Papers by Franklin N. Nyabuga
Journal of Insect Behavior, Jul 5, 2011
Journal of Pest Science, Jul 16, 2021
Yield loss caused by insect pests remains a substantial problem in agriculture. Chemical control,... more 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. Keywords Trifolium repens • White clover seed weevil • Agricultural pest • Dispersal distance • Clover seed production Key Message • The seed pest Protapion fulvipes severely limits white clover seed yields • We mapped dispersal and spatiotemporal distribution of the pest over 4 years in 45 seed fields • Weevil population and field size one year influence the weevil population the following year • Pest abundance decreases, and seed set increases, with distance to the previous year's field • Moving the seed field 2-3 km between years would allow spatial escape from the weevil pest
Journal of Economic Entomology, Feb 5, 2015
The clover seed weevils Apion fulvipes Geoffroy, 1785 and Apion trifolii L., 1768 (Coleoptera: Ap... more The clover seed weevils Apion fulvipes Geoffroy, 1785 and Apion trifolii L., 1768 (Coleoptera: Apionidae) cause major losses to seed production of white clover (Trifolium repens L.) and red clover (Trifolium pratense L.), respectively. Clover is important as animal forage and an alternative to inorganic fertilizers. Because clover is mainly pollinated by bees, the use of insecticides in management of these weevils is discouraged. To gain basic knowledge for development of alternative management strategies, we investigated weevil field abundance over two growing seasons, as well as feeding and olfactory host preferences by A. fulvipes and A. trifolii. Field trap catches in southern Sweden revealed that white clover was dominated by A. fulvipes and red clover by A. trifolii. For both weevil species, female catches were positively correlated to the number of clover buds and flowers in the field. In feeding and olfactory bioassays, females of A. fulvipes and A. trifolii showed a preference for T. repens and T. pratense, respectively. However, the feeding preference was lost when the antennae were removed, indicating a significant role of olfaction in host choice. Male weevils of both species did not show clear olfactory or feeding preferences for host plant species. The field study and laboratory bioassays demonstrate that, at least for female weevils, olfaction is important for selection of host plants. We discuss these novel results in the context of managing these important pests of clover by exploiting olfaction and behavioral attraction to host plant volatiles.
Molecular Ecology Resources, May 1, 2009
The status of vegetation and the impacts of mammalian herbivores on rangelands are complex, and s... more The status of vegetation and the impacts of mammalian herbivores on rangelands are complex, and such studies in Kenya are scanty. We investigated the dynamics of ground cover vegetation in Hell’s Gate National Park in relation to mammalian herbivory. Removal of palatable vegetation is postulated to enhance the development of invasive plant species. We investigated the influence of mammalian herbivores on vegetation diversity and dynamics in this rangeland. Three sampling blocks approximately 3 Km apart measuring 100 m x 50 m were established, each divided into three belt-transects (100 m x 10 m), and separated by a 10 m buffer zone. 2 m by 2 m quadrats at 20 m intervals were established in each transect. We measured composition the richness of plant and mammal species, and herbivory levels four times for six months (September 2018 to February 2019). Plant cover (P< 0.001) and species diversity (P< 0.001) differed significantly among sampling blocks and between seasons (P< 0...
In Kenya, small-scale farmers are increasingly turning to honeybee keeping to supplement their in... more In Kenya, small-scale farmers are increasingly turning to honeybee keeping to supplement their income. The decline of the honeybee population in Kenya has raised concerns following the important economic and ecological role played by the honeybees. By assessing microbial diversity associated with honeybees in Embu County, Kenya, we sought to determine the colony microbial composition of bees using culture-independent sequencing. Honeybee-associated microbial community in the hive materials was dominated by Lactobacillus, Leuconostoc, Fructobacillus, Bacillus, Gilliamella, Frischella, Enterobacter, Bombella and Serratia across the sampling environment. Across the sample types adult worker bees lacked the Lactococcus genus but had the other phylotypes consistently similar to those in the larvae samples. We report a potential disruption of the microbial bacteria community signified by the presence of genera Serratia and Enterobacter, which are opportunistic environmental microorganisms.
PLOS ONE
Tsetse flies use antennal expressed genes to navigate their environment. While most canonical gen... more Tsetse flies use antennal expressed genes to navigate their environment. While most canonical genes associated with chemoreception are annotated, potential gaps with important antennal genes are uncharacterized in Glossina morsitans morsitans. We generated antennae-specific transcriptomes from adult male G. m. morsitans flies fed/unfed on bloodmeal and/or exposed to an attractant (ε-nonalactone), a repellant (δ-nonalactone) or paraffin diluent. Using bioinformatics approach, we mapped raw reads onto G. m. morsitans gene-set from VectorBase and collected un-mapped reads (constituting the gaps in annotation). We de novo assembled these reads (un-mapped) into transcript and identified corresponding genes of the transcripts in G. m. morsitans gene-set and protein homologs in UniProt protein database to further annotate the gaps. We predicted potential protein-coding gene regions associated with these transcripts in G. m. morsitans genome, annotated/curated these genes and identified the...
Journal of Pest Science, 2021
Yield loss caused by insect pests remains a substantial problem in agriculture. Chemical control,... more 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 ofProtapion fulvipes,an economically imp...
Two tansy-feeding aphids – Macrosiphoniella tanacetaria (MA) and Metopeurum fuscoviride (ME) – we... more 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
Nine polymorphic microsatellite loci were isolated from the specialist aphid parasitoid, Lysiphle... more Nine polymorphic microsatellite loci were isolated from the specialist aphid parasitoid, Lysiphlebus hirticornis. In addition, two published loci from closely related Lysiphlebus species were also used. Allelic diversity and heterozygosity were quantified in samples collected from eight tansy plants growing in an area of approximately 150 m2 in Jena, Germany.
Crop Protection, 2020
Sweet potato is an important food security crop but its production is limited by various biotic c... more Sweet potato is an important food security crop but its production is limited by various biotic constraints including plant-parasitic nematodes (PPN). In Kenya, current PPN management practices in sweet potato have several limitations hence the need for alternative low-cost management strategies. This study evaluated the impact of intercropping maize and sweet potato (MS) and application of Tithonia diversifolia (MG), cow (CM) and goat manure (GM) on population dynamics of PPN and the effect on metabolic footprints, ecological and functional indices. Field experiments were established in a randomized complete block design involving the four treatments and unamended controls. Soil samples were collected during long (LR) and short (SR) rains seasons. Forty-seven nematode genera were identified in both seasons. Principle response curves analysis revealed that goat manure had the most pronounced effect on PPN. There were differences in metabolic footprints, ecological and functional indices during LR and SR. In CM plots, predator footprint was high during the long rains season. Functional metabolic footprints categorized all plots as degraded in both seasons except MS which was structured in SR. However, CM bordered a structured ecosystem in both seasons while GM bordered a structured ecosystem in LR. Goat manure may have enhanced the natural ability of soil to regulate PPN affecting sweet potato and it may provide an alternative sustainable method of PPN control for smallholders.
Journal of Chemical Ecology, 2019
Longhorn beetles are ecologically important insects in forest ecosystems as decomposers of woody ... more 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 chromatographyelectroantennography, gas chromatography-mass spectrometry, and field bioassays, we identified two compounds, 2-methyl-1butanol 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-2hexanone, 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.
Journal of Zoological Systematics and Evolutionary Research, 2016
2 CREA-ABP Consiglio per la ricerca in agricoltura e l'analisi dell'economia agraria-Centro di ri... more 2 CREA-ABP Consiglio per la ricerca in agricoltura e l'analisi dell'economia agraria-Centro di ricerca per l'agrobiologia e la pedologia, Florence Italy;
Journal of Insect Conservation, 2015
Administrative Board of Östergotland (various support). Thanks also go to David Heaver at Natural... more Administrative Board of Östergotland (various support). Thanks also go to David Heaver at Natural England for 26 comments on the research from a national monitoring perspective. Finally, a special thanks to all landowners who gave their permission to set up traps, and their commitment to the historical legacy of their land as well as its future management.
Das Verstehen von multitrophischen Interaktionen zwischen Parasitoiden und Blattläusen ist von th... more 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 ...
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Papers by Franklin N. Nyabuga