Aphidophagous lady beetles rely on multiple sources of food in their environment. Alfalfa fields provide both aphids and many alternate foods, such as other arthropod prey, pollen, and fungi. Alfalfa fields (Medicago sativa L.) in Utah have low aphid densities, which may require lady beetles to consume alternative sources of food. Many methods can be used to determine these diets; frass analysis is used here to compare the diets of the introduced species Coccinella septempunctata L. with two native species, C. transversoguttata richardsoni Brown and Hippodamia convergens Guérin-Méneville, that occur in the Utah alfalfa habitat. In initial laboratory experiments to examine the feasibility of frass analysis, 48 hours at 20oC was sufficient time for adult lady beetles to pass prey cuticle through their guts. When consumed by these adults, pea aphids (Acyrthosiphon pisum [Harris]), alfalfa weevil larvae (Hypera postica [Gyllenhall]), and C. septempunctata larvae produced distinctive fragments in the frass. Such fragments could also be distinguished in frass collected in a field experiment in which aphid densities in plots of alfalfa were manipulated. Furthermore, additional consumed foods could be distinguished in the field experiment, including pollen, fungi, and other types of arthropods. Frass analysis demonstrated higher use of aphid prey by C. septempunctata adults collected from high versus low aphid density plots during the field experiment. Use of other types of prey, such as alfalfa weevil larvae, other arthropods, pollen and fungi, was similar between plots with high and low aphid densities. A field census was performed over two years to track the diets of the three species of lady beetles during the first crop of alfalfa, when two sources of prey in particular were present, aphids and alfalfa weevil larvae. Comparisons of diets revealed that the three species utilized different types of prey to similar degree during both years. In general, however, higher percentages of C. septempunctata adults were found to have consumed aphids and weevils during both years. Also, C. septempunctata was found to produce more frass and consume larger quantities of prey than either native species during the second year.

The chemical defences of insects against predators are either passive or aggressive. Passive defence is achieved through crypsis, and aggressive defence is maintained by a conspicuous or 'aposematic' (Poulton, 1890) appearance that advertises some noxious quality of the insect harmful to a predator. Aposematism is mutually beneficial to both the bearer and its predator, whereas crypsis only benefits the prey species. It is therefore not surprising that the fascinating array of chemical defences in insects is both diverse and widespread (Roth and Eisner, 1962). Intro. p. 1.

Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2018-09-26T12:19:08Z No. of bitstreams: 1 2013 - Alice Teodorio Lixa.pdf: 7684993 bytes, checksum: f6675b748532a5b5835d14d6a4480870 (MD5) / Made available in DSpace on 2018-09-26T12:19:08Z (GMT). No. of bitstreams: 1 2013 - Alice Teodorio Lixa.pdf: 7684993 bytes, checksum: f6675b748532a5b5835d14d6a4480870 (MD5) Previous issue date: 2013-02-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Coccinellid predators are natural enemies of agricultural pests such as aphids and scale insects. They are known colloquially as ladybirds, ladybugs or lady beetles. Some species only complete their development and produce viable eggs and offspring when they consume their preferred prey. However, in the absence of this prey, or in presence with lower nutritional quality prey, the ladybugs tend to consume alternative foods, such as pollen and nectar, to ensure their survival. Thus, the choice and maintenance of useful floral resources to ladybugs in agroecosystems is a strategy favorable to the conservation of natural enemy populations in the production environment. Another line is the use of pesticides that cause fewer negative impacts on natural enemies of pests. This study worked on these two fronts, seeking to know floral species beneficial in situ conservation of biodiversity of ladybugs, and to evaluable the impact of pesticides used in organic agriculture on these insects. The thesis is organized in three chapters. Chapter I aimed to identify plant families and/or plant species are natural sources of pollen grains for predatory ladybug adults in diversified organic system. Adults were collected from 26 August 2010 to 22 August 2011, at area of Integrated Agroecological Production System (IAPS), in Serop?dica, RJ, Brazil. Baker's legs and wings have been removed to avoid contamination with pollen attached to the outside of the insects, the remainder of the body subjected to acetolysis analysis, aiming at the identification of pollen possibly ingested. We identified pollen from different plant species: star fruit (Averrhoa carambola, Oxalidaceae), coriander (Coriandrum sativum, Apiaceae), sunflower (Helianthus annuus, Asteraceae), maize (Zea mays, Poaceae), elderberry (Sambucus nigra, Adoxaceae), and different families: coming from Amaranthaceae, Asteraceae, Fabaceae, Malvaceae, Myrtaceae, and Passifloraceae. Pollens were found in seven species of ladybugs. Just Cycloneda sanguinea ingested pollen of all these families, and pollen unidentified families. Chapter II aimed to determine the diversity of adult ladybugs community in the area of IAPS, and characterize the population structure by faunistic indexes. Species richness was equal to seven [Cycloneda sanguinea, Hippodamia convergens, Coleomegilla maculate, Coleomegilla quadrifasciata, Eriopis connexa, Harmonia axyridis, and Olla v-nigrum]. C. sanguinea, H. convergens, and C. maculata were classified as dominant, being the first constant and others accessories. In Chapter III, the studies were conducted with C. maculata at laboratory conditions, with the objective of evaluating the effect of different concentrations of alternative pesticides used in organic agriculture (Natuneem?, Nim-I-Go?, Rotenat?, Lime sulfur, and Agrobio?) on biological aspects of this insect. The two neem based products (Natuneem and Nim-I-Go) to 2 % and the ?timb?? based product (Rotenat) 1% and 2 % decreased egg viability of C. maculata. Nim-I-Go at concentrations of 1% and 2% caused higher mortality than the control treatment (water) in all larval instars. Except Agrobio, all pesticides adversely affected the reproduction of C. maculata. The neem based products should be used sparingly to avoid negative effects on the development of C. maculata. / Dentre os inimigos naturais das pragas agr?colas, destacam-se os coccinel?deos predadores, tamb?m conhecidos como joaninhas. Algumas esp?cies s? completam seu desenvolvimento e produzem ovos e prog?nies vi?veis quando consomem sua presa preferencial. Todavia, na aus?ncia dessa presa ou na presen?a de uma presa com qualidade nutricional inferior, as joaninhas tendem a consumir alimentos alternativos, tais como p?len e n?ctar, para garantir sua sobreviv?ncia. Desse modo, a escolha e a manuten??o de recursos florais ?teis ?s joaninhas no agroecossistema ? uma estrat?gia favor?vel ? conserva??o de popula??es dos inimigos naturais no ambiente de produ??o. Outra linha ? o uso de defensivos que causem menos impactos negativos aos inimigos naturais das pragas. O presente trabalho atuou nessas duas frentes, buscando conhecer esp?cies florais ben?ficas a conserva??o in situ da biodiversidade das joaninhas e defensivos agr?colas, usados na agricultura org?nica, menos danosos a esses insetos. A tese foi organizada em tr?s cap?tulos. No Cap?tulo I objetivou-se identificar, em sistema org?nico diversificado, quais fam?lias e/ou esp?cies bot?nicas s?o fontes naturais de gr?os de p?len para adultos de joaninhas predadoras. Os adultos foram coletados de 26 de agosto de 2010 a 22 de agosto de 2011, em ?rea do Sistema Integrado de Produ??o Agroecol?gica (SIPA), em Serop?dica, RJ. Asas e pernas das joaninhas foram retiradas a fim de evitar contamina??es por polens presos ? parte externa dos insetos, sendo o restante do corpo submetido ? an?lise de acet?lise, objetivando a identifica??o dos polens possivelmente ingeridos. Foram identificados polens de diferentes esp?cies bot?nicas: carambola (Averrhoa carambola, Oxalidaceae), coentro (Coriandrum sativum, Apiaceae), girassol (Helianthus annuus, Asteraceae), milho (Zea mays, Poaceae), sabugueiro (Sambucus nigra, Adoxaceae); e de diferentes fam?lias: oriundos de Amaranthaceae, Asteraceae, Fabaceae, Malvaceae, Myrtaceae e Passifloraceae. Os polens foram encontrados em sete esp?cies de joaninhas afid?fagas. Apenas a Cycloneda sanguinea ingeriu p?len de todas essas fam?lias, al?m de polens de fam?lias n?o identificadas. No Cap?tulo II, objetivou-se determinar a diversidade comunidade de joaninhas adultas, em ?rea do SIPA, e caracterizar a estrutura das popula??es por meio da an?lise faun?stica. A riqueza de esp?cies foi igual a sete [Cycloneda sanguinea, Hippodamia convergens, Coleomegilla maculata, Coleomegilla quadrifasciata, Eriopis connexa, Harmonia axyridis e Olla v-nigrum]. C. sangu?nea, H. convergens e C. maculata foram classificadas como dominantes, sendo a primeira constante e as demais acess?rias. No Cap?tulo III, os estudos foram conduzidos com C. maculata, em condi??es de laborat?rio, com o objetivo de avaliar o efeito de diferentes concentra??es de produtos fitossanit?rios alternativos usados em agricultura org?nica (Natuneem?, Nim-I-Go?, Rotenat?, Calda sulfoc?lcica e Agrobio?), sobre aspectos biol?gicos desse inseto. Os dois produtos ? base de nim (Natuneem e Nim-I-Go) a 2% e o produto ? base de timb? (Rotenat) a 1% e 2% diminu?ram a viabilidade dos ovos de C. maculata. Nim-I-Go nas concentra??es de 1% e 2% causou maior mortalidade do que o tratamento controle (?gua) em todos os instares larvais. Com exce??o do Agrobio todos os produtos fitossanit?rios influenciaram negativamente a reprodu??o de C. maculata. Os produtos ? base de nim devem ser utilizados com parcim?nia para evitar efeitos negativos ao desenvolvimento de C. maculata.

"Summary: The larvae of predatory hoverfly Episyrphus balteatus DeGeer (Diptera: Syrphidae), have limited dispersal ability to forage. The selection of the oviposition site by gravid females is crucial for the survival larvae. Therefore hoverfly females should optimise their foraging behaviour by choosing suitable oviposition sites. The aim of this PhD thesis was to understand how hoverfly females assess aphid patch quality during their egg-laying behaviour. The impact of several factors on the oviposition response of E. balteatus females including host plant, aphid species, aphid colony size, semiochemicals emitted from aphids or their association with host plants, presence of intra- or interspecific competitors and females age, was clearly demonstrated during this research. In the first part, we have shown that E. balteatus females select their oviposition site according to aphid-host plant and aphid species, which is also shown to be related to offspring performance (fitness). Aphid species Myzus persicae (Sulzer) infested-Solanum tuberosum L. was the most preferred aphid-plant combination as an oviposition site by syrphid females. The E. balteatus survival was enhanced in this system and females laid numerous eggs when larvae were reared with M. persicae as prey, especially when the host plant was potato. Broad bean plants Vicia faba infested with Megoura viciae (Buckton) or Acyrthosiphon pisum (Harris) were equally attractive for E. balteatus females. Aphis fabae (Scopoli) was the least preferred aphid. Higher hoverfly fitness was also observed when larvae were reared on M. viciae or A. pisum compared to those reared on A. fabae. Moreover, it was also demonstrated that foraging hoverfly females is guided by different infochemical cues emitted by aphid host plant, such as (E)-β-farnesene, enabling them to locate aphid infested plant and to select an adequate oviposition site. In the second part, the leaf disc system was found to be a practical and efficient method to assess the hoverfly reproductive behaviour under different laboratory conditions. Results also showed that there was a significant quadratic relationship between the released (E)-β-farnesene amounts and aphid colony size, which means that this molecule play important role in oviposition decision made by hoverfly females in response to aphid colony size. In the third part, we have highlighted that the E. balteatus females avoid aphid colonies in which conspecific larvae or their tracks were already present. Similar response was also shown by females to the presence of Harmonia axyridis (Pallas) larval tracks. This oviposition deterring stimulus was also shown to be mediated by odourant cues emitted from larval tracks extracts. It was also demonstrated that the foraging behaviour of hoverfly females was modified by the presence of parasitoids Aphidius ervi (Haliday) in aphid colonies. Females did not exhibit any preference for plants infested with unparasitised or parasitised aphids for 7 days, but they are reluctant to lay eggs in response to the presence of mummies or their exuvia on broad bean plants. Oviposition preference of predatory hoverfly females according to the developmental state of the parasitoid larvae in aphid prey was also found to be related with larval performance. Finally, the age of hoverfly females was found to be an important factor affecting their reproduction ability, suggesting that younger E. balteatus females (2 to 5 weeks old) could be have potential to play a role in biological control of aphids because of their higher reproductive efficiency. All experiments were performed in a laboratory environment and most results obtained are discussed in relation to the context of biological control efforts/Résumé : Les larves du syrphe aphidiphage Episyrphus balteatus (Diptère, Syrphidae) ont une capacité de déplacement limitée. Le choix du site doviposition des femelles est donc crucial pour la survie larvaire. Pour cela, les femelles de ce diptère devraient optimiser leurs choix de sites doviposition pour maximiser les chances de survie de leurs progénitures. Le but de cette thèse de doctorat était de comprendre comment les femelles dE. balteatus évaluent la qualité de patches de pucerons au cours de leur comportement de ponte. La réponse de ponte des femelles dE. balteatus observées à travers plusieurs facteurs a été réalisée, parmi lesquels: la plante hôte, lespèce de pucerons, la taille de la colonie de pucerons, les substances sémiochimiques émises par les pucerons et leurs associations avec leurs plantes hôtes, la présence de compétiteurs intra- ou interspécifiques et l'âge de la femelle. Dans la première partie de ce travail, les résultats obtenus ont permis de mettre en évidence que les femelles dE. balteatus sélectionnent le site de ponte en fonction de la plante hôte et lespèce de puceron, et ce comportement a été aussi montré comme étant lié avec la performance du prédateur (fitness). La combinaison puceron/plante M. persicae/Solanum tuberosum a été la plus préférée par les femelles dE. balteatus, et le fitness de ce prédateur était plus élevé en particulier lorsque les larves sont nourries avec M. persicae élevées sur une plante de pomme de terre. De même, les femelles dE. balteatus ont montré une même préférence pour les deux combinaisons M. viciae/V. faba et A. pisum /V. faba, et un fitness supérieur du prédateur adulte a été aussi observé lorsque les larves sont nourries avec les deux espèces de pucerons. De plus, nous avons aussi montré que les femelles dE. balteatus en recherche de site de ponte sont guidées par des substances volatiles, en particulier le E-(β)-farnésène, émises par les pucerons infestant leur plante hôte. Dans la deuxième partie, le système feuille-disque est démontré comme étant une méthode pratique et efficace pour évaluer le comportement de ponte dE. balteatus au laboratoire sous différentes conditions. Les résultats ont aussi démontré quil y a une relation quadratique entre lémission du E-(β)-farnésène et la taille de colonie de pucerons, ce qui permet de seffectuer que cette molécule a un rôle important dans le comportement de ponte des femelles dE. balteatus en réponse à la taille de la colonie de pucerons. Les résultats obtenus dans la troisième partie, nous ont permis de montrer que les femelles dE. balteatus réduisent leurs pontes dans une colonie de pucerons contenant préalablement des larves de leur propre espèce ou leurs traces. Une réponse similaire a été aussi montrée en présence des substrats préalablement visitées par les larves de coccinelle Harmonia axyridis. Ainsi, la réduction de la ponte des femelles dE. balteatus est provoquée par des substances volatiles émises par les substrats des larves de syrphe. Nous avons aussi démontré que la présence du parasitoïde Aphidius ervi dans une colonie de pucerons a un effet significatif sur le comportement de ponte des femelles dE. balteatus. Les femelles dE. balteatus ne distinguent pas les plants infestées par les pucerons parasités ou non parasités, cependant les femelles réduisent leur pontes en réponse à la présence des pucerons momifiés ou des exuvies de momies. De plus, un fitness supérieur du prédateur a été aussi observé lorsque les larves sont nourries avec lespèce de pucerons A. pisum parasités ou non parasités. Enfin dans la dernière partie, lâge de la femelle dE. balteatus influence significativement leur reproduction, ce qui permet de proposer que les jeunes femelles (2 à 5 semaines) peuvent être plus efficaces dans la lutte biologique contre les pucerons car elles ont une grande efficacité de reproduction. Toutes les expériences ont été effectuées au laboratoire et la plupart des résultats obtenus sont discutés en relation avec le contexte de la lutte biologique".

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2017-06-20T20:36:51Z No. of bitstreams: 1 2012 - Vinicius de Abreu D'?vila.pdf: 623654 bytes, checksum: 2c91585552193e53bcefc6b559fe2a2f (MD5) / Made available in DSpace on 2017-06-20T20:36:51Z (GMT). No. of bitstreams: 1 2012 - Vinicius de Abreu D'?vila.pdf: 623654 bytes, checksum: 2c91585552193e53bcefc6b559fe2a2f (MD5) Previous issue date: 2012-08-31 / CAPES / The biological control is as important method to regulate the pest populations in a system of sustainable agricultural production, because it is a promising alternative to the use of the organic synthetic pesticides that cause great ecotoxicological impacts. The predator ladybeetles are part of the biological control agents of agricultural pests, could be management by the three biocontrol strategies: classical, conservative and augmentative. In the present work, it was tried to generate knowledge for using the aphidophagous predator ladybeetle Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae) under the perspective of the last two strategies. The conservative biological control involving predator insects bases on the fact that in the absence or scarceness of their preferential prey or in the presence of the other preys with inferior nutritional quality, they may use alternative foods, such as pollen, to guarantee their survivorship and, sometimes, their reproduction, and because of that botanical species that provide this floral resource might integrate the agricultural landscape, inside and/or around the agricultural property; meanwhile the augmentative control requests the multiplication of the predator in the laboratory, using natural or artificial preys. Even though some authors proved the visitation of the flowers of some species of Apiaceae by C. maculata, there are no records in the literature of the ingestion of pollen grains of this botanical family by this ladybeetle. In this context, this work was carried out with the aim to select the plant species whose flowers are source of pollen as alternative or complementary food to C. maculata in the perspective to compose the vegetation of the agroecosystems to contribute in the conservation of this ladybeetle, and /or to aid in its mass rearing in the laboratory conditions. The objective of the chapter I was to prove the ingestion of pollen of three species of the family Apiaceae [coriander (Coriandrum sativum L.), dill (Anethum graveolens L.), and fennel (Foeniculum vulgare Mill.)] from the provision of their flowers to the larvae of the 4th instar and adults of C. maculata. It was observed the presence of pollen grains in the five replicates of all treatments, proving the ingestion of the pollen of these three species of Apiaceae from their flowers by C. maculata. At 24 hours of exposition, adults fed on average more pollen of dill than pollens of coriander and fennel, while the larvae consumed more pollen of fennel. The objective of the chapter II was to determine the suitability of nine diets to C. maculata, including provision of pollen of the two species of Apiaceae (coriander and dill), under controlled conditions of the laboratory. Even though the diets with only flowers of these two Apiaceae did not provided the full development of C. maculata, they used as complementary food with eggs of Anagasta kuehniella Zeller (Lepidoptera: Pyralidae) resulted in reduction of larval period, increased the egg number by cluster, and increased the body weight. The diet with alive larvae of Drosophila melanogaster Meigen (Diptera: Drosophilidae) was proved to be an essential food as well as resulted in adults with higher body weight, and the number of eggs per cluster increased in comparison with the feeding with only eggs of A. kuehniella. / O controle biol?gico ? um importante m?todo para regular as populac?es de pragas em um sistema de produ??o agr?cola sustent?vel, pois ? uma alternativa promissora ao uso de agrot?xicos org?nicos sint?ticos que causam grandes impactos ecotoxicol?gicos. As joaninhas predadoras fazem parte dos agentes de controle biol?gico de pragas agr?colas, podendo ser manejadas pelas tr?s estrat?gias de controle biol?gico: cl?ssico, conservativo e aumentativo. No presente trabalho, buscou-se gerar conhecimento para uso da joaninha predadora afid?faga Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae) sob a perspectiva das duas ?ltimas estrat?gias. O controle biol?gico conservativo envolvendo insetos predadores baseia-se no fato de que, na aus?ncia ou escassez da presa preferencial ou na presen?a de outras presas de qualidade inferior, podem usar alimentos alternativos, tais como p?len, para garantir sua sobreviv?ncia e, por vezes, sua reprodu??o e, por isso, esp?cies bot?nicas provedoras desse recurso floral devem integrar a paisagem agr?cola, dentro e/ou no entorno da propriedade agr?cola; enquanto o controle aumentativo requer a multiplica??o do predador no laborat?rio, podendo se valer de presas naturais ou artificiais. Apesar de alguns autores comprovarem a visita??o das flores de algumas esp?cies de Apiaceae por C. maculata, n?o h? relatos na literatura da ingest?o de gr?os de p?len dessa fam?lia bot?nica por essa joaninha. Nesse contexto, este trabalho foi conduzido a fim de selecionar esp?cies de plantas cujas flores sejam fonte de p?len como alimento alternativo ou complementar para C. maculata na perspectiva de compor a vegeta??o dos agroecossistemas para contribuir na conserva??o dessa joaninha, e/ou auxiliar na cria??o massal da mesma em condi??es de laborat?rio. O objetivo do cap?tulo I foi comprovar a ingest?o de p?len de tr?s esp?cies da fam?lia Apiaceae [coentro (Coriandrum sativum L.), endro (Anethum graveolens L.) e erva-doce (Foeniculum vulgare Mill.)] a partir da oferta de suas flores para larvas de 4? instar e adultos de C. maculata. Constatou-se a presen?a de gr?os de p?len nas cinco repeti??es de todos os tratamentos, comprovando a ingest?o de p?len dessas tr?s Apiaceae a partir de suas flores por C. maculata. Em 24 horas de exposi??o, os adultos consumiram em m?dia mais p?len de endro em compara??o aos polens de coentro e erva-doce, enquanto que as larvas consumiram mais p?len de erva-doce. O objetivo do capitulo II foi determinar a adequabilidade de nove dietas para C. maculata, incluindo oferta de p?len de duas esp?cies de Apiaceae (coentro e endro), em condi??es controladas de laborat?rio. Apesar das dietas apenas com flores dessas duas Apiaceae n?o proporcionarem o desenvolvimento completo de C. maculata, elas usadas com complementa??o da alimenta??o com ovos de Anagasta kuehniella Zeller (Lepidoptera: Pyralidae) possibilitam a redu??o do per?odo larval, aumento no n?mero de ovos por postura e aumento do peso corp?reo. A dieta com larvas vivas de Drosophila melanogaster Meigen (Diptera: Drosophilidae) n?o foi s? comprovada como alimento essencial como tamb?m resultou em adultos de maior peso corp?reo e um aumento no n?mero de ovos por postura em compara??o ? alimenta??o apenas com ovos de A. kuehniella.

During the 1990s, over a period of just a few years, the multi-colored Asian lady beetle, Harmonia axyridis (Pallas) invaded the entire area of northern Europe. In parallel with this invasion, a decline in native coccinellid species was recorded in Belgium, Britain, and Switzerland, affecting mainly one common species: the two-spot ladybird, Adalia bipunctata L. An impressive trait of H. axyridis, that could explain both its high invasiveness and the decline of native coccinellids, is its predation behaviour. Intraguild predation is a trophic interaction between species that share the same prey – in this case, aphids. In order to determine the precise impact of this predation on the native coccinellid species, the predation behaviour of H. axyridis larvae was observed in Petri dishes and on plants. The resistance of H. axyridis to predation was also studied by exposing it without dorsal spines to native predator larvae, in order to test whether or not the dorsal spines are a physical defence against intraguild predation. In addition to these laboratory experiments, an original method was developed and used to track predation under field conditions. This method is based on the gas chromatography–mass spectrometry (GC-MS) detection of exogenous alkaloids in H. axyridis, especially alkaloids from native coccinellids likely to be subject to intraguild predation. My results show that, in the absence of aphids, H. axyridis consumes both A. bipunctata eggs and all larval instars in Petri dishes. On plants, depending to aphid density, this interaction can change with regards to larvae but not eggs. In addition to intraguild predation, competitive exclusion can occur because of quite aggressive behaviour towards competitors. Dorsal spines significantly reduce the number of bites inflicted, and thereby complement the other defense mechanisms of H. axyridis that enable it to remain dominant in competition for food resources. In semi-natural conditions, predation on the native coccinellids Adalia spp. Calvia spp. Coccinella septempunctata L. and Propylea quatuordecimpunctata (L.) was detected. The number of sites where this predation was observed suggests that this interaction is frequent. It was also observed that an H. axyridis larva can ingest several native coccinellid species, confirming its status as a predator of coccinellids. We can therefore conclude that intraguild predation by H. axyridis leads, as does resource competition, to a decline in native coccinellids./Introduite pour la lutte biologique dans les années 90, la Coccinelle asiatique, Harmonia axyridis (Pallas), a envahi en quelques années toute l’Europe du Nord. Parallèlement à cette invasion, un déclin de plusieurs espèces de coccinelles indigènes dont la très commune Coccinelle à deux points, Adalia bipunctata L. a été observé dans différents biotopes en Belgique, en Angleterre ainsi qu’en Suisse. Un des traits remarquables de la Coccinelle asiatique est son comportement de prédateur intraguilde qui pourrait expliquer à la fois ce déclin mais aussi en partie son caractère hautement invasif. La prédation intraguilde est une interaction trophique entre des espèces qui se nourrissent d’une même proie, dans ce cas-ci les pucerons. Afin de mieux connaître l’impact de cette prédation sur les coccinelles indigènes, le comportement de prédation des larves d’H. axyridis a été décrit en boîtes de Petri et sur plantes. Sa résistance à la prédation a également été étudiée en exposant des larves dépourvues d’épines dorsales à un prédateur indigène, dans le but de tester le rôle de ces épines en tant que défense physique à l’égard d’un prédateur intraguilde. En plus de ces expériences de laboratoire, une méthode originale a été développée et utilisée pour suivre cette prédation en conditions semi-naturelles. Elle se base sur la détection, en GC-MS, des alcaloïdes exogènes chez H. axyridis et en particulier des alcaloïdes produits par d'autres espèces de coccinelles susceptibles de subir une prédation intraguilde. Mes résultats montrent qu'en l'absence de pucerons, H. axyridis a un comportement de prédation vis-à-vis des œufs et de tous les stades larvaires d’A. bipunctata. La présence de pucerons, suivant leur densité, peut modifier cette interaction à l’égard des larves indigènes mais pas des œufs. En plus de la prédation intraguilde, une compétition par exclusion peut être aussi suspectée et expliquée par le comportement très agressif d’H. axyridis à l’égard de ses concurrents. Quant aux épines dorsales, elles permettent de réduire significativement le nombre de morsures et complètent ainsi les autres lignes de défense utilisées par H. axyridis pour s’imposer dans des ressources déjà exploitées par d’autres prédateurs. En conditions semi-naturelles, cette prédation à l’égard des coccinelles indigènes a été confirmée vis-à-vis d’Adalia spp. Calvia spp. Coccinella septempunctata L. et Propylea quatuordecimpunctata (L.). Vu le nombre de sites où cette prédation a été détectée, elle peut être considérée comme une interaction fréquente. De plus, une même larve de coccinelle asiatique peut ingérer plusieurs espèces de coccinelles indigènes confirmant indéniablement son statut de prédateur de coccinelles. Ainsi, nous pouvons conclure que la prédation intraguilde par H. axyridis sur les coccinelles indigènes participe très certainement au déclin de celles-ci et ceci très probablement au même titre que des phénomènes de compétition pour les ressources. / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished