Biomedical Engineering Reference
In-Depth Information
the insect, however, survived as indicated by the emergence of adults during an
incubation period for samples after the treatment. Therefore, an extended exposure
may be required for complete mortality of all life stages of
S
.
granarius
.
Hoey
79
reported on the use of CO
2
for the control of stored-grain insects in
Australia. The gas was introduced at a slow rate at the bottom of vertical steel silos
conforming to a satisfactory standard of gas tightness. After the initial purge at a
rate of 1 t CO
2
per 1000 t of grain, the gas was recirculated for at least 10 days.
The treated silos were generally insect-free for more than 4 months. Annis
80
studied
the effectiveness of CO
2
fumigation of bag stacks of rice sealed in flexible PVC
enclosures. The gas was added until the gas leaving an exit vent at the top of stack
contained >60% CO
2
. The stack was then sealed. All of the insects (
S
.
oryzae
) placed
in cages were killed. In another trial, the grain with a natural infestation of 15 live
insects per kilogram of rice, mainly
R
.
dominica
and
T
.
castaneum
, was subjected
to a similar gas treatment. No live insects were found in the bags opened 133 days
after the treatment.
D
EVELOPMENT OF
I
NSECT
R
ESISTANCE TO
CA
Bond and Buckland
81
investigated the response of
S
.
granarius
to selection under
high CO
2
atmospheres. The exposure of adults to 42% CO
2
for seven successive
generations, and to 75% CO
2
for four successive generations produced insects with
3.3- and 1.8-fold increases in their resistance to the elevated CO
2
. Navarro et al.
82
reported on the development of resistance to CO
2
-rich atmosphere among the adults
of
S
.
oryzae
. Two groups of insects were exposed to 40% CO
2
in air for seven
successive generations, and to 75% CO
2
in air for ten successive generations at 26°C
and 100% relative humidity. Insects subjected to selection pressure were compared
with those of a control for their lethal tolerance factor (LT
95
selected generation/LT
95
non-selected generation). The results indicated that
S
.
oryzae
has the genetic potential
to develop resistance to CO
2
-rich atmospheres. The tolerance factor at the 7th
generation (under 40% CO
2
) and 10th generation (under 75% CO
2
) was 2.15 and
3.34, respectively. Reduction of relative humidity to 60% and augmentation of O
2
concentration to 21% at these CO
2
levels did not markedly alter the tolerance factor
indicating that the tolerance in these insects was largely due to the action of CO
2
.
Removal of selection pressure for five generations in the case of the 40% CO
2
group
and for four generations in the case of the 75% CO
2
group resulted in a significant
reduction in their tolerance to the CO
2
-rich atmosphere indicating that the strains
obtained were not completely isogenic. Donahaye
83
exposed
T. castaneum
for 40
generations to atmospheres containing 65% CO
2
, 20%O
2
, and 15% N
2
at 95% RH.
A resistance factor to CO
2
of 9.2 was found and the offspring of the insects removed
from the selection pressure maintained their resistance to CO
2
.
Q
UALITY
C
HANGES IN
G
RAIN
U
NDER
CA S
TORAGE
Seed Viability
Grain can be stored for relatively long periods without a loss in viability, with a
decreasing scale for longevity in oats, rice, barley, wheat, triticale, rye, sorghum,
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