Flight capacity of Tetrastichus planipennisi, an introduced parasitoid of emerald ash borer Agrilus planipennis

Background/Question/Methods

Classical biological control programs aim to decrease densities of invasive species via reuniting those invasive species with natural enemies from the native range. The effectiveness of a biological control program hinges on multiple factors, ranging from the molecular to the landscape level. We aimed to determine the dispersal capacity of Tetrastichus planipennisi (Hymenoptera: Eulophidae), a classical biological control agent of emerald ash borer Agrilus planipennis (Coleoptera: Buprestidae). Emerald ash borer is capable of long distance dispersal, but T. planipennisi is a much smaller insect (~4 mm long) and knowledge of its dispersal capability remains scant. To determine the dispersal capacity of this parasitoid, we used 24 computer-monitored flight mills. Each insect examined was flown once in tethered flight for a 24-hour period. Maximum-likelihood methods were used to determine a 95-percent confidence interval for median dispersal.

 Results/Conclusions

We found that a small percentage of Tetrastichus planipennisi is capable of long distance dispersal (up to 7000m) over a 24-hour period, but that most individuals disperse shorter distances (< 1500m). Median dispersal was 905-1330m (95% CI). The willingness and capability of a biological control agent to disperse may be important for host location and maximizing coverage in the field but may also inform field releases and subsequent recovery sampling to determine parasitoid establishment. Furthermore, in its native range, this parasitoid is likely adapted to foraging for hosts that are patchily distributed at low densities. The results presented here, coupled with an understanding of the biology of T. planipennisi in its native range, suggest that T. planipennisi may be capable of significant coverage in the field and may inform current release guidelines.