关键词: 刺桐姬小蜂, 虫瘿, 发育, 形态特征, 解剖结构, 组织结构

Abstract:

[Objective]Quadrastichus erythrinae is an alien invasive gall-forming insect pest and specifically attacks Erythrina plants, a group of important ornamental plants worldwide. Since the pest invasion in 2004, these host plants have been heavily damaged in Hainan, China. Based on the morphological and anatomical characteristics, the gall development and its variation in structure at the five gall developmental stages were investigated. The five stages include the early growth phase, the later growth phase,maturation phase, and dehiscence, and the photosynthesis. [Method]Galled and ungalled, young and mature leaves were collected from potting Erythrina variegate grown in a laboratory in Hainan Normal University. For morphological studies, the weight, diameter, and height of the galls, and the size of the insect at the five stages were measured with the aid of the Motic Images advanced 3.2 microscope system. For histological studies, transverse sections of the samples were fixed in FAA, dehydrated in n-butyl series, and embedded in Paraplast. All the samples were sectioned into 10 m thickness and stained with astra blue and safranina. The anatomical structures of leaves (n=10 fields), petioles (n=10 fields) and the galls (n=10 fields) were observed with the aid of a clear camera coupled to a light microscope and Motic Images advanced 3.2 microscope system. [Result]The gall-midge females laid their eggs in young leaves. The young leaves, and the upper epidermis and spongy tissue were all thicker than the mature leaves and those tissues (P<0.01); However the upper epidermis and palisade tissue of the young leaves had less arrangement density than that in the older leaves (P<0.01); With the larvae development, the gall was increased rapidly firstly, later the speed of augmentation slowed down, and finally the gall decreased after adult insects left the galls; Plant organs began to change with the invasion of Q. erythrinae; The anatomical structure of the gall tissue formed gall-room, parenchyma layer, protective layer and epidermis layer from inside to outside, and the each layer of galls augmented firstly and then decreased slowly; The parenchyma layer served as the nutritive provider, and was significantly thickened at the third stage (P<0.05); Epidermis and protective layers that provided protection for the growth of larvae and pupae of Q. erythrinae were significantly thicker at the second stage (P<0.01). [Conclusion]Plant organs began to change with the oviposition of Q. erythrinae, and variations in gall structure were usually related to the host tissue age. Young tissues were generally more capable of reacting to gall induction than mature ones; the observation of five developmental phases of the gall proved that, while the gall external structure was determined by defensiveness, the internal structure diversification was probably related to nutritive supply. The results could well interprete the adaptive value of insect galls for the galling insect. Thus this study lays a foundation on which further experiments are conducted in an effort to determine the mechanism of gall formation in E. variegate.

Key words: Quadrastichus erythrinae, insect-gall, development, morphostructure, anatomical structure, histological structure