Department of Biological Sciences and Biotechnology, Botswana International University of Science and Technology, Palapye, Botswana.
Department of Zoology and Entomology, University of the Free State, Bloemfontein, South Africa.
Pest Manag Sci. 2021 Jan;77(1):184-193. doi: 10.1002/ps.6006. Epub 2020 Aug 18.
For many insects, including invasive species, overwintering survival is achieved behaviourally (e.g. through migration) or physiologically by entering diapause, a state of arrested physiological development that may be accompanied with depressed supercooling points (SCPs). Diapause allows in situ adaptation to adverse environmental conditions, providing sufficient parent propagules for insect pest proliferation when optimal conditions resurface. This phenomenon has however not been observed in the invasive South American tomato pinworm Tuta absoluta in its Mediterranean invaded areas. Moreover, no studies have looked at its overwintering survival in sub-Saharan Africa. Here, we thus investigated the cold hardiness of Tuta absoluta larvae and adults to better explain its local overwintering adaptation strategy.
Larval lower lethal temperatures ranged from -1 to -17 °C for 0.5 to 4 h durations. Adults showed lower temperature activity limits than larvae albeit freeze strategy experiments showed neither survived internal freezing. Fasting and dehydration pre-treatment generally depressed SCPs, although asymmetrically, conferring more negative SCPs for larvae. Ramping rates, synonymic to diurnal temperature changes also significantly affected SCPs while, inoculative freezing significantly compromised freezing temperatures in both larvae and adults.
Our results suggest that (i) Tuta absoluta larvae and adults are chill-susceptible and may successfully overwinter, (ii) larvae appear more cold hardy than adults and (iii) ecological factors e.g. inoculative freezing, cooling rates, feeding- and hydration-status may affect cold hardiness. These results are important in determining species range limits, population phenology, modelling pest risk status and allows temporal life-stage specific targeting of management strategies.
对于许多昆虫，包括入侵物种，越冬生存是通过行为（例如通过迁移）或生理上进入滞育来实现的，滞育是一种生理发育停滞的状态，可能伴随着过冷却点（SCP）的降低。滞育允许在原地适应不利的环境条件，当最佳条件再次出现时，为昆虫害虫的繁殖提供足够的亲代繁殖体。然而，这种现象在其地中海入侵地区的入侵性南美番茄潜叶蛾 Tuta absoluta 中尚未观察到。此外，没有研究探讨过它在撒哈拉以南非洲的越冬生存情况。在这里，我们因此研究了 Tuta absoluta 幼虫和成虫的耐寒性，以更好地解释其当地的越冬适应策略。
幼虫的致死低温范围为-1 至-17°C，持续时间为 0.5 至 4 小时。尽管冻结策略实验表明成虫和幼虫都无法存活于内部冻结，但成虫的温度活动极限低于幼虫。禁食和脱水预处理通常会降低 SCPs，尽管不对称，但会使幼虫的 SCP 更负。斜坡率，与昼夜温度变化同义，也会显著影响 SCPs，而接种冻结会显著降低幼虫和成虫的冻结温度。
我们的研究结果表明：（i）Tuta absoluta 幼虫和成虫易受冷害，可能成功越冬；（ii）幼虫比成虫更耐寒；（iii）生态因素，例如接种冻结、冷却速率、摄食和水合状态，可能会影响耐寒性。这些结果对于确定物种范围界限、种群物候学、建模害虫风险状况以及允许针对特定时间的生命阶段制定管理策略非常重要。
