Erinevate maastikuelementide mõju naeri-hiilamardika arvukusele ja vastsete parasiteerituse tasemele talirapsil
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Kuupäev
2014
Kättesaadav alates
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Põllumajandusmaastike pindalade suurenemisega väheneb bioloogiline mitmekesisus agroökosüsteemides. Selle tulemusena väheneb looduse poolt pakutavate ökosüsteemide teenuste (tolmeldamine, kisklus, parasiteeritus jms) hulk ja efektiivsus. Samas tekivad head tingimused taimekahjurite arvukuse suurenemiseks, kelle tõrjeks kasutatakse peamiselt insektitsiide, mille liigne kasutamine kahandab põllumajandusmaastike bioloogilist mitmekesisust ja arendab mürkide suhtes resistentseid kahjureid. Resistentsete kahjurite tõrjeks kasutatakse suuremaid mürgiannuseid ja tõstetakse pritsimiskordade arvu, millega kaasneb keskkonna saastekoormuse kasv, oht teiste organismide tervisele ning mürgijääkide esinemine lõpp-produktides. Taimekahjurite tõrjeks tuleb leida alternatiivseid keskkonnaohutumaid tõrjemeetmeid, nt kasutada kahjurite looduslikke vaenlasi ja nende arvukust soodustavaid maastikuelemente.
Töö eesmärgiks oli kindlaks teha looduslike, pool-looduslike ja mitteharitavate maastiku-elementide ja nende osatähtsuse mõju naeri-hiilamardika arvukusele ja tema vastsete parasiteerituse tasemele talirapsil.
Naeri-hiilamardikate arvukus oli katseaastal üldiselt madal kõikidel põldudel, kuid vastsete parasiteerituse tase oli üsna kõrge (kuni 53%). Valmikute arvukust mõjutas oluliselt maastiku mitmekesisus, maastikuelemendi tüüp, prooviala ja taimede asukoht rapsipõllu sees. Ka vastsete arvukus taime kohta sõltus proovialast ja sellega piirnenud maastikuelemendist. Parasiteeritud ja multiparasiteeritud vastsete tase sõltus oluliselt maastiku mitmekesisusest ja proovialast. Kõige arvukamalt leidus mardikaid kõrge elementide osatähtsusega maastikes ja kõige vähem madala osatähtsusega maastikes. Kõige suuremat valmikute ja vastsete arvukust toetas haljaskesa ning kõige vähem leiti neid rohuriba kõrval paiknenud põldudelt. Mardikaid leiti oluliselt rohkem põllu servas asunud taimedelt kui põllu sees kasvanutelt. Parasiteeritud ja multiparasiteeritud vastseid leiti kõige arvukamalt kõrge osatähtsusega maastikes, kus oli ka kõrgeim parasiteerituse tase (~40%), mis näitab, et neil aladel võivad parasitoidid kahjurite arvukust oluliselt vähendada, hoides seda allpool majandusliku kahju tekitamise piiri. Parasiteerituse tasemed olid suurimad kõrge mitmekesisusega maastikes rohumaaga, keskmise puhul metsaga ning madala puhul rohuribaga piirnevatel põldudel.
Seega saab parasitoidide efektiivsust mõjutada, kujundades põllumajandusmaastikke erinevate maastikuelementidega. Kõrge parasitoidide arvukuse ja parasiteerituse taseme tagamiseks peaksid põllualad paiknema mitmekesises maastikus, kus esineks palju looduslikke, pool-looduslikke ja kultiveerimata alasid (ühed eelistatumad oleks rohuribad) ja nendevahelisi ühendusteid, et parasitoididel oleks põldudele kergem levida, leiduks rohkelt toitu, elu- ja varjepaiku.
Agricultural landscape areas are increasing while biodiversity in agroecosystems is decreasing. Diverse habitats are being replaced by monocultures, making landscapes more simplified which causes the increasing fragmentation of habitats and decreasing biological diversity. As a result, the amount and effectiveness of ecosystem services (pollination, predation, parasitism rate, improving soil quality etc.) are decreasing. Prevailing of large monocultures fields leads to a good preconditions of population growth of insect pests. Insecticides are predominantly used for pest management, often routinely and prophylactically. The overuse of insecticides reduces the economic competitiveness of yield, as well as biological diversity in agricultural landscapes and contributes to the development of insecticides resistance in pests. To control these resistant pests, the use of greater amounts and more frequent application of insecticides are necessary. With this the burden of environmental pollution, the health risks for other organisms (including human) and the presence of toxic residues in the final food and feed are increasing. Therefore it is necessary to find alternative, environmentally safe methods for pest control, for example, the using of the natural enemies of pests and the landscape elements that contribute to their abundance increase and offer the habitats, shelter and hibernation places. The aim of this study was to identify the impact of natural, semi-natural and non-arable landscape elements and their proportions (landscape diversity) to our main oilseed rape pest, pollen beetle, abundance and larval parasitism rate on winter oilseed rape. Parasitoids are important group of natural enemies that are able to significantly reduce the size of pest populations and hold them below an economic threshold. The abundance of pollen beetle was generally low in all studied fields, but the larval parasitism rates were high (up to 53%). The number of adult pollen beetles was significantly affected by the landscape diversity, the type of landscape element and the location of samplings within the rape field. The abundance of larvae was significantly affected by sampling plot and landscape element. Landscape diversity and sampling plot (but not landscape element) had significant effect on the abundance of parasitized larvae on plant, parasitism rate, the abundance of multiparasitized larvae and multiparasitism rate. The location of sampled plants in the field had no significant effect on the larval abundance. Adult beetles were found most numerously in landscapes with high natural, semi-natural and non-arable area proportions and the least on landscapes where these proportions were low. From the fields bordered by fallow, the greatest abundance of adults and larvae were found and the lowest from fields that were bordered by linear herbaceous areas. Significantly more adult beetles were found from the plants growing on the edge of the field than on inside. Parasitized and multiparasitized larvae were most numerously found in landscapes with high diversity, which also had the greatest level of parasitism (~40%), indicating that parasitoids could significantly reduce the numbers of pests on these areas, keeping their numbers below an economic threshold. Although landscape element had no significant effect, the parasitism and multiparasitism rates were highest in fields located next to the linear herbaceous element and lowest in fields next to fallow. Linear herbaceous areas should be preferred in landscapes with high diversity while woody areas in landscapes with medium and low diversity (the number of pest larvae was the lowest in those elements). Parasitism rates were greatest in fields that were located next to the herbaceous area in landscapes with high diversity and in fields that were bordered by the linear herbaceous area in landscapes with medium and low diversity. The effectiveness of parasitoids as biological pestcontrol can be influenced by modifying the agricultural landscapes. For high parasitoid abundance and parasitism rate the fields should be located in diverse landscapes, with many natural, semi-natural and non-arable areas and with connections between them to offer plenty of food resources, shelter and habitats.
Agricultural landscape areas are increasing while biodiversity in agroecosystems is decreasing. Diverse habitats are being replaced by monocultures, making landscapes more simplified which causes the increasing fragmentation of habitats and decreasing biological diversity. As a result, the amount and effectiveness of ecosystem services (pollination, predation, parasitism rate, improving soil quality etc.) are decreasing. Prevailing of large monocultures fields leads to a good preconditions of population growth of insect pests. Insecticides are predominantly used for pest management, often routinely and prophylactically. The overuse of insecticides reduces the economic competitiveness of yield, as well as biological diversity in agricultural landscapes and contributes to the development of insecticides resistance in pests. To control these resistant pests, the use of greater amounts and more frequent application of insecticides are necessary. With this the burden of environmental pollution, the health risks for other organisms (including human) and the presence of toxic residues in the final food and feed are increasing. Therefore it is necessary to find alternative, environmentally safe methods for pest control, for example, the using of the natural enemies of pests and the landscape elements that contribute to their abundance increase and offer the habitats, shelter and hibernation places. The aim of this study was to identify the impact of natural, semi-natural and non-arable landscape elements and their proportions (landscape diversity) to our main oilseed rape pest, pollen beetle, abundance and larval parasitism rate on winter oilseed rape. Parasitoids are important group of natural enemies that are able to significantly reduce the size of pest populations and hold them below an economic threshold. The abundance of pollen beetle was generally low in all studied fields, but the larval parasitism rates were high (up to 53%). The number of adult pollen beetles was significantly affected by the landscape diversity, the type of landscape element and the location of samplings within the rape field. The abundance of larvae was significantly affected by sampling plot and landscape element. Landscape diversity and sampling plot (but not landscape element) had significant effect on the abundance of parasitized larvae on plant, parasitism rate, the abundance of multiparasitized larvae and multiparasitism rate. The location of sampled plants in the field had no significant effect on the larval abundance. Adult beetles were found most numerously in landscapes with high natural, semi-natural and non-arable area proportions and the least on landscapes where these proportions were low. From the fields bordered by fallow, the greatest abundance of adults and larvae were found and the lowest from fields that were bordered by linear herbaceous areas. Significantly more adult beetles were found from the plants growing on the edge of the field than on inside. Parasitized and multiparasitized larvae were most numerously found in landscapes with high diversity, which also had the greatest level of parasitism (~40%), indicating that parasitoids could significantly reduce the numbers of pests on these areas, keeping their numbers below an economic threshold. Although landscape element had no significant effect, the parasitism and multiparasitism rates were highest in fields located next to the linear herbaceous element and lowest in fields next to fallow. Linear herbaceous areas should be preferred in landscapes with high diversity while woody areas in landscapes with medium and low diversity (the number of pest larvae was the lowest in those elements). Parasitism rates were greatest in fields that were located next to the herbaceous area in landscapes with high diversity and in fields that were bordered by the linear herbaceous area in landscapes with medium and low diversity. The effectiveness of parasitoids as biological pestcontrol can be influenced by modifying the agricultural landscapes. For high parasitoid abundance and parasitism rate the fields should be located in diverse landscapes, with many natural, semi-natural and non-arable areas and with connections between them to offer plenty of food resources, shelter and habitats.
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