1377 S. Zhou et al. Journal of Insect Physiology 46 2000 1375–1385
side. Open ampoules containing pupae were placed on sticky tapes in the middle of the bag, with lids beside.
The open side of the bag was folded and sealed by clamping two thin and narrow plates on the folded area.
The outlet of the bag was clamped temporarily to inflate the bag with the mixed gases. Then the clamp on the
outlet was released and the gas in the bag was pushed out. This process was repeated 4–5 times until the gas
concentration in the bag reached the correct level, which was confirmed by drawing samples from the bag and
analyzing them by gas chromatography. The ampoules in the bag were then sealed with their lids through the
bag. The sealed ampoules were then taken out of the bag and placed into calorimeter cells for metabolic heat
rate measurement.
2.4. Metabolic response of pupae to controlled atmospheres
The number of pupae per ampoule varied with the test temperature 10 at 10
° C, 4 at 20
° C, and 2 at 30
° C to
allow the total measured heat rates at different tempera- tures to be close to each other. The metabolic heat rates
under air were first measured. The ampoules were then opened and an appropriate atmosphere was added to the
ampoules as described above. The metabolic heat rates under CA were then measured. After measurements the
pupae were dried in an 80
° C vacuum oven for at least
24 hours to obtain their dry weights. The percentage decrease of metabolic heat rate under an atmosphere
was calculated.
2.5. Respiration measurement The O
2
consumption rate RO
2
and CO
2
production rate RCO
2
of pupae under various O
2
concentrations were obtained by measuring the volume of O
2
VO
2
consumed and the volume of CO
2
produced VCO
2
at a given time in a closed syringe. Thirty pupae were
weighed and placed in a 20 ml syringe without its needle. The syringe, along with the plunger and a small
rubber septum, were placed in a plastic bag that was connected to a constant flow of a desired gas mixture as
described above. When the correct concentration of the gas in the bag was established, the plunger was pushed
into the syringe, leaving 18 ml of volume. Then the rub- ber septum was put on the tip of the syringe where a
needle is usually mounted to seal it. These operations were performed through the plastic bag while it was
sealed and the gas was flowing through it. Immediately after the sealed syringe was taken out of the bag, three
1-ml gas samples were taken from the syringe through the rubber septum and analyzed simultaneously for O
2
and CO
2
using an infra-red gas analyzer model PIR- 2000R, Horiba Instruments, Irvine, CA. The syringe,
now having a volume of 15 ml, was placed in a tempera- ture controlled room. The gas concentrations in the syr-
inge were analyzed again after 2 hours. The VO
2
and VCO
2
were calculated from the change between the initial and final O
2
and CO
2
concentrations. The pupae were then dried in an 80
° C vacuum oven for at least 24
hours to obtain pupal dry weight. The RO
2
s under vari- ous
CO
2
concentrations were
also measured
as described above.
2.6. Mortality test The mortality of pupae was tested under 20, 40, and
79 CO
2
at .90 RH all added to 21 O
2
, balance N
2
at 10, 20, and 30 °
C. Using flow boards, constant flow of gas mixtures at a rate of 150 mlmin passed
through a 1 liter treatment jar where test pupae were placed. The gas concentrations inside jars were sampled
daily during treatment and analyzed by gas chromato- graphy.
Controlled atmosphere treatments were conducted in controlled temperature rooms maintained at 10, 20, and
30 °
C. Thirty pupae were placed in a cup with a mesh top. The cup was placed in a jar through which an atmos-
phere was passed. The range of treatment times for each atmosphere at each temperature was determined by pre-
liminary tests, and corresponded with treatment times during which 10 to 100 mortality was expected. After
treatments the pupae were transferred to an incubator at 27
° C and 80–90 RH. Adult eclosion or lack thereof
was observed after 2 weeks to determine mortality. All treatments were replicated at least 3 times.
2.7. Statistical analysis The data for the percentage decrease of metabolic heat
rate, respiration rates, and respiration quotient RQ were analyzed by ANOVA GLM, SAS Institute, 1989.
Means for significant effects were separated by t-test LSD. Response surfaces were fitted for the percentage
decrease of metabolic heat rates under the combinations of reduced O
2
and elevated CO
2
. A separate probit curve for each treatment level was fitted with mortalities as
the dependent variables and treatment duration as the independent covariates PROC PROBIT, SAS Institute,
1989. The fitted probit curves were used to calculate LT
99
values.
3. Results
3.1. Temperature The metabolic heat rate under air 21 O
2
0.03 CO
2
was 1.2, 3.7, and 7.5 µ
Wmg at 10, 20, and 30 °
C, respectively. The Q
10
between 10 and 20 °
C was approxi- mately 3, and was 2 between 20 and 30
° C.
1378 S. Zhou et al. Journal of Insect Physiology 46 2000 1375–1385
3.2. Reduced O
2
The metabolic heat rate decreased with decreasing O
2
concentration Fig. 1. At all three temperatures, the decrease was slight until a critical O
2
concentration below which the decrease became rapid. The critical O
2
concentrations were higher at higher temperatures, being 6 O
2
at 10 °
C, 8 O
2
at 20 °
C, and 10 O
2
at 30 °
C Fig. 2A. Temperature had slight but significant
effects on the heat rate decreases Fig. 2A. The per- centage decreases were slightly higher at higher tem-
peratures at 6, 4, 2, and 1 O
2
. But at 10 and 8 O
2
the percentage decreases at 10 °
C were higher than at 20 or 30
° C. ANOVA results for reduced O
2
concentrations were highly significant P,0.0001 for O
2
concen- tration, temperature and O
2
concentration ×
temperature. The O
2
consumption rate RO
2
at 20 °
C decreased slightly with decreasing O
2
concentration down to 8 O
2
, and then decreased rapidly Fig. 3. The percentage decreases of RO
2
at 20 °
C, which were 11, 15, 25, 41, 77, and 83 at 10, 8, 6, 4, 2, and 1 O
2
, respectively, were comparable to the percentage decreases of meta-
bolic heat rate under various O
2
concentrations at 20 °
C except at 2 and 1 O
2
, where the percentage decreases of RO
2
were about 10 higher Fig. 2A. The percent- age decreases of CO
2
production rate RCO
2
, which were 9, 19, 21, 33, 58, and 70 at 10, 8, 6, 4, 2, and 1
O
2
, respectively, were comparable to those of metabolic
Fig. 1. Metabolic heat rate
µ Wmg dry wt. of 1–2 d old Platynota
stultana female pupae under various O
2
concentrationswith 0 CO
2
and various CO
2
concentrations with 21 O
2
at 10, 20 and 30 °
C. Vertical bars represent standard errors.
Fig. 2. The percentage decrease of metabolic heat rate of 1–2 d old
Platynota stultana female pupae under various O
2
concentrations with 0 CO
2
A and various CO
2
concentrations +
21 O
2
B at 10, 20 and 30
° C. Vertical bars represent standard errors.
Fig. 3. O
2
consumption rate RO
2
µ l·h
21
·g
21
dry wt., CO
2
pro- duction rate RCO
2
µ l·h
21
·g
21
dry wt., and respiratory quotient RQ of 1–2 d old Platynota stultana female pupae under various O
2
concentrationswith 0 CO
2
at 20 °
C. Vertical bars represent stan- dard errors.
1379 S. Zhou et al. Journal of Insect Physiology 46 2000 1375–1385
heat rate under all O
2
concentrations Fig. 2A. The respiratory quotient RQ showed no significant change
between 21 and 4 O
2
, with values between 0.65 and 0.80. However, the RQ increased significantly to about
1.3 when O
2
concentration was reduced to 2 and 1 Fig. 3. ANOVA results for various O
2
concentrations were highly significant P,0.0001 for RO
2
, RCO
2
, and RQ.
3.3. Elevated CO
2
The metabolic heat rate decreased rapidly between 0 and 20 CO
2
Fig. 1, with a 60 decrease at 10 and 20
° C and a 40 decrease at 30
° C under 20 CO
2
Fig. 2B. Further decrease of metabolic heat rate between
20 and 79 CO
2
was slight. At 10 °
C, there was no further decrease of metabolic heat rate between 20 and
79 CO
2
. At 20 °
C, the metabolic heat rate further decreased under 60 and 79 CO
2
, with a 72 decrease at 79 CO
2
. At 30 °
C, the metabolic heat rate continued to decrease from 20 to 79 CO
2
, but at a much slower rate than that from 0 to 20 CO
2
. The percentage decreases of metabolic heat rate at a certain CO
2
concen- tration were generally lower at 30
° C than at 10 and
20 °
C, which were mostly similar except at the two ends of the CO
2
spectrum Fig. 2B. ANOVA results for elevated CO
2
concentrations were highly significant P,0.0001 for CO
2
concentration, temperature and CO
2
concentration ×
temperature. The RO
2
at 20 °
C 660 µ
l•h
21
•g
21
decreased by 62 at 20 CO
2
250 µ
l•h
21
•g
21
and by 73 at 79 CO
2
185 µ
l•h
21
•g
21
. The percentage decreases of RO
2
were comparable to the percentage decreases of metabolic
heat rate under the same CO
2
concentrations Fig. 2B. 3.4. Combinations of elevated CO
2
and reduced O
2
Reducing O
2
concentration at 20 °
C decreased meta- bolic heat rate further at all CO
2
concentrations Fig. 4A and Table 1. However, the effects of reduced O
2
were smaller at higher CO
2
concentrations Table 2. The effects of elevated CO
2
on metabolic heat rates varied with O
2
and CO
2
concentrations Fig. 4B, Table 1. At 4 O
2
or higher, metabolic heat rate decreased rapidly between 0 and 20 CO
2
and there was little further decrease between 20 and 79 CO
2
. At 1 O
2
, only 20 and 79 CO
2
decreased the metabolic heat rate further. The additional percentage decreases in metabolic
heat rate contributed by elevated CO
2
were generally smaller at lower O
2
concentrations Table 3. At 10 O
2
, all CO
2
concentrations showed their full effects, with the additional percentage decreases similar to those at
21 O
2
. At 1 O
2
, however, there was little additional effect of CO
2
Table 3. The response surface of the percentage decrease of
metabolic heat rate fitted with a polynomial of term 3
Fig. 4. Metabolic heat rate
µ Wmg dry wt. of 1–2 d old Platynota
stultana female pupae under combinations of reduced O
2
and elevated CO
2
at 20 °
C; A effects of reducing O
2
concentration at various CO
2
concentrations; B effects of increasing CO
2
concentration at various O
2
concentrations. Vertical bars represent standard errors.
showed that the full additive effects on reducing metab- olism mostly occurred at combinations of 5 CO
2
and 4 O
2
Fig. 5. The combined effects of reduced O
2
and elevated CO
2
became increasingly overlapped as the O
2
concentration decreased and the CO
2
concentration increased.
3.5. Mortality responses to elevated CO
2
Temperature had a dominant impact on the mortality responses; the higher the temperature, the more suscep-
tible the pupae Fig. 6, Table 4. However, the effect of temperature varied with CO
2
concentration. At 20 CO
2
, lowering temperature from 20 to 10 °
C increased LT
99
greatly Table 4. At 79 CO
2
, however, lowering temperature from 20 to 10
° C did not change LT
99
sig- nificantly. CO
2
concentrations affected mortality, but the specific effects were dependent on temperature. Forty
and 79 CO
2
were more effective than 20 CO
2
at all three temperatures; however, 79 CO
2
was not more
1380 S. Zhou et al. Journal of Insect Physiology 46 2000 1375–1385
Table 1 Pecentage decrease of metabolic heat rate of 1–2d old Platynota stultana female pupae under combinations of CO
2
and O
2
at 20 °
C
a
CO
2
O
2
5 20
40 79
21 0.0 d, E
25.8 d, D 58.8 d, B
52.3 d, C 69.0 d, A
10 5.7 c, E
34.2 c, D 68.1 c, B
57.9 c, C 75.2 c, A
4 29.6 b, D
61.3 b, C 77.8 b, A
68.3 b, B 79.5 b, A
1 76.6 a, C
77.4 a, C 80.1 a, B
74.2 a, D 84.7 a, A
a
Within each column, mean differences are indicated by lower case letters t-test. Within each row, mean differences are indicated by upper case letters.
Table 2 The additional percentage decrease of metabolic heat rate caused by reduced O
2
when 1–2d old Platynota stultana female pupae were under various concentrations of CO
2
at 20 °
C CO
2
O
2
5 20
40 79
21 0.0
0.0 0.0
0.0 0.0
10 5.7
8.4 9.3
5.6 6.2
4 29.6
35.5 19.0
16.0 10.5
1 76.6
51.6 21.3
21.9 15.7
Table 3 The additional percentage decrease of metabolic heat rate caused by
elevated CO
2
when 1–2d old Platynota stultana female pupae were under various concentrations of O
2
at 20 °
C O
2
CO
2
21 10
4 1
0.0 0.0
0.0 0.0
5 25.8
28.5 31.7
0.8 20
58.8 62.4
48.2 3.5
40 52.3
52.2 38.7
22.4 79
69.0 69.5
49.9 8.1
effective than 40 CO
2
at 20 and 30 °
C. Increasing CO
2
concentration from 20 to 79 CO
2
greatly improved efficacy at 10
° C, but not at 20
° C.
An atmosphere of 40 CO
2
+ 21 O
2
at 20 °
C caused high mortality at short treatment durations, e.g., above
40 mortality with only 3 hours of exposure Fig. 6. This atmosphere also caused the pupal body fluid to leak
out immediately during exposure. This body fluid leak- age phenomenon did not occur under 20 and 79 CO
2
+ 21 O
2
, 0 to 21 O
2
, or even 40 CO
2
+ 1 O
2
.
4. Discussion
