1462 M.E. Salvucci, S.J. Crafts-Brandner Journal of Insect Physiology 46 2000 1461–1467
the effects of various dietary supplements and metabolic inhibitors on whole-insect metabolism.
In this report, we describe a system for measuring ste- ady-state respiration of homopteran insects during feed-
ing. The
system consists
of a
flow-through respirationfeeding chamber connected to a commer-
cially available IRGA system. Respiration rates of white- flies and cotton aphids were measured with this system
to determine how the metabolic rates of these tropicalsubtropical homopteran insects during feeding
compare to those of other insects. In addition, the system was used to determine the dependence of whitefly
metabolism on dietary sucrose concentration and tem- perature and for determining whole-organism thermotol-
erance by monitoring the rate at which whitefly respir- ation decreased at high temperature.
2. Materials and methods
2.1. Insect and plant material Adult silverleaf whiteflies Bemisia argentifolli Bel-
lows and Perring were reared in a glasshouse on cotton Gossypium hirsutum L., cv. Coker 100A glandless as
described previously Salvucci et al., 1997. The tem- perature in the glasshouse varied diurnally from 25
° C in
the morning to 38 °
C by 2:00 p.m. Whiteflies were col- lected from colony plants by gentle aspiration. Cotton
aphids Aphis gossypium Glover were collected in early summer from cotton plants growing in a field adjacent to
the Western Cotton Research Laboratory, Phoenix, AZ.
2.2. Respiration measurements Immediately following collection from colony plants,
approximately 200 to 250 adult whiteflies or about 150 aphids were placed in the bottom of a respiration
chamber. The chamber was constructed from a 2.54-cm- diameter plexiglas cylinder cut to a length of 2.4 cm
Fig. 1. The bottom end of the chamber was sealed with a rubber stopper and the surface of the stopper protrud-
ing into the chamber was covered with a layer of par- afilm. Two plastic luer lock fittings and a serum stopper
were inserted into holes drilled into the chamber. A type- T needle thermocouple was inserted through the serum
stopper to monitor chamber temperature. The upper sur- face of the respiration chamber was sealed with a 3.5-
dram snap-cap bottle inserted upside down i.e. cap-side down into the top of the chamber. A 1.5-cm-diameter
hole was cut into the plastic cap to support a 25-mm polytetrafluoroethylene membrane pore size
= 1
µ m,
Micron Separations Inc., Westborough, MA. A hole was drilled in the bottom of the bottle for addition of
diet and dietary supplements. Artificial diets consisting of 50 mM potassium phosphate, pH 6.5, 0.05 yellow
food-coloring dye and the indicated concentrations of sucrose were added to the surface of the membrane. The
chamber assembly was placed inside a 2 L water-jack- eted beaker and illuminated at 300
µ mol photons m
22
s
21
. In a typical experiment, nearly all of the whiteflies moved from the bottom of the respiration chamber to
the surface of the membrane within 1.5 h. The respiration chamber was connected to an IRGA
system LiCor 6400 Portable Photosynthesis System, Lincoln, NE by splicing into the inlet line leading to
the system’s sample IRGA. The tubing leading from the system’s pump was directed through a coil of bev-a-line
tubing Cole-Palmer, Vernon Hills, IL to the inlet of the insect respiration chamber. The coil of tubing was
inserted into the water-jacketed beaker to adjust the tem- perature of the incoming gas stream to that of the respir-
ation chamber. The outlet of the respiration chamber was connected to a glass cold-finger via bev-a-line tubing and
then to the tubing leading into the sample IRGA. The flow rate of the incoming gas was maintained at 52
µ mol
s
21
using the system’s internal pump and the tempera- ture of the respiration chamber was adjusted by varying
the temperature of the water-jacketed beaker that sur- rounded the chamber. The CO
2
concentration of the gas stream was measured with the system’s IRGA and
adjusted to the desired concentration using the system’s CO
2
mixer. Unless indicated otherwise, the mixer was programmed to maintain a constant CO
2
concentration of 350
µ l l
21
in the IRGA’s sample chamber. Data on CO
2
concentration, water vapor, temperature and flow rate, which were monitored continuously by the instru-
ment, were logged into the system’s on-board computer at regular intervals during the course of the experiment,
starting 2 h after transfer of the insects to the respir- ometer. Following each experiment, data were trans-
ferred to a spreadsheet program and used to calculate rates of respiration. Q
10
values were calculated using the formula Q
10
= R
2
R
1 10T
2
− T
1
, where R
2
and R
1
are the respiration rates at temperatures T
2
and T
1
, respectively. The number of insects used in each experiment was
determined at the end of the experiment by killing the cohort with either high temperature or sodium azide see
below. Groups of freshly killed whiteflies and aphids were weighed on a Mettler Model UMT2 microbalance
to determine an average weight. Values of 20 and 32
µ g
were used for the average weight of individual whiteflies and aphids, respectively.
3. Results
