24 THE BEAN THEIPS. 
marked by feeding of some tlirips furnishes good evidence that the 
bean thrips has been feeding there at some time. The larvae feed in 
much the same manner as the adult, the mouthparts being practically 
the same. They gradually scrape out the contents of the leaf, leav- 
ing silvery spots, which as they become abundant often unite and 
gradually destroy the vitality of the leaf. Most of the eggs seem to 
be laid on the underside of the leaves, although the writer has ob- 
served eggs to hatch from the upper side also. As a consequence 
the larvae begin feeding largely on the underside of the leaves. After 
hatching they do not move far before commencing to feed, during 
which time, under ordinary conditions, they move very little. When 
plants are first infested the larvae seem to feed close to the leaf 
veins, but as they become more abundant they scatter in groups over 
the entire leaf surface. Like those of the greenhouse thrips the 
larvae of this species seem to cluster in colonies and unless disturbed. 
or in need of fresh food, remain thus. The colonies are in many cases 
found in between two veins of the leaves. When disturbed the larvae 
will violently twitch the end of the abdomen with its drop of liquid 
and move away rapidly. Apparently this is used as a means of de- 
fense, for the writer, in work with a parasite of this thrips, observed 
at times that these larvae when touched from in front by the parasite 
flung the abdomen around and moved rapidly away. When this oc- 
curred the parasite generally retreated, but returned to the attack 
and later usually succeeded in ovipositing in its host. 
The larvae and adults of this thrips feed together in colonies, and 
as the leaves become crowded or dry from excessive feeding the 
larvae move in search of fresh food. Gradually the whole under- 
side of the leaf attacked becomes infested by the larvae and then 
the surface as well. In fact, the writer has seen leaves so heavily 
infested by the larvae of this tlirips as to give them a decidedly 
larvae move in search of fresh food food. Gradually the whole under 
reddish color, due to the bodies of the insects. So far this larva 
has not been observed feeding in the blossoms of any plant, 
but in some cases it has been observed feeding on green tomatoes, 
and when bean vines are badly infested the pods are also attacked. 
Indeed, when excessively abundant, these insects will not only 
cover both sides of the leaves, but the stem of the plant as well. 
The larvae as a rule feed unprotected on the leaf, but at times may 
be found feeding under the protection of red-spider webs. 
Apparently these minute creatures are not affected by dust, as 
the writer has found them feeding in large numbers on leaves of 
spiny lettuce in an alley in the city of Los Angeles when the leaves 
were so thickly covered with dust as completely to hide the surface. 
It would seem that with the enormous clouds of dust that arise in 
this section during the entire summer, completely coating the larvae, 
they would speedily succumb. 
