Bugs for Growers — Entomopathogenic nematodes

1. Flea beetles are called as flea beetles because they jump like fleas. Flea beetles are metallic black, blue, bronze or brown in color and about 1/16-1/8^th inch long.
2. Life cycle of flea beetles is very simple containing egg, larval and adult stages.  Flea beetles overwinter as adults by hiding under shelters including dry debris of plants (leaves and stems) left over from your garden crops or weeds. Early in the spring when temperature rises to about 50 F, the overwintering beetles become active and start feeding on the leaves of young plants. While feeding, they mate and lay eggs in the soil cracks around the root system of host plants or weeds in your garden or surrounding areas . Eggs hatch within 1-2 weeks and immediately larvae starts feeding on the roots of young host plants (see below) or weed hosts until they become mature. Then mature larvae pupate in the soil for 1-2 weeks; then emerge as adults and the life cycle continues. Generally this insect completes 2-3 generations in a year.
3. Flea beetles are known to cause economic damage to many different vegetable crops including beans, broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, corn, eggplant, kale, lettuce, melons, mustard,  peppers, potatoes, radishes, red Russian kale, rutabaga, spinach, squash, sunflowers, tomatoes, turnips and several species of weeds.
4. Adults are the most damaging stage of flea beetles. They generally feed on foliage by chewing small holes through leaves and their heavy infestation gives a sieve-like appearance to the plant leaves thus reducing their marketable value especially leafy vegetables. Also, the heavy infestation of flea beetles can kill young seedlings.
5. Flea beetle larvae feed on the plant roots but they do not cause a considerable economic damage to crop.
6.  As temperature starts declining in the fall, adult flea beetles start looking for a shelter to hide and overwinter. Therefore, the process of management of flea beetles should begin in the fall to target overwintering beetles to reduce their incidence and outbreak in the next spring. The management of flea beetles should include both cultural and biological methods. Although the chemical insecticides could be more effective than other methods in controlling flea beetles, their use in the organic gardens should be avoided due to their detrimental effects on the human/animal health and environmental pollution.
7. As a cultural control practice, keep your garden and its surrounding clean in the fall by removing all the plant debris including dry leaves and stems of harvested crops, weeds and other trash that may serve as the possible shelter for overwintering beetles.
8.  Biological control method includes use of entomopathogenic nematodes (also called as insect-parasitic or beneficial nematodes) to target and kill larval and pupal stages of flea beetles in the spring.  Entomopathogenic nematodes can also attack and kill flea beetle adults if they come in contact in the soil.  Application of entomopathogenic nematodes such as Steinernema carpocapsae, Heterorhabditis bacteriophora and Heterorhabditis indica in the mid-late spring in your garden can kill both larval and pupal stages of flea beetles and thus reduce the emergence second generation adults, which are the most damaging to your crop.
9. For the optimal rates and appropriate methods of application of entomopathogenic nematodes, read our blog at http://blog.bugsforgrowers.com/natural-predators/entomopathogenic-nematodes/beneficial-nematodes/how-to-deploy-your-nematode-army-and-kill-insect-pests/

What are Japanese beetles?

As name implies Japanese beetles, Popillia japonica are native to Japan but in the United States, they were first accidentally introduced into New Jersey in 1916. Currently, Japanese beetles have been distributed throughout the United State and causing economic loss to many agricultural and horticultural crops, and reducing aesthetic values of many ornamental plants. Japanese beetle adults are shiny and attractive metallic-green in color, oval shaped and about 1.5 inch long (Fig. 1.). These beetles cause a severe damage to leaves (Fig. 1), flowers (Fig.2) and ripening fruits of different plant species.  In case of severe infestation, adult Japanese beetles can completely skeletonize all the leaves (Fig. 3) and eventually defoliate the whole plants.  Larvae (also called grubs) of Japanese beetle make C- shape when they are disturbed (Fig. 4) and they possess three pairs of thoracic legs. They are whitish in color with yellowish-brown colored head capsule. Japanese beetle grubs generally feed on the roots of turf grass and many ornamental plants. The damage caused by Japanese beetle grubs to turf grass is easily recognized.   [caption id="attachment_483" align="aligncenter" width="179" caption="Fig.1. Japanese Beetles feeding on rose leaves"][/caption] [caption id="attachment_485" align="aligncenter" width="179" caption="Fig. 2. Adult Japanese beetles are feeding on the rose flowers"][/caption] [caption id="attachment_484" align="aligncenter" width="179" caption="Fig.3. Rose leaves are completely skeletonized by Japanese beetle adults"][/caption] [caption id="attachment_486" align="aligncenter" width="300" caption="Fig. 4. Japanese beetle larvae or grubs feed on the turfgrass roots."][/caption]

Signs of Japanese beetle infestation and damage to lawns and golf courses.

• At the beginning of infestation in your lawn, you will notice localized patches of dead turf grass, which is always confused with the symptoms of water stress.
• As the feeding activity of grubs on turf roots increases, small patches of dead turf are enlarged and joined together to form the large areas of dead turf.
• This dead turf is generally loose and can be easily picked up with hand like a piece of carpet.
• The most important sign of presence of Japanese beetle grubs in your lawn is that the infested areas of lawn is destroyed by digging animals such as raccoons and skunks or by birds that are looking for grubs to feast on them.

Life cycle of Japanese beetle:

For Japanese beetles, it takes about one year to complete egg to egg life cycle.  For example, adults of Japanese beetles emerge from pupae in the late June through July and start feeding on leaves, flowers and fruits. While feeding they mate and lay eggs in the soil near grass root zone at the depth of 1-2 inches. The eggs hatch within 1-2 weeks (i.e. in August) and first instar grub immediately starts feeding on grass roots and organic matter.  Grubs develop into two more instars August through October by continuously feeding on grass roots. In September and October they start moving deep into soil for overwintering.  When weather warms in April, grubs move back into the turf root-zone, start feeding on turf roots again and continue to develop and early in the June they pupate into the soil.  Then adults of Japanese beetles emerge from pupae in the late June, then they mate, lay eggs and life cycle continues.

What are entomopathogenic nematodes?

Entomopathogenic nematode are also called as insect-parasitic nematodes, which are defined as thread-like microscopic, colorless and un-segmented round worms. These round worms are the members of both Steinernematidae and Heterorhabditidae families and currently used as an excellent biological control agents against many soil dwelling insect pests of many economically important insect pests including Japanese beetles.  Entomopathogenic nematodes are sold when they are in the infective juvenile stage that also called as dauer juveniles. These infective juveniles always carry mutualistically associated symbiotic bacterial cells in their gut. Since these bacteria are pathogenic and capable of causing a disease to a variety of insect hosts, they are called as entomopathogenic nematodes.

Which species of entomopathogenic nematodes are effective against Japanese beetles?

Following species of entomopathogenic nematodes have been considered to be the most effective species against Japanese beetle grubs (see below for the optimum rates of nematodes).

• Heterorhabditis bacteriophora nematodes
• Heterorhabditis zealandica
• Heterorhabditis indica nematodes
• Steinernema scarabaei
• Steinernema carpocapsae nematodes
• Steinernema rivobrave

Why fall is the time to apply nematodes and reduce existing populations to prevent future outbreaks of Japanese beetles.

As we know that Japanese beetles overwinter in their larval stages. To do this, they will start moving deep into the soil in September and October (depending on the temperature). In some places the temperature has already started declining, which is an important cue for Japanese beetle larvae to get ready for winter weather.  Therefore, it is time to apply entompopathogenic nematodes which can target the Japanese beetle larvae that start going deep into the soil for overwintering.

What stages of Japanese Beetles can be targeted?

• All the immature stages of Japanese beetles are susceptible to entomopathogenic nematodes.
• Adults of Japanese beetles are also susceptible to entomopathogenic nematodes.

How can Entomopathogenic Nematodes kill Japanese beetle larvae?

When the infective juveniles of entomopathogenic nematodes are applied to the soil surface or thatch layer, they start looking for their hosts including Japanese beetle grubs. Once a grub has been located, the nematode infective juveniles penetrate into the Japanese beetle grub body cavity via natural openings such as mouth, anus and spiracles. Then these infective juveniles enter grub’s body cavity where they release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae and Photorhabdus spp. for Heterorhabditidae) from their gut in grub blood. When in the grub’s blood, multiplying nematode-bacterium complex causes septicemia and kills Japanese beetle grubs usually within 48 h after infection.  Nematodes generally feed on multiplying bacteria, mature into adults, reproduce and then emerge as infective juveniles from the cadaver to seek new Japanese beetle grubs or other insect host that present in the soil.

When, how and how many entomopathogenic nematodes should be applied for the effective control of Japanese beetles?

For details read our blog

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 147-166. Koppenhofer, A.M., Fuzy, E.M., Crocker, R.L., Gelernter, W.D. and Polavarapu, S. 2004. Pathogenicity of Heterorhabditis bacteriophora, Steinernema glaseri, and S. scarabaei (Rhabditida : Heterorhabditidae, Steinernematidae) against 12 white grub species (Coleoptera : Scarabaeidae). Biocontrol Science and Technology. 14: 87-92. Maneesakorn, P., An, R., Grewal, P.S.and Chandrapatya, A. 2010. Virulence of our new strains of entomopathogenic nematodes from Thailand against second instar larva of the Japanese Beetle, Popillia japonica (Coleoptera: Scarabaeidae). Thai Journal of Agricultural Science.43: 61-66. Mannion, C.M., McLane, W., Klein, M.G., Moyseenko, J., Oliver, J.B. and Cowan D. 2001. Management of early-instar Japanese beetle (Coleoptera : Scarabaeidae) in field-grown nursery crops. Journal of Economic Entomology. 94: 1151-1161.

Fleas are one of the medically important pests of both animals and humans as they are capable of transmitting different kinds of disease causing organisms. Fleas are wingless insects but they can jump on their hosts including cats, dogs, humans and rats. Fleas have piercing and sucking type of mouthparts with that they suck blood of their hosts.  Like other insect, fleas also develop through the four different developmental stages including eggs, larva, pupa and adult.  Only adult fleas feed on blood but larval stage feeds on organic matter.  Pupa is a non-feeding stage. Fleas generally lay eggs on host’s body but they fall off on the ground where their host usually rests or sleeps.  Eggs hatch within 1-2 weeks and larvae immediately starts feeding on the organic matter that present at the resting place of animal hosts. Larvae develop through three larval stages and pupate in soil inside the silken cocoons. After 1-2 weeks, adult fleas emerge from cocoons but generally they use different kinds of host cues such as carbon dioxide, heat and vibration to emerge from pupae.  Fleas generally overwinter as larval and pupal stages, which can be easily targeted and killed by using biological control agents such as entomopathogenic nematodes.

Why now it’s time to apply entomopathogenic nematodes and reduce the existing populations and future outbreaks of fleas.

As we know that fleas overwinter as larval and pupal stages. In some places now temperature is already started declining, which is an important cue for fleas to get ready for winter weather.  This means both larval and pupal stages are ready for overwintering in the areas where temperatures are cooling down. Therefore, it is now time to apply entompopathogenic nematodes and target the overwintering stages of fleas.

Which species of entomopathogenic nematodes are effective against fleas?

• Steinernema carpocapsae nematodes are effective against fleas. It has been reported that when Steinernema carpocapsae nematodes applied in the potting medium, sand and gravel infested with larval and pupal stages of fleas, they reduced over 70% emergence of adults of cat fleas (Henderson et al., 1995).

Where to apply entomopathogenic nematodes for the effective control of outdoor and indoor fleas?

As stated above entomopathogenic nematodes can kill only larval and pupal stages but not adults of fleas. These stages are generally present on a large scale on the ground where host animals rests, sleeps or spends lot of time. These areas are generally located outdoors. These outdoor areas also serve as a source of indoor infestation of adult fleas. Therefore, it is important to treat all the outdoor animal resting/ sleeping areas or any other suspected areas where fleas are breeding with entomopathogenic nematodes.

When to apply entomopathogenic nematodes for the effective control of outdoor and indoor fleas?

• To target larvae and pupae of fleas, entomopathogenic nematodes should be applied starting from early spring through late fall i.e. when overwintering larval stages of fleas are becoming active and before emergence of adults from the pupae (spring and summer) or in the fall (September to November) when both larvae and pupae are getting ready for overwintering.
• 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 the larval stages of fleas can be easily targeted because they are blind and do not like sunlight and therefore, they are generally active during night searching for food and easily found by entomopathogenic nematodes like Steinernema carpocapsae that uses sit and wait (ambush) strategy to attack its passing by host.  These nematodes can also find larvae and pupae that are hiding under organic matter during day time.

How many entomopathogenic nematodes should be applied for the effective control of fleas?

• See our Table for the exact quantity of Steinernema carpocapsae nematodes required to treat different square foot/meter areas.

How to apply entomopathogenic nematodes?

• Entomopathogenic nematodes that you receive in sponge as liquid formulation are thoroughly mixed in water and can be easily sprayed directly on the area where animal hosts rests/sleeps using traditional Knapsack/backpack sprayers or watering cans.
• However, at time of spraying care should be taken that the nematodes should not be allowed to settle at the bottom of sprayer or watering can to avoid their uneven distribution.
• To avoid the settling of nematodes at the bottom of sprayer or watering can, nematode suspension should be constantly agitated.
• However, nematodes will be easily damaged, if they are agitated through excessive recirculation of spray mix or if the temperature in the tank increases beyond 86^oF.
• Nematodes can also be applied through different types of irrigation systems but pumps should have proper pressure to avoid damage to nematodes and screen sizes should be larger than 50 mesh so that nematodes will pass through them live.
• Nematodes received in granular formulation can be directly applied by broadcasting with hand or for larger area by using traditional spreaders that are used for application of granular or pallet pesticides or synthetic fertilizers.
• Also, nematodes need about 20% moisture in the ground for survival. So please make sure nematode treated area should be watered immediately after the application of nematodes and continue to spray the area with water every few days.

[caption id="attachment_80" align="aligncenter" width="300" caption="Watering can for application of entomopathogenic nematodes on a small area"][/caption]

How Steinernema carpocapsae nematodes infect and kill fleas?

Infective juveniles of Steinernema carpocapsae enter their insect host through natural openings such as mouth, anus and spiracles and eventually reach in the insect body cavity, which is filled with the blood that is technically called as hemolymph.  The infective juveniles of Steinernema spp. carry in their gut species specific symbiotic bacteria of the genus, Xenorhabdus. Once infective juveniles of Steinernema spp. are in the insect body cavity, they release several cells of symbiotic bacteria, Xenorhabdus spp. 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.

Are entomopathogenic nematodes harmful to dogs, cats, chickens, birds, wild animals and humans?

• Entomopathogenic nematodes are absolutely not harmful to humans and any pet animals (dogs, cats, chickens and birds) and wild animals/birds, and even to beneficial insects like honeybees.

 Literature:

1. Henderson, G., Manweiler, S.A., Lawrence, W.J., Templeman, R.J. and Foil, L.D. 1995. The effects of Steinernema carpocapsae (Weiser) application to different life stages on adult emergence of the cat flea Ctenocephalides felis (Bouche). Vet. Dermatol. 6:159-163.
2. Smith, C.A. 1995: Current concepts: Searching for safe methods of flea control. JAVMA: 1137-1143.

A Symposium entitled “Entomopathogenic Nematodes and Multitrophic interactions in the Rhizosphere” has been organized by Raquel Campos-Herrera, Claudia Dolinski and Ganpati B. Jagdale at the Society of Nematologists 51^st Annual meeting, which would be held in Savannah, Georgia from August 12^th to 15^th 2012. Following topics by various authors/speakers on interactions among entomopathogenic nematodes and multitrophic groups in the rhizosphere will be discussed between 8.0- 10.0 am on Tuesday August 14, 2012 in Marriot Riverfront hotel, Savanna, GA.   Topics with authors:

1. Multitrophic interactions involving entomopathogenic nematodes applied against pine weevils in a forest ecosystem by Christine T. Griffin, A.M. Dillon, C.D. Harvey and C.D. Williams.
2. Entomophathogenic nematodes: Effects of the soil agroecosystem on biological control potential by David I. Shapiro-Ilan, T.C. Leskey, S.E. Wright, I. Brown, and L. Fall.
3. Interactions among entomopathogenic nematodes and other nematode trophic groups and plants in agroecosystems by Somasekhar Nethi, G.B. Jagdale and P.S. Grewal.
4. Herbivore induced plants volatiles and entomopathogenic nematodes as agents of plant indirect defense by Jared G. Ali, H.T. Alborn, R. Campos-Herrera, F. Kaplan, L.W. Duncan, C. Rodriguez-Saona, A.M. Koppenhöfer, and L.L. Stelinski.

Incidence of Kudzu bugs on Chinese long beans- bugsforgrowers

For the last couple of years, I have been growing Chinese long beans (Vigna unguiculata subsp. sesquipedalis) in my organic garden. Although this year (2012) I did not plant these beans in my garden, I noticed early in the spring that a few number of Chinese long bean seeds were voluntarily germinated. This means these seeds from last years crop were overwintered in the soil and germinated early in the spring when there was enough moisture in the ground and optimum temperature for their germination. So I let these voluntarily germinated vines/plants to grow in my organic garden. Over the growing season, these plants grew very well and healthy without the infestation of any insect pests. For the last few weeks these plants are producing a lot of pods that we have been harvesting at their maturity and shelling from them beans (grains) and preparing delicious curries. However, two weeks ago, I noticed that the vines of my Chinese long beans were heavily infested with Kudzu bug, Megacopta cribraria (Fig. 1). [caption id="attachment_387" align="aligncenter" width="300" caption="Fig.1. Chinese long bean vine is heavily infested with Kudzu bugs- Click on the image for its enlargement"][/caption] Last year, I did not see any infestation of Kudzu bugs on long beans but as shown in pictures, they are now feeding on the pods (Fig. 2), leaves and stem (Fig. 3) of my Chinese long beans.   [caption id="attachment_388" align="aligncenter" width="300" caption="Fig. 2. Several adult of kudzu bugs are feeding and causing severe damage to my organically grown Chinese long bean pods- Click on the image for its enlargement"][/caption] [caption id="attachment_389" align="aligncenter" width="300" caption="Fig. 3. Several nymphs of kudzu bugs are congregated and feeding on leaves and stem of Chinese long bean in my organic garden- Click on the image for its enlargement"][/caption] The immature and mature stages of Kudzu bugs are dark brown (Fig. 2) and greenish brown (Fig. 3) in color, respectively. Both mature and immature stages of Kudzu bugs feed on the long bean vine/plant. Since these Kudzu bugs have sucking type of mouthparts, they suck cell sap from leaves, stem and pods. The intensive feeding by these bugs can cause leaves, stem and pods to dry and eventually cause the death of vines/plants.

Possible organic control measures

• Although I don’t know how to control these Kudzu bugs organically, I have decided to spray garlic extract (prepared by grinding garlic in water) as a repellent. I will let you know the effects of garlic extract on the Kudzu bugs in my next blog.
• Meanwhile, I have also exposed both nymphs and adults of Kudzu bugs to entomopathogenic Steinernema carpocapsae nematodes in a petri dish. I will also communicate with you the results of this experiment in my next blog.