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Host Plant Quality (host + plant_quality)
Selected AbstractsCombined Effects of Host Plant Quality and Predation on a Tropical Lepidopteran: A Comparison between Treefall Gaps and the Understory in PanamaBIOTROPICA, Issue 6 2008Lora A. Richards ABSTRACT In tropical forests, light-gaps created from treefalls are a frequent source of habitat heterogeneity. The increase in productivity, through gap formation, can alter food quality, predation and their impact on insect herbivores. We hypothesized that in gaps, herbivores would be less resource-limited and more predator limited, whereas in the understory, we predicted the reverse. In this study, we investigate the combined effects of food quality and predation on the lepidopteran larva Zunacetha annulata feeding on its host plant Hybanthus prunifolius in two habitats; sunny treefall gaps and the shaded understory in Panama. In bioassays, Z. annulata feeding on sun leaves ate 22 percent less leaf area, grew 25 percent faster, and had higher pupal weights than larvae feeding on shade leaves. However, shade leaves had higher nitrogen content and specific leaf area. In gaps, predation was 26.4 percent compared to 13.8 percent in the understory. Larvae on understory plants traveled greater distances and spent more time searching and traveling than larvae on gap plants. These differences in behavior are consistent with lower predation risk and lower quality food in the understory. Using data from bioassays and field experiments we calculated 0.22 percent and 1.02 percent survival to adulthood for larvae in gaps and the understory, respectively. In conclusion, although these habitats were in close proximity, we found that larvae in the understory are more resource-limited and larvae in gaps are more predator limited. [source] Host plant quality and defence against parasitoids: no relationship between levels of parasitism and a geometrid defoliator immunoassayOIKOS, Issue 6 2008Netta Klemola Host plant quality has a major influence on the performance, and ultimately on the fitness of an herbivorous insect, but may also have indirect effects on the third trophic level by affecting an herbivore's defensive ability against natural enemies. In a three-year field study, we examined the effects of natural food quality on the ability of autumnal moths, Epirrita autumnata (Lepidoptera, Geometridae), to defend themselves against parasitoids. In each year, we confirmed the variation in quality of host trees (mountain birch, Betulapubescens ssp. czerepanovii) by determining the mass of pupae reared in mesh bags attached to the trees and the water content of leaves. Individuals grown on high quality trees possessed significantly higher encapsulation rate of a foreign antigen as pupae compared to those on low quality trees during the first and third study years; a parallel trend was also found in the second study year, although this difference was not statistically significant. However, in spite of observed differences in encapsulation rates, individuals reared on high and low quality trees did not differ in their levels of parasitisation when exposed to hymenopteran parasioids in the wild and thus were equally vulnerable. Accordingly, the encapsulation response seems not to play a major role on the population ecology scale in the studied system. Our findings also stress the importance of direct resistance tests, which should be conducted along with tests of insect immune function. [source] Spatial abundance structures in an assemblage of gall-forming sawfliesJOURNAL OF ANIMAL ECOLOGY, Issue 3 2004M. A. McGeoch Summary 1Examination of the fine-scale internal structure of species geographical ranges, and interspecific variation therein across landscapes, contributes to a more comprehensive understanding of the structure of geographical ranges. Two components of this internal structure that require further examination are the occurrence, extent and position of spatial autocorrelation, and relationships between the spatial abundance structures of closely related, ecologically similar species. 2Here we compare the abundance structures of an assemblage of gall-forming sawflies (Tenthredinidae) across a landscape. We identify the relative roles of spatial and non-spatial factors in explaining their abundance structures and test the hypothesis that sawfly density is explained by host plant quality, as has been demonstrated repeatedly at finer scales. We use these results to distinguish between alternative sets of mechanisms that may be operating at the landscape scale. 3Species densities were mainly multimodal across the landscape and significantly spatially structured, with patch, periodic and trend components. The abundance structures thus mimic those found generally for species across the full extent of their geographical ranges. 4Many abundance structure characteristics were unique to species, with differences in their correlogram profiles, distances over which densities were positively autocorrelated, and the absence of significant spatial structure in one species. 5In contrast to previous, fine-scale studies, host plant quality explained little of the variation in sawfly gall density across the landscape, whereas unexplained spatial structure contributed between 30% and 50%. Based on knowledge of the biology of these species and the absence of competitive interactions, species dispersal characteristics and the Moran effect are suggested as probable alternative hypotheses at this scale. 6Therefore, a spatial approach has identified the hierarchical nature of mechanisms underlying the population dynamics of this sawfly assemblage for the first time. Furthermore, it has highlighted the importance of spatial processes in explaining the densities of species at the landscape scale, as well as the individualistic nature of their abundance structures. [source] Poor host plant quality causes omnivore to consume predator eggsJOURNAL OF ANIMAL ECOLOGY, Issue 3 2003Arne Janssen Summary 1Omnivorous arthropods are known to change their diet when host plant quality is low. Consequently, it has been suggested that decreased plant quality has a twofold negative effect on herbivore populations: (1) a decrease in growth rate of herbivores; (2) omnivores include more herbivores in their diet. We hypothesized that decreased host plant quality may also cause omnivores to feed on predators, including their own enemies. 2We tested this hypothesis, using the omnivorous western flower thrips. This species is known to feed on many plant species, but also on the eggs of another herbivore, the two-spotted spider mite. Previous research has shown that a decrease in plant quality leads to increased feeding on spider mite eggs by western flower thrips. Western flower thrips also kill the eggs of various predatory mites, including those of the specialist predator of spider mites and those of a predatory mite that attacks western flower thrips itself. 3In this paper we investigate whether thrips larvae kill predator eggs to feed on them and whether this predation depends on host plant quality. 4Larval survival as well as developmental rate increased when plant tissue of low quality (sweet pepper) was supplemented with eggs of two predatory mite species or when it was supplemented with pollen, a high-quality food type. 5Supplementing high quality leaf tissue (cucumber) with predator eggs did not lead to increased survival and developmental rate. Thrips larvae fed significantly less on predatory mite eggs when pollen was available. 6Thus, thrips larvae indeed feed on predator eggs, including those of their predator, and they feed more on predator eggs when host plants are of low quality. [source] Discriminating tastes: self-selection of macronutrients in two populations of grasshoppersPHYSIOLOGICAL ENTOMOLOGY, Issue 3 2008DENNIS J. FIELDING Abstract The capacity to self-select an optimal balance of macronutrients (protein and carbohydrate) is studied in two populations of Melanoplus sanguinipes F. (Orthoptera: Acrididae). One population derives from the subarctic (interior of Alaska) and the other from the temperate zone (Idaho, U.S.A.). Over the duration of the fourth and fifth stadia, Alaskan grasshoppers consistently self-select a diet centred on a 0.90 ratio of protein : carbohydrate, whereas protein and carbohydrate intake by the Idaho grasshoppers is contingent on the particular food choices presented to them. When restricted to imbalanced diets, the Alaskan grasshoppers develop more rapidly than the Idaho grasshoppers, regardless of diet composition. The Idaho grasshoppers also have a greater amount of lipid than the Alaskan grasshoppers across all diets. Performance measures (body mass, survival, developmental times) are more sensitive to dietary imbalances in the Alaskan grasshoppers than in the Idaho grasshoppers. When fed diets with low, but balanced, proportions of protein and carbohydrate, grasshoppers of both populations are able to increase consumption to compensate for the low concentration of nutrients. The results suggest that demographic responses of insects to changes in host plant quality, such as may result from climate change, may differ among populations within a species. [source] | ||||||||||