Influence of potting media on the virulence of entomopathogenic nematodes against black vine weevil, Otiorhynchus sulcatus

It has been demonstrated that five different types of commercial potting media including peat, bark, coir, and peat blended with 10% and 20% compost green waste can influence the virulence of entomopathogenic nematodes against third-instar black vine weevil, Otiorhynchus sulcatus.  For example, Heterorhabditis species including Heterorhabditis bacteriophora UWS1 strain, H. megidis, H. downesi can cause 100% mortality of black vine weevil grubs in all the five types of media but  Steinernema species including Steinernema feltiae, S. carpocapsae, and S. kraussei can cause 100% black vine weevil grub mortality only in the peat blended with 20% compost green waste.  These results suggest that when growers are selecting entomopathogenic nematodes to control black vine weevil, Otiorhynchus sulcatus in their nurseries/greenhouses, they should take into consideration the type of potting media used in growing their plants. Please read following paper for the information on the method of nematode application rates and timings.

Ansari, M. A. and Butt, T. M. 2011.  Effect of potting media on the efficacy and dispersal of entomopathogenic nematodes for the control of black vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae). Biological Control 58: 310-318.

Ansari, M.A., Shah, F.A. and Butt, T.M. 2010.  The entomopathogenic nematodeSteinernema kraussei and Metarhizium anisopliae work synergistically in controlling overwintering larvae of the black vine weevil, Otiorhynchus sulcatus, in strawberry growbags. Biocontrol Science and Technology. 20: 99-105.

Control of the black vine weevil Otiorhynchus sulcatus infesting strawberry fields

It has been reported that entompathogenic nematodes including Heterorhabditis megidis and Steinernema kraussei are effective against the black vine weevil Otiorhynchus sulcatus infesting strawberry fields (Haukeland and Lola-Luz, 2010).  It has been suggested that the soil type and soil temperature plays a significant role in efficacy of these nematodes against the black vine weevil.  It is also noted that H. megidis performs better at soil temperatures above 10oC and S. kraussei at below 10oC. References:

Haukeland, S. and Lola-Luz, T. 2010.  Efficacy of the entomopathogenic nematodes Steinernema kraussei and Heterorhabditis megidis against the black vine weevil Otiorhynchus sulcatus in open field-grown strawberry plants. Agricultural and Forest Entomology.12363-369

Biological Control of Black Vine Weevil using Insect Parasitic Nematodes

• 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.