202 PLANF LICE. 
Nectarophora (Siphonophora) avene Fab. (The Wheat Plant- 
louse). 
Our wheat plants have a large number of enemies, and in 
some seasons the above plant-louse has caused great losses by 
sucking the sap from the leaves, stems, and young ears. Rye 
is also susceptible to injury. The winged insect, shown in Fig. 
159, is green, varying in shade, with a large egg-shaped spot on 
each side of the thorax, and with a row of blackish dots on each 
side of the abdomen. The feelers, also shown in Fig. 137, are 
about as long as the body, the legs have pale-greenish thighs, and 
dull ochre, black-tipped shanks. Other details are also given. 
The wingless forms are similar in shape, but are more uniformly 
green in color, and the very young lice are more elongated and 
of a deeper green. The sensoria or pit-like sense-organs are 
shown in the lower half of the first long joint. 
We repeatedly had invasions of such plant-lice, and they 
caused a decided shrinkage in our wheat crops. But happily so 
many parasites were at work that the lice soon disappeared for 
a number of seasons. 
With the new light thrown upon the life-history of the 
Apple Plant-louse, we can well understand why entomologists 
were unable to discover the male of this insect, and why there 
was no evidence that the species ever had a true egg state. 
Phorodon humili Schrank. (The Hop Plant-louse). 
This insect, in some years very destructive in the hop grow- 
ing regions of this country and of Europe, also has a very curi: 
ous life-history, the essential parts of which will be given. 
The insects during autumn leave the old hop-plants, and 
migrate to the different kinds of wild and cultivated plums, where 
they deposit their little glossy, black, ovoid eggs, on the terminal 
buds, especially in crevices where they are more or less protected 
(Fig. 160). From each winter-egg a stem mother hatches, Fig. 
160, which is stouter, longer-legged, and has shorter honey-tubes 
than the latter generations. Three parthenogenetic generations 
are produced upon the plum, the last one being winged, Fig. 162. 
This winged louse, sometimes called a “migrant,” instinctively 
flies to the hop-plant, which is entirely free from attack previous 
to this time. A number of parthenogenetic generations are now 
