Gallery structure of emerald ash borer larvae on artificial diet and ash bolts

Emerald ash borer (Agrilus planipennis, EAB) is an invasive pest that arrived in the U.S. in 2002 and spread rapidly, causing catastrophic damage to ash trees. In an effort to slow the spread of this pest, beneficial EAB parasitoids are being mass produced in a biological control facility located in Michigan and released across the U.S. in regions with high EAB infestations.The need to rear EAB on artificial diet is an urgent priority because finding ash host material is becoming increasingly more time consuming and expensive. Successful artificial diet for EAB requires a medium that substitutes for phloem wood tissue with enough cohesion and toughness for the formation of feeding galleries. Determining thickness of diet sheets is crucial, as it should be sufficient to support mobility and feeding by EAB larvae but thin enough to enable parasitoids to parasitize later-instar larvae embedded in the diet. Therefore, our objective was to determine the depth of natural feeding galleries of EAB larvae within ash phloem and to measure natural gallery width as an indicator of normal movement and feeding behavior. We peeled bark and identified the instar of live larvae found in infested ash bolts, and measured thickness and width of 3^rd and 4^th instar galleries using hand-held calipers. We compared these parameters with galleries made by the larvae in sheets of diet. Results from this study will help in determining the optimal diet thickness that will support mass rearing of EAB larvae on the artificial diet.