Table 6.--Thickness of wood permeable to 
IR radiation (summer 1962) 

Thickness (mn. ) 

English name 

O10, 6¥eye, 6 w 0.0 6 018, 0:6. 60 
oe: 07.0) @: 61(0) 0)<e) .e% a6 
60 (070 0 eee ee a 0 6 0 61 
ee) 






Oakes sna he arahevae 
Plum tree (domestic). 1-2 
Plum tree (wild)..... 1-125 
White uwalnwt. .cs.6.és\<tc.e00 .O 
Sibertan Pines wie. as Freely transmitting. 
YeuLoOw “Diners ss. ccseve ts Do. 
YELVow Gea eis. sievcrerehs Do. 
Tasmanian oak Do. 

wilepene lene 
sere eresr eee 
NOCTURNAL IR ENVIRONMENT 
Figure 16 
flying moth 
illustrates my views on the night- 
and the IR environment, During a 
day with a clear sky, the moth maintains a 
shortwave, "“light-adapted' eye and is not 
active. As the sun goes down, again as for the 
incandescent lamp and rheostat, the visible 
and ultraviolet decrease almost to the point 
of nonexistance, The longwave IR, although it 
may be of less intensity than the longwave 
rays of the sun, exists in its own right with- 
out the shortwave background interference of 
visible and ultraviolet light from the sun. 
It is precisely at this time that the moth, 
and indeed many insects, are stimulated to 
activity. It is as eminently logical that night- 
flying insects, whether mosquitoes or moths, 
should ''see'' or otherwise sense in this region 
as it is that man should develop nighttime IR 
instruments to aid in his nocturnal location 
problems. 
During the early part of their lives, sphingid 
and noctuid moths spend considerable time 
randomly wandering about the countryside. 
During this time, individuals from even an 
174 
extremely small spring population of five or 
six specimens per square mile would come 
within a 1- or 2-mile range of each other. 
Their proximity would be further enhanced 
by attraction to the host plant or into thermal 
pockets of optimum temperature. For such 
attraction to take place, weather parameters 
would be of supreme importance if IR is in- 
deed a means of host and mate detection. On 
a cool night with low absolute humidity (13 ¢g. 
of H,0 per m® at 80 to 90 percent RH), IR 
transmission, especially through the IR win- 
dows, would be excellent. In spite of the pres- 
ence in the area of a light trap with high 
power, plant emission could lure the moths. 
Suppose, on the other hand, the night were 
extremely warm, with high absolute humidity 
(26 g. of H,O per m® at 80 to 90 percent RH), 
the moth might still randomly wander. There 
would be no danger of desiccation at the high 
RH in either situation. In the second situation, 
however, the excessive number of water mole- 
cules and higher temperature would not only 
reduce the efficiency of the IR window but 
would also reduce the difference in IR emis- 
sion between the plant and the background or 
that between the vibrating moth and the back- 
ground. More moths might thus be collected 
at the light trap, which would be emitting 
tremendous amounts of IR radiation. 
The pitfall in this reasoning is, of course, 
the relativity of all things. Thus, during late 
summer periods when moth populations were 
extremely high, one might get more moths in 
the light trap at lower temperatures than at 
higher temperatures for the simple reason 
that with optimum weather conditions a greater 
part of the very high population would be 
flying around and spatially more moths would 
be close to the trap. The problem might be 
further complicated by one particular moth 
having at any one moment a slightly different 
eye configuration than another moth, simply 
because one moth might be facing the light 
from the trap and another moth facing away 
from the light. All these factors, no doubt, 
would account for the differences in catch 
from night to night, as well as the fact that 
the moths arrive at light traps in a stop-and- 
go pattern of activity. 
Assuming that moths are attracted into an 
area of host-plant emission or into thermal 
pockets, we may further assume that both 
