Bugs for Growers

Susceptibility of black cutworms to beneficial nematodes

June 09, 2012

In my last blog post, I demonstrated the cutworms were susceptible to beneficial entomopathogenic Steinernema carpocapsae nematodes. These results are confirmed by a recent finding of Ebssa and Koppenhofer (2012), who also demonstrated that the Steinernema carpocapsae nematodes were highly effective against cutworm Agrotis ipsilon. These researchers also demonstrated that the other species of beneficial nematodes including Heterorhabditis bacteriophora, Heterorhabditis megidis and Steinernema riobrave were effective in killing larval stages of cutworms.

Literature

Ebssa, L. and Koppenhofer, A.M. 2012. Entomopathogenic nematodes for the management of Agrotis ipsilon: effect of instar, nematode species and nematode production method.Pest Management Science 68: 947-957.

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Use entomopathogenic nematodes to control cutworms

March 25, 2012

Cutworms: A key pest of turfgrass foliage How to identify cutworms?

Adult cutworm moths are yellowish brown or dark gray in color with several black dots on the wings. Full grown cutworm caterpillars are reddish or blackish brown color with greasy look (see below photo of a full grown caterpillar, which was found on turfgrass in my yard) and as shown in the picture, they curled into a C-shaped ball when disturbed (see photo below).

[caption id="attachment_77" align="alignleft" width="300" caption="Full grown cutworm caterpillar"]

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[caption id="attachment_79" align="alignleft" width="300" caption="C-shaped cutworm larva"]

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Life cycle of Cutworms:

Cutworms develop through four different stages: Egg, caterpillar/larva, pupa and adult moth.
Adult moths are emerged from over-wintering pupae early in the spring.
Adult moths lay singly over 1200 eggs over several days near the tips of the turf grass leaf blades.
Under optimal environmental conditions, eggs hatch within 10 days.
After hatching from egg, young larval stage immediately starts feeding on grass foliage and molts (shed its cuticle) five times, go through six stages (instars) of development and depending upon length of season they can complete 3 to 6 generations.
In the late summer mature, larvae burrow into ground to form pupa, which survive during winter.

Damaging stages of cutworms:

All six stages/ instars of caterpillars/larvae of cutworms cause damage to grass or other host plants.
Adult moths do not cause any type of damage to grasses or other plants.

How is damage caused?

As name implies, at the time of feeding, all the six stages of caterpillars of cutworm cut off leaves or stems to the crown of turf grass. Caterpillars generally feed on grass at night but hide under thatch during day time. The damage caused by cutworms is easily identified because of the presence of circular spots of dead grass on lawns/golf courses. The presence of circular spots of dead grass in the middle of a lawn/golf course can reduce its aesthetic value.

Biological control of cutworms:

Both biological control agents including Bacillus thuringiensis var. kurstaki (a bacterium which produces a toxin and paralyzes the gut of the caterpillar) and entomopathogenic nematodes have a potential to manage cutworms.
Entomopathogenic nematodes also recognized as beneficial nematodes have showed promising results in controlling cutworms.

Why we should use entomopathoegnic nematodes?

They can kill cutworm larvae with 48 hours after application.
They are commercially available and easy to apply.
They are not harmful to children, dogs, cats, personnel involved in its application and beneficial insects like honeybees.
They do not need a special permission to apply because they are exempted by EPA.

Which species of entomopathogenic nematodes are effective against cutworms (see literature below)?

Steinernema carpocapsae (see picture on the right side about cutworm caterpillar/larva killed by Steinernema carpocapsae nematodes)
Heterorhabdtis bacteriophora [caption id="attachment_82" align="alignright" width="300" caption="Entomopathogenic nematode, Steinernema carpocapsae killed cutworm caterpillar cadaver in a white trap"][/caption]

What stages of cutworms can be targeted?

All six stages of caterpillars/ larvae are susceptible to entomopathogenic nematodes.
Pupae are also susceptible to entomopathogenic nematodes.

What is a recommended dosage of entomopathogenic nematodes required to control cutworms?

For the successful control of most of the soil dwelling insect pests, the optimal rate of 1 billion infective juvenile nematodes in 100 to 260 gallons of water per acre is generally recommended (See Table for appropriate amounts of nematodes required for different sizes of areas to be treated).

When to apply nematodes

To target cutworms, entomopathogenic nematodes should be applied starting in late spring i.e. when young larval (caterpillars) stages (instars) of cutworms are already hatched from eggs (laid in early spring) and started feeding on grass leaves.
Since nematodes are very sensitive to UV light, they will die within a minute or two when exposed to full sun. Therefore, nematodes should be applied early in the morning or late in the evening to avoid exposure to UV light.
Another advantage of applying nematodes late in the evening is that cutworm caterpillars can be easily targeted because they are generally active and searching for food during night and easily found by entomopathogenic nematodes like Steinernema carpocapsae that uses sit and wait (ambush) strategy to attack its passing by host. Since cutworm caterpillars are moving actively during night in search of food, they can easily come across to entomopathogenic nematodes like Heterorhabdits bacteriophora that uses cruising strategy to finds its host. These nematodes can also find caterpillars that are hiding under thatch during day time.

How entomopathogenic nematodes kill cutworms?

After application of either Steinernema spp. or Heterorhabditis spp. on the lawns, their their infective juveniles find cutworm larva or pupa and enter into its body cavity through natural openings such as mouth, anus and spiracles.
Once infective juveniles of both Steinernema spp. and Heterorhabditis spp are in the insect body cavity, they release several cells of symbiotic bacteria, Xenorhabdus spp. and Photorhabdus spp., respectively from their gut via anus in the insect blood.
Insect blood is conducive for the multiplication of symbiotic bacteria. In the blood, multiplying nematode-bacterium complex causes septicemia and kill their insect host usually within 48 h after infection.

Where can you buy entomopathogenic nematodes?

Both Steinernema carpocapsae and Heterorhabdtis bacteriophora nematodes are sold in our store.
Steinernema carpocapsae nematodes available both in liquid (sponge-water suspension) and granulated formulations.
Heterorhabdtis bacteriophora nematodes available only in liquid (sponge- water suspension) formulations.

How long does it take to deliver nematodes?

We can directly deliver entomopathogenic nematodes at your facility in person (this service available only in Athens,Georgia) or by UPS throughout US within 3 days after receiving order.

Literature:

Ebssa, L. and Koppenhofer, A.M. 2011. Efficacy and persistence of entomopathogenic nematodes for black cutworm control in turfgrass. Biocontrol Science and Technology 21: 779-796.

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