94 INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 



pest, and this accounts for the great and infinite numbers. It has 

 been estimated that a single stem-mother will give rise to one billion 

 insects during a single season. With the coming of cold weather, 

 and after the first frost, there is a rapid diminution in numbers, 

 and soon practically all of the winged individuals disappear. This 

 is brought about, by the development of true sexual forms, male and 

 female. 



Sexual Forms.— The viviparous females of the late fall, instead of 

 producing individuals of their own kind, give birth to true sexual 

 forms, male and female, both of which are apterous. 



Sexual Female.— The sexual egg-laying female is much smaller 

 than the summer form, and varies from a rich green to a brownish 

 or reddish color. The head, cornicles, feet and tips of antennas are 

 dark. 



Sexual Male. — The males are very small, hardly half as large as 

 t he other lice. They are easily recognized by their frail and slender 

 bodies, long legs and light yellow color. The head and tail are 

 noticeably dark. They are much more active than are the sexual 

 females, with which they associate and may be confused. These 

 sexes mate and the females lay the eggs which give rise to the first 

 stem-mothers in the spring already referred to. 



Nature of Work. — This aphis infests principally the tender terminal 

 shoots, causing the leaves to curl and turn yellow. The young fruit 

 is also attacked and rendered knotty and unfit for market. 



Distribution.— The green apple aphis is common throughout the 

 entire State and often proves to be a serious pest in many parts. 



Food Plants.— The food plants of the green apple aphis are not 

 many. It is found on the apple, pear, hawthorn, loquat, quince and 

 flowering crab. Of the apples, those which appear to be the favorites 

 are the Missouri Pippin, Rome Beauty, Black Twig, Ben Davis and 

 Greening, though it works just as effectively on many other varieties. 

 The Northern Spy is fairly free from its attacks. 



THE BEAN APHIS 01 



Aphis rumicis Linnseus 

 (Fig. 75) 



Description. — The adult apterous and winged females vary in color 

 from reddish-brown to almost black. The bodies are often covered 

 with a fine, white powder which may give them a grayish or even 

 whitish appearance. The young are light reddish-brown. 



Life History. — The life history of this species is the same as that 

 of the melon aphis. 



Distribution. — This aphis occurs throughout the entire State, but 

 is more abundant in the southern part. 



Host Plants.— Beans (all varieties), dock, English ivy and lambs- 

 quarters are attacked. 



"'In the first edition and previous works of the writer, this aphis has been listed 

 as Aphis hcricru Kalt. H. F. Wilson believes this species to be A. viburni Scop. Besides 

 ibove plants it also attacks nasturtium and snowball. The eggs are laid upon 

 the latter. 



