THE OVIPOSITION RESPONSE OF INSECTS 9 
phora vomitoria, indicate that odor is a much more important factor 
in oviposition than the physical character of the material on which 
the eggs are laid (23). A variety of substances, colored paper, o1l- 
skin, tin foil, when placed over a receptacle which contained meat, 
were oviposited upon provided an opening was made in the cover. 
Dead birds wrapped in paper envelopes were visited by blow-flies, 
but they did not lay their eggs on the paper or attempt to oviposit in 
slits in the paper folds. Fabre attributes this behavior to a mater- 
nal foresight of the fly for an opening through which the progeny 
may find their way to food. His results, however, do not preclude the 
possibility that this behavior resulted from differences in odor con- 
centration. The same explanation might also be offered to interpret 
his experiments on the larvipositing fly Sarcophaga carnaria L., (op. 
_cit., pp. 831-340). Wardle (SZ) recognizes two factors concerned in 
the oviposition of blow-flies, (1) the nature of the foodstuffs and (2) 
meteorological conditions. The stimulus for oviposition, whether 
olfactory or gustatory he was not sure, probably resides in the exud- 
ing juices of the food substances. Howlett (37) induced an Indian 
species of Sarcophaga to deposit larve in a flask which contained a 
solution of skatole. Subsequent experiments with skatole by Lodge 
(Proc. Zool. Soc. London, September-December, pp. 481-518, 1916), 
Roubaud and Veillon (68), and the writer (64) have failed to sub- 
stantiate the attractiveness which Howlett claimed for this com- 
pound. He also obtained eggs of Stomoxys calcitrans upon cotton 
wool soaked in valeric acid, but an attempt to duplicate the latter 
result in America failed (65). 
In the case of the house fly (Musca domestica) , although the odor of 
ammonia from ammonium carbonate will, under suitable conditions, 
induce the female to oviposit (63, 64, 66), the immediate environ- 
ment from which the ammonia arises also shares in determining 
whether egg laying will occur. If we place several pieces of solid 
ammonium carbonate with a little water in a glass dish, female 
house flies are attracted by the odor, but will not oviposit in or near 
the dish. A very slight response is obtained with moist cotton and 
ammonium carbonate which is increased when butyric or valeric acid 
is added. Pine sawdust is better than cotton but inferior to timothy 
chaff or acidulated horse manure. Wheat bran is a favorable nidus 
in the presence of ammonium carbonate, but eggs have not been 
found in fresh, moist bran which does not volatilize ammonia. It 
has been shown conclusively that carbon dioxide, a decomposition 
product of ammonium carbonate, is not in itself attractive to the 
gravid female house fly but, together with other factors, may exert 
an influence upon oviposition which has not been detected (17, 18, 66, 
68). Adolph (2) found that odor is a shght stimulus to egg lay- 
ing in Drosophila melanogaster, being most marked when flies 
could gain contact with the odorous solution. Texture, however, 
was more effective than odor, and suitable combinations of texture 
and odor (the flies were prevented from reaching the odorous sub- 
stance) gave responses nearly equal to those which prevail under 
natural conditions. Townsend (78), in a study of the tachinid flies, 
observed that Hupeleteria magnicornis Zett., which deposits living 
larvee on the foliage of plants, seeks for this purpose only those por- 
tions over which the host caterpillars have crawled. The parasitic 
22803—25 2 
