Developing an Effective and Efficient Rearing Method for the Emerald Ash Borer

Research Issue

A reliable source of large numbers of all stages of laboratory reared eab year round, especially outside the quarantine zone, will rapidly advance the biocontrol efforts and other insect control strategies that require laboratory bioassay. Most of the parasitoids of eab that have been identified currently have to be reared by extracting eab larvae from infested wood (larval parasitoids) or using eab adults that emerge from wood to lay the eggs (egg parasitoids). Without an effective and efficient laboratory rearing method for eab, mass rearing of parasitoids in numbers needed for field testing or release will be limited by the resources needed to extract the needed stage from infested wood, especially outside the infested zone. Efforts to screen pesticides are equally restricted by the resources needed to obtain the large numbers of even aged individuals from infested wood. Year round mass rearing would allow rapid screening of many pesticides.

Several groups are rearing eab with variable success. The period of time that adults can be obtained for use can be extended by holding infested logs in a cold room within the infested zone and bringing them out to allow adults to emerge. This method is limited, in that if the logs are held too long adults that emerge are less viable. Methods to hold adults and obtain eggs exist but inconsistent adult fecundity and longevity limit eab availability. Egg hatch is variable (at times 50-60%) compared to that of other laboratory reared insects. An artificial diet that contains ash sawdust can be used to rear larvae to the adult stage, but there is inconsistent larval survival and frequent diet changes are required. A diet containing cellulose instead of ash saw dust can be used to rear the older larvae but with mixed results. The specific conditions needed for pupation are not well understood even though there does not appear to be an obligate diapause. Thus, although substantial progress has been made in the ability to rear this insect in the laboratory, additional research to develop a system that is reliable and cost effective is needed.

 Our Research

1. Identify effects of biotic and abiotic factors on adult fecundity and longevity to maximize reproduction
2. Improve egg viability and hatch to maximize and increase numbers of larvae available for rearing.
3. Modify artificial diet and determine environmental conditions that will consistently sustain larvae through to the adult stage
4. Assess factors that influence and synchronize pupation to improve the predictability and productivity of rearing on artificial diet.

Expected Outcomes

A reliable method for rearing large numbers of all stages of laboratory reared eab year round, especially outside the quarantine zone, will rapidly advance the biocontrol efforts and other insect control strategies that require laboratory bioassay. 

Research Results

An experiment comparing different hosts and foliage ages is about 2/3 complete. The beetles do not survive or reproduce well when provided Fraxinus griffithii foliage. Beetles survive and reproduce well on hardened off foliage of landscape white ash, greenhouse Fraxinus uhdei, and greenhouse Fraxinus uhdei monus variety. When adults are provided new foliage of Fraxinus uhdei of either variety they survive for a shorter time and lay about 50% less eggs compared to adults fed hardened off foliage of the same variety. We have had beetles survive up to 22 weeks and most live 8 or more weeks with most producing large numbers of eggs (one female produced over 600 eggs). The best method for holding adults is currently a wide mouth glass quart jar with a mesh lid, a 1 oz water reservoir with a wick and the foliage (the leaf steam cut under water), one-third of a white tri-fold paper towel (this type of fold seems to mater for eggs laying), and a ¾” plastic bolt covered with butcher paper and wrapped with a ¾ inch wide purple curling ribbon. The environmental conditions are 25° C, 65% RH and 16:8 light:dark cycle.

Six artificial diets that do not contain host material are being evaluated in a variety of containers. Three of the diets seem to have the right consistency and moisture content to allow larvae to burrow in and survive. Presenting the diet to the larvae as a 3 mm thick sheet that is placed in the bottom of a petri dish seems to be the best method. We are still evaluating the survival and growth of the larvae on the diets.

Research Participants

Principal Investigators

• Melody Keena, US Forest Service- Northern Research Station Research Entomologist
• Juli Gould, USDA - Animal Plant Health Inspection Service - Entomologist

Research Partners

• Leah Bauer, US Forest Service- Northern Research Station Research Entomologist
• John Tanner, USDA - Animal Plant Health Inspection Service