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the plant-lice. The ladybirds, both larvae (Fig. 31, a) and adults 
(Fig. 31, c), are examples of the first class, and are usually to 
be found devouring plant-lice whenever the latter are abundant. 
The parasites of the plant-lice are minute wasp-like insects living 
within the bodies of their hosts. A parasitized aphid first becomes 
sluggish and then inactive, and a darkening and swelling of the 
body follow, the integument becoming hard and brittle, and the 
Fig. 31. Common Ladybird, Megilla maculata: a, 
larva; b, empty pupa skin; c, beetle. Knlarg-ed as indi¬ 
cated. (U. S. Dept, of Agriculture.) 
color finally changing to a uniform brown or blackish brown. The 
adult parasite emerges through a circular hole which it cuts near 
the posterior part of the body of the louse. Predaceous and par¬ 
asitic insects often check the plant-lice, and may sometimes pre¬ 
vent further injury by them during the season. 
Remedial Measures .—As a rule aphids on greenhouse plants 
may be easily held in check, or even eradicated, by fumigation 
with hydrocyanic acid gas, or with tobacco stems or one of the 
tobacco extracts. The former is preferable, and the method of 
using it is given in the discussion of remedies for the greenhouse 
white fly (pages 132-134). 
When it is undesirable to fumigate with the gas, one of the 
various commercial nicotine extracts and preparations which are 
now on the market under such trade names as “Nico-fume,” 
“Nicoticide,” “To-ba-keen,” “Aphis Punk,” etc., may be used. 
The reliable and standard brands are more effective than tobacco 
stems, tho more expensive. These preparations come in liquid 
and powder forms, and as rolls of commercially prepared ab¬ 
sorbent paper. The first must be evaporated, either by “painting” 
the steam pipes with it or by placing it in pans and applying heat. 
If the preparation is a powder it is placed in a dish and ignited; 
or if the paper is used, strips of it are suspended and lighted. 
