Paul E. Hatcher

THREE‐WAY INTERACTIONS BETWEEN PLANT PATHOGENIC FUNGI, HERBIVOROUS INSECTS AND THEIR HOST PLANTS

652 ( I ) Direct effects of non-vector herbivores 653 (2) Indirect effects, mediated through the host 654 IV. Root-shoot interactions 657 ( I ) Above-ground insects and below-ground fungi 657 (2) Above-ground fungi and below-ground insects 658 . . . . . . 11. The effect of plant pathogenic fungi on herbivorous insects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (c) Effects on insects . . . . . . . . . . . . 648 . . . . . . 111. The effect of herbivorous insects on plant pathogenic fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V. Induced resistance a common defence against pest and pathogen ? . . . . 660 ( I ) The hypersensitive response and lignification . . . . . . . . 661 ( 2 ) Phytoalexins . . . . . . . . . . . . . . 662 (3) Proteinase inhibitors 663 (4) Lipoxygenase 664

The role of interactions between trophic levels in determining the effects of UV-B on terrestrial ecosystems

Understanding the potential impact of ozone depletion on terrestrial ecosystems is constrained by lack of information on the effects of environmentally realistic UV-B doses on terrestrial organisms other than higher plants. Increasing UV-B may alter interactions between plants and consumers through direct effects on consumer organisms (herbivores, phytopathogens, decomposers, etc.). The effects of increasing UV-B on arthropods are not known. Significant UV-B effects on fungi have been reported, and may be either negative (inhibition of spore germination and mycelial growth) or positive (increased growth, induction of reproductive development and sporulation). However, in many cases consumers are unlikely to be directly exposed to UV-B in the field. In addition, UV action spectra for fungi suggest that this major group may be less sensitive to the effects of ozone depletion than higher plants. Host mediated effects of UV-B on consumers may include alterations in plant chemistry. While secondary metabolites such as phenolics may increase under increased UV-B, this is not invariably the case and evidence that such changes have significant effects on consumers is limited. In particular, there is no evidence that increased UV-B increases resistance of higher plants to fungal pathogens. Indeed, increased UV-B prior to inoculation results in no significant effect or increased disease. Such responses may be attributable to UV-B effects on host surface properties or on compounds other than phenolics. However, such changes are poorly known, and their potential effects on phytopathogens, herbivores or decomposers cannot be assessed. Understanding the effects of UV-B on terrestrial ecosystems is further limited since virtually nothing is known of possible impacts on higher trophic levels, i.e. predators, parasites or pathogens.

The effect of elevated UV-B radiation on herbivory of pea by Autographa gamma.

Leaves exposed to above‐ambient fluxes of ultraviolet‐B (UV‐B) radiation commonly contain increased concentrations of phenolic compounds which may influence herbivores. However, the hypothesis that elevated UV‐B modifies herbivory, whether mediated by phenolics or other plant constituents, has rarely been studied experimentally. We investigated the responses of the moth Autographa gamma L. (Lepidoptera: Noctuidae) to pea (Pisum sativum L.) grown at a range of plant‐effective UV‐B fluxes. Although total phenolics did increase significantly with increasing UV‐B, this change had little deleterious effect on the 5th instar larvae of A. gamma. However, tissue nitrogen also increased with increasing UV‐B. Increased nitrogen was correlated with an increase in the efficiency with which larvae utilized their food and in larval growth rate, but in a reduction in the amount of plant material consumed. The apparently major role of nitrogen in determining herbivore responses to changing UV‐B demonstrates the risks in predicting such responses soley on the basis of changes in phenolics and other secondary metabolites.

The effect of a foliar disease (rust) on the development of Gastrophysa viridula (Coleoptera: Chrysomelidae)

Abstract. 1 Gastrophysa viridula Degeer (Coleoptera: Chrysomelidae) and the pathogenic rust fungus Uromyces rumicis (Schum.) Wint. both occur on leaves of Rumex crispus L. and R.obtusifolius L. Individual stages of beetle development, and egg laying, were compared on healthy and infected leaves of each plant species in the laboratory. Oviposition choice was investigated in the field and laboratory. 2 Beetles reared on infected leaves of each species had greater larval mortality and slower development than those reared on healthy leaves. Although larvae feeding on infected leaves consumed up to 2.5 times more dry weight than those reared on healthy leaves, they had a lower relative growth rate and pupated at a lower weight. These changes were consistent with the reduced nutritive quality of rust‐infected Rumex leaves. 3 Fecundity of beetles reared on infected leaves of both species was considerably reduced. Eggs laid by beetles feeding on infected R.crispus leaves also had a reduced viability. 4 The beetle developed consistently poorer on healthy R.crispus than on healthy R.obtusifolius throughout its life‐cycle. Differences in larval performance were greater between host species than between infected and healthy leaves. 5 Oviposition was similar on infected and healthy R.crispus in both the laboratory and field. However, adults consumed less, and laid fewer eggs on infected than on healthy R.obtusifolius. The pattern of egg laying on different aged leaves was affected by rust infection: a greater proportion of eggs was laid on the older, infected leaves, than on the equivalent aged leaves on the healthy plants. Few larvae survived from eggs laid on rusted leaves in the field.

Interactions Between Rumex spp., Herbivores and a Rust Fungus: Gastrophysa viridula Grazing Reduces Subsequent Infection by Uromyces rumicis

The chrysomelid beetle Gastrophysa viridula and the rust fungus Uromyces rumicis both occur on leaves of Rumex crispus or Rumex obtusifolius. We investigated reciprocal interactions between herbivory and infection. In both Rumex species the amount of leaf eaten by Gastrophysa viridula was not affected by prior rust infection of the same leaf, whereas there was a significant reduction in infection when the same leaves had been previously grazed by Gastrophysa viridula. Herbivory induced an 80 % reduction in pustule density within and immediately around the feeding site within 1 day of feeding damage; it also induced resistance throughout the undamaged portion of the leaf, and a less effective, and slower, resistance in undamaged leaves (...)

Interactions between Rumex spp., herbivores and a rust fungus: the effect of Uromyces rumicis infection on leaf nutritional quality

1. The rust fungus Uromyces rumicis infects leaves of Rumex crispus and R. obtusifolius causing premature senescence and leaf death. We investigated the effect of infection on nutritional quality of leaves with respect to the chrysomelid beetle Gastrophysa viridula and measured larval survival and growth on rusted and unrusted plants. 2. A smaller biomass of G. viridula was produced and a greater area of leaf consumed per unit biomass gained, by egg batches reared on rusted compared to unrusted R. obtusifolius, although no difference was observed between larvae reared on rusted or unrusted R. crispus. 3. Concentrations of total non-structural carbohydrates were not changed in the pustule and non-infected leaves but were increased in the inter-pustule area. Infection changed the partitioning to different carbohydrates, increasing the proportion of starch in R. crispus and decreasing it in R. obtusifolius. 4. The concentration of total nitrogen, both in the pustule and the inter-pustule area, decreased in both species with time after rust infection. 5. In both species, considerably higher oxalate concentrations occurred in the interpustule area and significantly lower concentrations in the uninfected leaves of these plants. Calcium concentrations altered similarly and were correlated with oxalate concentrations. 6. We conclude that rust infection does not improve the nutritional quality of the leaves for G. viridula and is unlikely to do so for other invertebrate herbivores