The biological control agent Tetrastichus planipennisi
Yang (Hymenoptera: Eulophidae) is a gregarious larval endoparasitoid of the emerald ash borer, Agrilus planipennis
Fairmaire (Coleoptera: Buprestidae), an invasive cambium-feeding species responsible for recent, widespread mortality of ash (Fraxinus
spp.) in North America. T. planipennisi
is known to prefer late-instar emerald ash borer, but the cues used to assess host size by this species and most other parasitoids of concealed hosts remain unknown. We sought to test whether vibrations produced by feeding emerald ash borer vary with larval size and whether there are any correlations between these cues and T. planipennisi
progeny number (i.e., brood size) and sex ratio. The amplitudes and rates of 3-30-ms vibrational impulses produced by emerald ash borer larvae of various sizes were measured in the laboratory before presenting the larvae to T. planipennisi
. Impulse-rate did not vary with emerald ash borer size, but vibration amplitude was significantly higher for large larvae than for small larvae. T. planipennisi
produced a significantly higher proportion of female offspring from large hosts than small hosts and was 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 emerald ash borer sound data. Because vibration amplitude varied significantly with host size, however, we are unable to entirely reject the hypothesis that T. planipennisi
and possibly 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 also may be important.
Ulyshen, Michael D.; Mankin, Richard W.; Chen, Yigen; Duan, Jian J.; Poland, Therese M.; Bauer, Leah S. 2011. Role of emerald ash borer (Coleoptera: Buprestidae) larval vibrations in host-quality assessments by Tetrastichus planipennisi (Hymenoptera: Eulophidae). Journal of Economic Entomology. 104: 81-86.