THE BIOLOGY OF CONOMELUS ANCEPS (GERMAR) (HOMOPIERA : DELPHACIDAE). by G.H.L.Rothschild, B.Sc. A Thesis submitted in part fulfilment of the requirements for the Degree of Doctor of Philosophy in the University of London. May, 1962. Imperial College Field Station, Silwood Park, Sunninghill, Ascot, Berkshire. ABSTRACT. This thesis is divided into three sections. The first deals with the general biology of Conomelus, including the life history and descriptions of the immature stages. Sexual maturation of the adults and oviposition in relation to host plant characters, have been studied in detail. The internal and external effects of pipunculid and Strepsipteran parasites on adult hosts are described. The second section deals with the biology of the predators and parasites associated with Conomelus. Various species have been studied in detail, including a nymphal pipunculid parasite, two predatory mirid species, and a fungal egg parasite, the life histories of which were previously un— known. The seasonal occurrence of 91 species of predator in the rush plot is outlined, with reference to their association with Conomelus. The third section deals with studies on a Conomelus population between autumn 1959 and autumn 1961. Particular reference is made to the mortality factors affecting the egg, nymphal and adult stages, including parasitism and predation. The precipitin reaction has been used to evaluate predation in the field. Dispersal of nymphs, and brachypterous and macropterous adults, within and from the rush habitat, has been studied. TABLE OF CONTENTS. Page INTRODUCTION 1 SECTION 1. BIOLOGY OF CONOMELUS ANCEPS. Description of the stages 3 Habitat and host plants 5 Methods of rearing 9 Life history. (i) Egg stage 10 (ii) Nymphal stages 17 (iii)Adult stage 19 Sexual maturation 19 Effects of parasitism on the reproductive organs 30 SECTION 2, BIOLOGY OF THE PREDATORS AND PARASITES OF C.ANCEPS. Methods 43 Parasites of the egg stage 44 Parasites of the nymphal and adult stages 52 Predators of the egg stage 61 Predators of the nymphal and adult stages 65 SECTION 3. POPULATION STUDIES. Methods 76 Population estimates (i) Numbers of eggs 86 (ii) Numbers of nymphs 87 (iii) Numbers of adults.., 90 SECTION 3 CONT. Page, Estimates of mortality. (i) Egg mortality 92 Discussion 101 (ii) Nymphal and adult mortality 106 Discussion 133 Dispersal Methods 141 Nymphal movements 143 Adult movements 143 SUMMARY 154 PLATES 158 ACKNOWLEDGMENTS 177 REFERENCES 178 APPENDIX 184 INTRODUCTION The object of this work has been to study the biology of Conomelus anceps (Germar) and its predators and parasites. C.anceps feeds only on Juncus spp., and populations within a patch of Juncus are, therefore, self- contained and suitable for quantitative studies. Later discussion in Section 3 will, however, indicate the difficulties of sampling the rush habitat, and how these difficulties affect the estimation of delphacid and predator numbers. The only published account giving both biological and quantitative data for a delphacid species in the field is that of Kanervo (1957). This work on Delphacodes pellucida (Fab.) does not include any data on egg and nymphal populations or any estimations of predation. None of the other work is quantitative but deals almost entirely with the biology of the delphacids and their parasites, in particular the pipunculids and Strepsiptera. This literature includes the studies of Hassan (1939), Lindberg (1939), Morcos (1953) and Williams (1957). There are also numerous references to the sugar-cane delphacid Perkinsiella saccharicida Kirk. and its associated natural enemies - Perkins (1905 a, b, c, d, 1906 a, b, 1907). In 1961 the present author came across the unpublished work of Whalley (1958) on the homoptera associated with Juncus in North Wales, including various leafhopper species, C.anceps, Delphacodes fairmairei (Perris) and a jassid Tettigella viridis (L.). Whalley gives estimates of nymphal and adult populations and shows the effect of parasitism on the numbers of delphacids in the field. This author also deals with the biology of C.anceps, and in particular the egg stage. 2. Most other references to leafhopper populations deal with jassids of economic importance; these include the 'cork of Carter (1930), Hanna (1950), Mulla (1957), and Joyce (1961). In Finland KontKannen (1950) sampled leafhopper populations over a wide area to obtain data on the habitat preferences of over 20 species of delphacids and jassids. The present work on C.anceps is divided into three sections; the first deals with the biology of the delphacid; the second section deals with the biology of the parasites and predators; the third section includes the population studies and an account of the importance of the natural enemies; this is followed by a general discussion. This work was conducted at Imperial College Field Station, Silwood Park, near Ascot, from September 1959 until May 1962. 3. SECTION I. The biology of Conomelus anceps (Germar). Introduction. China (1950) has dealt with the nomenclature of this species listing the single British member of the genus as: Conomelus Fieber 1866 anceps (Germar 1821) limbatus (Fabricius 1794 nec Oliver 1791). Edwards (1896) describes the delphacid as Liburnia limbata (Fab.). Le Quesne (1960) states that the species is widespread and common on Juncus spp. in the British Isles, the remainder of Europe and North Africa. The only previous work on the biology of C.anceps is, firstly, that of Hassan (1939) who describes the egg and fourth inster nymph, and outlines the life cycle, and, secondly, Whalley (1958) who deals particularly with the egg stage. • Description of the stages. The Egg: Figured by Hassan (1939). Mean length 1.09 mm. (10 eggs), greatest width 0.22 mm.; elongate, curved, tapering towards the operculum. Chorion smooth, translucent. Yellow yolk body present at either pole depending upon the age of the egg. Nymphal stages: The present author has described the nymphal stages using measurements of head—width and femur—length to separate the instars. The characters cif the hind tibiae and tarsi used by Williams (1957) to separate nymphs of Perkinsiella saccharicida were also present in C.anceps. After 4. completion of these nymphal descriptions the author came across the unpublish- ed work of Whalley (1958) who also described the nymphs, using tibial lengths to separate the stages. The data in Table 1 show that measurements of head-width and femur-length are suitable for separation of the instars, no overlapping occurring at any stage; body-length, however, is rather variable. First instar (Plate 1, Fig.l): length 1.05 mm.; grey, inter- segmental areas, and foveae of he.ad and thorax, pale; median facial 'keels darker grey; legs pale grey with terminal part of femur, base of tibia and tarsal points dark; abdomen may be white or yellow ventrally; eyes reddish; hind tibiae and tarsus (Plate 2, Fig.l), tibia with four spines distally; tarsus is two-segmentedf with the first segment bearing four spines distally. Second instar: length 1.30 mm.; as first instar, but borders of thoracic and abdominal sclerites darker grey; hind tibia and tarsus (Plate 2, Fig.2), tibia bears two small spines, one basally and another in the distal one-third, largest tibial spur now articulated. Third instar (Plate 1, Fig.2): length 1.53 mm.; greyish-brown, with pale areas on abdominal tergites; eyes reddish-brown; hind tibia and tarsus (Plate 2, Fig.3), articulated tibial spine itself bears two to three small spurs, five non-articulated tibial spines distally; first tarsal joint also with five distal spines. Fourth instar: length 2.05 mm.; colouration as third instar, hind tibia and tarsus (Plate 2, Fig.4), articulated tibial spine bears four 5. to five spurs; second tarsal segment now has two to three median spurs. Fifth instar (Plate 1, Fig.3, 4): length 2.62 mm.; pale greyish,. brown, pale markings on most tergite ventral side of abdomen of female nymph white, and male nymphs yellow; nymphs can also be sexed by the terminal abdominal segments (Plate 2, Fig.6, 7); wing pads of macropterous nymphs (Plate 1, Fig.3) longer than brachypterous forms (Plate 1, Fig.4); hind tibia and tarsus (Plate 2, Fig.5), articulated tibial spine serrated for most of length; three tcrsal segments, the first bears five to six distal spines, and the second segment three to four spines. Adult: is described by Edwards (1896) and Le Quesne p960). Table 1. Nymphal measurements. Body-length Head-width Femur-length Instar Mean .Min. Max. Mean Min. Max. Mean Min. Max. First 1.05 0.77 1.20 0.31 0.27 0.35 0.15 0.15 0.17 Second 1.30 1.17 1.47 0.42 0.40 0.45 0.22 0.22 0.25 Third 1.53 1.27 1.70 0.52 0.50 0.55 0.31 0.30 0.32 Fourth 2,05 1.70 2.25 0.66 0.62 0.70 0.42 0.40 0.45 Fifth 2.62 2.45 2.90 0.85 0.80 0,90 0.60 0.60 0.65 Measurements in mm. (10 individuals of each instar). Habitat and host plants. The plOt studied in the present work is situated in an area of Silwood Park known as Pond Field. The centre of the field is 6. poorly— drained and supports a dense stand of Juncus, forming an area of 1267 square yards. Unlike the open tussock—growth of Juncus in better— drained pasture, the Pond field plot was covered by a uniform cover of rushes. The edges of the rush area merge with well—drained grassland and here the open Juncus tussocks are found. In the wettest parts of the plot the commonest plants are: Juncus effusus L. J.articulatus L. Stellaria alsine Grimm. The following species are found in other parts of the plot: Holcus lanatus L.