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Thermal Activity Thresholds of Parasitoids Aphidius avenae and Aphidius gifuensis (Hymenoptera: Braconidae): Implications for Their Efficacy as Biological Control Agents in the Same Location

Abstract Aphid parasitoids are important components in biological control of aphid populations in a variety of crop systems. Aphidius avenae Haliday and Aphidius gifuensis Ashmead (Hymenoptera: Braconidae) are key biological control agents for Sitobion avenae (F.) (Hemiptera: Aphididae), which causes serious damage to wheat worldwide. This study aimed to evaluate their parasitic potentials focusing on their thermal biological characteristics in a temperate area. Based on supercooling temperature recording techniques, the freezing point, minimum temperature for walking, and the temperature for activity recovery after chill coma of A. gifuensis females (−19.8, −5.1, and 5.9 °C, respectively) were significantly lower than those of A. avenae (−18.1, −3.3, and 7.8 °C, respectively). The results showed that A. gifuensis had lower temperature tolerance compared with A. avenae, illuminating that it could take precedence in suppressing population growth of S. avenae when aphid colonies were still small in early spring.