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.
Varietal differences in ovicidal response to the white-backed planthopper Sogatella furcifera (Hemiptera: Delphacidae) and susceptibility to Southern rice black-streaked dwarf virus in rice
The recent spread of Oryza sativa L. (rice) ssp. indica-derived cultivars in East and Southeast Asia increases the risk of white-backed planthopper, Sogatella furcifera, and Southern rice black-streaked dwarf virus (SRBSDV) outbreaks. We compared the degree of ovicidal response to S. furcifera and susceptibility to SRBSDV among two Oryza sativa ssp. japonica, two Oryza sativa ssp. indica and one Oryza sativa ssp. indica-derived rice cultivars. The ovicidal response of the O. sativa ssp. indica-derived cultivar was significantly higher than that of the tested O. sativa ssp. indica cultivars and was equivalent to that of the O. sativa ssp. japonica cultivars that we used, supporting previous findings that the ovicidal response is higher in O. sativa ssp. japonica cultivars than in O. sativa ssp. indica cultivars and is a quantitative trait controlled by a few relevant genes. Contrary to the varied ovicidal response, the SRBSDV infection rate among the cultivars and the height of SRBSDV-infected plants between most pairs of cultivars did not differ significantly, although twisting of the leaf tips, a typical symptom of SRBSDV, was not observed in the O. sativa ssp. japonica cultivars. These results indicate that damage by S. furcifera and SRBSDV can occur in O. sativa ssp. japonica as well as in O. sativa ssp. indica and O. sativa ssp. indica-derived cultivars; therefore, in the cultivation of O. sativa ssp. japonica, measures should also be taken against white-backed planthopper during high levels of emergence.
Experimental studies on the flight of planthoppers by the tethered flight technique. I. Characteristics of flight of the brown planthopper Nilaparvata lugens Stal and effects of some physical factors.
トビイロウンカの飛しょう行動の特徴とそれに与える物理的環境条件の影響を明らかにするため,いわゆる宙吊り飛しょう法(tethered flight)の方法を適用した。宙吊り飛しょうには3種の飛しょう型が観察された。第1は長時間継続飛しょう型,第2は短時間飛しょうをくり返し,飛しょう時間は第1の型とあまり違わない型,第3はほとんど飛しょうしない型であった。しかし,ほとんどの個体は第1の型に属し,その特徴からいって,本種が長距離移動型の性質を持っていることが明らかとなった。飛しょうによる体重減少量ははじめの数時間が大きく,それ以後だんだん小さくなった。飛しょう前期間の長さは気温が高い程短かく,雌のそれは27.5°Cの条件で約1日であった。雄の飛しょう前期間は雌にくらべて,数時間短かかった。飛しょう行動の温度閾値は約16.5°Cであって,その値以上の気温の違いによる飛しょう時間の差はほとんどなかった。風速が強い条件程飛しょう時間は短く,約5.5m/秒で飛ぶことができなくなった。相対湿度が高い程,絶食寿命が長く,飛しょう時間も長かった。とくに85%RHにおいては,ほとんどの個体が10時間以上飛しょうした。標準条件とした27.5°C, 60%RH, 3m/秒の風速における平均飛しょう時間は約4時間であったが,10時間以上飛ぶ個体もあって,その個体差は非常に大きく,その原因として体の構造上などの外的要因よりも,内的な物質の量の差によるものと考えられた。これらの結果から,比較的低い気温,高湿度,弱い風速の3条件がそろえば,ほとんどの個体が長時間飛しょうする。とくに高湿度条件と風向によって,日本の梅雨期にあたる季節の長距離移動が可能になることを明らかにした。