Kill black cutworms (Agrotis ipsilon Hufnagel) with Entomopathogenic Nematodes / by Ganpati Jagdale

  • The black cutworm, Agrotis ipsilon (Hufnagel), is a polyphagous pest, feeding on almost all vegetables, many grain crops, ornamentals, turf grasses and weeds.
  • The plants damaged by black cutworms include beans, broccoli, cabbage, carrot, Chinese broccoli, Chinese cabbage, Chinese spinach, clover, corn, cotton, eggplant, flowering white cabbage, green beans, head cabbage, lettuce, mustard, potato, spinach, sugarcane, sweet potato, tomato, turnip, alfalfa, rice, sorghum, strawberry, sugarbeet, tobacco, bluegrass (Poa pratensis), curled dock (Rumex crispus); lambsquarters (Chenopodium album), yellow rocket (Barbarea vulgaris) and redroot pigweed (Amaranthus retroflexus).
  • There are five to nine larval instars that generally feed on seedlings at ground level by cutting off the stem causing a significant damage especially in newly planted fields. They also feed on roots and the below ground stem.
  • They can damage turfgrass by clipping off their blades and shoots.
  • The biological control agents including a bacterium Bacillus thuringiensis var. kurstaki, and entomopathogenic nematodes have a great potential against black cutworms.
  • Bacillus thuringiensis var. kurstaki produces a toxin that paralyzes the gut of the caterpillar.  This toxin does not kill the caterpillars quickly, but it does cause the caterpillars to stop feeding, which in turn reducing the intensity of the damage.
  • Since caterpillars of cutworms are highly mobile insects, the entomopathogenic nematodes with ambush type of foraging strategy can be used very effectively for the management of cutworms.
  • For example, Steinernema carpocapsae, is an ambusher nematode species that can control black cutworms very effectively if applied at a rate of 1 billion nematodes/acre on golf course greens.

How Entomopathogenic Nematodes Kill Black Cutworms

  • When the infective juveniles are applied to the soil surface or thatch layer, they start searching for their hosts, in this case caterpillares.
  • Once a caterpillar has been located, the nematode infective juveniles penetrate into the caterpillar body cavity via natural openings such as mouth, anus and spiracles.
  • Once in the body cavity, infective juveniles release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae) from their gut in the caterpillar blood.
  • In the blood, multiplying nematode-bacterium complex causes septicemia and kills shore fly larvae usually within 48 h after infection.
  • Nematodes feed on multiplying bacteria, mature into adults, reproduce and then emerge as infective juveniles from the cadaver to seek new larvae in the potting medium/soil.