Citrus cutworm—Egira (=Xylomyges) curialis
Citrus cutworm (family Noctuidae) is a pest only on citrus. It feeds on other hosts such as oaks but does not cause significant damage to them.
Identification
The adult is a dark gray moth about 3/4 inch long. Eggs occur in a single or double layer of about 40 to 225 eggs on the upper side of leaves. Eggs are spherical and initially milky white, become cream colored, and before hatching turn bluish or dark.
The larvae are mostly brown, gray, green, or pinkish and grow up to about 1 inch long. Except for the youngest larvae, citrus cutworms have a continuous, whitish, lengthwise stripe along each side of the abdomen, head, and thorax. Their skin appears smooth to the naked eye, lacking conspicuous bumps (tubercles) or hairs. When disturbed, older larvae curl and drop to the ground.
Pupae occur underground in an egg-shaped cell composed of soil particles. Pupae initially are pale colored then become dark brown before the adult emerges.
Life cycle
Citrus cutworm develops through four life stages: egg, larva, pupa, and adult. The adults emerge from soil where they pupated in early January through April. They soon mate and females lay eggs on citrus or other hosts. As is common with moths, the adults rest during the day and fly and lay eggs at night.
After hatching, larvae (the cutworms) develop through 5 increasing larger instars. They can be present on citrus from mid-March to early May. Larvae mature after 3 to 6 weeks of feeding, the shorter time when temperatures are warmer.
After completing their feeding, mature last instars (prepupae) drop to the ground and pupate in organic litter or in the top 2 inches of soil. The cutworm remains as an inactive prepupa or pupa for approximately 8 or more months.
Citrus cutworm can complete its entire life cycle on citrus. It has only one generation per year.
Damage
Citrus cutworms early in the season chew and feed on foliage. Healthy trees tolerate this damage. After petal fall the larvae commonly feed on young fruit. Citrus cutworm can cause more fruit damage than other caterpillar species because each larva moves throughout the tree and takes one or a few bites from numerous small fruit. This chewing causes irregular to roundish, brownish scars to form on rinds once fruit grow larger.
Citrus cutworm can generally be ignored in residential citrus trees. Its feeding scars do not affect the internal quality of fruit and older fruit are rarely attacked.
Solutions
Natural enemies commonly provide excellent biological control of citrus cutworm if no broad-spectrum insecticides are applied to citrus trees. Two larval parasitoids (parasites) are highly effective in reducing the next year’s cutworm population. An ichneumonid wasp (Ophion species) lays its eggs in nearly mature larvae. The parasite larva develops and consumes its host after the cutworm constructs its pupal chamber. This biological control is generally overlooked because Ophion larvae and pupae occur hidden in the cutworm’s soil cell. Another ichneumonid (Banchus species) lays its eggs in larvae and kills the cutworms before they mature into pupae. The Banchus larva exits dead cutworms and forms a slender, black pupa.
Trichogramma species egg parasites commonly kill the eggs. In some locations a fungal pathogen sometimes kills up to about 25% of the cutworm pupae. Insect predators of the adults or caterpillars include assassin bugs, ground beetles, larvae of green lacewings, and spiders.
Control ants, reduce dust (e.g., periodically hose off small plants), and avoid the application of broad-spectrum insecticides for all pests on citrus trees to increase the effectiveness of natural enemies. See Protecting Natural Enemies and Pollinators for more tips on conserving parasites and predators.
Citrus cutworm generally does not warrant control action in residential citrus trees. If caterpillars are abundant and intolerable, Bacillus thuringiensis (Bt) or spinosad can be sprayed to thoroughly cover infested plant parts. Add horticultural oil to spinosad to increase its persistence and also control moth eggs and certain other pests directly contacted by the spray. Because spinosad is toxic to bees and some natural enemies, avoid applying it when trees are blooming.
Adapted from Integrated Pest Management for Citrus, University of California Statewide Integrated Pest Management Program (UC IPM).
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