LIBRARY

334 COLLEGE ENTOMOLOGY
the twigs of the current year's growth, The adults normally perish
before winter.
The forms discussed above represent normal development in the cooler
temperate regions of species having alternate host plants. There are, however,
many common species like the green peach aphid, Myzus persiaE (Sulzer),
the geum or potato aphid, Macrosiphum euphorbire (Thos.), and the cotton
aphid, Aphis gossypii Glover, which are omnivorous feeders and do not normally
require specific hosts to ensure development but disperse or wander from plant
tl) plant within the range of the winged or crawling migrants. Even in the
case of the mealy plum aphid, which requires alternate hosts, the apterous
forms may crawl from one primary host to another and give rise to new colonies
throughout the entire summer along the mild coastal areas of middle
California. Then, too, species which require alternate hosts and others which
produce sexuales and overwintering eggs in the cooler limits of their distribution
may alter their requirements when inhabiting warmer or milder regions.
Thus in parts of California such common species as the green apple aphid, '
Aphis pomi DeGeer and the rosy apple aphid, A. malifolial Fitch, may repro- '
duce parthenogenetically throughout the entire year by maintaining colonies on
evergreen hos1.s (Cotoneaster, Pyracantha, Cratregus, etc.) during the winter
months. The rose aphid, Macrosiphum roSiE (Linn.), the cabbage aphid, Brevicoryne
brassicre (Linn.), and innumerable other species apparently never produce
sexuales or eggs at all in subtropical and tropical areas. The mealy plum
aphid and other species with complicat.ed life requirements in the north temperate
regions have quite simple habits in the tropics where they may reproduce
parthenogenetically throughout the year on a single host.
The eggs are very small, regularly oval or with a constriction at one end
(Myzocallis arundinarial Essig). They are pale yellow or green when firs1. laid
but soon turn shiny black. Certain species cover the eggs with waxy threads
[Plocomaphis jioccutosa (Weed)] or with transparent waxy rods [Hyalopterus
arundinis (Fab.)], but these accessories soon weather away, leaving the eggs
unprotected save for their location near a bud or in a crack of the bark. They
hatch as the buds begin to swell or open in the spring, and the young feed upon
the developing leaves. Maturity is reached in a very short time, from 2 to 3
weeks, and embryos may be developing in the nymphs even before the last
molt.
A discussion of all the various forms of aphids is impossible here, and a
synopsis of important characters only is included:
I. Females
1. Apterre or wingless parthenogenetic individuals - the commonest memo
bers throughout most of the year. Body more or less undifferentiated
but with distinct head, large eyes, and antennre usually only with
primary sensoria; a few with secondary. UsuallY unicolored - green.
yellow, reddish or maroon, brown, olive, black, and mottled; sometimes
with black pigmentations. Often red and green individuals in