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Reproductive and developmental blology of Aleochara bilineata • Gyllenhal (Coleoptera: Staphyllnidae)
By
Marie-Jasée Gauvin
A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of requirements of the degree of Masters in Sciences •
Department of Natural Resource Sciences (Entomology) Macdonald Campus of McGiII University
Sainte-Anne-de-Bellevue t Québec, Canada August 1998
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Canad~ Abstract • M.Sc. Entomology Reproductive and developmental blology of Aleachar. bi/lneat. Gyllenhal (Coleoptera: Staphylinldae)
ln Quebec 11 840 kg of insecticides are used against the cabbaga maggot, Delia radicum L. (Diptera: Anthomyiidae) each year. lt is possible ta decrease this quantity of insecticide by using natural enemies such as fungi, nematodes, predators and parasitoids. Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) is a natural enemy of the cabbage maggot. Adults of this species are predators of eggs and larvae of cabbage maggot and the tirst instar larvae are ectoparasitoids of cabbage maggot pupae. A. bilineata oviposits its eggs in the soil, near plants infested with cabbage maggots.
Differences in size have been noted in the e9gs of A. bilineata. In insects • several factors can affect egg size. Certain females can oviposit smail trophic eggs which serve as food for emerging larvae or egg size can be affected by factors such as size and age of female, as weil as, food and host quality. These factors have baen studied in A. bilineata in order to determine the conditions that favor the production of small eggs. There is an increase in size and number of eggs oviposited by females that have access to food either with or without the presence of hasts. However, these eggs do not have a better hatching rate than eggs oviposited by unfed females. The age of females also affects the egg size laid.
A. bilineata eggs are hydropic (absorption of water from their environment) and increase in volume between 30 ta 50 hours of development. Using scanning and transmission electronic microscopy, the modifications in the egg envelope • morphology have baen followed during hydropy. The endochorion, which is very dense and regular bafore swelling, becomes fragmented after swelling forming a • mosaic pattern. Variation in larval weight may influence survival thus affecting the reproductive success of the temale. To evaluate the fitness of first instar larvae three parameters have bean used: longevity, walking rate and searching capacity in relation ta larval weight. Large larvae Iived longer, walked taster as weil as found and parasitized hasts more rapidly than small larvae. Based on these results we can conclude that large larvae have a better fitness than smalliarvae.
•
• ii Résumé • M.Sc. Entomologie Biologie de la reproduction et du développement chez Aleochars billneata Gyllenhal (Coleoptera: Staphylinidae)
Chaque année au Québec, 11 840 kg d'insecticides sont utilisés contre la mouche du chou, Delia radicum L. (Diptera: Anthomyiidae). Il est possible de diminuer cette quantité d'insecticides en utilisant des ennemis naturels comme les champignons. les nématodes, les prédateurs et les parasitoïdes. Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) est un ennemi naturel de la mouche du chou. Les adultes de cette espèce sont prédateurs des oeufs et des larves de la mouche du chou et le premier stade larvaire est un ectoparasitoïde des pupes de cette même mouche. A. bilineata pond ses oeufs sur le sol près des plants infestés par la mouche du chou.
• Des différences dans la taille des oeufs de A. bilineata ont été observées. Chez les insectes, plusieurs facteurs peuvent affecter le volume des oeufs. La femelle peut pondre des petits oeufs trophiques qui serviront de nourriture pour les larves qui auront émergé ou la taille des oeufs peut être affectée par la grosseur et l'âge de la femelle ou la qualité de l'hôte et de la nourriture. Ces facteurs ont été étudiés chez A. bilineata pour déterminer quelles sont les conditions qui favorisent la production de petits oeufs. Les femelles qui ont accès à la nourriture (en présence ou absence d'hôtes) pondent plus d'œufs et des œufs plus gros que les femelles non nourries. Par contre, ces œufs plus gros n'ont pas un meilleur taux d'éclosion que les petits œufs. L'âge de la femelle affecte aussi la grosseur des œufs.
Les oeufs de A. bilineata sont hydropiques (absorption d'eau durant leur développement) et, après 30 heures de développement, ils augmentent en • volume jusqu'à 50 heures. En utilisant la microscopie électronique à balayage et iii à transmission, nous avons observé les modifications à la morphologie des enveloppes de l'oeuf durant le phénomène d'hydropie. L'endochorion, qui est • très dense et régulier avant le gonflement, devient fragmenté à l'apparence d'une mosaïque après le gonflement.
La variation dans le poids des larves peut influencer leur survie et par le fait même affecter le succès reproducteur de la femelle. Pour évaluer le fitness des larves de premier stade. trois paramètres ont été utilisés: la longévité, la vitesse de marche et la capacité de recherche en relation avec le poids de la larve. Les grosses larves ont une longévité plus longue. marchent plus vite et trouvent et parasitent l'hôte plus rapidement que les petites larves. Donc, nous pouvons conclure que les grosses larves ont un meilleur fitness que les petites larves. •
• iv Remerciements • Acknowledgments e voudrais remercier mon directeur de recherche Dr Guy Boivin pour son J support, son expertise, sa disponibilité et surtout pour sa patience. Un énorme merci à Danielle Thibodeau du laboratoire d'entomologie d'Agriculture et Agro-alimentaire Canada (St-Jean-sur-Richelieu) pour son aide constante lors de mes expériences, avec mes élevages, pour sa disponibilité et pour son support. Merci beaucoup au Dr Lucie Royer pour m'avoir transmis ses connaissances en entomologie plus particulièrement sur Aleochara bilineata et de s'être montrée aussi disponible pour répondre à mes questions et résoudre mes problèmes.
n gros merci au programme de coopération scientifique et technologique U franco-québecois pour mon stage effectué à l'Université de Rennes 1 en France. Merci au Dr Jean-Pierre Nénon du laboratoire d'écobiologie des insectes parasitoïdes de m'avoir accueilli, de m'avoir supervisé dans mes • recherches au cours de ce séjour et d'avoir été et d'être toujours disponible pour mes questions. Merci à toutes les personnes qui m'ont permis de travailler efficacement et rapidement durant mon séjour: Joe Le Lannic (microscopie électronique à balayage), Jean-Paul Roland (microscopie électronique à transmission), Marie-Rose Allo (microscopie électronique à transmission et fixation des échantillons), Frédéric Obé (développement des photos prises en microscopie), Dr Xavier Langlet (photos utilisées dans cette thèse et pour nos discussions), Dr Georges Vannier et Dr Georges Chauvin pour leur discussion.
erci au Dr. Daniel Cormier pour m'avoir aidé dans mes analyses M statistiques, pour ses nombreux conseils et ses encouragements. Merci à Dr. Clément Vigneault pour s'être dévoué à adapter le programme d'analyse d'image pour la vitesse de marche des larves et ses nombreux • conseils. Merci à Bernard Panneton pour le programme d'analyse des données. v Merci à Laetitia Lainé et Nicole Simard pour leur aide durant mes expériences et pour avoir compilé les données sur ordinateur. Merci à François Fournier pour sa • disponibilité et la révision du chapitre 4.
hanks to Dr Robin K. Stewart from Natural Sciences Department at TUniversity of McGiII (Campus Macdonald) for his correction, help in English and his patience. Thanks to Marie Kubecki from Natural Sciences Department at University of McGill (Campus Macdonald) for her guidance and her patience.
erci à Annie Tardif pour avoir entendu et réentendu mes protocoles, mes M séminaires et les problèmes qui sont survenus durant ma maîtrise. Merci beaucoup pour son soutien, son temps et son ordinateur. Merci à Jean Marsolais pour son aide et sa compréhension, pour les derniers milles qui ont été difficiles. • erci à toute les personnes du laboratoire d'entomologie à Agriculture et M Agro-alimentaire Canada (St-Jean-sur..Richelieu) pour leur soutien et leurs encouragements (David Biron, Julie Frénette, Daniel Gingras, Claude Godin, Lise Lachance, Martine Lagacé, Caroline Roger, Josiane Vaillancourt).
n million de mercis à toute les personnes de ma famille et mes amis (es) U pour leur support, leurs encouragements et drayoir cru en moi. Merci à Roch Chenel, Isabelle Demers, Nancy Drolet, Ghislain Cubé, Etienne Gauvin, Harold Gauvin, Jonny Gauvin, Eve-Lyne Lamontagne, Mariette Lloyd (correction de l'anglais), Nathalie Massé, Karine Sergerie et tous les autres. Et finalement un énorme merci à ma petite maman (Ginet Gauvin) pour son support.
• À la vie...
vi • Table of contents Abstract i Résumé iii Remerciements (Acknowledgments) v Table of content vii List of figures xi List of tables xiv
1~1rFlc:»[)lJ<:TIc:»~ ..••••••••••.•••••••••••...... ••••••••••.•••••.•••....••.••••••••.••.•••.•.... 1 Thesis format 4 References 5
CHAPTER 1: LI1rERA1rURE REVIEW 6 1. Reproductive strategy in insect. 7 1.1 Investment in e9gs 7 • 1.1.1 Ice Box Hypothesis 7 1.1 .2 Egg size 9 1.1.3 Hydropy 10 1.2 Fitness of larva 12 2. Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) 14 2.1 Distribution and Iife history of Staphylinidae 14 2.2 Distribution and Iife history of Aleochara spp 15 2.3 Evolution of A/eochara spp. .. 16 2.4.Morphology and biology of Aleochara bilineata 17 2.4.1 Adult 17 2.4.2 Egg 19 2.4.3 First instar larva 20 2.4.4 Second instar larva 22 2.4.5 Third instar larva 22 • 2.4.6 Pupa 23 vii 2.5 Geographical distribution 24 3. Delia radicum L. (Diptera: Anthomyiidae) 25 • 3.1 Morphology 25 3.1.1 Adult 25 3.1 .2 Egg 25 3.1.3 Larva 26 3.1.4 Puparium 26 3.2 Biology 27 3.3 Geographical distribution 28 3.4 Control 28 3.4.1 Cultural control 28 3.4.2 Chemical control 29 3.4.3 Biological control 29 References 32 Figures 43 • Tables 59 CHAPTER II: IMPACT Of fOOD AND HOST AVAILABILITY ON SIZE AND SURVIVAL Of EGG OF ALEOCHARA BILINEATA GYLLENHAL (COLEOPTERA: STAPHYLINIDAE) 63 Abstract 64 Introduction 65 Materials and methods 66 General conditions 66 Oviposition strategy according to hast and food availability 67 Statistics 68 Results 68 • viii Presence of trophic eggs 68 Influence of host and food availability 68 • Discussion 69 References 72 Figures 75 Connecting text 79
CHAPTER III: DEVELOPMENT AND ENVELOPE STRUCTURE OF ALEOCHARA BILINEATA GYLLENHAL (COLEOPTERA: STAPHYLINIDAE) EGGS 80 Abstract 81 1ntroduction 82 Materials and methods 85 Egg size and weight 85 Morphology of eg9 envelope 86 Statistics 87 • Results and discussion 88 Change in eg9 volume with time 88 Weight variation in time 88 Morphology of egg envelope 90 References 94 Figures 98 Connecting text 112
CHAPTER IV: EFFECT Of SIZE ON FITNESS IN THE LARVAE Of ALEOCHARA BILINEATA GYLLENHAL (COLEOPTERA: STAPHYLINIDAE) 113 Abstract 114 Introduction 115 • Materials and methods 117
ix General conditions 117 Longevity 118 • Walking rate 118 Searching capacity 118 Statistics 119 Resu Its and discussion 120 Longevity 120 Walking rate 121 Searching capacity 122 Impact of size of fitness 122 References 124 Figures 127
GENERAL DISCUSSION 133 • References 137
• x List of figures
• Figure 1.1: A- Aleochara bilineata and B- A. bipustulata showing red spots on its elytra (Taken fram Langlet, 1997) (Scale bar = 2 mm) 43 Figure 1.2: A- Aleochara bilineata feeding on Delia radicum eggs (Taken from Langlet, 1997) (Scale bar = 2 mm). 8- Mating behavior in Aleochara bilineata whare the male bends its abdomen over its head and its claspers are extruded (Taken from Langlet, 1997) (Scale bar = 2 mm) 45 Figure 1.3: A- Egg of Aleochara bilineata before hatching showing the visible eye spots and mandibles (Taken from Langlet, 1997) (Scale bar = 0.1 mm). B- First instar larva of Aleochara bilineata (Taken from Langlet, 1997) (Scale bar = 0.2 mm) 47 Figure 1.4: Pupa of Delia radicum parasitized by Aleochara bilineata with the entry hole of the parasitoid larva and the first instar of A. bilineata • visible through the puparium (Taken trom Langlet, 1997) (Scale bar = 1 mm) 49 Figure 1.5: Nymph of Aleochara bilineata A- early stage and B- later stage (Taken trom Langlet, 1997) (Scale bar = 1 mm) 51 Figure 1.6: A- Male and B· tamala of Delia radicum (Taken from Langlet, 1997) (Scala bar = 2 mm) 53 Figure 1.7: Eggs of Delia radicum (Takan from Langlet, 1997) (Scale bar =0.5 mm) 55 Figure 1.8: A· Larva of Delia radicum (Scala bar = 1 mm). B- Pupaa of Delia radicum (Scala bar =2 mm) 57
Figure 2.1: Distribution of agg volume produced by Aleochara bilineata over a period of 15 days by A- 7 fed couples with hosts, B- 7 fed couples without host and C- 6 unfed couples with hasts 75 • xi Figure 2.2: Oviposition cycle over 15 days for females of Aleochara bilineata according to treatments ( -- :8 fed couples with hosts , :10 • fed couples without host and :10 unfed couples with hosts). Day one being the first day where the female laid 77
Figure 3.1 :Temporal variation of egg volume (± SO) in Aleochara bilineata at 20°C 98 Figure 3.2: Fresh and dry weight (± SD) of Aleochara bilineata eggs before (1 ±
1 hour) A- and after (68 ± 1 hours) B· swelling at 20°C. ** P<0.0001 (Student test) 100 Figure 3.3: A· General view of an oocyte of Aleochara bilineata. Scale bar =100 IJm. B· Detail of the surface of an oocyte of Aleochara bilineata. Scale bar = 1 ~ m 102 Figure 3.4: Oocyte of Aleochara bi/ineata with follicular cells (FC), granules (G) and vitellus (V). A· Young oocyte with follicular cells and many • granules. Scale bar =5 J,lm. B· Old oocyte with follicular cells. Scale bars = 5 J.Lm 104 Figure 3.5: A· Aleochara bilineata e99 24 hours-old with fungus (F), minerai particles (P) and bacteria (B). Scale bar = 10 J,lm. B· Egg 24 hours old of A. bilineata with granules (G) and spermatozoids (5). Scale bars = 1 J,lm. C- A. bilineata egg 24 hours-old with granules (G) and minerai particles (P). Scale bar =1 J,lm. D· General view of e99s 24 hours-old of A. bilineata. Scale bar =100 J,lm. E· General view of egg seven days-old of A. bilineata with larva present (L). Scale bar = 1OOJ,lm 106
• xii Figure 3.6: A- Egg envelopes of Aleochara bilineata 1 hour after oviposition. Presence of granules (G) in exochorion (EX). EN = endochorion. • Scale bar = 5 ~m. B· Egg envelopes 17 hours-old. The exochorion (EX) is irregular. EN = endochorion. V = vitellus. VM = vitelline membrane. Scale bars = 1 ~m. C- Egg envelopes 30 hours-old. Exochorion (EX). Endochorion (EN). Vitellus (V). Vitelline membrane (VM). Scale bar =3 J.lm 10S Figure 3.7 A- Egg envelopes of 40 hours-old Aleochara bilineata eggs. The endochorion (EN) is fragmented. The serosal cuticle (SC) is formed of severallayers. EX =exochorion. E =embryo. Scale bar =5 J.lm. B Egg envelopes of 6 days-old egg. Presence of granules (G) in exochorion (EX). EN = endochorion. Scale bar = 3 }lm. C Transverse view (SEM) of e9g envelopes of 6 days-old egg. EX = exochorion. EN =endochorion. VM =vitelline membrane. Scale bar =1 J.lm. D- Inside view (SEM) of fragmented endochorion of 6 days- • old e9g. Scale bar =1 J,lm 110 Figure 4.1: Schematic representation of the experimental setup 127 Figure 4.2: Distribution of weight of 185 larvae of Aleochara bilineata 30 ± 30 minutes after hatching 129 Figure 4.3: Percentage of small and large Aleochara bilineata larvae that did not find a host, found a host but did not penetrate and found a host penetrate after a period of 48 hours 131
• xiii • List of tables Table 1.1: Groups of animais where cannibalism behavior is known (Fox, 1975; Elgar & Crespi, 1992) 59 Table 1.2: Synonymy of Aleochara bilineata Gyllenhal (1810) and references 60 Table 1.3: Length and width of Aleochara bilineata eggs according ta authors.. 61 Table 1.4: Lifetime and details consumption of preys by Aleochara bilineata by different authors 61 Table 1.5: Synonymy of Delia radicum L. according ta ragions and authors 62
•
• xiv •
INTRODUCTION
•
• ln Quebec, cruciferous crops such as cabbage, Brussels sprouts, cauliflower and broccoli are important as they occupy an area of 4 893 ha. These • crops represent 36 million dollars at harvest (Statistiques Canada, 1998). These crucifers are attacked by severai pests: Lepidoptera (P/ute/la xylostelJa L., Artogeia rapae L. and Triehop/usia ni Hübner), Coleoptera (Phyllotreta eruciferae Goeze, P. robusta LeConte, P. strio/ata F., P. a/bionica LeConte and Entomoseelis americana Brown), Dermaptera (Forficula aurieu/aria L.), Homoptera (Brevicoryne brassicae L. and Lipaphis erysimi Kaltenbach) and Diptera (Delia radicum L.) (Godin, 1997; Richard & Boivin, 1994). In Quebec, 11 840 kg of insecticide are used against the cabbage maggot, D. radicum L. (Diptera: Anthomyiidae), each year. This represents 9°,/0 of ail insecticides used in Cuebec (Chagnon & Payette, 1990). Young plants are preferred oviposition sites for cabbage maggot females. When attacked, cabbage plants either grow more slowly or die, which affects total yield. Ta decrease this quantity of insecticides and keep a control on the cabbage maggot, several natural enemies can be used including Aleochara bi/ineata Gyllenhal (Coleoptera; Staphylinidae). A. bi!ineata • adults are predators of cabbage maggot eggs and larvae while tirst instar larvae are ectoparasitoids of pupae.
ln the Iiterature, little data is available on factors affecting the oviposition behavior of the female, the developmental biology of eggs and the larval efficiency of Aleochara bilineata. Several reproductive strategies can be used by insect females to increase their fitness at the individual and species level. At the individual level, the female can oviposit sterile eggs that serve as food for larvae. It can also invest different quantities of resources in eggs according to environmental and physical conditions. At the species level, the female can oviposit numerous small eggs containing few resources. These eggs need to absorb oxygen, nutrient or water trom their environment to complete their development. In this thesis these three strategies are examined to understand the oviposition behavior, the developmental biology of eggs and the impact of • this investment in eggs on the larval fitness. 2 A. bilineata female oviposits a large range of egg sizes. Our tirst objective was to determine the conditions in which these smail and large eggs were • oviposited. The Ice Box Hypothesis where the female oviposits sterile trophic eggs when resources are scarce (Alexander, 1974) has been tested. The impact of availability of food and host as weil as temale age and size on the oviposition of A. bilineata have been studied. This is to discover whether these factors permit the production of small eggs.
The second chapter deals with the reproductive strategy at the species level (Iittle investment in small eggs) and the developmental biology of these eggs of A. bilineata. Our tirst objective was to determine the change in eg9 volume over time. Our second objective was ta prove the morphological reason for this increase in size. We hypothesized that the egg absorbs a certain quantity of water during its development (hydropy). We then compared fresh and dry weight of eggs before and after swelling and also examined the modification of egg envelopes during swelling with scanning and transmission electronic • microscopy. At emergence, different weights of larvae have baen measured. The last chapter investigates the efficiency of larvae by measuring the fitness of large and small larvae. Three parameters have been used to evaluate larval fitness. The tirst includes longevity whereby the larva is followed from emergence until death. The second parameter consisted of walking rate while using an image analysis system. Finally we determined the searching capacity of larva when it was in the presence of pupa for a period of 48 hours.
• 3 Thesls format
• "Candidates have the option of including, as part of the thesis, the text of a paper(s) submitted or ta be submitted for publication, or the clearly-duplicated text of a published paper(s). These texts must be bound as an integral part of the thesis. If this option is ehosen, connecting texts that provide logieal bridges between the different papers are mandatory. The thesis must be written in such a way that it is more than a mere collection of manuscripts; in other words. results of a series of papers must be integrated. The thesis must still conform ta ail other requirements of the "Guidelines for Thesis Preparation". The thesis must include: A Table of Contents, an abstraet in English and French, an introduction which clearty states the rationale and the objectives of the study, a comprehensive review of the Iiterature. a final conclusion and summary, and a thorough bibliography or referenee Iist. Additional material must be provided where appropriate (e.g. in appendices) and • in sufficient detail ta allow a clear and precise judgment to be made of the importance and originality of the research reported in the thesis. ln the case of manuscripts eo-authored by the candidate and others, the candidate is required to make an explicit statement in the thesis as to who contributed to such work and to what extent. Supervisors must attest to the accuracy of sueh statements at the doctoral oral defense. Since the task of the examiners is made more difficult in these cases, it is in the candidate's interest ta make perfectly clear the responsibilities of ail the authors of the co-authored papers. Under no circumstanees can a co-author of any component of sueh a thesis serve as an examiner for that thesis."
The third chapter Developmental and envelope structure of Aleoch.,. bllln••t. Gyllenha' (Coleoptera: Staphyllnldae) eggs will be submitted to Int. • J. Insect Morphol. & EmbyoL, co-authored by the candidate's supervisor Dr G. 4 Boivin and the candidate, Dr J.P. Nénon. Dr G. Boivin and Dr J.P. Nénon • provided supervision, read and revised the manuscript. The fourth chapter Effect of size on fitness in the larvae of Aleochara billneata Gyllenhal (Coleoptera: Staphylinidae) will be submitted to Oikos, co authored by the candidate's supervisor, Dr G. Boivin. Dr G. Boivin provided supervision, read and revised the manuscript.
References
Alexander, R.D. 1974. The evolution of social behavior. Annu. Rev. Eco!. Syst. 5: 325-383.
Chagnon, M. 81 A. Payette. 1990. Modes alternatifs de répression des insectes dans les agro-écosystèmes québécois. Tome 1 : Document synthèse. Ministère de l'Environnement et Centre québécois de valorisation de la • biomasse. Québec. 81 p. Godin, C. 1997. Seasonal occurrence and parasitism of Lepidoptera pests of crucifers, and host age selection by a potential control agent: Trichogramma. Macdonald Campus of McGiII University. Department of natural resource sciences (entomology). 144p.
Richard, C. 81 G. Bolvln. 1994. Maladies et ravageurs des cultures légumières au Canada. La Société Canadienne de Phytopathologie et la Société d'entomologie du Canada. Ottawa. 590 p.
Statistiques Canada. 1998. Production de fruits et légumes. Février. Vol. 66. No. 2. • 5 •
CHAPTER 1
LITERATURE REVIEW •
• 6 • 1. REPRODUCTIVE STRATEGY IN INSECT Inseet adults use several reproductive strategies to increase their fitness. These strategies can be at the species levaI. An example of this is spatial strategies whereby males or females either disperse to copulate thus decreasing the probability of inbreeding or copulate at emergence without dispersal therefore gaining time especially in time-Iimited species. The strategies can be visual, where males and females aggregate in swarms to copulate, again saving time (Wickman & Jansson, 1997). The resources that a female invests in eggs will vary between species. While sorne species oviposit a few eg9s that are rich in resources, other species oviposit numerous small eggs containing Uttle re50urces (hydropic eg95). These hydropic e99s will absorb water, nutrient or oxygen from their habitat (Smith & Fretwell, 1974; McGinley et al., 1987). Within a species, individual females may either oviposit most of their e99s in one or few sites, or disperse them in several sites (Berger, 1989; Elgar & Crespi, 1992). A female can oviposit sterile eg9s to serve as food for larvae (Ice Box Hypothesis) or • invest different quantities of resource in eggs depending of environmental and physical conditions (Alexander, 1974). In this Iiterature review three strategies will discussed. The two firsts are at individuallevel (Ice Box Hypothesis and e99 size) and the third is at species level (hydropic egg).
1.1 Investment in eggs
1.1.1 lee Box Hypothesls
Elgar and Crespi (1992) define cannibalism as eating conspecifics, which are either dead or aUve prior to the interaction. Cannibalism is a behaviour that may reduce population size before acute resource shortage causes severe physiological stress (Fox, 1975). This behaviour has been reported in several • groups of animais, including insects (Table 1.1). Elgar and Crespi (1992) divided 7 cannibalism into two categories: non·kin and kin cannibalism. In non-kin cannibalism, preyed individuals are not restricted to their own species. They may • not even discriminate between conspecific and other preys. This type of cannibalism can be described more accurately as indiscriminate or incidental cannibalism (Elgar & Crespi, 1992). Kin cannibalism can be divided into filial and sibling cannibalism. Filial cannibalism is observed when a parent kills and consumes its own progeny, as in Nicrophorus vespilloides Herbst (Coleoptera: Siliphidae) (Elgar & Crespi, 1992). The adults of this species oviposil eg9 clutches near vertebrate corpses that they have previously placed in a burial chamber or crypt. After hatching, the larvae migrate to the corpse and develop inside. The three tarval instars are found inside the corpse and the insect pupates in the Boil. Male and female are present during larval development to repair the chamber, feed the larvae and protect the clutch against predators. The adults eat up to half the offspring when food supply is limited. This serves to regulate the number of larvae in a corpse (Elgar & Crespi, 1992). • Sibling cannibalism occurs when a larva eats an egg or a younger larva of the same clutch. In Plagiodera versicolora Laicharting (Coleoptera: Chrysomelidaa), the famala oviposits egg clutches and the larvae form an aggregated feeding group that persist during the tirst two instars. An e9g clutch is almost exclusively laid by one temale but the tamale may have had multiple mating. Therefore, the female laid groups of eggs contain both full sibs (brothers and sisters) and halt-sibs (half-brothers and halt-sisters). The larvae are very cannibalistic for a period of 24 hours after hatching and eat eggs tram their clutch. After this period, the larvae are herbivorous. For an individual, it is advantageous to be cannibalistic as it insures a rapid growth. However on a group level, the advantages are less obvious. These larvae have social behaviors (feeding coordination, group defensive displays and synchronous molting) and there is a positive correlation between tarval group size and survivorship. • Therefore, cannibalism is disadvantageous in terms of reduced group size. 8 Evolution should therefore select a frequency of cannibalism that reaches a • balance between individual and group advantages (Breden &Wade, 1985). Sorne species may present more than one type of cannibalism. The milkweed leaf beetle, Labidomera clivicollis Kirby (Coleoptera: Chrysomelidae) exhibits three types of cannibalism. The first type is cannibalism of eggs byadult females (filial cannibalism). The second and the third type are sibling cannibalism where larvae eat either eggs or younger larvae of the same cluich. There is a positive correlation between clutch size and the proportion of eggs cannibalized. L. clivicollis oviposits an average of 15-170/0 of eggs which will never develop embryos (Dickinson, 1992). These eggs, named trophic eggs, are generally cannibalized along with sorne fertile eggs, and constitute ovarian-derived structures or fluids, homologous ta fertile eggs (Elgar & Crespi, 1992). This phenomenon is further explained by the Ice Box Hypothesis which predicts that when the survivorship of offspring varies unpredictably, females may gain by increasing clutch size. As a result, when resources are abundant, ail offspring • may prosper but, when lass resources are available, sorne offspring serve as food for others (Alexander, 1974; Elgar & Crespi, 1992).
1.1.2 Egg slze
Variation in egg size can be explained by variation in femala size or aga, food quality or host quality (Karlsson, 1987; Berger, 1989; Fitt, 1990; Wallin et al., 1992; Fox, 1993; Braby, 1994; Fox, 1994). For example, in Chilo partellus Swinhoe (Lepidoptera: Pyralidae) large females lay larger eggs than small femalas (Berger, 1989). In Pararge aegeria L. (Lepidoptera: Satyrinae) eg9 weight and oviposition rate decrease with famale age (Karlsson, 1987). There are severai indications that there is a correlation betwean egg size and offspring performance (Wallin et al., 1992; Fox, 1993; Braby, 1994; Fox, 1994). In Callosobruchus maculatus F., (Coleoptera: Bruchidae), the larvae tram large • eg9s develop faster and emerge as larger adults in comparison ta the larvae from
9 small e9gs (Fox, 1994). In Pterostichus cupreus L. (Coleoptera: Carabidae), larvae trom large eggs survive longer and hatch earlier than larvae from small • eggs (Wallin et al., 1992).
1.1.3 Hydropy
Insect e99s comprise several envelopes, which are either derived maternally or trom the embryo. Two maternally derived envelopes secreted by follicular cells exist at oviposition time: the chorion and the vitelline membrane (Biemont et al., 1981; Chauvin et al., 1988; Larink & Bilinski, 1989; Neveu et al., 1997). The chorion is often composed of the exoehorion and endoehorion and can be covered by mueoproteins secreted by the accessory glands of the female. These proteins are used ta secure the egg to the substrate and their presence explains the development of baeteria on the egg surface (Chauvin & Chauvin, 1980; Biemont et al., 1981 ; Nénon et al., 1995). After oviposition other • envelopes, seereted by the embryo, are added: the serosal and embryonie cutieles (Chauvin et al., 1973; Chauvin & Chauvin, 1980; Hinton, 1981; Chauvin et al., 1988). Ali envelopes are essential to proteet the egg against hydrie and thermie variations and predators however they also play a role in hydrie and respiratory exehanges (Chauvin & Chauvin, 1980; Chauvin et al., 1988).
ln sorne speeies, females produce fewer eggs and their reproduction rate is reduced. However, more investment is placed in each egg. The mortality rate is generally lower and these eggs do not need to absorb nutrients, water or oxygene By investing more into each egg, the fitness of individual offspring increases (Smith & Fretwell, 1974; McGinley et al., 1987). In others species, females produce more eggs per unit of time thus placing a smaller investment in each egg. In such species, the rate of mortality is high but it is compensated by the fact that there are many eggs. These eggs, named hydropic eggs, can absorb nutrients, water or oxygen to complete their development. Many aquatic • and terrestrial eggs of Orthoptera, Heteroptera, Homoptera, Coleoptera,
10 Hymenoptera and Diptera require water to develop (Hinton, 1981; Chauvin et al., 1991). The water absorbed is in a Iiquid phase and this absorption causes an • increase in the egg volume during its development.
ln hydrapic eggs, the water is absorbed by three types of hydropyles or hygropyles (argans specialized for the absorption of Iiquid water (Hinton, 1981)): serosal hydropyles, serosal cuticle hydropyles and chorionic hydrapyles. These hydropyles cells do not actively absorb water. However, they secrete a specialized form of serosal cuticle of the hydropyle and regulate its permeability to water (Hinton, 1981).
• Serosal hydropyles are present in same Orthoptera and Hemiptera and their usual position is at the anterior pole of the e9g. • Serosal cuticle hydropyles are known in Acrididae (Orthoptera) where two serosal cuticles are formed, the outer and the inner, and both take part in the • formation of hydropyle at the posteriar pole. There is a change in the permeability of the hydropyle cuticle: when diapause is initiated, the outer layer becomes impermeable. When diapause is completed. it becomes permeable to water (Hinton, 1981). • Chorionic hydropyles are present in severai orders such as Heteroptera, Homoptera and Coleoptera. The principal characteristic of these eggs is the presence of a respiratory air layer with aeropyles in the shell of the egg even if the egg is dried (Hinton, 1981). • However, hydropyles have nat been recognized in most eggs of Hymenoptera and Coleoptera that are known to absorb Iiquid water.
ln general, insect e9gs are in contact with Iiquid of osmotic pressure lower than that of the embryonic fluids and tissues. Thus. passive absorption occurs (osmosis) (Hinton, 1981). The absorption of Iiquid water often results in an increase in e9g size and modification in the egg envelopes. Several acridids, • mirid bugs and dytiscid beetles have a chorion that fragments during water
11 absorption (Hartley, 1961; Lincoln, 1961). In Dytiscus marginalis L. (Coleoptera: Dytiscidae), the egg chorion splits during water absorption and the serosal cuticle • serves to support and protect the developing eggs (Blunck (1914) in Lincoln, 1961). When the egg swells, in other insects, the chorion stays intact. In Ocypus a/ens Müller (Coleoptera: Staphylinidae) the chorion simply stretches when the volume of the egg increases (Slifer, 1937; Lincoln, 1961). In Tetrix vittata Zetter (Orthoptera: Tetrigidae), the anterior horn appears as an expansion chamber allowing the egg to swell (Lincoln, 1961; Hartley, 1962).
1.2 Fitness of larva
The fitness is a measure of the response of a population of organisms to natural selection. This is based on the number of offspring contributing to the next generation in relation to the number of offspring required to maintain the • particular population constant in size (Abercombie et al., 1980). The fitness has been used ta indicate a measure of general adaptedness, and to indicate a short term measure of reproductive success (de Jong, 1994). However in certain kind of social behavior, such as altruism, certain traits with a low individual fitness can be favored by selection since these traits increase the population fitness (Queller, 1996).
The fitness of a female parasitoid depends on the environment and her constraints such as longevity, fecundity, host-finding ability and size. The size fitness hypothesis proposes that fitness of female increases with increasing size (de Jong, 1994; Godfray, 1994; Visser, 1994; Kazmer & Luck, 1995). There are many measures to estimate the relationship between parasitoid size and fitness: egg load at emergence, egg size, longevity, searching efficiency on patches, travel speed... (Visser, 1994). For instance in comparison to small females, in Aphaerata minuta Nees (Hymenoptera: Barconidae), larger Jemales have more • eggs available, larger eggs, live longer and have a higher searching efficiency
12 within patches (Visser, 1994). In gregarious parasitoids, adult size decreases as the number of developing progeny increases in similar-sized hosts. However in • solitary parasitoid, adult size is positively correlated with host size (Kazmer & Luck, 1995). Moreover when the energy expended on individual offspring is increased, the number of offspring that parents can produce is decreased. When the energy expended on individual offspring increases, the fitness of individual offspring increases (Smith & Fretwell, 1974).
Fitness applies to individuals, therefore fitness parameters can be measured in larvae (Wiklund & Persson, 1983; Fox, 1993; Braby, 1994). Braby (1994) has measured three titness parameters in butterflies of the genus Mycalesis. These parameters were larval survival, larval developmental time and pupal weight in relation to e9g size. Under field conditions, there is a correlation between e99 size and offspring fitness suggesting that larvae tram larger eg9s may do better than those trom smaller eggs. No measure of the fitness of A. • bilineata larvae is available at the moment.
• 13 2. ALEOCHARA BILINEATA GYLLENHAL • (COLEOPTERA: STAPHYLINIDAE)
2.1 Distribution and life history of Staphylinidae
There are more than 14 000 species of Staphylinidae (Coleoptera) worldwide (Eggleton & Belshaw, 1992) and in North America, nearly 2 900 species live in a variety of habitats. The majority of species live in decaying materials such as dung and carrion. Other species dwell under stones and other abjects on the ground, along streams and seashores, in fungi and leaf litter and in nests of birds. mammals, ants and termites (Borror et al., 1954). Staphylinidae that are not scavengers can be predaceous or parasitoid.
The Staphylinidae are characterized by short elytra and an elongate body. Beneath the elytra, large and fully functional wings are folded. The Staphylinidae have the habit of elevating their abdomen when disturbed. When they run, they • frequently raise the tip of their abdomen, as do scorpions. The mandibles are very long. slender and sharp and are generally crossed in front of the head. Most Staphylinidae are brown or black and measure about 25 mm in length (Borror et al., 1954).
Many Staphylinidae that live as parasitoids attack pupae on or in the soil but occasionally sorne species find pupae on or in plants. For example, Maseochara valida Lee. attacks pupae of Copestylum marginatum Say (Diptera:
Syrphidae) 1 a syrphid fly that develops in the semiliquid material in the decaying leaves of cactus (Clausen, 1940; Eggleton &Belshaw, 1992). • 14 • 2.2 Distribution and life history of Aleochara spp. The genus Aleochara Grovenhorst has about 300 species worldwide, (Klimaszewski, 1984); ail species for which the life history is known, are parasitoids. In North America, the genus Aleochara is divided into seven subgenera: Coprochara Mulsant and Rey (A. bimaculata Gravenhorst, A. bilineata Gyllenhal and A. verna Say (synonymous of A. bipustulata L.)), Xenochara Mulsant and Rey (A. tristis Gravenhorst, A. lacertina Sharp, A. taeniata Erichson and A. puberula Klug), Aleochara Mulsant and Rey (A. curtula Goeze and A. lata Gravenhorst), Emplenota Casey (A. Iittoralis Maklin and A. pacifica Casey) Ca/ochara Casey (A. vil/osa Mannerheim), Echochara Casey (A. lucifuga Casey) and Maseochara Sharp (A. valida LeConte). These species are parasitoids of Muscidae, Anthomyiidae, Calliphoridae, Sarcophagidae, Coelopidae, Sepsidae and Syrphidae, which are ail dipteran species (Wadsworth, 1915; Klimaszewski, 1984).
• ln 1836, Say (in Wadsworth, 1915) described A. verna in America. Forty four yaars later, Sprague, in Europe, described A. nitida. He was the tirst to discuss that Ale0chara sp. emerged from a cabbage maggot pupae in his laboratory (Wadsworth, 1915). But Sprague did not find the hole by which the Staphylinidae could have entered the puparium: IIthus proving beyond a doubt that either the eggs, or what seems more probable, the young larva of this Staphy/inus (genus Aleochara) entered the fly larvae long before they had arrived at maturity" (Wadsworth, 1915). Fletcher (1890) was the first one to consider Aleochara sp. as a true parasitoid (in Wadsworth, 1915). A few years later, in 1894, Slingerland (in Wadsworth, 1915) mentioned an Aleochara attacking the cabbage maggot Delia radicum (Diptera: Anthomyiidae). This AJeochara was considered to be identical with A. nitida (Gravenhorst) which was identified by Say in 1836. • 15 Klimaszewski (1984) revised the genus Aleochara. In these species, the larva is an ectoparasitoid within puparia of cyclorrhaphous Diptera where they • undergo hypermetamorphism. The adults of these species are predators of the larvae and eggs of the same Diptera species (Klimaszewski, 1984).
2.3 Evolution of Aleochara spp.
The 1 600 species of Coleoptera parasitoids are distributed in 11 families. Thirteen acquisitions of the parasitoid Iifestyle are necessary to explain these 11 families away which one acquisition for the 500 species of Staphylinidae that are parasitoid (Eggleton & Belshaw, 1992; Eggleton & Belshaw, 1993). Fuldner (1960) has proposed an evolutionary pathway for the acquisition of parasitic Iife in Staphylinidae. Many Staphylinidae, including the genus Aleochara, are necrophagous, .aeding on animal corpses where dipteran larvae are present. Sorne necrophagous staphylinids have probably started to predate on these • dipteran or other prey in the same habitat. In thase adult predators living and developing in this habitat, the larvae specialized to become parasites of the same species pupae (Fuldner, 1960; Eggleton & Belshaw, 1992; Eggleton & Belshaw, 1993). Sorne species such as Aleochara curtula Goeze, A. intricata Mannh, A. bilineata Gyllenhal and A. bipustulata L. evolved as ectoparasitoids and show polymetamorphism (Fuldner, 1960). In A. curtula and A. intricata, the first instar is campodeiform and enters the dipteran puparia to eat the pupa. The second and third instars are eruciforms while the third instar exhibits campodeiform behavior, because it exits the host puparium to pupate in the sail. Another group ·,f species, including A. bilineata and A. bipustulata, are completely ectoparasitoid. Thair third instar larva is aruciform and pupates in the hast puparium. For thase species, the third instar larva is not able to live outside of hast puparium. After feeding on the pupa, the third instar larva spins its cacoon insida the host pupariurn. According to Fuldner (1960) the larval life of A. bilineata and A. bipustulata is an advanced form of parasitism in Dipteran pupae because the • parasitoid pupates in the host.
16 • 2.4 Morphology and blology of Aleochara bilinea'a
A. bilineata is a species in the subgenus Coprochara. The synonymy of this species is presented in table 1.2.
2.4.1 Adult
The imago of A. bilineata is slender and shining black with short elytra lacking the spots found on the elytra of A. bipustulata L. (Figure 1.1). It abdomen is pointed and its wings are functional. The adult can tly at least five kilometers (Tomlin et al., 1992). The average size of the femala is 5.81 mm, larger than the male that measures 5.40 mm (Colhoun, 1953). The male has an average of sixteen short sting·like bristles on the sixth abdominal tergum. However in females, there is an average of twenty bristles that are longer than those of • males (Colhoun, 1953). Adults of Aleochara are predators of Diptera eggs and larvae (Colhoun, 1953; Raad, 1962; Bromand, 1980) (Figure 1.2A). Upon biting the cuticle of Diptera larvae, A. bilineata ingests the haemolymph of its prey through a combination of lapping and sucking motions. According to Bromand (1980), a couple of A. bi/ineata under greenhouse conditions can eat approximately 2 400 cabbage maggot eggs or first instar larvae, or about 250 cabbage maggot third instar larvae in their Iifetime. An adult feeding on eggs or one to two day old larvae destroys an average of 23.8 Diptera per day throughout its life. However this consumption decreases with time. When an adult feeds on third instar larvae or pupae, it destroys an average of 2.6 Diptera per day (Read, 1962) (Table 1.3). Fuldner (1960) stated that the fluid of the Diptera larva or egg attracts other predators because when one A. bi/ineata adult feeds on a larva other A. bilineata • arrive rapidly. 17 There is no apparent courtship period in copulation. The male bends its abdomen over its head and its claspers and aedeagus are extruded (Figure • 1.2B). According to Colhoun (1953), the copulation lasts between 20 and 65 seconds. The pre-ovipasition period can vary from 36 to 96 hours (Wadsworth, 1915; Colhoun, 1953). This species is synovogenic as there is continuous production of aggs through\)ut the Iifetime (Langlet, 1997). Adults A. bilineata can live an average of 49.7 days (40 to 72 days) (Read, 1962). In Ouebec and Ontario there are two generations of A. bilineata per year. The tirst generation of adults is in mid-June and the second in August or September (Nair & McEwen, 1975; Boivin et al., 1996).
A. bilineata is a solitary parasitoid but superparasitism is a common occurrence. Up to five larvae can enter a hast puparium (Wilde (1947) in Jones et al., 1993) but only one Jarva eventually survives (Colhoun, 1953; Read, 1962; Royer et al., 1998a). In Delia floralis Zetter, the turnip maggot (Diptera: Anthomyiidae), multiparasitism by A. bilineata and Trybliographa rapae Westwood (Hymenoptera: Eucoilidae) is trequent (Bromand, 1980). According to
• 1 Wishart and Monteith (1954) in ail cases where both T. rapas and A. bilineata or A. bipustulata were in competition, the T. rapae larva died. The A. bilineata larva attacks and destroys bath host and T. rapae larva.
The famale oviposits in the sail surrounding plants which are attacked by the dipteran host. The femala is attracted by bath decomposing cruciferous plants and plants attacked by Diptera hosts (Bromand, 1980). Colhoun (1953) states that the femala oviposits approximately 15 eggs per day for an average of 700 eggs during her life. The female selects particular plants as suitable for mating, foraging and oviposition sites (Tomlin et al., 1992). If the female is starved but has copulated, it will not oviposit because the ovaries will not develop (Colhoun, 1953). In the laboratory, the female does not show preference for laying eggs on or near host puparia (Delia radicum) (Colhoun, 1953). Adults • burrow galleries in the soil near infested plants to lay eggs near host puparia 18 (Wilde (1947) in Fuldner, 1960). The female oviposits eggs throughout her life but more than 90 per cent of eggs are laid between five and 50 days after • emergence (Read, 1962).
A. bilineata is a generalist that attacks severai Anthomyiidae such as Delia floralis Zetter (turnip maggot), D. florilega Zetter (potato maggot), O. platura Meigen (seedcorn maggot), D. antiqua Meigen (onion maggot) and O. radicum L. (cabbage maggot) with no apparent preference (Wishart, 1957; Fuldner, 1960; Moore & Legner, 1971; Klimaszewski, 1984; Jones et al., 1993; Ahlstrôm-Ollson, 1994; Jonasson, 1994). Other Anthomyiidae can be attacked such as Delia planipalpus Stein, Pegomya hyoscyami Curtis (spinach leafminer) or Muscidae such as Musca domestica L. (housefly) and Calliphoridae, Calliphora erythrocephala Meigen (Klimaszewski, 1984).
2.4.2 Egg
• The ellipsoid egg is milky white at the beginning of its development and its chorion is smooth. The egg varies between 0.38 ta 0.50 mm in length and 0.32 to 0.37 mm in width (Wadsworth, 1915; Colhoun, 1953: Fuldner, 1960) (Table 1.4).
Twenty hours before hatching (at 23.8°C) it is possible to see through the chorion, the brown mandibles, black eye spots, antennae, legs of the larva and four chitineous dorsal protuberance (Colhoun, 1953; Fuldner, 1960). At this time the chorion turns yellow (Figure 1.3A) and the larva is curled along the longitudinal axis of the egg. Hatching occurs three to 19 days after oviposition, depending on temperature (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960). The chorion is broken by the pressure of the head and by a twisting movement, the larva soon trees itself tram the chorion. Hatching takes place in five ta ten • seconds (Colhoun, 1953).
19 2.4.3 Flrst instBr IBNB
• The tirst instar larva is campodeiform and as such has functionallegs. The size of the larva varies between 1.25 to 1.62 mm in length and 0.12 to 0.25 mm in width (Wadsworth, 1915: Colhoun, 1953: Fuldner, 1960).
The larva is a very pale yellowish brown, with the intersegmental areas creamy white (Wadsworth, 1915) (Figure 1.38). These intersegmental areas are extensible (Fuldner, 1960). The head capsule, mandibles, legs and anal region are darker than the other regions of the body. The head of the larva is fiat, has many sensorial bristles and possesses hard mandibles (Fuldner, 1960). The eye spots measure 0.015 mm in diameter and are conspicuous on each side of the head (Wadsworth, 1915). Each antenna has three well-developed segments. The larval abdomen has 10 segments and the last two are more sclerotized. The eighth segment bears pseudocerci that are used Iike tactile organs. The last segment has a pygopod that it used for locomotion and to anchor the larva ta the • host pupa (Fuldner, 1960). The respiratory system is weil developed. There is a single pair of thoracic spiracles and one pair of spiracles on each of the first eight abdominal segments. At the end of the first instar, after feeding, the larva has increased its size ta 2.2 ta 2.5 mm in length and 0.37 mm in width (Colhoun, 1953: Fuldner, 1960).
Upon emergence, the first instar larva (between one ta three days old) searches for the hast pupae. When it finds one, it drills a small hole in the puparium and enters (Reader &Jones, 1990) (Figure 1.4). When only one larva attacks the hast, the entrance hale is more frequently on the dorsum of the puparium (55%) than laterally (250/0) or ventrally (20%) (Royer et al., 1998b). When there are more than one larva, the hole can be on the ventrum of the puparium (Colhoun, 1953). The size of this hole is 0.08 to 0.17 mm in length and 0.015 in width (Wadsworth, 1915; Royer et al., 1998b). The process of drilling the • hole takes from 12 ta 36 hours (Colhoun, 1953; Fuldner, 1960). During ils 20 exploration of the pupae, the tirst instar larva may search the external surface of the puparium and determine zones with fewer or lower transverse ridges (Royer • et al. 1998b). The larva orients its mandibles parallel ta the ridges and minimizes the number of ridges encountered (Royer et al. 1998b). Once it has entered, the larva is very active and is attached to the puparium with its pygopods. The tirst instar larval stadium lasts five ta eight days in the presence of hasts (Wadsworth, 1915; Bromand, 1980; Royer et al., 1998a).
The larva overwinters as a diapausing tirst instar inside the puparium ot its host (Colhoun, 1953; Bromand, 1980; Whistlecraft et al., 1985) which overwinters in diapause as a pupa. The emergence of the tirst generation adults is not synchronized with host emergence (Nair & McEwen, 1975; Whistlecraft et al., 1985) but rather with the presence of host pupae. Overwintered A. bilineata adults emerge no later than 2 weeks after the host adults had emerged (Nair & McEwen, 1975). • At emergence, the larva has a fixed quantity of nutrients in the torm of fat globules. After twelve hours several globules have disappeared (Fuldner, 1960) and after six to eight days without food, fifty percent of the larvae are dead (Colhoun 1953; Royer et al., 1998a). A. bilineata is an ectoparasitoid feeding on the hast pupa and ingesting haemolymph by small punctures on the vertex of the head of the pupa. After entering the puparium, A. bilineata closes the hale, between two feeding periods, with excrement and the contents of malphigian tubules (Fuldner, 1960; Bromand, 1980). Before the hale is completely filled or if it is imperfectly sealed, it is possible for nematodes or spores of fungus (Fusarium sp.) to enter the host puparium. If this oceurs, the first instar larva of A. bilineata is killed and the hast pupa destroyed (Wadsworth, 1915; Bromand, 1980). • 21 2.4.4 Second instar larva
• The larva, which was campodeitorm in its tirst instar, turns into an erucitorm larva (caterpillar form) in its second instar. This change in form indicates hypermetamorphism (Wadsworth, 1915: Colhoun, 1953). At the beginning of its second instar, the larva measures 2.8 mm in length (Colhoun, 1953; Fuldner, 1960). Ali characteristics of the first instar are lost; the legs are rudimentary and the bristles on the body are smalier than during the first instar. Il is possible to observe through the larva malpighian tubules that are white and opaque.
The second instar larva is immobile and it rests on the thorax of the host pupa as does the first instar (Colhoun, 1953). A parasitized puparium appears identical to an unparasitized one except that there are small brownish spots on puparium that appear with punctures made by the parasitoid. During the second • instar, the larva does not excrete except for occasional minute drops of a clear fluid substance that exits the anus. The second instar lasts five days (Colhoun, 1953). At the end of this stage, the larva measures 3.60 to 3.69 mm in length (Colhoun, 1953; Fuldner, 1960).
2.4.5 Third Instar larva
This instar is eruciform but the larva is more sclerotized than the second instar. The size ranges between 5.0 to 7.6 mm in length and 1.64 ta 2.00 mm in width (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960). The respiratory systems of the second and the third instar are similar ta the first instar.
The feeding behavior of the third instar is very similar ta that of the second. However it feeds more voraciously, beginning with the hast head, then the thorax and finally the abdomen (Colhoun, 1953). The third instar larva is U-shaped and • its head now points toward the caudal end of the puparium. The head and thorax
22 of the larva continue to move in this direction until the body is straight. When the host has been completely eaten, except for the cuticle, the larva moves until its • head is in the cephalic end of the puparium (Colhoun, 1953). The third instar has a duration of six days (Colhoun, 1953). Wadsworth (1915) hypothesized that the larva is then very active because the excreted substance is saon plastered over the inner surface of the puparium. The puparium becomes opaque. making observation of larvae difficult. This excretion phase has a duration of 36 hours and, after two to three days of quiescence, the pupa starts to form (Colhoun,
1953; Fuldnert 1960).
2.4.6 Pupe
The pupa measures between 4.25 and 4.66 mm in length (Wadsworth,1915; Colhoun, 1953). The host pupa is completely consumed by the larva and the pupa fills the puparium. In the beginning of this stage the pupa • is white although towards the end it is black (Figure 1.5).
The pupal stage has a duration of 14 days (Colhaun, 1953; Bromand 1980). The size of the hast puparia determines the size of the A. bilineata adult (Bromand, 1980). The adult emerges through a ventro-cephalic hole in the puparium made with its mandibles (Colhoun, 1953; Fuldner, 1960).
• 23 2.5 Geographieal distribution
0 0 • - A. bilineata is found throughout holarctic ragion (35 60 N) (Jonasson et al., 1995; Langlet, 1997). According to Horion in 1967 (in Klimaszewski, 1984) it is assumad that A. bilineata was introduced to North America trom Europe. A. bilineata ranges trom British Columbia to Newfoundland in Canada and, to the south, to Oregon, Illinois and Massachusetts in United States (Klimaszewski, 1984).
•
• 24 • 3. Delia radicum L. (Dlptera: Anthomyiidae)
Bouché has first described the cabbage maggot in 1833 as Anthomyia brassicae (Coaker & Finch, 1971). The synonymy of this specias is presented in table 1.5. The cabbage maggot is an important pest of cruciferous crops in Canada (cabbage, turnip. rutabaga, cauliflower, Brussels sprouts...) and il is one of the hosts of Aleochara bilineata.
3.1 Morphology
3.1.1 Adult
The cabbage maggot is similar ta the housefly, but smaller and more slender. The cabbage maggot adult is gray and is about 6 mm long (Smith. 1927) (Figure 1.6). The sexes can be distinguished by the fact that the male eyes are • holoptic white the eyes of the female are dichoptic. The male has a hind femur which is very hairy on the basal half of the anterior surface. The female has a middle femur with strong anteroventral bristles near its base. The front femur has three to six smalt, erect bristles on its anterior surface and the front tibia has two posterior bristles (Brooks. 1951).
3.1.2 Egg
The egg of D. radicum is cylindrical, white and with a length ranging from 0.93 mm to 1.02 mm and is 0.3 mm wide at its median part (Figure 1.7) (Smith, 1927; Coaker & Finch, 1971; Neveu et al., 1997). The chorion is sculptured into longitudinal ridges and its convex side shows a longitudinal strip. Its anterior pole has a depression where micropyles are present. Its posterior pole is rounded and • has several aeropyles (Neveu et al., 1997). 25 3.1.3 Larva
• The cabbage maggot larva has three instars. The first instar larva has a cephalopharyngeal skeleton consisting of one median hook with a paired plate on each side (Brooks, 1951). The first instar larva measures about 1 mm in length (Smith, 1927) and has only posterior spiracles. The second and third instars also have anterior spiracles. The second instar larva (2 to 4 mm in length (Smith, 1927)) has posterior spiracles with two slits contrary to the third instar which has three slits. Whereas the mouth hooks of second instar larvae have two teeth on their ventral surfaces, those of the third instar are smooth (Coaker & Finch, 1971). The third instar varies from 2 to 8 mm in length and from 1 to 2 mm in diameter (Smith, 1927) (Figure 1.8A).
3.1.4 Puparlum
The puparium is milky white at the beginning of the pupal stage and • becomes reddish-brown and black toward the end, just before emergence. Its form is sub-elliptical with smoothly rounded sides. According to Smith (1927), the average puparium measures 6 to 7 mm long by 3 mm wide at the center (Figure 1.88). The external surface of the puparium is characterized by transverse ridges (Royer et al., 1998b). According to Fraenkel & Bhaskaran (1973), these ridges appear during the formation of the puparium when a longitudinal muscular contraction shortens the length of the larva by one quarter.
• 26 3.2 Blology
• The number of generations of D. radicum varies according to the region. There are one to three generations in North America (Turnock &Boivin, 1997). In Canada, there is one complete generation with a partial second in Newfoundland however, in southwestern Ontario and southern British Columbia, there are three generations (Nair & McEwen, 1975; MAPAO, 1987; Turnock & Boivin, 1997). In Ouebec, there are two to three generations each year (Chagnon & Payette, 1990; Turnock & Boivin, 1997). In southwestern Ouebec, the first generation adults oviposit from the end of May until the end of June, (MAPAQ, 1987; Richard & Boivin, 1994). The second generation oviposits in mid-July. Generally, after a pre-oviposition period of about six to eight days (Coaker & Finch, 1971), the female oviposits on or just below the soil surface close to the main stem of the cruciferous plants. Young plants are preferred oviposition sites for cabbage maggot females. According to Finch (1974), under laboratory conditions the female oviposits 299 ± 48 eg9s in her life. The female has a oviposition cycle of • 40 to 50 eggs, after which it has to feed. Eggs hatch within a week in the field (the egg developmental time depends on the temperature, and varies between two and fourteen days (Coaker & Finch, 1971)) and the first instar larva descends into the soil and feeds on the secondary roots of the cruciferous plant. After three ta four weeks of larval feeding, the third-instar larva exits the root and pupates in the soil (Read, 1973). However, when the sail is very dry, the third instar larva can pupate in the root (Read, 1973). Cool and moist temperatures increase the survival of the Jarva and it is under these conditions that the highest lasses are experienced by growers (Richard & Boivin, 1994). Alter two weeks of pupation, the adults emerge and live trom two to five weeks (Smith, 1927). • 27 • 3.3 Geographiesl distribution The cabbage maggot is native of Palaearctic Region, ranging trom the Atlantic to the Pacifie Oceans and tram Rabat, Morocco (38°02'N) ta Murmansk, Russia (68°59'N) (Turnock & Boivin, 1997; Turnock et al., 1998). According to Coaker and Finch (1971), the cabbage maggot is restricted to the temperate zone of the holarctic region (35° - 60° N). It was introduced in North America from Europe before 1856 (Turnock & Boivin, 1997; Turnock et al., 1998).
3.4 Control
ln vegetable crops in Canada (1990), losses amount to 15.5% by diseases, 12.5% by insects and 10.5% by weed. The production losses can be due to several types of pathogenic agents and pests such as bacteria, fungus, nematodes, insects, acarids, spiders, slugs, snails, weeds, parasitic plants... • (Richard & Boivin, 1994). The cabbage maggot is an important pest of ail cruciferous crops such as rutabaga, turnip, cabbage and cauliflower but also of radish, broccoli and Brussels sprouts. There are several methods ta control the cabbage maggot population.
3.4.1 Cultural control
Several cultural methods are used for cabbage maggot control. It is recommended to delay planting until the beginning of July to prevent serious damage. However, these late plantings should not be in proximity to early cruciferous crops with high cabbage maggot populations (Read, 1973). Crop • rotation and destruction of infested plants are also used. 28 3.4.2 Chemlcal control
• Each year in Ouebec. 11 840 kg of insecticides are used against the cabbage maggot, which represents 9% of ail insecticides used in Ouebec (Chagnon & Payette, 1990). Adults can be deterred trom ovipositing around hast plants by treating the roots of the plant or the sail around them with ashes, lime sulfur or other similar noxious substances. Although trequent treatments are necessary and this technique is not feasible on a large scale (Coaker & Finch, 1971). Two types of treatments are recommended in Quebec against the cabbage maggot (MAPAO, 1987). The tirst is the treatment of transplantation water with GUTHION 50-W. The second treatment is after transplantation. This is done by applying 3.75 liters in 1000 Hters of water ot BIRLANE 400-E or 2.40 4.80 Iiters in 1000 liters ot water of LORSBAN 4-E. However, bath these treatments can damage plant foliage. Moreover. these insecticides cause a reduction in the number of predatory beetles (Wright et al., 1960). • 3.4.3 Blologlcal control A variety of organisms have been used against the cabbage maggot. These include fungi (Empusa muscae Cohn kills the adults and Strongwellsea castrans Batko sterilizes the adults), nematodes (Steinemema fe/tise), predators and parasitoids (Hugues & Salter, 1959; Wright et al., 1960; Coaker & Finch, 1971; Nair & McEwen, 1975; Finch, 1989; Chagnon & Payette, 1990). Sorne organisms have also been used ta diminish the oviposition of the cabbage maggot like the garden-pebble moth. Evergestis forficalis L. (Lepidoptera: Pyralidae) whose larvae have sinapic acid in their frass. This acid deters cabbage maggot oviposition on otherwise acceptable plants (Finch. 1989). • 29 The immature stages of the cabbage maggot are preyed upon by many arthropods. The e9gs are food for trombidid mites, ants, carabid and staphylinid • beetles. The larvae are food for ants, beetles and other anthomyiid larvae. Finally, the adults are food for many predators although only a few cases have been reported (Coaker & Finch, 1971).
There are four major predators, the first one being the carabid beetle, Bembidion lampros Herbst (C01eoptera: Carabidae) and the second one Trechus quadristriatus Schrank (Coleoptera: Staphylinidae) which feed on cabbage maggot eggs (Wright et al., 1960; Coaker & Williams, 1963; Coaker & Finch, 1971). In England, these two major predators are responsible for destroying more than 90% of the eggs laid (Hugues, 1959; Wright et al., 1960; Coaker & Williams, 1963). The third and fourth predators are Aleochara bilineata and A. bipustulata which feed on cabbage maggot e99s and larvae.
• Several parasitoids Hymenoptera attack the larval stages of the cabbage maggot but only kill after pupation. There are five species of braconids, three species of cynipids and four species of ichneumonids (Wishart et al., 1957; Hugues & Salter, 1959; Coaker & Finch, 1971). In Ouebec, two species of Hymenoptera are observed: Trybliographa rapae Westwood (Eucolidae) and Aphaerata pallipes Say (Braconidae) (Boivin et al., 1993).
Most of the parasitism is due to staphylinids (Coleoptera) which attack the pupal stage (Nair & McEwen, 1993). Two species are known: Aleochara bilineata and A. bipustulata, the latter being more abundant (Wishart, 1957). In 1990 at Ste-Clotilde in southwestern Ouebec, in a sample of cabbage maggot pupae, 55°k was parasitized by A. bilineata (Boivin et al., 1993). Moreover, A. bilineata can parasitize up to 95% of cabbage maggot pupae independent of the type of sail or plant species (Boivin et al., 1993). Nair and McEwen (1975) consider pupal parasitism as a stabilizing factor. In 1987 and 1988 in London (Ontario) an • experiment was performed with marked A. bilineata in urban gardens. Only 3°J'o of
30 A. bilineata were recaptured and population in gardens was not increased. Moreover, the adults were capable of flying at least 5 km under urban conditions • to select particular gardens as suitable mating, foraging and oviposition sites (Tomlin et al., 1992).
•
• 31 • References
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•
• 42 •
Figure 1.1: A- Aleochara bilineata and B- A. bipustulata showing red spots on its elytra • (Taken trom Langlet, 1997) (Scale bar =2 mm).
• 43 •
•
• •
Figure 1.2: A- Aleochara bilineata feeding on Delia radicum eggs (Taken trom Langlet, • 1997) (Scale bar = 2 mm). B· Mating behavior in Aleochara bilineata where the male bends its abdomen over its head and its claspers are extruded (Taken fram Langlet, 1997) (Scale bar = 2 mm).
• 45 •
•
• 46 •
Figure 1.3: A· Egg of Aleochara bilineata betore hatching showing the visible eye spots and mandibles (Taken trom Langlet, 1997) (Scale bar =0.1 mm). B· First • instar larva of Aleochara bilineata (Taken trom Langlet, 1997) (Scale bar = 0.2 mm) .
• 47 •
•
• 48 •
Figure 1.4: Pupa cf Delia radicum parasitized by Aleochara bilineata with the entry hale of the parasitoid larva and the first instar of A. bilineata visible through the • puparium (Taken trom Langlet, 1997) (Scale bar =1 mm).
• 49 •
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Figure 1.5: Pupae of Aleochara bilineata A- earty stage and B- later stage (Taken fram • Langlet, 1997) (Scala bar = 1 mm).
• 51 •
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• 52 •
Figure 1.6: A- Mala and B- femala of Delia radicum (Taken from Langlet, 1997) (Scala • bar =2 mm).
• 53 •
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• •
Figure 1.7: Eggs of Delia radicum (Taken trom Langlet, 1997) (Scale bar = 0.5 mm). •
• 55 •
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Figure 1.8: A· Larva of Delia radicum (Scala bar = 1 mm). B· Pupaa of Delia • radicum (Scala bar =2 mm).
• 57 •
•
• 58 • • •
Table 1.1 :Groups of animais where cannibalism behavior is known (Fox, 1975: Elgar & Crespi, 1992). Phylum Class Order Family -Platyhelminthes -Aschelminthese -Protozoa -Mollusca -Arthropoda ..,.. -Arachnida -Chilopoda -Insecta ,.... -Coleoptera ..,.. -Bostrychidae eCarabidae eChrysomelidae eCoccinellidae -Cucujidae eGyrinidae -Scolylidae -Silphidae -Staphylinidae -Tenebrionidae -----...... ~ -Oiptera -Heteroptera -Hymenoptera -Lepidoptera -Neuroptera eOdonata eOrthoptera -Thysanoptera -Trichoptera eChordata
59 Table 1.2: Synonymy of Aleochara bilineata Gyllenhal (1810) and references. • Names References A. agilis Stephens (1832) Klimaszewski (1984) A. immaculata Stephens (1832) Klimaszewski (1984) A. nitida Erichson (1839) Wadsworth (1915) & Klimaszewski (1984) A. a/picola Heer (1839) Klimaszewski (1984) A. nigricornis Gredler (1866) Klimaszewski (1984) A. anthomyiae Sprague (1870) Wadsworth (1915) & Klimaszewski (1984) Baryodma ontarionis Casey (1916) Colhoun (1953), Wishart (1957) & Klimaszewski (1984) A. bimaculata Burks (1952) Wishart (1957) & Klimaszewski (1984) •
• 60 • • • Table 1.3 : Details consumptions of Delia radicum preys by Aleochara bilineata. Authors Eggs and first Instar larvae Third Instar larvae Raad (1962) 952 (40 days x 23.8/day) 104 (40 days x 2.6/day) 1714 (72 days x 23.8/day) 187 (72 days x 2.6/day) Bromand (1980) 2400 250 Langlet (1997) 2526 (60 days) ------
Table 1.4: Length and width of Aleochara bilineata e9g5 according to authors. Authors Length Width Age when measured Wadsworth (1915) 0.38 mm 0.32 mm Unknown Colhoun (1953) 0.50 mm 0.37 mm 24 hours Fuldner (1960) 0.45 ± 0.03 mm 0.36 ± 0.03 mm 48 hours
61 • • • Table 1.5: Synonymy of Delia radicum L. according ta regions and authors. Names Region Reference Anthomyiae brassicae Bouché (1833) First name Coaker & Finch, 1971 Hy/emya brassicae Bouché United States Colhoun, 1953; Brooks. 1957; Read. 1962; Coaker & Canada Finch. 1971; Nair & McEwen. 1975; Finch, 1989. Corthophila brassicae Bouché France Wadsworth, 1915; Smith, 1927; Coaker & Finch. 1971. Germany Russia Phorbia barssicae Bouché France Coaker & Finch. 1971; Finch. 1989. Germany Russia Erioischia brassicae Bouché Belgium Coaker & Finch. 1971; Finch. 1974; Finch. 1989. England Hylemyia brassicae Bouché France Smith. 1927; Coaker & Finch. 1971; Finch. 1989. Germany Russia
62 •
CHAPTER II
IMPACT OF FOOD AND HOST AVAILABILITY ON SIZE AND SURVIVAL OF EGGS OF ALEOCHARA BILINEATA GYLLENHAL (COLEOPTERA: STAPHYLINIDAE) •
• 63 • ABSTRACT Several factors can influence egg size in insects, including food and host availability or age and size of the ovipositing female. In Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae), egg size is highly variable and ranges from 0.010 mm3 to 3 0.042 mm • We have tested the Ice Box Hypothesis that states that when resources are scarce, a female should oviposit a larger proportion of trophic eggs to be eaten by emerging larvae. Our results indicate that when female A. bilineata were without food they oviposited signifieantly smaller eg9s but the presence or absence of potential hosts for the larvae did not influence egg size. However, when the proportion of hatched egg was compared between fed and unfed females, no signifieant difference was found. The Ice Box Hypothesis was not supported by these results. Egg size in A. bilineafa appeared to be influenced positively by age of the ovipositing female and developmental stage of the egg.
• Key wards: Aleochara bilineata, egg size, Ice Box Hypothesis
• 64 • Introduction When survivorship of offspring varies unpredictably, females may gain by increasing clutch size such that when resources are abundant, most offspring survive. However when resources are scaree, sorne eggs may serve as food far affspring (Ice Box Hypothesis) (Alexander, 1974; Elgar & Crespi, 1992). In Labidomera clivicollis Kirby (milkweed leaf beetle) (Caleoptera: Chrysomelidae), an average of 15-170/0 of eggs are trophic and sterile. These eggs are homologous to fertile eggs, but they cannot develop into viable offspring. A certain amount of these sterile eggs are eaten by older larvae from earlier hatching eg9 elutches (Dickinson, 1992; Elgar & Crespi; 1992).
Many factors such as female size and age, food and, for parasitoid species, hast quality can influence the size of the eggs laid (Karlsson, 1987; Berger, 1989; Fitt, 1990; Wallin et al., 1992; Fox, 1993a; Braby, 1994; Fox, 1994). For example, in Chilo partellus Swinhoe (Lepidoptera: Pyralidae), large females lay larger eg9s than small females • (Berger, 1989) and in Pararge aegeria L. (Lepidoptera: Satyrinae), egg weight and oviposition rate decrease with female age (Karlsson, 1987).
Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) adults are predators of dipteran eg9s and larvae including the cabbage maggat, Delia radicum L. (Diptera: Anthomyiidae). The first instar larvae of A. bilineata are ectoparasitoids of the pupae of the same species (Fuldner, 1960; Bromand, 1980).
After a pre-oviposition period of 36 to 96 hours, the females of A. bilineata oviposit approximately 15 eg9s per day for an average of 700 e99s during their lifetime which ranges between 40 to 72 days (Wadsworth, 1915; Colhoun, 1953; Read, 1962). A. bi/ineata oviposits in the soil surrounding plants attaeked by the cabbage maggot (Bromand, 1980). The eg9 size varies between 0.38 to 0.45 mm in length and 0.32 to 0.36 mm in width (Wadsworth, 1915; Colhoun. 1953; Fuldner. 1960). At oviposition. the egg is ellipsoid and white but. as it matures, its chorion turns yellow. Twenty-four hours • belore hatching, the mandibles, eye spots, antennae and legs of the larva are visible 65 through the chorion (Colhoun, 1953). Hatching occurs between three days at 33°C to nineteen days at 10°C after oviposition (Wadsworth, 1915; Colhoun, 1953; Fuldner, • 1960). After hatching, the campodeiform larva searches for its host, drills a small hole in the puparium and enters (Reader & Jones, 1990). A. bilineata completes its three larval instars and pupates inside the puparium (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960; Bromand, 1980; Whistlecraft et al., 1985).
ln this paper, the oviposition strategy of A. bilineata Jemales in response to food and host (cabbage maggot) availability and the impact of female age and size on egg size and hatching rate have been studied in laboratory. The oviposition cycle and the pre-oviposition period of the famale as weil as developmental lime of egg have been established.
Materials and methods
• General conditions
Ali rearing and experiments were done at 20°C, 60% RH and 16L:8N. A. bilineata was reared on the cabbage maggot. Cabbage maggot adults were fed with water, 10% honey solution and a mixture of 75:25 of brewer's yeast and soya flour. These were placed in presence of one-half rutabaga deposited in a dish covered with humidified sand (Royer et al.,1998). These adults oviposited on the sand and the larvae entered the rutabaga to feed and pupate in the sail. For experiments, third instar larvae and pupae were used.
Bath male and female A. bilineata, 24 hours-old, were sexed at mating and placed in a 5.0 cm dish containing a humidified piece of cotton. This experiment was done to determine the distribution of egg size and the effect of the presence of food and hosts on egg size and hatching rate. The adults A. bilineata were fed with third instar • larvae of cabbage maggot every second day and were in presence of eight hast pupae 66 of the same species. During a period of 15 days, the eg9s were collected daily with a brush. With a binocutar (100X), the eg9s were measured in length and width. The eggs • were individually placed in polyethylene capsules until hatching. These capsules were placed in 37 ml closed Soloe cups containing a humidified filter paper. The eggs are ellipsoid in form and their volume can be calculated as (Royer & McNeil, 1993):
n( width 2 *length) V=~----~ 6
Oviposition strateay accordlng ta hast and food avallabllity
ln this experiment, the percentage of trophic e9gs oviposited with or without food or pupae were measured. Eggs that did not hatch were considered as trophic e9gs. The oviposition cycle, duration of pre-oviposition period of female and the distribution of e99 sizes according to treatment were measured as weil as developmental time of egg according to egg size. Finally, the relation between egg size and female age and size • were established. To measure the effect of food and host on egg size and hatching rate, 40 couples were used: 10 were fed in the presence of hosts, 10 were fed without hosts, 10 were unfed with hosts and 10 were unfed without hosts.
A correlation between weight of female and male and eg9 size were calculated. The adults were frozen and the width and length of their pronotum measured. Royer (personal communication) has establish a correlation between the weight (mg) of A. 2 bilineata adults and the surface of their pronotum (mm ): 1 2 f(x) =1.7975 * 10"1 X + 3.4118 * 10- ;R = 0.77 for female and f(x) =1.2843 * 10-1x + 4.4911 * 10"1; R2=O.67 for male where x is the weight of A. bilineata adults. • 67 • Statlstlcs A Kruskal·Wallis test has been used to compare hatching rate according to treatments. Normality has been verified by Kolmogorov-Smirnov tests on: the impact of food and hast availability on egg size, oviposition cycle, duration of pra-oviposition period and famale weight. The data were analyzed by ANOVA followed by Fishers PLSD tests. The relations betwean egg size and adult weight, female age and developmental time of egg were established by Unear ragression. An unpaired Student-t test has been used to compare volume of hatched and sterile eggs.
Results
Presence of trophlc eaas
• No signifieant difference in hatching rates was found between treatments: (mean ± confidence interval of proportion) 86.34 ± 30.31 % for fed couples with hosts, 78.07 ±
33.72 % for fed couples without hosts, 71.19 ± 41.22 % for unfed couples with hosts. No eggs were laid by unfed couples without hosts (H=5.32; df=2; 0.10 < P < 0.05). 3 However, the eg9s that did not hatch were smaller (0.018 ± 0.003 mm ) than viable eggs 3 (0.019 ± 0.004 mm ) (t=3.827; df=1526; P=0.0001) but this difference was very small.
Influence of host and food avallabliity
There was a signifieant differenee in egg size according to treatments (F=7.8020; 3 df=2,1370; P=0.0004). Eggs laid by fed couples with (mean ± SO: 0.019 ± 0.004 mm ) 3 or without (0.019 ± 0.004 mm ) hosts were significantly larger than those laid by unfed 3 couples with hosts (0.017 ± 0.004 mm ) (Figure 2.1). • 68 The age and weight of femala can also affect the egg size laid. There was a weak positive correlation between egg size and female age (Y=O.018+1.072x1 0-4X; R2=0.009; • P=0.0004) and between egg size and weight of female (Y=O.17+0.001 X; R2=0.004; P=0.0181). There was no signifieant differenee in female weight between treatments (F=0.269; df=2,17; P=0.7675). The average female weights were: fed with hosts = 1.913 ± 0.436 mg, fed without hasts = 1.839 ± 0.226 mg and unfed with hasts = 1.972 ± 0.376 mg. Moraover, larger males did not stimulate production of larger eggs by females as there was no correlation between male weight (1.90 ± 0.39 mg) and egg size (Y=0.019+3.672x10-sX; R2=1.39 x 10'5; P=O.8949).
Fed females with hasts laid signifieantly more eggs per day (8.56 ± 4.85 eggs) than fed females without hasts (5.91 ± 3.59 eggs) and signifieantly more than unfed females with hosts (0.67 ± 1.31 eggs) (F=23.313; df=3,48; P<0.0001) (Figure 2.2). In ail treatments, the average developmental time of egg was 6.0 ± 0.5 days at 20°C, which corresponds to reports in the literature (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960). Moreover, there was a correlation between egg size and developmental time • (Y=0.026+0.001X; R2=0.024; P<0.0001). There was a signifieant difference in pre oviposition periods between ail treatments. When females were in the presence of food and hasts, the pre-aviposition period was significantly shorter (2.87 ± 0.34 days) than when only food (3.14 ± 0.52 days) and signifieantly shorter than only hasts were available (5.58 ± 2.47 days) (F=454,649; df=2,1370; P Discussion Sorne trophic eggs can be laid by female to serve as food for other larvae. The lee Box Hypothesis predicts that, when resources available for females are scarce, sorne eggs serve as food for other larvae of the same clutch but when resources are abundant ail offspring may prosper. There is no difference of hatching rate according to • treatments, therefore the presence of food or host had no influence on the proportion of 69 sterile eggs. The females did not produce more eggs that did not hatch in conditions of availability of food or host but we cannot conelude that these eggs, even if smaller than • viable eggs, were trophie or aborted. No eggs were laid by unfed females without host. These females were starved and the ovaries probably did not develop (Colhoun, 1953). Contrary to unfed couples with hasts, sorne hosts were eaten by the adults. This source of food permitted ovary development and subsequently, oviposition. The availabiHty of food and hast can affect the egg size laid by the female. The hypothesis is: when resources (food or hast) are scarce, females oviposit smaller eggs than when resources are available. In the experiment, the presence of food had a positive impact on egg size but the presence of hosts did not affect the egg size laid by the female where fed females laid larger eggs than unfed females. This differenee in e9g size according to the availability of food can be explained by the oogenesis. Fed females had more resources ta invest in their eggs than females with no or limited food. Sorne females without food (third instar larvae of cabbage maggot) have been feeding on hast pupae and therefore had a Iimited aecess to food. However this Iimited food was not enough to produce large e9gs such as fed famales. However, the difference in average 3 • egg size between treatments (0.017 to 0.019 mm ) was small comparatively to the range 3 observed (0.010 to 0.042 mm ) in ail treatments (Figure 2.1). The difference in eg9 size can also be explained by biologieal factors: female age and weight. First, female age had an impact on eg9 size which increases with female age. Generally, in other insects, egg size decreases with famale age, however an inerease or no change in egg size has also been reported (Fox, 1993b). Secondly, female weight did not offer an explanation for the difference in egg size. The larger females did not oviposit larger eggs as in Chilo partellus Swinhoe (Lepidoptera: Pyralidae) (Berger, 1989). The presence of food and hast have a positive impact on daily oviposition where females laid more e99s in presence of food and host. However, the daily oviposition rate • observed with availability of food and hast has been lower (8.5 e9gs par day) than what 70 is reported in the literature (15 eggs per day) (Colhoun, 1953; Read, 1962), perhaps due to the fact food was offered only every second day in our experiment compared to every • day in the literature. Moreover, larger e9gs developed faster as in Callosobruchus macu/atus Fabrichus (Coleoptera: Bruchidae) where the larvae from larger eggs develop faster and emerge as larger adults (Fox, 1994). Hence, food and hast affect the pre-oviposition periode In the literature, the pre oviposition period varies between 1.5 to 4 days (36 to 96 hours) (Wadsworth, 1915). This corresponds to our fed couples but is shorter than when we measured in unfed couples. The females need food ta develop their ovaries and also need time ta evaluate the environment where they oviposit. In the treatment when no hosts were offered, females waited before ovipositing. Our objective was to understand the factors affecting egg size. The availability of food and host did not have an impact on the hatching rate of eggs, but we cannot conclude whether the eggs that did not hatch were trophic or aborted. The famalas that • had access to food had a shorter pre-oviposition period and laid more eggs than females that had no access to food. Moreovar, those females laid larger eggs than unfed females. The females laid larger eg9s with time and the development of the larger eg9s was faster than smaller ones. But these factors explainad only part of the difference in eggs size. ln this experiment, since the measures (Iength and width of eggs) were taken once per day, the eggs were not ail of the same age when measured. The age of the eggs varied between less than 1 hour to 24 hours-old. This difference in age was especially important because A. bi/ineata eggs swell during their development. Thus, young eggs had not begin their swelling whereas those 24 hours-old had begin their swelling. The resulting variability precludes firm conclusions. However, subsequent experiments (chapter 3) concluded that A. bi!ineata eggs do absorb water during their • development and this absorption produces swelling. 71 • References Alexander, A.D. 1974. The evolution of social behavior. Annu. Rev. Ecol. Syst. 5: 325 383. Berger, A. 1989. Egg weight, batch size and fecundity of the spotted stalk borer, Chilo partellus in relation ta weight of females and time of oviposition. EntamaI. Exp. Appl.50:199-207. Braby, M.f. 1994. The significance of egg size variation in butterflies in relation ta hostplant quality. Oikos 71 :119-129. Bromand, B. 1980. 1nvestigations on the biological control of the cabbage rootfly (Hylemya brassicae) with Aleochara bilineata. Bull. SROPIWPRS 3:49-62. Colhoun, E.H. 1953. Notes on the stages and the biology of Baryodma ontarionis • Casey (Coleoptera: Staphylinidae), a parasite of the cabbage maggot, Hylemya brassicae Bouché (Diptera: Anthomyiidae). Cano Entamai. 85:1-8. Dickinson, J.L. 1992. Egg cannibalism by larvae and adults of the milkweed leat beetle (Labidomera clivicollis, Coleoptera: Chrysomelidae). Ecolo Entomol. 17:209-218. Elgar, M.A. & B.J. Crespl. 1992. Cannibalism: ecology and evolution among diverse taxa. Oxford University Press. Oxford. 361 p. Fltt, G.P. 1990. Comparative fecundity, clutch size, ovariole number and eg9 size ot Dacus tryoni and D. jarvisi, and their relationship to body size. EntamaI. Exp. Appl. 55:11-21. • 72 Fox, C.W. 19938. Maternai and genetic influences on egg size and larval performance in a seed beetles (Ca/losobruchus maculatus): multigenerational transmission of • a maternai effect. Heredity 73:509-517. Fox, C.W. 1993b. The influence of maternai age and mating frequency on e9g size and offspring performance in Ca/losobruchus maculatus (Coleoptera: Bruchidae). Oecologia 96: 139-146. ___a 1994. The influence of egg size on offspring performance in the seed beetle, Callosobruchus maculatus. Oikos 71 :321-325. Fuldner, O. 1960. Beitrage zur morphologie und biologie von Aleochara bilineata Gyll. und A. bipustulata L. (Coleoptera: Staphylinidae). [Traduction: Contribution à la morphologie et à la biologie de Aleochara bilineata Gyll. et A. bipustulata L. (Coleoptera: Staphylinidae)) Z. Morph. Okol. Tiere. 48:312-386. • Karlsson, B. 1987. Variation in egg weight, oviposition rate and reproductive reserves with female age in a natural population of speckled wood butterfly, Pararge aegeria. Ecol. EntamaI. 12:473-476. Read, D.C. 1962. Notes on the life history of Aleochara bilineata (Gyll.) (Coleoptera: Staphylinidae), and on its potential value as a control agent for the cabbage maggot, Hylemya brassicae (Bouché) (Diptera: Anthamyiidae). Can. Entomol. 94:417-424. Reader, P.H. a T.H. Jones. 1990. Interactions between an eucoilid (Hymenoptera) and a staphylinid (Coleoptera) parasitoid of the cabbage root fly. Entomophaga 35:241-246. • 73 Royer, L. & J.N. MeNeli. 1993. Male investment in the European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae): impact on famale longevity and reproductive • releases in urban gardens. Entomophaga 37:55-63. Royer, L., S. Fournet, E. Brunei & G. Bolvln. 1998a. Intra- and interspecific host discrimination by host-seeking larvae of Coleopteran parasitoids. Oecologia in press. Wadsworth, J.T. 1915. The Iife-history of Aleochara bilineata, Gyl!., a staphylinid parasite of Chortophila brassicae, Bouché. J. Econ. Biol. 10:1-27. Wallin, H., P.A. Chlverton, B.S. Ekbom & A. Borg. 1992. Diet, fecundity and eg9 size in sorne polyphagous predatory carabid beetles. Entomol. Exp. Appl. 65: 129-140. Whlstlecraft, J.W., C.R. Harris, J.H. Tolman & A.D. Tomlln. 1985. Mass-rearing technique for Aleochara bilineata (Coleoptera: Staphylinidae). J. Econ. Entamol. • 78:995-997. • 74 • Figure 2.1: Distribution of eg9 volume produced by Aleochara bilineata over a period of 15 days by A- 7 fed couples with hosts, B· 7 fed couples without hosts and • C- 6 unfed couples with hasts. • 75 • • • DI J> o Humber of egga Humber of eggs Humber of eggs ~ -61\)1\) -6 ... 1\) ~ ..... 1\) 1\) U1 0 U1 0 U1 U1 o Ut 0 Ut 0 Ut 00000 0 o 0 8 ~ 8 0.006 iî '. 1 l , \ 0.006 0.006 1 ,,, \ 1 0.01 0.01 0.01 ~ 0.014 ~ ..,. 0.014 -,._ . :::::I-i:~ .. .' ._. ~.. . 0.018 '-. ,-, 0.018···~~·· ..·. ~ ~ ~- . _. --- .. ~ .... - 0.022.-~ ; ~ 0.022 ~ 0.022 .'.- • • r~ . .. 'i 0.026 3' 0.026 3' 0.026 3 3 ~ 3 w 0.03 .!:! ~ ~ 0.03 - 0.03 ~ Il ~ 0.034 ...... 0.034 0.034 Il (",) ...... ~I ...... 0.038 0.038 1\) 0.038 Q) 0.042 0.042 • 1 0.042 ~ • Figure 2.2: Oviposition cycle over 15 days for females of Aleochara bilineata according to treatments ( __ : 8 fed couples with hosts J __ : 10 fed couples without host and : 10 unfed couples with • hosts). Day one being the tirst day of oviposition. • n CI) l' • , (Of) 1 r ...... C'I •~ 1 .. ~ i ...... 'O.:. t1 1 a 1 •1 1 r ...... t <> 1 1 ,- ...... co 1 1 >- .. .. 1 ~ 1 • , ...... 1 •~ " i Il J • li 0 ~1+ -0 1 i 1 1 1 ; 1 ..... 1-"+ L(.) , i \ 1 ,. 14 ~ 1 1 1 1 1- •••••• ... -. (Of) \ . \, ;...... ::e C't .. 2J/ " / .. " / 1 " / 10 10 a L(.) a N ~ • peillOdIAO saee e80JeAY • Connecting text ln the preceding chapter, we have demonstrated that the presence of food and the age of female Aleochara bilineata increased egg size laid. Moreover, fed females of A. bilineata oviposited more eggs and had a shorter pre-oviposition period than unfed females. The presence of hosts had no effect on the size of the egg but shortened the pre-oviposition period of females. While the presence of food and the age of females explained sorne of the variability in egg size, this variability remained unusually high. Subsequent preliminary experiments showed that A. bilineata eg9s increased in size during theïr development and measurements taken at different time of their development yield highly variable results, as observed in the previous chapter. Such increase in siz\~ could be due to hydropy, and, in arder to demonstrate it, we followed egg size throughout its • development, showed that they absorb water and, finally, described the morphology of the egg envelopes. These data are presented in the following chapter. • 79 • To be submitted: Int. J. Insect Morphol. &Embryol. CHAPTER III DEVELOPMENT AND ENVELOPE STRUCTURE OF ALEOCHARA BILINEATA GYLLENHAL (COLEOPTERA: • STAPHYLINIDAE) EGGS. • 80 • ABSTRACT Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) oviposits in soil microhabitats likely ta contain the dipteran pupae which are hosts of its ectoparasitoid first instar larvae. A. bilineata eggs are hydropic and, after 30 hours of development, start ta increase in volume and do so until 50 hours. This increase in volume is due to an absorption of water. The eggs increase their initial volume by a factor of 1.68 which corresponds to an increase of 44.44% of initial weight. During the swelling, the endochorion which was initially dense and regular becomes fragmented. Key words: Aleochara bilineata, hydropic, endochorion, egg, absorption, water, swelling. • • 81 • Introduction At oviposition, insect eggs have two maternai envelopes that caver the oocyte membrane; the vitelline membrane and the chorion. These envelopes are secreted by the follicular cells of the female. The chorion comprises the outer exochorion and the inner endochorion (Chauvin & Chauvin, 1980; Biernont et al., 1981; Chauvin et al.,1988; Larink & Bilinski, 1989; Neveu et al., 1997). The exochorion may be covered with mucoproteins secreted by the accessory glands of the female. This mucus helps secure the e9g to its substrate and prevents a direct contact between the chorion and the substrate. Bacteria are often seen growing on chorion (Chauvin & Chauvin, 1980; Nénon et al., 1995). After oviposition, the serosal cuticle is secreted by the ernbryo (Chauvin & Chauvin, 1980; Biemont et al., 1981; Hinton, 1981; Chauvin et al., 1991). ln some insect species, the female produces few e9gs but invests more of • its resources in each eg9. The reproduction rate of such species is low but the mortality rate of the e99s is also expected to be low. These e99s normally do not need ta absorb nutrients, water or oxygen from their environment (Smith & Fretwell, 1974; McGinley et al., 1987). In other species, the female lays many smalt eggs containing less resources. The reproduction rate of these species is increased but at the cost of a higher eg9 mortality risk. These eggs often need ta absorb nutrients, water or oxygen from their environment to complete their development. When they increase in size doing so, they are called hydropic e9gs. Hydropic e9gs require an absorption of water trom their environment to complete their development (Hinton, 1981; Chauvin et al., 1991). These hydropic eg9s are found in many aquatic and terrestrial insect species of Orthoptera, Hemiptera, Homoptera, Hymenoptera, Diptera and Coleoptera (Hinton, 1981). This absorption of water produces an increase of e99 volume corresponding to • modifications in the e99 membranes (Lincoln, 1961). The chorion of hydropic 82 e9gs can either stretches while keeping its integrity, as in Ocypus a/ens Müller (Coleoptera: Staphylinidae) and Trybliographa rapae Westwood (Hymenoptera: • Eucolidae) (Slifer, 1937; Lincoln, 1961), becomes fragmented to allow the size increase, as in Dytiscus marginalis L. (Coleoptera: Dysticidae) (Lincoln, 1961) or shows a specifie structure such as Tetrix vittata Zetter (Orthoptera: Tetrigidae) where an anterior horn serves as an expansion chamber to permit swelling (Lincoln, 1961; Hartley, 1962). Hydropic eggs can absorb water passively by osmosis when in contact with Iiquids of osmotic pressure lower than that of the embryonic fluids and tissues. When osmotic pressure is higher than that of embryonic fluids and tissues, the absorption of water has to be an active process. Kerenski (1930) has shown such an active absorption of water in Anisop/ia austriaca Reitter (Coleoptera: Scarabidae) whose eggs absorb water even when placed in a 4% solution of sodium chloride (in Hinton, 1981). This phenomenon is often observed in endoparasitic insects whose eggs are immersed in host fluids of relative high • osmotic pressure (Hinton, 1981). The absorption of water either passively or actively, is generally performed through specialized organs (hydropyles). There are three types of hydropyles: serosal, serosal cuticle and chorionic hydropyles (Hinton, 1981). Serosal hydropyles are found in sorne Orthoptera and Hemiptera and are usually present on the anterior pole of the egg. The serosal cuticle hydropyles, described in Acrididae (Orthoptera), do not absorb water directly but rather change the permeability of the cuticle hydropyles. These serosai cuticle hydropyles are found generally on the posterior pole of the egg. Finally, the chorionic hydropyles are known from e9gs of Heteroptera, Homoptera and Coleoptera that show a respiratory air layer even if the e9g is dried. In some species of Hymenoptera and Coleoptera, there are no apparent structure or specialized organ enabling • the egg to absom water. For these species, the absorption of water may occur 83 through the egg surface and not through a specialized organ (Hinton, 1981; • Chauvin et al., 1991). Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) is both a predator and an ectoparasitoid of the cabbage maggot, Delia radicum L. (Diptera: Anthomyiidae), an important pest for cruciferous crops. Adult A. bilineata feed on the eggs and larvae of Diptera while its first instar larva is an ectoparasitoid of the same Diptera pupae. The female A. bilineata oviposits in the soil surrounding plants attacked by Diptera. Egg development lasts from three days at 29-30°C to nineteen days at 10-11 oC (Colhoun, 1953; Fuldner, 1960). Upon hatching, the tirst instar A. bilineata searches for a host pupa and drills a small hole in the puparium of its hast to enter. A. bilineata is an ectoparasitoid, feeding and completing its transformation inside the puparium but outside of the pupa (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960; Read, 1962; Bromand, 1980). An increase in volume in the eg9 of A. bilineata has already been reported • (Fuldner, 1960; Bromand, 1980). ln this paper, changes in size and weight of A. bilineata e99s were followed throughout the egg development. Modifications in the egg envelopes morphology were followed during hydropy using scanning and transmission electronic microscopy. • 84 • Materials and methods Rearing and ail experiments were done at 20°C, 60% relative humidity and a photoperiod of 16L:8N. Adults of O. radicum were fad with water, 10% honey solution and a mixture of 75:25 of brewer's yeast and soya flour. This was placed in the presence of one-hait rutabaga deposited in a dish covered with dampened sand (Royer et al., 1998). These adults oviposited on the sand and the larvae entered the rutabaga to feed. Adults of A. bilineata were placed in a dish containing damp cotton. They were fad with third instar D. radicum larvae in the presence of host pupae of the same spacies. The eggs were collected with a brush and placed individually in polyethylene capsules. These capsules were placed in closed 37 ml Solo cups containing a damp filter paper. • Eaa slze and welaht To follow changes in egg volume during development, 30 eggs, 1 ± 1 hours-old, were collected from the aviposition site of A. bilineata adults. These egg8 were measured (Iength and width) with a binocular (SaX) at specified times during their development until hatching. These egg8 have an ellipsoid farm and their volume was calculated as (Royer & McNeil, 1993): 1C(W 2 * 1} V=~-....;;... 6 Where W= Width and 1= length. To quantify the increase in weight during hydropy, 30 e9gs before (1 ± 1 hour-old) and 30 e9gs after (68 ± 1 hour-old) hydropy were collected and placed on a filter paper. These eggs were wei9hed without filter paper on a scale Cahn 25 weighting at 0.0001 mg (Vannier, 1974; Biemont et al., 1981). These eggs • were desiccated with potassium hydroxide (KOH) for five days then weighed 85 again. Based on these fresh and dry weights, the quantity of water absorbed by • egg during swelling was determined (Vannier, 1974; Chauvin & Vannier, 1983). MorpholoGY of eGa envelope Based on the data on egg weight (Figure 3.1), observations were made before oviposition (oocyte), just after oviposition (1 hour), between oviposition and swelling (17 hours), at the beginning of swelling (30 hours), during swelling (40 hours) and before hatching (6 days). The oocytes were collected directly from the female oviducts. Scanning electron microscopy: The samples were placed in polyamide filters and fixed with progressive dehydration with alcohol (70%, ao%, 90%, 95%), 100% and 100%). Each bath lasted ten minutes. After dehydration, the samples were stored in 100% acetone • until observation. Just before observation, the samples were dried with the critical-point method using a dryer Balzers CPD 010 where the acetone was replaced by Iiquid CO2• The samples were gold-palladium coated with a JEOL JFC 110 metaliser and then observed with a SEM JEOL 6400. Transmission electron microscopy: The samples were fixed using the Karnovsky technique (1965). The eg9s were fixed in a prefixation solution of 4% paraformaldehyde and 5% glutaraldehyde in O.lM (pH=7.4) of sodium cacodylate buffer for four hours at 4°C. The eggs were eut to allow the fixative to penetrate overnight. They were rinsed in a 0.1 M sodium cacodylate buffer (pH=7.4), and postfixed for one hour in 1°k osmium tetroxide in the same buffer. They were rinsed again in cacodylate % % buffer and dehydrated in acetone (10 minutes each in a series of 50 , 60 , % 0 70ok, 80 , 90 k and 100% solution acetone). The samples were embedded in • epon-araldite, and silver and gold sections were sectioned (50-100 nm). These 86 ultrathin sections were stained with 5°1'0 uranyl acetate for 45 minutes and lead • citrate for five minutes and then observed with a Philips CM 30 microscope. Statlstlcs Only hatched eggs were used to calculate the mean development period and to compare e9g volume before and alter swelling. A paired Student-t test was used to compare egg volume bafora and after swelling. A unpairad Student-t test was used to compare fresh and dry weight of eggs before and after swelling. • • 87 • Results and discussion Change in eaa volume w'th tlme Twenty-four e9gs completed their development, rapresenting 80% hatching. At 20°C, the eggs hatched in 7.07 ± 0.22 days (mean ± 50). This corresponds to the reports in the Iiterature (Colhoun,1953; Fuldner, 1960). The eggs bagan to increase in volume 30 ± 1 hours after oviposition and continued to do so until 50 ± 1 hours (Figure 3.1). Fuldner (1960) mentioned this increase of egg volume and concluded that it represented an absorption of water in A. bilineata and A. bipustulata aggs. The increase started between 12 to 24 hours after oviposition and lasted until 48 hours at 22°C (A. bilineata and A. bipustulata). A difference in temperature may explain why the swelling began later in our experiment (between 30 and 50 hours). The average egg volume 1 ± 1 hour after oviposition was 0.020 ± 0.003 3 • mm , significantly less than at 167 ± 1 hours, just before hatching (0.034 ± 0.005 3 mm ) (t=20.914; df=23; P<0.0001). This represents an increase of 1.68 over initial volume. Similar results are reported for Abax ater Viller (Coleoptera: Carabidae), a species with hydropic eggs whose egg volume increases trom 3 3 about 5 mm ta 8 mm , an increase of 1.6 of initial volume. The A. bilineata eggs increased in length by 75 ± 23 J.1m and in width by 70 ± 24 J.1m during swelling. These increases are similar to reports in the Iiterature for A. bilineata (70 f.Lm in length and 60 J.lrn in width (Fuldner, 1960; Bromand, 1980)). We'aht variation in tlme During their development, the e995 also increased in fresh weight by 44.440/0, from 0.020 ± 0.004 mg at 1 ± 1 hour ta 0.036 ± 0.004 mg at 68 ± 1 hours • (t=15.623; df=56; P 88 to absorption of liquid water by the egg from its environment. By comparing fresh (0.020 ± 0.004 mg) and dry (0.012 ± 0.002 mg)weights of eggs, a water content • of 40.7 ± 7.1 % was found before swelling which was lower than after swelling (fresh; 0.036 ± 0.004 mg and dry; 0.017 ± 0.005 mg), where the water content of the egg increased ta 54.5 ± 10.9% (t= 5.621; df = 53; P< 0.0001). This confirms that there is an absorption of water during eg9 development. In Ocypus olens Müller (Coleoptera: Staphylinidae), water contents of 63.20/0 before swelling and 79.5% after swelling were found (Lincoln, 1961). The dry weight of eggs significantly increased from 0.012 ± 0.002 mg at 1 ± 1 hour to 0.017 ± 0.005 mg at 68 ± 1 hours (t=5.067; df=53; P<0.0001). This signifieant increase in dry weight suggests that, at 68 ± 1 hours-old, the embryology is advanced and that sorne water has been fixed by the embryo (Chauvin et al., 1991). • Ovipositing many smaller hydropic eggs might be advantageous for A. bilineata females as, in this species, it is the first instar larva that searches for hosts. By investing less resources in each egg, the female can oviposit more thus increasing the probability of having sorne larvae finding an host. Hydropic eggs require Iittle invastment but they have to absorb nutrients, water or oxygen from their environment to complete their development. However when e9gs need resources from thair environment, the choice of an adequate oviposition site is very important. In A. bilineata, females oviposit near the host pupae in decomposing cruciferous plants where Iiquid is available (Bromand, 1980). Within such a humid environment, the female can invest lower energy in each egg as compared to a species that oviposits in a dry habitat. • 89 Morpholoay of eaa envelopes • Oocyte (before oviposition): With no evidence of hydropyles, the surface of the oocyte was smooth with small holes and a few bumps (Figure 3.3A). In most Coleoptera and Hymenoptera species where water is absorbed by the egg, hydropyles have not been identified (Hinton, 1981). When no hydropyles are present, water is absorbed through the entire surface of the egg (Larink & Balinski, 1989; Chauvin et aL, 1991). In contrast, in O. olens, there are about 4000 chorionic hydropyles (aeropyles) throughout the outer layer of the chorion in an equatorial band around the egg (Lincoln, 1961). Traces of follicular cells with granules were visible on the oocyte (Figure 3.38). These cells synthesize successively the vitelline membrane and the chorion. In young oocytes, the follicular cells contained many granules, that • constitute the vitelline membrane, and formed a layer 3.23 J.1m in width (Figure 3.4A). In old oocytes, the follicular cells contained few granules and measured 13 ~m in width by 15 J.1m in length (Figure 3.48). Egg: The exochorion of A. bilineata eggs at 1 ± 1 hour-old had an irregular thickness of 1.5 J.1m. While the endochorion, dense and regular, measured approximately 1.5 JJm in thickness (Figure 3.68). After oviposition, numerous bacteria, fungus, spermatozoids and granules were found on the egg surface (Figure 3.SA-C). They were always present but did not prevent egg development (Figure 3.SC-E). In Listronotus oregonensis LeConte (Coleoptera: Curculionidae), a mucus coating was also found on the egg surface (Nénon et al., 1995). This mucus is deposited in the oviduct by the • accessory glands of the female when the oocyte passes through. After 90 oviposition. this mucus allowed the development of numerous bacteria (Biemont et al.• 1981; Nénon et al.• 1995). Such mucus has probably a role in preventing a • direct contact between the chorion and the plant sap. It also secures the egg to the substrate (Chauvin & Chauvin. 1980; Nénon et aL. 1995). No mucus was observed in A. bilineata eggs but the exochorion of the egg may permit attachment of these particles. Spherical granules, trom 2 to 5 ~m in diameter. were sparsely distributed on the surface of the egg (Figure 3.5C and 3.7B). Granules were also observed in high density on the external membrane of eggs of Heteromurus nitidus Templeton (Collembola: Entomobryidae) (Larink & Bilinski. 1989) but these granules are spherical or oval and vary in diameter from 0.2 to 1 ~m, thus smaller than in A. bilineata (Larink & Bilinski. 1989). These authors suggest that these granules. in H. nitidus, are not an integral part of the outer envelopes since they can be easily detached tram it. These granules are produced in the oviduct after deposition of the egg envelopes. Moreover, in both A. bilineata and H. nitidus, • granules were associated with bacteria-like organisms. In H. nitidus the granules are deposited on the surface of the egg. In A. bilineata, the granules were present on the egg surface and in the exochorion (Figure 3.6A). The granules in the exochorion measured between 0.1 and 0.5 ~m in diameter. Such granules within the external eg9 envelopes have al50 been observed in Locusta migratoria migratorioïdes Reiche & Farmaire (Orthoptera: Acrididae) but their size varied between 6 to 8 ~m in length and about 4 ~m in width, therefore bigger than in A. bilineata (Hartley. 1961). Just before swelling. at 30 hours old. the chorion is dense and regular (Figure 3.6C). At 40 hours. during hydropy, the appearance of the chorion changed (Figure 3.7A-C). The exochorion remained irregular but in the endochorion fractures have appeared giving it a mosaie pattern (Figure 3.70). • However. the endochorion remained as thick as before swelling. The serosai 91 cuticle was visible, formed by severai layers secreted by the embryo with a • thickness of 8 J.Im at 40 hours of development (Figure 3.7A). An increase in egg volume was observed from 30 hours until 50 hours after oviposition. This swelling was produced because the egg absorbed Iiquid water during its development. Moreover, after this swelling there was a fracturing of the endochorion. Coleopteran eggs are diverse both in their form, being ellipsoid, spherical or cylindrical, and in the habitats where they are laid. Coleopteran species exploit most terrestrial and aquatic habitats and they oviposit, for example, in plant tissues (Curculionidae), in water (Noteridae) or in or on the sail surface (Staphylinidae) (Lincoln, 1961; Hinton, 1981; Paulian, 1988; Nénon et a/., 1995). A. bi/ineata, that oviposits in the soil near plants infested by its prey/host, is a good representative of the oviposition sites selection in Coleoptera. The same • behavior is also observed in other Coleoptera families such as Scarabaeidae. ln general, the chorion of Coleoptera e9gs is soft (Crowson, 1981; Hinton, 1981). The egg chorion of A. bi/ineata is rigid, which is rare in hydropic e9gs that have normally a soft chorion, as in Trybliographa rapae (Hymenoptera: Eucolidae), to facilitate water absorption (Lincoln, 1961). Hydropic e9gs with a hard chorion are also known from another Staphylinidae species, Ocypus a/ens (Lincoln, 1961; Crowson, 1981). The presence of a hard chorion in these hydropic eggs could be explained by the fact that, although these eggs need water to complete their development, they also need physical protection against external pressure or small predators. A. bilineata and O. a/ens oviposit respectively in and on the soil surface and these eggs are less protected than jf they were laid in plant tissues. Hydropy is not generalized in Coleoptera, being present in certain species • in only four families: Staphylinidae, Scarabaeidae, Elateridae and Elmidae 92 (Hinton, 1981; Paulian, 1988). Most species from these families oviposit in habitats where water is readily available (Hinton, 1981), as sorne species of • Scarabaeidae that oviposit in plant tissues where water is available as plant sap. ln the case of A. bilineata, eggs are laid near infested plant where water could be available for the eg9s. The eggs of A. bilineata are atypical for Coleopteran eggs, being hydropic and having a hard chorion. The presence of this hard chorion probably influences the water absorption ability of these e9gs. Both relative humidity and the presence of tree water at the soil surface probably influence eg9 survival in A. bilineata. In addition, the tact that the hard chorion is tractured at the time of hydropy could be further investigated. In particular, it could be interesting ta determine if these fractures appear before hydropy and theref,')re permit it or if they are a result of hydropy. • • 93 • References Blemont, J.C., G. Chauvin & C. Hamon. 1981. Ultrastructure and resistance to water loss in eggs of Aeanthosee/ides obtectus Say (Coleoptera: Bruchidae). J. Insect Physiol. 27:667-679. Bromand, B. 1980. Investigations on the biologieal control of the cabbage rootfly (Hylemya brassicae) with A/eoehara bilineata. Bull. SROPIWPRS 3:49-62. Chauvin, G. & G. Vannier. 1983. Effet d'une augmentation de la température ambiante sur la transpiration des larves, nymphes et adultes de Tinea pellionella L. (Lepidoptera: Tineidae) placés en atmosphère sèche. Bull. Zool. 50:257-262. Chauvin, G., G. Vannier & P. Vernon. 1988. Structure fine et rôle, dans la • rétention hydrique, des enveloppes de l'oeuf d'un diptère subantarctique, l'Anata/anta aptera Eaton (Sphaeroceridae). Cano J. Zool. 66:2421-2427. Chauvin, G., C. Hamon, M. Vancassel & G. Vannier. 1991. The e9gs of Forficu/a aurieu/aria L. (Dermaptera, Forficulidae): ultrastructure and resistance ta low and high temperatures. Cano J. Zool. 69:2873-2878. Chauvin, J.T. & G. Chauvin. 1980. Formation des reliefs externes de l'oeuf de Mieropteryx calthella L. (Lepidoptera: Micropterigidae). Cano J. Zool. 58:761-766. Colhoun, E.H. 1953. Notes on the stages and the biology of Baryodma ontarionis Casey (Coleoptera: Staphylinidae), a parasite of the cabbage maggot, Hy/emya brassieae Bouché (Diptera: Anthomyiidae). Cano • Entomol. 85:1-8. 94 Crowson, R.A. 1981. The biology of the Coleoptera. Academie Press. London. • 802p. Fuldner, D. 1960. Beitrâge zur morphologie und biologie von A/eochara bilineata Gyll. und A. bipustulata L. (Coleoptera: Staphylinidae). [Traduction: Contributions à la morphologie et à la biologie de Aleochara bililleata Gyll. et A. bipustu/ata L. (Coleoptera: Staphylinidae)]. Z. Morph. ëkol. Tiere. 48:312..386. Hartley, J.C. 1961. The shell of Acridid eggs. Quart. J. Micr. Sei. 102:249-255. ___. 1962. The eg9 of Tetrix (Tetrigidae, Orthoptera) with a discussion on the probable significance of the anterior horn. Quart. J. Mier. Sei. 103:253 259. • Hlnton, H.E. 1981. Biology of inseet egg5. Pergamon Press. Oxford. 1125p. Karnovsky, M.J. 1965. A formaldehyde-glutoraldehyde fixative of high osmolality for use in eleetron microscopy. J. Cell. Biol. 276:137A-138A. Larlnk, O. & S.M. Billnski. 1989. Fine structure of the egg envelopes of one proturan and two collembolan genera (aptorygota). Int. J. Inseet Morphol. & Embryol. 18:39-45. Lincoln, D.C.A. 1961. The oxygen and water requirements of the egg of Ocypus a/ens Müller (Staphylinidae, Coleoptera). J. Inseet Physiol. 7:265-272. McGlnley, M.A., O.H. lemme and M.A. Geber. 1987. Parental investment in offspring in variable environments: theoretical and empirical • considerations. Am. Nat. 130:370-398. 95 Nénon, J.P., G. Bolvln & M.R. Allo. 1995. Fine structure of egg envelopes in Listronotus oregonensis (LeConte) (Coleoptera: Cureulionidae) and • morphological adaptations to oviposition sites. Int. J. Inseet Morphol. & Embryol. 24:333-342. Neveu, N., X. Langlet, E. Brunei, M. Lahmer, G. Bolvin, M.R. Allo & J.P. Nénon. 1997. The fine structure of the egg shells of the cabbage maggot, Delia radicum L. (Diptera: Anthomyiidae) and its relation with developmental conditions and oviposition site. Cano J. Zool. 75:535-541. Paullan, R. 1988. Biologie des Coléoptères. Éditions Lechevalier. Paris. 719p. Aead, D.C. 1962. Notes on the Iife history of Aleochara bi/ineata (GyIL) (Coleoptera: Staphylinidae), and on its potential value as a control agent for the cabbage maggot, Hylemya brassicae (Bouché) (Diptera: • Anthomyiidae). Cano EntamaI. 94:417-424. Royer, L. & J. N. MeNeil. 1993. Male investment in the European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae): impact on femala longevity and reproductive performance. Funct. Ecolo 7:209-215. Royer, L., S. Fournet, E. Brunei & G. Bolvln. 1998a. Intra- and interspecific host discrimination by host-seeking larvae of Coleopteran parasitoids. Oeeologia in press. Sllfer, E.H. 1937. The origin and fate of the membranes surrounding the grasshopper egg; together with sorne experiments on the source of the hatching enzyme. Quart. J. Micr. Sei. 79:493-508. Smith, C.C. and 5.0. Fretwen. 1974. The optimal balance between size and • number of offspring. Am. Nat. 108:499-506. 96 Vannier, G. 1974. Variation du flux d'évaporation corporelle et de la résistance cuticulaire chez Tetrodontophora bielanensis (Wagg.), insecte collembole, • vivant dans une atmosphère à régime hygrométrique variable. Rev. Ecol. Biol. 50111 :201-211. Wadsworth, J.T. 1915. The journal of economic biology on the life-history of Aleochara bilineata J Gyll., a staphylinid parasite of Chortophila brassicae, Bouché. J. Econ. Biol. 10:1-27. • • 97 • Figure 3.1 :Temporal variation of e99 volume (± SO) in Aleochara bilineata at • 20°C. • 98 • . y , 1 1 : . ., ~ . ~ - 8 · a - ao · • . 1 7 ... , , . , ., 1 ~ - i 1 . l'. ,Y i 1 ," . '" " i o L,t)o q 8 ~ ~ ro-o -o 8 o a d 0 a d o ci (tww) ewnlOA 8ei • • Figure 3.2: Fresh and dry weight (± 50) of Aleochara bi/ineata e99s befere (1 ± 1 heur) • A- and after (68 ± 1 heurs) B- swelling at 20°C. ** P • 100 • ID .. " : ..... C • .. C··c. I----f-----t------i'-----+-I--+-----+--+--1--l ~ o ~ E ~ 8 § ci ci ci ci ci ci • (8w) l'lI'8M • Figure 3.3: A- General view of an oocyte of Aleochara bilineata. Scale bar =100 ~m. B- Detail of the surface of an oocyte of A. bilineata with traces of • follicular ceUs (FT). Scale bar = 1 ~m . • 102 • • • 103 • Figure 3.4: Oocyte of Aleochara bilineata in ovariole with follicular ceUs (Fe) 1 granules (G) and vitellus (V). A- Young oocyte with follicular cells • and many granules. Scale bar = 5 J,lm. B- Cid oocyte with follicular ceUs. Scale bar =5 J,lm. • 104 • • • • Figure 3.5: A- Aleochara bilineata e9g 24 hours-old with fungus (F) and bacteria (B). Scale bar = 10 Jlm. B- Egg 24 hours-old of A. bilineata with • granules (G) and spermatozoids (5). Scale bars = 1 J,lm. C- A. bilineata eg9 24 hours-old with granules (G) and minerai particles (P). Scale bar = 1 J.Lm. D- General view of 24 hours-old e9gs of A. bi/ineata. Scale bar =100 Jlm. E- General view of seven days-old e99 of A. bilineata with larva present (L). Scale bar = 100 J,lm. • 106 • • • 107 • Figure 3.6: A· Egg envelopes of Aleochara bi!ineata 1 hour after oviposition. Presence of granules (G) in exochorion (EX). EN = endochorion. Scale bar =5 J,lm. B· Egg envelopes 17 hours-old. The exochorion (EX) is irregular. EN = endochorion. V = vitellus. VM = vitelline • membrane. Scale bars = 1 J..lm. C- Egg envelopes 30 hours-old. Exochorion (EX). Endochorion (EN). Vitellus (V). Vitelline membrane (VM). Scale bar =3 J,lm. • 108 • • • • Figure 3.7 A- Egg envelopes of 40 hours-old Aleochara bilineata eggs. The endochorion (EN) is fragmented. The serosal cuticle (SC) is formed of several layers. EX = exochorion. E = embryo. Scale bar = 5 J!m. • B- Egg envelopes of 6 days-old egg. Presence of granules (G) in exochorion (EX). EN = endochorion. Scale bar = 3 J,lm. C Transverse view (SEM) of egg envelopes of 6 days-old egg. EX = exochorion. EN =endochorion. VM =vitelline membrane. Scale bar =1 J,lm. 0- Inside view (SEM) of fragmented endochorion of 6 days old e9g. Scale bar =1 J.lm. • 110 • • c - • • Connecting text We showed, in the preceding chapter, that the important variability in Aleochara bilineata egg size was due in large part to the fact that these eg9s are hydropic. Sorne 30 hours after oviposition, they start to absorb water and increase in size until 1.68 their initial volume. By ovipositing smaller hydropic e9gs, the female can invest less resources in each egg and can therefore probably increase the number of e99s laid. During hydropy, we also showed that the endochorion of the egg splits, permitting the increase in egg volume. However, hydropy does not explain completely the variability in egg size. Before and after hydropy, there are still e9gs that are up to 2 times large. Differences in eg9 size are known to result in difference in larval size and consequently in larval fitness. In the next chapter, we examine the affects of larval size on the capacity of larvae to survive as tirst instar, their searching • capacity and walking rate, ail parameters related ta fitness. • 112 • Ta be submitted: Oikos CHAPTER IV EFFECT OF SIZE ON FITNESS IN THE LARVAE Of ALEOCHARA BILINEATA GYLLENHAL (COLEOPTERA: • STAPHYLINIDAE) • 113 • ABSTRACT Variation in larval weight may influence larval survival and therefore affect the reproductive success of the female. To evaluate the fitness in the tirst instar larva of Aleochara bi/ineata Gyllenhal (Coleoptera: Staphylinidae), an ectoparasitoid of Diptera pupa, three parameters have been used: longevity 1 walking rate and searching capacity in relation to larval weight. Large larvae have a greater longevity, walk faster and find and parasitize hasts more rapidly than small larvae. We can conclude that large larvae have significantly batter fitness than smalliarvae. Key wards: A/eochara bilineata, fitnass, larvae • • 114 • Introduction Fitness can be measured by the response of a population of organisms to natural selection. It is based on the number of offspring contributing to the next generation in relation to the number of offspring required to maintain the particular population constant in size (where fitness < 1 population decrease, fitness = 1 population is constant and fitness > 1 population increase) (Abercombrie et al., 1980). Fitness is a short-term measure of reproductive success and general adaptedness (de Jong, 1994). Severai parameters contribute to fitness including: viability, fecundity, egg load at emergence, egg size, travel speed and searching efficiency (de Jong, 1994; Visser, 1994). While most studies examine the fitness of adults, the fitness of larvae can be measured with the same parameters. Brady (1994) has measured three offspring fitness parameters in butterflies of the genus Mycalesis; larval survival, larval developmental lime and pupal weight in relation to egg size. There was a correlation between egg weight and larval fitness. Larvae from heavier eggs had a higher survival, developed faster and produced larger pupae than larvae from lighter eggs. Such a relationship is not always present, in • Pararge aegeria L. (Lepidoptera: Satyrinae) there was no correlation between egg weight and egg survival, larval survival, larval developmental Ume and pupal weight (Wiklund & Persson, 1983). However, variation in offspring size or weight may influence survival and thus affect the reproductive success of the female (Braby, 1994). Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) adults are predators of eggs and larvae of diptaran species and its first instar larvae are ectoparasitoids of dipteran pupae (Reader & Jones, 1990). A. bi/ineata femalas oviposit in the soil near plants infested by the dipteran host (Colhoun, 1953; Read, 1962; Bromand, 1980). Hatching occurs three to 19 days after oviposition, depending on the temperature (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960). At emergence, the larva varies in size between 1.25 to 1.62 mm in length and 0.12 to 0.25 mm in width (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960) and it has a • fixed quantity of nutrients in the form of fat globules that start disappearing after twelve 115 hours (Fuldner. 1960). After six to eight days without food. 500/0 of larvae are dead (Colhoun. 1953; Royer et al.. 1998). A. bilineata is a solitary parasitoid aven if • superparasitism is common but then only one larva eventually survives. No measure of the fitness of Aleochara bilineata larvae is available at the moment. ln female para5itoids, there are four principal constraints which affect their fitness: longevity (time-limited), fecundity (egg-Iimited. where pro-ovogenic females have a fixed number of egg5 and synovogenic females produce e99s during ail thaïr lifetime). hast finding ability (optimal foraging, to maximize the research) and environmantal conditions (temperature, humidity) (Driessen & Hemerik, 1992; Visser, 1994). In parasitoid species where the larvae search for a host, many constraints affect their fitness. The first is longevity because if the larva does not find a host, it cannat develop. Second. the host finding ability of the larva can be affected by many factors. In A. bilineata larvae, soil humidity is an important factor, as humidity can soften the host puparium and facilitate entrance for the larva (Wadsworth, 1915; Fuldner, 1960). The third factor is the developmental stage of the host pupa. A. bilineata first instar larva enters the host • puparium after the last molt of the host pupa. It does this because, at this time, there is a space between the pupa and the puparium (Fuldner, 1960). This pupa host is at the stade phanerocephalic (Fraenkel & Bhaskaran, 1973). The fourth factor is the level of superparasitism which is common and inevitably results in larval mortality. This occurs since A. bilineata is a solitary parasitoid (Calhoun, 1953; Fuldner, 1960; Read, 1962). After a larva has found a host, it drills a small hale in the puparium and enters. The second and third instars are eruciform (no functionallegs), and A. bilineata pupates in the host puparium. We observed an important variability in A. bilineata egg size before and after swelling; before: 0.013 to 0.026 mm3 and after 0.021 ta 0.043 mm3 (Gauvin, unpublished data). We assume that larvae hatching from small eggs are smaller than those hatching from large eggs as for Callosobruchus maculatus F. (Coleoptera) or the genus Mycalesis (Lepidoptera) where egg size is positively correlated with larval size • (Fox, 1993a; Fox, 1993b; Braby, 1994). 116 ln this paper, the impact of size on the fitness of A. bilineata larvae has been • evaluated with three parameters: longevity, walking rate and hast searching capacity. Materials and methods General conditions Ali experiments and rearing (parasitoids and hosts) were made at 20°C, 60% relative humidity and a photoperiod of 16L:8N. A. bilineata has been reared on the cabbage maggot, Delia radicum L. (Diptera: Anthomyiidae). Adults of cabbage maggot were fed with water, 10% honey solution and a mixture of 75:25 of brewers yeast and soya \clour. They were placed in the presence of one-half rutabaga deposited in a dish containing damp sand (Royer et al., 1998). • Twenty adults of A. bilineata (sax ratio 1:1) were placed in a dish containing a dampened piace of cotton for oviposition. Five oviposition dishes were used. They were fed with third instar larvae and host pupae of cabbage maggot were present. The eggs were collected with a brush and placed individually in polyethylene capsules until hatching. The capsules were placed in closed 37 ml SOLOe cups containing moist filter paper. Each hour, hatching was verified ta obtain larvae 30 ± 30 minutes-old for ail experiments. The larvae were weighed with a Cahn 29 scale capable of weighing up to 0.0001 mg and classified as small or large larvae. The average weight of 185 larvae was 0.027 ± 0.002 mg. We used this value to classity our larvae. Larvae weighing less than 0.025 mg were classified as smaillarvae while large larvae were those weighing more than 0.029 mg. The small and large larvae represented respectively 32.40/0 and 41.1 % of ail larvae weighed (Figure 4.1). For these • experiments, larvae between ]0.025; 0.029[ were not considered. 117 Lonaevlty • To evaluate the effect of larval size on longevity, 30 small and 30 large larvae of 30 ±30 minutes were used. The day and hour of emergence of each larva was noted to calculate its longevity. The larvae had no access to food. They were placed individually in polyethylene capsules within a closed 37 ml SOLO~ cup and covered with a piece of moist filter paper. Twice a day, at 9:00 and 16:00, the larvae were checked until found dead (complete absence of movement by the larva) and the day and hour of death were noted. Walklna rate An image analysis system has been developed to measure the mean diameters of air bubbles in a water tank (Vigneault et al., 1992; Orsat et al., 1993). This technique has been modified and adapted to study insect behavior (Vigneault et al., 1996; Vigneault et al., 1997). The system was comprised of background Iight, an acrylic plate, • an incubator at 20°C, monochrome camera (Panasonic) with a lens of 16 mm, video VHS, two computer monitors, one TV monitor and an IBM-AT compatible personal computer (Figure 4.2). Each larva (20 small and 20 large) was placed individually in a 5.0 cm diameter arena and observed for 300 seconds. This system analyzes the path of larvae. The following parameters were measured: mean walking rate, number of stops, duration of stop and real walking rate (mean walking rate minus time stopped). Selrchlna c8paclty A phanerocephalic pupa (average of 7.0 mm) of the cabbage maggot was placed in the center of a 37 ml SOLOe cup on 1 ml of sand moistened with 0.3 ml of distilled water. The pupa was covered with 2 ml of sand moistened with 0.3 ml of distilled water. • Each A. bi/ineata larva was individually placed on a 25 mm2 diameter filter paper on the 118 surface of the sand at the center of the cup. The cup was then closed and placed in an incubator for 48 hours. After that period, the pupa was extracted from the sand. It was • then examined by transmitted light using a transillumination unit for brighttieldldarkfield (Royer et al., 1998). The position of A. bilineata first instar larvae was noted: larva did not find host pupa, larva in contact with host but not entered and larva entered the puparium of the hast. This experiment was replicated for 20 small and 20 large A. bilineata larvae. Statistlcs Unpaired Student tests were used for longevity, mean walking rate, number of stops, duration of stops and real walking rate according to tarval categories (small or large). A G·test was used ta compare the A. bilineata larvae did not find host, on the host and inside the host. • • 119 • Results and discussion Lonaevlty Large larvae Iived longer (mean ± SO; 160.64 ± 41.04 hours) than small larvae (132.89 ± 61.85 hours) (t= 2.242; df= 58; P= 0.0282). It is the first instar larva that searches for the host, increased longevity is advantageous sinee the larvae do not necessarily emerge near the host. The inerease in longevity of the larva increases the possibilities of finding and parasitizing a host. A femala parasitoid that has short longevity and lays many eggs may have a higher fitness than a parasitoid with high longevity but that lays few eggs. However, this may be the opposite in a different environment. One important charaeteristic of the environment for parasitoid is the abundance of hasts because longevity increases in importance with decreasing encounter rate of hasts (Visser, 1994). The large larvae had 17.270/0 more time than small larvae to find and parasitize a hast. Therefora, we can conclude that they had a • better fitness. ln Pararge aegeria L. (Lepidoptera) famales lay their eggs on the host for larval feeding immediately after the larvae have hatchad. The capacity ta withstand starving conditions is not important rNiklund & Persson, 1983). This capacity becomes especially important when the femalas lay eggs quite a distance from the larval host plants as with Oenis jutta and Erebia ligea bath Lepidoptera (Wiklund & Persson, 1983). In the genera Chrysopa and Chrysoperla (Neuroptera), the larva must search and capture prey that may be distant from the oviposition sita. The e9g size and the survival of larvae during host searching increase with increasing maternai allocation of resources by the lemale (Tauber et al., 1990). A. bilineata larva is similar to these cases because the female oviposits her eggs near an infested plant. However, this is not necessarily near host pupae and the larva may hava to search for a hast (Colhoun, 1953; Raad, 1962, Bromand, 1980). Therefore, the capacity to withstand starving conditions of first instar larva of A. bilineata is important and this capacity can be measured by the larval • longevity. In A. bilineata larva there is a fixed quantity of nutrient in the form of fat 120 globules and these have already disappeared after twelve hours (Fuldner, 1960). These fat globules probably allow A. bilineata larvae to withstand starving conditions. This may • be due to the tact that larger larvae have a relatively greater food reserve than smaller larvae. Walklng rate Large larvae had a higher mean walking rate (0.406 ± 0.134 mm/s) than small larvae (0.264 ± 0.132 mmls) (t=3.368; df=38; P=O.0017), stopped less often (26.1 ± 23.2 stops) than small larvae (40.85 ± 29.61 stops) (t=-1.754; df=38; P=O.0875) and for a shorter time (23.53 ± 20.98 s) than small larvae (60.40 ± 54.03 s) (t=-2.691; df=38; P=O.010S). As a result, large larvae had a higher real walking rate (0.441 ± 0.137 mmls) than small larvae (0.318 ± 0.120 mm/s) (t=3.023; df=38; P=0.0045). Therefore large larvae had an increased chance ta find a host as compared to smail farvae. This is due to the fact that they walked 27.89% (real walking rate) faster and covered more ground. For a larval parasitoid, the searching capacity is especially important when its longevity is short. Royer et al. (1998) mentioned that, after six to eight days, 500/0 larvae of starved • A. bilineata are dead. The larva reduced his chance to parasitize a host, if it takes more than 6 to 8 days to find a hast due ta factors such as walking slowly or stopping tao often or for too long (because it has not enough energy). The capacity to walk rapidly increases the probability of parasitizing a host which has not already parasitized. This factor is important since A. bilineata is a solitary parasitoid, and only one larva completes its development in the host. In addition, small larvae have more chance of being attacked by generalist predators because their stopped time was longer as compared ta large larvae. ln sorne species, the ability of young hatchlings ta successfully disperse to a host plant is correlated with egg size (Braby, 1994). In Lymantria dispar L. (Lepidoptera), large larvae have greater resources and disperse quicker than smaller larvae (Berger, 1989). In Lepidoptera, females oviposit their eg9s on the host-plant. Therefore, the • efficiency of movement and travel speed are not important. However, this factor 121 becomes important for an insect where the female oviposits her eg9s quite a distance from the larval environment. In the genus Chrysopa (Neuroptera), the egg size is • positively correlated with tibiallength. The authors suggest that tibiallength is related to the speed and efficiency of movement (Tauber et al., 1990). The speed and efficiency of movement are especially important for A. bilineata larva that searches and captures its prey. Searchina capaclty The percentage of large larvae in each category (hast not found, on and inside hast) was significantly different tram small larvae (G2=6.619; P=0.0365) (Figure 4.3). Large larvae are 1.6 more efficient at finding (on hast: 20% and inside hast: 70%) hasts as compared to smalliarvae (on hast: 15% and inside hast: 40%). Visser (1994) has evaluated the searching efficiency (optimal foraging) of • Aphaereta minuta Nees (Hymenoptera) female for discovering patches. This is measured as the total time spent on patches in a female lifetime. Visser states that a number of factors influence the total time spent on patches in the Iifetime of a female: its longevity, its ability ta locate patches and its travel speed. In A. minuta the longevity of a female is positively correlated with its size (no correlation with other factors). In A. bilineata longevity, travel speed and the ability ta locate patches (searching capacity) are positively correlated with larval size. Ali three factors contribute to an increased probability of successful hast finding, therefore increasing fitness. The large larvae Iived 17.27°..10 longer, walked 27,89°;/0 laster and found hasts 1.6 more frequently than small larvae. •mD.ct of .Ize of fltness There is a cast to producing large larvae as the female has ta aUccate a larger quantity of resources in comparison to smaller eggs. However, this cast is compensated • by a high fitness for large larvae. If the fitness increases with larval size (and egg size), 122 we may ask why femalas lay smail egg5. At the larvallevel, the fitness is nat necessarily the same as at the parentallevel. When females have fewer resaurces ta invest in their • eggs, it may be beneficial ta invest scarce resources in numeraus small eggs (Braby, 1994). When females oviposit their eggs they do not always have access to suitable dipteran food (eggs or larvae) which allaws for the production of larger eggs. However they may be in the presence of dipteran hast pupae, which are suitable hasts for first instar larvae hatching out of the eggs. In the case of high pupa abundance the fitness of females will be increased with the number of eggs oviposited. This occurs even if these eggs have a small amount of resources. It is possible that there are disadvantages for large larvae in particular conditions. At times, this pressure may favar the production of many small offspring by the female. ln Tyria jacobaeae L. (Lepidaptera), low temperatures (15°C) in egg size is positively correlated with hatching success. However at high temperature (22°C), there is disadvantage for large eggs by decreasing hatching success (Braby, 1994). When the species Mycalesis are reared on the sotter nitrogen-rich host-plant, the advantage to larger larvae diminishes (Braby, 1994). As with these species, the large larvae of A. • can be disadvantaged in certain conditions. A disadvantage for the large larva bilineata could be reduced mobility in the soil. The larval size can be negatively correlated with the mobility in certain sail conditions (for example, compressed sail) and the larva cannot parasitize a hast. • 123 • References Abercomble, M., C.J. Hlckman & M.L. Johnson. 1980. The Penguin dictionary of biology. 7e edition. Penguin reference. London. 323p. Berger, A. 1989. Egg weight, batch size and fecundity of the spotted stalk borer, Chilo partellus in relation to weight of females and time of oviposition. Entomol. Exp. & Appl. 50: 199-207. Braby, M.F. 1994. The significance of egg size variation in butterflies in relation ta hostplant quality. Oikos 71 :119-129. Bromand, B. 1980. Investigations on the biological control of the cabbage rootfly (Hylemya brassicae) with Aleochara bilineata. Bull. SROPIWPRS 3:49-62. • Colhoun, E.H. 1953. Notes on the stages and the biology of Baryodma ontarionis Casey (Coleoptera: Staphylinidae), a parasite of the cabbage maggot, Hylemya brassicae Bouché (Diptera: Anthomyiidae). Cano Entamol. 85:1-8. de Jong, G. 1994. The fitness of fitness concepts and the description of natural selection. Quart. Rev. Biol. 69: 3-29. Drlessen, G. & L. Hemerik. 1992. The time and egg budget of Leptopilina clavipes, a parasitoid of larval Drosophila. Ecolo EntamaI. 17:17-27. Fox, C.W. 19938. Maternai and genetic influences on egg size and larval performance in a seed beetles (Callosobruchus maculatus): multigenerational transmission of a maternai effect. Heredity 73:509-517. • 124 Fox, C.W. 1993b. The influence of maternai age and mating frequency on egg size and ottspring performance in Callosobruchus maculatus (Coleoptere: Bruchidae). • Oecologia 96: 139-146. Fox, C.W. 1994. The influence of egg size on offspring performance in the seed beetle, Callosobruchus maculatus. Oikos 71 :321-324. Fraenkel, G. & G. Bhaskaran. 1973. Pupariation and pupation in cyclorrhaphous flies (Diptera): terminology and interpretation. Ann. Entomal. Soc. Am. 66:418-422. Fuldner, D. 1960. Beitrage zur morphologie und biologie von Aleochara bilineata Gyll. und A. bipustulata L. (Coleoptera: Staphylinidae). [Traduction: Contribution à la morphologie et à la biologie de Aleochara bilineata Gyll. et A. bipustulata L. (Coleoptera: Staphylinidae)). Z. Morph. ëkol. Tiere. 48:312-386. Orsat, V., C. Vigneault, G.S.V. Raghavan. 1993. Air diffusers characterization using a • digitized image analysis system. Am. Soc. Agr. Eng. 9: 115-121. Read, D.C. 1962. Notes on the life history of Aleochara bilineata (Gyll.) (Coleoptera: Staphylinidae), and on its potential value as a control agent for the cabbage maggot, Hylemya brassicae (Bouché) (Diptera: Anthomyiidae). Cano Entomol. 94:417-424. Aeader, P.H. & T.H. Jones. 1990. Interactions between an eucoilid (Hymenoptera) and a staphylinid (Coleoptera) parasitoid of the cabbage root fly. Entomophaga 35:241-246. Aoyer, L., S. Fournet, E. Brunei & G. Balvln. 1998. Intra- and interspecific hast discrimination by host-seeking larvae of Coleopteran parasitoids. Oecologia in • press. 125 Tauber C.A., M.J. Tauber & M.J. Tauber. 1990. Egg size and taxon: their influence on survival and development of chrysopid hatchlings after food and water • deprivation. Cano J. Zool. 69:2644-2650. Vigneault, C., B. Panneton & G.S.V. Raghavan. 1992. Real time image digitizing system for measurement of air bubbles. Cano Agr. Eng. 34:151-155. Vigneault, C., B. Panneton, o. Cormier & G. Solvln. 1996. Automated system to quantify the behavior of small insects in a four-pointed star olfactometer. Am. Soc. Agr. Eng. 13:545-550. Vigneault, C. F. Fournier, K.P.C. Hui & G. Balvln. 1997. Système d'analyse d'images adapté pour l'étude du comportement de trichogrammes. Cahier d'Agricultures 6:289-292. Visser, M.E. 1994. The importance of being large: the relationship between size and • fitness in famales of the parasitoid Aphaereta minuta (Hymenoptera: Braconidae). J. Anim. Ecol. 63:963-978. Wadsworth, J.T. 1915. The Iife-history of Aleochara bilineata, Gyll., a staphylinid parasite of Chortophila brassicae, Bouché. J. Econ. Biol. 10:1-27. Wlklund, C. & A. Persson. 1983. Fecundity. and the relation of egg weight variation to offspring fitness in the speckled wood butterfly Pararge aegeria, or why don1t butterfly females lay more e991 Oikos 40:53-63. • 126 • Figure 4.1: Distribution of weight of 185 larvae of Aleochara bilineata 30 ± 30 minutes • after hatching. • 127 • T 1 ~~·o c:::::::f t'Cro ~ T6&0.0 E ~e&o'o+ § .,. o 1 .1 : .Leo·o r-- C"! t o "-----...19&0·0 Il .....'--_----_+...... , 5&0'0 Q r en ---~, +1 ~ .... w:o'o c- ~ ...--~. B Il lttC'O :ez ~ ...... , Zl:O'O r '...... , ~to·o ,... ~--_.,T .....------...... tto'O 6Z0'0 Ci .....------=1r ! ,..,------oIl~ ezo'o ~ .,. ~ ....------i'..... --.; ...... , LZO·O •If t • ,...------~, 9Z0'O .....------fszo'O + ...... __.....1 ,zO'O t ..... --.., tzo'O .....------...... f~·o ...------~I ~zo·o + 1 -co -CD -c co • • Figure 4.2: Schematic representation of the experimental setup. • • 129 • • • ------~--- ",~ .... " ... Video ~ ...... ,'" " ....' .." ,/,,'" 1 /' \ " " " " \ " \ " - " \, ,l " ,l \,, / Television \ , Monitor \ , , / , 1 , - ...~ \ 1 ...... \ j 1 ...... 1 1 ...... _------ t;amer, Computer Incubator Acrylic table Monitor Li~ht table 130 • Figure 4.3: Percentage of small and large Aleochara bilineata larvae that did not find a hast, faund a host but did not penetrate and faund a hast and penetrate • after a period of 48 hours. • 131 • 100% P 90% e 800/0 r 700/0 c 600/0 1 i0 Inside host 1 e 500/0 1 1 1 [JOn host 1 n 400/0 r Host not found 1.! • 300/0 g 20% e 10% 0% Small Large Larv:a::e~ _ • • 132 • GENERAL CONCLUSION • • 133 The objectives of this research were; (1) to evaluate the impact of food and hast availability along with age and weight of female on egg size of • Aleochara bilineata; (2) ta understand the developmental biology of hydropic eggs of A. bilineata; (3) ta measure the impact of size on the fitness of A. bilineata first instar larvae. We have observed that the presence of food increased egg size and that famales needed food ta develop their avaries and produce eggs. Moreover, eider females laid larger a9gs than younger females. Under our experimental 3 conditions, we observed a wide range of eg9 size (0.010 to 0.042 mm ). However, the factors studied (availability of food and hast as weil as female age and weight) accounted for a small, although significant, difference in average 3 egg size (0.017 to 0.019 mm ). The wide range of egg size can be explained by the fact that, in our experiments, the age of the A. bilineata eggs was not constant when they were measured. • Thirty hours after oviposition, these e9gs began to absorb water and, as a result, swelled. This absorption continued up to 50 hours after oviposition, after which the egg volume remained stable until emergence. In transmission and scanning electronic microscopy, we observed that this swelling produced a splitting of the endochorion. However, hydropy did not explain completely the variability in egg size. After sweiiing, a wide range in e9g size (0.021 to 0.043 3 mm ) was still observed. Differences in egg size are known to result in difference in larval size and consequently in larval fitness. When parameters related to larval fitness were measured, we showed that larger first instar larvae of A. bilineata lived longer. walked faster and displayed a better hast searching capacity. These three parameters are very important for A. bilineata first instar larvae because they increase the • probabilities ta find and parasitize hast. 134 The absorption of water by the egg is observed in severai aquatic (e.g. Plecoptera. Hemiptera and Coleoptera) and terrestrial insects (e.g. Orthoptera, • Hymenoptera and Coleoptera). In terrestrial insects, ovipositing hydropic eggs can be costly when no water is available because mortality rate will be higher since water absorption is necessary to complete egg development. In such species. females oviposit their eggs in situations where water is normally available or at least available at certain time (Hinton, 1981). In A. bilineata, famale oviposits their eggs near the host pupae (the female makes galleries in the soil) in damaged cruciferous plant where water is present (Wilde (1947) in Fuldner, 1960; Bromand. 1980). This is similar to Ocypus a/ens Müller (Staphylinidae), whose females oviposit their hydropic eggs on soil surface where water is normally available as humidity or rain (Lincoln, 1961). In Coleoptera. two others families have hydropic eggs, the Scarabaeidae and Elateridae that bath oviposit their e9gs in plant tissues and in soil where water is available at certain time (Hinton, 1981; Paulian, 1988). • By investing fewer resources (water) in each hydropic egg, a female can oviposit more eg9s. Increasing its progeny can be very important for a female parasitoid when it is the first instar larva that has to search and locate the host. Larvae that search for hast are present in Lepidoptera (10 species), Neuroptera (50 species). Hymenoptera (500 species), Coleoptera (3 590 species) and Diptera (8 600 species) (Eggleton & Belshaw, 1992: Godfray. 1994). Because of the expected high mortality rate of these searching larvae either through predation. parasitism or simply lack of suitable hosts, most of the species where larvae searches for host have a high fecundity as in A. bilineata. Two scenarios can explain the presence of hydrapic eggs in A. bilineata. The first one is that hydropic eggs were present in Staphylinidae before sorne species became parasitoids. The second one is that hydropic eggs appeared as a secondary character of the parasitoid mode of Iife. According ta Eggleton & • Belshaw (1992). there is only one acquisition of parasitism for the Staphylinidae 135 which includes 500 parasitoid species out of 30 000 species. We know that O. olens, that is not a parasitoid, has hydropic eggs. This fact alone suggests that • hydropie eg9 is an ancestral character present in bath parasitoid and non parasitoid Staphylinidae. However, a thorough research more specifie on Staphylinidae eggs would be required to confirm this hypothesis. Severai other aspects remain ta be studied in A. bilineata reproduction biology. The effect of relative humidity on egg hatching rate could be studied along with oviposition site selection by females. The impact of sail conditions (texture, humidity) on larval mobility needs also ta be studied to evaluate larval fitness. Finally, verifying the fitness of the larvae on a longer period of time (> 48 hours) would provide a better understanding of the respective fitness of large and smaillarvae. • • 136 • References Bromand, B. 1980. Investigations on the biological control of the cabbage rootfly (Hy/emya brassicae) with Aleochara bilineata. Bull. SROPIWPRS 3:49-62. Eggleton, P. & R. Belshaw. 1992. Insect parasitoids: an evolutionary overview. Phil. Trans. R. Soc. Lond. 337:1-20. Fuldner, D. 1960. Beitrage zur morphologie und biologie von Aleochara bi/ineata Gyll. und A. bipustulata L. (Coleoptera: Staphylinidae). [Traduction: Contribution à la morphologie et à la biologie de Aleochara bi/ineata Gyll. et A. bipustulata L. (Coleoptera: Staphylinidae)]. Z. Morph. Okol. Tiere. 48:312-386. Godfray, H.C.J. 1994. Parasitoid behavioral and evolutionary ecology. Princeton • University Press, Princeton, New Jersey. 473p. Hlnton, H.E. 1981. Biology of insect eggs. Pergamon Press. Oxford. 1125p. Lincoln, D.C.A. 1961. The oxygen and water requirements of the e99 of Ocypus o/ens Müller (Staphylinidae, Coleoptera). J. Insect Physiol. 7:265-272. Paulian, A. 1988. Biologie des Coleoptères. Éditions Lechevalier. Paris. 719 p. • 137