Do food‐plant preferences of modern families of phytophagous insects and mites reflect past evolution with plants?

The evolutionary history of phytophagous insects and mites and of their food-plants is traced in the conservative preferences of modern-day insects for plants. Based on UK data in the Phytophagous Insects Data Bank, a correspondence analysis displays 182 insect families and 117 plant families in a bi-variate plot. The overall pattern suggests the expansion of diversity of insects and host plants from Gymnosperms to Dicots. Plots for phytophagous insect orders and major plant clades are described, with families provisionally ranked as evolutionarily basal, intermediate or advanced. There are blurred patterns of evolutionary advancement from basal insect families with more species on conifers and on ferns and Eurosid I trees. Intermediate families are commoner on Malpighiales and Fabales, and advanced insects more frequent on later evolved euasterids II (Asterales and Lamiales), Caryophyllales and Gramineae. Basal Hymenoptera have associations with conifers, basal Lepidoptera to Eurosid I trees, and Diptera are mainly advanced families on commelinids (grasses) and Asteraceae. Blurred traces of similar phylogenetic sequences are described for subfamilies within eight example insect families. Basal families and clades tend to have fewer species than derived advanced clades. Insect communities on plants should be seen in the light of this linked past evolutionary background.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 51–83.     

Diversity and abundance of insect herbivores foraging on seedlings in a rainforest in Guyana

1. Free-living insect herbivores foraging on 10 000 tagged seedlings representing five species of common rainforest trees were surveyed monthly for more than 1 year in an unlogged forest plot of 1 km² in Guyana. 2. Overall, 9056 insect specimens were collected. Most were sap-sucking insects, which represented at least 244 species belonging to 25 families. Leaf-chewing insects included at least 101 species belonging to 16 families. Herbivore densities were among the lowest densities reported in tropical rainforests to date: 2.4 individuals per square metre of foliage. 3. Insect host specificity was assessed by calculating Lloyd’s index of patchiness from distributional records and considering feeding records in captivity and in situ. Generalists represented 84 and 78% of sap-sucking species and individuals, and 75 and 42% of leaf-chewing species and individuals. In particular, several species of polyphagous xylem-feeding Cicadellinae were strikingly abundant on all hosts. 4. The high incidence of generalist insects suggests that the Janzen–Connell model, explaining rates of attack on seedlings as a density-dependent process resulting from contagion of specialist insects from parent trees, is unlikely to be valid in this study system. 5. Given the rarity of flushing events for the seedlings during the study period, the low insect densities, and the high proportion of generalists, the data also suggest that seedlings may represent a poor resource for free-living insect herbivores in rainforests.     

Ecological and taxonomic trends in macrolepidopteran host plant selection

Patterns of host plant use by larvae of macrolepidoptera feeding on trees and shrubs in Britain and Canada are examined. The incidence of polyphagous species varies among different lepidopteran taxa. Among largely monophagous taxa host plant switching has often occurred. The greater similarity of insect faunas on closely related plants is documented using cluster analysis. The Canadian data reveal that lepidopterans feeding on conifers are less specific in their host plant choice than species feeding on angiosperms. The numerical analyses also provide evidence of greater overlap in the insect faunas of plants belonging to the same ecological association. These results are discussed with particular reference to Lepidoptera-plant coevolution.     

Does mother know best? The preference–performance hypothesis and parent–offspring conflict in aboveground–belowground herbivore life cycles

1. A substantial amount of research on host‐plant selection by insect herbivores is focused around the preference–performance hypothesis (PPH). To date, the majority of studies have primarily considered insects with aboveground life cycles, overlooking insect herbivores that have both aboveground and belowground life stages, for which the PPH could be equally applicable. 2. This study investigated the factors influencing the performance of the root‐feeding vine weevil (Otiorhynchus sulcatus) larvae and whether this was linked to the oviposition behaviour of the maternal adult living aboveground. 3. Maternal insects feeding aboveground reduced root biomass by 34% and increased root carbon by 4%. Larvae feeding on plants subjected to aboveground herbivory had reduced mass. Irrespective of the presence of maternal herbivory, larval mass was positively correlated with root biomass. 4. Larval mass was also reduced by conspecific larvae, previously feeding on roots (19% reduction). However, the mechanism underpinning this effect remains unclear, as in contrast to maternal herbivory aboveground, prior larval feeding did not significantly affect root biomass or root carbon concentrations. 5. Maternal insects did not distinguish between plants infested with larvae and those that were free of larvae, in terms of their egg‐laying behaviour. Conversely, maternal insects tended to lay eggs on plants with smaller root systems, a behaviour that is likely to negatively affect offspring performance. 6. The PPH is not supported by our findings for the polyphagous vine weevil feeding on the host plant raspberry (Rubus idaeus), and in fact our results suggest that there is the potential for strong parent–offspring conflict in this system.     

Feeding patterns of monophagous,oligophagous, and polyphagous insect herbivores: The effect of resource abundance and plant chemistry

Summary Leaf tissue preferences of monophagous, oligophagous, and polyphagous insect herbivores were determined using young and mature leaf tissue abundances and herbivore feeding observations. Larvae of monophagous and oligophagous herbivores preferred young leaf tissues while, overall, larvae of polyphagous species preferred mature leaves of their various host plants. Even though a species is often polyphagous over its geographical range, larvae from local populations may be very specialized in their diet. When this occurs these specialized larvae prefer the more nutritious and perhaps more toxic young leaves of some of their host plants. Resource abundance and plant chemistry are discussed as major factors influencing herbivore feeding patterns.     

The interplay between toxin-releasing β-glucosidase and plant iridoid glycosides impairs larval development in a generalist caterpillar, Grammia incorrupta (Arctiidae)

Herbivores with polyphagous feeding habits must cope with a diet that varies in quality. One of the most important sources of this variation in host plant suitability is plant secondary chemistry. We examined how feeding on plants containing one such group of compounds, the iridoid glycosides, might affect the growth and enzymatic activity in a polyphagous caterpillar that feeds on over 80 plant species in 50 different families. Larvae of the polyphagous arctiid, Grammia incorrupta, were reared exclusively on one of two plant species, one of which contains iridoid glycosides (Plantago lanceolata, Plantaginaceae) while the other does not (Taraxacum officinale, Asteraceae). Larval weight was measured on the two host plants, and midgut homogenates of last instar larvae were then assayed for activity and kinetic properties of β-glucosidases, using both a standard substrate, 4-nitrophenyl-β-D-glucose (NPβGlc), and the iridoid glycoside aucubin, one of the two main iridoid glycosides in P. lanceolata. Larvae feeding on P. lanceolata weighed significantly less and developed more slowly compared to larvae on T. officinale. While the larval midgut β-glucosidase activity determined with NPβGlc was significantly decreased when fed on P. lanceolata, aucubin was substantially hydrolyzed and the larval β-glucosidase activity towards both substrates correlated negatively with larval weight. Our results demonstrate that host plants containing high concentrations of iridoid glycosides have a negative impact on larval development of this generalist insect herbivore. This is most likely due to the hydrolysis of plant glycosides in the larval midgut which results in the release of toxic aglycones. Linking the reduced larval weight to the toxin-releasing action of an iridoid glycoside cleaving β-glucosidase, our results thus support the detoxification limitation hypothesis, suggesting fitness costs for the larvae feeding solely on P. lanceolata. Thus, in addition to the adaptive regulation of midgut β-glucosidase activity, host plant switching as a behavioral adaptation might be a prerequisite for generalist herbivores that allows them to circumvent the negative effects of plant secondary compounds.     

Predispersal seed-predation by insects in the Venezuelan Central Plain: Overall patterns and traits that influence its biology and taxonomic groups

Predispersal seed predation (PSP) by insects was studied in a plant community of the Venezuelan Central Plain (VCP). The main goal was to examine to what extent vegetation structure and fruit–seed attributes determined the incidence of PSP by insects at the community level. We studied a total of 187 species from 59 families, in five habitat types. The proportion of seed-predated plant species (N=89; 47.6% of the total) was explained by different factors such as the abundance of legume families, plant species richness, fruit dehiscence, seed biomass, and starch content. Coleoptera was the most diverse taxonomic order of insect seed predators, with Bruchidae and Curculionidae showing the largest number of genera and species, followed by Lepidoptera (Pyralidae). Bruchidae and Pyralidae, but not Curculionidae, tended to be separated according to vegetation attributes, such as vegetation structure and flowering and fruiting phenology. In addition, Bruchidae was associated with dehiscent fruits, legumes, epizoochory, and granivory, whereas Curculionidae was more related with indehiscent fruits and endozoochory, and Pyralidae with abiotic seed dispersal. Bruchid larvae tended to prey upon single seeds, whereas larvae of Lycaenidae usually preyed upon more than one seed per fruit; Curculionidae did not show any clear pattern on this. One larva developing in a single seed (Type I) was the most common type of PSP, closely followed by one or more larvae developing outside seeds within the fruit (Type II). Type III (seed predation by adult insects inside the fruit) was the least common. Type I appears to occur most frequently in climbers, in the forest–savanna transition habitat, and in those cases in which insect adults emerged during the rainy season. By contrast, Types II and III tended to be associated with annual herbs, the lowest stratum (0.05–0.6 m), and disturbed areas. Moreover, Type I was usually found in samaras, drupes, and indehiscent fruits, whereas Type II and Type III were more commonly observed in capsules. Type I and Type II seeds differed in their nutritional composition, which in turn appears to affect seed predation specialization. The number of insect seed predator species and plant richness per habitat were positively correlated. The number of seed predator species was associated with the abundance of trees and climbers because more complex plant life forms offer a large variety of resources, woody species frequently had fruits and seeds larger than herbaceous species, and trees and climbers showed the lowest values of host specificity. To our knowledge, this study is the first one that characterizes the community of predispersal seed predators and simultaneously evaluates ecological, morphological, and nutritional factors determining the groups of seed predators and how PSP occurred.     

Evolutionary responses by butterflies to patchy spatial distributions of resources in tropical environments

The greatest diversity of butterflies and their host plants occurs in tropical regions. Some groups of butterflies in the tropics exhibit monophagous feeding in the larval stage, exploiting only one family of plants; others are polyphagous, feeding on plants in two or more distinct families. The two major types of tropical habitats for butterflies, namely primary and secondary forests, offer very different evolutionary opportunities for the exploitation of plants as larval food. Butterflies are faced with the major logistical problem, as are many other herbivorous insects, of depositing eggs on the correct plant for successful larval feeding. This paper, using the concepts of phenotype set and spatial patchiness of resources, attemps to make some predictions as to the optimal phenotypic systems for monophagous and polyphagous feeding in tropical butterflies, as related to the spatial patchiness of larval host plants in primary and secondary forests. In addition to the secondary compound chemistry of larval host plants as playing a role in the evolution of monophagy and polyphagy, the assumption is made that the spatial patchiness of host plants within and among different families also acts as a major factor in determining optimal ranges of phenotypes for different patterns of larval feeding. Owing to the high spatial patchiness of primary forest species of canopy trees and vines, it is predicted that butterflies exploiting these will be mostly polyphagous, whereas secondary forests having stable formations of fewer plant species and larger patches of these plants, will have mostly monophagous species. Forest understories may have both monophagous and polyphagous species, depending upon the layer of forest and the general type of understory (i.e. palmaceous or dicotyledonous). Field data on some groups of butterflies from tropical America support these predictions. Polyphagous butterflies are predicted to possess a genetic system of mixed morphs with a population being polymorphic as a whole; monophagous butterflies are predicted to have individuals all more or less similar genetically, and with a high amount of genic variation within individuals. Other forms of monophagy may evolve in species that are essentially monomorphic but with various mechanisms (physiological, developmental, behavioral) of phenotypic flexibility at the individual level. Although the environment is essentially coarse-grained for larvae since most are sedentary and polymorphism is an optimal adaptive strategy, the oviposition strategy of the adult must also be considered and some situations (i.e. forest canopy) have resources (host plants) distributed in a fine-grained fashion. Other forms of limited polyphagy may result from monomorphic genetic systems in which there is considerable phenotypic flexibility.     

上海临港新城河岸带昆虫群落特征

临港新城是上海大都市圈中一个快速城市化的滨海城区。为掌握临港新城河岸带在快速城市化下昆虫群落的特点,2009年10月—2010年9月对临港新城河岸带昆虫分不同生境及不同季节进行了调查,共获得昆虫7755头,隶属于13目、84科、199种。该区域河岸带昆虫优势类群为半翅目(Hemiptera)、双翅目(Diptera)和膜翅目(Hymenoptera)昆虫,分别占总数的37.7%、23.5%和16.5%;水生昆虫种类数及个体数分别占所调查昆虫的12.1%和11.2%;从Shannon多样性指数看,人工林昆虫多样性最高为1.73,其他生境依次为次生林(1.69)>绿地(1.48)>荒地(1.46)>农田(1.42);季节动态变化和生境类型对昆虫的数量、种类、丰富度和均匀度影响较大;该区域河岸带昆虫依食性可分为6类:植食性、捕食性、寄生性、腐食性、杂食性和访花昆虫,植食性昆虫种类和数量分别占62.8%和55.5%,其他食性的昆虫偏少,人类的干扰活动及河岸带景观植被对原有植被的破坏是主要原因。     

Studies on host preference and its biological effects on the red palm weevil,Rhynchophorus ferrugineus Olivier in Egypt The fruit trees

A comparative bioassay (choice or non-choice) was developed to evaluate the efficacy of different species of fruit trees as alternative host plants on the morphological and biological aspects of the red palm weevil, Rhynchophorus ferrugineus and also the latent effect of feeding the larvae on pupal and adult stages. Highly significant differences exist between averages of larval body weight of R. ferrugineus larvae fed on fruit trees. The lowest average of larval weight occurred in the larvae fed on the pieces of sour orange, mandarin followed by olive and lime trees. A small increase in body weight appeared in larvae fed on mango, fig and guava in comparison with those fed on date palm trees (control). The larval mortality reached the highest percentages (100%) by obligatory feeding of R. ferrugineus insects on olive, lime, sour orange and mandarin followed by mango (97%) and guava (96%) compared with control (0%), respectively. The latent effect of obligatory feeding on the larvae of R. ferrugineus was highly decreased during pupation (4%, 4% and 8%) when the insect fed on mango, guava and fig, compared with 100% pupation in the case of larvae fed on ornamental palm or date palm, respectively. Most pupae resulting from the treated larvae by R. ferrugineus failed in adult emergence especially those insects fed on olive, lime, sour orange and mandarin trees compared to untreated insects (95.6–96.2%), respectively. Data also proved that if an insect is forced to feed on a non-preferred host plant, this results in death of the insect often during the larval stage, a decrease of pupation or failure of adult emergence. These results led to the conclusion that mango, fig, and guava trees are believed to be vulnerable hosts for red weevil attack. The lowest percentage of food consumption appeared in those larvae fed on mandarin, sour orange, lime and olive trees compared with those fed on palm. The present results emphasise the need to test the efficiency of the compounds extracted from these host plants if it is considered as an insecticide or an alternative host protectant for management of the red palm weevil R. ferrugineus.     

Host shifting by Operophtera brumata into novel environments leads to population differentiation in life-history traits

Abstract.  1. Operophtera brumata L. (Lepidoptera: Geometridae), a polyphagous herbivore usually associated with deciduous trees such as oak Quercus robur L . , has expanded its host range to include the evergreen species heather Calluna vulgaris (L.) Hull and, most recently, Sitka spruce Picea sitchensis (Bong.) Carrière.
2. Phenology, morphology, and survival of O. brumata were measured at several life-history stages in populations from the three different host plant communities sampled from a range of geographical locations. The data were used to test for population differences, reflecting the marked differences in host-plant secondary chemistry, growth form, and site factors such as climate. The hypothesis that spruce-feeding populations originated from populations feeding on moorland, commonly sites of coniferous afforestation, was also tested.
3. Altitude, not host plant species, was the major influence on the timing of adult emergence. An effect of insect population independent of altitude was found, implying that additional unidentified factors contribute to this phenological variation. Larval survival and adult size varied between populations reared on different host plant species. Survival of larvae was affected negatively when reared on the novel host plant, Sitka spruce, versus the natal plant (oak or heather) but oak and heather-sourced insects did not differ in survivorship on Sitka spruce.
4. Host range extension into novel environments has resulted in population differentiation to the local climate, demonstrating that host shifts pose challenges to the herbivore population greater than those offered by the host plant alone. The hypothesis that Sitka spruce feeding populations have arisen predominantly from moorland feeding populations was not supported.     

Arbuscular mycorrhizal fungi affect phytophagous insect specialism

The majority of phytophagous insects eat very few plant species, yet the ecological and evolutionary forces that have driven such specialism are not entirely understood. The hypothesis that arbuscular mycorrhizal (AM) fungi can determine phytophagous insect specialism, through differential effects on insect growth, was tested using examples from the British flora. In the UK, plant families and species in the family Lamiaceae that are strongly mycorrhizal have higher proportions of specialist insects feeding on them than those that are weakly mycorrhizal. We suggest that AM fungi can affect the composition of insect assemblages on plants and are a hitherto unconsidered factor in the evolution of insect specialism.     

盾负泥虫对鸭跖草的专食性

盾负泥虫Lema scutellaris (Kraatz.)1年发生1代, 以成虫滞育。用与鸭跖草Commelina communis L. 同科及近缘科,属的植物对其食性进行测定,结果是食性单一,只取食鸭跖草。盾负泥虫的发生期与鸭跖草的苗期同步,幼虫的喜食与鸭跖草的多分枝特性相吻合。取食营养位与粘液细胞在鸭跖草植株上的分布及细胞的含糖量关系密切。     

Host‐associated differentiation in a highly polyphagous,sexually reproducing insect herbivore

Insect herbivores may undergo genetic divergence on their host plants through host‐associated differentiation (HAD). Much of what we know about HAD involves insect species with narrow host ranges (i.e., specialists) that spend part or all their life cycle inside their hosts, and/or reproduce asexually (e.g., parthenogenetic insects), all of which are thought to facilitate HAD. However, sexually reproducing polyphagous insects can also exhibit HAD. Few sexually reproducing insects have been tested for HAD, and when they have insects from only a handful of potential host‐plant populations have been tested, making it difficult to predict how common HAD is when one considers the entire species' host range. This question is particularly relevant when considering insect pests, as host‐associated populations may differ in traits relevant to their control. Here, we tested for HAD in a cotton (Gossypium hirsutum) pest, the cotton fleahopper (CFH) (Pseudatomoscelis seriatus), a sexually reproducing, highly polyphagous hemipteran insect. A previous study detected one incidence of HAD among three of its host plants. We used Amplified fragment length polymorphism (AFLP) markers to assess HAD in CFH collected from an expanded array of 13 host‐plant species belonging to seven families. Overall, four genetically distinct populations were found. One genetically distinct genotype was exclusively associated with one of the host‐plant species while the other three were observed across more than one host‐plant species. The relatively low degree of HAD in CFH compared to the pea aphid, another hemipteran insect, stresses the likely importance of sexual recombination as a factor increasing the likelihood of HAD.     

Plant stress and insect behavior: cottonwood,ozone and the feeding and oviposition preference of a beetle

Summary Adults and larvae of the beetle Plagiodera versicolora preferred to feed on and consumed more of cottonwood, Populus deltoides, plant material that had been previously exposed to an acute dose of ozone (0.20 ppm, 5 h), compared to controls in choice experiments. However, females preferred to oviposit on the unexposed controls. Results were consistent for 2 cottonwood clones over 3 years in disc, leaf and whole-plant choice tests. The differential feeding and oviposition response of this insect to stressed plants could have at least 3 unexpected consequences: 1. An immediate increase in damage to stressed trees, but a subsequent decrease in damage. 2. A subsequent increase in damage to unstressed adjacent trees. 3. Changes in the insect and pathogen communities of both stressed and unstressed trees. These complex scenarios show that predicting outcomes of plant stress on plant-insect interactions will require comprchensive examination of behavioral, growth and reproductive responses of insects to stressed plants.     

Decreased losses of woody plant foliage to insects in large urban areas are explained by bird predation

Despite the increasing rate of urbanization, the consequences of this process on biotic interactions remain insufficiently studied. Our aims were to identify the general pattern of urbanization impact on background insect herbivory, to explore variations in this impact related to characteristics of both urban areas and insect–plant systems, and to uncover the factors governing urbanization impacts on insect herbivory. We compared the foliar damage inflicted on the most common trees by defoliating, leafmining and gall‐forming insects in rural and urban habitats associated with 16 European cities. In two of these cities, we explored quality of birch foliage for herbivorous insects, mortality of leafmining insects due to predators and parasitoids and bird predation on artificial plasticine larvae. On average, the foliage losses to insects were 16.5% lower in urban than in rural habitats. The magnitude of the overall adverse effect of urbanization on herbivory was independent of the latitude of the locality and was similar in all 11 studied tree species, but increased with an increase in the size of the urban area: it was significant in large cities (city population 1–5 million) but not significant in medium‐sized and small towns. Quality of birch foliage for herbivorous insects was slightly higher in urban habitats than in rural habitats. At the same time, leafminer mortality due to ants and birds and the bird attack intensity on dummy larvae were higher in large cities than in rural habitats, which at least partially explained the decline in insect herbivory observed in response to urbanization. Our findings underscore the importance of top‐down forces in mediating impacts of urbanization on plant‐feeding insects: factors favouring predators may override the positive effects of temperature elevation on insects and thus reduce plant damage.     

Insect herbivores associated with Baccharis dracunculifolia (Asteraceae): responses of gall-forming and free-feeding insects to latitudinal variation

The spatial heterogeneity hypothesis has been invoked to explain the increase in species diversity from the poles to the tropics: the tropics may be more diverse because they contain more habitats and micro-habitats. In this paper, the spatial heterogeneity hypothesis prediction was tested by evaluating the variation in richness of two guilds of insect herbivores (gall-formers and free-feeders) associated with Baccharis dracunculifolia (Asteraceae) along a latitudinal variation in Brazil. The seventeen populations of B. dracunculifolia selected for insect herbivores sampling were within structurally similar habitats, along the N-S distributional limit of the host plant, near the Brazilian sea coast. Thirty shrubs were surveyed in each host plant population. A total of 8 201 galls and 864 free-feeding insect herbivores belonging to 28 families and 88 species were sampled. The majority of the insects found on B. dracunculifolia were restricted to a specific site rather than having a geographic distribution mirroring that of the host plant. Species richness of free-feeding insects was not affected by latitudinal variation corroborating the spatial heterogeneity hypothesis. Species richness of gall-forming insects was positively correlated with latitude, probably because galling insect associated with Baccharris genus radiated in Southern Brazil. Other diversity indices and evenness estimated for both gall-forming and free feeding insect herbivores, did not change with latitude, suggesting a general structure for different assemblages of herbivores associated with the host plant B. dracunculifolia. Thus it is probable that, insect fauna sample in each site resulted of large scale events, as speciation, migration and coevolution, while at local level, the population of these insects is regulated by ecological forces which operate in the system.     

Insect assemblages attacking seeds and fruits in a rainforest in Thailand

Insect seed predators are important agents of mortality for tropical trees, but little is known about the impact of these herbivores in rainforests. During 3 years at Khao Chong (KHC) in southern Thailand we reared 17,555 insects from 343.2 kg or 39,252 seeds/fruits representing 357 liana and tree species. A commented list of the 243 insect species identified is provided, with details about their host plants. We observed the following. (i) Approximately 43% of identified species can be considered pests. Most were seed eaters, particularly on dry fruits. (ii) Approximately 19% of parasitoid species (all Opiinae) for which we could determine whether their primary insect host was a pest or not (all Bactrocera spp. breeding in fruits) can be considered beneficials. (iii) The seeds/fruits of approximately 28% of the plant species in this forest were free of attack. Phyllanthaceae, Rubiaceae and Meliaceae were attacked relatively infrequently; in contrast, Annonaceae, Fabaceae, Sapindaceae and Myristicaceae were more heavily attacked. There was no apparent effect of plant phylogeny on rates of attack but heavily attacked tree species had larger basal area in the KHC plot than rarely attacked tree species. (iv) Insects reared from fleshy fruits were more likely to show relatively stable populations compared to insects reared from dry fruits, but this was not true of insects reared from dipterocarps, which appeared to have relatively stable populations throughout the study period. We tentatively conclude that insects feeding on seeds and fruits have little effect on observed levels of host abundance in this forest.