POPULATION ECOLOGY AND INTEGRATED MANAGEMENT OF SOFT WAX SCALE (CEROPLASTES DESTRUCTOR) AND CHINESE WAX SCALE (C. SINENSIS) (HEMIPTERA: COCCIDAE) ON CITRUS A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University Peter L. La Lincoln University 1994 Abstract of a thesis submitted in partial fulfilment of the requirements for the Degree of Ph.D. POPUlATION ECOWGY AND INTEGRATED MANAGEMENT OF SOFT WAX SCALE (CEROPLASTES DESTRUCTOR) AND CHINESE WAX SCALE (c. SINENSIS) (HEMIPTERA: COCCIDAE) ON CITRUS Peter L. La Soft wax scale (SWS) Ceroplastes destructor (Newstead) and Chinese wax scale (CWS) C. sinensis Del Guercio (Hemiptera: Coccidae) are indirect pests of citrus (Citrus spp.) in New Zealand. Honeydew they produce supports sooty mould fungi that disfigure fruit and reduce photosynthesis and fruit yield. Presently, control relies on calendar applications of insecticides. The main aim of this study was to provide the ecological basis for the integrated management of SWS and CWS. Specific objectives were to compare their population ecologies, determine major mortality factors and levels of natural control, quantify the impact of ladybirds on scale populations, and evaluate pesticides for compatibility with ladybirds. Among 57 surveyed orchards, SWS was more abundant than CWS in Kerikeri but was not found around Whangarei. Applications of organophosphates had not reduced the proportion of orchards with medium or high densities of SWS. Monthly destructive sampling of scale populations between November 1990 and February 1994 was supplemented by in situ counts of scale cohorts. Both species were univoltine, but SWS eggs hatched two months earlier than those of CWS, and development between successive instars remained two to three months ahead. The start of SWS crawler emergence varied by seven weeks between 1988- 1993. A linear relationship between scale size and fecundity was found for both species. The variation in mean scale size amongst orchards corresponded to large differences in egg production. ii Survivorship curves and life tables were compared between populations with high and low levels of ladybird predation. Over 90% of crawlers failed to settle. At four orchards with high numbers of ladybirds, 99% of settled first and second instar scales died. The key mortality factor occurred at this stage where ladybirds were abundant. In contrast, where ladybirds were scarce, mortality of first and second instar scales was approximately 82% and some scales survived to breed. Mortality of third ins tar and adult scales was approximately 80% and 50% respectively. Parasitised scales were incubated and parasitoids identified from emerged adults. Diseased scales were cultured to identify fungal entomopathogens. One primary and one secondary parasitoid (Euxanthellus philippiae Silvestri and Coccidoctonus dub ius (Girault) respectively) and two fungal pathogens (Verticillium lecanii (Zimmermann) Viegas and Fusarium spp.) attacked one or both of these stages of SWS and CWS. Parasitoids and pathogens each caused less than 30% mortality. Density-dependent mortality was not shown by any of the natural enemies. The effect of ladybirds on scale popul~tions was assessed by sampling and experiments where branches and trees were covered to exclude or include ladybirds. Ladybirds predated first and second instar scales and could reduce local scale populations to extinction. Both larval and adult steel blue ladybirds (SBL) Halmus chalybeus (Boisduval), Rhyzobius forestieri (Mulsant), and adult Cryptolaemus montrouzieri Mulsant and Rodolia cardinalis (Mulsant) fed on SWS in laboratory experiments. Adult SBL and R. forestieri consumed approximately 15 scales per day in the field. SBL comprised 98% of ladybirds in visual and manual searches. Pesticides were screened for toxicity to SBL by a slide dip method, and for disruption to predation by the reduction in feeding on treated leaves. Fungicides and insecticides inhibited feeding by SBL and reduced their numbers. Copper-based fungicides reduced predation by about 80% compared with approximately 30% by non-copper fungicides. Buprofezin was non-toxic and non-disruptive to SBL. Mineral oils were moderately toxic but caused some disruption to predation. Organophosphates, synthetic pyrethroids and an insecticidal soap were highly toxic to SBL at recommended label rates. Three fungicides were evaluated in an iii orchard. Both copper and non-copper fungicides reduced numbers of ladybirds. Nine-spray programmes reduced numbers more than 5-spray programmes. SWS were more abundant than CWS probably in part because their phenology made them less vulnerable to adverse environmental conditions and ladybirds. Currently, SBL are the key to biological control of SWS and CWS, but with present spray programmes particularly those involving organophosphates, ladybirds cannot be relied on to be sufficiently abundant at the right time of year to achieve control. Orchardists should avoid or reduce applications of copper fungicides during spring and summer to minimise disruption to predation of SWS by ladybirds. The introduction of parasitoids such as those which control SWS in South Mrica and Australia would complement the existing biocontrol from ladybirds and should be investigated. Keywords: soft wax scale, Ceroplastes destructor, Chinese wax scale, Ceroplastes sinensis, Coccidae, population ecology, biological control, integrated pest management, steelblue ladybird, Halmus chalybeus, parasitoids, fungal pathogens, fungicides, insecticides, citrus, New Zealand IV Acknow ledgements I am indebted to my supervisors Roddy Blank (The Horticulture and Food Research Institute of New Zealand), Bruce Chapman (Lincoln University) and David Penman (Lincoln University) for their advice and guidance throughout my research. I thank HortResearch (and prior to 1992, the Ministry of Agriculture and Fisheries Technology) for supporting this study. The New Zealand Citrus Planning Council generously provided financial assistance. Roger Barber (MAP Technology) was instrumental in setting up the project. Discussions with Andrew Beattie (Biological and Chemical Research Institute, New South Wales) helped with my initial planning. John Waller and David Saville (New Zealand Pastoral Agriculture Research Institute) assisted with the statistical analyses. The thesis has benefited greatly from the comments of my supervisors and Steve Wratten (Lincoln University). Many orchardists allowed me to collect samples of scales and ladybirds from their orchards. In particular, I thank Rick Curtis, Peter Fiske, Peter Hendl, Miles Hibbert-Foy, Lyn Rhodes, Murray Strang and John Willetts for setting aside parts of their orchards to allow me to conduct experiments. My colleagues at HortResearch, especially Murray Olson, Jean Kelly, Brya Tapper and George Gill have helped in many ways and provided cheerful encouragement throughout this study. The help of Hua Hock Goh (HortResearch) and Jo Berry (Landcare Research) in identifying entomopathogens and parasitoids respectively is gratefully acknowledged. Last but not least is my debt to Kay Clapperton for her support throughout this study and for thoroughly reviewing each chapter. v Contents Page Abstract ii Acknowledgements v Contents vi List of tables viii List of figures ix Chapter 1 INTRODUCfION 1.1 Citrus industry 1 1.2 Scale insects 2 1.3 Soft wax scale and Chinese wax scale 3 1.4 Methods of control 7 1.5 Integrated pest management 8 1.6 Aim and objectives 10 Chapter 2 POPULATION DYNAMICS OF SOFT AND CHINESE WAX SCALE 2.1 Introduction 11 2.2 Relative abundance 12 2.3 Phenology 14 2.4 Scale size and fecundity 20 2.5 Survival of scale populations 26 2.6 Life tables 29 2.7 Key factors and density-dependent mortality 36 2.8 Summary 40 Chapter 3 P ARASITOIDS AND DISEASE OF SOFT AND CHINESE WAX SCALE 3.1 Introduction 42 3.2 Parasitoids 43 3.3 Disease 47 3.4 Levels of mortality and density dependence 48 3.5 Discussion 52 3.6 Summary 55 VI Chapter 4 IMPACf OF PREDATION BY LADYBIRDS, P ARTICULARLY THE STEELBLUE LADYBIRD, ON SCALE POPULATIONS 4.1 Introduction 56 4.2 Ladybird species and their seasonal abundance 58 4.3 Vulnerability of scale instars to ladybird predation 63 4.4 Comparison between the densities of scales and ladybirds 67 4.5 Ladybird feeding rates 69 4.6 Do ladybirds reduce scale populations? 72 4.7 Summary 76 Chapter 5 EFFECfS OF PESTICIDES ON STEELBLUE LADYBIRDS 5.1 Introduction 78 5.2 Toxicity of pesticides to adult steel blue ladybirds 79 5.3 Pesticide disruption to predation of soft wax scale by steelblue ladybirds 82 5.4 Effect of field applications of fungicides on numbers of steelblue ladybirds 86 5.5 Discussion 89 5.6 Summary 92 Chapter 6 SYNTHESIS AND DISCUSSION 93 References 102 Appendices 111 Vll List of tables Table Page 2.1 Number of citrus orchards with various levels of abundance of soft and Chinese wax scale in October/November 1990, categorised according to whether organophosphate insecticides had been applied in the previous 12 months. 13 2.2 Annual degree-days above 120C for the year to November, and starting date of soft wax scale crawler emergence at Kerikeri. 18 2.3 Adult size, fecundity and egg size of soft and Chinese wax scale on citrus orchards, and ANOV A between orchards and years. 22 2.4 Life tables for soft wax scale on citrus at two orchards with low and high densities of ladybirds in Kerikeri, 1993. 31 2.5 Life tables for Chinese wax scale on citrus at two orchards with low and high densities of ladybirds in Kerikeri and Whangarei, 1992. 32 3.1 Number of parasitoids and percentage of each species in soft and Chinese wax scales collected in Northland, March 1991-February 1994. 44 3.2 Percentages of soft and Chinese wax scale infected with pathogenic fungi. 47 3.3 Correlation coefficients (r) for relationships between scale density and the percentages of parasitised and diseased scale on individual branches. 49 4.1 Percentage of larvae, pupae and adult ladybirds recorded on citrus orchards by visual searches, Northland, January 1991 - February 1994. 60 4.2 Comparison between number of ladybirds per tree recorded by manual and visual searches, and percentage of manual totals seen by visual searches.