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.
Analysis of yearly fluctuations in the occurrence of migratory rice planthoppers, nilaparvata lugens stal and sogatella furcifera horvath, based on light-trap data in northern kyushu
長距離移動性イネウンカ類(トビイロウンカ,セジロウンカ)の発生動態の年次変化の実態を明らかにし,その原因について考察するため,九州農業試験場(福岡県筑後市)における1951～1990年の予察灯の日別誘殺数データを解析した。1) 飛来侵入世代および増殖世代の誘殺数は,トビイロウンカでは変動しつつ減少する傾向があり,セジロウンカでは1970年代中ごろから一貫して増加する傾向があった。1980年代のトビイロウンカの飛来侵入世代,増殖世代およびセジロウンカの飛来侵入世代の年次間変動幅(分散値)は他の年代にくらべて増加した。セジロウンカの増殖世代の年次間変動は1960年代から一貫して減少する傾向があった。2) 回帰分析の結果から,両ウンカとも飛来侵入世代の増加に対して増殖率の低下が認められた。セジロウンカでは1980年代の回帰係数の絶対値は他の年代より大きく,増殖率の密度依存的低下がもっとも強かった。トビイロウンカでは他の年代にくらべ1980年代の増殖率が低い傾向にあった。3) 各世代の誘殺数の対数値を用いた主成分分析の結果から,両ウンカとも発生パターンを3群に分けることができた。群I, IIは飛来侵入世代誘殺数は同程度だが後半の世代の増殖率が大きく異なった。その要因としてトビイロウンカでは飛来開始時期の早期と8月の気温が,セジロウンカでは9月の降水量が影響することが示された。群IIIはG0は非常に多いが,その後の増殖率が上がらないパターンを示した。1980年代の主成分特性値は非常に極端な値を示すことが多かった。
Spatial distribution of root lesion nematodes (Pratylenchus spp.) in a long-term no-till cropping system and their relationship with soil and landscape properties
The Cook Agronomy Farm of Washington State University is a long-term precision agriculture study site. Since 2000, the farm has been in various three-year no-till rotations with winter wheat, spring wheat, and various rotation crops such as barley, canola, peas, lentils, and chickpea. The spatial distribution of root lesion nematodes (Pratylenchus spp.) and their relationships with soil and terrain variables were studied by collecting soil samples at 127 and 124 geo-referenced points in two 12-ha fields during the spring of 2010 and 2011, respectively. Pratylenchus spp. were detected in more than 85% of the sampled locations in both fields. Nematode densities spatially mapped using ArcGIS software occurred in an aggregated pattern. Previous rotation crops had no effect on the spatial distribution. Classification and regression tree analysis (CART) using soil and terrain variables, and nematode density, explained 61 and 34% of the variability associated with nematode density in 2010 and 2011, respectively. Soil edaphic factors, such as organic matter, were stronger predictors of nematode populations than rotation effects.