BIOLOGICAL AND MICROBIAL CONTROL Suitability and Accessibility of Immature Agrilus planipennis (Coleoptera: Buprestidae) Stages to Tetrastichus planipennisi (Hymenoptera: Eulophidae)

Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), a gregarious larval endoparasitoid, is one of three biocontrol agents from Asia currently being released in the United States to combat the invasive emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). The current protocol for rearing T. planipennisi involves presenting thewaspswith artiÞcially infested ash sticks made by placing Þeld-collected larvae into shallow grooves beneath ßaps of bark. Although third and fourth instars are readily accepted by T. planipennisi in these exposures, the suitability of younger or older developmental stages, which are often more readily available in the Þeld, has not been tested. In this study, we used both artiÞcially infested ash sticks and naturally infested ash logs to test which emerald ash borer developmental stages (second to fourth instars, J larvae [preprepupae], prepupae, and pupae) are most suitable for rearing T. planipennisi. T. planipennisi parasitized all stages except for pupae, but parasitized fewer J larvae and prepupae in naturally infested logs than in artiÞcially infested ash sticks. This is probably because, in naturally infested ash logs, these stages were conÞned to pupal chambers excavated in the sapwood and may have been largely beyond the reach of ovipositing T. planipennisi. The number of T. planipennisi progeny produced was positively correlated (logarithmic) with host weight, but this relationship was stronger when J larvae and prepupae were excluded from the data set. Fourth instars yielded the most parasitoid progeny, followed by, in approximately equal numbers, J larvae, prepupae, and third instars. Second instars yielded too few parasitoid progeny to beneÞt rearing efforts.