THE COLORADO POTATO BEETLE
This is one of the worst pests of the potato. As the name would imply it
came originally from Colorado but is common now all over the country.
The full grown insect is short and thick with a hard shell, striped with
yellow and black. The grubs, on the other hand, are soft and red or
orange with black spots. Both the grubs and the beetles feed on potatoes
and often completely strip them of their leaves. Since they feed on
foliage they can be very quickly destroyed by dusting or spraying the
plants with a poison such as Paris green or arsenate of lead. The
patches of yellow or reddish eggs are found mostly on the under side of
the potato leaves. When the fat grubs are full-fed they go into the
ground and change to pupae and later to the striped beetles. This pest
should not be mistaken for the so-called old-fashioned potato beetles
which are long and slender and either bluish grey in color or striped
with yellow and black. These are blister beetles and are entirely
different.
OBSERVATIONS AND STUDIES
Watch for the first appearance of the adult beetles in the spring when
the potatoes are just beginning to come up. They pass the winter under
ground and in the spring come out ready to lay eggs on the young
potatoes. Collect and examine the adults. How many stripes have they?
Collect packets of eggs and count them. How many eggs in most packets?
How are they attached to the leaf? How large are the grubs when they
hatch from the egg? Examine the grubs where they are feeding on
potatoes. Do they eat holes through the leaf, or do they eat away the
entire leaf? How fast do they grow? Collect a few in a glass tumbler.
Feed them and watch them grow. What do they do when you touch them? What
does the hard backed beetle do when it is touched? Collect some of the
large grubs with tightly stuffed bodies and put them in a jar with dirt
or sand and see where they go. After a week dig them out and see what
they look like.
[Illustration: The Colorado potato beetle showing stages of development
and work on a potato plant. Note the small patch of eggs and different
sized grub on the plant and the grub, pupa and adult at side.]
Write a short description of the eggs, grubs and beetle, its work and
means of killing it when it is feeding on potatoes. Make careful
drawings of a cluster of eggs, the grub and the beetle.