101 
The Diamond-back Moth 
Pliitella maculipennis Curt. 
(P. crucifer arum, Cero stoma brassicella) 
The small green larva of the diamond-back moth (Pliitella 
maculipennis) was found in 1909 destroying stock and sweet 
alyssum in several Illinois greenhouses, where it has been known 
as a serious pest for several years. It riddles the leave with holes, 
killing small plants outright, and greatly disfiguring and weaken¬ 
ing the larger ones. 
This insect, originally imported from Europe but now of 
world-wide distribution, has been known in Illinois for years as 
a pest of cabbage and related crops. It was in 1883 that Dr. C. V. 
Riley* first found it attacking wallflower (Cheiranthus cheiri ) and 
stock (Matthiola annua) in greenhouses, and in 1890 that Dr. 
James Fletcherf noted it as a troublesome pest of garden stocks 
and wallflowers in Canada. In 1906, Miss Edith M. Patcht re¬ 
ported its occurrence in a greenhouse at Ellsworth, Maine, where 
stocks were greatly damaged. 
The abundance of this insect in greenhouses has no doubt been 
entirely due to the growing of cabbages in the vicinity of the 
houses. In the fall of 1909 Mr. Hild, one of the florists troubled 
with this pest, destroyed, at our suggestion, all of the cabbages 
growing around his houses, and he has since had practically no 
trouble from this pest. 
The slender light green larva (Fig. 15, a, b, c) measures less 
than two fifths of an inch when full grown. For a short time 
after hatching it mines between the upper and lower surfaces of 
the leaf, being entirely concealed, but it soon begins to feed fully 
exposed on the lower leaf-surface, and gradually riddles the leaf. 
If the worms are abundant the plants may be completely de¬ 
foliated, especially in the case of stocks and sweet alyssum. They 
are very active, wriggling away when disturbed, and usually drop¬ 
ping, suspending themselves from the leaf by a single silken 
thread. When full grown the larva makes a thin, lacelike cocoon 
(Fig. 15, e) on the under side of the leaf, on the stem, near its 
base, or in any convenient place of concealment, and in this it 
changes to the pupa (Fig. 15, d, i), which may be seen within 
the cocoon as a pale green or brownish spindle-shaped object. 
^Report of the Entomologist. Ann. Rep. [U. S.] Comm. Agr., 1883 , pp. 
129 - 130 . 
tReport of the Entomologist and Botanist. Ann. Rep. Exp’t’l Farms, 
Canada, 1890 , p. 165 . 
flnsect Notes for 1906 . Bull. Me. Agr. Exper. Station, No. 134 (Dec., 
1906 ), pp. 223 - 224 . 
