Hostplant-Related Causes of Unequal Parasitoid Exploitation of Two Leafminers, Tildenia Georgei and Tildenia Inconspicuella (Lepidoptera: Gelechiidae), on Solanaceous Weeds (Defensive Behavior, Life History, Plant Trichomes, Species Richness, Enemy-Free Space)
Gross, Paul
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Permalink
https://hdl.handle.net/2142/77622
Description
Title
Hostplant-Related Causes of Unequal Parasitoid Exploitation of Two Leafminers, Tildenia Georgei and Tildenia Inconspicuella (Lepidoptera: Gelechiidae), on Solanaceous Weeds (Defensive Behavior, Life History, Plant Trichomes, Species Richness, Enemy-Free Space)
Author(s)
Gross, Paul
Issue Date
1985
Department of Study
Ecology, Evolution, and Conservation Biology
Discipline
Ecology, Evolution, and Conservation Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Ecology
Language
eng
Abstract
Two leafminers (Tildenia georgei on groundcherry, Physalis heterophylla var. ambigua, and Tildenia inconspicuella on horsenettle, Solanum carolinense), sampled in a large old field in Mason Co., Illinois, U.S.A., June-August, 1977-1980, differed markedly in vulnerability to parasitoids. Only two primary parasitoid species consistently parasitized T. georgei (n = 2317 leafminers reared). T. inconspicuella (n = 3354) was attacked by these two plus seven other species that never attacked T. georgei. Mean yearly parasitoid species richness/hostplant patch/sampling date was 2-5 times higher and species diversity and richness/date were 2-3 times greater on T. inconspicuella despite similar leafminer densities and correction for possible sampling, rearing, and patch location biases. T. inconspicuella generally suffered higher % parasitism.
The leafminers had geographical ranges of comparable extent, similar sizes, coloration and developmental rates. Both had five larval instars, pupated in the soil, and were multivoltine. T. georgei mines occurred on all parts of groundcherry leaves, and in tied and folded leaves. Silk and frass were deposited externally. Larvae freely moved out of mines when disturbed or to feed elsewhere. In contrast, T. inconspicuella mines were confined to horsenettle leaf edges. Silk and frass were deposited internally; larvae were completely endophytic.
Three experiments failed to support a prediction derived from the theory of "enemy free space," that differences in parasitism were attributable solely to leafminer niche differences. Parasitoids of T. inconspicuella failed to parasitize T. georgei larvae transferred to horsenettle. Parasitism was no different for T. inconspicuella on horsenettle vs. planted eggplant or for T. georgei in tied vs. untied leaves.
An alternative hypothesis, differences in leafminer mobility, was supported with evidence for two predictions: (1) Horsenettle stellate trichomes prevented penetration by older larvae into leaves. Groundcherry hairs did not. (2) Ectoparasitoids, which are sensitive to host mobility, accounted for 42% of the parasitism on T. inconspicuella but only 1.5% of that on T. georgei.
It is argued that T. inconspicuella's endophytic lifestyle is an adaptation to horsenettle morphology (most relatives are partly exophytic) and this has made it more vulnerable to parasitoids whose host finding and oviposition behaviors restrict them to immobile concealed hosts.
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