Leaf-mining Insects Research Articles

Impact of Forest Management on Insect Abundance and Damage in a Lowland Tropical Forest in Southern Cameroon

The rate of deforestation in West Africa was around 2% (12 000 km 2 ) per annum during the 1980s, and recent evidence from Cameroon suggests that the rate of deforestation there has increased during the 1990s. In contrast, only 360 km 2 of plantation forests were established annually during the mid-1980s in West African countries. Recent research in the Mbalmayo Forest Reserve in southern Cameroon has examined contrasting silvicultural techniques for regenerating degraded forest with West African tree species such as Terminalia ivorensis. These techniques included complete clearance, where all existing trees were felled and these and all other vegetation removed from the plots; and partial clearance methods (partial manual clearance, partial mechanical clearance and line planting), where tree-felling resulted in a reduction of 50% of the canopy cover. This paper describes a study of the impact of these techniques on arthropod abundance and the damage caused to T. ivorensis by insect pests within the Mbalmayo Forest Reserve. The amount of damage caused by leaf-mining insects, the abundance of gall-forming mites, and the number of trees affected by shoot borers were not affected by silvicultural practice. The amount of damage caused by leaf-chewing insects was greater in the line planting plots than the complete clearance plots, but the leaf area removed by insects rarely exceeded 6%. It is concluded that the degree of forest clearance before establishing plantations of T. ivorensis. does not markedly affect the amount of damage caused by arthropod pests at the spatial scale at which this study was carried out. Arthropod abundance was assessed by insecticide knockdown fogging in two study sites within the Mbalmayo Forest Reserve. A mean total of 196 arthropods m -2 was recorded, ants being the most common arthropod group (63%), followed by adult Diptera (10%) and then Hymenoptera other than ants (4%), Homoptera (4%), Thysanoptera (4%), adult Coleoptera (3%) and other groups (13%). Ants, Diptera, Araneae, Thysanoptera, Homoptera, Coleoptera and Orthoptera were significantly more abundant in the partial manual clearance plot than the complete clearance plot in one or both of the study sites. Because several of these groups are composed mainly of predatory and parasitic species, it is possible that, despite the pest damage results summarized above, the long-term likelihood of pest outbreaks occurring on T. ivorensis is lower in partial clearance than complete clearance plantations. However, our current lack of knowledge of the species composition of different arthropod groups limits the relevance of these findings.

The Evolution and Adaptive Significance of the Leaf-Mining Habit

Feeding inside leaves by leaf-mining insects has been viewed as an adaptive innovation for consuming foliage. The leaf mine presumably provides its occupant shelter from the detrimental effects of the physical environment, protection from attack by natural enemies, and potentially a means of avoiding plant defenses concentrated in particular layers of leaf tissue. We examine several hypotheses concerning the adaptive significance of leaf mining using both the published literature and experiments. We also examine the notion that leaf mining is an innovation that has led to an adaptive radiation by examining the phylogeny and species richness of leaf-mining lineages and their sister groups. Both advantages and disadvantages accrue to insects that feed inside leaf mines in comparison to external-feeding folivores. The advantages of feeding within a leaf mine include: a lower incidence of disease infection, a microenvironment with lower evaporative demand and therefore protection from desiccation, protection from the direct and indirect effects of UV radiation by the leaf-mine epidermis, and avoidance of plant defenses resulting in higher feeding efficiencies. The disadvantages of feeding inside a leaf mine include: lower mobility resulting in higher mortality from parasites, higher mortality associated with premature leaf-abscission, and smaller average body size and lower fecundity. Leaf mining is certainly a viable means of feeding upon foliage, and in particular instances it might be the most successful means of feeding on leaves. However, the lower species richness of leaf-mining lineages in comparison to their external-feeding sister groups indicates that the evolution of leaf mining does not represent an innovation that has led to an adaptive radiation. Perhaps the evolution of leaf-feeding per se and the evolution of the ability to feed externally on leaves rather than concealed feeding modes such and mining and galling represent innovations that have resulted in adaptive radiations in the Insecta.

Population Dynamics: New Approaches and Synthesis.

Introduction. N. Cappuccino, Novel Approaches to the Study of Population Dynamics. Observation and Comparative Approaches: P. Turchin, Population Regulation: Old Arguments and a New Synthesis. A.F. Hunter, Ecology, Life History and Phylogeny of Outbreak and Nonoutbreak Species. N. Cappuccino, H. Damman, and J.-F. Dubuc, Spatial Behavior and Temporal Dynamics of Outbreak and Nonoutbreak Species. M.J. Auerbach, E.F. Connor, and S. Mopper, Minor Miners and Major Miners: Population Dynamics of Leaf-Mining Insects. Mechanisms and Processes of Population Dynamics: R.F. Denno and M.A. Peterson, Density-Dependent Dispersal and its Consequences for Population Dynamics. S. Harrison and N. Cappuccino, Using Density-Manipulation Experiments to Study Population Regulation. I. Hanski and M. Kuussaari, Butterfly Metapopulation Dynamics. S.J. Walde, Internal Dynamics and Metapopulations: Experimental Tests with Predator-Prey Systems. J. Roland and P.D. Taylor, Herbivore-Natural Enemy Interactions in Fragmented and Continuous Forests. G. Dwyer, Simple Models and Complex Interactions. J.H. Myers and L. Rothman, Field Experiments to Study Regulation of Fluctuating Populations. M.C. Rossiter, Impact of Life History Evolution on Population Dynamics: Predicting the Presence of Maternal Effects. Case Studies: C. Solbreck, Long-Term Population Dynamics of a Seed-Feeding Insect in a Landscape Perspective. T. Ohgushi, Adaptive Behavior Produces Stability in Herbivorous Lady Beetle Populations. P.W. Price, T.P. Craig, and H. Roininen, Working Toward Theory on Galling Sawfly Population Dynamics. J.D. Reeve, M.P. Ayres, and P.L. Lorio, Host Suitability, Predation, and Bark Beetle Population Dynamics. G.E. Belovsky and A. Joern, The Dominance of Different Regulating Factors for Rangeland Grasshoppers. Conclusion: P.W. Price and M.D. Hunter, Novelty and Synthesis in the Development of Population Dynamics. Subject Index.

Leaf-Mining Insects and Fluctuating Asymmetry in Elm Ulmus glabra Leaves

Fluctuating asymmetry, which represents small, random deviations from bilateral symmetry, arises as a result of an inability to control development under genetically and environmentally stressful conditions. Herbivory is also particularly common in plants growing under stressful conditions. It was hypothesized that herbivory would be particularly prevalent in plants with leaves demonstrating high degrees of fluctuating asymmetry. This prediction was tested for the leaf-mining insect, Rhynchaenus rufus, which commonly attacks elm Ulmus glabra. Leaves with mines were significantly more asymmetrical in the width of their two halves and the distance between side-ribs, than the nearest neighbouring leaf without a mine. Elm trees with a high incidence of leaf mines had significantly more asymmetric leaves than the nearest neighbouring elm tree with a low incidence of leaf mines. This was the case regardless of whether affected or unaffected leaves were compared. The incidence of leaf mines across trees was positively related to the degree of leaf asymmetry of the tree. Developmental stability of leaves, as measured by fluctuating asymmetry, was therefore associated with susceptibility to one kind of herbivory in elm trees. Leaves of elm trees watered with a large amount of fertilizer were more asymmetric than leaves of trees just provided with water, suggesting that one kind of stress increased the level of leaf asymmetry. The relationship between foliar asymmetry and herbivory appeared to be causal since increased asymmetry caused by the fertilizer treatment gave rise to an increased abundance of leaf miners.

LOCAL ADAPTATION AND AGENTS OF SELECTION IN A MOBILE INSECT.

The deme-formation hypothesis states that selection can produce adaptive genetic variation within and among phytophagous insect populations. We conducted three field experiments and tested this prediction by transferring eggs and measuring performance of a mobile leafmining insect, Stilbosis quadricustatella. In Experiment 1, we compared the rate of mine initiation of leafminers transferred to natal and novel sites. In Experiment 2, we compared mine-initiation rate of leafminers transferred to natal and novel host-plant species. In Experiment 3, we compared the mine-initiation rate, mine-completion rate, and sources of mortality of miners transferred to neighboring natal and novel Quercus geminata trees. In the first, second, and third experiments, leafminer larvae initiated significantly more mines at the natal site, on the natal plant species, and on the natal Q. geminata tree, evidence for adaptive differentiation. Furthermore, plant-mediated mortality was significantly lower among miners transferred to natal Q. geminata trees. This result supports a key assumption of the deme-formation hypothesis: insects adapt to the defensive phenotypes of individual trees. However, natural-enemy mortality was significantly higher among miners transferred to natal trees, essentially reversing the plant effect. Therefore, rates of successful mine completion were similar on natal (19%) and novel (17%) trees. This experiment suggests that host plants and natural enemies may represent opposing forces of selection. Leafminers adapted to individual trees may realize a selective advantage only when natural-enemy densities are low.

Interactions between arbuscular mycorrhizal fungi and foliar-feeding insects in Plantago lanceolata L.

A field experiment was conducted to investigate whether infection by arbuscular mycorrhizal (AM) fungi has any effect on herbivory by foliar-feeding insects. Plants of PI ant ago laureolata L. were grown in a randomized block design and natural levels of mycorrhizal infection reduced by the application of the granular fungicide iprodione. Plant growth responses were examined and herbivore bioassays performed by rearing both a chewing and sucking insect on the leaves of mycorrhizal and fungicide-treated plants. Fungicide application successfully reduced mycorrhizal infection, and this led to reductions in foliar biomass, caused by lower leaf number. However, fungicide-treated plants suffered consistently higher levels of damage by centralist chewing and leaf-mining insects, which colonized the plants. The chewing insect bioassay confirmed the field results, in that larvae of Arttia caja L. (Lepidoptera: Arctiidae) consumed more leaf material from plants in which infection was reduced. There was no evidence that AM fungi altered food quality for the chewing insect. Instead, infection caused an increase in the carbon/nutrient balance, which in turn led to increased levels of the carbon-based feeding deterrents, aucubin and catalpol, The sucking insect, Mvzus perskae (Sulzer) reacted in an opposite fashion to the ehewtr. with performance being greater on mycorrhizal plants. Again, there was no evidence that an alteration in food Quality was the cause, and in this case infection may result in changes in leaf morphology which benefit the insect. We suggest that under conditions of high light and low nutrient availability. AM infection can alter the carbon/nutrient balance of plants, leading to an increased allocation to carbon-based defences. This can have important consequences for insect herbivore performance and the patterns of herbivory in field situations.

The Structure of a Tropical Host-Parasitoid Community

1. A parasitoid web is a subset of a food web containing data on parasitoids and their hosts; connectance parasitoid webs embody information only about the presence or absence of an interaction, while quantitative parasitoid webs include information about the relative densities of all species. 2. Connectance and quantitative parasitoid webs are described for a community of leaf-mining insects and their parasitoids in regrowth tropical dry forest in Costa Rica. The webs were centred on a study site that contained 88 species of plants, 92 species of leaf miners and 93 species of parasitoids. 3. An average of 1.22 species of miner were found per species of plant, with more species on monocots than on plants with other growth forms. Leaf-miners were highly host-specific

Environmental and Clonal Influences on Host Choice and Larval Survival in a Leafmining Insect

The larvae of Phytomyza ilicicola (native holly leafminer) generally have higher survivorship and densities on Ilex opaca (American holly) grown in cultured suburban settings than on natural forest trees. Survival and density also vary among trees within these two habitats; natural enemies and host-plant factors are thought to generate between-habitat variation in Phytomyza densities, while mainly host factors generate within-habitat variation. We explored the latter by examining the effects of fertilization, clonal variation, exposure to sunlight and site of exposure to attack (forest or open field) on Phytomyza success using potted holly clones in a common garden setting

Bionomics of Leaf-Mining Insects

Recapitulation des donnees portant sur le cycle de vie, l'ecologie, les parasites des insectes mineurs de feuilles, ainsi que leurs relations avec les plantes hotes

Rapid Leaf-Miner Colonization of Introduced Trees and Shifts in Sources of Herbivore Mortality

We measured diversity and abundance of leaf-mining insects on two introduced members of the Fagaceae, an oak, Quercus acutissima, and a chestnut, Castanea crenata, in north Florida. In less than 20 yr populations of both trees have recruited leaf-miner faunas as diverse as those found on native oaks, but some species recorded on Q. acutissima and C. crenata never completed larval development. Discounting unsuccessful colonists, the introduced host with more local native congeners, Q. acutissima, has a greater diversity of associated miners than does C. crenata. Abundance of miners differs greatly among C. crenata, Q. acutissima, and Q. nigra, a native host for most species. Castanea crenata consistently has higher density of miners than does Q. acutissima, although most of this difference is attributable to two species. Larval survivorship and sources of mortality of all miners, and of numerically dominant species analyzed separately, also vary among host species. So does foliar nitrogen content. Survivorship of all miners is highest on C. crenata, intermediate on Q. acutissima, and lowest on Q. nigra, resulting in part from significantly lower parasitism rates on C. crenata than on Q. nigra. The greater foliar nitrogen content of C. crenata compared with Q. nigra also appears responsible for enhanced survivorship of at least one dominant miner on the introduced host.

Ovipositor length in parasitoids and tentiform leaf mines: adaptations in Eulophids (Hymenoptera: Chalcidoidea)

Eulophids attacking hosts with tentiform mines show a tendency to elongate the ovipositor. We interpret tentiform mines as a defence strategy against parasitoids in leaf mining insects.

Impact of Irrigation and Experimental Drought Stress on Leaf-Mining Insects of Emory Oak

The hypothesis that drought-stressed trees suffer higher levels of herbivory than unstressed trees was tested experimentally with two as yet undescribed species of Cameraria leaf miners. Densities and site selection of the species differ within a common host plant. Several roots of four trees in a wash were severed and four trees at a more xeric site were irrigated. Densities of leaf miners on the experimental trees and also on four control trees were monitored at each of the two sites.

Leaf Size Selection by Leaf-Mining Insects on Quercus emoryi (Fagaceae)

Leaf size selection by four species of leaf-mining insects on their host plant, Quercus emoryi, was studied in central Arizona, USA. Two species (Stigmella sp. and Tischeria sp.) that produced small mines also selected small leaves. One species, Stilbosis juvantis, which has an intermediate-sized mine, did not select larger or smaller leaves than the average leaf size available. Only one species, Cameraria sp. nov., showed a relationship between its survivorship and leaf size; it selected large leaves and experienced greater survivorship on large leaves. Survivorship of the other species was not related to leaf size.

Indirect Interactions Between Temporally Separated Herbivores Mediated by the Host Plant

I tested the hypothesis that early season herbivory by leaf—chewing insects affects distribution, densities, and survivorship of late—feeding, leaf—mining insects; early chewing may physically and chemically alter quality of leaf miners on the shared host plant, Quercus emoryi. Proportions of intact leaves and leaves damaged by native leaf chewers on six control and six experimental trees were determined over two growing seasons. I manually damaged °50% of leaves on experimental trees to increase the total fraction of damaged leaves to °75%. Leaf—miner densities, distribution, survivorship, and mortality were monitored on control and experimental trees and in intact and damaged leaves within trees. Leaf miners occurred more frequently than expected by chance on intact than damaged leaves for both control and experimental trees. Leaf—miner densities did not differ between control and experimental trees. This result suggests ovipositing leaf miners did not discriminate between damaged and undamaged trees, but selected leaves within trees. More leaf miners survived intact than damaged leaves in both growing seasons. Survivorship was less in damaged leaves because of significantly increased rates of parasitism on these leaves. However, death from other causes (including bacterial and fungal death) was significantly less for leaf miners on damaged leaves. This positive effect did not compensate for overall lower survivorship of leaf miners in damaged leaves due to increased parasitism. Survivorship and mortality did not differ between control and experiment trees when damaged and intact leaves were pooled within treatments. However, in 1982—1983, survival was lower and parasitism greater for leaf miners in control—damaged leaves than experimental—damaged leaves. Survival and parasitism were not different between control—intact and experimental—intact leaves. These result suggest that (1) the effect of early season herbivory on leaf miners was inversely density dependent and, (2) occurrence of leaf miners on intact leaves may be caused by avoidance of damaged leaves rather than preference for intact leaves. Early season herbivory caused localized changes in phytochemistry within trees, and these chemical alterations were consistent with observed distributions and survivorship of leaf miners. Both early season herbivory and experimental damage resulted in higher levels of condensed tannins and lower protein content in damaged leaves within trees, but herbivory had no effect on between—tree chemistry differences. Leaf miner distributions correspond to these localized chemical changes: leaf miners avoided damaged leaves within trees but showed no between—tree preferences. Parasitism of miners on damaged leaves was higher, possibly because parasitoids used physical and chemical changes as cues to locate leaf—miner hosts, or because exposure of leaf miners to parasitoids was prolonged. However, when many leaves were damaged (experimental trees), the negative effect of parasites was mitigated because physical and chemical cues associated with damaged leaves were less effective. Lower leaf—miner mortality from other causes may be related to the bactericidal of fungicidal properties of increased tannins in damaged leaves. This study demonstrates that temporally separated guilds can interact subtly at low levels of herbivory through changes in the host plant. Current theories of within— and between—guild organization of phytophagous insects may need to be re—evaluated if such interactions are common.

Experimental Evidence for Intraspecific Competition in a Lepidopteran Leaf Miner

We manipulated field densities of the leaf—mining insect Cameraria sp. nov. (Lepidoptera: Gracillariidae) by caging them on branches of Quercus emoryi in central Arizona to test for intraspecific competition. High density cages (n = 7 replicates) had mean larval densities about 3 times those of low—density cages (n = 3 replicates). Our results demonstrate intraspecific competition in the form of density—dependent larval mortality. While mortality for leaf miners co—occurring on leaves was higher than for those occurring singly on leaves, larval mortality on leaves with multiple mines was just as high in low— as in high—density cages. That is, high mortality in high—density treatments was not related to interactions of larvae co—occurring on leaves. Rather, greater mortality in high density treatments resulted from increased mortality of miners on singly mined leaves in high—density treatments compared to those on singly mined leaves in low—density treatments. We suggest that ovipositing Cameraria compete with one another via interference when searching for leaves of superior quality. Natural field densities of Cameraria were highly variable. We conclude that natural high—density aggregations of Cameraria may result in some intraspecific competition, but, for the most part, Cameraria remains at low levels such that the competitive effect we found would not usually operate. However, intraspecific competition may act as a ceiling that prevents Cameraria aggregation on branches of Emory oak from exceeding the levels we observed in the field. Phytophagous insects that are commonly aggregated may compete to some degree even at relatively low densities, such as those of many leaf miners, if leaf quality (chemical/physical) is variable and leaves superior for insect growth and survival are rare.

Leaf-mining and gall-forming insects: tools for teaching population ecology

Distinctive mines and galls are produced by some insect species. These insects can be used in the field and laboratory to teach the principles of population ecology, and have a number of advantages over other insect species. By reference to results from personal research and student exercises, methods of assessing population size, success, and spatial distribution are discussed. Such methods can readily be modified to suit all levels of education

Leaf mines: their effect on leaf longevity.

The effects of a number of factors, notably leaf mining insects, on the longevity of beech and holm oak leaves have been studied. The regular monitoring of individually labelled leaves was complemented by analysis of leaf fall data. Both methods confirm that these mining insects have only a slight impact on their host trees. The presence of first generation Phyllonorycter maestingella mines on beech leaves and winter generation P. messaniella mines on holm oak leaves accelerates leaf loss. Beech leaves mined by second generation P. maestingella and Rhynchaenus fagi did not show this accelerated loss. Their patterns of leaf fall can be explained by within-tree variation in both mine distribution and the timing of leaf fall. It is argued that this premature leaf fall is a damage response, and is not an attempt by the tree to regulate miner numbers.

Leafminers on Oak: The Role of Immigration and In Situ Reproductive Recruitment

The roles of overwintering reproductive recruitment and intertree immigration are examined for leaf—mining insects on oak trees. Full—exclusion caged trees that exclude immigrants, litter exclusion caged trees that exclude overwintering recruits, and control trees were sampled to determine leafminer abundance and species richness. Full—caged trees had little overwintering recruitment, and populations went extinct during the season's first generation. Litter exclusion trees recruited as many species as did control trees, but had lower leafminer densities. However, further experiments indicate that the lowered densities were a caging artifact. This result suggest that most leafminer populations on oak trees are maintained by yearly reimmigration from safe overwintering sites and not from in situ reproductive recruitment. Therefore, the distribution and abundance of leafminers on oak should not be viewed as the turnover of reproductive populations on individual trees, but rather as the immigration and failed colonization of species whose movements encompass several trees.

Insect herbivore guilds and species—area relationships: leafminers on British trees

Abstract. 1. 239 species of leafmining insects have been recorded from thirty‐seven species of trees and large shrubs in Britain.2. A significant species—area relationship was obtained for these insects, but it explained only 19% of the variation about the regression he. A further 23% of the variation may be accounted for by taxonomic relationship of host plants.3. A significant correlation was established between the number of species of leafminers and those of mesophyll‐feeding leafhoppers for twentyeight host tree species. Both guilds are dominated by host specific feeders.4. It is suggested that species—area effects are important in determining species richness of phytophagous insects mainly when groups of closely related host plants are considered. With more diverse arrays of hosts, taxonomic influences, which are probably mainly chemical, may outweigh such area related effects.

Abundances and Diversity of Leaf-Mining Insects on Three Oak Host Species: Effects of Host-Plant Phenology and Nitrogen Content of Leaves

We monitored abundances and occurrences of leaf-mining insects on three oak species, Quercus falcata, Q. nigra, and Q. hemisphaerica, that vary in leaf persistence times. When densities and species richness are compared among oak species, we found no significant differences as predicted by Rhoades and Cates' and Opler's hypotheses regarding leaf miners that feed on oaks with different leaf durations. Furthermore, densities of leaf miners are significantly and negatively correlated with total nitrogen content of leaves, a result contradictory to Feeny's study on lepidopteran species that feed on another oak. We conclude that if leaf persistence or, more directly, nitrogen content, at all affects abundances and numbers of leafmining species on oaks, the effect is inconsequential compared to that of parasitism, predation, abiotic factors, and overwintering success. We did find significant variation in leaf miner densities within and between trees and season. Much of the variation within and between trees may be attributable to ovipositional preference of adult females or secondarily to differential mortality of eggs or larvae. The within and between season variability appears to be caused by the specificity of some leaf miners to certain leaf stages, the build-up of densities through successive cohorts of multivoltine species, and large fluctuations in year-to-year densities of a few species.