Aspects of the biology and growth of three species of Ectobius (Dictyoptera: Blattidae). by Valerie Kathleen BROWN, B.Sc.(Lond.), A.R.C.S. Thesis submitted for the Degree of Doctor of Philosophy November 1969 Imperial College of Science and Technology, Silwood Park, Sunninghill, ASCOT, Berkshire. -1- ABSTRACT This thesis concerns three species in the genus Ectobius Stephens which occur in Britain. The basic life histories of the species are clarified and several biological topics are considered in more detail. Aspects of the oviposition behaviour in mated and unmated females and the extent of parthenogenesis in the species are investigated. The oothecae pass the winter in a state of dormancy which has been confirmed as a diapause in Ectobiuslayponicus. (Linnaeus). Oothecae are subject to attack by the Evaniid parasite, Brachygaster minutus (Olivier); the life history of this species is considered in relation to that of the host. The overwintering behaviour of the nymphal instars of E. lapponicus and Ectobius 1,allidus (Olivier) in a range of intermediate instars has been found to involve a diapause in the former species. The relationship between the proportion of nymphs entering the winter in each instar and the nature of the adult emergence the following summer is discussed. The post-embryonic growth of two species with different life cycles, E. lapponicus and Ectobius panzeri Stephens, is considered mainly from an analytical standpoint. A means of determining the sex of the nymphal instars is described and thus permits a more detailed study. The post-embryonic development is analysed by several techniques, each of which is applied to a large number of characters. Dyar's Law (1890) and its extension by Richards (1949) are assessed. A detailed appraisal of simple allometry of growth, including alternative methods of deriving the constants and a full range of significance tests, is made. However, emphasis is focused on the more sensitive multivariate techniques which have only recently been applied to animal growth. In this work, for the first time, several of the available techniques, including a generalisation of the allometry equation, are applied to the same body of data, thereby enabling an evaluation of these methods in the study of insect growth. -2- TABLE OF CONTENTS. Page ABSTRACT 1 TABLE OF CONTENTS 2 GENERAL INTRODUCTION 7 GENERAL MATERIALS AND METHODS (i) Collecting Methods 8 (ii)Culture Methods 10 SECTION A: THE BIOLOGY OF ECTOBIUS SPECIES Introduction and Review of Literature 17 Introduction to the Biology of the Species (i) General a. Life History 23 b. Habits 26 (ii) Habitat Preference a. List of Collecting Sites 29 b. Description of Habitats 31 c. Overwintering Sites 33 SELECTED BIOLOGICAL TOPICS I. REPRODUCTIVE BIOLOGY 36 (i) Aspects of Oviposition in Mated and Unmated Females under Natural and Controlled Conditions and the Hatching of the Resultant Eggs a. The Number of Oothecae Deposited 39 b. The Preoviposition Period 41 c. The Interval between the Deposition of Oothecae 43 d. The Number of Eggs per Ootheca 44 e. The Weight of the Ootheca 46 -3- Page f. The Size of the Ootheca (i) Length 48 (ii)Width 50 g. The Period of Retention of the Ootheca 51 h. The Direction of Rotation of the Ootheca 53 i. The Method of Deposition of the Ootheca 57 j. The Percentage of Oothecae which Hatch and the Number of Nymphs which Emerge from an Ootheca 58 (ii) The Longevity of Mated Males and Females 62 II. THE EGG STAGE (i) Description of the Ootheca 64 Key to the Oothecae of the British Species of Ectobius 70 (ii)Determination of Diapause in the Oothecae of E. lapponicus 71 (iii)Water Relations of the Oothecae 86 (iv)Hatching and Description of Pronymph 93 III. OVERWINTERING OF THE NYMPHAL INSTARS 98 (i) Field Collections of Nymphal Instars 99 (ii)Overwintering Behaviour of Nymphs in an Outdoor Insectary 100 (iii)The Occurrence of an Abnormal Instar under Experimental Conditions 102 (iv)Determination of Diapause in the Nymphs of E...lapponicus 103 (v) The Effect of a Short Day Regime on the Nymphs of E. lapponicus 110 (vi)Relationship between the Overwintering Stages and Adult Emergence 113 Page IV. BIOLOGY OF THE EGG PARASITE, BRACHYGASTER MINUTUS (OLIVIER) Materials and Methods a. Collecting Methods 119 b. Culture Methods 119 (i) Life History and Habits 120 (ii)Mating 123 (ii) Oviposition 124 (iv)Emergence 126 GENERAL DISCUSSION 130 SUMMARY OF THE BIOLOGY SECTION 137 SECTION B: THE GROWTH OF ECTOBIUS SPECIES Introduction and Review of Literature 140 Introduction to the Growth of the Species (i) Key to the Nymphal Instars of the British Species of Ectobius 154 (ii)The Development of the Genital Segments and their use in Distinguishing the Sexes 168 ANALYSIS OF GROWTH Materials and Methods 188 I. SUMMARY AND STORAGE OF DATA 193 II. DYAR'S LAW (i) Application of Dyar's Law 194 (ii)Application of Richards' Extension of Dyar's Law 198 (iii)Application of Przibram's Rule 203 -5- Page III. ALLOMETRIC ANALYSIS (i) The Choice of a Reference Dimension 208 (ii) Fitting the Allometric Equation 208 (iii) Significance Tests 220 a. The Significance of the Slope of the Line 221 b. The Significance of Deviations from a equal to Unity 221 c. The Significance of Deviations from Linearity 225 (iv) Growth Gradients 231 a. Growth Gradient in the Mid-Dorsal Line 232 b. Growth Gradient in the Mid-Ventral Line 234 c. Growth Gradient in the Legs 236 d. Growth Gradient in the Antennae 243 (v) Growth Contours 246 IV. MULTIVARIATE ANALYSIS (i) Eigenanalysis of Correlation Matrices Introduction to the Technique 257 Outline of Statistical Methods and Details of Programs utilised 258 a. The Correlation Matrix 258 b. The Latent Roots and Vectors of the Correlation Matrix 263 (ii) Principal Component Analysis Introduction to the Technique 276 Outline of Statistical Methods and Details of Programs utilised 277 a. Correlation Matrix 278 b. Log. Covariance Matrix 297 c. The Generalised Allometry Parameter 309 (iii) Factor Analysis 316 -6- Page (iv) Multiple Discriminant Analysis Introduction to the Technique 319 Test for Homogeneity of Covariance Matrices 320 Outline of Statistical Methods and Details of Programs utilised 321 a. Untransformed Data 322 b. Logarithmically Transformed Data 329 GENERAL DISCUSSION 346 SUMMARY OF THE GROWTH SECTION, including an Evaluation of the MethodS used in the Analysis of the Growth of Two Species of Ectobius 352 ACKNOWLEDGMENTS 356 REFERENCES 357 STATISTICAL APPENDIX 374 -7- GENERAL INTRODUCTION. Lucas (1920) in his monograph of British Orthoptera recorded three species in the genus Ectobius Stephens. These native species, Ectobius lapponicus (Linnaeus), the Dusky Cockroach, Ectobius pallidus (Olivier), the Tawny Cockroach and Ectobius panzeri Stephens, the Lesser Cockroach are the subject of this thesis. The thesis is presented in two sections. The first part is concerned with the general biology of the species. Very little is known to date of the biology of native, field-dwelling cockroaches, the wealth of literature on the Dictyoptera being centred around the cosmopolitan, domestic species. The second part of the thesis deals with the post-embryonic growth of two of the species, E. lapponicus and E. panzeri. Dyar's Law and the Law of Simple Allometry have in the past constituted the only analytical methods to be applied to growth data, and these were usually restricted to a limited range of characters in a single species. In the present work emphasis has been placed on the application of multivariate analyses to the growth of the species; a field which seems very well suited to these more sensitive techniques. This is, to some extent, an exploratory study in which several separate analyses are applied to a wide range of characters measured on two closely related species. -8- GENERAL MATERIALS AND METHODS. (i) Collecting Methods. The collection of specimens proved to be both time-consuming and tedious. Many collecting methods were attempted but only one or two were utilised when large numbers of insects were required. Generally E. lapponicus and E. pallidus were collected by similar methods, but different methods had to be adopted for E. panzeri. Method 1. All developmental stages of both E. lapponicus and E. pallidus were collected in substantial numbers by lifting the dead, fallen fronds of bracken, Pteridium aquilinum (Linnaeus) Klihn, and inserting a metre square beating tray under them. The fronds were then gently shaken, and the debris on the beating tray sorted. The bracken had to be dry for this method to be efficient. This means of collection became totally impractical once the young bracken shoots commenced the new season's growth. Method 2. An equally good procedure was the beating of low-lying branches onto a beating tray. This was particularly effective when grass blades mingled with the lowermost branches of trees and shrubs. Numerous specimens of E. pallidus were collected in this way from the branches of Viburnum lantana Linnaeus, and in particular Picea abies (Linnaeus)Karst, the Norway Spruce, yielded vast numbers of E. lapponicus. Moderate numbers of both.species were found on young branches of Quercus Linnaeus species, and all stages of E. lapponicus were found on young bushes of broom Sarothamnus scoparius (Linnaeus) Wimmer. Method 3. The most rewarding method for the collection of E. lapponicus and E. pallidus involved the "preparation" of the habitat and the revisiting of the site for collecting several days later. The preparation entailed lifting the dead grass from the cores of large tussocks. This could be efficiently performed by -9- thrusting a garden fork through the base of the tussock, just above ground level and drawing it vertically upwards, thus freeing the considerable quantity of dry, dead grass. The latter was condensed into a clump and placed back on the surface of the tussock.