10 BULLETIN 1324, IT. S. DEPARTMENT OF AGRICULTURE 



larvae are usually placed 011 stems where a silken thread has been 

 left by a caterpillar, and Townsend suggests that the sense of smell 

 induces the flies to larviposit in such locations. Picard (60) states 

 that the functioning of the ovipositor of Pintpla instigator is a re- 

 flex determined by an olfactory sensation, but that the tactile sense 

 governs the actual deposition of the egg in the host. The investiga- 

 tions of Hase show that odor is all important in the discovery of 

 the host by Habrobracon juglandis but that tactile stimuli are neces- 

 sary to bring about the deposition of the egg (34 ; cf . also Die Natur- 

 wissenschaft, Jahrg. 11, Heft 39, p. 801, 1923). 



CONTACT WITH CHEMICAL SUBSTANCES 



In addition to the effects produced by the purely physical char- 

 acter of surfaces there yet remains the possibility that the oviposi- 

 tion behavior may be influenced by direct contact of the insect's body 

 with chemical substances. Responses due to the sense of taste and 

 to the general chemical sense probably belong here. Mclndoo (51, 52) 

 believes that the senses of smell and taste in insects are inseparable. 

 Minnich (54, 55, 56), however, has recently described a chemical 

 sense analogous to taste located on the tarsi of two species of Lepi- 

 doptera, Pyrantels atalanta L. and Vanessa antiopa L. Experi- 

 ments on Drosophlla melanogaster (1) indicate that the taste of an 

 aqueous glucose solution is much more effective in evoking oviposi- 

 tion than the odor of a solution which contains a mixture of acetic 

 acid and alcohol, although the latter mixture has a marked food at- 

 traction for this fly (5) . Sharma and Sen (72) , in a study of the ovi- 

 position of mosquitoes, find that weak solutions of sodium chloride, 

 sodium citrate, sodium tartrate, and certain other salts are conducive 

 to egg laying, while the corresponding acids are repellent. Observa - 

 tions of Hancock (33) on the oviposition of the grasshopper Orchell- 

 ntum glaoerrlmum Burm. reveal the interesting fact that this insect, 

 when searching for a place to lay its eggs, either ignores the plants 

 distasteful to it or subjects them to a brief mouth test (cf. 4-, P- 134)- 

 Although not proving the point, these observations suggest that 

 taste plays a part in the selection of the plant. Brues (11) places 

 taste among the senses which direct gravid female insects to plants. 



DISCUSSION 



Insects which spend most of their lives upon substances that offer 

 food for themselves or their offspring probably exhibit the simplest 

 oviposition responses. When the internal physiological conditions 

 are right, simple contact with the stimulating medium appears to be 

 all that is necessary to release the eggs. The behavior of the ovi- 

 positing queen bee suggests that the response is largely determined 

 by the tactile sense and this may also be true of other colonial in- 

 sects. The webbing clothes moth (Tlneola blselllella), which ovi- 

 posits as readily upon the surfaces of indigestible materials as upon 

 the natural food of its larva, likewise seems to lay its eggs largely 

 in response to tactile stimuli. 



Contrasted with these simpler cases, the oviposition response of 

 many active free-living species is much more complex. The inten- 



