The influence of temperature on the flight capacity of emerald ash borer Agrilus planipennis and its parasitoid, Tetrastichus planipennisi: implications to biological control

The success of classical biological control programs often hinges on an appropriate climatic match between a novel ecosystem and an imported natural enemy. In particular, temperature is the most important factor mediating survival, developmental synchrony, and dispersal of invasive pests and their natural enemies. We used computer-monitored flight mills to investigate the roles of temperature and humidity in the flight distance, flight speed, number of flights, and post-flight mortality of emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) and its parasitoid Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) in laboratory settings. Flight distance had a concave, parabolic relationship with temperature for both insects. Maximum flight distances in 24 h occurred at 27.9 °C (1.13 km) for emerald ash borer and 26.5 °C (1.81 km) for T. planipennisi. Flight speed and post-flight mortality increased with temperature for both insects. Relative humidity was inversely related to flight speeds for emerald ash borer, but positively correlated with the number of flights and post-flight survival by T. planipennisi. We integrated the relationship between flight distance and temperature for both insects with landscape temperatures and flight periods for insects at ten locations across the continental USA to develop a flight index. The flight index offers a relative scale of flight capacity across locations based solely on temperature. We found that the flight index for Detroit was intermediate to low compared to other locations, with the smallest and largest flight indices projected in Minneapolis and Seattle for emerald ash borer and Seattle and Atlanta for T. planipennisi. The implications of results for host–parasitoid dispersal patterns and release protocols for distributing T. planipennisi are discussed.