138 
qiient fumigation with tobacco and tobacco extracts, or with hydro- 
cyanic acid gas. 
Clean culture is very important, since thrips hibernate on weeds 
and grasses along the edge of the onion fields. By plowing up all 
weedy and grassy land late in fall, after the thrips have left the 
onions, or by thoroly burning over such land during the winter, 
the number of thrips can be greatly diminished. Entire com- 
munities should practice these farming methods, for otherwise 
fields properly cared for may become reinfested from diose 
neglected. 
GARDEN PEAS 
Garden peas are grown to a considerable extent by many of 
the market gardeners, and one insect pest, the pea-louse, has been 
found to do great injury to this crop in Illinois. 
The Pea-louse 
MacrosipJiuin pisi Kalt. 
(NcctaropJiova destructor, Siplioxopliora pisi, .Ipliis pisi) 
This plant-louse (Fig. 29) is common in all parts of the United 
States, and is a pest of some importance in Europe, its original 
N 
\ 
r 
\ 
tf 
■ 
\ 
9^ i 
1 
■*SP^HF 
H 
..^ 
^^H 
Fig. 29. Pea-louse, Macrosipliuui pisi, on stems of red clover 
Natural size. 
