M. Loosjes Institute of Phytopathological Research, Wageningen Ecology and genetic control of the onion fly, Delia antiqua (Meigen) qp Centre for Agricultural Publishing and Documentation Wageningen - 1976 Z 0 ( ( ?^ Abstract Loosjes, M. (1976) Ecology and genetic control of the onion fly, Delia antiqua (Meigen). Agric. Res. Rep. (Versl. landbouwk. Onderz.) 857. Pudoc Wageningen. ISBN 90 220 0611 5. (vii) + 179 p., 95 figs, 39 tables, 331 refs, Eng. and Dutch summaries. Also: Doctoral thesis Leiden and Meded. Inst, plziektenk. Onderz. 743 Literature data on the onion fly's biology are given. The field work on its ecology, relevant for genetic control, is reported, with an emphasis on dispersal. The methods used are discussed, especially marking the flies at emergence, releasing sterilized pupae dug in the soil, recapturing flies by flight interception traps, and sampling of pupae. Some data are given on the prediction of emergence, the incidence of diapause and Entomophthora infection of the flies. The distribution of damage and pupae can be descri bed by the negative binomial, and problems are encountered in estimating confidence intervals for the mean density. Densities of pupae normally are some 1 000 -20 000 per ha. From estimates of the life-span distribution of female flies and the frequency of oviposition phases the fecundity is estimated. Reproduction factors are found to be about 7 and 3 for the two flights, respectively. Dispersal is shown to be in general independent of the wind direction. Several methods of estimating a diffusion coefficient to describe the fly dis persal are applied. The best results are obtained by computer simulation with heterogeneity in time and space, yeilding 2 000 m /day in onion fields and 14 000 m^/day outside these. Dispersal is age dependent, occurring less in reproductive phases. The logarithm of the total number recaptured of the released group is about linearity related to the distance from the release site. Field trials on control by sterile males are described, and data on competitiveness and reproduction are given. In an onion growing area I ha treatment gave successful control. A release schedule for the practical application of genetic control to the onion fly is given with estimates for release site density, barrier zone depth, over- flooding ration, and optimal distribution of available steriles over the two flights and the subsequent years. For the Netherlands, an estimated mass-rearing output of 1.5 x 10^ competitive fly equivalents is needed. Free descriptors: Anthomyiidae, competitiveness, damage distribution, diapause, diffusion, Diptera, dispersal, flight interception trap, release strategies, reproduction, sampling methods, simulation, sterile insect technique. ISBN 90 220 0611 5 The author graduated as Doctor of Science at the State University of Leiden, the Nether lands, on a thesis with the same title and contents, on 15 December 1976. © Centre for Agricultural Publishing and Documentation, Wageningen, 1976. No part of this book may be reproduced and/or published in any form, by print, photoprint, microfilm or any other means without written permission from the publishers. Contents 1 INTRODUCTION ' 2 INTRODUCTORY DATA ON THE ONION FLY AND ITS CONTROL 3 2.1. GENERAL BIOLOGY 3 2.1.1 Taxonomy 3 2.1.2 Morphology 3 2.1. S Geographical distribution 7 2.2 ECOLOGY 8 2.2.1 Life cycle 8 2.2.2 Population dynamics 10 2.2.3 Niche 11 2.3 ONION GROWING AND PEST CONTROL 13 2.3.1 Onions in the Netherlands 13 2.3.2 Damage 14 2.3.3 Pest control 17 2.4 SUMMARY 19 3 ENVIRONMENT AND DISCUSSION OF MATERIALS AND METHODS 21 3.1 ENVIRONMENT 21 3.1.1 Experimental area 21 3.1.2 Weather 24 3.2 FLIES USED FOR THE EXPERIMENTS 26 3.2.1 Mass rearing 26 3.2.2 Sterilization 27 3.3 DISCUSSION OF METHODS 28 3.3.1 Marking 28 3.3.1.1 Marking larvae 28 3.3.1.2 Marking emerging flies 29 3.3.1.3 Marking by sterilization 30 3.3.1.4 Wing vein aberrations 31 3.3.1.5 Size 31 3.3.2 Releasing 32 3.3.2.1 Releasing pupae 32 3.3.2.2 Releasing flies \ 35 3.3.3 Trapping flies 36 3.3.3.1 Flight interception traps 36 3.3.3.2 Attraction 39 3. S.4 Obtaining eggs 41 3.3.5 Sampling flies, larvae and damage 42 3.3.6 Sampling pupae 43 3.3.7 Fly inspection 46 3.3.8 Field observation of fly behaviour 47 3.4 SUMMARY 48 50 ONION FLÏ ECOLOGY 50 4.1 LIFE CYCLE 4.1.1 Prediction of emergence •)" 4.1.2 Flight curves •" 4.1.3 Incidence of diapause •'•' 4.1.4 Number of flights 58 4.2 NICHE 59 59 4.2.1 Oviposition site 62 4.2.2 Larval and adult food 63 4.2.3 Parasitoids 4.2.4 Entomophthora "^ 66 4.2.5 Predators 67 4.3 ESTIMATION OF DAMAGE INTENSITY AND POPULATION DENSITY 67 4.3.1 Damage intensity 67 4.3.1.1 Damage pattern 4.3.1.2 Distribution of damage 70 4.3.1.3 Precision estimation 73 4.3.1.4 Plot size 74 4.3.1.5 Damage frequency in time 4.3.2 Pupal population density ^ 4.3.3 Fly population density 78 4.3.4 Relation between density and damage 83 4.4 MORTALITY 83 4.5 REPRODUCTION 87 4.5.1 Mating 87 4.5.2 Oviposition 89 4.5.3 Reproduction factor 92 4.6 SUMMARY 93 DISPERSAL 95 5.1 PRELIMINARY DISPERSAL EXPERIMENTS 95 5.2 FACTORS AFFECTING DISPERSAL 96 5.2.1 Weather and onions 96 5.2.2 Barriers 99 5.2.3 Passive dispersal 100 5.2.4 Fly properties 101 5.3 DIFFUSION 102 5.3.1 Introduction 102 5.3.2 Calculation of diffusion coefficient from field observations of fly behaviour 103 5.3.S Calculation of diffusion coefficient from release-recapture experiments 105 5.4 DISPERSAL SIMULATION 107 5.4.1 Simulation model 107 5.4.2 Analysis of a release-recapture experiment 109 5.5 NUMBERS VERSUS DISTANCE 113 5.6 AGE-DEPENDENT DISPERSAL 119 5.6.1 Trapping place versus age 119 5.6.2 Age distribution of immigrating flies 122 5.6.3 Dispersal with regard to genetic control 123 5.6.4 Migrated fractions of reproducing populations, in relation to distance 126 5.7 SUMMARY 126 6 GENETIC CONTROL 129 6.1 FIELD TRIALS AT THE SCHUILENBURG 129 6.1.1 Introduction 129 6.1.2 Reproduction 131 6.1.3 Competitiveness 132 6.2 GENETIC CONTROL FIELD EXPERIMENT ON OVERFLAKKEE 134 6.2.1 Introduction 134 6.2.2 Fly sterility 136 6.2.3 Competitiveness 139 6.2.4 Egg sterility 141 6.2.5 Damage 143 6.2.6 Sampling of pupae 143 6.2.7 Reproduction 144 6.3 A NORMALIZED FIELD EXPERIMENT 146 6.4 RELEASE STRATEGIES 147 6.5 SUMMARY 153 7 CONCLUDING REMARKS 154 7.1 DISPERSAL 154 7.2 PEST SITUATION 154 7.3 GENETIC CONTROL 155 SUMMARY 158 SAMENVATTING 160 ACKNOWLEDGMENTS 163 REFERENCES 164 APPENDIX 177 1 Introduction The main insect pest of onions in temperate regions of the northern hemisphere is the onion fly, Delia antiqua (Meigen) (e.g. Hennig, 1953; Balachowski & Mesnil, 1935; Essig, 1926; Miller, 1956; Metcalf & Flint, 1962). It may destroy up to 50-1004 of the crop. Effective chemical control measures have been developed and applied mainly during the past few decades (Dustan, 1938; Wright, 1938; McLeod, 1946; Maan, 1947). Research on the onion fly has been done on its general biology (e.g. Eyer, 1922; Kästner, 1929b; Isaev, 1932; Maan, 1945; Miles, 1956, 1958a; Rygg, 1960; Perron and co workers, 1951-1972; Ellington, 1963) and on special aspects like laboratory rearing (Friend & Pattern, 1956; Friend et al., 1957, 1959; Allen & Askew, 1970), attractants (Peterson, 1924; Matsumoto & Thorsteinson, 1968a, 1968b; Matsumoto, 1970) and reproduction (Missoimier & Stengel, 1966). A bibliography has been given by Scott (1969), more selected references are found in Hennig (1974). Literature compilations on its life history have been made by Beirne (1971) and Schnitzler (1967). Development of resistance against pesticides used (Howitt, 1958; Anonymous, 1967; Brown, 1974) and the hazards that pesticides constitute for the environment caused re search to be started aiming at the development of genetic control of the onion fly in the Netherlands (Noordirik, 1966) and also in Canada (McClanahan & Simmons, 1966; McEwen et al., 1973). The method of genetic control was first applied by Knipling (1955), Baumhover et al. (1955) and Lindquist (1955). The development of the genetic control method has been reviewed by Proverbs (1969), Smith & von Borstel (1972) and Whitten & Foster (1975). The ordinary type of genetic control is the sterile insect technique or sterile male technique. By release of sterilized males of the same species in high numbers, the possi bility of a wild female to mate with a wild male is lowered to the extent that the average number of reproducing offspring per female is less than two, resulting in a population decline. Other possibilities of genetic control are based on more subtle genetic manipu lations, like induced chromosome rearrangements. This report contains the ecological part of the research for the development of ge netic control of the onion fly in the Netherlands, carried out by a research team at Wageningen. Other aspects examined by this research team are: - mass rearing (Ticheler & Noordirik, 1968; Ticheler, 1971; Noorlander, in prep.), - sterilization (Ticheler & Noordink, 1968; Noordink, 1971), - use of radioisotopes (Noordink, 1971), - histopathology (Theunissen, 1971, 1973a, 1973b, 1976), - sterile-male field trials (Ticheler et al., 1974a; Theunissen et al., 1974, 1975), - chromosome rearrangements (Wijnands-Stäb & van Heemert, 1974; Robinson & van Heemert, 1975; van Heemert, 1973a, 1973b, 1975; Vosselman, in prep.), 1 - simulation of control strategy (Wijnands-Stäb & Frissel, 1973). The team's research on the sterile insect technique and general aspects is reported in: Jaarverslag Instituut voor Plantenziektenkundig Onderzoek 1964 (1965) and following, and more condensed in Annual Report Institute for Phytopathological Research 1972 (1973) and following. The genetic research part is covered by: Application of atomic energy in agriculture, Annual report 1969 association Euratom-ITAL (1970) and following. Together these data can be found in: Commission of the European Community Euratom, Annual report 1971, programme biology - health protection, Luxembourg (1972) and subsequent issues. The aim of the study was to provide data on the ecology of the onion fly, necessary for application of genetic control, and to investigate the feasibility of genetic control under normal field conditions. At least partly because of this programme, and because of the limited manpower made available, the data presented are a somewhat unbalanced account of the onion fly's biology. Especially the data on the life cycle and niche are limited to mere incidental observations. More details are presented on densities and reproduction, as these aspects are closely linked to the dispersal which is the main object studied. Reproduction and mortality were not chosen as the main object because investigations in change of population size have to start by delimiting populations and measuring the degree of exchange among them. Also, the experimental analysis of population dynamics is rather laborious, whereas the data relevant in a sterile male control program can be ob tained from only executing and analysing pilot projects with sterile releases, as pointed out by for example Lindquist (1969) and Weidhaas (1973). The data collected, especially those from a pilot experiment, are used to provide an outlook on the practical application of sterile males in Dutch onion growing. As the research on chromosomal rearrangements is not yet in a field testing stage, the field work will be considered only in relation to the sterile insect technique. The experiments were carried out from 1970 to 1974. The field work was done mainly on the former island of Overflakkee in the SW of the Netherlands, with a base at the Foundation Dutch Onion Federation (SNUiF) at Middelharnis. The laboratory experiments were done at the Institute for Phytopathological Research (IPO) at Wageningen. Also some of the data obtained from a series of field trials on control by sterile males at the experimental farm 'the Schuilenburg' near Wageningen (Ticheler et al., 1974a; Theunissen et al., 1974, 1975) are included in this report. 2 Introductory data on the onion fly and its control 2.1 GENERAL BIOLOGY 2.1.1 Taxonomy The onion fly is a dipteron, belonging to the family Anthomyiidae. The synonyms cur rently in use are Chortophila antiqua (Meig.), Delia antiqua (Meig.)» Phorbia antiqua (Meig.), Hylemya antiqua (Meig.) and Hylemyia antiqua (Meig.). The last is a later cor rection of the orthographical mistake in Hylemya. Following the recent revision of the Anthomyiidae (Hennig, 1974), Delia is used here. In earlier publications of the onion fly research team Hylemya has been used because of its predominance in international use. In earlier applied entomological literature also the following synonyms occur: Anthomyia antiqua Meig., A. ceparum Meig., Hylemyia cepetorum (Meade), H. ceparum (Meig.), Pegomyia cepetorum (Meade), P. ceparum (Meig.), Phorbia cepetorum Meade, P. ceparum (Meig.) and Leptohylemyia antiqua (Meig.). 2.1.2 Morphology Adult The species Delia antiqua can mostly be identified from its general appearance (Fig. 1): its size, its olive grey (males) or slightly yellowish grey (females) dorsal part of the thorax which is practically unstriated, and the general shape of the male genitalia in side view. In case of doubt the following characteristics can be used. Males have a typical irregular row of relatively short hairs on the tibia of their 3rd leg, at the medial-caudal side (Fig.2). Females have two hairs at the lateral-rostral side of the 2nd tibia, whereas most resembling species have only one hair there. Resembling species with two hairs there have the pre-alar hair on the thorax as long as the other thoracical hairs, in contrast to the onion fly and several of its relatives where it is only half as long (Fig. 3). The main sex differences are, apart from the thorax colour and the other characteris tics mentioned, the abdomen (males: slender, with a black longitudinal line, external ge nitalia; females: rounded, light grey) and the size of the eyes (males: eyes nearly tou ching each other; females: eyes clearly separated). For a more detailed description of the adult male morphology, and figures of the male genitalia, see Hennig (1974). For the morphology of the related bean seed flies, D. platura and D. florilega, see Hennig (1974) (males) and Ageeva (1968) (males and fe males) . The determination characteristics mentioned are rather variable. Once a male onion fly Fig. 1. Onion fly adult. Right male, left female; on top dorsal view, below side view;x6|. was found without its left prealare hair. The number of hairs on the female tibia-2 ran ged from 1 to 4. Rarely the upper one of the two 'normal' hairs was absent. At either side of this pair of hairs an additional smaller hair could occur. Several aberrations in wing veins were found. These were mostly appendages and thick enings of the cross veins. They occurred in different populations with frequencies of 5-251. Similar aberrations have been described for the onion fly by Saager (1959) and for several related species by Sick (1967) in frequencies of 0.01-4.351. 4 Fig. 2. Male onion fly, ventral view of right 3rd leg, x20. Fig. 3. Onion fly, side view of thorax with pre-alar hair indicated, *20. The laboratory rearing of the onion fly usually produced a few percent of aberrant males. These had characteristics intermediate between the males and the females: the eyes were separated but not as much as in the females, and the shape of the abdomen was inter mediate. Reduced male external genitalia were present. They contained testes and no Ova ria. In wild populations 3 such males were found among 7057 individuals. A similar onion fly was mentioned by Tiensuu (1935), also reared in a laboratory. Such aberrations in the sex expression have been mentioned for related species by Sick (1967), Hennig (1974, D. platura), and Smith (1971, 1972, D. brassicae). Sometimes a considerable fraction, up to 20%, of the laboratory reared females had a misformed ovipositor: it could hardly be extruded. The ovaries of these females only de veloped until the start of yolk formation (Theunissen, 1973a: stage S5). Also they did not mate. Egg The egg is 1.1-1.3 mm long, whitish, and its chorion has a characteristic rim struc ture (Fig. 4). It is opened by the emerging larva along one of the sides of the suture running along the rostral half. Eggs of D. platura are maximally 0.96 mm, significantly shorter than D. antiqua eggs (Miles, 1953; Dusek, 1969; Buth, 1976).