137 
The use of commercial fertilizers, to force the plants rapidly 
at first, will greatly lessen the amount of injury by the maggot. 
The Onion Thrips 
Thrips tabaci Lind. 
In July or August one sometimes sees whitened onion plants 
in numbers sufficient to give the entire field a hoary look. This 
"white blast," as it is often called, is due to a tiny winged insect, 
the thrips of the onion, sometimes incorrectly called the "onion- 
louse," which often appears in great numbers, feeding first at the 
axils of the leaves. It does not actually eat the leaves, for its 
Fig. 28. Onion Thrips, Thrips tabaci: a, adult; b, antenna of 
same ; c, young larva ; d, full-grown larva. All highly 
magnified. 
mouth parts, which form an inverted cone projecting from the 
under side of the head, are not of the true biting type. It pierces 
the epidermis of the leaf, and by moving the tip of the cone back- 
ward and forward it makes an opening, thru which it sucks the 
juices of the plant. Since this thrips is a general feeder, attacking 
many cultivated plants as well as weeds, it is of great economic 
importance, not only to the truck gardener but to the florist also. 
It is often injurious to cabbage and to cucumber plants in green- 
houses. 
Its eggs are deposited just within the leaf tissue. The young 
( Fig. 28, c) are very minute at hatching, elongate, and pale yellow- 
ish. The adults (Fig. 28, a) closely resemble the young in shape, 
but differ by their darker color, and usually by the possession of 
wings. There are several generations a year, the number varying 
according to the season. The winter is passed in either the larval 
or the adult stage. 
Natural Checks. — The insect enemies of this thrips are of no 
importance, but the character of the weather has a noticeable in- 
fluence on its abundance, wet weather being decidedly to its dis- 
advantage. * 
Remedial Measures. — The standard insecticides for thrips are 
kerosene emulsion and whale-oil soap. Spraying must begin at the 
first appearance of the insects, and must be repeated in a week or 
ten days. The most effective indoor remedies are thoro and fre- 
