雑食性の捕食者タバコカスミカメは，植物種によってはその植物質のみを摂食しても増殖できる。このような植物は，代替寄主や代替餌なしで，バンカー植物として利用できる。これまで，ゴマ，クレオメ，バーベナ，スカエボラのバンカー植物としての利用が提案されてきた。本研究では，植物質のみで増殖できるバンカー植物のさらなる候補として，スイートアリッサムをとりあげ，本種の発育，生存，産卵を25℃，16L8Dの条件下で調べ，ゴマあるいはクレオメを与えた場合と比較した。その結果，スイートアリッサムの葉と花の両方を与えた場合の卵期，幼虫期の平均発育日数は，それぞれ9.7日，19.3日，その間の生存率は100％，58％であり，羽化後21日間の雌1頭当たりの平均総産卵数は25.1卵，21日後の生存率は71％であった。また幼虫期の平均発育日数，雌1頭当たりの平均総産卵数はクレオメの葉を与えた場合と有意差はなかったが，ゴマの葉を与えた場合より，発育日数は有意に長く，産卵数も有意に少なかった。以上より，花の存在するスイートアリッサムのバンカー植物としての適性は，花無しのゴマより劣るものの花無しのクレオメと同程度と考えられた。スイートアリッサムはバンカー植物としての利用の可能性が期待される。

　This paper chiefly uses microdata for 2000 and 2015 from the agricultural census to investigate structural changes particularly among beef cattle breeders in South Korean livestock farming since South Korea proactively entered into free trade agreements in the 2000s.　Our analysis uncovered the following points.

　First, the rankings of beef cattle breeders by the scale of herds being raised have changed.　In 2000, the ratio of small-scale beef cattle breeders to total beef cattle breeders was 93.5%, while the percentage of beef cattle raised to the total number of beef cattle was 50.1%.　By 2015, the number of small-scale breeders had considerably declined to merely 59.2% of all cattle breeders.　In addition, they accounted for only 12.3% of all cattle being bred.

　Second, many farmers raising small herds of beef cattle on the side, while cultivating rice, have exited the beef cattle business.　Numerous small-scale operations consisted of farmers raising beef cattle in addition to their main business of growing rice and other crops.　Between 2000 and 2015, the total number of beef cattle breeders declined by approximately 180,000, while small-scale cattle breeders raising cattle in addition to a main business of rice cultivation declined by approximately 160,000.

　Third, areas with high concentrations of large-scale herds are increasing, while areas with high concentrations of small-scale herds are shrinking.　Looking at the percentage of small-scale breeders by area, 80% or more of small-sized breeders （i.e., areas with high ratios of small cattle breeders） that constituted 85.7% of all areas in 2000 diminished to 3.3% by 2015.

　Between 2000 and 2015, the number of South Korean farmers engaged in cattle-raising operations, particularly with small herds with rice cultivation as a main business, dropped precipitously.　The ratio of beef cattle produced on a small scale dropped as well.　At the same time, the percentage of large-scale farms steadily increased, along with their share of beef cattle production.

JEL Classification:Q12