Made available in DSpace on 2015-03-26T13:30:23Z (GMT). No. of bitstreams: 1 texto completo.pdf: 4132587 bytes, checksum: 53555e9cb478a99bc00044828810a751 (MD5) Previous issue date: 2008-09-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Chrysomelidae is one of the most important families in the Coleoptera order. Currently, it is estimated that from 35,000 to 50,000 chrysomelid species are known. They are known as leaf beetles which may be important forest regulation factors. The aim of this research was to identify Chrysomelidae taxa at the Estação de Pesquisa, Treinamento e Educação Ambiental Mata do Paraiso (EPTEAMP) in Viçosa, Minas Gerais State, Brazil, and to study relationships between temperature, relative humidity and rainfall on the species richness and leaf beetles number, and to identify population dynamics related to the rainy and dry periods. A traditional light trap was weekly used for insects collecting during January 1981 to November 2007. All 610 collected chrysomelid beetles were used for taxa determinations. They are represented by 113 species, 62 genus, seven tribes and three subfamilies. Thirty-four genus and thirty-six species are new records for Minas Gerais State; thirty-six genus and forty-two species are new records for Viçosa Region. Species number was higher than other studies carried out for the same subfamilies. EPTEAMP is a Semi-deciduous Seasonal Forest fragment of the Atlantic Rain Forest, then it deserves attention because these news records increase information about the geographic distribution of registered taxa. Relative humidity did not affect species number neither chrysomelid adults, but rain amount and temperature level affected the population dynamics. Outbreaks of species or beetles were found in the rainy periods, but not in dry periods. We concluded that weather, rain and temperature affect species and leaf beetles number in the EPTEAMP; rainy and dry periods affected the population dynamics, whereas the largest percentage of species was found in the rainy period. / A família Chrysomelidae é uma das três mais importantes na ordem Coleoptera. Estima-se que sejam conhecidas, atualmente, entre 35.000 e 50.000 espécies nesta família. As variações na dinâmica populacional destes insetos podem estar associadas com a presença das chuvas. Os objetivos deste trabalho foram determinar os taxa de Chrysomelidae ocorrentes na Estação de Pesquisa, Treinamento e Educação Ambiental Mata do Paraíso (EPTEAMP), em Viçosa, Minas Gerais, determinar a relação da temperatura, umidade relativa e precipitação pluviométrica com a quantidade de espécies e de indivíduos adultos destes besouros e, ainda, determinar a variação destas populações em função das estações climáticas chuvosa e seca. Para as coletas dos crisomelídeos, foi utilizada armadilha luminosa, semanalmente, no período de janeiro 1981 a novembro de 2007. Para a determinação dos taxa, foram utilizados todos os 610 besouros coletados durante todo o período de coleta, obtendo-se 113 espécies, 62 gêneros, sete tribos e três subfamílias. Destes, 34 gêneros e 36 espécies são registros novos para o Estado de Minas Gerais; 36 gêneros e 42 espécies são registros novos para a Região de Viçosa, MG. Em relação à quantidade de espécies, levando-se em consideração somente as três subfamílias registradas neste estudo, a quantidade de espécies coletadas foi superior aos relatos de ocorrência realizados até o momento. Neste sentido, a EPTEAMP merece destaque, pois com estes novos registros, amplia-se as informações sobre a distribuição geográfica destes besouros. As variáveis climáticas temperatura e umidade relativa não afetaram significativamente as quantidades de espécies e nem a de indivíduos adultos dos crisomelídeos, já a variável precipitação pluviométrica afetou positiva e significativamente as populações destes besouros; na medida em que ocorreu aumento na precipitação pluviométrica, ocorreram simultaneamente aumentos nos valores das quantidades de espécies e de indivíduos adultos dos crisomelídeos. Pode-se concluir que a precipitação pluviométrica afeta a quantidade de espécies e a quantidade de indivíduos em Chrysomelidae num ecossistema como o da EPTEAMP. A estação chuvosa e a estação seca afetaram significativamente as populações dos crisomelídeos, onde o maior percentual de espécies e o de adultos foi encontrado no período da estação chuvosa. Os picos populacionais das quantidades de espécies e de indivíduos foram obtidos no período chuvoso e não no período de seca. Assim sendo, pode-se concluir que a variação da quantidade de espécies e de indivíduos adultos de Chrysomelidae é maior na estação chuvosa, do que na estação seca, em Viçosa-MG, e que esta é uma informação pioneira para esta família de coleópteros, nesta região.

The tobacco (Nicotiana tabacum L.) is a crop of major importance to Rio Grande do Sul and Brazil, but there are few studies on biodiversity associated with cultivation. Therefore, the aim of this study was to survey the families of Coleoptera associated with organic cultivation of tobacco, analyzing richness and abundance, as well as the temporal and spatial distribution of these insects. Furthermore, it also aims to perform a comparative analysis between organic and conventional cultivation of tobacco. The study was conducted on a crop with organic management in harvest 2009/2010 and 2010/2011, in Santa Cruz do Sul, RS. In the 2009/2010 harvest was also assessed a crop managed conventionally, for comparative analysis. In organic cultivation, three sampling lines were defined in order "inside-out" of crop, corresponding to: (1) line whose edge shows the adjacent vegetation abundant, mainly composed of trees and shrubs of medium and large; (2) line whose adjacent vegetation consisted of native shrub and tree species with size smaller; and (3) line with the adjacent vegetation composed of forage plants. On the other hand, in conventional cultivation, a line sample single was delimited, towards out within the crop, for comparison purposes with the line "2" of organic crop. In each line were determined three sampling points ("outside, border and inside"); and a single point within the sampling, called "middle" point. At sampling points were installed four pit-fall traps and one Malaise. In organic cultivation, the samplings were conducted, weekly, from November 20th, 2009 to March 19th, 2010 and from November 3th, 2010 to January 21th, 2011. In conventional cultivation, was from November 23th, to December 28th, 2009. In organic cultivation, were collected 49.269 coleopterans, distributed into two suborders, 13 superfamilies and 32 families. Six families accounted for about 90% of the total collected, namely: Staphylinidae (37.28%), Chrysomelidae (33.40%), Nitidulidae (7.50%), Curculionidae (5.25%), Carabidae (3.10%) and Elateridae (3.09%). The temporal distribution of Coleopterans is related, primarily, to the cycle of culture, and a reduction in the number of insects collected occurs due the subsequent harvests of tobacco leaves. On points "inside" and "middle" and on sampling lines "1" and "2", the community of coleopterans was numerically larger. The chrysomelids, being phytophagous insects, were distributed in places where there was greater food availability. However, the landscape composition of vegetation adjacent to cultivation was instrumental in the spatial distribution of predator insects belonging to Staphylinidae, considering that the highest abundance was observed in areas with greater plant diversity. The management adopted in conventional cultivation had an impact on the community of Coleoptera, especially when considering the decrease in abundance of the insects of the families Chrysomelidae and Staphylinidae. / O tabaco (Nicotiana tabacum L.) é uma cultura de reconhecida importância para o Rio Grande do Sul e para o Brasil, porém existem poucos estudos a respeito da biodiversidade associada ao cultivo. Portanto, o objetivo do presente estudo foi realizar um levantamento das famílias de Coleoptera associadas a cultivo orgânico de tabaco, analisando a riqueza e a abundância, assim como a distribuição temporal e espacial desses insetos. Ainda, realizar uma análise comparativa entre cultivos orgânico e convencional de tabaco. O estudo foi conduzido em uma lavoura com manejo orgânico, nas safras 2009/2010 e 2010/2011, no município de Santa Cruz do Sul, RS. Na safra 2009/2010 foi avaliada, também, uma lavoura manejada convencionalmente, para análise comparativa. No cultivo orgânico, foram definidas três linhas de amostragem, no sentido fora-dentro da lavoura, correspondendo a: (1) linha cuja borda apresenta a vegetação adjacente abundante, composta principalmente por árvores e arbustos de médio e grande porte; (2) linha cuja vegetação adjacente foi constituída por espécies arbustivas e arbóreas nativas de menor porte; e (3) linha com a vegetação adjacente composta por plantas forrageiras. Já em cultivo convencional, foi delimitada uma única linha amostral, no sentido fora-dentro da lavoura, para fins de comparação com a linha 2 do cultivo orgânico. Em cada linha foram determinados três pontos de coleta ( fora, borda e dentro ); e um ponto único no interior da lavoura, denominado ponto meio . Nos pontos de coleta, foram instaladas quatro armadilhas tipo pit-fall e uma Malaise. No cultivo orgânico, as coletas foram realizadas, semanalmente, de 20 de novembro de 2009 a 19 de março de 2010; e de 3 de novembro de 2010 a 21 de janeiro de 2011. Já no cultivo convencional foi de 23 de novembro a 28 de dezembro de 2009. No cultivo orgânico, foram coletados 49.269 coleópteros, distribuídos em duas subordens, 13 superfamílias e 32 famílias. Seis famílias corresponderam a cerca de 90% do total coletado, sendo elas: Staphylinidae (37,28%), Chrysomelidae (33,40%), Nitidulidae (7,50%), Curculionidae (5,25%), Carabidae (3,10%) e Elateridae (3,09%). A distribuição temporal dos coleópteros está relacionada, sobretudo, ao ciclo da cultura em campo, sendo que ocorre uma redução no número de insetos coletados devido às colheitas sucessivas das folhas do tabaco. Nos pontos dentro e meio e nas linhas 1 e 2 de amostragem a comunidade de coleópteros foi numericamente maior. Os crisomelídeos, por serem insetos fitófagos, distribuíram-se em locais onde havia maior disponibilidade de alimento. Entretanto, a composição paisagística da vegetação adjacente à lavoura foi determinante na distribuição espacial dos insetos predadores pertencentes à Staphylinidae, tendo em vista que a maior abundância foi verificada nas áreas com maior diversidade vegetal. O manejo adotado em cultivo convencional teve impacto sobre a comunidade de Coleoptera, principalmente, ao se considerar a diminuição da abundância dos insetos das famílias Chrysomelidae e Staphylinidae.

Made available in DSpace on 2014-07-29T12:05:37Z (GMT). No. of bitstreams: 1 Tese Mayra Pimenta.pdf: 1174963 bytes, checksum: 7ad5f60f55916118d1a33e942aa966e9 (MD5) Previous issue date: 2011-03-18 / Knowledge of the composition of natural communities and their responses to anthropogenic alterations is essential for determining the conservation status of a given system and prioritizing management actions. Anthropogenic impacts could cause a reduction in biodiversity not only due to habitat loss, but also due the loss of habitat heterogeneity across given landscape, especially in systems characterized by a mosaic of different elements (e.g. the Cerrado vegetation in central Brazil). Here we evaluate leaf beetle Coleoptera/Chrysomelidae) as bioindicators in a system whith varying intensities of human impacts and different phyto-physionomies (from open field to forests). We collected 1117 leaf beetle belonging to 245 species, of which 12 species and 5 genus were considered possible bioindicators based on IndVal measure. Higher species richness was observed in forests and regenerating fields, and habitats with lower species richness included pastures, mines and veredas. Only the Eucalyptus areas had a high abundance of Chrysomelidae, followed by forests and the other habitats, which were not significantly different from each other. Natural fields, regenerating fields, natural cerrados and forest had higher values of β-diversity. In general, the proportion of Chrysomelidae over total Coleoptera and over herbivorous Coleoptera were not able to distinguished among the habitats. The large number of rare leaf beetle species, the high proportion of restricted species and the high β-diversity of the natural areas made it difficult to utilize individual of species as a bioindicator. The use of the genus Chrysomelidae as a biondicator of habitat quality, was considered more effective than using individual species. Bioindicator systems that include not only species richness and abundance but also assemblage composition are needed to allow for a better understanding of Chrysomelidae response to environmental disturbance. OBS: Summary of chapter 1. Thesis with three chapters. / O conhecimento da composição das comunidades naturais e de suas respostas as alterações antropogênicas é essencial para determinar o estado de conservação de um determinado sistema e priorizar ações de manejo. Impactos antropogênicos poderiam causar uma redução da biodiversidade, não só devido à perda de habitat, mas também devido à perda de heterogeneidade de habitats em determinada paisagem, especialmente em sistemas caracterizados por um mosaico de diferentes elementos (por exemplo, a vegetação de Cerrado no Brasil Central). Aqui nós avaliamos crisomelídeos (Coleoptera / Chrysomelidae) como bioindicadores em um sistema com diferentes intensidades de impactos humanos e diferentes fitofisionomias (de campo aberto às áreas florestais). Foram coletados 1117 crisomelídeos, pertencentes a 245 espécies, das quais 12 espécies e 5 gêneros foram considerados bioindicadores possíveis, baseada na métrica de IndVal. Uma maior riqueza de espécies foi observada em florestas e campos de regeneração, e os habitats com menor riqueza de espécies foram pastagens, minas e veredas. Áreas de eucalipto apresentaram uma grande abundância de Chrysomelidae, seguido por matas e outros tipos habitats, que não foram significativamente diferentes entre si. Campos naturais, campos em regeneração, cerrados e matas apresentaram maiores valores de diversidade beta. Em geral, a proporção de Chrysomelidae sobre o total de coleópteros e de coleópteros herbívoros não foram capazes de apontar variações entre os tipos habitats. O grande número de espécies raras de crisomelídeos, a alta proporção de espécies de distribuição restrita e os altos valores de diversidade beta das áreas naturais dificultam a utilização de espécies como bioindicadores. O uso do gênero de Chrysomelidae como biondicador da qualidade do habitat, foi considerado mais eficaz do que a utilização de espécies individuais. Sistemas biondicadores, que incluam não apenas a riqueza de espécies e abundância, mas também a composição das assembléias, são necessários para permitir um melhor entendimento da resposta Chrysomelidae às perturbações ambientais. OBS: Resumo do capítulo 1. Tese com 3 capítulos

The interactions between plants and their insect herbivores are one of the main generators of biological diversity. A fundamental process generating this outstanding diversity is diet expansion to novel host plants. During the last four decades scientists accumulated evidence showing that co-adaptation between plants and herbivores is a major process assembling plant-herbivore interactions. However, rescent research suggests that adaptation is not always a prerequisite to generate novel plant-herbivore interactions. Novel associations between plants and insect herbivores may be assembled by ecological fitting - an ecological process whereby herbivores colonize novel host plants as a result of the suites of preadapted traits that they carry at the time of colonization. A widespread assumption concerning the architecture of insect herbivore genotypes is the "Jack of all trades master of none" principle. This principle proposes that there is a trade-off in genotype performances between host plants. The main prediction of this principle is that genotype performance will be negatively correlated among hosts. Genotypes displaying high performance on a given host will perform poorly on other hosts. This constraint of adaptation to multiple host plants implies that diet specialization will be selected over generalization. Contrary to these theoretical expectations, in most cases, genotypes that perform well in one host will also perform well in other host plants. Positive correlations in cross-host performance represent ecological and evolutionary dynamics opposite to the "Jack of all trades" principle. In this scenario genotypes with high performance on one host plant also have high performance on other plants, promoting generalization. The predictions of the current theory on the assemblage of novel plant-herbivore interactions focus on the fact that most insect herbivores are specialists. However, to fully understand the processes underlying the assembly of novel plant-insect interactions, it is necessary to study diet expansions in both specialist and generalist insect herbivores. This dissertation was performed at La Selva Biological Station, a tropical rain forest in Costa Rica, Central America. We studied a group of neotropical herbivores, the "rolled-leaf beetles" (Cephaloleia, Chrysomelidae: Cassidinae) and their host plants, neotropical plants in the order Zingiberales. Cephaloleia beetles have evolved with neotropical Zingiberales for the last 40-60 MY. Four paleotropical and one South American members of the Zingiberales have been introduced to La Selva during the last decade. After these introductions, currently seven Cephaloleia beetles are expanding their diets to exotic Zingiberales. These incipient diet expansions represent an opportunity to understand: 1) the relative roles of adaptation vs ecological fitting on the demography and colonization success of novel hosts in generalist and specialist herbivores and 2) whether genotypic performance across original and novel hosts are negatively correlated, as predicted by the "Jack of all trades" principle, or genotype performances across original and novel hosts are positively correlated. For most of the experiments included in this dissertation, I focused on the performance of larvae and adults of two generalist (Cephaloleia belti, C. dilaticollis) and two specialist beetles (Cephaloleia dorsalis, C. placida) reared in the laboratory on native or exotic Zingiberales. Generalist and specialist species display similar responses when changing their diets to novel hosts. Larvae preferred and performed better in the original than in the novel hosts. Adults usually displayed the opposite pattern, i.e. higher preference for and longevity on the exotic than on the novel hosts. In most novel interactions between Cephaloleia beetles and exotic Zingiberales, larval performance required adaptation, but adult performance was pre-adapted to the novel hosts. Therefore, both adaptation and ecological fitting are playing a role during diet expansions to novel hosts. Vital rates estimated through experimental demography show that population growth is reduced on novel host plants for both generalist and specialist Cephaloleia. Although in some cases population growth on the novel hosts is negative, suggesting the potential outcome of extinction after colonization or source-sink dynamics, several beetle species displayed positive population growth in the novel host plants. Positive instantaneous population growth rates in novel hosts supports diet expansions without substantial initial evolutionary change through ecological fitting. In quantitative genetics experiments testing for cross-host genetic correlations in performance between the original and novel host plants, we did not find evidence for negative genetic correlations, as predicted by the "Jack of all trades" principle. Most genetic correlations in performance between original and novel hosts were either not significant or they were positive. These results represent very different ecological and evolutionary dynamics than those predicted by the "Jack of all trades" principle. In this case, genotypes with high performance on original hosts also displayed high performance on novel hosts, promoting generalization. In conclusion, interactions between Cephaloleia beetles and plants from the order Zingiberales are labile. In some cases diet expansions may occur without substantial evolutionary change. In addition the genetic architecture of genotypes promotes generalization during diet expansions to novel hosts.

Thesis (Ph. D.)--Mississippi State University. Department of Entomology and Plant Pathology. / Title from title screen. Includes bibliographical references.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2004. / Härtill 5 uppsatser.

Thesis (M. Sc. (Zoology and Entomology))--Rhodes University, 2006.

Lantana camara Linnaeus (Verbenaceae), commonly known as lantana, is a highly invasive weed in many parts of the world. In South Africa it is naturalized in several provinces where it invades pastures, riverbanks, mountain slopes and valleys and commercial and natural forests, forming dense, impenetrable thickets. Chemical and mechanical control methods are expensive, labour intensive and provide only temporary relief as cleared areas are rapidly reinfested by seedlings and coppice growth. A biological control programme was initiated in South Africa in the 1960s, but despite the establishment of 11 agent species, it was considered to have had limited success. Several factors are thought to restrict the impact of the biocontrol agents. Firstly, L. camara occurs in a range of climatic regions, some of which are unsuitable for the establishment of agent species of tropical and subtropical origin. Secondly, L. camara is the result of hybridization between several Lantana species, forming a complex of hybridized and hybridizing varieties in the field, which match none of the Lantana species in the region of origin. This causes partial insect-host incompatibility, displayed as varietal preference. Thirdly, parasitism appears to have significantly reduced the effectiveness of several natural enemies. In spite of all these constraints, biological control has reduced invasion by L. camara by 26%. However, the weed is still very damaging and additional natural enemies are required to reduce infestations further. A flea-beetle species, Alagoasa extrema Jacoby (Coleoptera: Chrysomelidae), was collected from several sites in the humid subtropical and tropical regions of Mexico, and imported into quarantine in South Africa and studied as a potential biocontrol agent for L. camara. Favourable biological characteristics of this beetle included long-lived adults, several overlapping generations per year, and high adult and larval feeding rates. Observations from the insect’s native range and studies in South Africa suggest that A. extrema would probably be more suited to the subtropical, rather than the temperate areas in South Africa. Laboratory impact studies indicated that feeding damage by A. extrema larvae, over a period spanning the larval stage (16 to 20 days), reduced the above-ground biomass of L. camara plants by up to 29%. Higher larval populations resulted in a higher reduction of biomass. Varietal preference and suitability studies indicated that A. extrema exhibits a degree of varietal preference under laboratory conditions, with one of the white pink L. camara varieties proving the most suitable host. This variety is one of the most damaging varieties in South Africa and is particularly widespread in Mpumalanga Province. Although A. extrema proved to be damaging to L. camara, laboratory host range trials showed it to be an oligophagous species, capable of feeding and developing on several non-target species, especially two native Lippia species (Verbenaceae). The host suitability of these species was marginally lower than that of L. camara and the potential risk to these indigenous species was deemed to be too high to warrant release. It was therefore recommended that A. extrema not be considered for release in South Africa.

Ce travail s’intègre dans le cadre général de l’étude de l’écologie chimique des insectes dont il aborde deux aspects distincts. Dans la première partie de cette thèse, nous avons étudié l’origine biogénétique des glycosides triterpéniques présents dans la sécrétion défensive de Platyphora kollari. A cet effet, nous avons développé des schémas de synthèse originaux pour préparer la [2,2,3-2H3]-amyrine [48] et l’acide [2,2,3-2H3]oléanolique [56]. Ces précurseurs marqués au deutérium ont ensuite été incorporés chez Platyphora kollari. Après incorporation, l’analyse des sécrétions par HPLC-ESIMS ont montré que cette espèce transforme efficacement l’acide oléanolique [34] en le glycoside triterpénique [27]. Par ailleurs, l’-amyrine [36] est beaucoup moins bien incorporée dans ce glycoside que la -amyrine [33]. Ces résultats, combinés à ce qui avaient déjà été établi précédemment, nous ont permis d’avancer le schéma de biosynthèse présenté ci-dessous : Dans la deuxième partie de ce travail, nous avons identifié la phéromone de piste qui est aussi la phéromone sexuelle mâle de Zootermopsis nevadensis et Zootermopsis angusticollis (Termopsidae, Termopsinae). Pour ce faire, nous avons mis au point la synthèse racémique du mélange syn-anti du 4,6-diméthyldodécanal [69] et du syn 4,6-diméthyldodécanal [111]. La comparaison des temps de rétention et des spectres de masse (GC-MS) du mélange des 4 stéréoisomères du 4,6-diméthyldodécanal [69] et des deux énantiomères du syn-4,6-diméthyldodécanal [111] avec ceux des sécrétions naturelles des Zootermopsis a montré que la phéromone de piste (et la phéromone sexuelle mâle) de ces termites est le dl, d ou l syn-4,6-diméthyldodécanal. Par ailleurs, afin d’identifier la nature de la phéromone de piste des termites Hodotermopsis sjoestedti et H. japonicus, nous avons effectué la synthèse racémique du 4-méthyldodécanal [70]. La comparaison de l’indice de rétention et du spectre de masse du 4-méthyldodécanal synthétisé [70] avec ceux de la sécrétion naturelle d’Hodotermopsis japonicus a montré que la phéromone naturelle est différente du 4-méthyldodécanal.

The aim of this thesis project was to elucidate patterns and processes associated with the biotic interactions in a natural plant–herbivore–parasitoid food web characterized by spatial and temporal heterogeneity with regard to species composition. The system examined is based on island populations of the perennial herb Meadowsweet (Filipendula ulmaria, Rosaceae), located in the Skeppsvik Archipelago. The area is subject to isostatic rebound, amounting to 0.85 cm per year; this makes it possible to calculate the age of the rising islands. Meadowsweet colonizes new islands when they are about 100 years old. Meadowsweet is consumed by two major herbivores in the study area: Galerucella tenella and Altica engstroemi (Coleoptera: Chrysomelidae). Both herbivores overwinter in the topsoil and successful colonization occurs when the islands reach a height that prevents the beetles from being removed or killed as a result of wave wash during the winter. I found that both herbivores significantly reduced individual plant fitness and population growth rate. A “cafeteria experiment” with Galerucella showed that this beetle discriminated between plants from different islands, avoiding plants from old islands which contained high concentrations of putative defence compounds, while readily accepting plants from younger islands which contained lower concentrations of these chemicals. Further, the plant species exhibited a trade-off between growth and production of the putative defence compounds. Taken together, these results were interpreted as providing evidence of herbivore-driven evolution of resistance in Meadowsweet. Further, laboratory studies suggested that Galerucella gradually includes a less preferred host plant (Rubus arcticus, Rosaceae) in its diet as Meadowsweet resistance increases. This implies that Galerucella drives its own host-breadth enlargement by selectively inducing a ‘rent rise’ in the original host, Meadowsweet. In a number of field studies I showed that the oligophagous parasitoid Asecodes mento (Hymenoptera: Eulophidae) has a strong positive effect on Meadowsweet seed set by removing large numbers of G. tenella larvae. This top-down effect is, however, altered by the presence of a close relative of G. tenella, namely G. calmariensis, which is monophagous on Purple loosestrife (Lythrum salicaria, Lythraceae). G. tenella experiences associational susceptibility when coexisting with G. calmariensis since the latter supports a higher and more fit pool of shared parasitoids and because Meadowsweet attracts a higher proportion of the shared parasitoid females than Purple loosestrife. This implies that G. tenella densities are very low in coexisting populations and that Meadowsweet experiences associational resistance and produces more seeds when co-occurring with Purple loosestrife. Thus, selection for increased resistance in Meadowsweet is likely to be relaxed in populations mixed with Purple loosestrife. I conclude that the evolution of plant resistance is likely to depend on the length of time and intensity of selection. When Meadowsweet colonizes new islands it experiences a period of enemy-free space; followed by a midlife and ageing with selection by herbivores. The intensity of this selection does, however, depend on the presence of additional plant and herbivore species.