4 THE FLORIDA ENTOMOLOGIST 
ing effect of injury and drought, by crowding aphids on a limb, - 
and by adding chemical solutions to their food in growing plants, 
cut stems, and injections in growing stems. In no instance was 
a larger number of winged forms of aphids produced than in the 
checks iiving under natural conditions. 
It is generally believed that an aphid will develop wings and 
fly away if its host plant dies or if crowding lessens the food 
supply and endangers its existence. In the case of mature pine 
aphids this was not found to be true. They all died whey the 
host plant dried up. In fact it is unreasonable to believe that 
they can develop wings after maturity. Grove (19)* has made a 
careful study of the anatomy of winged and apterous aphids, and 
finds distinct differences, not only in external characters but also 
in the internal anatomy, such as the nervous system, the tracheal 
system, the size and shape of the alimentary canal, etc. There- 
fore, if an aphid were to develop wings due to unfavorable ex- 
ternal conditions it must change its entire anatomy, and this 
probably is beyond the power of any organism. 
A young aphid when born has its adult conditions as regards 
presence or absence of wings already determined, and no change 
of environment can effect this. First instar nymphs of both Lach- 
nus pint and Myzus persicae which showed wing pads developed 
wings in every case, even though kept under the most favorable 
condition. On the other hand, young aphids which did not show 
wing pads developed apterous when raised under adverse con- 
ditions. 
In the case of Lachnus pini an alternation of winged and ap- 
terous forms was determined. Although not exhibiting a per- 
fect alternation, the offspring of each individual showed a ma- 
jority of the opposite type. No changes in environment such as 
injury to host, crowding, or adding chemicals to the food of the 
host would change this alternation. A majority of apterous forms 
was always obtained from winged parents even under unfavora- 
ble conditions of life. With Myzus persicae and Aphis gossypu 
this alternation does not exist, since several generations were 
raised without securing any winged forms. 
Kellogg (23) says that Clarke was able to produce winged 
forms of aphids at will by changing the sap of the host plant 
through addition of chemical salts. He used tip cutting of rose 
stems in sterilized sand and watered with solutions of mag- | 
nesium salts of varying strengths. In this way he says he pro- 
*Numbers refer to references cited. 
