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Water 
Water 
Figure 14,--IR spectrum (2.5 to 7“) of piece of exoskeleton from sphingid moth, Two major 
water absorption bands of plant or animal tissue would not transmit well because these 
frequencies have low transmission coefficients, 2,9 # would transmit better at 0,689 than 
6.1 HW at 0,260, Water vapor coefficients are in decimal parts of 1.0, where w = precipitable 
water, cm, at sea level (table after Hackforth 1960), iF 
were made with a Perkin-Elmer ® Model 237 
Spectrophotometer, with an attenuated total- 
reflectance accessory. This attachment per- 
mits analysis of solid samples without control 
of the sample thickness. If in figure 13 we 
consider the 8- to 13- uw window, where good 
atmospheric transmission occurs, we note 
that the absorption signal was somewhat 
stronger in this window for the silk of the 
susceptible variety than it was for the re- 
sistant variety. If, because of some chemical 
or physiological factor, IR emission is dif- 
ferent for one part of the plant than for 
another, the total plant may then be presenting 
a different pattern to the insect eye that it 
customarily sees. 
Strong water absorption bands in the 3- and 
6-4 region complicate the IR pattern, but, as 
figure 14 illustrates, these bands donottrans- 
mit well through the atmosphere. At 6.lu, 
for instance, the water vapor transmission 
172 
is very low (only 0.260) compared with the 
4- 4 region (0.997) or the 8- to 13-u window. 
In spite of poor atmospheric transmission 
in these regions, however, water itself has a 
high emissivity of 0.98 (table 1) and radiates 
as a blackbody from 4 to 13 w (Clark and 
Frank 1963), In the blacked-out room the moth 
of the cotton leafworm (Alabama argillacea 
(Hubner), which prefers moist areas, was 
attracted to a flat pan of water. Some 42 out 
of 60 released moths located and drowned in 
the pan in total darkness. Blackbodies of all 
sorts in a totally dark room seem to be highly 
attractive to night-adapted flying moths. 
TRANSMISSION THROUGH 
MATERIALS 
Callahan (1965d) postulated that certain of 
the IR frequencies may play a part in the con- 
trol of diapause. The numerous spines of 
