l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



of the second instar in 50 per cent; one larva of the third instar in 

 60 per cent ; and one larva of the sixth instar in 85 per cent. Several 

 recently hatched larvae went to the pieces of cork in 40 per cent of 

 the chances offered to them and others passed over the squares in 

 30 per cent of the chances. 



These results indicate that smell and sight aid in locating objects, 

 the former being the more important in perceiving odorous objects. 

 Therefore, since larvae of the first instar have photopositive eyes, 

 they remain in the open on apple-tree foliage and search freely for 

 food, apparently not being aided by their senses until within a few 

 millimeters of the food, because in these tests they wandered about 



Fig. 2. — Tracings of cliemotactic responses of recently hatched codling-moth 

 larvae (see p. 17 for further explanation). A, Positive responses to small cubes 

 of green apple ; B, negative responses to synthetic apple oil on small cubes of 

 cork. 



aimlessly and did not perceive the pieces of apple and cork until near 

 them, when they often turned and went directly to them. 



Two tests were conducted with a repellent. Pieces of cork, after 

 being dipped into concentrated synthetic apple oil, were laid inside 

 the circle, and within a few moments the oil had spread on the paper 

 around the cork. A recently hatched larva was given 10 chances to 

 touch the cork, but not once was it touched. When approaching a 

 piece of cork the larva often circled around the margin of oil on 

 the paper. The following day the same pieces of cork were tested 

 with another recently hatched larva. To the writer the cork was 

 highly scented, but it did not wet the paper. In 10 chances this larva 

 was turned 12 times from its course by the repellent odor (fig. 2, B). 



