Thermal treatments in controlling Plodia interpunctella (Lepidoptera: Pyralidae) on sunflower seeds and their effect on seed vitality

This work aimed to assess the potential of thermal treatments for controlling P. interpunctella on sunflower seeds, based on its tolerance to high/elevated temperatures and effect on seed vitality. The tests involved mature larvae (L5) and pupae, exposed to 35, 40, 42, 44, 45, 50, 55 and 60 °C, for 15 and 30 min, and 1, 2, 6, 24, 48 h. Larval mortality and survival, Probyt analysis, developmental dynamics, longevity analysis, progeny production and the effect on sunflower seed vitality (germination energy and germination) were assessed. Larval mortality of 75.9% was achieved after 30 min of exposure at 44 °C, 77.0% at 45 °C after 15 min, and 100% after 45 min. At 60 and 65 °C total mortality was achieved already after 15 min of exposure. Lethal exposure time (LT₅₀) needed to kill 50% of larval population was 15 min at 44.2 °C, 30 min at 43.3 °C, 45 min at 42.1 °C or 41.8 °C at 60 min, respectively. LT₉₀ can be achieved after 15 min of exposure at 45.2 °C, 30 min at 44.3 °C, 45 min at 43.3 °C, or 60 min at 42.1 °C. Pupal LT₅₀ was 15 min at 56.7 °C, 30 min at 53.1 °C, 45 min at 52.4 °C or 60 min at 52.2 °C, while LT₉₀ was 15 min at 59.7 °C, 30 min at 56.3 °C, 45 min at 56.1 °C or 60 min at 55.6 °C. The fastest development, and the highest progeny production was in treatments when the parenteral population was exposed to 40 °C for 1, 2 and 6 h. The developmental duration was significantly shortened when parenteral population was exposed to 40 °C for 48 h. The temperature and exposure did affect the duration of the adult life stage only when exposed for 2, 3, 6, 24 and 48 h to 40 °C. The germination of sunflower seed (86.7%) was inhibited by heat at 45 °C when exposed for 24 h.