Is selection of host plants by Plagiodera versicolora based on plant‐related performance?

Plant-related performance may be one of the most important factors in the selection of host plants by insect herbivores. We investigated the importance of plant-related performance in host selection by the willow leaf beetle, Plagiodera versicolora (Laicharting) (Coleoptera: Chrysomelidae), on four willow species: Salix chaenomeloides Kimura, Salix eriocarpa Fr. et Sav., Salix   integra Thunb., and Salix serissaefolia Kimura (Salicaceae). Bagging experiments in the field revealed that the performance of P. versicolora adults and larvae differed significantly among willow species under enemy-free conditions and at constant densities. Egg clutch and larval abundance were positively related to adult abundance. Plagiodera versicolora adults did not discriminate strongly among willow species for feeding and oviposition. Larval performance did not differ among willow species in the presence of natural enemies, suggesting that interspecific differences in host quality were overridden by mortality from natural enemies. Adult and egg clutch abundance of P. versicolora changed seasonally despite the temporal stability of adult and larval performance under enemy-free field conditions. Thus, plant-related performance of P. versicolora adults and larvae may contribute little to population growth and temporal dynamics of host use in P. versicolora . Potential factors that reduce discrimination of P. versicolora among host willow species are discussed.     

Demographic models reveal the shape of density dependence for a specialist insect herbivore on variable host plants

1. It is widely accepted that density-dependent processes play an important role in most natural populations. However, persistent challenges in our understanding of density-dependent population dynamics include evaluating the shape of the relationship between density and demographic rates (linear, concave, convex), and identifying extrinsic factors that can mediate this relationship. 2. I studied the population dynamics of the cactus bug Narnia pallidicornis on host plants (Opuntia imbricata) that varied naturally in relative reproductive effort (RRE, the proportion of meristems allocated to reproduction), an important plant quality trait. I manipulated per-plant cactus bug densities, quantified subsequent dynamics, and fit stage-structured models to the experimental data to ask if and how density influences demographic parameters. 3. In the field experiment, I found that populations with variable starting densities quickly converged upon similar growth trajectories. In the model-fitting analyses, the data strongly supported a model that defined the juvenile cactus bug retention parameter (joint probability of surviving and not dispersing) as a nonlinear decreasing function of density. The estimated shape of this relationship shifted from concave to convex with increasing host-plant RRE. 4. The results demonstrate that host-plant traits are critical sources of variation in the strength and shape of density dependence in insects, and highlight the utility of integrated experimental-theoretical approaches for identifying processes underlying patterns of change in natural populations.     

Testing the potential for conflicting selection on floral chemical traits by pollinators and herbivores: predictions and case study

1.  There are myriad ways in which pollinators and herbivores can interact via the evolutionary and behavioural responses of their host plants.
2.  Given that both herbivores and pollinators consume and are dependent upon plant-derived nutrients and secondary metabolites, and utilize plant signals, plant chemistry should be one of the major factors mediating these interactions.
3.  Here we build upon a conceptual framework for understanding plant-mediated interactions of pollinators and herbivores. We focus on plant chemistry, in particular plant volatiles and aim to unify hypotheses for plant defence and pollination. We make predictions for the evolutionary outcomes of these interactions by hypothesizing that conflicting selection pressures from herbivores and pollinators arise from the constraints imposed by plant chemistry.
4.  We further hypothesize that plants could avoid conflicts between pollinator attraction and herbivore defence through tissue-specific regulation of pollinator reward chemistry, as well as herbivore-induced changes in flower chemistry and morphology.
5.  Finally, we test aspects of our predictions in a case study using a wild tomato species, Solanum peruvianum , to illustrate the diversity of tissue-specific and herbivore-induced differences in plant chemistry that could influence herbivore and pollinator behaviour, and plant fitness.     

Differential herbivory of the specialist beetle Stolas punicea on chemical phenotypes of its host Mikania micrantha

We assessed the preference of two populations of the specialist beetle Stolas punicea, on plants from three phytochemically differentiated geographical mosaics of the American weed Mikania micrantha. Our results show a significant geographic variation in host preference in S. punicea that could affect its success as a biocontrol agent.     

Plant volatiles moderate response to aggregation pheromone in Colorado potato beetle

Abstract:  The orientation of the Colorado potato beetle, Leptinotarsa decemlineata , to a male-produced aggregation pheromone, ( S )-3,7-dimethyl-2-oxo-oct-6-ene-1,3-diol, a three-component plant attractant blend [comprised of ( Z )-3-hexenyl acetate + (±)-linalool + methyl salicylate], and other potato volatiles (nonanal and 2-phenylethanol) were tested. All compounds were previously shown to be active in coupled gas chromatography/electroantennogram experiments. Both the three-component plant attractant blend and 2-phenylethanol were attractive to adult beetles. While male beetles oriented preferentially to both plant attractants vs. a control, females showed little preference. Combining the plant attractants with the pheromone resulted in sexually dimorphic responses similar to those seen with either plant attractant alone. Addition of nonanal abolished the sexually dimorphic response to the pheromone + 2-phenylethanol blend; the new three-component blend was attractive to both sexes. In both laboratory bioassays and field experiments, a combination of the pheromone + the three-component plant attractant was preferred over the plant attractant alone. Thus, it seems likely that combinations of pheromone + plant volatiles may be the most efficacious for field use.