WAITI. INSTII'UTE à1.3. 1b t.IP,RÅRY THE ECoLOGY 0F THE GUM TREE SCALE ( ERI0COCCUS CORIACEUS MASK.), AND ITS NATURAL ENEMIES BY Nei'l Gough , B. Sc. Hons . A thesis submitted for the degree of Doctor of Philosophy in the Faculty of Ag¡icultural Science at the UniversitY of Adelaide. Department of Entomoì ogY' l^laite Agricultural Research Institute' Unj versi ty of Adelaide. .l975 May 't CONTENTS Page SUMMARY viii DECLARATION xii ACKNOl^lLEDGEMENTS xiii 1. INTRODUCTION I l 1 I Introduction I 2 Histori cal information 1 4 1 3 The study area tr I 4 The climate of Ade'laide 6 1 5 A brief description of the biology of E. coriaceus l 6 Initial observations 9 1.64 First generations observed 9 1.68 The measurement of causes of rnortality to the female scale and of the ìengths of the survivors l0 'l .6C Reproduction by the female scale. November 1971 t3 'l .6D The estimation of the number of craw'lers produced '15 in the second generation. November and December l97l l.6E The estimation of the number of nymphs on the tree l6 'l 7 Conc'lus ions f rom the 'i ni ti al observati ons and general p'l an of the study 21 2 ASPECTS OF THE BIOLOGY OF E. CORIACEUS 25 2 .t Biology of the irmature stages 25 2.1A The nymphal stages 25 2.18 The ínfluence of the density of nymphs on their rate of sett'ling 27 2 .2 The adult female 30 2.2A The adul t femal e sett'l i ng patterns 30 2.28 The distribution of the colonies on the twigs 30 2.2C Settl ing on the leaves 33 2.20 Seasona'l variation in the densities of the co'lonies of femal es 33 11. Page 2.28 Possible reasons for the formation of co'lonies 34 2.2F Natura'l mortality to the adult female under f avourab'l e condi ti ons 37 2.2G Number of generations a Year 38 2.3 Comments on fecundìty and reproduction 41 2.34 Fecundity and the influence of the length of the fema'le on the number of young produced 4'l a. Materials and methods 4t b. Resul ts 43 '1973 2.38 Reproduction in the fie'ld, July - August 45 2.3C Seasonal variation in the length of the fema'le sca'le at the time of reProduction 49 2.4 Seasonal variation in the sex ratio of the young 52 2.4A A discussion of the methods of sex determinat'ion in cocci ds 53 2.5 Life history of the male 56 2.5A Genera'l b'io1 ogY 56 2.58 Wing forms in the male 58 3. POPULATION DYNAMICS OF E. CORIACEUS 62 3.'l Sampling ìn the field 62 3.14 Populations samPled 62 3.18 Methods for an accurate estimation of the number of adu'lt female scale in a population 64 3.'l C The devel opment of a sampl i ng p1 an 65 3.lD The area of the coìonY 65 3.'lE The densjty of the females in the co'lony 66 3.tF The size distribution of the basic sampìing units 67 3.'lG The estimation of sample size for a certain error 70 3.'lH The inspection of the tree 73 3.lI Further comments on the estimation of the dens'ity of co'lonies 73 111. Page 3.lJ Sampling for populations of scale on leaves 74 3.1K The timing of sampì'ing to determine survivaì of females and causes of mortalìtY 75 3.2 Trends in the numbers of female scale 77 3.24 Analysis of numbers of females. August 1971 March 'l973 78 3.28 Analysis of indices of population trend. August l97l - March '1973 80 3.3 Survival of the female scale and the causes of rnorta'lity 83 3.34 Trends Ín the survival of the female scale at the time of reproduction 83 3.38 Causes of morta'lity to the fema'le scale 84 3.3C The natural enemies 85 3.30 Seasonal variation in the causes of mortality 86 3.4 Seasonal va¡iation in the fecundity of the fema'le scale 92 3.5 Concl usi ons 94 4. THE MUTUALISTIC RELATION SHIP BETWEEN ANTS AND E. CORIACEUS 96 4. I Introduction 96 4.lA Honeydew of E. coliaceus 97 4.'lB The species of ants attending E. coriaceus 98 4.2 The influence of the attendance of ants on the rate of excretion of honeydew and the assimilation of nutrients by E. coriaceus 100 4.2A Introduction 100 4.28 Behaviour of ants and E. coriaceus when excreting honeydew l0l 4.2C The influence of ant attendance on the rate of excretion of honeYdew 104 4.2D The influence of ant attendance on rate of growth 'l06 and fecunditY of E. coriaceus 4'.3 The influence of ant attendance on the surviva'l of E. coriaceus in the field 108 1V. Page 4.3A Resul ts 112 4.38 The influence of ant attendance on surviva'l and '113 extent and causes of mortality a. Survi val I 1 3 b. Mortality caused by natura'l enemiesr especial'ly 'l 'l cocci nel 'l i ds 3 c . SummarY l'l 4 4.4 The numbers of attending ants 115 4.4A Ant attendance in the maior experiment 115 4.48 The relationship between numbers of scale and '116 numbers of ants more clearly defined 4.4C Comparison of survival in small and large attended 'l popu'l ati ons 1 7 4.5 The interactions between ants and predators, especially 't &. ventrali s 19 4.54 Resume of the life hìstorY of Rhizobius ventralis 119 4.58 The diurnal rhythms of activity in Rhizobius ventralis 't9 and Iridomynnex s p. B ì 4.5C An t attack on Rhizobius ventralis 122 a. Dawn on a cool morning 123 b. Noon 123 123 c. N'i ght 4.5D Significance of the protective effect 125 4.5E Influence of ants on the survival of larvae of R. ventralis and Chrysopa rglrburi 127 4.6 Survival of the nymphs of E. coriaceus produced by the females studied in 4.3 128 4.7 Factors influencing nocturnal attendance by I ri domvrmex 'l3l sp. B 4.8 Di scussi on t34 .CORIACEUS t37 5 THE NÀTURAL ENEUIES OF E: V Page 5..| I n trodu ct i on 137 't37 5.2 Neuroptera: ChrysoPidae: Chrvsopa ramburi Schneider 't40 5.3 Coleoptera: Coccinel I idae 5.34 Rhizobius ventra'lis Er. Introduction 142 5.38 The life history of R. ventralis 144 a. The egg 144 b. The larvae 144 c. The pupa 146 d. The adult t46 5.3C Rate of devel opment of R. ventra'l i s 147 5.3D The influence of the size of the female scale on feeding and ovi posi tion by R. ventra'li s t49 5.3E Comments on the seasonal occurrence of R. ventralis with observations made in the experiment on the protective influence of ants 152 a. The increase in numbers of adult R. ventralis in October 1972 154 b. Dec'li ne i n numbers of adul t R. ventral i s i n 't55 November 1972 c. The di sappearance of adu'lt &. ventral i s 157 5.3F The relationship between the initial number of 't6t sca'le per tree and the number of adult R. ventralis 5.3G The influence of the size of the population of E-. coriaceus on the percentage of the sca'le killed by cocci ne] I i ds 162 '163 5.4 Di ptera 5.44 Syrphi dae: Mel angyna ( Austros hus sp. near '163 demastor ( wa I ter) 5.48 Chamaemyi i dae: Pseudol eucopi s benefi ci a Ma] I . 163 5 .5 Lepidoptera 165 5.5A Stathmopo didae: Stathmopoda me'l anochra Meyr. 165 5.58 Noctuidae: Gatobtemma dubia (gutl . ) Catoblenrna mesotaenia Turn. 168 vi. Page 5.5C Cyclotornidae: Cyclotorna sp. near egena Meyrick 175 5.6 Hymenoptera 176 5.64 Encyrtidae: APhYcoPsis sPP. 177 5.68 Eri apo rinae: Myiocnema s p. t78 5.6C Encyr tídae: Cheiloneurus s p. 179 5.6D Encyrtidae: Quaylea sP. 179 5.6E Unidentified species 180 't81 5.7 Arachni da 5.74 Araneida t8l 5.78 Acarina 18'| 5.8 The influence of colony sìze on the survival of E. coriaceus and the extent and causes of mrta'lity 182 6. INTRA-SPECIFIC MECHAN ISMS AND THEIR IMPORTANCE IN THE ECOLOGY OF E. CORIACEUS 184 6. t Ini ti a'l observati ons 185 6 .'lA Emi grati on of the mobi 1e stages 185 6.18 The influence of population density on the size of the fema'le scale at the time of reproduction 185 6.1C The influence of popuìation density on the sex ratio of the Young Produced 187 6.1D The influence of co'lony density on the fecundity 't88 of the females 6.2 The experimental examination of certain consequences of crowdi ng 190 6.2A Methods 19'l 6.28 Resu'lts t95 a. The influence of the initia'l numbers of second instar fema'les on those remaining and sett'ling as adult females 195 b. The influence of density of fema]e second stage nymphs on mean length of adu'lt fema'les derived from them 196 vii. Page c The influence of popu'lation density on tree growth 200 d The inf'luence of population density on the sex ratio of the young from the reProductive femal es 201 e The influence of the number of female second instar nymphs on the density of the female col oni es 202 6.3 Discussion 203 7.