40) SOME INSECTS INJURIOUS TO TRUCK CROPS. 
The moisture conditions which are favorable were determined in 
the laboratory. The larvee lived in soil that was quite wet, but when 
it was saturated they were drowned. On the other hand, a slightly 
moist soil seemed most favorable, and when it dried out they soon 
died. Any soil with a moderate moisture content appears to be favor- 
able for the growth of the larvae, the texture having no influence 
whatever upon them. 
Food.—The majority of larve are located close around the hop 
vine where the soil is filled with tender filamentous roots (fig. 12). 
A few, however, were found around the roots of lambs-quarters, 
chickweed, and mangel. All of these tender rootlets, and perhaps 
many others, are fed upon by the larve. 
THE ADULT. 
Food plants —The hop flea-beetle has been observed feeding upon a 
large number of plants. Some of these are distinctly preferred ; 
others are accepted after the beetles have fed upon the hop or mangel ; 
and still others are attacked in the field, but not after the insects 
have eaten of their preferred food plants. 
A series of experiments was conducted to determine which plants 
were preferred and their order of preference. Beetles were confined 
on several species of plants, and each day when fresh food was sup- 
plied the species which was eaten the most was left out. Thus by 
elimination the order of preference was obtained. This order for 
beetles captured on the hop was found to be quite different from that 
for beetles captured on the mangels, as is shown by the following 
list : 
TABLE II.—fFood plants of the hop flea-beetle. 
In order of preference of beetles taken from In order of preference of beetles taken from 
the hop. the mangel. 
Hop (Humulus lupulus W..). Nettle (Urtica dioica L.). 
Nettle (Urtica dioica L.). Rhubarb (Rheum officinale Baill.). 
Tomato (Lycopersicum esculentum Radish (Raphanus sativus L.). 
Mill.). Mustard (Brassica nigra 1.). 
Mangel (Beta vulgaris Moq.). Lambs-quarters (Chenopodium  al- 
Radish (Raphanus sativus L.). bum 1..). 
Mustard (Brassica nigra L.). Mangel (Beta vulgaris Moq.). 
Lambs-quarters (Chenopodium al- Hop (Humulus lupulus L.). 
bum T..). Watermelon  (Citrullus vulgaris 
Watermelon  (Citrullus vulgaris Schrad.). 
Schrad.). 
82 
