Host utilization, reproductive biology, and development of the larval parasitoid Tetrastichus planipennisi as influenced by temperature

Duan, J. J., Schmude, J. M., Wang, X.-Y., Watt, T. J., & Bauer, L. S. (2018). Host utilization, reproductive biology, and development of the larval parasitoid Tetrastichus planipennisi as influenced by temperature: Implications for biological control of the emerald ash borer in North America. Biological Control, 125, 50-56. PDF.

Summary

 Emerald ash borer, or EAB, is a devastating pest of ash trees that has spread through much of the central and eastern United States.  A number of biological control agents have been introduced to limit EAB populations, including Tetrastichus planipennisi, a parasitic wasp and important natural enemy of EAB in its native range.  This study sought to understand how T. planipennisi will perform across the climatic range of EAB by examining how temperature influences life stages and vital rates of this parasitic wasp.  Researchers measured T. planipennisi larval development rate, adult longevity, parasitism rate, and fecundity across a range of temperatures (15, 20, 25, 30, and 35°C) in lab-based enclosures.  Larvae and adults who experienced cooler (15°C) temperatures lived longer than those in warmer enclosures, however they experienced longer development times, and decreased rates of reproduction and parasitism.  Development speed, reproductive rate and parasitism rates all increased with temperature, reaching a maximum at 25-30°C.  A temperature threshold was reached around 35°C where T. planipennisi experienced marked declines in egg survival and rates of parasitism.

 The authors used results of these experiments to estimate, based on temperature, locations in the U.S. where T. planipennisi will be able to complete multiple generations in a year, and locations where temperature may be limiting to populations.  Climate zones 4 – 6 were predicted to be optimal for T. planipennisi population growth.  Central and southern regions of the U.S. were predicted to have a greater number of generations of T. planipennisi, however high temperatures (exceeding 35°C) may limit population growth and parasitism by agents.  Colder zones (7 +) may experience high overwintering mortality and slow growth of populations.

Take home points

• The development of and parasitism of EAB by T. planipennisi wasps is highly dependent on temperature, with 25-30°C being optimal for maximizing parasitism rates and minimizing development time

• T. planipennisi is unlikely to be an effective agent when temperatures exceed 35°C for an extended period of time

• Releases of T. planipennisi should be timed to avoid low (spring and fall in zones 4-6) or high (mid-summer in zones 2-3) temperatures

Management implications

Managers using T. planipennisi to manage EAB should consider their climate and time releases to ensure that conditions will support wasp populations and parasitism.  With the spread of EAB into more northern and southern regions outside the ideal temperature range, managers may want need to source T. planipennisi from regions with similar latitudes to intended release location, or consider a different biocontrol agent.

Keywords

Shifting Seasons; Impact Study; Experiment; Invasive Invertebrate; Tetrastichus planipennisi; Tetrastichus planipennisi