THE DISTRIBUTION OF APHID INFESTATION IN RELATION TO LEAF AGE

Infestations of apterous Aphis fabae Scop, on potted sugar beets have been followed in detail for several weeks. The plants were somewhat stunted and their crowns presented an unusually complete series of leaf ages. Records were kept of the changing number and size of the leaves and of their stage of growth. Parallel records were kept of the changing population of aphids on every leaf, and the figures are analysed in various ways to show how suitability for the aphids varied through the life cycle of the leaves.
The leaves were very suitable when young, became unsuitable as they matured, became suitable again just after maturity and then unsuitable again as they senesced. But among leaves at any given stage, those which were growing or senescing rapidly were more suitable than those changing slowly, unless the rate of senescence was very high. The differences of population density on different-aged leaves were due largely to the preferences exercised by the apterous adults. The added effect of differences in the fecundity of these mothers while feeding on different leaves was not excluded, but could not be assessed. It is concluded that the physiological development of the plant as a whole determines, through the growth and senescence among its total complement of leaves, the progress and pattern of its aphid infestation.     

柑桔新害虫——高氏瘤粉虱研究

高氏瘤粉虱ＡｌｅｕｒｏｔｕｂｅｒｃｕｔｕｓｔａｋａｈａｓｈｉＤａｖｉｄｅｔＳｕｂｒａｍａｎｉａｍ是福建福州郊区桔园新发现的一种小型刺吸性害虫。国外在印度最早发现,并于１９７６年被鉴定命名。本文通过该虫在替换寄主茉莉花上的田间调查和室内饲养观察,对该虫的形态特征、生物学特性及防治对策作了初步探讨。高氏瘤粉虱在福州年发生约８－９代,主要以成虫、若虫刺吸为害柑桔和茉莉叶片,在２８±１℃条件下,世代历期为２６－３１天。以高龄若虫或拟蛹越冬。其寄生性天敌有桨角蚜小蜂（Ｅｒｅｔｍｏｃｅｒｕｓｓｐ．）、恩蚜小蜂（Ｅｎｃａｒｓｉａｓｐ．）等,寄生率为７．０７－１７．８４％。     

PHYLLODE THEORY IN RELATION TO LEAF ONTOGENY IN SANSEVIERIA TRIFASCIATA

Shoot apices of Sansevieria trifasciata have a three-layered mantle, a zone of subapical initials, a central meristem, and a peripheral meristem. Leaf initiation begins with periclinal divisions in L-3 and is followed by periclinal divisions in L-2 and anticlinal divisions in L-l. At first, the primordium is a mound of tissue at one point on the flank, but it soon takes the form of a low ridge encircling the apex. An ephemeral adaxial meristem differentiates in L-2 of the primordium when it is about 50 μ high and is active until the primordium is about 450 μ high. Then it ceases basipetally and is not observable after the primordium is about 600μ high. As the adaxial meristem ceases at the base of the radial tip, its two lateral regions become the submarginal meristems of the expanded portion. Marginal meristems differentiate from the protoderm, and oblique-anticlinal divisions of the marginal initials result in the formation of an abaxial and adaxial epidermis. These derivatives undergo a few anticlinal divisions, increasing marginal width, and then they divide periclinally, increasing marginal thickness. After the primordium is about 600-700 μ high it continues to grow in length by a diffuse basal intercalary meristem. When the leaf is 3 dm long, an adaxial rounding meristem differentiates in the region just above the sheath. Leaf vasculature consists of parallel bundles which anastomose acropetally. Vascular bundles are arranged in a semicircle in the expanded portion and in a circle in the radial tip. There is one centrally located bundle at the apex as a result of lateral anastomoses. Present evidence from leaf ontogeny and mature vasculature in S. trifasciata is interpreted as supporting the concept that the liliaceous leaf is homologous with the phyllodes of A corns and Acacia.     

THE EFFECT OF MODERATE SALT STRESS ON LEAF ANATOMY IN HIBISCUS CANNABINUS (KENAF) AND ITS RELATION TO LEAF AREA

Kenaf responded to salt stress in a manner that was typical of moderately salt tolerant non-halophytes. Increase in leaf area was more sensitive to salinity than either leaf emergence rate or dry matter accumulation. Dry weight was reduced only above a threshold of approximately 37 mM NaCl while leaf area was already significantly reduced at this salt concentration. Measurement of epidermal cell cross sectional area and epidermal cell numbers showed that the salt induced reduction in leaf area was due primarily to smaller epidermal cell size. Epidermal cell numbers were also significantly reduced by salinity. Stomatal density increased with increasing salt stress and there was no effect on leaf thickness.     

广西木虱科大新种(同翅目:木虱总科)

本文记述了采自我国广西及海南的木虱科6新种,隶属于木虱属Psylla和喀木虱属Cacopsylla;在标本的采集中承蒙广西农科院周至宏同志、王助引同志的帮助和支持,谨致谢意。模式标本保存于北京农业大学昆虫标本馆。