The water hyacinth (Eichhornia crassipes (Mart.) Solms-Laub (Pontederiaceae)) biological control programme makes use of tight plant-insect interactions to control the weed, by reestablishing the interactions between the plant and its natural enemies. Since the beginning of the water hyacinth biological control initiative, the impact of biological control agent herbivory on water hyacinth’s population growth and fitness have been well documented; however, very few investigations have been conducted to determine whether herbivory elicits insect-induced responses by water hyacinth. Studies were conducted to determine the presence and function of water hyacinth insectinduced responses, using the plant activator, BION®, in attempt to determine the plant hormone-mediated pathways regulating the final expressions of insect-induced defences in response to herbivory by the phloem-feeder, Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae) and the leaf chewer, Neochetina bruchi Hustache (Coleoptera: Curculionidae). BION® (Syngenta, acibensolar-S-methyl (benzothiadiazole)) is a dissolvable, granular formulation that contains a chemical analogue of the plant hormone, salicylic acid (SA), which typically regulates defences against pathogens. The application of BION® results in the induction of the SA-mediated defence pathways in plants (activation of defences against pathogens), and consequently the inhibition of the jasmonic acid (JA)- mediated defence pathways (de-activation of defences against insect herbivores). To test for induced defence responses in water hyacinth, plants treated with BION® and then subjected to herbivory, were compared to un-treated plants that were also subjected to herbivory, BION®-only treated plants and control plants. The application of BION® did not confer resistance against the two insect herbivores, as herbivory, reductions in chlorophyll content and plant growth (leaf production and second petiole lengths) significantly increased in comparison to non-BION® treated plants. Furthermore, palatability indices significantly increased (>1.00) in BION® treated plants, reflecting increased weevil preferences for SAinduced water hyacinth plants. This concluded that SA-mediated defences are not effective against insect herbivory in water hyacinth plants, but are in fact palatable to insect herbivores, which reflects ecological and physiological costs of SA-mediated defences (pathogen defences) in water hyacinth. Biochemical analyses of leaves exhibited increases in nitrogen content in BION® treated plants. These elevated levels of nitrogenous compounds account for the increases in mirid and weevil preferences for BION® treated plants. The increases in nitrogenous compounds are probably structural proteins (e.g. peroxidises), because leaves treated with BION® increased in toughness, but only when exposed to herbivory. Regardless, insect herbivory was elevated on these leaves, probably because the nitrogenous compounds were nutritionally viable for the insects.

No description available.

El tomàquet és una de les hortalisses més importants a escala mundial i el sud-estespanyol n'és una de les majors zones productores. Part de la producció fora detemporada s'obté en hivernacles en els quals el control de plagues i malalties del cultiues basa en aplicacions freqüents de pesticides. L'objectiu d'aquesta tesi és el d'establirles bases biològiques per al disseny d'un programa de control integrat de plagues encultiu de tomàquet de tardor-hivern sota plàstic.El seguiment de les plagues i de la seva fauna útil associada, en 10 hivernacles detomàquet de Múrcia i Alacant durant les campanyes de tardor-hivern del 1991-1992 i del1992-1993, va posar de manifest que les plagues principals d'aquest conreu són elsaleuròdids Trialeurodes vaporariorum i Bemisia tabaci. L'abundància relativa d'aquestesespècies va anar canviant en el decurs del cultiu. B. tabaci va ser l'espècie majoritàriadesprés del trasplantament mentre que T. vaporariorum ho va ser a finals del cultiu. Enaquestes condicions les alliberacions inoculatives d'Encarsia formosa no varen controlarles poblacions de mosca blanca. D'altra banda, la fauna útil autòctona associada a lesmosques blanques va ser escassa, tant pel petit nombre d'espècies identificades(Eretmocerus mundus i Nesidiocoris tenuis) com per la seva abundància. Les plaguessecundàries més importants van ser els minadors de fulla Liriomyza bryoniae i L trifolii(en alguns casos controlats per poblacions autòctones de Diglyphus sp.), l'àcarAculops lycopersici i el noctúid Helicoverpa armígera.Amb l'objectiu de definir una unitat de mostratge que permeti avaluar poblacionsbarrejades de T. vaporariorum i B. tabaci, es va estudiar la distribució vertical d'aquestesdues espècies en tomaquera. En un assaig de semicamp fet a la primavera, els adults iels ous de T. vaporariorum van presentar una estratificació molt acusada i se situarenprincipalment en les fulles més joves, mentre que els adults i els ous de B. tabaci es vansituar en fulles més madures. A les densitats enregistrades en aquest experiment, cap deles dues espècies va modificar la seva distribució vertical a dins de la planta pel fetd'estar barrejada amb l'altra. En el seguiment fet en tomaqueres de tardor-hiverncultivades en hivernacles sense calefacció, els ous de T. vaporariorum es van trobarprincipalment en el terç superior de la planta i els de B. tabaci en el terç central. Les larves deis darrers estadis i les pupes de les dues espècies es van localitzar majormenten el terç baix de la tomaquera. A l'hora de definir la millor unitat de mostratge es vaestudiar la possibilitat de comptar els ous i les larves de 7*. vaporariorum i de B. tabaci enun o dos cercles (0=1,15 cm) tallats a l'atzar de cada folíol, en lloc de fer-ho en el folíolsencer. Els resultats indiquen que aquesta simplificació pot usar-se per estimar lapoblació d'ous però no la de larves. Tenint en compte el cost d'agafar i processar lesmostres, per densitats inferiors a 25 ous per folíol, el menys laboriós és fer el recompted'ous de mosca blanca en un cercle per folíol agafat de folíols del terç alt de la planta.Per densitats majors a 25 ous per folíol i, segons la proporció relativa de T. vaporariorumi B. tabaci, és menys treballós fer el recompte en un cercle per folíol de folíols del terçmig. En canvi, l'estimació de la densitat de larves s'ha de fer en folíols sencers de l'estratde baix de la planta, i es redueix el temps de mostreig comptant les larves a ull nu.Per avaluar la possibilitat d'utilitzar el mírid depredador Dicyphus tamaninii per al controlbiològic de T. vaporariorum i B. tabaci en tomaqueres de tardor-hivern, es van estudiaralguns paràmetres de la seva biologia en condicions hivernals, així com la sevapreferència enfront d'aquests aleuròdids. A termofotoperíode 16:11°C i 9,5L:14,5F, tantles femelles de D. tamaninii criades a 25°C i fotoperíode 16L:8F, com les criades encondicions d'hivern van pondre ous. Aquests ous van trigar 3,4 vegades més endescloure que a 25°C. En condicions hivernals, el mírid va completar el desenvolupamentpostembrionari en 62 dies alimentant-se només de larves de B. tabaci però amb unabaixa supervivència postembrionària (53%), la supervivència de les femelles als 60 diesva ser elevada i la seva fecunditat diària baixa. A 25 °C, D. tamaninii va matar més larvesde mosca blanca que adults. Els mascles i les nimfes del mírid van depredar menyslarves d'aleuròdid que les femelles. D. tamaninii no va mostrar preferència entre elsadults de T. vaporariorum i els de B. tabaci. En oferir-li larves de les dues mosquesblanques i, quan només es va considerar el nombre total de larves depredades, ni lesfemelles ni les nimfes del mírid van tenir preferència per cap de les dues espècies,mentre que els mascles van preferir les larves de T. vaporariorum. En canvi, quan es vaconsiderar l'ordre en què es van depredar les preses (índex de Rodgers) tant les nimfescom els mascles i les femelles del mírid van preferir les larves de T. vaporariorum a lesde B. tabaci. Els resultats obtinguts indiquen que D. tamaninii pot sobreviure i reproduirsea termofotoperíode 16:11°C i 9,5L:14,5F i, per tant, es pot descartar l'existència dediapausa de les femelles o dels ous en aquestes condicions ambientals. Aquestdepredador accepta bé alimentar-se de larves de T. vaporariorum i B. tabaci, fins i totquan estan barrejades, tot i tenir una certa preferència per les larves de T. vaporariorum. / El tomate es, a nivel mundial, una de las hortalizas más importantes, siendo el sudesteespañol una de las mayores zonas productoras. Parte de la producción fuera detemporada se obtiene en invernaderos en los que el control de plagas y enfermedadesdel cultivo se basa en frecuentes aplicaciones de pesticidas. El objetivo de esta tesis esestablecer las bases biológicas para el diseño de un programa de control integrado deplagas en cultivos de tomate de otoño-invierno bajo plástico.El seguimiento de las plagas y de su fauna útil asociada en 10 invernaderos de tomate deMurcia y Alicante en las campañas de otoño-invierno de 1991-1992 y 1992-1993, puso demanifiesto que las principales plagas del cultivo son los aleuródidos Trialeurodesvaporariorum y Bemisia tabaci. La abundancia relativa de estas especies fue variable enel curso del cultivo. B. tabaci fue la especie mayoritaria después del trasplante mientrasque T. vaporariorum lo fue al final del cultivo. En estas condiciones las introduccionesinoculativas de Encarsia formosa no controlaron las poblaciones de mosca blanca. Porotra parte, la fauna útil asociada a estas moscas blancas fue escasa tanto en el númerode especies identificadas (Eretmocerus mundus y Nesidiocoris tenuis) como en suabundancia. Las plagas secundarias más importantes fueron los minadores de hojaLiriomyza bryoniae y L trifolii (en algunos casos controlados por poblaciones autóctonasde Diglyphus sp.), el acaro Aculops lycopersici y el noctuido Helicoverpa armígera.Con objeto de definir una unidad de muestreo que permita evaluar poblacionesmezcladas de T. vaporariorum y B. tabaci se estudió la distribución vertical de estas dosespecies en tomatera. En un ensayo de semicampo realizado en primavera, los adultos ylos huevos de T. vaporariorum presentaron una estratificación muy acusada situándoseprincipalmente en las hojas más jóvenes, mientras que los adultos y los huevos deB. tabaci se situaron en hojas más maduras. A las densidades registradas durante elexperimento ninguna de las dos especies modificó su distribución vertical en la plantacomo consecuencia de hallarse mezclada con la otra especie. En el seguimientorealizado en tomate de otoño-invierno cultivado en dos invernaderos sin calefacción, loshuevos de T. vaporariorum se hallaron principalmente en el tercio superior de la planta ylos de B. tabaci en el tercio central. Las larvas de los últimos estadios y las pupas deambas especies se localizaron mayoritariamente en el tercio inferior de la tomatera. Paradefinir la mejor unidad de muestreo se ha estudiado, también, la posibilidad de contar loshuevos y las larvas de T. vaporariorum y de B. tabaçi en uno o dos círculos (0=1,15 cm) cortados al azar de cada foliólo, en vez de contarlos en el foliólo entero. Los resultadosindican que esta simplificación puede usarse en el caso de los huevos pero no en el delas larvas. Teniendo en cuenta el coste de recoger y procesar las muestras, paradensidades inferiores a 25 huevos por foliólo, lo menos trabajoso es realizar el recuentoen un círculo por foliólo de foliólos del tercio superior de la planta. Para densidadesmayores de 25 huevos por foliólo, y según de la proporción relativa de T. vaporariorum yB. tabaci, resulta menos laborioso hacer el conteo en un circulo por foliólo de foliólos deltercio central de la planta. La estimación de la densidad de larvas debe realizarse enfoliólos enteros tomados del tercio inferior de la tomatera y se reduce el tiempo demuestreo contando las larvas sin la ayuda del binocular.Para evaluar la posibilidad de utilizar el mírido depredador Dicyphus tamaninii para elcontrol biológico de T. vaporariorum y B. tabaci en tomate de otoño-invierno, se estudióalgunos parámetros de su biología en condiciones invernales, así como su preferenciafrente a estos aleuródidos. A termofotoperíodo 16:11°C y 9,5L: 14,50, las hembras deD. tamaninii criadas a 25°C y fotoperíodo 16L:80 y las criadas en condiciones de inviernopusieron huevos. Estos huevos tardan 3,4 veces más en eclosionar que a 25°C. Encondiciones invernales, el mírido completó su desarrollo postembrionario en 62 díasalimentándose únicamente de larvas de B. tabaci, aunque con una supervivenciapostembrionaria baja (53%), la supervivencia de las hembras a los 60 días fue elevada ysu fecundidad diaria baja. A 25 °C, D. tamaninii mató más larvas de mosca blanca queadultos. Los machos y las ninfas depredaron menos larvas de aleuródido que lashembras. El mírido no mostró preferencia entre los adultos de T. vaporariorum y los deB. tabaci. Al ofrecerle larvas de las dos moscas blancas y, cuando únicamente se tuvo encuenta el número total de larvas depredadas, ni las hembras ni las ninfas del míridotuvieron preferencia por ninguna de las dos especies mientras que los machos prefirieronlas larvas de T. vaporariorum. En cambio cuando se tuvo en cuenta el orden en que sedepredaron las presas (índice de Rodgers), las ninfas, los machos y las hembras delmírido prefirieron las larvas de T. vaporariorum a las de B. tabaci. Los resultadosobtenidos indican que D. tamaninii puede sobrevivir y reproducirse a termofotoperíodo16:11°C y 9,5L:14,50, por lo que puede descartarse la existencia de diapausa de lashembras o de los huevos en estas condiciones ambientales. Este depredador aceptabien alimentarse de larvas de T. vaporariorum y B. tabaci, incluso cuando se encuentranmezcladas, aunque tiene cierta preferencia por las larvas de T. vaporariorum.

L'objectif de ce travail est d'améliorer notre compréhension des mécanismes et d'évaluer les facteurs agro-écologiques impliqués dans la dynamique spatio-temporelle des populations naturelles de Sahlbergella singularis. Le calcul des tables de vie sur une population d'élevage a révélé que S. singularis est une espèce à croissance lente. Ceci expliquerait le fait que le ravageur est généralement présent à de faibles densités dans les plantations. L'étude des paramètres démographiques de la population d'élevage a montré que la fécondité est un paramètre-clé des fluctuations saisonnières des populations naturelles. Leur croissance serait liée à la présence de jeunes cabosses sur les cacaoyers fournissant aux femelles une ressource alimentaire favorable à la reproduction. L'étude de l'influence des facteurs agro-écologiques sur les densités de populations de S. singularis en plantation a révélé que les densités dépendent des conditions parcellaires de culture du cacaoyer. Parmi les pratiques culturales, les traitements insecticides, l'ombrage et le recours aux variétés hybrides sont des facteurs déterminants. En outre, les populations du ravageur sont fortement agrégées dans les zones des plantations bénéficiant d'un ensoleillement maximal. Enfin, l'ombrage fourni par les arbres forestiers s'est avéré plus homogène que l'ombrage d'arbres fruitiers et par conséquent moins propice au développement des poches à mirides. Les recommandations de lutte préconisées par la recherche agronomique sont rarement appliquées par les planteurs. Aussi, nos résultats ont-ils été discutés dans l'optique d'adapter ces recommandations au contexte de culture du cacaoyer qui prévaut actuellement au Cameroun

The biological control of the weedy complex Lantana camara (L.) (Verbenaceae) has been ongoing in South Africa for over 40 years. Despite this, the weed is still not under sufficient control and continues to invade new territories in the country. The biological control programme needs to be bolstered with releases of new and potentially damaging biological control agents. A promising biological control agent endemic to Central America, Falconia intermedia (Distant) (Hemiptera: Miridae), was imported into quarantine from Jamaica in 1994. This agent was released on sites in KwaZulu-Natal and Limpopo provinces of South Africa in 1999. Even though it initially established and damaged L. camara, populations died out at most of the release sites. As varietal difference and adverse climate have been cited as the reason for non-establishment and ineffective control in L. camara biocontrol programmes worldwide, this study attempts to investigate the role that these two factors play in this weed herbivore relationship. Laboratory no-choice trials were conducted to determine the varietal performance of F intermedia, among five Eastern Cape varieties of the weed from East London, Whitney Farm, Heather Glen Farm, Port Alfred and Lyndhurst Farm, and a variety from the Plant Protection Research Institute (PPRI), Pretoria. However, there were differences in performance as the adult mirids performed better on white-pink varieties from Whitney Farm and Heather Glen Farm. To test varietal preference in field conditions, field releases of F intermedia were also made at East London, Whitney Farm, Heather Glen Farm, Port Alfred and Lyndhurst Farm. Post release evaluations were conducted monthly for two years (2002 and 2003). The insect established at East London and Whitney Farm, both of which have white-pink varieties. Insect populations quickly died out at the Lyndhurst Farm and Port Alfred sites, which have dark pink varieties. It is suggested that field conditions may have resulted in poor plant quality and led indirectly to varietal preference, and to non-establishment at these two sites. With the onset of cooler weather, populations disappeared at Heather Glen Farm. This suggested that F. intermedia was suitable for release in more subtropical areas within South Africa where climatic conditions would be suitable throughout the year. The mirid performed well at Whitney Farm, resulting in significant reduction in plant growth parameters such as height and percentage cover, and increasing the cover of other flora growing beneath L. camara plants. Finally, ways to improve the efficacy of this agent are considered in an effort towards better control of L. camara in South Africa.

Interactions between insects have been shown to be important regulators of population abundances and dynamics as well as drivers of spatial segregation and distribution. These are important aspects of the ecology of insects used in biological control and may have implications for the overall success of a particular programme. In the history of biological control there has been a tendency to release a suite of agents against a weed, which in some cases has increased the level of success, while in others little change has been observed. In most of these cases the implications of increasing the level of complexity of the system is not taken into account and there is little research on the effect of releasing another agent into the system. A brief meta-analysis was done on all the biological control programmes initiated in South Africa. Emphasis was placed on multi-species releases and the effects that overlapping niches were having on the number of agents responsible for the success of a programme. Where overlapping niches were present among agents released the number of agents responsible for success was lower than the number established. Water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach in South Africa has more arthropod agents released against it than anywhere else in the world, yet control has been variable. If the biology and host utilisation of all the agents against water hyacinth is considered, a definite overlap of niches is apparent in at least one life stage of all the agents. Therefore the probability of these insects interacting is high, especially if they are established at the same site in the field. Three of the insects released in South Africa have been selected to investigate possible interactions. They are Neochetina eichhorniae Warner, Neochetina bruchi Hustache and Eccritotarsus catarinensis (Carvalho). Y-tube olfactometer bioassays were used to measure responses of these insects to water hyacinth with prior feeding damage by either conspecifics or heterospecifics. This was done to determine whether olfactory cues played a role in host acceptability and avoidance of conspecifics or heterospecifics. The insects were given a choice between damaged and undamaged plants in various combinations. There was a significant preference for the undamaged plants when given a choice between undamaged and damaged plants. However when the insects were given a choice between two damaged plants there was no discrimination between heterospecific or conspecific damaged plants. This may indicate that there is little or no ecological cost for the insect to share a plant with other insects utilising a similar resource. Insect – insect interactions were investigated in a common garden plot experiment to measure the impact that pairwise combinations of the insect may have on their performance. There was a significant interaction between the mirid E. catarinensis and the weevil N. eichhorniae, with the weevil not performing as well when in combination with the mirid than when alone. Interestingly there was a negative interaction between the two weevil species when in combination, however it was impossible to determine which species was being affected if not both. None of the insects performed significantly better when in combination with another insect. A field study on Wriggleswade Dam in the Eastern Cape, South Africa was initiated to determine whether the relationship between the mirid E. catarinensis and the weevil N. eichhorniae could be determined in the field. The performance of the insects at the different sites in the field suggests that there was an interaction between the agents. This interaction did not limit the establishment of either insect at a site, but it did result in one insect dominating at a site over another. Interactions between the three species of insect tested in this thesis suggest that there are both negative and neutral relationships between them. A basic comparison between the insect performances from 15 sites around the country was done to determine if the spatial segregation observed in the field could be extrapolated to the natural South African situation. The interaction observed between N. eichhorniae and E. catarinensis does seem to extrapolate to the general South African situation where there is definite spatial segregation on a landscape level. The co–occurrence of the two Neochetina weevils at these sites suggests that the negative relationship observed between them in the common garden experiment does not extrapolate to the field. The results from this thesis suggest that the interactions between the agents tested would not limit establishment or have significant ramifications on performance. However, there may be spatial and temporal segregation of these species in the introduced range.

Lantana camara L. (Verbenaceae) remains a highly invasive and ecologically damaging weed in South Africa, despite some 50 years of biological control efforts. Lack of success has been ascribed to varietal differences, climate and predation of agents but these have not been tested. In this study, the effects of ant predation were tested on populations of three biological control agents for L. camara. Colonies of two species, Crematogaster sp. 1 and 2 were investigated. Crematogaster sp. 1 colonies were offered no choice between immature stages of the agents Hypena laceratalis Walker (Lepidoptera: Noctuidae), Falconia intermedia Distant (Hemiptera: Miridae) or Teleonemia scrupulosa Stål (Hemiptera: Tingidae) on lantana shoots. Density-dependent predation on F. intermedia and T. scrupulosa nymphs on lantana shoots was tested using Crematogaster sp. 2 colonies. In choice experiments Crematogaster sp. 2 colonies were offered F. intermedia or T. scrupulosa nymphs on potted lantana plants. Preliminary food trials confirmed that colonies foraged for protein, thereby validating results of no-choice experiments. Crematogaster sp.1 foragers removed 50% of F. intermedia nymphs, followed by 45% of H. laceratalis larvae and only 9% of T. scrupulosa nymphs. Foragers recruited most actively to H. laceratalis larvae and significantly more H. laceratalis biomass was removed than either F. intermedia or T. scrupulosa. A trade-off existed in prey size selection because larger larvae provided considerably more biomass but required forager cooperation and a longer time to subdue than did smaller prey. This increases both forager energy expense and mortality risk by other predators. This study showed that all Crematogaster sp. 1 colonies removed small (≤10mm) H. laceratalis larvae more frequently than larvae larger than 10mm. Thus, of these biological control agents, predators probably prefer small H. laceratalis larvae. Significantly more F. intermedia than T. scrupulosa nymphs were removed by Crematogaster sp. 1, while Crematogaster sp. 2 colonies removed comparable numbers of both agent species. Falconia intermedia nymphs' fast movement triggered a predatory response by these ant species. In contrast, the relatively immobile behaviour of T. scrupulosa nymphs was identified as a highly effective predator avoidance strategy. Since T. scrupulosa nymphs are unable to escape predators by moving, they appear to depend on the presence of alternative prey attracting predator attention. At high agent and/or forager density, T. scrupulosa nymphs attempted escape, but foragers identified them as prey once they moved and caught them. Predation on F. intermedia was also density dependent in that at high nymph and/or forager densities, escape routes were congested and nymphs were more easily caught. Survival of F. intermedia and T. scrupulosa nymphs in particular was low on ant-accessed shrubs in choice experiments and high on ant-excluded shrubs. It is likely that ants significantly depress F. intermedia populations in the field since besides predation, ant foragers probably interrupt F. intermedia feeding and ovipositioning. The combination of parasitism and predation on early instar larvae may explain why H. laceratalis occurs across lantana's range in South Africa but populations remain low. It is unlikely that T. scrupulosa nymphs are habitually preyed on by ant species unless they attract attention by being mobile. Although biological control of L. camara is influenced by climate and physiological defence mechanisms, this study has shown that predation by two ant species severely impacts leaf-feeding agents for L. camara. Thus, it is recommended that future selection of additional agents to control lantana should exclude leaf-feeding .

Die paläarktische omnivore Weichwanze Dicyphus errans Wolff (Heteroptera, Miridae, Bryocorinae) zeichnet sich durch ein ausgesprochen breites Spektrum an besetzten Wirtspflanzen und konsumierten Beutetieren aus. Über 150 von D. errans akzeptierte Pflanzenarten sind erstmalig belegt worden. Der erfolgreiche Verzehr von 15 Beute-tierarten wurde quantitativ nachgewiesen. Eine weitere Besonderheit der Wanze besteht in der Präferenz für glandulär behaarte Pflanzen. Die Weichwanze besetzt somit von vielen anderen Insekten gemiedene Nischen. Untersuchungen im Botanischen Garten der Technischen Universität Dresden (2000 bis 2002) ließen auf eine bemerkenswerte räuberische Aktivität und Anpassungsfähigkeit an unterschiedliche Habitate, Beutetiere und Klimabedingungen schließen. Die fortführenden Studien im Rahmen der vorliegenden Dissertation (2002 bis 2005) erbrachten umfassende Erkenntnisse über die Art D. errans im Hinblick auf deren Morphologie, Vermehrung und Haltung, Bionomie und Ökologie (Fekundität und Ontogenese in Abhängigkeit von ausgewählten Einflussfaktoren, Dormanz), Aufenthalt und Fortbewegung (räumliche Orientierung und strukturanalytische Studien zu den Interaktionen zwischen Wanze und Pflanzenoberflächen), den Nahrungserwerb (Verzehrleistung und Omnivorie) sowie Videodokumentationen der Lebensweise und des Verhaltens. Der Generalist und Opportunist D. errans integriert sich als Pflanzensaftsauger regulierendes Kompartiment neben echten Räubern und Parasitoiden in Biozönosen. Als omnivores Insekt übernimmt die Wanze eine intermediäre und supplementäre Position in Nahrungsnetzen. Die Lebensweise dieser Weichwanzenart erscheint sehr komplex. Die enge Assoziation mit Pflanzen tritt stark in den Vordergrund. Sie ist in jeglichen Betrachtungen von D. errans unbedingt zu berücksichtigen und bietet außerdem als ein Modellsystem ein spannendes Forschungsfeld im Hinblick auf die Adaptation partiell räuberisch lebender Insekten an behaarte Pflanzen. / The omnivorous mirid bug Dicyphus errans Wolff (Heteroptera, Miridae, Bryocorinae) lives on a wide range of host plants and feeds on various preys. Over 150 plant species accepted by the mirid bug have been identified. It was experimentally shown that 15 prey species are efficiently consumed. Another characteristical features of D. errans is that it preferes hairy plants. Thus, the mirid bug occupies unique niches avoided by many other insects. Investigations, carried out at the Botanical Garden of the Technical University of Dresden (2000-2002) gave evidence for a remarkable predatory activity and ability to adaptation to different habitats, preys and climate conditions. The studies presented in the dissertation (2002-2005) gave the comprehensive knowledge about the species D. errans, especially its morphology, rearing, bionomy and ecology (fecundity and ontogenesis depending on selected factors, dormancy), habitat preference and locomotion (spatial orientation and structural-analytical studies of the interactions between the bug and plant surfaces), foraging and food ingestion (predatory capacity and omnivory). In addition, video documentation of the modus vivendi and the behavior was performed. The generalist and opportunist D. errans lives together with predators and parasitoids and takes part in a biological control of phytophagous insects in biocenoses. The life history of this bug species appeared to be very complex. The close association to plants has to be considered. Dicyphus errans offers a model system for further research on omnivorous predatory insects connected with hairy plants.

Die paläarktische omnivore Weichwanze Dicyphus errans Wolff (Heteroptera, Miridae, Bryocorinae) zeichnet sich durch ein ausgesprochen breites Spektrum an besetzten Wirtspflanzen und konsumierten Beutetieren aus. Über 150 von D. errans akzeptierte Pflanzenarten sind erstmalig belegt worden. Der erfolgreiche Verzehr von 15 Beute-tierarten wurde quantitativ nachgewiesen. Eine weitere Besonderheit der Wanze besteht in der Präferenz für glandulär behaarte Pflanzen. Die Weichwanze besetzt somit von vielen anderen Insekten gemiedene Nischen. Untersuchungen im Botanischen Garten der Technischen Universität Dresden (2000 bis 2002) ließen auf eine bemerkenswerte räuberische Aktivität und Anpassungsfähigkeit an unterschiedliche Habitate, Beutetiere und Klimabedingungen schließen. Die fortführenden Studien im Rahmen der vorliegenden Dissertation (2002 bis 2005) erbrachten umfassende Erkenntnisse über die Art D. errans im Hinblick auf deren Morphologie, Vermehrung und Haltung, Bionomie und Ökologie (Fekundität und Ontogenese in Abhängigkeit von ausgewählten Einflussfaktoren, Dormanz), Aufenthalt und Fortbewegung (räumliche Orientierung und strukturanalytische Studien zu den Interaktionen zwischen Wanze und Pflanzenoberflächen), den Nahrungserwerb (Verzehrleistung und Omnivorie) sowie Videodokumentationen der Lebensweise und des Verhaltens. Der Generalist und Opportunist D. errans integriert sich als Pflanzensaftsauger regulierendes Kompartiment neben echten Räubern und Parasitoiden in Biozönosen. Als omnivores Insekt übernimmt die Wanze eine intermediäre und supplementäre Position in Nahrungsnetzen. Die Lebensweise dieser Weichwanzenart erscheint sehr komplex. Die enge Assoziation mit Pflanzen tritt stark in den Vordergrund. Sie ist in jeglichen Betrachtungen von D. errans unbedingt zu berücksichtigen und bietet außerdem als ein Modellsystem ein spannendes Forschungsfeld im Hinblick auf die Adaptation partiell räuberisch lebender Insekten an behaarte Pflanzen. / The omnivorous mirid bug Dicyphus errans Wolff (Heteroptera, Miridae, Bryocorinae) lives on a wide range of host plants and feeds on various preys. Over 150 plant species accepted by the mirid bug have been identified. It was experimentally shown that 15 prey species are efficiently consumed. Another characteristical features of D. errans is that it preferes hairy plants. Thus, the mirid bug occupies unique niches avoided by many other insects. Investigations, carried out at the Botanical Garden of the Technical University of Dresden (2000-2002) gave evidence for a remarkable predatory activity and ability to adaptation to different habitats, preys and climate conditions. The studies presented in the dissertation (2002-2005) gave the comprehensive knowledge about the species D. errans, especially its morphology, rearing, bionomy and ecology (fecundity and ontogenesis depending on selected factors, dormancy), habitat preference and locomotion (spatial orientation and structural-analytical studies of the interactions between the bug and plant surfaces), foraging and food ingestion (predatory capacity and omnivory). In addition, video documentation of the modus vivendi and the behavior was performed. The generalist and opportunist D. errans lives together with predators and parasitoids and takes part in a biological control of phytophagous insects in biocenoses. The life history of this bug species appeared to be very complex. The close association to plants has to be considered. Dicyphus errans offers a model system for further research on omnivorous predatory insects connected with hairy plants.

A highly variable invasive shrub, Lantana camara L. (Verbenaceae), has been notoriously difficult to control thus far despite a well established biological control programme in South Africa. A promising leaf-feeding biological control agent, Falconia intermedia (Distant) (Hemiptera: Miridae), released to control this invasive plant eventually crashed at three out of five sites in the Eastern Cape Province. In the Mpumalanga Province, after initially colonising and building up high numbers on the L. camara stands the agent populations crashed. Several reasons for these population crashes have been suggested, but induced plant defences have not been investigated. Although plants face the challenge of herbivory by various organisms while remaining immobile, some plants may possess the ability to induce physical and/or chemical defensive responses following feeding and thus prevent further plant tissue damage and loss. Laboratory trials were conducted to determine the existence, nature and effect of physical and chemical feeding-induced responses of L. camara on the performance of the leaf-feeding biological control agent, F. intermedia. Lantana camara plants used in the study were obtained from five localities in the Eastern Cape Province, South Africa, while the insect culture was established from field populations. Plants from all varieties on which F. intermedia was released significantly increased the toughness of their leaves compared to control treatment plants. In addition, plants from three localities: Lyndhurst Farm, East London and Port Alfred, significantly increased trichome density after prolonged feeding by F. intermedia. On the three varieties showing increases in these two factors (i.e. leaf toughness and trichome density), oviposition, survival and feeding damage by the mirid agent was significantly lower on previously damaged plants. A significant negative correlation between trichome density and population numbers was found (R²= 0.52, p < 0.0003), suggesting that an increase in trichome density strongly contributes to a reduction in F. intermedia's growth. The growth and reproduction of the resistant plants was not significantly impacted by F. intermedia feeding. The defensive responses were found to be plant systemic and rapidly induced as they were elicited and expressed throughout the plant in both damaged and undamaged leaves within five weeks after insect release. Leaf toughness and trichome density were not significantly increased after feeding on plants from Whitney Farm and Heather Glen Farm. On the contrary, mirid individuals performed significantly better on plants from Whitney Farm and Heather Glen Farm than on plants of other varieties, indicating their susceptibility and suitability to the agent and the lack of induced resistance against the agent. Plants from all localities besides East London showed some level of tolerance and overcompensated for feeding damage by increasing plant growth and reproductive factors on plants fed upon. This was however only significant in two variables of the more susceptible localities, Whitney Farm and Heather Glen Farm. This increase in plant fitness did however indicate an induced defence response by these plants to feeding, a response designed to lessen the effects of agent feeding. Headspace volatile analysis was used to investigate any volatile chemical responses by L. camara due to F. intermedia feeding at two of the five localities chosen: East London and Whitney Farm. There was no significant difference in headspace volatiles emitted by leaves of plants from the East London insect infested and control treatment plants. On the Whitney Farm damaged plants however there was a 2.5 fold increase in the emission intensity of one of the three main compounds, later identified as Beta-caryophyllene. Three major chemical constituents which were found to be common to leaf volatiles of the two varieties were identified through gas chromatography-mass spectrometry (GC-MS) from the damaged and undamaged leaves of these two varieties. The methods used in collecting leaf volatiles were shown to be significant in the strength of chromatogram peaks. Using general authentication methods and purified standards, one of these was identified as the sesquiterpene, Beta-caryophyllene (C₁₅H₂₄). This compound is one of the major constituents found in isolations of L. camara varieties worldwide. This is the first such work done on a variety of L. camara in South Africa, and hopefully the beginning of more in-depth studies of the volatile organic chemicals from the numerous naturalised varieties of L. camara. It is suggested that the sum of these responses may play a role bigger than is currently understood in this plant-insect relationship. It is also argued that feeding induced plant defences may play an important role in attempts to control alien plants using insect agents.