The Embryonic Development Of Spodoptera Exigua

The course and characters of the embryonic development of beet armyworm, Spodoptera exigua HUbner, were studied with paraffin sections and scanning electron microscopy in this paper. The ovicidal function of diflubenzuron, a kind of specific pesticide, was researched and discussed by the way of histology and biochemistry, anil the most sensitive phase to diflubenzuron for the beet armyworm embryo was also found, which meaned the best opportunity of applying diflubenzuron to kill eggs of the beet armyworm was known.The embryo period of beet armyworms was about 71 hours under the condition of 25 "C, 80%RH, 14 hours lighting per day. The egg was suboblate, multicolor and covered with villi. The periplasm of eggs included two layers. Daughter nuclei moved towards the egg surface in the form of cometic energids, which changed the spread of yolk. The yolk would become yolk sphere later which contained one or two vitellophages. Daughter nuclei in the posterior pole of eggs became cap-shaped primordial germ cells after cleavage, moved in two masses to the laterodorsal abdomen of embryo, and then were enveloped by mesoderm to form germinal ridge. The germ band was so long at the beginning as to be about 3/4 of the egg equator perimeter, and then became longer and longer so that the head and cauda were immersed into yolk, as well as the head curling and twisting. The germ band started to be delaminated into two layers with the appearance of gastral groove. The outer layer would become ectoderm and the inner would form mesoderm and endoderm. Serosa formed earlier and broke later than amnion, the latter forming temporary body wall in the later development. Neuroblasts appeared early and the nervous system developed very quickly. The ventral nerve cord looked like a ladder. Protocerebrum would developed into procerebrum and deutocerebrum, while tritocerebrum came from premandibular ganglion. The stomodaeal nervous system comprised frontal ganglion and ingluvial ganglion. Six pairs of lateral ocelli came out of ectodermal cells near lobus opticus. Hypodermal cells began to secrete chitinous epidermis at 50th hour around. The embryo body was covered densely with crests and chaetae before hatching. The foregut and hindgut derived respectively from the stomodaeum and proctodaeum. The foregut would be differentiated into oesophagus, crop and proventriculus while the hindgut would be composed of ileocolon and rectum. Themidgut came from anterior mesenteron rudiments and posterior mesenteron rudiments.Six Malpighian tubes formed crytonephridiel by putting their tube ends into the rectum wall. The ectodermal cells of mesothorax, metathorax and 1 to 8 abdomen got in to form the respiratory system. The spiracles at mesothorax moved to prothorax and spiracles at metathorax disappeared in the later development. Oenocytes derived from ectodermal cells of 1 to 8 abdomen. The mesoderm differentiated into somatic mesoderm and splanchnic mesoderm after coelomic sals appeared, the former developing into musculus parietalis, fat body etc., and the latter forming muscles of the alimentary canal. The median mesoderm turned into haemocytes. Cardioblasts came out of cells between somatic and splanchnic mesoderm, then formed heart after dorsal enclosure and connected with the large artery to form the dorsal vessal. The blastokinesis included four phases: germ band elongating and twisting; embryo shortening and unwinding; embryo reversing; embryo elongating and twisting again. Dorsal enclosure took place from head and cauda to center nearly at the same time of embryo reversing. The embryo ate up yolk unenveloped into the midgut before hatching. According to the characters of embryo shape, die whole embryonic development of the beet armyworm could be divided into five phases: the phase of early developing, germ band elongating, embryo shortening, embryo reversing and dorsal enclosure, embryo elongating again and maturing.Through the experiments of determining the sensitive phase of beet armyworm eggs to diflubenzuron, the outcome showed t...