ELECTROMAGNETIC COMMUNICATION IN INSECTS--ELEMENTS OF THE 
TERRESTRIAL INFRARED ENVIRONMENT, INCLUDING GENERATION, 
TRANSMISSION, AND DETECTION BY MOTHS? 
P, S, Callahan, 
Entomology Research Division, Agricultural Research Service, 
U.S, Department of Agriculture, Tifton, Ga. 
Jean Henri Fabre, the great 19th century 
French entomologist, in his classic work on 
the great peacock moth, established that cer- 
tain species of moths could locate their mates 
over great distances. He hypothesized that 
either scent or hertzian waves were respon- 
sible for location and attraction of night-flying 
moths. Experiments I performed at the U.S. 
Department of Agriculture, Southern Grain In- 
sects Research Laboratory, Tifton, Ga., in- 
dicated that for certain species of noctuids 
and sphingids location and attraction are 
accomplished by infrared electromagnetic 
radiation and that scent is responsible for 
species identification. Thus, in a sense, Fabre 
was correct in his hypothesis with regard to 
both scent and electromagnetic waves. 
Sir William Herschel, in 1800, discovered 
the invisible electromagnetic energy of wave- 
lengths beyond the red part of the spectrum, 
We now know that all objects whose tempera- 
tures are above absolute zero emit infrared 
(IR) radiation. Over the years, the gap in our 
knowledge of the spectrum between IR radia- 
tion and microwave radio frequencies has been 
slowly narrowed, Glagolewa-Arkadiewa (1924) 
demonstrated IR radiation of about 90 uw by ex- 
citing small hertzian oscillations in the form 
of brass filings in oil. Nichols and Tear (1923), 
using a diffraction grating for the measure- 
ments, demonstrated hertzian (far infrared) 
waves of wavelengths down to 220n. 
The standard for IR definition is the back- 
body, essentially any object that absorbs all 
received radiation. The intensity and wave- 
length of IR radiation depend on the absolute 
temperature in degrees Kelvin (°K.) of the 
emitting object and on its surface finish. The 
radiation and absorbing efficiency of an object 
are called its emissivity (€) factor (table 1) 
Table 1.--IR emissivities (€) for different 
objects at ambient temperatures (after 
Barnes 1963) 
Material 
Emissivity 

Green plantsmi eminence eieieere BIO= 9H 
LampribLackey a seve cre pereiele reoe eke .95 
Concrete; iglassiy. Aan ieee .94 
Paper teDiLasiGadichivartosciiio ee aO2 
PLASU UES weletavars acetone mee terete .88 
Stainless! steely ironses sheseae . 10 
Plowed, sielids; pravely a ycuc sree iere .28-,44 
Polished cast iron, lead. 2... 5 TAUS 5 P48) 
CHROME SK ierepersiererarcve stolen eiorekeroreenetens 08 
Miroir O25, ha) Sapes ce ore Sie ain Octo e ore oreNere 02 
and is unity (1) for a blackbody. A mirror is 
a poor radiator and absorber of IR, having an 
emissivity factor near zero. A black rough 
surface, such as lamp black, is extremely 
efficient as a radiator and absorber and ap- 
proaches unity. Objects with an e of less than 
unity are termed gray bodies. Most objects, 
including the moth and the human body, fall 
into this category. 
IR radiation is often wrongly termed heat 
radiation, because it generates heat in any 
absorbing object in its path. However, light 
rays, X-rays, and even high-intensity radar 
beams have the same property. Since the IR 
band falls between visible light and radio 
(7.5X10-* mm. to 1 mm., or in terms of 
microns 0.75 u to 10° , it is extremely in- 
triguing and demonstrates many of the char- 
acteristics of both. It may be focused by lenses 
and yet can be transmitted like radar or radio 
through materials that block visible light. As 
1 After this Paper was presented at Montreal, the author received a critical review from Dr, E, Okress of the In= 
stitute of Electrical and Electronics Engineers, Some of his comments are so pertinent that parts are quoted in 
this paper, 
