抄録
キャベツ畑に,ハーブ類のカモミール(カミツレ)およびキンレンカ(ノウゼンハレン)をそれぞれ混作した区と,キャベツを単作して化学合成殺虫剤を施用した区および施用しない区をもうけ,キャベツの主要害虫であるダイコンアブラムシ・モンシロチョウ・コナガの個体数変動と捕食寄生性天敵による寄生率を比較した。試験の結果,各害虫ともそれぞれの個体数がほぼピークとなる時期に,処理区間で個体群密度に有意な差がみられた。ダイコンアブラムシは,カモミール混作区における個体群密度がキンレンカ混作区やキャベツ単作/殺虫剤無施用区または施用区よりも高かった。モンシロチョウの幼虫個体数は,キャベツ単作/殺虫剤無施用区>キンレンカ混作区>カモミール混作区>キャベツ単作/殺虫剤施用区の順に多かった。また,モンシロチョウの卵数は,両ハーブの混作区における値がキャベツ単作区(殺虫剤施用および無施用)における値よりも多かった。コナガは,キャベツ単作/殺虫剤施用区およびカモミール混作区で幼虫の個体数が多かった。いっぽう,モンシロチョウの幼虫におけるアオムシコマユバチの寄生率は,キャベツの生育中期において,キンレンカ混作区およびキャベツ単作/殺虫剤無施用区で最も高かった。これに対し,コナガ幼虫におけるコナガコマユバチの寄生率は,処理区間で有意な差は認められなかった。
Population dynamics of cabbage pests including the cabbage aphid (CA), Brevicoryne brassicae, the diamond back moth (DBM), Plutella xylostella and the cabbage white butterfly (CWB), Pieris rapae crucivora and their natural enemies were compared in the plots of monocropped cabbage without insecticide application, cabbage mix-cropped with nastatium, Tropaeolum majus, cabbage mix-cropped with German chamomile, Matricaria recutita and monocropped cabbage with insecticide application. Significant difference in the population of each pest was observed at its peak. The average number of CA on the cabbage with German chamomile was larger than that on other treatments at 17 days after planting (DAP). On the other hand, the levels of larval population of DBM in the plots of monocropped cabbage with insecticide application and mix-cropped chamomile were relatively high at 45 DAP. Meanwhile the larval population of CWB was different at 31 DAP between four treatments, namely monocropped cabbage without spray>cabbage mix-cropped with nastatium>cabbage mix-cropped with German chamomile>cabbage with insecticide spray. The average numbers of CWB eggs laid in the two mix-cropped plots were less than those in the plots of monocropped cabbage with and without insecticide application. The parasitism rate in CWB by Apanteles glomeratus in the nastatium-mix-cropped plots was significantly high at 52 DAP. The parasitism rates in DBM by Cotesia plutellae were not significantly different between the treatments throughout the experiment.
