107 



JIealy Plum Arms i niiiiloiitrni.s iiriiiu) 



is a species of aphis whieh attaclis tlio young shoots anil under sides of the 

 leaves of plum and prune trees. When first hatched they are whitish in colour, 

 but as they increase in size they become darker. The insects and infested 

 leaves are covered with a whitish powder. 



Their life history i.s similar to that of the green a|ihis, and the remedies 

 used for that pest should be applied, taking care to wet the under sides of the 

 leaves, and repeat the sjiraying to insure the destrucliim ot the pests. 



Hor .\iMns (Plioroflon Jiiiiiiiili ) . 



Wlierever it occurs, whether in England or on the continent of Europe, in 

 New York. Wisconsin, or on the Paciflc Coast, the Hop Plant Louse (Phorodnn 

 humuU) has substantially the same life round. The eggs are laid in the fall 

 on different varieties and species of the plum, both wild and cultivated. They 

 are small, glossy, black, ovoid, and are attached to the terminal twigs. 

 especially in the more or less protected crevices around the buds. 



From an egg hatches in the spring, abont the time when the ]ilura linds 

 begin to burst, a stout female ]ilaut-lonse. known as the stem-mother, which 

 differs from the summer individuals by having shorter legs and shorter honey 

 tubes. 



She gives birth without the intervention of the male, to living young, and 

 this method of propagation continues initil the last generation of the season. 

 The second generation grows to full size and gives birth to a third, which 

 becomes winged and develoi)S after the hops have made consid(>rable growth in 

 the yards. The winged plant-lice then tly from the plums to the hops, deserting 

 the plum tree entirely and settling upon the leaves of the hops, where they begin 

 giving birth to another generation of wingless individuals. They multiply with 

 astonishing rapidity. Each female is capable of producing on an average 

 about one hundred young, at the rate of three per day, under favourable con- 

 ditions. Each generation begins to breed about the eighth day after birth, so 

 that the issue from a single individual runs up. in the course of a summer, to 

 trillions. The issue from a single stem-mother may thus, under favourable 

 circumstances, blight hundreds of acres in the course of two or three months. 

 From live to twelve generations are jiroduced in the course of the summer, 

 carrying us in point of time to the hoi)-l>ifking season. Tliere then develops a 

 generation of winged females (sexuparie), which fly back to /lie plum tree and 

 give birth to the true sexual females, which never ac(]uire wings and never 

 leave the plum tree. By the time this generation has matured, which requires 

 but a few da.vs, varying according to the temperature, belated winged indi 

 vidnals. which are the true males, fly in from the hop-fields. These fertilise 

 the wingless true female upon the plum leaves, and these soon thereafter lay 

 the winter eggs. Thus there is but one generation of sexed individuals pro- 

 duced, and this at the close of tlie life round — the females wingless on plum 

 trees; the males winged on hojis. All intervening generations are composed of 

 virgin females only {iiiirtliciioiinirtii-) . This is the invariable round of the 

 insect's life. 



