8 BULLETIN 616, U. S. DEPARTMENT OF AGRICULTURE. 
A few eggs also pass the winter in the ripening fruit and are thus 
distributed to practically every part of the United States. Some 
of these eggs may hatch and survive from fruit marketed in tropical 
and subtropical climates, but there is very little danger of the insects 
becoming established in any of the localities where oranges are 
marketed generally. 
Thrips larvse are to some extent distributed on nursery stock 
and, though not so difficult to detect as eggs, would be overlooked 
very largely in commercial inspection because of their minute size 
and habit of hiding in crevices in the bark. It is probable that 
occasionally the larvae are shipped on fruit, especially on the Valencia 
orange, but nearly mature fruit has little attraction for them, and 
it is further probable that few survive the handling incidental to 
picking and packing. 
Local spread is accomplished largely by flight. The citrus thrips 
is a very ready flier when disturbed or when it desires better food. 
An observer standing in a favorable position with regard to the 
light may see numJbers of these minute insects leave one tree and 
make for another, usually disappearing at a distance of 4 or 5 feet 
because of the light not striking just right. The insect will leave 
either tree or orchard as soon as leaves, stems, and fruit become 
somewhat tough. Thus in a grove of young Valencia trees where 
thrips were present to the number of 80 to 150 per leaf at one exami- 
nation, not a single adult thrips could be found two weeks later. 
The explanation was that the leaves had hardened and were no 
longer suitable as food, while on some older navel trees near by a 
luxuriant growth of leaves had just reached prime condition for 
food, and here the insects were found in as large numbers as they 
had been found on the trees they had deserted. 
The citrus thrips usually takes a rapid spiral or zigzag course in 
short-distance flights, but in extended flights the course is more direct. 
The flight somewhat resembles that of katydids and grasshoppers. 
By mounting in a strong wind the thrips undoubtedly would fly a 
mile or possibly more. 
FOOD PLANTS. 
Although the citrus thrips thrives best and reaches its maximum 
abundance on plants of the citrus group, it feeds continuously or 
occasionally on plants widely separated botanically from the citrus 
group. In Table I the food plants are arranged according to the 
extent of infestation as nearly as possible in the order of their im- 
portance as food for thrips. There is very little difference, however, 
in the extent to which the different plants in Group III are infested, 
and certain plants in Group II are infested almost as badly as any 
of the citrus fruits of Group I. It will be noted in Table I that the 
