12 research outputs found
Parasitoids: metapopulation ecology and genetics, mating behaviour, and aphid host resistance
Das Verstehen von multitrophischen Interaktionen zwischen Parasitoiden und Blattläusen ist von theoretischem und praktischem Interesse. In dieser Arbeit wurden folgende Aspekte untersucht: 1) Metapopulationsdynamik und Genetik eines spezialisierten Parasitoiden und dessen Blattlaus-Wirtes, 2) Paarungsverhalten von Parasitoiden am Schlupfort und deren Beeinflussung durch Interaktionen mit Ameisen, und 3) Resistenzentwicklung von Blattläuse und deren Auswirkung auf die Fitness von Parasitoiden.
Lysiphlebus hirticornis ist ein solitärer Parasitoid der die Blattlaus Metopeurum fuscoviride parasitiert, die ihrerseits auf Rheinfarn, Tanacetum vulgare, spezialisiert ist. T. vulgare kommt typischerweise in einer sehr lückenhaften Verteilung vor. Populationen von L. hirticornis folgen einer klassischen Metapopulationsdynamik, geprägt durch Prozesse des Aussterbens und der Wiederbesiedlung. Dieses tritrophische System wird verwendet um i) die genetische Differenzierung von L. hirticornis auf einer kleinen räumlichen Skala zu überprüfen und daraus das Ausbreitungspotenzial abzuleiten, ii) die Veränderung von Allelhäufigkeiten während einer Saison zu bestimmen und um iii) zu analysieren, wie das System unter hohem Parasitoidendruck fortbestehen kann. Dazu wurden L. hirticornis infizierte Blattlausmumien alle zwei Wochen zwischen Juni und Oktober 2007 an 11 verschiedenen Standorten von unterschiedlichen T. vulgare Pflanzen im Feld gesammelt. Die Standorte lagen in Distanzen von 217m bis 15000m voneinander entfernt. Die Phänologie der Pflanzen und die Populationsdynamik von M. fuscoviride und L. hirticornis wurden jeweils aufgenommen. Die DNA, von im Labor geschlüpften Parasitoiden, wurde zur Bestimmung des Genotyps extrahiert. Neun polymorphische Mikrosatelliten-Marker konnten von L. hirticornis isoliert werden und zwei weitere wurden in einem Cross-Amplification-Screening von bereits bekannten Markern zweier anderer Lysiphlebus Arten gefunden. Insgesamt wurden 11 polymorphische Mikrosatelliten für die populationsgenetische Arbeit verwendet. L. hirticornis Blattlausmumien konnten im Feld an allen Sandorten gefunden werden. Auf einigen Pflanzen-Geneten wurden ausschließlich parasitierte Blattläuse gefunden, wohingegen Blattlauskolonien anderer Geneten gänzlich von Parasitierungen verschont blieben. Die Bestimmung der Genotypen zeigt, dass sich die Anzahl der Allele der verschiedenen Standorte, unabhängig von der Stichprobengröße unterscheidet. Parasitoiden-Populationen verschiedener Standorte grenzten sich genetisch signifikant voneinander ab. Ein hoher Prozentsatz der Allel-Variation konnte durch den Pflanzen-Geneten erklärt werden, was darauf hindeutet dass die Einheit der Differenzierung eher der Genet als der Standort sein könnte. Diese Resultate bestätigen, dass L. hirticornis nur eine geringe Ausbreitung und einen hohen Grad an Inzucht aufweist. Eine räumliche Isolierung der Populationen konnte nicht nachgewiesen werden. Während der Saison nahm die Allelvielfalt ab und die Heterozygotie war im Sommer zunehmend und gegen das Ende der Saison abnehmend. Die Differenzierung der Parasitoiden-Populationen nahm tendenziell mit jener der Blattläuse zu, wobei die Blattlaus-Populationen jeweils stärker differenziert waren. Dies deutet darauf hin, dass der Differenzierungsprozess der Parasitoiden dem der Blattläuse hinterherhinkt. Somit könnte in Kombination mit Variationen in der Phänologie der Pflanzen und Heterogenität der Allele das gemeinsame Fortbestehen von Parasitoiden und Blattläusen erklärt werden
Dispersal and spatiotemporal distribution of Protapion fulvipes in white clover fields: implications for pest management
Yield loss caused by insect pests remains a substantial problem in agriculture. Chemical control, with potential negative effects on non-target organisms, is still the main tool for pest management. For pest species with limited dispersal capacity, rotation of the crop in time and space has potential as an alternative management measure. This is particularly important in organic farming, where most agrochemicals are prohibited, but also relevant as a complementary pest management strategy in conventional agriculture. Clover is an important crop used for animal feed and as green manure; however, seed-eating weevils can severely limit the seed yield. We hypothesized that the previous year's clover seed fields constitute the major sources of weevil pests. Consequently, a greater distance to, and a smaller pest load from, this source should reduce the number of weevils colonizing the new seed fields. To map population dynamics and dispersal range of Protapion fulvipes, an economically important seed weevil specialized on white clover, we conducted field studies over four years in 45 white clover seed fields. We found that P. fulvipes overwinters close to its source field and disperses to new fields in early spring the following year. Pest abundance increased with pest load in the previous year's seed field, but decreased by 68% per km distance to the previous year's field. Thus, separation of seed production fields between years by 2-3 km would create a spatiotemporal pest management tool to reduce the pest infestation below the estimated economic injury level
Revealing hidden species distribution with pheromones: the case of Synanthedon vespiformis (Lepidoptera: Sesiidae) in Sweden
Synanthedon vespiformis L. (Lepidoptera: Sesiidae) is considered a rare insect in Sweden, discovered in 1860, with only a few observations recorded until a sex pheromone attractant became available recently. This study details a national survey conducted using pheromones as a sampling method for this species. Through pheromone trapping we captured 439 specimens in Southern Sweden at 77 sites, almost tripling the number of previously reported records for this species. The results suggest that S. vespiformis is truly a rare species with a genuinely scattered distribution, but can be locally abundant. Habitat analyses were conducted in order to test the relationship between habitat quality and the number of individuals caught. In Sweden, S. vespiformis is thought to be associated with oak hosts, but our attempts to predict its occurrence by the abundance of oaks yielded no significant relationships. We therefore suggest that sampling bias and limited knowledge on distribution may have led to the assumption that this species is primarily reliant on oaks in the northern part of its range, whereas it may in fact be polyphagous, similar to S. vespiformis found as an agricultural pest in Central and Southern Europe. We conclude that pheromones can massively enhance sampling potential for this and other rare lepidopteran species. Large-scale pheromone-based surveys provide a snapshot of true presences and absences across a considerable part of a species national distribution range, and thus for the first time provide a viable means of systematically assessing changes in distribution over time with high spatiotemporal resolution
Bacterial diversity in honey bee environment: Embu County, Kenya
In Kenya, small-scale farmers are increasingly venturing into honeybee keeping supplementing their income. However, cases of honeybee populations decline characterized by colony losses, hive absconding and migrating swarms have been documented, resulting in a decline in the number of colonized hives thus raising concerns about their sustainability. Honeybee and colony fitness is dependent on bacterial symbioses, and their disruption leads to disease susceptibility. To assess bacteria associated with honeybees in Kenya, we collected honeycombs, honey, adult worker bees and frame scraping samples from different agro-ecological zones within Embu County. To determine the bacterial composition we characterized the hive microbiota using the targeted metagenomic culture-independent 16S rRNA gene sequencing. Honeybee-associated bacteria community in the hive materials was dominated by Lactobacillus, Leuconostoc, Fructobacillus, Bacillus, Gilliamella, Frischella, Enterobacter, Bombella and Serratia across the sampling environment. In the sample types, adult worker bees lacked the Lactococcus genus but had the other phylotypes consistently similar to those in the larvae samples. Genus Saccharibacter however was absent in honeycomb and larvae samples. Genus Lactococcus was present in all the sample types except in the adult worker bee samples. The significant observation was the presence of genera Serratia and Enterobacter, opportunistic environmental bacteria. High levels of these bacteria in adult and larva samples may present a potential disruption of the microbial community and increase disease susceptibility. Honey production declines as a result of the weakened colony. Regular monitoring will be ideal in maintaining the colony health and thus respond to the growing global market and achieving the African union's Agenda 2063 on agricultural productivity and production
Dispersal and spatiotemporal distribution of Protapion fulvipes in white clover fields : implications for pest management
Yield loss caused by insect pests remains a substantial problem in agriculture. Chemical control, with potential negative effects on non-target organisms, is still the main tool for pest management. For pest species with limited dispersal capacity, rotation of the crop in time and space has potential as an alternative management measure. This is particularly important in organic farming, where most agrochemicals are prohibited, but also relevant as a complementary pest management strategy in conventional agriculture. Clover is an important crop used for animal feed and as green manure; however, seed-eating weevils can severely limit the seed yield. We hypothesized that the previous year’s clover seed fields constitute the major sources of weevil pests. Consequently, a greater distance to, and a smaller pest load from, this source should reduce the number of weevils colonizing the new seed fields. To map population dynamics and dispersal range of Protapion fulvipes, an economically important seed weevil specialized on white clover, we conducted field studies over four years in 45 white clover seed fields. We found that P. fulvipes overwinters close to its source field and disperses to new fields in early spring the following year. Pest abundance increased with pest load in the previous year’s seed field, but decreased by 68% per km distance to the previous year’s field. Thus, separation of seed production fields between years by 2–3 km would create a spatiotemporal pest management tool to reduce the pest infestation below the estimated economic injury level
Data from: Stay at home aphids: comparative spatial and seasonal metapopulation structure and dynamics of two specialist tansy aphid species studied using microsatellite markers
Two tansy-feeding aphids – Macrosiphoniella tanacetaria (MA) and Metopeurum fuscoviride (ME) – were studied at a small spatial scale in and around Jena (< 80 km2) using polymorphic microsatellite markers. Both species were found in ~ 60% of sites formerly known to harbour the aphids, although generally when they did occur, they occurred singly (MA ~ 50%; ME ~60%) and rarely together on the same plant at the same time (~10%) and then usually only in the early part of the growing season. This difference may be due to quasi-apparent competition effects elicited to ants farming ME aphids, and preferentially actively eliminating or disturbing MA aphids. In terms of population genetics, both aphids showed extreme genetic heterogeneity within a metapopulation structure, ME more than MA, i.e. higher FST values, ~ 0.4 vs. 0.15, respectively, and limited levels of interpopulation gene flow. Subpopulations often deviated from Hardy-Weinberg equilibrium and showed linkage disequilibria, as expected in animals with extended parthenogenetic reproduction, and had positive FIS values for most large samples, suggesting inbreeding, and possibly philopatry, certainly in ME. Hierarchical analysis (allele range and number per locus, analysis of molecular variance and FST) strongly suggested that the plant rather than site governs the level of genetic variation. Bayesian clustering analysis revealed that both species had heterogeneous historical genetic patterning, with K (number of subgroups) ranging from 3-7. Evidence is also provided from isolation by distance (IBD) and private allele analyses, that in MA, the presence of winged autumn males, absent in ME where males are wingless, influences comparative population genetic structuring, such that ME subpopulations are comparatively more inbred and genetically differentiated than MA subpopulations. Lastly, additional spatial arrangement (ALLELES-IN-SPACE) analysis showed that in both species, certain subpopulations were genetically isolated from the remainder, probably due to geographical barriers, including intervening buildings and woods. As such, the biology of these tansy aphids living in semi-natural habitats is very different from many pest aphid species examined within agro-ecosystems and infesting ephemeral crops, since the former seem much more reluctant to fly and hence show contrastingly much higher levels of interpopulation divergence, even at small spatial scales as here investigated. Indeed, the number of genotypic clusters found for tansy aphids found using Bayesian approaches is similar to that for the major pest the peach-potato aphid, Myzus persicae, globally
Characterization of olfactory sensory neurons in the red clover seed weevil, Protapion trifolii (Coleoptera : Brentidae) and comparison to the closely related species P. fulvipes
Protapion trifolii and P. fulvipes (Coleoptera: Brentidae) are major pests in European clover seed production. Previous studies have reported a high host plant fidelity of these weevils for red and white clover species, respectively, driven by host plant olfactory cues. Given the specific host preferences observed in these weevils, we aimed to elucidate to which extent such selectivity is reflected in their peripheral olfactory systems. Using an electrophysiological approach, we performed the first functional characterisation of olfactory sensory neurons (OSNs) in P. trifolii to a panel of volatile compounds emitted by red clover plants, and compared the results with the reported OSN types of P. fulvipes. Nineteen OSN classes were characterized in P. trifolii, with the majority of these neurons responding strongly to common volatiles released by the host plant. Based on response profiles, eight of these OSN classes have clear matches to OSN classes in P. fulvipes. The OSN colocalisation patterns and antennal frequency of these classes are similar in the two species. Additionally, the responses of these OSNs are generally highly conserved in the two species, with clear response shifts only revealed for two of the OSN classes. These response shifts in combination with additional response dissimilarities for compounds that vary in abundance between red and white clover plants may underlie the species-specific host preferences. Further behavioural and field experiments should focus on these differentially detected compounds to elucidate their potential role in host selection and use in semiochemical-based control of these pests
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Common Cerambycid Pheromone Components as Attractants for Longhorn Beetles (Cerambycidae) Breeding in Ephemeral Oak Substrates in Northern Europe
Longhorn beetles are ecologically important insects in forest ecosystems as decomposers of woody substrates, microhabitat engineers, and as components of forest food webs. These species can be greatly affected both positively and negatively by modern forestry management practices, and should be monitored accordingly. Through headspace sampling, coupled gas chromatography-electroantennography, gas chromatography-mass spectrometry, and field bioassays, we identified two compounds, 2-methyl-1-butanol and 3-hydroxy-2-hexanone, that constitute aggregation-sex pheromone attractants of three cerambycid species which breed primarily in different types of fresh, recently dead oak wood in Northern Europe: Pyrrhidium sanguineum (L.), Phymatodes alni ssp. alni (L.), and Phymatodes testaceus (L.) (Cerambycinae: Callidiini). Analyses of headspace volatiles collected from live insects indicated that the male-produced aggregation-sex pheromone of P. sanguineum is a 1-15:100 blend of (R)-2-methyl-1-butanol and (R)-3-hydroxy-2-hexanone, whereas the corresponding ratios for P. alni were 70-110:100. In field bioassays, adult P. sanguineum and P. alni were significantly attracted to multiple blends with varying ratios of the two compounds. When tested individually, the compounds were minimally attractive. In contrast, adult P. testaceus exhibited nonspecific attraction to both of the individual compounds and to different blends, despite the hydroxyketone not being part of its pheromone, which consists of (R)-2-methyl-1-butanol alone. Overall, our results suggest that a blend of 50:100 of racemic 2-methyl-1-butanol and 3-hydroxy-2-hexanone is appropriate for parallel, cost-efficient pheromone-based monitoring of all three species. In particular, these species could serve as useful indicators of how modern forestry practices affect a whole guild of saproxylic insects that require ephemeral deadwood substrates for successful breeding
Tansy aphid collecting sites, Jena - May 2007 (09.12.08)
Tansy aphid collecting sites, Jena - May 2007 (09.12.08