59 - 
ance and limited to innoxious numbers by natural enemies, no better 
example could be cited than is afforded by this plant-louse. Its 
natural enemies include several species of ladybirds or " lady bugs," 
syrphus flies, aphis lions, the larvae of lace-wing flies, numerous 
species of minute hymenopterous parasites, and a parasitic fungus. 
The insect enemies are most effective in destroying the plant-lice in 
dry and warm weather. In a cool, damp atmosphere, which is apt to 
be encountered early in the season when plants are first set out, the 
insect enemies are as a rule less active, and at such times injury by 
plant-lice is likely to be most severe. 
The species shown in figure 58, known as the convergent ladj^bird 
{Hippodamia co7ivergens)^ is one of the most beneficial insects, as it is 
Fig. 5S.—Hippoda7nia convergens: a, 
adult; b, pupa; c, larva- 
Entomology). 
-all much enlarged (original, Division of 
a most active destroyer of plant-lice which feed on vegetables. It 
is common on sugar beets, and it is interesting to note that on one 
occasion it was reported as feeding on the leaves of that plant in 
Oregon (Bui. 26, o. s., Div. Ent., p. 11). 
METHODS OF CONTROL. 
The melon louse, although a difficult insect to treat when it occurs 
on cucurbits and some other plants, can be more readily controlled on 
beets. In fact, all of the leaf -infesting plant-lice can be destroyed on 
beets by means of sprays and other washes and by some of the ordi- 
nary general methods of farm practice. 
Kerosene emulsion. — The standard remedy for plant- lice is kerosene- 
soap emulsion, made by combining 2 gallons of kerosene, half a pound 
of whale-oil or fish-oil soap or 1 quart of soft soap, with 1 gallon of 
water. 
In preparing this eniulsion the soap is first dissolved in boiling 
water and then poured while boiling hot, but away from the fire^ into 
the kerosene. The mixture is then churned somewhat violently for 
about five minutes by means of a force pump and direct discharge 
