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The grape root borer, Vitacea polistiformis is one of economically important pests of grapes in eastern USA.  Larva stages of this insect feed on grape roots and can cause severe economic damage to the commercial grape industry by killing entire vineyards.  Beneficial nematodes have potential to use as biological control agent to target both larval and pupal stages of root borers.  It has been demonstrated that the beneficial nematodes including Heterorhabditis bacteriophora, H. zealandica and Steinernema carpocapsae can cause over 70% mortality of grape root borer larvae under laboratory conditions (Williams et al., 2002).

Read following paper for more information on interaction between beneficial nematodes and grape root borer.

Williams, R.N., Fickle, D.S., Grewal, P.S. and Meyer, J.R. 2002.  Assessing the potential of entomopathogenic nematodes to control the grape root borer, Vitacea polistifirmis (Lepidiptera: Sesiidae) thorough laboratory bioassays. Biocontrol Science and Technology. 12: 35-42. 

Entomopathogenic nematodes including Steinernema riobrave and Heterorhabditis indica were evalusted against a small hive beetle Aethina tumida Murray (Coleoptera: Nitidulidae) in the field. According to Ellis et al. (2010) both nematode species caused over 76% mortality of hive beetles. Shapiro-Ilan et al. (2010) tested efficacy of H. indica and Steinernema carpocapsae against hive beetles and demonstrated that both nematode species when applied through infected host cadavers can cause up to 78% control in hive beetles. This suggests that entomopathogenic nematodes have a potential to use as biological control agents against hive beetles.

Read following papers for detail information on effect of entomopathogenic nematodes on the small hive beetles.

Ellis, J.D., Spiewok, S., Delaplane, K.S., Buchholz, S., Neumann, P. and Tedders, W.L. 2010.  Susceptibility of Aethina tumida (Coleoptera: Nitidulidae) larvae and pupae to entomopathogenic nematodes. Journal of Economic Entomology. 103: 1-9.

Shapiro-Ilan, D.I., Morales-Ramos, J.A., Rojas, M.G. and Tedders, W.L. 2010.  Effects of a novel entomopathogenic nematode-infected host formulation on cadaver integrity, nematode yield, and suppression of Diaprepes abbreviatus and Aethina tumida. Journal of Invertebrate Pathology. 103: 103-108.

• The leaf beetles, Altica quercetorum and Agelastica alni are serious pests of urban trees including Quercus sp and Alnus sp, respectively.  The elm leaf beetle Xanthogaleruka luteola is a serious pest that causes defoliation of eml trees (Ulmus spp.) in North America. Adults of these beetles generally feed on leaves by chewing holes through the leaf tissue.  Larvae skelotonize leaves by feeding on leaf tissues leaving veins and upper epidermis intact.
• Entomopathogenice nematodes including Heterorhabditis megidis, Steinernema carpocapsae and S. feltiae can be used as potential biocontrol agents against different species leaf beetles (read Grewal et al., 2005 for more information).  It has been shown that both the pre-pupal and pupal stages of A. quercetorum and A. alni are very susceptible to H. megidis when applied in the soil. The last instar larvae of X. luteola are highle susceptible to S. carpocapsae when applied to the mulch.

How Entomopathogenic Nematodes kill leaf beetles

When the infective juveniles are applied to the soil surface or mulch, they start searching for their hosts, in this case leaf beetles grubs. Once a beetle grub has been located, the nematode infective juveniles penetrate into the grub body cavity via natural openings such as mouth, anus and spiracles. Infective juveniles of Heterorhabditis also enter through the intersegmental members of the grub cuticle. Once in the body cavity, infective juveniles release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae and Photorhabdus spp. for Heterorhabditidae) from their gut in grub blood. In the blood, multiplying nematode-bacterium complex causes septicemia and kills grubs 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 soil.

References: Refer following book to read more about efficacy of entomopathogenic nematodes against leaf beetles

1. Grewal, P.S. Ehlers, R.-U., Shapiro-Ilan, D. (eds.). Nematodes As Biocontrol Agents. CAB publishing, CAB International, Oxon

• The Japanese beetle, Popillia japonica, is a most economically important pest of many ornamental plants and turf grasses. Larvae of these beetles are called white grubs that generally feed on roots of over 300 plants but their primary food source is grass roots. Severe damage caused by these grubs can result in dead patches of turf that can be picked up like a loose carpet.  Adults mostly feed on leaves and flowers by chewing the tissue between the veins, a type of feeding called skeletonizing.  Chemical insecticides including Imidacloprid (Merit), Chlorpyrifos, Isofenphos, and Diazinon are generally used to manage white grubs but due to human health and environment pollution concerns their use is restricted.
• Currently, environmentally safe biological control agents including a milky disease causing bacterium Bacillus popilliae (Milky spores) and entomopathogenic nematodes have been used to control this pest.  Three entomopathogenic nematodes including Heterorhabditis bacteriophora GPS11 and TF strains, H. zealandica X1 strain and Steinernema scarabaei have been considered to be the most effective species against Japanese beetle grubs.  It has been demonstrated that the application of H. bacteriophora GPS11 and TF strains, H. zealandica X1 strain and S. scarabaei at rate of 2.5 billion infective juveniles per hectare can cause about 96, 98 and 100%, respectively control of Japanese beetle grubs infesting turfgrass (for more information read Grewal et a., 2005).  Nematodes can be applied using traditional sprayers that are used for the application of insecticides.  Nematodes perform better when they are applied to target small stages of grubs.  Nematodes also survive better and remain efficacious when field/lawns are irrigated before and after nematode applications

• How Entomopathogenic Nematodes kill Japanese beetles

When the infective juveniles are applied to the soil surface or thatch layer, they start searching for their hosts, in this case Japanese beetle grubs. Once a Japanese beetle 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. Infective juveniles of Heterorhabditis also enter through the intersegmental members of the grub cuticle. Once in the body cavity, infective juveniles release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae and Photorhabdus spp. for Heterorhabditidae) from their gut in grub blood. In the blood, multiplying nematode-bacterium complex causes septicemia and kills Japanese beetle grubs 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 soil.

References

1. 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.

• Black vine weevil, Otiorhynchus sulcatus is a common insect pest of over 150 plant species that grown in the greenhouses and nurseries. Some of the plant species damaged by black vine weevils include Azalea, Cyclamen, Euonymus, Fuxia, Rosa, Rhododendron and Taxus.  Grubs (Larvae) of these weevils generally girdle the main stem, and feed and damage roots leading to nutrient deficiencies.  Adults feed on leaves and flowers by notching their edges thus reducing aesthetic value of plants.
• The entomopathogenic nematodes species including Heterorhabditis bacteriophora, H. megidis and Steinernema carpocapase, S. feltiae and S. glaseri have been found to be effective alternatives to chemical insecticides such as chlorpyrifos (Dursban) in controlling black vine weevils.  Susceptibility of black vine weevil to nematodes is species and strain specific.  The rate of application of the nematode species/strains that tested against black vine weevil varies (5,000- 60,000 infective juveniles/pot) among different studies but nematodes applied at the rate of 5000- 20,000 infective juveniles/pot can cause up to 100% grub mortality.  Nematodes can be easily applied in water suspension as spray applications to the surface of plant growing medium but if nematodes are injected at depths deeper than 5 cm i.e. near to grubs they can cause highest mortality of grubs (70-93%) than those nematodes applied to the surface.  All the four larval stages (instars) and pupae of black vine weevil are susceptible to all entomopathogenic nematode species.  However, Heterorhabdtis bacteriophora can cause higher mortality of first and second instars than S. carpocapase and S. glaseri.  Also, all the three nematodes species are equally effective against third and fourth instars of black vine weevil.

How Entomopathogenic Nematodes Kill Black Vine Weevil

When the infective juveniles are applied to the surface of plant growing medium or injected in the potting medium, they start searching for their hosts, in this case black vine weevil grubs and pupae.  Once a grub/pupa has been located, the nematode infective juveniles penetrate into the grub or pupa body cavity via natural openings (mouth, anus and spiracles).  Infective juveniles of Heterorhabditis also enter through the intersegmental members of the grub/pupa cuticle.  Once in the body cavity, infective juveniles release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae and Photorhabdus spp. for Heterorhabditidae) from their gut in the grub blood.  Multiplying nematode-bacterium complex in the blood causes septicemia and kills the grub 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 grubs or pupae in the potting medium/soil.

Entomopathogenic nematode life cycle

• EPNs complete most of their life cycle in insects with an exception of infective juveniles, the only free-living stage found in soil.
• Infective juveniles of both Steinernema and Heterorhabditis locate a host and enter through its natural body openings such as mouth, anus or spiracles.
• Infective juveniles of Heterorhabditis also enter through the intersegmental members of the host cuticle.
• Infective juveniles then actively penetrate through the midgut wall or tracheae into the insect body cavity (hemocoel) containing insect blood (haemolymph).
• Once in the body cavity, infective juvenile releases symbiotic bacteria from its intestine in the insect haemolymph.
• Bacteria start multiplying in the nutrient-rich haemolymph and infective juveniles recover from their arrested state (dauer stage) and start feeding on multiplying bacteria and disintegrated host tissues.
• Toxins produced by the developing nematodes and multiplying bacteria in the body cavity kill the insect host usually within 48 hours.
• These bacteria also produce a plethora of metabolites, toxins and antibiotics with bactericidal, fungicidal and nematicidal properties, which ensures monoxenic conditions for nematode development and reproduction in insect cadaver.
• Heterorhabditid and Steinernematid nematodes differ in their mode of reproduction. For example, in heterorhabditid nematodes, the first generation individuals are produced by self-fertile hermaphrodites (hermaphroditic) but subsequent generation individuals are produced by cross fertilization involving males and females (amphimictic). In Steinernematid nematodes with an exception of one species, all generations are produced by cross fertilization involving males and females (amphimictic).
• Depending on availability of food resource, both heterorhabditid and steinernematid nematodes generally complete 2-3 generations within insect cadaver and emerge as infective juveniles to seek new hosts.
• Generally, life cycle of entomopathogenic nematodes (from infective juvenile penetration to infective juvenile emergence) is completed within 12- 15 days at room temperature. The optimum temperature for growth and reproduction of nematodes is between 25 and 30⁰C.
  

  Life cycle of Steinernematid and Heterorhabditid entomopathogenic nematodes- By Ganpati Jagdale

Nematodes are defined as thread-like microscopic, colorless, unsegmented round worms found in almost all habitats especially in soil and water. Nematodes may be free-living, predacious and parasitic. Nematodes that are considered our friends include entomopathogenic nematodes, insect-parasitic nematodes, slug-parasitic and free-living nematodes.

Nematodes are called free-living because they are not parasitic to either plants or animals, live freely in soil and can play an important role in nutrient cycling in the soil food web. These nematodes are currently used as bio-indicators of soil health because they have diverse feeding habits, some of them can survive harsh, polluted, or disturbed environments better than others, and some have short life cycles and can respond to environmental changes rapidly.

Nematodes are called insect-parasitic because they benefit for their development and reproduction at the insect host’s expense. The best examples are the members of the family Mermithidae.

Nematodes are called slug-parasitic because they benefit for their development and reproduction at the slug’s expense. These nematodes nematodes are mutualistically associated a bacterial smbiont, which is capable of causing disease and killing several species of slugs. Example is Phasmarhabditis hermaphrodita, which belongs to a family Rhabditidae in the order of Rahbdita and symbiotically associated with a gram-negative bacterium, Moraxella osloensis .

Nematodes are called entomopathogenic because they are mutualistically associated with a species specific pathogenic bacterial symbiont, which are capable of causing disease in insect hosts. All the entomopathogenic nematodes are members of two families Steinernematidae and Heterorhabditidae in the order of Rhabdita.

In this blog, I will be providing the information on only entomopathogenic nematodes/insect-parasitic nematodes.