Earlier this month, Nebraska Extension reported that caterpillars feeding in a western Nebraska sugar beet field were suspected to be beet armyworm, a migratory pest that can cause significant defoliation in a variety of crops. After nearly three weeks of raising collected larvae, adult moths (Figures 1 and 2) were identified by the Entomology Diagnostic Lab in Lincoln as clover cutworm (Anarta trifolii), also known as the nutmeg. Parasitoids (Figure 4) also emerged from one of the collected larvae.
Clover cutworm is a cutworm species with a wide host range. Its larvae feed on more than 20 cultivated crops, including alfalfa, soybean, onion, cabbage, tomato, sugar beet, sunflowers, corn and canola. Adult moths have a wingspan of around 1.25 inches with a mottled pattern of sandy brown, dark brown and gray. Like many cutworms, the larvae feed on the foliage, may cut off young plants and are primarily active at night, often curling up when disturbed. Unlike beet armyworm, which migrates north each year, clover cutworm typically overwinters in Nebraska as pupae in the soil and produces two generations annually.
It is important to note that clover cutworm caterpillars can resemble beet armyworm at first glance. However, clover cutworms have differently colored body stripes and lack the distinctive black spot behind the head and above the second pair of legs that is characteristic of beet armyworm (Figure 3).
Although clover cutworm moths have previously been captured in blacklight traps in the Nebraska Panhandle, this is the first known report of clover cutworm feeding in Nebraska sugarbeet. Researchers believe the insect is an occasional pest whose populations likely increased following the mild winter in the Panhandle, allowing larvae to feed on sugar beet fields in early summer.
Fortunately, the producer reported that feeding lasted less than a week and caused relatively little defoliation — likely less than 25%. The plants have since recovered from the damage.
Researchers also found an unexpected ally in the field. Parasitoid wasps that emerged from one of the collected cutworms were identified as members of the genus Meteorus, a large group of beneficial wasps in the family Braconidae that parasitize caterpillars and fly larvae. Their presence highlights the important role beneficial insects play in naturally suppressing crop pests. Because broad-spectrum insecticides can also kill these beneficial insects, their use should be limited or avoided whenever possible.
