400 A. E. Verrill—The Bermuda Islands. 812 
Physopoda or Thysanoptera. (Thrips.) 
Onion Thrips ; Tobacco Thrips. (Thrips tabaci.) Figure 187. 
This very small insect is sometimes so abundant as to do consid- 
erable damage to the onion crop, its bites causing the leaves to turn 
yellow and wither, thus stopping the growth of the bulbs. It— 
spreads very rapidly through the onion fields. ‘The larva is whitish, 
but the body of the winged imago is blackish. It is very active. 
Probably spraying with kerosene emulsion is the best remedy, but it 
should be repeated two or three times at short intervals, in order to 
reach all of them, for the winged insects can fly away some distance 
when disturbed and thus many may escape. Solutions of copperas, 
etc. are used as a spray both against the thrips and the fungous 
disease. It is considered the same as the thrips that often does 
much damage to tobacco. 
This insect was first recorded as occurring on the onion in Ber- 
muda by A. G. Shipley, Bull. No. 10, p. 18, Miscell. Information, 
Royal Kew Gardens, 1887. For full descriptions of adult and larva, 
see Th. Pergande, Insect Life, vii, p. 391-3; and W. E. Hinds, Proc. 
U.S. Nat. Mus., xxvi, p. 179, pl. vii, figs. 69-71, 1902. 
It not only attacks onions and tobacco, but also many other culti- 
vated plants, including melons, cucumber, squash, turnip, cabbage, 
cauliflower, parsley, and many flowering plants. Its effect on onions 
is sometimes called “ white blast.” 
In the United States it was first recorded on onions in Massa- 
chusetts, and as having been known as early as about 1857. It has 
long been known as injurious to tobacco in Europe. 
k.— Pseudoneuroptera. 
Odonata ; Dragonflies. 
A considerable number of Dragon-flies, some of them large and 
handsomely colored, are found in summer. Their larve must be 
very useful in destroying the larve of mosquitoes in the marshes 
and tanks. Whether part of them were introduced by man is uncer- 
tain, but there is no reason to doubt that the larger and stronger- 
winged species might fly directly from the United States, as do 
some of the butterflies, and thus they may have arrived indepen- 
dently of man. The larve or eggs of others may have been brought 
in the water-casks of vessels, and in other ways. 
