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 setae 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. 4 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 tibiaee 
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 
the 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 
Un 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 18, 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. 
