Overwintering conditions affect cold hardiness,survival, and post-overwintering fitness of the pea leaf weevil

Overwintering conditions affect the physiological state of ectotherms, and therefore, their cold hardiness and survival. A measure of the lethal and sublethal impacts of overwintering conditions on pest populations is crucial to predict population dynamics and to manage pests the following spring. The impact of winter conditions can be most intense for invasive insects undergoing range expansion. Insect herbivores can display plastic host use behaviours that depend on their body condition following winter. The pea leaf weevil, Sitona lineatus L. (Coleoptera: Curculionidae), is an invasive pest of field peas, Pisum sativum L., and faba bean, Vicia faba L. (Fabaceae). Pea leaf weevil has expanded its range in North America to include the Prairie Provinces of Canada. This study investigated the effects of temperature and microhabitat on overwintering survival and cold hardiness of pea leaf weevil in its expanded range. Further, we investigated the sublethal effect of overwintering temperature and duration on post-overwintering survival, feeding, and oviposition of pea leaf weevil. We also investigated the role of juvenile hormone in modulating body condition of overwintering weevils. The overwintering survival of pea leaf weevil adults increased with soil temperature and varied with region and microhabitat. More weevils survived winters when positioned near tree shelterbelts compared to open alfalfa fields. The supercooling point of pea leaf weevil varied throughout its expanding range but did not differ for weevils held in the two microhabitats. The average threshold lethal temperature of pea leaf weevil at all three sites was −9.4 °C. Weevils that overwintered for a longer duration and at a higher temperature subsequently fed more on faba bean foliage and laid more eggs compared to those which overwintered for a shorter duration at a lower temperature. Our findings highlight that warm winters would increase overwintering survival and post-overwintering fitness, facilitating further pea leaf weevil invasion northward in the Prairie Provinces of Canada.     

扶桑绵粉蚧的过冷却点和体液结冰点测定

本文测定了扶桑绵粉蚧Phenacoccus solenopsis Tinsley除卵期以外其它各虫态的过冷却点和结冰点.结果表明,该虫过冷却点以1龄若虫最低,为-24.02℃;雄虫预蛹次之,为-22.13℃;雄虫蛹、雄虫2龄若虫、雌虫3龄若虫、雄成虫、雌虫2龄若虫、雌成虫过冷却点逐渐升高,分别为-21.08℃、-20.25℃、-19.05℃、-18.42℃、-17.91℃、-16.89℃.体液结冰点也以1龄若虫最低,为-23.2℃;雄虫预蛹次之,为-19.09℃;雄虫蛹、雄虫2龄若虫、雌虫3龄若虫、雌虫2龄若虫、雌成虫、雄成虫体液结冰点逐渐升高,分别为-16.64%、-15.81℃、-13.92℃、-13.20℃、-12.85℃、-12.79℃.试验结果表明扶桑绵粉蚧过冷却点低,耐寒性较强,可能适宜在中国北部更广泛的区域生存.     

赤松毛虫越冬幼虫生化物质变化与抗寒性的关系

昆虫的抗寒性与其体内生化物质的种类、含量密切相关。测定了赤松毛虫(Dendrolimusspectabilis)越冬幼虫体内和血淋巴内抗寒物质含量的变化,结果表明,血淋巴内小分子碳水化合物总量1月份为10月份的3.8倍,其中以葡萄糖、海藻糖和山梨醇增加幅度较大,依次为10月份的10.08倍、2.84倍、7.44倍。3月份有较大幅度的下降,虫体内糖原含量下降了56.5%。越冬期苏氨酸、丝氨酸、谷氨酸、丙氨酸、胱氨酸增加幅度较大,分别比越冬前增加了493.8%、433.7%、474.2%、21.5%和47.1%,甘氨酸、天门冬氨酸、蛋氨酸、亮氨酸、酪氨酸、苯丙氨酸、组氨酸、精氨酸、脯氨酸含量则有较大幅度的降低。越冬幼虫体内脂肪含量下降,蛋白质含量上升。应用蛋白质垂直平板电泳法对糖蛋白进行电泳分析发现糖蛋白含量增加,为越冬前的300%。综合分析认为赤松毛虫越冬幼虫体内抗寒物质系统为小分子碳水化合物类(山梨醇、海藻糖、葡萄糖)-糖蛋白-氨基酸类(丙氨酸、苏氨酸、谷氨酸等)。该系统可随生态条件的改变而变化。     

黄脊雷蓖蝗越冬卵的滞育发育特性

黄脊雷蓖蝗Rammeacris kiangsu Tsai是我国竹林的重要害虫,1年发生1代,以卵越冬。为弄清其卵滞育发育特性,调查了卵期温度及低温处理对其卵孵化的影响,检测了恒温条件下胚胎的发育进度及卵粒含水量、过冷却点的变化。结果表明,在不同的卵期温度条件下黄脊雷蓖蝗卵的孵化前期均较长,且孵化不整齐、孵化期间长;低温处理30、60或90 d可显著促进其卵的孵化,低温处理的时间越长效果越明显。说明黄脊雷蓖蝗的卵存在滞育现象,低温能明显降低其卵滞育强度。胚胎头幅、触角长度及体长的测量结果显示,25℃温度条件下的黄脊雷蓖蝗的胚胎发育可划分为3个阶段,即前期的持续发育阶段、中期的发育延迟阶段和后期的发育恢复阶段。产卵后40 d左右卵进入滞育,40—75 d为卵的深度滞育期。黄脊雷蓖蝗的卵粒产下后水分含量较低,在25℃的温度条件下,于产卵后25 d前后有一快速的吸水过程,其后卵粒的含水量增加缓慢,可见其卵粒的吸水发生在进入滞育状态之前。在25℃的条件下,黄脊雷蓖蝗卵粒过冷却点的变化亦包含3个阶段,即胚胎发育初期的较高阶段、中期持续而稳定的较低阶段及后期的提升阶段,可以认为黄脊雷蓖蝗越冬卵耐寒性的提高与其滞育的发生密切相关。     

中华通草蛉成虫抗寒能力季节性变化

中华通草蛉（Chrysoperla sinica）成虫在自然条件下抗寒能力的季节性变化研究表明,雌、雄成虫的抗寒能力均呈现出季节性的变化趋势,即随着冬季低温的到来,其抗寒能力逐渐增强,冬季过后又随气温的回升,其抗寒力逐渐减弱.雌、雄成虫的体内含水量、过冷却点（SCP）和结冰点（FP）均随气温的降低而降低,升高而升高,但体内总脂肪的含量却随气温的降低而升高,升高而降低.越冬代在越冬的前期和中期,雌、雄成虫体内的含水量和SCP均显著低于生长季节的其它各代,越冬代后期的含水量和SCP与生长季节其它各代没有显著差异.经回归分析发现,雌、雄成虫体内含水量与SCP之间均存在极显著负相关关系（p＜0.01）;越冬代成虫（特别是越冬前期）的体内总脂肪含量显著高于其它时期,并且雌成虫体内的总脂肪含量与SCP之间呈显著正相关（p＜0.05）,雄成虫体内总脂肪含量与SCP之间没有显著相关性（p＞0.05）.在一年的不同世代中,雌、雄成虫体内含水量只是在越冬前期有显著差异,SCP和体内总脂肪含量却在越冬后期有显著差异.     

烟草潜叶蛾的过冷却点测定

为了明确烟草潜叶蛾的抗寒能力，对烟草潜叶蛾三龄幼虫、四龄幼虫、蛹的过冷却点进行了测定，并初步明确了不同龄期、不同寄主植物、冷驯化等因素对其过冷却点的影响。结果表明：不同龄期下过冷却点由低到高排列顺序为蛹、三龄幼虫、四龄幼虫，其中蛹的过冷却点显著低于三龄、四龄幼虫的过冷却点。以烟草和马铃薯为寄主的蛹和四龄幼虫的过冷却点没有显著差异。经过冷驯化处理的四龄幼虫过冷却点低于未经冷驯化的对照组，但差异不显著；经过冷驯化的蛹的过冷却点高于对照组。本研究有助于了解烟草潜叶蛾的抗寒性及其越冬分布区域。     

A simple moder for estimating the ice content of freezing ectotherms

1. 1.Although body ice content is an important variable affecting freeze tolerance, present calorimetric methods for its measurement necessarily require the termination of a freezing protocol.

2. 2.A simple iterative model, based on the colligative properties of solutions and requiring precise measurements of only equilibrium freezing point (of the unfrozen organism) and of core body temperature, allows estimation of the percentage of body water frozen at any time during a freezing episode.

3. 3.This model can also predict the lethal temperature for a freezing ectotherm, assuming that death occurs due to osmotic dehydration when 67% (of any other known lethal fraction) of the body water is frozen.

4. 4.The basic model is easily extended to evaluate the effects of variables such as: body mass, initial body water content, initial osmotic concentration, and test chamber microenvironment.

5. 5.This model is not intended to supplant existing more exact biophysical models of freezing kinetics. Rather it is proposed as a first approximation which is generally supported by published data and which should be of significant practical value for investigators of freeze tolerant organisms.

Does plant height determine the freezing resistance in the páramo plants?

Neotropical ecosystems between treeline and snowline, called páramos, stretch along Andean ranges from Costa Rica to northern Peru. The páramo climate is characterized by regular night frosts occurring throughout the year. Páramo plants use two strategies to deal with freezing temperatures. They either avoid ice formation in the tissues or tolerate extracellular ice formation. We tested the microclimate hypothesis, which suggests that the freezing resistance of the páramo plants is determined by plant height, that is, that taller plants experience a milder microclimate and avoid freezing, whereas smaller plants are exposed to the more extreme thermal conditions near the ground and tolerate them. We measured the temperature at which ice formed inside the plants (the ‘exotherm’), and compared it with the temperature at which 50% damage to the tissue occurred (Lt50); a significant difference between the exotherm and Lt50 would indicate freezing tolerance whereas the absence of a difference would indicate avoidance by supercooling. We analysed the freezing resistance of 38 common Ecuadorian páramo species. We found no correlation between plant height and freezing resistance mechanism or injury temperature and reject the microclimate hypothesis. Tolerant plants reach higher altitudes than avoidant plants, but their altitudinal ranges largely overlap and the Lt50 does not differ between them. These results suggest that there is no qualitative difference between the two strategies to survive the páramo frosts. Shrub leaves were injured at significantly lower temperatures than other life forms, such as herbs, which may reflect leaf anatomical differences among the plants.     

Freeze tolerance in larvae of the winter-active Diamesa mendotae Muttkowski (Diptera: Chironomidae): a contrast to adult strategy for survival at low temperatures

The winter-active Diamesa mendotae Muttkowski (Diptera: Chironomidae) is freeze intolerant in the adult stage with a low mean supercooling point (SCP) of ~−20 °C. However, cold-hardiness strategies for immatures of this species are unknown. In this study, we measured SCP values for D. mendotae larvae, pupae and adults using surface-contact thermometry. In addition, the lower lethal temperature (LLT) was determined for the larval stage. The mean SCPs for larvae (−7.4 °C) and pupae (−9.1 °C) were relatively high compared to adults (−19.7 °C). Our results indicate that the larvae of D. mendotae are freeze tolerant with a LLT₉₉ (−25.4 °C), ~−10 °C lower than their minimum SCP (−15.6 °C). Freeze tolerance in these larvae may be a strategy to provide protection from short-term exposures to ice crystals or to permit diapause within frozen substrates. The change in cold-hardiness strategy from freeze tolerant to freeze intolerant between the larval and adult stages of this species is likely a result of the different habitats occupied by these two life stages.