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Food selection and fitness optimisation in insects

Bracht Jörgensen, Helene LU (2002)
Abstract (Swedish)
Popular Abstract in Swedish

Populærvidenskablig sammenfatning på dansk



Både løbebiller og springhaler er nyttedyr i det danske landbrugsland. Løbebiller er oftest betragtet som rovdyr, der spiser skadelige insekter i marken og er derved medvirkende i skadedyrsbekæmpelsen. Springhaler er minder insekter, som oftest lever i de øverste jordlag og som hovedsagelig spiser svampehyfer. Svampene nedbryder organisk materiale og optager derved næringsstoffer i hyferne. Når springhalerne spiser af hyferne frigives næringsstofferne til jorden og deved til planterne. Selv om springhalerne er små kan de optræde i tusindtals i en landbrugsjord og derved være af stor betydning for næringsomsætningen i jorden.

... (More)
Popular Abstract in Swedish

Populærvidenskablig sammenfatning på dansk



Både løbebiller og springhaler er nyttedyr i det danske landbrugsland. Løbebiller er oftest betragtet som rovdyr, der spiser skadelige insekter i marken og er derved medvirkende i skadedyrsbekæmpelsen. Springhaler er minder insekter, som oftest lever i de øverste jordlag og som hovedsagelig spiser svampehyfer. Svampene nedbryder organisk materiale og optager derved næringsstoffer i hyferne. Når springhalerne spiser af hyferne frigives næringsstofferne til jorden og deved til planterne. Selv om springhalerne er små kan de optræde i tusindtals i en landbrugsjord og derved være af stor betydning for næringsomsætningen i jorden.



I det økologisk landbrug, hvor der ikke bruges pesticider og kunstgødning, er det vigtigt at udnytte den naturlige faunas kapacitet optimalt, for at opnå så stort et udbytte af afgrøder som muligt. Forudsætningen for at kunne pleje den naturlige fauna og derved opnå maximal effekt er, at man for det første er fortrolig med nyttedyrets biologi og for det andet kender til de interaktioner der foregår organismerne imellem. Formålet med denne afhandling har været at øge kenskabet til fødebiologien for nogle af markens løbebiller og springhaler og at undersøge om ændringer i første trofiske niveau kan medføre effekter i flere trofiske niveauer i fødekæden.



Harpalus rufipes og Armara similata er to almindeligt forekomne løbebiller fra det danske landbrugsland, som er forskellige set i forhold til andre løbebiller idet en stor del af deres føde består af plantefrø; i stor udstrækning ukrudtsfrø. Maveindholdsunder-søgelser har vist, at biller fanget i marken har spist bladlus, og derved måske medvirket i en bladlusebekæmpelse, men hvad får billerne ud af at spise bladlus? Ingenting, ser det ud som om! De voksne billers fekunditet og larvernes overlevelse er uændret om deres diæt har bestået af blandede ukrudtsfrø eller blandede ukrudtsfrø + bladlus og andre insekter. Derimod var både fekunditet og overlevelse forværret hvis billerne havde fået en ren insekt diet i forhold til, når der var ukrudtsfrø blandet i diæten. Dog overlevede larverne længere på en blandet insekt diæt end hvis de slet ingen mad fik. Dette viser, at billerne måske kun spiser andre insekter, når der er mangel på føde af højere kvalitet, og at de gør det for at øge deres overlevelseschancer.



Fødeindtaget hos en tredie art af løbebiller blev undersøgt, men med en lidt anden indgangsvinkel. Hvis en plante får inkorporeret et gen, der kan få planten til at producerer en proteinasehæmmer, så kan et eventuelt angreb af et herbivor insekt formindskes. Det eller de insekter der spiser af planten vil ved indtag af proteinasehæmmeren ikke kunne nedbryde proteiner og derved ikke kunne spise så meget af planten som hvis der ingen hæmmer var til stede. Men hvad vil der ske med de nyttige predatorer i marken, der spiser af skadedyerne? Vi fandt, at løbebillen vil spise mindre af skadedyrene hvis de havde spist herbivorer, der havde spist en føde hvori der var proteinasehæmmer. Dette er en utilsigtet effekt, som måske i nogen grad vil kunne ophæve den positive effekt af proteinasehæmmeren.



Når springhalerne græsser af de forskellige svampe i jorden, så kan dette have en indvirkning på svampenes nedbrydningsevne. Svampene kan respondere positivet, hvis græsningstrykket ikke er for højt, ved at vokse hurtigere og dermed øge nedbrydningen af det organiske stof. Derimod, hvis græsningstrykket er højt, så vokser svampen langsommere. I laboratorieforsøg har det vist sig, at springhalerne er meget selektive når de vælger hvilken svamp de vil græsse på. Det galdt også undersøgelserne her, hvor springhalerne blev præsenteret for 8 forskellige svampearter, som findes i den samme jord, som springhalerne lever i. De svampe, som springhalerne foretrak at græsse på, var de svampe der fik springhalerne til at vokse hurtigst, hvor de fik flest afkom og hvor overlevelsen var størst. En af springhalerne, Folsomia fimetaria, var endda i stand til at vælge mellem een svamp, der havde vokset på tre forskellige naturlige substrater, ren jord, jord blandet med halm og jord blandet med kløver og udvælge svampen voksende på det substrat, der gav springhalen størst fordel. Dette viser, at en ændring i et lavere trofisk niveau, her det organiske materiale, kan have en kaskerende effekt i de højere trofiske niveauer i fødekæden. Hvis springhalerne er lige så selektive i marken som de er i laboratoriet, så er der svampe, der vil blive græsset meget stærkt, og andre der knapt vil blive rørt hvilket muligvis vil have indvirkning på nedbrydningsprocesserne.



Men trods de mange laboratorieforsøg ved man stadig meget lidt of springhalernes selektivitet ude i marken. Derfor har vi udviklet en metode, som skal gøre det muligt at detektere hvilke organismer springhalerne har spist, når de bliver fanget i marken. Den går ud på at opformere det DNA, der findes i springhalernes tarme, og ud fra dette materiale afgøre hvilke arter af svampe der har indgået i kosten. Denne metode vil i fremtiden gøre det muligt at undersøge fødeselektiviteten hos en lang række jordlevende insekter. (Less)
Abstract
To optimise fitness is a continuous process which assists species survival in changing environments. Choosing an optimal diet is an essential part of the optimisation process and a key element of optimal foraging theory. The relationship between food choice and fitness optimisation has been tested on three ground beetles and several collembolan species by using food items naturally occurring in the same habitat as the animals. The ground beetles Harpalus rufipes and Amara similata are considered being seed-eaters but can include insects in their diet in the field. An addition of insect species to a mixture of seeds did not improve beetle fitness, though a seed mixture was of a higher quality to the beetles than seeds of single plant... (More)
To optimise fitness is a continuous process which assists species survival in changing environments. Choosing an optimal diet is an essential part of the optimisation process and a key element of optimal foraging theory. The relationship between food choice and fitness optimisation has been tested on three ground beetles and several collembolan species by using food items naturally occurring in the same habitat as the animals. The ground beetles Harpalus rufipes and Amara similata are considered being seed-eaters but can include insects in their diet in the field. An addition of insect species to a mixture of seeds did not improve beetle fitness, though a seed mixture was of a higher quality to the beetles than seeds of single plant species. However the beetles did not show a high degree of selectivity between the specific seed species and their choice was not always in agreement with the quality of the seeds. The collembolans, on the other hand, showed a high degree of selectivity and Folsomia fimetaria, Protaphorura armata and Heteromurus nitidus preferred fungi that optimised their growth, survival and fecundity. Folsomia fimetaria could even select the optimal food when a fungal species was grown in different soil substrates. The high degree of selectivity corresponding to food quality that was seen in the collembolans might be due to a production of fungal odour that can be detected by the collembolans.



Plants producing proteinase inhibitors experience reduced attacks by herbivores thus the effect on predators feeding on the herbivores was studied. The herbivorous caterpillar Helicoverpa armigera was fed an artificial diet containing a proteinase inhibitor and the ground beetle Harpalus affinis was fed with H. armigera. H. affinis reduced its feeding when the caterpillars had been fed the proteinase inhibitor containing diet. This indicates that changes in food quality at the plant trophic level cascaded to the predator trophic level.



In spite of the many laboratory studies we still lack knowledge of selection of food in the field for this insects. A PCR-based method to detect DNA of ingested food species has been developed. Diversity of fungi found in the gut of collembolans was low compared to that of whole animals. This might be due to the dissection method where the head with mouthparts and the uppermost part of the gut was discharged, which presumably contains most undigested fungal material. This method will make it possible to study food selective behaviour of cryptic soil organisms in the future. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof Verhoef, Herman A.
organization
publishing date
type
Thesis
publication status
published
subject
keywords
food preference, nested PCR, fungal DNA, växtparasitologi, plant parasitology, Entomology, Entomologi, fungi, seeds, ground beetles, collembolans
pages
100 pages
publisher
Helene Bracht Jørgensen, Lund University, Dep. of Animal Ecology, Ekologihuset, Sölvegatan 37, S-223 62 Lund, Sweden,
defense location
Blå Hallen, Ekologihuset, Sölvegatan 37, Lund
defense date
2002-12-13 10:15
ISBN
91-7105-182-1
language
English
LU publication?
yes
id
01ab506d-fb21-4d81-bd3c-79dfa07254e0 (old id 465241)
date added to LUP
2007-09-04 13:49:49
date last changed
2016-09-19 08:45:09
@misc{01ab506d-fb21-4d81-bd3c-79dfa07254e0,
  abstract     = {To optimise fitness is a continuous process which assists species survival in changing environments. Choosing an optimal diet is an essential part of the optimisation process and a key element of optimal foraging theory. The relationship between food choice and fitness optimisation has been tested on three ground beetles and several collembolan species by using food items naturally occurring in the same habitat as the animals. The ground beetles Harpalus rufipes and Amara similata are considered being seed-eaters but can include insects in their diet in the field. An addition of insect species to a mixture of seeds did not improve beetle fitness, though a seed mixture was of a higher quality to the beetles than seeds of single plant species. However the beetles did not show a high degree of selectivity between the specific seed species and their choice was not always in agreement with the quality of the seeds. The collembolans, on the other hand, showed a high degree of selectivity and Folsomia fimetaria, Protaphorura armata and Heteromurus nitidus preferred fungi that optimised their growth, survival and fecundity. Folsomia fimetaria could even select the optimal food when a fungal species was grown in different soil substrates. The high degree of selectivity corresponding to food quality that was seen in the collembolans might be due to a production of fungal odour that can be detected by the collembolans.<br/><br>
<br/><br>
Plants producing proteinase inhibitors experience reduced attacks by herbivores thus the effect on predators feeding on the herbivores was studied. The herbivorous caterpillar Helicoverpa armigera was fed an artificial diet containing a proteinase inhibitor and the ground beetle Harpalus affinis was fed with H. armigera. H. affinis reduced its feeding when the caterpillars had been fed the proteinase inhibitor containing diet. This indicates that changes in food quality at the plant trophic level cascaded to the predator trophic level.<br/><br>
<br/><br>
In spite of the many laboratory studies we still lack knowledge of selection of food in the field for this insects. A PCR-based method to detect DNA of ingested food species has been developed. Diversity of fungi found in the gut of collembolans was low compared to that of whole animals. This might be due to the dissection method where the head with mouthparts and the uppermost part of the gut was discharged, which presumably contains most undigested fungal material. This method will make it possible to study food selective behaviour of cryptic soil organisms in the future.},
  author       = {Bracht Jörgensen, Helene},
  isbn         = {91-7105-182-1},
  keyword      = {food preference,nested PCR,fungal DNA,växtparasitologi,plant parasitology,Entomology,Entomologi,fungi,seeds,ground beetles,collembolans},
  language     = {eng},
  pages        = {100},
  publisher    = {ARRAY(0xc303100)},
  title        = {Food selection and fitness optimisation in insects},
  year         = {2002},
}