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The importance of search behavior and movements for spatial distributions of herbivorous insects
Stockholm University, Faculty of Science, Department of Botany.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Insect populations commonly show large spatial variation in density, and much variation have been shown to be explained by the search behavior applied by the insect when locating habitat patches. This thesis explores the importance of odor-mediated attraction for immigration rates of herbivorous insects in relation to the size of the patches and the density of host plants within the patches. By using electroantennogram and measuring moth antennal responses to sex pheromones and thereby estimating the relative odor-mediated attraction from odor patches in field experiments (Paper I, III), I show that the length of the odor plumes emanating from the patches increase proportional with the square-root of the number of odor sources. In laboratory and field experiments (with the weevils Cionus scrophulariae and C. tuberculosus and the host plant figwort Scrophularia nodosa; Paper II) and meta-analyses on multiple insect herbivores (Paper III), I examined whether the relative increase in plume length could also predict the immigration rates of olfactory searching insects in relation to patches with increasing area and increasing density of host plants. The experiments (Paper II) and meta-analyses (Paper III) showed that the observed immigration rates of olfactory searching insects was well predicted by the relative increase in plume length, as estimated from the electroantennogram measurements (Paper I, III). The importance of immigration rates, relative to the effect of emigration and local growth was also investigated for the Cionus weevils in natural S. nodosa patches (Paper IV). This study showed that the density-patch size relationships of the weevils during early season were predicted by the net scaling of emigration and immigration rates, and differences in density-patch size relationships between the two species could be explained by inter-specific differences in their emigration rates from small patches. In conclusion, this thesis shows that search behavior can be used to predict immigration rates and spatial distributions of insects, with implications for pest control, conservation ecology and general ecological theory.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University , 2011. , 51 p.
Keyword [en]
Olfactory search, Habitat heterogeneity, Species-traits, Immigration, Scaling relationships, Patch size, Plant-insect interactions, EAG, Odors, Pheromones
National Category
Ecology
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-62464ISBN: 978-91-7447-368-1 (print)OAI: oai:DiVA.org:su-62464DiVA: diva2:442052
Public defence
2011-10-27, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Epub ahead of print. Paper 3: Submitted. Paper 4: Submitted.

Available from: 2011-10-05 Created: 2011-09-20 Last updated: 2013-08-14Bibliographically approved
List of papers
1. How insects sense olfactory patches: the spatial scaling of olfactory information
Open this publication in new window or tab >>How insects sense olfactory patches: the spatial scaling of olfactory information
2013 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 122, no 7, 1009-1016 p.Article in journal (Refereed) Published
Abstract [en]

When searching for resources in heterogeneous environments, animals must rely on their abilities to detect the resources via their sensory systems. However, variation in the strength of the sensory cue may be mediated by the physical size of the resource patch. Patch detection of insects are often predicted by the scaling of sensory cues to patch size, where visual cues has been proposed to scale proportional to the diameter of the patch. The scaling properties of olfactory cues are, however, virtually unknown. Here, we investigated scaling rules for olfactory information in a gradient of numbers of odour sources, relevant to odour-mediated attraction under field conditions. We recorded moth antennal responses to sex pheromones downwind from pheromone patches and estimated the slope in the scaling relationship between the effective length of the odour plumes and the number of odour sources. These measurements showed that the effective plume length increased proportional to the square root of the number of odour sources. The scaling relationship, as estimated in the field experiment, was then evaluated against field data of the slope in the relationship between trap catch and release rate of chemical attractants for a wide range of insects. This meta-analysis revealed an average slope largely consistent with the estimated scaling relationship between the effective plume length and the number of odour sources. This study is the first to estimate the scaling properties of olfactory cues empirically and has implications for understanding and predicting the spatial distributions of insects searching by means of olfactory cues in heterogeneous environments.

National Category
Ecology Environmental Sciences
Identifiers
urn:nbn:se:su:diva-92120 (URN)10.1111/j.1600-0706.2012.00037.x (DOI)000320618900006 ()
Funder
Swedish Research Council, 621-2006-2996
Note

AuthorCount:3;

Available from: 2013-07-22 Created: 2013-07-19 Last updated: 2017-12-06Bibliographically approved
2. Immigration of olfactory searching insects into host plant patches: testing scaling rules for olfactory information
Open this publication in new window or tab >>Immigration of olfactory searching insects into host plant patches: testing scaling rules for olfactory information
2011 (English)In: Arthropod-Plant Interactions, ISSN 1872-8855, E-ISSN 1872-8847, Vol. 5, 269-277 p.Article in journal (Refereed) Published
Abstract [en]

Herbivorous insects are commonly faced with host plants being distributed in scattered patches across a landscape. Immigration rates into habitat patches may strongly depend on the sensory cues used in the patch location process, and immigration rates of insects can be predicted based on the scaling of sensory cues. Here, we tested recent estimates of the scaling of olfactory information to patch size, which predicts a scaling coefficientf z = -0.5 (A^z, where A = patch size, z = scaling coefficient). We predicted that immigration rates of olfactory searching insects into patches of different sizes should scale according to the estimated slope. We investigated attraction of the weevils Cionus tuberculosus and Cionus scrophulariae to odors from figwort Scrophularia nodosa and quantified immigration rates of weevils into differently sized patches. We also investigated oviposition rates of the sawfly Tenthredo scrophulariae. The slope in the regression between density and patch size for herbivores was then compared with the predicted scaling coefficient. Using olfactometers, we found that weevils were attracted to figwort odors. Weevil densities were significantly affected by patch size, and the slope in the relationship between density and patch size was z = -0.53. The slope in the relationship between larval densities of sawflies and patch size was less negative with a slope of z = -0.15, indicating differences in search behavior compared with the weevils. The density–patch size relationship for the weevils closely matched the predicted slope and supported the previous estimations of the scaling of olfactory informationto patch size.

National Category
Ecology Environmental Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-62444 (URN)10.1007/s11829-011-9148-1 (DOI)000297341900002 ()
Note
authorCount :2Available from: 2011-09-19 Created: 2011-09-19 Last updated: 2017-12-08Bibliographically approved
3. Insect density-plant density relationships – a modified view of insect responses to resource concentrations
Open this publication in new window or tab >>Insect density-plant density relationships – a modified view of insect responses to resource concentrations
(English)Article in journal (Refereed) Submitted
National Category
Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-62446 (URN)
Available from: 2011-09-19 Created: 2011-09-19 Last updated: 2011-09-20Bibliographically approved
4. What shapes local density?: The importance of migration rates and local growth for density-patch size relationships in two Cionus weevils
Open this publication in new window or tab >>What shapes local density?: The importance of migration rates and local growth for density-patch size relationships in two Cionus weevils
2012 (English)In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 37, no 1, 90-98 p.Article in journal (Refereed) Published
Abstract [en]

1. The relative effect of migration and local growth on the spatio-temporal density-distribution of two co-existing herbivorous weevils, Cionus scrophulariae L. and C. tuberculosus Scop., in 32 host plant Scrophularia nodosa L. patches of varying sizes was investigated. 2. Predictions of the temporal development of the slope in the density-patch size relationships were derived from a basic population model with scale-dependent migration rates. The model indicated that the slopes in the density-patch size relationships during the early season should be reflected by the net scaling of immigration and emigration rates, whereas the slopes during the later season should increase as a result of local growth. 3. Emigration rates of the weevils were estimated in a field experiment, were the weevils coexisted in space and time. These results were then combined with a previous estimate of immigration rates in order to determine the net scaling of migration rates. 4. The emigration rate differed between species, caused by different movement rates in small patches, which could explain differences in the general slope of the density-patch size relationships of the weevils in the natural figwort patches throughout the summer. The slopes in the relationships in the early season were largely predicted by the net scaling of migration rates. The slope also increased in the later season for C. tuberculosus, whereas the slope decreased for C. scrophulariae. 5. It was concluded that the understanding of both inter- and intra-specific variations in density-patch size relationships of insect herbivores can be improved using population models incorporating scale-dependent migration and local growth.

Keyword
Cionus scrophulariae, Cionus tuberculosus, emigration, herbivores, immigration, patch size, scaling relationships, Scrophularia nodosa
National Category
Botany
Identifiers
urn:nbn:se:su:diva-76311 (URN)10.1111/j.1365-2311.2011.01339.x (DOI)000299253000011 ()
Note
2Available from: 2012-05-15 Created: 2012-05-10 Last updated: 2017-12-07Bibliographically approved

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