102 
The delicate moth emerging, is about a fourth of an inch in 
length, and the wing expanse is three fourths of an inch. The 
wing-pattern is quite variable, but the typical markings are shown 
in the accompanying figures (Fig. 15, /, g, h). Soon after emer¬ 
gence, usually the night after, the moths mate, and numbers of 
minute, round, yellowish eggs are deposited singly on the lower 
Fig. 15. Diamond-back Moth, Plutella ntaculi- 
■bennis; a , larva; b, one segment of same, more en¬ 
larged, as seen from above; c , same, side view; d, 
pupa; e, pupa in lacelike cocoon; /, adult; g, right 
wings of dark variety of same; h, adult at rest, with 
wings folded;/, tip of pupa. Enlarged as indicated. 
(U. S. Dept, of Agriculture.) 
or upper leaf surface or on the stalk near its base, usually on the 
stalk. Being translucent, the eggs take on the greenish color of 
the plant tissue, and are easily overlooked. 
Our breeding experiments during July gave us the following 
results as to the length of the various stages. The eggs hatched 
4 j 4 to 6 (average, 5) days after being deposited. The larval 
stage lasted from 10 to 14 days, with an average of a little less 
than 11 days. The pupal period varied more in length than the 
other stages, its maximum, minimum, and average duration be¬ 
ing respectively 8, 4, and 5 J 4 days. Thus, under what may be 
regarded as optimum conditions, the maximum, minimum, and 
average lengths of the life cycle were respectively 28, 18p?, and 
2 i l / 2 days. 
Natural Enemies .—A small ichneumonid parasite, probably 
Limneria tibiator Cr., was of great value in holding the Plutella 
in check, fifty or seventy-five percent being usually infested by it. 
The parasite deposits its eggs on the Plutella larva, but not until 
after the latter has made its cocoon does the parasitic larva kill 
and devour the green worm. Its own oval cocoon is made within 
that of its host. 
One florist reports that early in the fall, humming-birds en¬ 
tered his greenhouses and caught thousands of the Plutella larvae. 
Remedial Measures .—Clean culture—in this case preventing 
the growth of cruciferous weeds around greenhouses and the 
