16 THE EED SPIDER ON HOPS IN CALIFORNIA. 
covered and often connected by a web which appeared reddish-brown 
or silvery, according to the number of mites present. The mites were 
frequently found clustered like swarms of bees (PL I, figs. 1, 2), and 
the lower ones in dropping off were blown several inches by the wind. 
That migration did not take place during the early part of the sea- 
son was evidenced by the fact that 26 vines which were planted that 
season were noted to be free from mites July 25, 1911, while the sur- 
rounding older vines were thoroughly infested. Soon after the migra- 
tions commenced, however, mites were seen upon these vines. 
FOOD PLANTS. 
Tetranychus bimaculatus has a remarkably large number of host 
plants, and as will be seen from the following list, these plants belong 
to a wide range of families, including glabrous and hirsute plants. 
For convenience the following list has been divided into three parts. 
The first part contains a list of greenhouse and ornamental plants 
attacked by the mites; the second, a list of plants attacked hi the field; 
and the third, a list of plants which were observed to be infested hi 
and around the hopyards hi the Sacramento Valley, Cal. 
List of food plants of Tetranychus bimaculatus. 
Greenhouse and ornamental plants, etc. — Rose, violet, carnation, mignonette, clematis, 
pelargonium, abutilon, fuchsia, passiflora. manettia, bouvardia, feverfew, verbena, 
heliotrope, honeysuckle, hydrangea, salvia, morning-glory, moonflower. cypress vine, 
phlox, aster, chrysanthemum, dahlia, sunflower, goldenglow (Rudbeckia sp.), calla, 
Easter lily, Boston smilax, mimulus. slipper flower (Calceolaria sp.). canary bird vine 
(Tropxolum peregrinum), thunbergia. wedding bells (Burgmansia arborea), castor-oil 
bean. Asparagus plumosus. cuphea, godetia. caladium. tomato, cucumber, onion, 
and sweet pea. 
Field plants, shrubs, and trees.- — Bean, lima bean, cowpea, pea. cucumber, chayote 
(Sechium edule). cantaloupe, watermelon, squash, celery, eggplant, pepper, tomato, 
pepino (Solanum muricatum), cotton, okra, corn, raspberry, blackberry, table and 
sugar beets, hops, hemp, alfalfa, clover, peanut, groundnut (Apios apios), English ivy, 
ferns, privet, hollyhock, Kentucky coffee tree (Gymnocladus canadensis), wistaria, hop 
tree (Ptelea trifoliata), pecan, ornamental sassafras, cedar, arborvitse, Colorado blue 
spruce, maple, horse-chestnut, Carolina poplar, and birch. 
Host plants in and near hopyards. — Mat-grass (Lippia nodifiora), Amaranthus blitoides, 
hedge mustard (Sisymbrium officinale), wild sunflower (Helianthus lenticularis), alkali 
mallow (Disella hederacea), Persicaria lapathiflora (perennial of Persicaria), rough pig- 
weed (Amaranthus retroflexus) , prickly lettuce (Lactuca scariola), blessed thistle 
(Cnicus benedictus), alfalfa (Medicago sativa), burdock (Arctium lappa), bun- clover 
(Medicago hispida), wild morning-glory (Convolvulus sp.), and cheese weed (Malva 
parviflora). It has also been observed on Jamestown or Jimson weed (Datura stra- 
monium), ironweed, Jerusalem-oak weed, wild geranium (Geranium memlatum), and 
Ligustrum amurense. 
From the foregoing list it is evident that this mite is nearly omniv- 
orous x so far as plant life is concerned, and without doubt there are 
many other food plants not included in this list. 
i It is more than likely, since its feeding habits are of a suctorial nature, that this mite will thrive upon 
nearly any form of vegetation in which the pubescence of the underside of the leaf is not so heavy or luxuriant 
as to prevent its direct attack upon the leaf tissue proper. 
