Managing A Challenging Subterranean Clover Pest: Sustainable Control Using Insect Pathogens

View the project final report

Commodities

• Agronomic: general hay and forage crops

Practices

• Pest Management: biological control, integrated pest management

Insect pathogens provide an effective means of suppressing pests but have received less attention compared with other biological control agents. For pests that develop below ground, insect pathogens may offer the best management option. The goal of this project is to investigate the virulence of insect pathogens against the clover root borer, an economically important and unique bark beetle pest inadvertently introduced into the United States over 100 years ago. While bark beetles typically develop in the trunks of trees in forests, the clover root borer develops below ground within the roots of red clover. Red clover is an important legume used as a cover crop and as a forage mix for pastures. Seeds used nationwide are produced in western Oregon. Red clover is a perennial, but when it is attacked by the clover root borer, the crop can only be raised for two years due a drastic reduction in yield. Hence, the clover root borer causes considerable economic hardship. For many decades the clover root borer was controlled with application of organochlorine insecticides. Their long residual effect killed the beetles when they emerged from the roots to disperse and infest new plants during a short period in spring. Since the time when this group of insecticides was banned in the 1970s, the pest has been a challenge to manage as newer insecticides have limited residual effect. As a result, no pest suppression strategy currently exists for this pest. In the absence of insecticide applications to the soil, naturally occurring insect pathogens (entomopathogens) have had an opportunity to build their populations over the years. Hence, the time is right for an assessment of entomopathogenic fungi and nematodes in red clover seed fields in western Oregon. The principal investigator will collect clover root borers and isolate and identify pathogens associated with adults and larvae. The principal investigator will also compare their virulence against the pest with commercially available microbial products for use in developing a biological control program. Entomopathogens can also be incorporated into an autoinoculation management strategy in which infected beetles further disperse the pathogens. Hence, The principal investigator will also assess the extent to which each pathogen species is transmitted horizontally to conspecifics. The red clover-clover root borer system provides a unique opportunity for examining the host-pathogen interaction in a bark beetle that attacks an unusual non-tree host, and for assessing the growth of virulent strains of entomopathogens in the prolonged absence of insecticide applications for pest management. The research will provide valuable information for development of biological control and autoinoculation programs that can lead to sustainable and economic red clover seed production beyond two years.

1. Determine the presence and abundance of naturally occurring soil dwelling insect pathogens of the clover root borer.

2. Compare the virulence of entomopathogens of the clover root borer:

• • Assess virulence of entomopathogenic fungi against the clover root borer

• • Assess virulence of entomopathogenic nematodes against the clover root borer

• • Assess horizontal transfer of entomopathogens in the clover root borer

Rationale: The clover root borer has been a pest in red clover seed fields in western Oregon for over a hundred years. Until the ban on organochlorine insecticides in the 1970s, the pest was controlled with applications of insecticides such as aldrin, dieldrin, and heptachlor. These insecticides had long residual action and were thus effective in killing the pest during the short period when adults emerged from the roots below ground and dispersed to infest new hosts. After the ban, the newer insecticides that were developed had shorter residual action for mitigating negative impacts on the environment, but none were effective for controlling the pest. Thus, insecticides have not been used against the clover rot borer since the 1970s. The principal investigator hypothesizes that this provides a unique opportunity for species-specific strains of entomopathogenic fungi and nematodes to thrive in red clover seed fields. Rockwood (1926) reported the presence of a single entomopathogen associated with clover root borers, namely the fungus Beauveria globulifera, now known as Beauveria bassiana. In the preliminary survey conducted in 2013, the principal investigator detected the presence of both entomopathogenic fungi and nematodes infecting clover root borers collected from red clover seed production fields. The principal investigator will conduct more extensive surveys in 2014 and 2015 to document the species, location, and abundance of naturally occurring entomopathogenic fungi and nematodes in western Oregon. The studies will also document the virulence of each species at different doses and their efficacy in killing clover root borers compared with commercial products. A significant aspect of the research will be the information gathered on potential buildup of entomopathogenic fungi and nematodes in a system where for decades no soil insecticides have been used.

Timeline for the one year study:

Objective 1: Field surveys and entomopathogen isolation and identification will be conducted in Fall 2014 and Winter/Spring 2015.

Objective 2: The virulence of entomopathogens and horizontal transfer experiments will be conducted in Summer and early Fall 2015.