CONTROL OF THE WORST PEST OF ROSES (バラ最悪の害虫バラクキバチ対策)

 

Syrista similis is the most detestable and worst rose pest in our gardens. In spring, when the new shoots of roses are growing and budding, the adult flies in and lays its eggs on the shoots. Not only do they lay eggs, but they also cut the pith of the shoots with their knife-like tail. Naturally, the shoots soon wither and die. Soon after hatching from the eggs, the larvae feed on the inside of the stem and move down the stem. The wilted shoots do not flower. Our garden has been affected by this every April, and in some years up to 120 shoots have been destroyed. It is very shocking. 

The pest is small, less than two centimetres in length, plain and inconspicuous in colour, and difficult to catch as it flies about quickly. Insecticides do not help. We have been struggling for a long time to find a solution. 

This season, we have decided to try a new strategy. This is a method of preventing the adult insects from getting close to the shoots. Cut a piece of newspaper about 15 cm wide and 25 cm long, wrap it around the shoots and staple it in three or four places. This is easy to do and reuses the newspaper. However, newspaper can cause problems if it gets wet and becomes weak and heavy. So I cut a plastic bag to the same size and used that. This might be better as it also lets light through. I attached both to many shoots in the garden. The damage will be almost finished by the end of April, so if there are no problems until then, I will keep them attached and test their effectiveness and problems.

バラクキバチは私たちの庭でもっとも憎むべき最悪のバラの害虫です. 春にバラの新しい枝が伸びて蕾をつけてくるころに、成虫が飛んできてその新梢に卵を産み付けます. 産み付けるだけなら被害は少ないですが、その時にナイフのような尻尾の突起物で新梢の髄を切ってしまいます. 当然その新梢はすぐに萎れてしまいます. まもなく卵から孵化した幼虫は茎の中を食べて、茎の下の方に移動していきます. 萎れた新梢が花を咲かせることはありません. 私たちの庭では毎年四月にこの被害を受けてきましたが、多い年には120本ぐらいの新梢がダメになりました. とてもショックです. 

この害虫は体長は2センチ以下で小さく、色は地味で目立ちにくく、素早く飛び回るため、捕獲は困難です. 殺虫剤も役には立ちません. なかなか対策がなくてずっと困っていました. 

今シーズンは、新しい対策を考えて試してみることにしました. 成虫が新梢に近づけないようにする方法です. 新聞紙を横15センチ、縦25センチぐらいのサイズに切って、新梢に巻いてホッチキスで３，４か所留めます. 簡単にできますし、新聞紙の再利用です. しかし新聞紙は雨に濡れると弱くなったり重くなったりして問題を起こすかもしれません。そこで、ビニール袋を同じサイズに切って、それを使ってみました. 光も通すのでこの方が良いかもしれません. 両方を庭のたくさんの新梢に取り付けてみました. 被害はほぼ四月末には終わるので、それまで問題がなければ取り付けたまま効果や問題点を検証していこうと思っています. 

First damaged rose shoots of the year
今年最初の被害のバラの新梢

Peeling of wilted shoots reveals the cut pith. Usually in the shape of a gull in flight, but this time it has been cut in a spiral shape. 
萎れた新梢の皮を剥くと切られた髄が良く見える. 通常はカモメが飛ぶ形だが、今回はらせん状に切られている. 

When cut in the middle, there were tiny larvae that had hatched inside.
真ん中で切ると、中に孵化した小さな幼虫がいた

Magnified image of larvae
幼虫の拡大像

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