtectus and six bean varieties (Red haricot,
Mwitemania, Rose coco, Nyayo, Canadian wonder and Mwezi moja)
under cultivation in Kenya were studied under laboratory
conditions. Experiments were conducted to investigate: (1)
The effects of bean varieties on oviposition site preference
by the beetles. (2) The effects of bean varieties on
fecundity (3) The effects of delayed bean provision on
oviposition (4) The
" susceptibility of bean varieties to
attack by the beetles using a susceptibility index.
Similarly, bean seed sizes, testae thicknesses and
hardness of seeds of the various bean varieties were
determined. Later on they were used to find out whether their
variations could be used to explain the differences in
preference, fecundity and susceptibilities. The experimental
room was maintained at temperatures of 27 ± 1°c and 70 ± 5 %
relative humidity.
The results indicated that Mwezi moja was the most
preferred variety as oviposition site, whereas Mwitemania was
the least preferred. Number of eggs laid by the beetles were
significantly different between varieties (X2 = 32.1, d.f =
5, P < 0.05). Beetles laid the highest number (54.6 ± 4.7) of
eggs in Mwezi moja
and the least (35.4 ± 5.2) in Mwitemania. Egg laying
-xiduration
(days) was not significantly different between
varieties (F = 0.62, d.f = (5, 54), P > 0.05). Beans induced
oviposition in the majority of females. When provision of
bean varieties was delayed for 0 - 16 days, beetles laid the
highest number (15) of eggs on Mwezi moja and the least (7)
on Mwitemania. Delayed bean provision reduced fecundity and
prolonged the egg laying duration.
Number of progeny of A. obtectus emerging were
significantly different between bean varieties (X2 = 77.0,
d.f = 5, P < 0.05). The highest number' (490.4 ± 40.1) of
progeny emerged from Mwezi moja and the least (299.7 ± 39.9)
from Mwitemania. Duration taken by 50 % of progeny to emerge
was significantly different between varieties (F = 6.55, d.f
= (5, 54), P < 0.05). Beetles took the shortest period (36.6
± 0.1 days) to emerge from Mwezi moja and the longest period
(39.2 ± 0.5 days) from Mwitemania. Susceptibility index was
significantly different between bean varieties (F = 3.33, d.f
= (5, 54), P < 0.05). Mwezi moja was the most susceptible
variety to attack by A. obtectus with a susceptibility index
of 5.81 ± 0.4 and Mwitemania was the least susceptible with
a susceptibility index of 3.36 ± 0.6.
Seed size and thickness of testa affected fecundity of
the beetles. The differences in preference of bean varieties
by the beetles was attributed to seed size. Physical
characteristics of seeds of the bean varieties played a
subordinate role on
varieties.
susceptibility
in most of the bean | en |
