Flea beetles (Coleoptera, Chrysomelidae, Halticinae) on rapeseed and sugarbeet in Finland

Surveys of the incidence of flea beetles on sugarbeet and rapeseed were carried out in eight localities in southern and central Finland in 1972 and 1980—83. The first flea beetles emerged from overwintering in late April to early May, depending on the temperature. The majority, however, appeared during the second half of May, when daily temperatures occasionally reached +20°C. Flea beetles found their host plants by olfactory orientation. Two population peaks occurred during the growing season. The overwintered flea beetles formed the first peak in late May to early June and the adults of the new generation the second peak starting in late July. The incidence of flea beetles fluctuated greatly on the cultivation, as the flea beetles moved only short distances and showed thus very local occurrence. The availability of host plants greatly affected their reproduction rate, and thus the annual and regional differences in the incidence of the flea beetles were great and depended solely on the availability of host plants. Therefore it was difficult to establish any countrywide differences in the incidence of the beetles. Only Phyllotreta undulata (Kutsch.) and P. striolata (F.) were of any importance aspests of rapeseed. P. undulata made up some 80—90 % and P. striolata some 10 % of the total number of flea beetles on rapeseed. P. striolata was more abundant on radish than on rapeseed. Sugarbeet was damaged only by Chaetocnema concinna (Marsh). Other species of flea beetles were also observed in small numbers on rapeseed, radish and sugarbeet. They did not, however, cause any damage, but spread from adjacent cultivated plant species or weeds. The suction trap collected only a few flea beetles, but clearly revealed their activity periods. Damage caused by flea beetles is most harmful during the short seedling stage. At that time one flea beetle per plant was considered the threshold level for control measures. Later, even several flea beetles did not significantly hamper the growth. Seed coating efficiently prevented damage by flea beetles. The general incidence of flea beetles observed during this study was so low that coating of the seed was not justified. Chemical control of blossom beetle efficiently reduced flea beetles as well. The abandoning of the cultivation of winter rape also reduced the total number of flea beetles

Flea beetles (Coleoptera, Chrysomelidae, Halticinae) on rapseed and sugarbeet in Finland

Julkaisussa on vanha ISSN 0024-8835.vokKirjasto Aj-KKirpat (Coleoptera, Chrysomelidae, Halticinae) rypsi- ja sokerijuurikasviljelyksill

Kirpat (Coleoptera, Chrysomelidae, Halticinae) rypsi- ja sokerijuurikasviljelyksillä

Surveys of the incidence of flea beetles on sugarbeet and rapeseed were carried out in eight localities in southern and central Finland in 1972 and 1980—83. The first flea beetles emerged from overwintering in late April to early May, depending on the temperature. The majority, however, appeared during the second half of May, when daily temperatures occasionally reached +20°C. Flea beetles found their host plants by olfactory orientation. Two population peaks occurred during the growing season. The overwintered flea beetles formed the first peak in late May to early June and the adults of the new generation the second peak starting in late July. The incidence of flea beetles fluctuated greatly on the cultivation, as the flea beetles moved only short distances and showed thus very local occurrence. The availability of host plants greatly affected their reproduction rate, and thus the annual and regional differences in the incidence of the flea beetles were great and depended solely on the availability of host plants. Therefore it was difficult to establish any countrywide differences in the incidence of the beetles. Only Phyllotreta undulata (Kutsch.) and P. striolata (F.) were of any importance aspests of rapeseed. P. undulata made up some 80—90 % and P. striolata some 10 % of the total number of flea beetles on rapeseed. P. striolata was more abundant on radish than on rapeseed. Sugarbeet was damaged only by Chaetocnema concinna (Marsh). Other species of flea beetles were also observed in small numbers on rapeseed, radish and sugarbeet. They did not, however, cause any damage, but spread from adjacent cultivated plant species or weeds. The suction trap collected only a few flea beetles, but clearly revealed their activity periods. Damage caused by flea beetles is most harmful during the short seedling stage. At that time one flea beetle per plant was considered the threshold level for control measures. Later, even several flea beetles did not significantly hamper the growth. Seed coating efficiently prevented damage by flea beetles. The general incidence of flea beetles observed during this study was so low that coating of the seed was not justified. Chemical control of blossom beetle efficiently reduced flea beetles as well. The abandoning of the cultivation of winter rape also reduced the total number of flea beetles.Maatalouden tutkimuskeskuksessa Vantaalla sekä seitsemällä muulla paikkakunnalla Etelä- ja Keski-Suomessa selvitettiin vuosina 1972 ja 1980—83 kirppojen esiintymistä rypsi- ja sokerijuurikasviljelyksillä. Etelä-Suomessa ensimmäiset kirpat lähtivät liikkeelle talvehtimispaikoistaan lämpötilan mukaan huhti- ja toukokuun vaihteessa. Suurin osa kirpoista ilmestyi kuitenkin toukokuun loppupuoliskolla, kun päivälämpötilat ajoittain kohosivat 20°C:seen. Kirpat suunnistivat ja löysivät isäntäkasvinsa hajun perusteella. Kasvukauden aikana oli kaksi runsaushuippua. Ensimmäisen muodostivat talvehtineet yksilöt touko- ja kesäkuun vaihteessa ja toisen uuden sukupolven aikuiset heinäkuun lopussa. Kirppojen esiintymisrunsaus viljelyksillä vaihteli paljon, sillä kirpat liikkuivat vain lyhyitä matkoja; täten niiden esiintyminen oli hyvin paikallista. Isot vuotuiset runsausvaihtelut johtuivat lähinnä isäntäkasvitilanteen muutoksista. Tämän vuoksi oli vaikeata nähdä, vaihteliko kirppojen esiintymisrunsaus alueittain. Ainoastaan Phyllotreta undulata (Kutsch.) ja P. striolata (F.) olivat merkittäviä tuholaisia rypsiviljelyksillä. P. undulata:n osuus oli 80—90 % ja P. striolata:n n. 10 % kirppojen kokonaismäärästä. P. striolata oli yleisempi retiisi- kuin rypsiviljelyksillä. Sokerijuurikasta vioitti ainoastaan Chaetocnema concinna (Marsh). Myös muita kirppalajeja esiintyi vähäisinä määrinä rypsi-, retiisi ja sokerijuurikasmailla. Nämä eivät kuitenkaan aiheuttaneet tuhoja. Imupyydys keräsi vähän kirppoja, mutta se osoitti silti selvästi kirppojen esiintymisajankohdat. Kirpat aiheuttivat eniten vahinkoa lyhyen sirkkataimivaiheen aikana. Torjunnan kynnysarvo oli tuolloin yksi kirppa/kasvi. Myöhemmin useatkaan kirpat eivät enää estäneet kasvua. Kirppojen esiintymisrunsaus oli tutkimuksen aikana niin pieni, että siementen torjunta-ainekuorrutus oli tarpeeton. Syysrypsin viljelyn loppuminen näytti olevan osasyynä kirppojen vähäiseen määrään. Toisaalta tuholaistorjunta rapsikuoriaista vastaan tehoaa myös kirppoihin