Kõdra- ja varre-peitkärsaka kahjustuse ja parasiteerituse tase talirapsil
Abstract
Raps (Brassica napus L.) ehk õlikaalikas on tänapäeval maailmas üks tähtsamaid
õlikultuure (Hatzig et al., 2018). Rapsi kasvupindala laienemine on suurendanud ka
ristõielistele taimedele spetsialiseerunud putukate arvukust ja levikut. Käesolevas töös
käsitletakse rapsi kahjuritest kõdra-peitkärsakat (Ceutorhynchus obstrictus (Marsham)
syn. C. assimilis (Paykull)) ja varre-peitkärsakat (Ceutorhynchus pallidactylus
(Marsham)), kes Eestis kahjustavad peamiselt talirapsi. Rapsil kontrollitakse kahjurite
arvukust peamiselt sünteetiliste putukamürkidega (Heimbach, Müller, 2013; Zimmer et
al., 2014), mis aga hävitavad lisaks kahjuritele ka teised lülijalgsed, sh kahjurite
looduslikud vaenlased (Jonsson et al., 2008; Kovács, 2018). Kiletiivalised (Hymenoptera)
parasitoidid on peitkärsakate ühed kõige olulisemad looduslikud vaenlased. Kõdrapeitkärsaka kolm peamist parasitoidi on: Trichomalus perfectus (Walker), Stenomalina
gracilis (Walker) ja Mesopolobus morys (Walker) (Haye et al., 2015; Ulber et al., 2010).
Antud töö eesmärgiks oli välja selgitada kõdra- ja varre-peitkärsaka kahjustuse suurus
talirapsi põldudel ja kas seda mõjutas kaugus eelmise aasta talirapsi põllust. Selgitati kui
suur oli kõdra-peitkärsaka parasiteerituse tase ja kas seda mõjutas kaugus eelmise aasta
rapsipõllust. Lisaks selgitada, milline oli kõdra-peitkärsaka parasitoidide liigiline koosseis
ja kas eelmise aasta rapsipõllu kaugus mõjutas nende arvukust ja koosseisu. Lähtuvalt töö
eesmärkidest püstitati hüpoteesid: (i) kõdra- ja varre-peitkärsaka kahjustuse taset ei
mõjuta kaugus eelmise aasta rapsipõllust; (ii) kõdra-peitkärsaka parasiteerituse tase on
suurem nendel talirapsi põldudel, mis asuvad lähemal kui 500 meetrit eelmise aasta
talirapsi põllust; (iii) kaugus eelmise aasta talirapsipõllust mõjutab kõdra-peitkärsaka
parasitoidide liigilist koosseisu. Kokku oli 12 katsepõldu, millest kuus asusid lähemal ja
kuus kaugemal kui 500 meetrit eelmise aasta talirapsi tootmispõllust. Leiti, et kõdrapeitkärsaka kahjustuse taset mõjutas kaugus eelmise aasta talirapsi põllust, kuid
parasiteerituse taset ei mõjutanud. Domineerivaks kõdra-peitkärsaka parasitoidiks oli T.
perfectus, kuid leiti ka S. gracilis’e ning M. morys’e isendeid. Varre-peitkärsaka
kahjustuse suurust mõjutas oluliselt kaugus eelmise aasta talirapsipõllust. Põldudel, mis
asusid lähemal kui 500 meetrit eelmise aasta talirapsi põllust oli kahjustuse tase oluliselt
kõrgem kui põldudel, mis asusid kaugemal kui 500 meetrit eelmise aasta talirapsi põllust.
Insektitsiidide kasutamine põldudel mõjutas oluliselt positiivselt kõdra- ja varrepeitkärsakate kahjustuse taset ning oluliselt negatiivselt kõdra-peitkärsaka parasiteerituse
taset. Oilseed rape (Brassica napus L.) is one of the most important oil crops in the world
(Hatzig et al., 2018). The increase in the cultivation area has also increased the abundance
and distribution of oilseed rape pests. Cabbage seed weevil (Ceutorhynchus obstrictus
(Marsham) syn. C. assimilis (Paykull)) and cabbage stem weevil (Ceutorhynchus
pallidactylus (Marsham)), are two abundant and important oilseed rape pests and mainly
harm winter rape oilseed rape in Estonia. Pest management in oilseed rape is mainly based
on the use of synthetic insecticides (Heimbach, Müller, 2013; Zimmer et al., 2014), which
in addition to pests, also kills the natural enemies of pests (Jonsson et al., 2008; Kovács,
2018). Hymenopteran parasitoids are one of the most important group of pest’s natural
enemies. There are three main parasitoid species of cabbage seed weevil: Trichomalus
perfectus (Walker), Stenomalina gracilis (Walker) and Mesopolobus morys (Walker)
(Haye et al., 2015; Ulber et al., 2010). The aim of this work was to find out the extent of
damage done by the cabbage seed weevil and cabbage stem weevil on the winter rape and
whether it was affected by the distance from the previous year's winter oilseed rape fields.
In addition, to find out the parasitism rate of the cabbage seed weevil and whether the
distance of the last years fields affected it. In addition, whether the species composition of
parasitoids was affected on the distance from the previous year's winter oilseed rape fields.
Based on the aims there were three hypotheses: (i) the damage rate of the cabbage seed
weevil and cabbage stem weevil is not affected by the distance of the previous year oilseed
rape fields; (ii) the parasitism rate of cabbage seed weevil is greater in those winter oilseed
rape fields that are located closer than 500 m from the previous year's winter oilseed rape
field; (iii) the distance from the previous year's oilseed rape fields affects the species
composition of parasitoids. In total, there were 12 experimental fields, 6 of which were
located closer than 500 meters from the previous year's winter oilseed rape fields and 6
were further than 500 meters from the previous year's winter oilseed rape fields. We found
that the cabbage seed weevil damage rate was affected by the distance from last year's
winter rape field, but the level of parasitism was not affected by the distance of last year's
winter oilseed rape fields. Trichomalus perfectus was the predominant parasitoid but also
S. gracilis and M. morys were found. The damage rate of the cabbage stem weevil was
significantly influenced by the distance from the previous year’s winter oilseed rape fields.
The damage rate was significantly greater in fields that were closer than 500 meters from
previous years winter oilseed rape fields compared to the fields that were more than 500
meters away from previous years winter oilseed rape fields. The use of insecticides in the
fields significantly reduced the damage rate of the cabbage seed weevil and cabbage stem
weevil and significantly negatively affected the parasitism rate of cabbage seed weevil.