Developmental Thresholds and Thermal Requirements of Two Pupal Parasitoids of the Invasive Fall Webworm

The fall webworm is an injurious pest for many host plants in agriculture, forest, and urban environments. Recent observations showed that the faster spread of this pest can be supported by temperature increases, with a subsequent higher severity of the outbreaks and higher impact on the environment. Traditional chemical control is not effective on this pest, while biological control is a valuable alternative, especially if native natural enemies are used. In this study, the performance of Turkish populations of two parasitoids-<i>Chouioia cunea</i> and <i>Psychophagus omnivorus</i>-at different temperatures is evaluated. Laboratory trials were conducted in climatic chambers under five constant temperatures (10, 15, 20, 25, and 30 °C) and cold storage conditions (6 and 12 °C) for periods of 15, 30, and 45 days. The optimal developmental temperature and the upper thermal threshold of the two parasitoids were similar, while <i>C. cunea</i> showed a lower thermal threshold temperature. Both species could develop and survive between 20 and 30 °C, whereas development below 20 °C for <i>C. cunea</i>, and below 15 °C for <i>P. omnivorus</i> was not possible, respectively. <i>Chouioia cunae</i> was less tolerant to temperature changes than <i>P. omnivorus</i> in terms of offspring survival, development, reproduction, and parasitism. Under cold storage temperatures, the two species did not develop into adults. This study provided relevant eco-biological information that can further support biological control programmes.