Quick Facts...
- Many species of caterpillars attack Colorado crops; the species
involved will affect control decisions. Use the following
descriptions to identify pests.
Corn Earworm or Tomato Fruitworm
Heliothis zea (Boddie). These caterpillars range in color
from light green (light phase) to almost black (dark phase).
Stripes also vary, but there usually is a pair of narrow dark
lines down the middle of the back and broad dark bands on each
side.
The head is yellow or orange with a light net-like
pattern. Most distinctive are the many microspines on the
skin, as seen with a hand lens. This insect attacks a wide variety
of field and vegetable crops, with sweet corn, tomato and soybean
most important in Colorado. Damage is caused by feeding on ear
tips, fruit, pods and blossoms. Corn earworm does not overwinter
in Colorado. Egg laying activity usually occurs in July.
Western Bean Cutworm
Loxagrotis albicosta (Smith). This small brown caterpillar
is identified by faint diamond markings on the back. Mature
larvae are brown to pale grey with dark brown bands behind the
head. Ear tips are preferred in corn and developing pods in
beans. This insect overwinters in Colorado, although egg laying
does not occur until late July.
Saltmarsh Caterpillar
Estigmene acrea (Drury). These caterpillars are similar in
appearance to the yellow woolly-bear caterpillar, except the
saltmarsh caterpillar has a black head while the yellow woolly-
bear has a yellow head. Both are distinguished from other crop
caterpillars by their long dense hairs. Many garden crops are
attacked, although bean and sugarbeet infestations are most
important in Colorado. Two generations occur per year in
Colorado, with most important damage occurring in August.
Armyworm
Psuedaletia unipuncta (Haworth). The head has dark net-like
markings on a light brown background. Dark brown bars diverging
above the mouth are present on the head capsule. Alternate light
and dark stripes are present on the abdomen and an orange stripe
on each side. The armyworm prefers grass crops such as corn,
small grains and milo (sorghum), but some broadleaf crops may
occasionally be damaged. Larvae are usually found in sheltered
locations or below the soil surface during daylight. Several
generations occur per year with the first damage occuring very
early in the growing season.
Zebra Caterpillar
Melanchra picta (Harris). This insect is easily
distinguished from other crop caterpillars by two bright yellow
stripes running along each side of the body and separated by
alternating black and white stripes running around the body.
This insect can be found defoliating a variety of broadleaf field
and vegetable crops, ornamental trees and flowers. It is
generally not considered to be a serious pest. Damage from these
insects can be expected in late May and June and again in late
August and September.
Clover Cutworm
Scotogramma trifolii (Hufnagel). This is a greenish or
brown climbing cutworm with a broad pink or yellow stripe on
either side of the body. The abdominal spiracles are surrounded
by black. Elongate black spots are sometimes found on the back.
This insect is mostly important as a defoliator of sugarbeet, but
has damaged clover. The clover cutworm has two to three
generations per year in Colorado.
Beet Armyworm
Spodoptera exigua (Hubner). A greenish striped caterpillar closely
resembling the clover cutworm but lacking the black markings around the
abdominal spiracles. This insect will attack a variety of broadleaf and
grass crops, but sugarbeet is a preferred host. The beet armyworm has
two to three generations per year in Colorado.
Alfalfa Caterpillar
Colias eurytheme (Boisduval). This caterpillar is dark
green with a narrow white stripe on each side of the body and a
fine red line running through the stripe. The alfalfa
caterpillar is distinguished from other Colorado crop
caterpillars by short, dense, velvet-like hairs covering the head
and body. Occasionally, this caterpillar will be found in other
leguminous crops but is primarily an alfalfa pest. Infestations
are foretold by swarms of yellow butterflies, the adult stage.
Several generations occur per year in Colorado.
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