1922] Uichanco — Notes on Parthenogenetic Macrosiphum 75 



during feeding, as in ecdysis, which has been previously des- 

 cribed. One or both of the following explanations may account 

 for this peculiar behavior: (1) In order to avoid the rays of the 

 sun from streaming directly into the eyes. (2) For mechanical 

 advantage, the feeding apparatus perhaps attaining its maximum 

 efficiency or the strain on the muscles being probably minimized 

 when the aphid assumes this position. The second explanation 

 is purely speculative. This characteristic position is evidently 

 not an adaptation to any peculiarity in the structure of the host. 



3. The setse of this aphid apparently do not penetrate very 

 deeply into the plant tissue. 



IV. "Death-Feigning." The habit of dropping to the 

 ground when disturbed and remaining motionless for a time is a 

 very peculiar characteristic which is exhibited by many species 

 of Macrosiphum.* M. tanaceti responds readily in this manner 

 and on reaching the surface of the ground, the insect behaves in 

 either of the following two ways, depending on its position after 

 it drops: (1) If it lands on its ventral side, it simply stands on 

 its legs and remains motionless in this attitude. The antennae 

 are directed posteriorly. (2) If it lands on any part of the body 

 other than the ventral side, the legs are folded so that the tibisee 

 are also directed posteriorly and the insect remains perfectly 

 quiet. 



The nymphs of the first instar do not seem to have the ability 

 of ''death-feigning" to any marked degree. They are practically 

 the only ones that remain on the plant, after the latter is jarred 

 and individuals of the second and later instars drop to the ground. 

 The adult individuals always regain their standing position very 

 quickly and remain in this position, no matter which portion of 

 th"e body touches the ground first. The wings remain folded and 

 the insect does not seem to use them as it falls. 



The biological significance of this peculiar behavior has been 

 the subject of discussion and speculation by various workers who 



4In my own work, I have not come across a single species of Macrosiphum which does not 

 exhibit "death-feigning." However, Dr. A. C. Baker, of the Bureau of Entomology, U. S. 

 Department of Agriculture, in a letter dated at Washington, D. C, January i8, 1922, informs 

 me that there are some Macrosiphum species which do not possess this habit. He further men- 

 tions the interesting fact that "death-feigning" is not confined to Macrosiphum, for this 

 peculiarity is also met with in the Callipterina. 



