For many parasitoid species, the final step of host location occurs on plants whose structure varies in time and space, altering the capacity of parasitoids to exploit hosts. Plant structure can be defined by its size, heterogeneity and connectivity. We tested the hypothesis that these three components and all possible interactions affect the level of parasitism of Trichogramma evanescens and that parasitism can be predicted if the structure of a plant is measured. We quantified and varied the structure of three-dimensional artificial plants to determine which component(s) of plant structure explain variability of parasitism and to develop a model that predicts parasitism by Trichogramma females. This model was validated with three natural tritrophic systems. The experiment with artificial plants revealed that plant structure affected host-finding success, which was higher on plants with a simple structure and low on plants with a complex structure. A response surface regression showed that the linear and quadratic terms of connectivity were highly significant, indicating that connectivity best explained the variability in the rate of parasitism obtained. The interaction between connectivity and heterogeneity was also significant. Observed values of parasitism from experiments with three natural tritrophic systems fit predicted values of parasitism generated by the model, indicating that parasitism can be predicted if heterogeneity and connectivity of a plant are known. Consequences of these results in regard to population dynamics, evolution and biological control are discussed.

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Glass-deposited monolayers of polystyrene-coated gold nanoparticles with controlled interparticle distance have been prepared. Normal incidence extinction spectra show a progressive red shift of the plasmon resonance wavelength as the interparticle gap within the film is reduced. Polarized extinction spectra were measured at in-plane incidence using an optical waveguide lightmode spectroscopy (OWLS) setup. The in-plane (TE)-polarized spectra show a red shift with decreasing interparticle gap, whereas the out-of-plane (TM)-polarized component shows no visible change. These observations are typical of dipolar near-field interparticle plasmon coupling. Simulations using the discrete dipole approximation have been conducted to compare the decay rate of the red shift with increasing interparticle gap for different particle arrangements (pair, row of 5 and 2D hexagonal array of 19). The calculations show that the variation of the relative red shift with the relative interparticle spacing follows a first-order exponential decay law in all three structures, with a decay constant similar to results previously reported. A secondary, slower decay rate, occurring at relative interparticle gap values above 1.25, is found for the 2D array. The decay constant of this large-distance regime is close to that of the measured extinction spectra of the polystyrene-coated gold nanoparticles monolayers, which present relative interparticle distances within this range. This second decay constant may be the result of an increased contribution of higher-order modes.