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    Bugs for Growers — Steinernema carpocapsae Nematodes

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    Susceptibility of black cutworms to beneficial nematodes

    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.

    Tent worms are susceptible to entomopathogenic nematodes

    Last Monday, I read an article about eastern tent caterpillars on the website of Crossville Chronicle (http://crossville-chronicle.com/features/x1221402699/PLATEAU-GARDENING-Reader-inquires-about-Eastern-tent-caterpillars) and thought that I should share the results of my small experiment that I conducted about an interaction between tent worms and [caption id="attachment_292" align="aligncenter" width="300" caption="Tent worm caterpillar- bugsforgrowers"]"Tent worm caterpillar"[/caption] entomopathogenic nematodes. I hand picked four tent worms, which were crawling on my driveway and tested their susceptibility to an entomopathogenic Steinernema carpocapsae nematodes. In this experiment, I transferred 400 infective juveniles of Steinernema carpocapsae nematodes (100 juveniles/larva of tent worms) in 1 ml of water on a filter paper placed in a plastic dish (9 cm diameter) and then four tent worm larvae were transferred in the same plastic dish. [caption id="attachment_294" align="aligncenter" width="300" caption="Entomopathogenic Steinernema carpocapsae nematode infected Tent worm caterpillars"]"Entomopathogenic nematode infected Tent worms"[/caption] These plates were then incubated at room temperature for 48 hours. After 48 hours of incubation, I found that all the four tent worm larvae were dead.  This means entomopathogenic Steinernema carpocapsae nematodes infected and killed tent worms within 48 hours of infection. This showed me that the tent worms were susceptible to Steinernema carpocapsae nematodes. In order to confirm the infection by entomopathogenic nematodes, tent worm cadavers were transferred in a White trap for the emergence infective juveniles of entomopathogenic Steinernema carpocapsae nematodes. [caption id="attachment_295" align="aligncenter" width="300" caption="Entomopathogenic nematode Steinernema carpocapsae infected cadavers of Tent worm caterpillars in a White trap"]"Entomopathogenic nematode and Tent worms"[/caption] After 12 days, I saw under microscope that the thousands of infective juveniles of Steinernema carpocapsae were emerged from tent worm cadavers in a White trap . Thus these results suggest that the entomopathogenic nematodes can be used to kill tent caterpillars. However, for better I believe that you have to apply nematodes when tent worms are crawling are on the ground.

    Colorado potato beetles on my organic potato plants

    Yesterday (Saturday May 12, 2012), I found a bunch of Colorado potato beetle grubs (also called as larvae) were feeding on all of my four potato plants (Photo 1) that I had planted in December of 2011. This is the first time I have planted potatoes in my organic garden but did not expect that they will be attacked by Colorado potato beetles or any other insect pests.   [caption id="attachment_273" align="aligncenter" width="300" caption="Photo 1. Potatoes were planted in a organic garden in December 2012"]"Organically grown Potato plants"[/caption] I found that all the different stages of Colorado potato beetle grubs feeding at the same time on the potato leaves (Photo 2) but I did not come across the presence of their adult stages on plants. This means that these grubs are not from a same generation but they were from several different generations of beetles.   [caption id="attachment_274" align="aligncenter" width="300" caption="Photo 2. Different stages of Colorado potato beetle grubs found on organic potato plants"]"The different instars of Colorado potato beetle grubs"[/caption] I saw that all the stages of grubs were voraciously feeding (I wish, I had a video to record feeding) on the leaves as seen in photo number 3 these grubs have completely skeletonized the potato leaves.   [caption id="attachment_275" align="aligncenter" width="300" caption="Photo 3. Severe damage caused by Colorado potato beetle grubs to potato plants"]"The severe damage to potato leaves by Colorado potato beetle grubs"[/caption] I have collected almost all the mixed stages of grubs of Colorado potato beetle with my hand from my all potato plants in a container (photo 4).   [caption id="attachment_276" align="aligncenter" width="300" caption="Photo 4. Mixed stages of Colorado potato beetle grubs are collected for exposing to entomopathogenic Steinernema carpocapsae nematode"]"The grub stages of Colorado potato beetles"[/caption] I am going to expose these collected larvae of Colorado potato beetle to an entomopathogenic nematode, Steinernema carpocapsae. In my next blog post, I will share results of efficacy of Steinernema carpocapsae against these Colorado potato beetle larvae. I also noticed several masses of yellow colored eggs laid by Colorado potato beetles on the under side of several different potato leaves (Photo 5).   [caption id="attachment_277" align="aligncenter" width="200" caption="Photo number 5 showing a yellow egg mass laid by Colorado potato beetle female on the underside of a leaf of potato plant"]"The egg mass of Colorado potato beetle is yellow in color"[/caption] This means when these eggs will hatch there will be a heavy infestation of Colorado potato beetles on my potato plants. Therefore, to reduce future infestation of Colorado potato beetles I need to destroy all the egg masses on the leaves. I have destroyed the eggs by plucking the leaves with eggs and crushed them. This type of mechanical control of Colorado potato beetle is possible because I have only four potato plants in my garden. However, if you have large acreage of potato crop then you cannot destroy eggs this way but you have to let grubs hatch from eggs and then use any chemical pesticides or biological control agents such as entomopathogenic nematodes to manage a high population of hatched larvae Colorado potato beetles.

    Control sod webworms with beneficial nematodes

    Sod webworms: One of the most damaging pests of turfgrass foliage

    How to identify Sod webworms?

    Full grown larvae/caterpillars of sod webworms are easy to identify as they are about 1 inch long having 4 parallel rows of distinct dark spots along the length of their body and coarse hair distributed all over the body. Also, depending upon species, caterpillars can be gray, brown or greenish in color. Adult sod webworm moths are light, brown or dull ash gray in color.

    Life cycle of sod webworms:

    Sod webworms develop through four different stages including egg, caterpillar/larva, pupa and adult moth. Sod webworms over-winter as caterpillar in silk-lined tunnels prepared in thatch and/or soil. In the spring, overwintering caterpillars resume feeding on new turfgrass growth, while feeding molts (shed its cuticle) 5-9 times and go through 6-10 stages (instars) of development. Last instar larva pupates inside the cocoons built from soil particles and plant debris in May through June. After 10-15 days of pupation, adult moths emerge from pupae and begin mating. After mating, female moths generally start laying their eggs individually while they are flying and dropping them randomly into the grass. Each moth lays up to 500 eggs during a life span of usually 10 to 15 days. Under optimal environmental temperatures, eggs hatch within 7-15 days. After hatching from egg, larval stage starts immediately feeding on grass foliage. These second generation caterpillars of sod webworms feed through September then overwinter and life cycle continues.

    Damaging stages of sod webworms:

    All six – ten stages/ instars of sod webworm caterpillars also called larvae cause damage to different grass species or other host plants. Adult moths do not cause any type of damage to any grass species.

    How damage is caused?

    All the stages of sod webworm caterpillars feed on a variety of grasses. Caterpillars generally chew leaves and stems at the crown of turfgrass causing thinning of grass in small areas. As the infestation progresses, these damaged small areas turn into large brown patches.  When infestation of sod webworms is very high, the damage caused by them is easily noticed as large and irregular brown patches are seen throughout lawns or golf course.  Sod webworm caterpillars feed at night but hide in the silk-lined tunnels prepared by them in thatch and/or soil during day time. The presence of irregular brown patches of dead grass caused by feeding of sod webworm in the middle of a lawn or golf course can reduce its aesthetic value.

    Biological control of sod webworms:

    Biological control agents including Bacillus thuringiensis (a bacterium which produces a toxin and paralyzes the gut of the caterpillar) and entomopathogenic nematodes also recognized as beneficial nematodes have a potential to manage sod webworms. However, beneficial nematodes have showed promising results in controlling sod webworms.

    Why we should use beneficial nematodes?

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

    Which species of beneficial nematodes are effective against sod webworms (see literature below)?

    • Steinernema carpocapsae
    • Heterorhabdtis bacteriophora

     What stages of Sod webworms can be targeted?

    All the stages of caterpillars/ larvae and pupae can be targeted because both larvae and pupae are susceptible to beneficial nematodes. 

    What is a recommended rate of beneficial nematodes required to control sod webworms?

    For the successful control most of the soil dwelling insect pests, the optimal rate of 1 billion infective juveniles of beneficial 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 sod webworm infested areas to be treated).

    Where you can buy beneficial 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 it takes to deliver nematodes?

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

    When to apply beneficial nematodes

    • To target sod webworms, beneficial nematodes should be applied starting from early spring through late summer i.e. when young larval (caterpillars) stages (instars) of sod webworms are already hatched from eggs 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 sod webworm caterpillars can be easily targeted because they are generally active and searching for food during night and easily found by Steinernema carpocapsae nematodes that uses sit and wait (ambush) strategy to attack its passing by host.  Since sod webworm caterpillars are moving actively during night in search of food, they can easily come across to Heterorhabdits bacteriophora nematodes that uses cruising strategy to finds its host. Heterorhabdits bacteriophora nematodes can also find caterpillars that are hiding under thatch during day time.

    How beneficial nematodes kill sod webworms?

    After application of either Steinernema spp. or Heterorhabditis spp. on the lawns, their their infective juveniles find sod webworm 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 sod webworm blood, which is conducive for the multiplication of symbiotic bacteria. In the blood, multiplying nematode-bacterium complex causes septicemia and kill sod webworm caterpillar also called larvae usually within 48 h after infection.

    Literature:

    Grewal, P.S. Koppenhofer, A.M. and Choo, H.Y. 2005. Lawn, turfgrass and pasture applications. In: Nematodes As Biocontrol Agents. Grewal, P.S. Ehlers, R.-U., Shapiro-Ilan, D. (eds.). CAB publishing, CAB International, Oxon. Pp 115-146.

    Optimal rates of beneficial nematodes required to treat different sizes of area

    How many nematodes should be applied?

    For the successful control 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.

    Table1. Showing the number of nematodes required to treat different sizes [area in sq ft (sq M)] of lawns or fields

    Nematode species

    Area in sq ft (sq meter)

    1 (0.093)

    10.76 (1)

    108 (10)

    1076 (100)

    2500 (233)

    5000 (465)

    10000 (930)

    43560 (4047) (an acre)

    Heterorhabdtis bacteriophora

    22.9 thousand

    229.6 thousand

    2.3 million

    22.6 million 57.4 million 114.8 million 229.6 million 1.0 billion

    Heterorhabdtis indica

    22.9 thousand

    229.6 thousand

    2.3 million

    22.6 million 57.4 million 114.8 million 229.6 million 1.0 billion

    Steinernema carpocapsae

    22.9 thousand

    229.6 thousand

    2.3 million

    22.6 million 57.4 million 114.8 million 229.6 million 1.0 billion

    Steinernema feltiae

    22.9 thousand

    229.6 thousand

    2.3 million

    22.6 million 57.4 million 114.8 million 229.6 million 1.0 billion