Influence of density on interspecific competition between Spathius galinae and Tetrastichus planipennisi, larval parasitoids of the invasive emerald ash borer (Agrilus planipennis)

Authors: JENNINGS, DAVID - University Of Maryland; XIAO-YI, WANG - Chinese Academy Of Forestry; Duan, Jian

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2019
Publication Date: 2/13/2019
Citation: Jennings, D.E., Xiao-Yi, W., Duan, J.J. 0219. Influence of density on interspecific competition between Spathius galinae and Tetrastichus planipennisi, larval parasitoids of the invasive emerald ash borer (Agrilus planipennis). Environmental Entomology. 48(2), 2019, 404–409. https://doi.org/10.1093/ee/nvz008.
DOI: https://doi.org/10.1093/ee/nvz008

Interpretive Summary: The emerald ash borer (EAB) has become a devastating forest pest in North America, killing hundreds of millions of native American ash trees since its discovery in Michigan in 2002. A new species of parasitic wasp from the Russian Far East was approved for environmental release for biological control of EAB in the USA in 2015. Because this new parasitic wasp attacks the same larval stages of EAB as a previously introduced parasitic wasp, the potential exists for competition between the two wasps in the same habitats. However, results from laboratory experiments may not always reflect those in the field, as experimental densities may be artificially inflated. To mitigate this problem, we examined the effects of parasitic wasp densities using different sizes of cages on the competition between two larval parasitoids of EAB. Results of the study showed no significant effects of parasitic wasp density (or cage size) on percent parasitism, nor on the number of progeny produced by each species. These findings complement existing research suggesting that competition between these two species in the field will likely be negligible.

Technical Abstract: The outcomes of interspecific interactions between parasitoids depend on a variety of factors. Understanding the influence of these factors is important for classical biological control, where the success of parasitoid releases partly depends on interactions with native and other introduced species. However, results from laboratory experiments may not always reflect those in the field, as experimental densities may be artificially inflated. To mitigate this problem, we examined the effects of multiple densities on interspecific competition between two larval parasitoids of Agrilus planipennis, the emerald ash borer: Spathius galinae and Tetrastichus planipennisi. Parasitoid species were tested individually or together at two different densities, and we measured the effects on percent parasitism and progeny production and calculated their interaction strengths. We found no significant effects of parasitoid density on percent parasitism, but the effect of competition on parasitism generally was reduced at the lower density. However, there were significant differences in parasitism by species, with S. galinae parasitizing more larvae than T. planipennisi. There were also no significant effects of parasitoid density on the number of progeny produced by each species, though the effect of competition on progeny production was greater at the higher density. There were significant differences in the number of progeny produced between species. Tetrastichus planipennisi consistently produced larger broods than S. galinae. Our findings complement existing research suggesting that competition between these two species in the field will likely be negligible.