BACKGROUND:Numerous studies have investigated cospeciation between parasites and their hosts, but there have been few studies concerning parasitoids and insect hosts. The high diversity and host specialization observed in Anicetus species suggest that speciation and adaptive radiation might take place with species diversification in scale insect hosts. Here we examined the evolutionary history of the association between Anicetus species and their scale insect hosts via distance-based and tree-based methods.RESULTS:A total of 94 Anicetus individuals (nine parasitoid species) and 113 scale insect individuals (seven host species) from 14 provinces in China were collected in the present study. DNA sequence data from a mitochondrial gene (COI) and a nuclear ribosomal gene (28S D2 region) were used to reconstruct the phylogenies of Anicetus species and their hosts. The distance-based analysis showed a significant fit between Anicetus species and their hosts, but tree-based analyses suggested that this significant signal could be observed only when the cost of host-switching was high, indicating the presence of parasite sorting on related host species.CONCLUSIONS:This study, based on extensive rearing of parasitoids and species identification, provides strong evidence for a prevalence of sorting events and high host specificity in the genus Anicetus, offering insights into the diversification process of Anicetus species parasitizing scale insects.

Cotesia flavipes (Cameron) (Hym.: Braconidae), como outros cenobiontes, é capaz de regular seu hospedeiro, criando um ambiente que sustenta e promove o desenvolvimento de suas larvas, comumente em detrimento do hospedeiro. Substâncias derivadas do trato reprodutivo das fêmeas (proteínas ovarianas, veneno e polidnavírus) são injetadas no hospedeiro, afetando a resposta imune e outros processos fisiológicos com o propósito de regular os níveis hormonais, nutrição e comportamento. O presente trabalho teve por objetivo avaliar o papel dessas substâncias no crescimento e desenvolvimento de Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae), e avaliar como o parasitismo afeta a resposta imune do hospedeiro. Todas as substâncias derivadas da fêmea foram obtidas após a dissecação do parasitóide, através da coleta do reservatório de veneno ou dos ovários (proteínas ovarianas e polidnavírus) em tampão resfriado. As secreções foram processadas adequadamente e injetadas logo após a coleta. O veneno e as proteínas ovarianas + polidnavírus (PDV) foram injetados juntos ou separadamente em lagartas entre 0-12h do 6º instar. O efeito de cada um dos componentes isolados do parasitóide no desenvolvimento e crescimento do hospedeiro foi avaliado através de observações no ganho de peso, duração e viabilidade da fase larval e pupal. Os efeitos do parasitismo na resposta imune do hospedeiro foram avaliados tanto ao nível celular, através da contagem do número total de hemócitos e capacidade de encapsulação, como ao nível bioquímico, medindo-se a ativação da profenoloxidase e produção de óxido nítrico na hemolinfa das lagartas de D. saccharalis em diferentes estágios de desenvolvimento do parasitóide (0, 1, 3, 5, 7 e 9 dias após o parasitismo). As proteínas ovarianas do parasitóide e o PDV sozinho, ou co-injetado com o veneno, suspenderam o desenvolvimento larval do hospedeiro, enquanto que o veneno, sozinho, afetou o processo de metamorfose. A resposta imune do hospedeiro também foi afetada por C. flavipes, de maneira dependente do tempo. Lagartas parasitadas apresentaram declínio no número total de hemócitos a partir do 3º dia e a capacidade de encapsulação foi afetada ao longo do desenvolvimento do parasitóide. A atividade da fenoloxidase do hospedeiro foi alterada apenas no final do desenvolvimento imaturo do parasitóide, enquanto que o óxido nítrico foi afetado nas 24 h iniciais após parasitismo. / Cotesia flavipes (Cameron) (Hym., Braconidae), as other koinobionts, is capable of regulating the host development to produce an suitable host environment to sustain and promote its own larval development at the host expenses. Female-derived substances from the reproductive tract (ovarian proteins, venom, polydnavirus) are injected into the host, affecting the host immune response and other physiological processes aiming to regulate the host hormone levels, nutrition and behavior. Our goal was to evaluate the role of these substances on Diatraea saccharalis (F.) (Lepidoptera: Crambidae) growth and development, and how the parasitism affects the host immune response. All female-derived substances were collected after parasitoid dissection by collecting the venom reservoir or the ovaries (ovarian proteins and polydnavirus). Dissections were carried out in ice-cold buffer, collected tissues were processed accordingly and the desired substances injected immediately after collection. Venom and ovarian proteins+polydnavirus (PDV) were injected jointly and separated in 0-12 hold 6th instars of D. saccharalis. The effect of these substances on host development and growth was evaluated by measuring the host weight gain, larval and pupal survivorship and developmental time. The effects of the parasitism on the host immune response was evaluated either at the cellular level, by measuring the total hemocyte count and the encapsulation capacity, and at the biochemical level, by measuring the prophenoloxidase activity and nitric oxide levels at different stages of parasitoid development (0, 1, 3, 5, 7 and 9 days after parasitism). Parasitoid ovarian proteins and PDV alone or co-injected with the venom arrested the host larval development, while the venom by itself only affected the host metamorphosis process. The host immune response was also affected by C. flavipes at a time-dependent manner. The total hemocyte count dropped at day 3 of parasitism, while the host encapsulation capacity was reduced during parasitoid development. The host prophenoloxidase activity was also affected mainly towards the end of parasitoid larval development, while the nitric oxide at the first 24 h after parasitism.

Cotesia flavipes (Cameron) (Hym.: Braconidae), como outros cenobiontes, é capaz de regular seu hospedeiro, criando um ambiente que sustenta e promove o desenvolvimento de suas larvas, comumente em detrimento do hospedeiro. Substâncias derivadas do trato reprodutivo das fêmeas (proteínas ovarianas, veneno e polidnavírus) são injetadas no hospedeiro, afetando a resposta imune e outros processos fisiológicos com o propósito de regular os níveis hormonais, nutrição e comportamento. O presente trabalho teve por objetivo avaliar o papel dessas substâncias no crescimento e desenvolvimento de Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae), e avaliar como o parasitismo afeta a resposta imune do hospedeiro. Todas as substâncias derivadas da fêmea foram obtidas após a dissecação do parasitóide, através da coleta do reservatório de veneno ou dos ovários (proteínas ovarianas e polidnavírus) em tampão resfriado. As secreções foram processadas adequadamente e injetadas logo após a coleta. O veneno e as proteínas ovarianas + polidnavírus (PDV) foram injetados juntos ou separadamente em lagartas entre 0-12h do 6º instar. O efeito de cada um dos componentes isolados do parasitóide no desenvolvimento e crescimento do hospedeiro foi avaliado através de observações no ganho de peso, duração e viabilidade da fase larval e pupal. Os efeitos do parasitismo na resposta imune do hospedeiro foram avaliados tanto ao nível celular, através da contagem do número total de hemócitos e capacidade de encapsulação, como ao nível bioquímico, medindo-se a ativação da profenoloxidase e produção de óxido nítrico na hemolinfa das lagartas de D. saccharalis em diferentes estágios de desenvolvimento do parasitóide (0, 1, 3, 5, 7 e 9 dias após o parasitismo). As proteínas ovarianas do parasitóide e o PDV sozinho, ou co-injetado com o veneno, suspenderam o desenvolvimento larval do hospedeiro, enquanto que o veneno, sozinho, afetou o processo de metamorfose. A resposta imune do hospedeiro também foi afetada por C. flavipes, de maneira dependente do tempo. Lagartas parasitadas apresentaram declínio no número total de hemócitos a partir do 3º dia e a capacidade de encapsulação foi afetada ao longo do desenvolvimento do parasitóide. A atividade da fenoloxidase do hospedeiro foi alterada apenas no final do desenvolvimento imaturo do parasitóide, enquanto que o óxido nítrico foi afetado nas 24 h iniciais após parasitismo. / Cotesia flavipes (Cameron) (Hym., Braconidae), as other koinobionts, is capable of regulating the host development to produce an suitable host environment to sustain and promote its own larval development at the host expenses. Female-derived substances from the reproductive tract (ovarian proteins, venom, polydnavirus) are injected into the host, affecting the host immune response and other physiological processes aiming to regulate the host hormone levels, nutrition and behavior. Our goal was to evaluate the role of these substances on Diatraea saccharalis (F.) (Lepidoptera: Crambidae) growth and development, and how the parasitism affects the host immune response. All female-derived substances were collected after parasitoid dissection by collecting the venom reservoir or the ovaries (ovarian proteins and polydnavirus). Dissections were carried out in ice-cold buffer, collected tissues were processed accordingly and the desired substances injected immediately after collection. Venom and ovarian proteins+polydnavirus (PDV) were injected jointly and separated in 0-12 hold 6th instars of D. saccharalis. The effect of these substances on host development and growth was evaluated by measuring the host weight gain, larval and pupal survivorship and developmental time. The effects of the parasitism on the host immune response was evaluated either at the cellular level, by measuring the total hemocyte count and the encapsulation capacity, and at the biochemical level, by measuring the prophenoloxidase activity and nitric oxide levels at different stages of parasitoid development (0, 1, 3, 5, 7 and 9 days after parasitism). Parasitoid ovarian proteins and PDV alone or co-injected with the venom arrested the host larval development, while the venom by itself only affected the host metamorphosis process. The host immune response was also affected by C. flavipes at a time-dependent manner. The total hemocyte count dropped at day 3 of parasitism, while the host encapsulation capacity was reduced during parasitoid development. The host prophenoloxidase activity was also affected mainly towards the end of parasitoid larval development, while the nitric oxide at the first 24 h after parasitism.

In host-parasitoid systems, there is a continuous coevolutionary arms race where each species imposes a strong selection pressure on the other. The host needs to develop defence strategies in order to escape parasitism and the parasitoid must evolve counter-defence strategies in order to overcome the host’s immune defence and successfully reproduce. This makes host-parasitoid systems excellent model systems for understanding evolutionary processes underlying host race formation and speciation. In order to gain a better understanding of the complexity of host-parasitoid interactions several aspects must be considered, such as search behaviour and host selection in the parasitoid, the development of immune responses in the host and counter-defence strategies in the parasitoid. In this thesis, I investigate interactions and coevolution in a natural host-parasitoid system, consisting of five species of Galerucella leaf beetles and three species of Asecodes parasitoids, by combining behavioural ecology with chemical ecology and immunology. In the studies performed, I found that pheromone production and responses in the beetles are connected to the phylogenetic relatedness between the Galerucella species (Paper I). I found no evidence that Asecodes exploits the adult pheromone to locate host larvae, but observed an ability in the parasitoids to distinguish a better host from a less suitable one based on larval odors (Paper II). The studies also revealed large differences in immune competence between the Galerucella species, which were linked to differences in hemocyte composition in the beetle larvae (Paper III, IV). Further, the results suggest that parasitism success in polyphagous Asecodes is strongly affected by former host species of the parasitoid (Paper IV). In conclusion, the results of this thesis suggest an on-going evolution in both parasitoid virulence and host immune responses in the Asecodes-Galerucella system. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.</p>

L'espèce Plutella xylostella (L.) (Lepidoptera : Plutellidae) défoliatrice des choux constitue surtout un problème dans les régions tropicales et subtropicales. La lutte chimique a rapidement montré ses limites du fait de l'apparition de résistance dans les populations. Des moyens de lutte alternatifs ont été mis en place, impliquant principalement des insectes parasitoïdes, parmi lesquels Oomyzus sokolowskii (Kurdjumov) (Hymenoptera : Eulophidae) et Cotesia vestalis (Haliday) (Hymenoptera : Braconidae) qui sont les plus couramment utilisés en raison de leur spécificité envers P. xylostella. Afin de contribuer à une meilleure connaissance du contrôle de la teigne en région tropicale, nous avons étudié les relations hôteparasitoïde entre P. xylostella et O. sokolowskii d’une part, et P. xylostella et C. vestalis d’autre part, en conditions de laboratoire et sur le terrain au Sénégal et au Bénin. Au Sénégal, quatre espèces de parasitoïdes sont présentes sur les chenilles : O. sokolowskii, Apanteles litae, C. vestalis et Brachymeria citrae. Au Bénin, seule l'espèce C. vestalis est présente. Au Sénégal comme au Bénin, les facteurs climatiques contribuent au développement de la teigne et les précipitations ne régulent pas les populations du ravageur. Dans ces deux pays, la teigne n’est pas contrôlée par ses ennemis naturels. La lutte biologique par conservation y est à prendre en considération et l’utilisation de plantes compagnes cultivées en association avec le chou peut être envisagée pour réduire les populations de la teigne. Les études en laboratoire ont montré qu’Oomyzus sokolowskii est un parasitoïde larvo-nymphal performant. ConcernantC. vestalis, les femelles détectent et reconnaissent leur hôte grâce aux lipides cuticulaires émis par les chenilles. Des marqueurs moléculaires (isozymes et ISSR) ont confirmé une forte variabilité entre les populations de P. xylostella à l’échelle mondiale, les populations d’Australie et du Japon étant très différentes des autres et formant deux groupes distincts. La structuration des populations semble influencée par le type de climat : tropical et non tropical. / The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is the most destructive pest of Brassicaceae worldwide and poses particularly acute problems in tropical areas. Chemical control is impaired by multiple-insecticide resistance in this species. Alternative methods are based on biological control by parasitoids, such as Oomyzussokolowskii (Kurdjumov) (Hymenoptera: Eulophidae) and Cotesia vestalis (Haliday) (Hymenoptera: Braconidae), which are commonly used due to their specificity towards DBM. To help to improve the biocontrol of the moth in the tropics, we studied host-parasitoid relationships between P. xylostella and these two parasitoids under both laboratory and field conditions in Senegal and Benin. In both countries, climatic conditions are favourable for the development of DBM and rainfall does not limit populations of this pest. In Senegal, four parasitoid species are present on DBM larvae: O. sokolowskii, C. vestalis, Apanteles litae, and Brachymeria citrae. In Benin, C. vestalis is largely dominant. In neither of these countries, the moth is sufficiently controlled by natural enemies. Conservation biological control might be combined with the use of companion plants in cabbage crops to reduce DBM populations. Laboratory studies have shown that O. sokolowskii is an efficient larval-pupal parasitoid. In C. vestalis, females detect and recognize their host using cuticular lipids produced by the caterpillar. Studies of molecular markers (isozymes and ISSR) have confirmed high variability among DBM populations around the world, those from Australia and Japan being distinct and very different from any other population. Population structure seems to be influenced by the type of climate (tropical vs. non-tropical).

Cette thèse porte sur l’analyse des dimensions spatiale et temporelle du fonctionnement et de la diversité taxonomique et fonctionnelle d’une guilde. Au sein d’une guilde, les espèces exploitent un même type de ressources; pour cette raison, les niches écologiques fondamentales des membres d’une guilde sont similaires et une relation de compétition interspécifique se met en place si la ressource partagée est limitante. Quatre questions principales sur le fonctionnement d’une guilde ont été abordées : (1) à quelles échelles spatio-temporelles se structurent la guilde et les ressources exploitées, (2) quelles sont les influences respectives des filtres environnementaux et des interactions interspécifiques sur les traits fonctionnels des membres de la guilde, (3) quelle est la stratégie d’exploitation de ressources d’un membre de la guilde face à une faible disponibilité de ressources et (4) quel est l’impact du contexte climatique sur la structure d’une guilde et de son réseau trophique, et sur le degré de spécialisation écologique des espèces de la guilde sur la ressource. Le modèle biologique de cette étude a été une guilde de parasitoïdes de pucerons de céréales (Hymenoptera : Braconidae : Aphidiinae). Ces parasitoïdes s’attaquent aux pucerons (Homoptera : Aphididae) inféodés aux céréales dans les agroécosystèmes. Les variations d’abondance relative des parasitoïdes et de leurs hôtes ont été importantes aux échelles interrégionale et interannuelle, mais très faibles à l’échelle intra-régionale. La divergence des traits fonctionnels des parasitoïdes s’est maintenue sur trois régions et deux années, et le contexte local a influencé les traits de la guilde dans son ensemble. Pendant la saison hivernale, une période marquée par une faible densité de pucerons, le parasitoïde Aphidius rhopalosiphi a présenté des stratégies contrastées pour maximiser sa fitness en exploitant les hôtes Sitobion avenae et Rhopalosiphum padi, mais une forte spécialisation écologique sur le terrain a été observée en présence d’une espèce compétitrice : Aphidius avenae. Cette présence a pu être corrélée à une hausse des températures hivernales. / This thesis is an analysis of the spatial and temporal dimensions of the functioning and taxonomic and functional diversity of a guild. In a guild, species exploit the same type of resources; consequently, fundamental ecological niches of guild members are similar and an interspecific competitive relationship is established if shared resources are limiting. Four main questions on the functioning of a guild are addressed: (1) the spatiotemporal scales to which guilds the guild and its exploited resources are structures, (2) the respective weight of environmental filtering and interspecific interactions on the configuration of realized niches of guild members, (3) the strategy of resource exploitation in a guild member facing low resource availability and (4) the impact of climatic context on the structure of a guild and its food web, and the degree of specialisation on resources. The biological model chosen in this study was a cereal aphid parasitoid guild (Hymenoptera: Braconidae: Aphidiinae). Those parasitoids attack aphids (Homoptera: Aphididae) in agroecosystems, which are anthropised environments marked by high disturbance rates and in which host resources are variable in density and in quality. Relative abundance variations in parasitoids and in their hosts were considerable at interregional and interannual scales, but weak at the intra-regional scale. Functional trait divergence in parasitoids was maintained across three regions and two years, and regional and annual environmental contexts influenced guild traits as a whole. In winter, a period marked by low aphid density, the parasitoid Aphidius rhopalosiphi presented contrasted strategies to maximise fitness whilst exploiting Sitobion avenae and Rhopalosiphum padi hosts, but a high degree of ecological specialisation in the field was observed in the presence of a competitive species, Aphidius avenae. This presence was correlated to an increase in winter temperatures.