No description available.

This study focuses on the effective biocontrol agent Chilocorus nigritus (Fabricius). Its behaviour and ecology were compared with other Chilocorus spp. where appropriate, to elucidate why this species is such an effective biocontrol agent, and how to improve methodology for its deployment as a natural enemy. An artificial diet for C. nigritus was developed, but was still sub-optimal. Asterolecanium miliaris (Boisduval) was a suitable prey for all life stages of C. nigritus and the adults of Chilocorus bipustulatus (Linnaeus) and Chilocorus infernalis Mulsant, but was inadequate for larvae of the last two species. Adult weight, measured at one day after adult eclosion, was an appropriate indicator of the effects of larval treatment on their development and on the fitness of subsequent adults. There was no improvement in culture vigour due to a behavioural response of individuals within one generation to fluctuating as opposed to constant temperature. starvation for between 10h and 24h was appropriate for standardisation of hunger. Measuring feeding rate at a range of static temperatures did not reflect differences in the climatic adaptations of six Chilocorus spp., but mortality rates at increasingly high temperatures were useful. Chilocorus spp. showed little ability to choose between prey species. Prey substitutions adversely affected adults and larvae. Introduction of adults was the most effective method for field establishment. Giant bamboo Dendrocalamus giganteus Munro was a valuable site for field releases of C. nigritus, but less useful for C. bipustulatus and C. infernalis. Counter to assumptions on which interference models have been based, no significant intraspecific interference, reducing predatory efficiency, was observed. Visually prominent features on the horizon and a specific leaf shape, were attractive to foraging C. nigritus. The location of prey patches by adults was facilitated by prey odour, but not so for larvae. Adults detected individual prey olfactorily and visually over short distances, but physical contact was required for detection by larvae. Prey location by larvae and adults was facilitated by alterations in movement patterns in response to prey consumption. Differences in prey detection and the effects of prey substitutions, between the life stages, were related to field behaviour. The relevance to biological control, of responses to rearing conditions and feeding and foraging behaviour, was investigated. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

Dans le cadre de ce travail, nous avons poursuivi l’étude de la biosynthèse d’alcaloïdes défensifs des coccinelles. Trois espèces ont été plus particulièrement étudiées : Adalia bipunctata (qui produit l’adaline [32]), Coccinella septempunctata (contenant la coccinelline [29]) et Harmonia axyridis (produisant l’harmonine [34]). Afin d’identifier le (ou les) acide(s) gras précurseur(s) de ces alcaloïdes, nous avons dans un premier temps synthétisé des acides gras spécifiquement marqués. Nous avons ainsi préparé les acides [14-3H]myristique, [16-3H]palmitique, [18-3H]stéarique, [18-13C]stéarique et [11,11,12,12,13,13,14,14,15,15,16, 16,17,17,18,18,18-2H]stéarique. Les différents acides gras marqués au tritium sur le méthyle terminal ont ensuite été incorporés successivement chez les trois espèces de coccinelles mentionnées ci-dessus, en utilisant la technique d’incorporation in vitro mise au point par Laurent et al. ( ) Les incorporations chez Adalia bipunctata ont montré que l’acide myristique est incorporé préférentiellement dans l’adaline. Chez Coccinella septempunctata par contre, l’acide stéarique est incorporé dans la coccinelline environ 25 fois plus efficacement que les acides myristique et palmitique. Enfin, les incorporations chez Harmonia axyridis ont établi que l’acide stéarique est le précurseur de l’harmonine. De plus, grâce à l’incorporation de l’acide [11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,18-2H]stéarique, le mécanisme de formation de l’amine secondaire a été précisé. / In spite of their red-orange colors, which could increase risks of predation, Coccinellidae are rarely exploited as food sources by predators. Many of them owe their protection, at least in part, to the presence of repellents and, in some cases, toxic alkaloids in the hemolymph emitted during a process called "reflex bleeding". Previous studies have shown that the biosynthesis of these alkaloids is related to fatty acid metabolism. In our doctoral thesis, we wanted to clarify what are the fatty acids precursors of adaline (Adalia bipunctata), coccinelline (Coccinella septempunctata) and harmonine (Harmonia axyridis), with the use of various techniques of labelling (3H, D, 13C, etc.).

This study investigated effects of insect growth regulators (IGRs), recommended for use on citrus in southern Africa, on non-target organisms, particularly species of Coccinellidae in and around three citrus estates in the lowveld region of Swaziland, i.e. Tambuti, Tambankulu and Tunzini estates. Some of the species are important predators of citrus pest insects. The distribution of coccinellids within an agricultural land mosaic and factors affecting this distribution pattern were also investigated. Results showed that coccinellid densities and species diversity were lowest in the natural veld surrounding the orchards. In contrast, citrus orchards had the highest coccinellid densities and diversity. River borders, along the Great Usuthu river, had intermediate densities and diversity. While temperature, relative humidity and ground insolation had no significant effect on coccinellid population densities, the presence / absence of prey (host plant), on the other hand, was an important factor. This was the case both for phytophagous and predatory coccinellid species. These showed close patterns of distribution with their respective host plants or prey species. Economically important species, such as Rodolia spp., were restricted to the orchards, while other species, especially those whose economic role is uncertain, such as Cheilomenes lunata and Scymnus spp., were found in most habitat types. Coccinellid population densities were assessed during four treatment programmes: 1) an integrated pest management (IPM) programme where no IGRs were used, 2) a programme where any of the recommended IGRs were to be applied, 3) conventional pesticide programme, and 4) an orchard which did not receive any chemically treatment over the last four years (at Tambankulu estate only). Significant differences between treatment programmes were observed at all three estates, when only economically important coccinellid species were assessed. Orchards under an IPM programme (with no IGRs) were found to have significantly higher population densities compared to those in IGR-treated or under a conventional pesticide regime. The untreated orchard at Tambankulu, however, had significantly higher coccinellid densities of economically important species and higher overall population densities than any of the managed orchards. Of the three estates assessed, Tunzini had significantly higher population densities of all beneficial coccinellids, (excluding the untreated orchard at Tambankulu). Natural vegetation around Tunzini and Tambuti contributed to the higher coccinellid densities compared to Tambankulu, which was surrounded by other agricultural land. Laboratory and field experiments on two non-target species, the ladybird Chilocorus nigritus (Fabricius) (all stages) and the moth Bombyx mori (Linnaeus) (larval stage) assessed specific IGR effects, if any. Three IGRs, buprofezin, teflubenzuron (both chitin synthesis inhibitors) and pyriproxyfen (a juvenile hormone analogue) were used. All three pesticides are currently recommended for use on citrus in southern Africa and were tested at the recommended dosages. Laboratory experiments showed that all three IGRs have a negative impact on both non-target species. When B. mori received direct applications, there was larval mortality as a result of the failing to complete moulting or dying immediately after moulting. In addition, no larvae were able to pupate after having fed on contaminated leaves. In the case of C. nigritus, larvae fed IGR-treated scale or sprayed with buprofezin suffered significantly higher mortality than controls, while IGR effects on those sprayed with, or fed scale-treated with, pyriproxyfen or teflubenzuron were not significant. No adults however, emerged from any pupae in any of the treatment groups. All three IGRs had ovicidal activity on C.nigritus eggs. Adult fecundity in both field and laboratory experiments was not affected significantly after exposure to any of the three IGRs. In field experiments, the proportion of larvae of the moth and ladybird that developed up to the reproductive adult stage, after exposure to buprofezin, was not significantly different from the control. This was not the case for pyriproxyfen and teflubenzuron. Buprofezin was therefore found to be the least detrimental of the three IGRs tested. Minimal drift was observed when a knapsack sprayer was used. However, there was spray drift up to 32m (the furthest distance assessed here) where commercial sprayers were used. This suggests that pesticide drift from orchards to adjacent areas would have serious implications for biological diversity in the river borders and rivers adjacent to the estates. The sensitivity of the non-target species to the IGRs tested needs serious consideration, as it indicates a broader spectrum of activity for the compounds than what is promoted. Additionally, natural control may be affected. This is because the timing of IGR applications and increasing coccinellid populations coincide, resulting in a reduced pool of coccinellid predators. This study emphasised the importance of an appropriately heterogenous landscape to maximise habitat availability for the coccinellids. Although the economic role of the multihabitat coccinellid species recorded here is unknown, they nevertheless clearly contribute to citrus pest control. Such a mosaic landscape, in conjunction with IPM, with no IGR use, promotes ecological diversity and controls pests with minimum disruption to biodiversity. The use of IGRs in citrus thus needs carefiil reconsideration in light of the non-target effects observed on the two species, especially the valuable predatory species, C. nigritus. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1998.

L'étude menée durant quatre années consécutives (2003-2007) a caractérisé écologiquement et faunistiquement le peuplement des coccinelles en Algérie. 48 espèces ont été répertoriées dont 46 sont des agents de lutte biologiques. Elles se répartissent dans huit sous-familles, 12 tribus et 23 genres. La richesse spécifique est très élevée dans les secteurs du nord d'Algérie. Cette zone est caractérisée par des bioclimats humide, sub-humide et semi aride regroupant 41 espèces. Elle est par contre très faible dans le secteur de l'Atlas saharien et le Sud algérien avec respectivement 12 et 16 espèces. L'étude des spécificités trophiques, spatiales et temporelles des principales espèces, nous a conduits à définir leurs niches écologiques dans les différents agro écosystèmes de l'Algérie. Ainsi, la distribution spatiale des espèces peut apparaître comme quelque chose de statique. Il s'agit en réalité d'un processus dynamique dont le moteur est la disponibilité d'habitat favorable qui abrite la proie préférentielle. La communauté de coccinelles fonctionne sur le principe de partage des ressources et les interactions entre espèces organisent la communauté en réseaux trophiques. L'analyse de la distribution des coccinelles à travers les différents secteurs géographiques montre que les espèces: C. septempunctata, H. variegata, S. punctillum et, H. argus présentent une forte valence écologique. En revanche, les espèces: P. ovoideus, P. numidicus, E. pubescent forme apicalis, H. marmottani, et Pullus sp semblent être spécifiques aux régions sahariennes et plus particulièrement au Sahara septentrional. / The study led during four consecutive years (on 2003-2007) shed light on the species composition, and habitat characteristics of the communities of ladybirds in Algeria. 48 species were listed among which 46 are biological control agents. They divide up in 8 sub-families, 12 tribes and 23 genera. The specific richness is very high in the sectors of the North of Algeria (41 species). This zone is characterized by bioclimates wet, sub-wet and semi-dry grouping. It is very low on the other hand in the sector of the Saharan Atlas and the Algerian South with respectively 12 and 16 species. The study of trophic interactions, spatial and temporal distribution of the main species, led us to define their ecological niches in the various agro-ecosystems of Algeria. So, the spatial distribution of the species can appear as something static. It is in reality a dynamic process the engine of which is the availability of favorable habitats that shelter ladybird preferential prey. Communities of ladybird works on the principle of division (sharing) of the resources and the interactions between species organize the community in trophic networks. The analysis of the distribution of ladybirds through the various geographical areas shows that the C. septempunctata, H. variegata, S. punctillum, and, H. argus present strong ecological valence. On the other hand, P. ovoideus, P. numidicus, E. pubescens forme apicalis, H. marmottani, and Pullus sp are specific to the Saharan regions and more particularly to northern Sahara.

En réponse aux pertes de biodiversité et à une insécurité alimentaire croissante, l’agriculture moderne doit se tourner vers une gestion plus durable des paysages agricoles. L’Agriculture Biologique (AB) est considérée comme une solution prometteuse à ces enjeux. En effet, ses pratiques agricoles étant globalement plus favorables aux ennemis naturels de ravageurs que celles de l’Agriculture Conventionnelle (AC), elle pourrait permettre de remplacer l'utilisation des pesticides par celle du contrôle biologique. Cependant, les études évaluant ces effets restent contradictoires, probablement car elles ne tiennent pas compte de la diversité des pratiques réalisées en AB et en AC. A plus large échelle, les pratiques ont par ailleurs rarement été considérées dans la description de l’hétérogénéité paysagère, bien que la nature et l’organisation spatiale de la matrice agricole soit susceptible d’affecter les espèces qui y vivent. L’objectif de ce travail de thèse est d’évaluer les effets de la diversité et de l’organisation spatiale des pratiques en AB et en AC sur les insectes auxiliaires, à l’échelle de la parcelle et du paysage. Un travail de terrain a été réalisé en 2012 et 2013 en Ille et Vilaine. Quarante paires de parcelles de blé d’hiver en AB et en AC ont été sélectionnées, réparties le long d’un gradient paysager de surfaces en AB. Dans chaque parcelle, les communautés d'ennemis naturels de pucerons (coccinelles, carabes, parasitoïdes) ont été échantillonnées. Des enquêtes ont permis de caractériser les pratiques agricoles réalisées par les agriculteurs dans les parcelles suivies et dans leur environnement paysager. Nous avons mis en évidence l’existence d’une large diversité de pratiques agricoles dans les systèmes en AB et en AC. A l’échelle parcellaire, les effets des pratiques sur la diversité des insectes auxiliaires sont forts, les systèmes en AB leur étant globalement plus favorables. Considérer un niveau plus fin de description des pratiques nous a permis d’identifier celles qui affectent réellement les insectes et de montrer qu’il est possible de favoriser leur présence, quel que soit le mode de production. A l’échelle du paysage, nous n’avons mis en évidence aucun effet de l’étendue et de l’organisation de l’AB sur les ennemis naturels. Une description plus fine des pratiques nous a malgré tout permis de souligner l’importance de certaines stratégies de pratiques, à certaines échelles. A partir de ces résultats, nous proposons des pistes pour l’aménagement des paysages agricoles. Les problèmes méthodologiques liés à la description des pratiques agricoles à l’échelle du paysage sont également discutés. / Due to the loss of biodiversity and increasing food insecurity, modern agriculture must evolve toward a more sustainable management of agricultural landscapes. Organic Farming (OF) is considered as a promising solution to meet this challenge. Organic practices are indeed generally more favorable to pest natural enemies than Conventional Farming (CF), suggesting that pesticides could be replaced by biological control. However, studies evaluating these effects are contradictory, probably because they do not consider the diversity of practices implemented in OF and CF. On a broader scale, practices have rarely been considered in the description of landscape heterogeneity, although the nature and configuration of farmland must affect species. The target of this PhD work is to evaluate the effects of the diversity and spatial organization of organic and conventional farming practices on insect natural enemies, at field and landscape scales. A fieldwork was conducted in 2012 and 2013 in Brittany. Forty pairs of organic and conventional winter wheat fields were selected, distributed along a landscape gradient of OF area. In each field, aphid natural enemies (ladybirds, carabid beetles, parasitoids) were sampled. We interviewed farmers to characterize farming practices implemented in fields and their surrounding landscape. We observed a wide diversity of farming practices in OF and CF. At field scale, effects of practices on the diversity of natural enemies were strong, OF being overall more favorable. Considering a finer description of practices allowed us identifying those really affecting insects, and showing they can be enhanced regardless of the farming type. At landscape scale, we found no effect of the OF area and configuration on natural enemies. With a more detailed description of practices, we however highlighted the importance of some farming strategies, at some scales. Based on these results, we open up avenues to manage agricultural landscapes. Methodological issues related to the description of farming practices on large areas are also discussed.

Thesis (M. Tech) --Central University of Technology, Free State, 2008 / Aphids (Hemiptera: Aphididae) are amongst the most destructive insects in agricultural crop production systems. This reputation stems from their complex life cycles which are mostly linked to a parthenogenetic mode of reproduction, allowing them to reach immense population sizes within a short period of time. They are also notorious as important and efficient vectors of several plant viral diseases. Their short fecund life cycles allow them to be pests on crops with a short growth period, e.g. lettuce (Lactuca sativa L.). It is common practice to provide this crop with some degree of protection from environmental extremes on the South African Highveld. Shadehouses are popular in this regard, but aphids are small enough to find their way into these structures, and their presence on lettuce is discouraged due to phytosanitary issues. In addition, the excessive use of insecticides is criticized due to the negative influence on human health, and because aphids can rapidly develop resistance. This necessitates the use of alternative control options in order to suppress aphid numbers. Biological control is popular in this regard and the use of predatory ladybirds (Coleoptera: Coccinellidae) is a popular choice. This study investigated the aphid and coccinellid species complex encountered under varying shadehouse conditions on cultivated head lettuce in the central Free State Province (South Africa). Their seasonality was also examined, along with variations in their population size throughout a one-year period. Finally, the impact of varying aphid populations on some physical characteristics of head lettuce was examined, and recommendations for aphid control (using naturally occurring coccinellid predators) were made. Two shadehouse structures were evaluated during this study. One was fully covered with shade netting and designed to exclude the pugnacious ant, Anoplolepis custodiens (Hymenoptera: Formicidae), while the other was partially covered with shade netting (on the roof area) allowing access to the ants. Six cycles of head lettuce were planted and sampled four times during each cycle. These were scheduled to monitor the seedling, vegetative and heading stage of lettuce. Four important aphid species were recorded on the lettuce, namely Acyrthosiphon lactucae, Nasonovia ribisnigri, Myzus persicae and Macrosiphum euphorbiae. Both structures harboured similar aphid and coccinellid species, but their population dynamics differed. A. lactucae dominated in the absence of A. custodiens in the fully covered structure (whole study), while N. ribisnigri dominated in the partially covered structure in the presence of these ants during the warmer months (December – January). M. euphorbiae replaced this species as the dominant species in the absence of A. custodiens (April – September). M. persicae occured during the winter (May – August) in the fully covered structure. Promising coccinellid predators were Hippodamia variegata and Scymnus sp. 1, and to a lesser extent, Exochomus flavipes and Cheilomenes lunata. However, the fully covered structure hampered the entrance of the larger adult coccinellid species, resulting in their lower occurrence. Aphid and coccinellid activity peaked during the summer months (October – January), and the fully covered structure attained the highest aphid infestation levels and coccinellid larval numbers during this time. On the other hand, aphid numbers were higher in the partially covered structure during the cooler months of the year (April – July) and this structure also harboured more adult coccinellids. In most cases, aphid infestation levels did not affect the amount of leaves formed. However, symptomatic damage in terms of head weight reduction did occur under severe infestation levels. Specific environmental conditions within a shadehouse structure concurrently contributed to this reduction, with less favourable conditions accelerating this condition. Results from this study have shown that even though the type of shadehouse structure does not influence the insect species complex found on lettuce, it does have an influence on detrimental and beneficial insect population dynamics. Aphid species infesting lettuce have been identified, along with coccinellid predators that could potentially be used in their control. Both types of structures had advantages and disadvantages, and therefore, decisions concerning shadehouses should not be focused on which type of structure to use, but rather which type of structure to use during different seasons of the year.

Dans le cadre de ce travail, nous avons poursuivi l’étude de la biosynthèse d’alcaloïdes défensifs des coccinelles. Trois espèces ont été plus particulièrement étudiées :Adalia bipunctata (qui produit l’adaline [32]), Coccinella septempunctata (contenant la coccinelline [29]) et Harmonia axyridis (produisant l’harmonine [34]).<p>Afin d’identifier le (ou les) acide(s) gras précurseur(s) de ces alcaloïdes, nous avons dans un premier temps synthétisé des acides gras spécifiquement marqués. Nous avons ainsi préparé les acides [14-3H]myristique, [16-3H]palmitique, [18-3H]stéarique, [18-13C]stéarique et [11,11,12,12,13,13,14,14,15,15,16, 16,17,17,18,18,18-2H]stéarique.<p>Les différents acides gras marqués au tritium sur le méthyle terminal ont ensuite été incorporés successivement chez les trois espèces de coccinelles mentionnées ci-dessus, en utilisant la technique d’incorporation in vitro mise au point par Laurent et al. ( )<p>Les incorporations chez Adalia bipunctata ont montré que l’acide myristique est incorporé préférentiellement dans l’adaline. <p>Chez Coccinella septempunctata par contre, l’acide stéarique est incorporé dans la coccinelline environ 25 fois plus efficacement que les acides myristique et palmitique.<p>Enfin, les incorporations chez Harmonia axyridis ont établi que l’acide stéarique est le précurseur de l’harmonine. De plus, grâce à l’incorporation de l’acide [11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,18-2H]stéarique, le mécanisme de formation de l’amine secondaire a été précisé.<p>/<p>In spite of their red-orange colors, which could increase risks of predation, Coccinellidae are rarely exploited as food sources by predators. Many of them owe their protection, at least in part, to the presence of repellents and, in some cases, toxic alkaloids in the hemolymph emitted during a process called "reflex bleeding". Previous studies have shown that the biosynthesis of these alkaloids is related to fatty acid metabolism. <p>In our doctoral thesis, we wanted to clarify what are the fatty acids precursors of adaline (Adalia bipunctata), coccinelline (Coccinella septempunctata) and harmonine (Harmonia axyridis), with the use of various techniques of labelling (3H, D, 13C, etc.).<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

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