Population dynamics of the whitebacked planthopper,Sogatella furcifera (Hemiptera: Delphacidae) with special reference to the relationship between its population growth and the growth stage of rice plants
A population census was conducted to describe the effects of the growth stage of rice on the population dynamics ofS. furcifera, in particular, on immigration, seasonal abundance, population growth rate, and wing-form expression. The number of immigrants was highest on rice plants 17 to 30 days after transplanting (DAT), which suggested that immigrants prefer to settle or remain more on rice plants at the tillering stage (approximately 20–30 DAT). Population growth rate from immigration to the 1st generation decreased with an increase in rice plant age. In contrast, population growth rate from the 1st to 2nd generation was not influenced by rice plant age and was negatively density-dependent. The percentage of macropters (flyers) was positively related to the growth stage of rice when rice was in the vegetative or early part of the reproductive stage, and reached 100% at about 10 days before heading (booting stage). Threafter, most adult females molted into macropters regardless of population density. The roles of host plant age and crowding effect on the population dynamics ofS. furcifera are discussed.
Outline of long-term yearly fluctuations of the rice planthopper occurrence from light-trap data at Kyushu National Agricultural Experiment Station.
1.初 誘殺 日 トビイロウ ンカとセジロウンカの全調査期間 を通 した 平年初誘殺 日はいつれ も6月13~14日 で あったが,最 も 早い初誘殺 日は,そ れ ぞれ5月7日(1972)お よび5月 12日(1983)で,最 も遅 い初誘殺 日は7月11日(1982) および7月6日(1958)で あ り,両 種 とも著 しい年次変 動 を示 した。 しか し最近 の約15年 間に限 って変動傾向 を 見た場合,セ ジロ ウンカの初誘殺 時期 は徐 々に早 まる傾 向が認 め られるのに対 して,ト ビイロウンカの初誘殺 日 は逆 に遅 くな りつつ あ る(第1図)。 このため1981年 以 降,セ ジ ロウンカが トビイロウンカよ りも早期 に初誘殺 され る状態 が顕著 になってい る。 2.5~7月 の誘殺数 両 種 とも6月4半 旬か ら誘殺数が明 らかに増加 し始 め, 7月1・2半 旬 にピー クを示 し,誘 殺 数の増加 時期 は雨 量の増加時期 と一致 して いた(第2図)。
D'une application pratique des indices bio-météorologiques
Abstract The purpose of the author is to determine statistically in what part of Switzerland maize could be cultivated with certain chance of rentability. The author gives first the method he used for determining the biometeorological index of four species of maize which were selected by the Swiss agronomical research stations. He has considered two possibilities for the growing period: ( a ) raising-ripening (l'approche globale); ( b ) raising-flowering, flowering-ripening (l'approche fractionee). From the biometeorological index, he calculated retrospectively the ripening time of these four species in the years 1901–1965. Assuming a priori that maize should be harvested before October 15th at the latest, he calculated, for a number of meteorological stations, the relative number of years when such conditions were fulfilled. Dividing the country in regions of similar mesoclimates and sorting these stations per region, it is possible to average the maximum altitude where maize can ripen at least 7, 8, 9 and 10 times within 10 years. Finally, taking into account the exposure and ground slope, he draws maps of the theoretically possible extension area, which maps are more reliable and detailed than the ones derived from actual means.