Study on Delphacodes striatella Fallén (Homoptera, Delphacidae) in Norm China.

Delphacodes striatella Fallen is one of the most important insect pests on rice inNorth China. According to the results observed in the laboratory during 1959—1961 atthe vicinity of Tientsin, it possesses generally 4—5 generations per year. The eggs of thesixth generation may occur. Though these eggs may hatch into nymphs but they dieeventually in the middle of November. It appears that the different generations areoverlapping one another. The overwintering stage is the 3—5 instar nymphs of the 4th or 5th generation. Inwinter these nymphs hid themselves among those weeds along the sides of the paddy-fields, streams and the rice stubbles, and migrate partly to the soil crevices about 0.5-1cm underground. This insect possesses a migrating habit during the development, such as the nymphsafter overwintering migrate to the weeds in late February, and the adults emerged fromthe overwintering nymphs migrate to the wheat field at the end of April and producethe first generation there. The adults of the first generation migrate then to the rice-field. When the rice is harvested in September, these insect migrate back to the weedsagain. The egg stage is in an average of 6.4—19.5 day. The nymphal stage has 2—7 in-stars, but generally with 5 instars. The first instar is in an average of 3.1—8.9 days,second instar 2.6—8.8 days, third instar 2.2—11.1 days, fourth instar 2.2—10.1 days,fifth instar 3.5—6.8 days, sixth instar 3.3 days, seventh instar 2.5 days. The adults may be classified into the long-wing type and short-wing type. But ac-cording to the observations made in the field during 1958—1961, very few of the maleadults are of the short-wing type in this area. The appearance of the short-wing typeadults is influenced by the weather and food supply. The higher temperature and thefeeding on Echinochlod crusgalli Beauv. are favorable to the appearance of the short-wing type. The number of eggs laid by each female are significantly different in both types ofadults. The female of long-wing type may lay in an average of 119.2 eggs, while ofthe short-wing type 158.1 eggs. In the paddyfield, the appearance of this pests is from early June to the first decadeof July. But the abundant season is from late July to the middle of September. Duringthe abundant season, the higher temperature after precipitation is favorable to the in-crease in number of the pest. According to the observations during years 1959—1961,however, the reduced precipitation and long lighting of July and August, in North Chinacondition, are probably the main factor to stimulate the autumnal outbreak of the pest.