Tosh Colin R., Powell Glen, Hardie Jim
Aphid Biology Group, Department of Biological Sciences, Imperial College at Silwood Park, Berks SL5 7PY, Ascot, UK
J Insect Physiol. 2002 Jun;48(6):619-629. doi: 10.1016/s0022-1910(02)00084-7.
Aphids are phloem feeders and an important assumption has been that reproduction is initiated only after phloem ingestion. Here we investigate the plant tissue location of parturition cues in winged and wingless, summer virginoparae and autumn migrants (gynoparae) of the black bean aphid, Aphis fabae. These seasonal forms have different host preferences. Using electrical penetration graph (EPG: to observe activity of the mouthparts) and video-monitoring procedures we demonstrate that the time to first parturition after host-plant contact is significantly shorter than the time to first registered phloem contact in the summer winged form. In gynoparae, the time to first parturition does not significantly differ from time to first phloem contact but is shorter than time to first phloem ingestion. Times to first parturition, first registered phloem contact and first phloem ingestion do not differ significantly in the summer wingless form. Simultaneous EPG and video recording procedures show that a high proportion of individuals of all morphs (45-70%) initiate reproduction before sustained phloem activities (salivation/ingestion). The only behaviours that all individuals demonstrate before first parturition are 'non-penetration' (aphid on plant surface with mouthparts outside plant) and stylet 'pathway activity', including secretion of gelling saliva and penetration of the non-vascular (epidermis and mesophyll) cells. A short period of penetration of the peripheral plant tissues (five cell punctures per individual) by aphids tethered and monitored by EPG decreases the time to first parturition of the winged summer form when subsequently placed on a Parafilm sachet containing 15% sucrose solution. This treatment also significantly increases the incidence of reproduction and individual reproductive output of gynoparae over a 24-h period. No detectable effects of tissue penetration on subsequent reproductive output are observed in the wingless summer form. Additionally, EPGs reveal that a number of aphids of all morphs display xylem ingestion, which occurs predominantly before initiation of phloem feeding but is not necessary to initiate parturition. It is concluded that aphids are likely to detect parturition cues during stylet punctures of cells within peripheral tissue layers, before reaching the phloem vessels.
蚜虫以韧皮部为食，一个重要的假设是只有在摄取韧皮部之后才开始繁殖。在此，我们研究了黑豆蚜有翅和无翅夏季孤雌蚜及秋季迁移蚜（雌性蚜）分娩信号的植物组织定位。这些季节性形态具有不同的寄主偏好。利用刺吸电位图谱（EPG：用于观察口器活动）和视频监测程序，我们证明了在夏季有翅形态中，寄主植物接触后到首次分娩的时间显著短于首次记录到与韧皮部接触的时间。在雌性蚜中，首次分娩的时间与首次韧皮部接触的时间没有显著差异，但短于首次摄取韧皮部的时间。在夏季无翅形态中，首次分娩、首次记录到韧皮部接触和首次摄取韧皮部的时间没有显著差异。同步的EPG和视频记录程序表明，所有形态的蚜虫中很大一部分（45 - 70%）在持续的韧皮部活动（流涎/摄取）之前就开始繁殖。所有个体在首次分娩前唯一表现出的行为是“非刺探”（蚜虫在植物表面，口器在植物外部）和口针“路径活动”，包括分泌凝胶状唾液和穿透非维管束（表皮和叶肉）细胞。通过EPG系留并监测的蚜虫对周围植物组织进行短时间的穿刺（每个个体穿刺五个细胞），会缩短随后置于含有15%蔗糖溶液的保鲜膜小袋上的有翅夏季形态的首次分娩时间。这种处理还显著增加了雌性蚜在24小时内的繁殖发生率和个体繁殖产量。在夏季无翅形态中未观察到组织穿刺对后续繁殖产量有可检测到的影响。此外，EPG显示所有形态的许多蚜虫都有木质部摄取现象，这主要发生在开始取食韧皮部之前，但并非开始分娩所必需。结论是，蚜虫可能在到达韧皮部血管之前，在外围组织层细胞的口针穿刺过程中检测到分娩信号。
