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k m w e P m l a i f m B m y r o ©if 'MMmmss mBsmmme l Andrew W. Sheppard Department of Pure and Applied Biology Imperial College Silwood Park Ascot, Berkshire. Submitted as the requirement for a Doctorate of Philosophy at the University of London. Abstract: This field based research project was designed to study the influence of insect herbivores on the population dynamics of Heracleum sphondvlium subsp. sphondvlium, and to conduct field manipulation experiments to test interspecific competition theory in the structuring of different insect herbivore guilds. The action of insects on H. sphondvlium populations of different densities was established in three ways. First, three populations were monitored. Second, artificial damage treatments were applied to flowering plants, and the seeds produced used in germination experiments. Third, a factorial-design experiment was conducted incorporating different herbivore loads. Basal stem diameter (BSD) was correlated with seed number and mean seed weight. After stem formation any defoliation (artificial) above 50%, reduced the seed number. Mean seed weight, for a particular BSD, decreased only when defoliation approached 100%, Seed production after defloration of primary umbels occurred largely on normally unreproductive lower secondary umbels, and was not completely compensatory. Complete plant destruction by insects was a rare occurrence; the plants affected showed no recovery in the same season. Germination and survival were greatest in damp meadow conditions. Heavy seeds (1° umbel) germinated later, but survived better than light seeds (2° umbel) in the dense sward. Detailed insect population observations produced positive correlations that demonstrated spatial co-occurrence to be the norm for most herbivores. On average, 40-50% of the specialist herbivores were found at any one site and these were mostly temporally separated. The insect addition/removal experiments to detect asymmetric interspeeific competition between Phaedon tumidulus (Germar). (Col.: Chryscmelidae, leaf-chewer) and Depressaria pastinacella. (Dupcnchel), (Lep.: Oecophoridae, flower/seed feeder) showed an interaction. Moth oviposition was enhanced on beetle-damaged, low density plants, but was reduced on such plants at high density. Density dependent larval mortality compensated for the egg distribution differences. There was no evidence to support interspecific competition, resource limitation or spatially density dependent parasitism for either herbivore. ’ Table of Contents. Abstract........... 2 List of Tables. 7 List of Figures 9 1. Introduction............................................ -.............................................10 1.1 The Project..........................................................................................10 1.1.1 Why hogweed?...................................................................................11 1.1.2 The use of field experiments......................................................12 1.2 Population Dynamics of Plants and their Insect Herbivores....... 13 1.3 The Action of Insects on Forbs.......................................................14 1.4 Plant-Herbivore Dynamics.................................................................. 23 1.5 The Importance of Interspecific Competition...............................28 1.5.1 What is competition?.................................................................... 28 1.5.2 A brief history of competition...............................................31 1.5.3 Herbivore competition: hypotheses and re v ie w s...................32 1.5.4 Testing for interspecific competition......................................35 1.5.5 Competition within insect herbivore guilds.............................40 1.5.6 Competition between insect herbivore guilds........................... 44 2. The Biology and Natural History of Heracleum sohondvlium and its Insect Herbivores..................................... 46 2.1 The Biology of Hogweed................................................................... 46 2.1.1 Plant description......................................................................... 46 2.1.2 Biology and life history dynamics........................................... 4? 2.1.3 Floral biology and pollination................................. ............... 52 2.1.4 Habitat....................................... ..................................... ........... 56 2.1.5 Geographical and altitudinal distribution.......----........ 60 2.1.6 Plant chemistry.............. ................. .......................................... 61 2.1.7 Han and vertebrate herbivores..................................... .......... 63 2.1.8 Hogweed herbivores, parasites, pathogens & saprophytes..... 65 2.2 The Herbivores of Hogweed......................... ................................ 71 2.2.1 The leaf chewers.......... ............................................................... l & 2.2.1.1 Phaedon tumidu-lus (Coleoptera: Chryscmel idae) ................ 2.2.1.2 Lioohloeus tessulatus (Coleoptera: Curculionidae)........... 74 2.2.1.3 Eoermenia chaerophvllei la (Lepidoptera: Epermenidae).... 76 3 2.2.2 The leaf miners.............................................. .............................79 2.2.2.1 Eulela heraclei (Diptera: Tephrltidae).............................. 79 2.2.2.2 Phvtomvza spondvlii (Diptera: Agromyzidae)....................... 82 2.2.2.3 Phvtomvza heracleana (Diptera: Agromyzidae)..................... 83 2.2.3 The leaf rollers---- ! ...................................................................85 2.2.3.1 Agonopterix heracleana (Lepidoptera: Oecophoridae).........85 2.2.4 The gall formers...........................................................................86 2.2.4.1 Macrolabis heraclei (Diptera: Cecidomyiidae)................8 6 2.2.4.2 Continarina nicolavi (Diptera: Cecidomyi idae)..................87 2.2.4.3 Lasioptera carophi la (Diptera: Cecidomy i idae)..................88 2.2.5 The sap suckers............................................................................88 2.2.5.1 Evsarcoris fabric! (Hemiptera: Pentatomidae)....................88 2.2.5.2 Polvcoris baccarum (Hemiptera: Pentatomidae)....................89 2.2.5.3 Cercopis vulnerata (Homoptera: Cercopidae)....................... 89 2.2.5.4 Phi 1 aenus spumaris (Homoptera: Cercopidae)..................... 89 2.2.5.5 Euptervx aurata (Homoptera: Cicadel 1 idae).........................90 2.2.5.6 Cavariella pastinacae (Homoptera: Aphidae)......................91 2.2.5.7 Dvsaphis 1 auberti (Homoptera: Aphidae).............................. 91 2.2.6 The stem borers........................................... 92 2.2.6.1 Melanaqromvza angeliciphaga (Diptera: Agromyzidae).........92 2.2.7 The flower/seed feeders............... ....94 2.2.7.1 Depressaria pastinaceila (Lepidoptera: Oecophoridae)....94 2.2.7.2 Cvdia aurana (Lepidoptera: Tortricidae)...........................96 2.2.7.3 Liriomvza 1 utea (Diptera: Agromyzidae).............................. 98 2.2.8 The root borers............................................................................98 2.2.8.1 Chei losia paoana (Diptera: Syrphidae)................................99 2.2.8.2 Cheilosia illustrata (Diptera: Syrphidae).............. .....100 3. The Influence of Insect Herbivores on the Population Biology of Hogweed.................... 101 3.1 Introduction................... 101 3.2 Methods....................................................... ..................................................................... 104 3.2.1 Hogweed population studies........................................................10,4 3.2.2 Growth and development of plants of a known weight.............105 3.2.3 Defoliation and defloration experiments..............................106 3.2.3.1 Defoliation experiment 1982..........................................106 3.2.3.2 Defol iation experiment 1983................................. i ............ 107 3.2.3.3 Defloration experiment................................ ........ : ........ ..107 3.2.4 Germination experiments............................................... 108 4 3.2.5 Insect damage and plant density experiment.......................... I l l 3.3 Resul ts ............................................................................................... 117 3.3.1 Hogweed population studies........................................................117 3.3.2 Weighed plants............................................................................. 125 3.3.3 Defoliation and defloration...................................................... 12? 3.3.3.1 Defoliation experiments.................................... 12? 3.3.3.2 Defloration experiment..........................................................133 3.3.4 Germination experiments............................................................. 136 3.3.5 Factorial experiment of the effect of plant density and insect damage levels on plant reproduction...................14? 3.4 Discussion..........................................................................................158 4. The Population Dynamics of some Hogweed Insect Herbivores and Studies of the Competitive Interactions between them.......... 168 4.1 Introduction................................... 168 4.2 Methods............................................................................................... 173 4.2.1 Monitoring the hogweed herbivore community...........................173 4.2.2 Insect culturing and studies of population parameters......