Two beneficial entomopathogenic nematodes for the control of strawberry root weevils-Nematodeinformation
Strawberry root weevils [Otiorhynchus ovatus] are one of the most important insect pests of strawberry crop. Adults of strawberry root weevil feed on the edges of strawberry leaves [leaf notching] but this damage is not considered as economically important like the damage caused by their larval stages to strawberry roots [root pruning]. An adult strawberry root weevil can be considered as one of the nuisance household pests especially during hot and dry weather conditions. All the larval stages of strawberry root weevil cause damage by tunneling in the roots and crowns but most serious damage is caused by third and fourth larval stages early in the spring. The main symptoms of damage caused by larvae of strawberry weevils include weakening, stunting and eventually killing of plants. Strawberry growers can follow different cultural, chemical or biological approaches to manage the strawberry root weevils, the most economically important pest.
This method includes hand picking of strawberry root weevil adults and killing them. However, this method is only possible when there is a low population of adult weevils and small garden area to monitor.
Chemical method may be very effective in controlling strawberry weevils but it may have detrimental effects on human health and environment. Also, chemical pesticides may kill honeybees that we need for pollination of our crops in the garden and they may kill beneficial natural enemies like carabid beetles, Pterostichus vulgaris that feed on many different insect pests.
Biological method is a very safe and effective alternative to chemical insecticides as it is not harmful to humans, children, pets, birds and beneficial insects. Biological control agents including beneficial entomopathogenic nematodes and carabid beetles, Pterostichus vulgaris have a potential to control strawberry weevils.
1. Entomopathogenic nematodes
Beneficial entomopathogenic nematodes are lethal insect parasites. Their infective juveniles penetrate into the body cavity of host insect via natural openings and release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae and Photorhabdus spp. for Heterorhabditidae). Nematode-bacterium complex causes septicemia and kills the host usually within 48 h after infection. Nematodes feed on bacteria, reproduce and then emerge as infective juveniles from the cadaver to seek new hosts in the soil.
Currently, entomopathogenic nematodes including Heterorhabditis bacteriophora, Steinernema carpocapsae are commercially marketed worldwide as biopesticides for the control of many economically important pests of different crops. However, these nematodes are not harmful to people and animals and other beneficial insects like honeybees.
As larval stages and pupae of strawberry weevils live in the soil, they can be easily targeted with entomopathogenic nematodes. I t has been demonstrated that to beneficial entomopathogenic nematodes including H. bacteriophora and S. carpocapsaecan controlling over 68% population of strawberry weevils [Simser and Roberts, 1994] .
For effective control of weevils, beneficial entomopathogenic nematodes are generally applied at the rate of 1 billion nematodes per acre using traditional sprayers.
2. Predatory beetles
The predatory ground beetles including a carabid beetle, Pterostichus vulgaris know to feed on larval, pupal and adult stages of strawberry root weevils.
Berry, R.E., Liu, J. and Groth, E. 1997. Efficacy and persistence of Heterorhabditis marelatus (Rhabditida: Heterorhabditidae) against root weevils (Coleoptera: Curculionidae) in strawberry. Environmental Entomology 26: 465-470.
Booth, S.R., Tanigoshi, L.K. and Shanks, C.H. 2002. Evaluation of entomopathogenic nematodes to manage root weevil larvae in Washington state cranberry, strawberry, and red raspberry. Environmental Entomology 31: 895-902.
Simser, D. and Roberts, S. 1994. Suppression of strawberry root weevil, Otiorhynchus-ovatus, in cranberries by entomopathogenic nematodes (Nematoda, Steinernematidae and Heterorhabditidae. Nematologica 40: 456-462.
Vainio, A. and Hokkanen, H.M.T. 1993. The potential of entomopathogenic fungi and nematodes against Otiorhynchus-ovatus L and O. dubius strom (Col, Curculionidae) in the field. Journal of Applied Entomology-Zeitschrift fur Angewandte Entomologie. 115: 379-387.