Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 2010
Publication Date: February 1, 2011
Citation: Ulyshen, M.D., Mankin, R.W., Cheng, Y., Duan, J.J., Poland, T.M., Beauer, L.S. 2011. The role of emerald ash borer (Coleoptera: Buprestidae) larval vibrations in host-quality assessment by Tetrastichus planipennisi (Hymenoptera: Eulophidae). Ecological Entomology. 104:81-86. Interpretive Summary: The parasitic wasp, Tetrastichus planipennisi, is one of three natural enemies from Asia currently being released in the United States to control the emerald ash borer (EAB), an invasive insect that has destroyed millions of ash trees in the U.S. This wasp prefers to attack large EAB larvae feeding in ash trees, but cues used to assess the EAB host size (or quality) by this wasp remain unknown. In this study, we tested whether vibrations produced by feeding EAB larvae inside ash sticks vary with size, and whether there is a relationship between these cues and the number and sex ratio of resulting parasitic wasp offspring. Findings from this study shows that vibrations produced by feeding EAB larvae varied significantly with larval size, suggesting that this parasitic wasp might use vibration-cues to assess EAB host quality for reproduction.
Technical Abstract: 1. The biological control agent, Tetrastichus planipennisi Yang, is a gregarious larval endoparasitoid of the emerald ash borer (EAB), an invasive phloem-feeding species responsible for recent, widespread mortality of ash (Fraxinus spp.) in North America. 2. Tetrastichus planipennisi is known to prefer late-instar EAB but the cues used to assess host size by this species and most other parasitoids of concealed hosts remain unknown. 3. Vibrations produced by host movement and feeding activities are known to be used by many parasitoids to locate hosts. We sought to test whether vibrations produced by feeding EAB vary with larval size and if there are any correlations between these cues and T. planipennisi progeny number and sex ratio. 4. The amplitudes and rates of 3-30-ms vibrational impulses produced by EAB larvae of various sizes were measured in the laboratory before presenting the larvae to T. planipennisi. 5. Impulse-rate did not vary with EAB size but vibration amplitude was significantly higher for large larvae than for small larvae. Tetrastichus planipennisi produced a significantly higher proportion of female offspring from large hosts than small hosts and has been shown in previous work to produce more offspring overall from large hosts. There were no significant correlations, however, between the T. planipennisi progeny data and the EAB sound data. 6. Because vibration amplitude varied significantly with host size, we are unable to entirely reject the hypothesis that T. planipennisi and other parasitoids of concealed hosts use vibrational cues to assess host quality, particularly given the low explanatory potential of other external cues. Internal chemical cues, however, may also be important.