Cameraria Ohridella Research Articles

Long‐distance dispersal and human population density allow the prediction of invasive patterns in the horse chestnut leafminerCameraria ohridella

SummaryAfter its initial discovery in Macedonia in 1985, during the last 19 years the leafminer mothCameraria ohridellahas invaded most of Central and Western Europe. The species, which causes aesthetic damage to horse chestnuts, is generally observed first in highly populated locations before colonizing the countryside. This pattern is consistent with a stratified dispersal process combining long‐distance movements and local diffusion.Using large‐scale spatial data on damage caused byCameraria ohridellain Germany, three stochastic spatial models of spread are compared: a diffusion model, a leptokurtic dispersal model and a stratified dispersal model that assumes a two‐scale dispersal process. In addition, the association between human population and moth invasion is tested in this last model by linking long‐distance infestation probability to human population density. Finally, these spatial models constructed with data from Germany are tested at the European scale and compared to historical records of first occurrence.The fat‐tailed dispersal kernel models (leptokurtic and stratified dispersal models) allowing for long‐distance dispersal provide better predictions than the diffusion model. Among these models, the stratified dispersal model incorporating the effect of human population density provides the best description of the spread ofCameraria ohridellain Germany in predictive (lowest sum of squared errors) and qualitative (similar fractal dimension) terms.The roles of short‐distance and long‐distance dispersal inCameraria ohridellainvasion ecology in relation to human population are discussed, together with the models’ scale‐dependence and limitations.

Poor control of the horse chestnut leafminer, Cameraria ohridella (Lepidoptera: Gracillariidae), by native European parasitoids: a synchronisation problem

Horse chestnut trees in many regions of Europe have suffered from epidemic infestations of C. ohridella for more than ten years. There has been no obvious decrease in the infestation level anywhere on the continent. One reason is, that the native natural enemies have not been able to control mass outbreaks of the leafminer. Parasitoid Hymenoptera have very little impact on the first generation of the moth in early summer, regardless of the number of parasitoids that overwintered in horse chestnut leaves. This study revealed that there is a considerable time lag between the emergence of the parasitoids from the leaflitter in spring and the appearance of suitable host instars in early summer. The poor control of C. ohridella by natural enemies may partly be due to the poor synchronisation between the life cycles of the introduced host and native parasitoid wasps.

Cultural control of Cameraria ohridella on horsechestnut in urban areas by removing fallen leaves in autumn

Since the 1990s, the leafminer Cameraria ohridella has spread in central and southern Europe causing heavy damage on horsechestnut (Aesculus hippocastanum). Because biological control of the pest is not yet a reality, other measures must be adopted. Cultural control by removing fallen leaves of horsechestnut in autumn has often been proposed, and with this 3-year study the effectiveness of this practice under urban conditions has been shown and measured. The almost complete removal of leaves caused a significant reduction in infestation. The area of leaf surface injured decreased on average by more than 90% in early June, three quarters in late July, and a third in late August, and early leaf fall was always avoided. The proximity to sites with no leaf removal reduced the benefits of leaf removal as the season advanced. In the context of Integrated Pest Management, this cultural method contributes significantly to reduce C. ohridella damage.

Visual, semi‐quantitative assessments allow accurate estimates of leafminer population densities: an example comparing image processing and visual evaluation of damage by the horse chestnut leafminer Cameraria ohridella (Lep., Gracillariidae)

Abstract: Qualitative or semi‐quantitative visual assessments are most often used for estimating population size of herbivorous insects. The precision of these estimates, however, is often difficult to establish. A ‘simulation game’ with the horse chestnut leafminer, Cameraria ohridella Deschka & Dimic (Lep., Gracillariidae) shows that visual, semi‐quantitative assessments can provide accurate information. Damaged areas of 411 horse chestnut leaves collected in 100 sites were closely related to mine numbers despite some variability in mine and leaf size (R2 = 0.915; n = 411; P < 0.001). On the basis of this relationship, two methods of population assessment are compared: (i) digital image processing of leaf damage and (ii) visual assessment using a damage key reflecting the relative infested area on each leaf (0, 0%; 1, 0–2%; 2, 2–5%; 3, 5–10%; 4, 10–25%; 5, 25–50%; 6, 50–75%; 7, 75–100%). Both methods used to estimate damage presented a similar, close relationship to the ‘real’ numbers of mines (R2 = 0.858; n = 777; P < 0.001 for image processing and R2 = 0.905; n = 777; P < 0.001 for visual assessment). The potential of using visual assessments as an accurate and fast method in situ at the tree scale is discussed.

Date of leaf litter removal to prevent emergence of Cameraria ohridella in the following spring

completely defoliates trees already in summer. The leafdamage is particularly spectacular in cities where horsechestnut trees are abundant and the defoliation of treesin streets, parks, and gardens in early summer raisessignificant public concern. The aesthetic problems and thelost filter function of defoliated trees in the city climate areconsidered to be the main consequence of damage. Thepest is thus mostly an urban problem which is managed onthe scale of cities.The first mass appearance of

Spatial patterns and infestation processes in the horse chestnut leafminer Cameraria ohridella: a tale of two cities

AbstractSpatial patterns of the horse chestnut leafminer Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae) population density was analysed in the cities of Bern and Brussels in order to explore its spatial population dynamics. The surveys were carried out in Bern in 1998 and 2000 and in Brussels in 2001 to assess population density in relation to local characteristics. In Brussels, population density was also measured using pheromone traps distributed over the city and collected twice per moth generation. A quantitative relationship was found between local population density (measured by pheromone traps and survey observations) and the amount of leaves left on the ground the previous fall. Several other factors were related to observed infestation levels: the occurrence of the pathogen Guignardia aesculi was inversely related to infestation by C. ohridella in Bern in 1998 and 2000, the number of horse chestnut trees within 800 m distance was positively related to infestation level in Bern in 2000, and the proportion of green areas within 100 m and the number of other horse chestnut trees within 2000 m were positively related to infestation levels in the 2001 Brussels survey. The pattern of infestation levels as a function of distance to potential population reservoirs suggested that C. ohridella re‐invades areas where overwintering leaves have been cleaned from refuge areas such as parks or urban forests. Our results indicate that the removal of leaves is a feasible first aid control measure to reduce moth population densities. However, leaf removal may not reduce moth densities when done improperly. In places where proper leaf removal is not feasible, other control measures are needed.

Morphology of female sex pheromone gland in the horse chestnut leafminer Cameraria ohridella (Lep., Gracillariidae)

Abstract: The internal and external morphology of the female sex pheromone gland in Cameraria ohridella Deschka & Dimic, an European pest on Aesculus hippocastanum L., has been investigated by histological and electron microscopic techniques. The gland consists of a single layer of modified epidermal cells in the dorsal part of the intersegmental membrane between the eighth and ninth abdominal segments and laterally extends to the posterior apophyses. The epithelium contains large columnar‐ and cone‐shaped cells with basally situated nuclei. The cuticle, which covers the glandular region, has a wrapped appearance and is divided into a hyalin and thickened endocuticle and a thin outer epicuticle: it considerably expands when the gland is protruded and provides a sufficiently large surface for evaporation of the pheromone. The cuticle does not show any orifices of pore channels. In the retracted position, the gland is folded within the body cavity of the seventh and eighth abdominal segments but is exposed to the environment by extension of the abdominal tip along with female calling. In virgin females, pheromone glands are well developed at least within the first days after eclosion; if copulation occurs, glandular epithelia degenerate soon. According to the current classification, the glandular type of C. ohridella most easily is consistent with eversible dorsal scent folds that are widely distributed amongst diverse taxa of Lepidoptera. However, this is the first report on the morphology of pheromone glands in the Gracillariidae.

Effects of defoliation by horse chestnut leafminer ( Cameraria ohridella ) on reproduction in Aesculus hippocastanum

In large parts of Europe horse chestnut trees (Aesculus hippocastanum) suffer from severe defoliation by an alien invasive species, the specialist leaf mining moth Cameraria ohridella (Lepidoptera; Gracillariidae). Heavily infested trees have a drastically shortened period for photosynthesis. We quantified the effect of moth infestation on reproduction of horse chestnut trees in two different cities in central Europe, Bern and Munich. C. ohridella negatively affected seed and fruit weight of A. hippocastanum at both locations. In Munich, seed weight of heavily damaged trees was reduced by almost half. However, the number of seeds per fruit, the number of fruits per inflorescence, and the number of inflorescences per tree did not change due to herbivory. We conclude that C. ohridella mining affects seed quality but not seed quantity. The reduced seed weight may severely impair growth and survival of horse chestnut seedlings and thus may endanger the long-term persistence of A. hippocastanum in its endemic forests in south-east Europe.

Effects of defoliation caused by the leaf miner Cameraria ohridella on wood production and efficiency in Aesculus hippocastanum growing in north-eastern Italy

The leaf miner Cameraria ohridella causes premature defoliation of Aesculus hippocastanum trees. Repeated defoliation has been reported to cause decrease in radial growth of trees and a progressive decline due to reduced production and allocation of photosynthates. Our study represents an attempt to estimate the impact of C. ohridella on annual wood increments and the hydraulic properties of the wood as well as on the dry mass of seeds. Twenty-two adult horse chestnut trees were selected, four of which had been chemically treated to prevent attack (controls). All other trees were heavily infested. The ground cover (GC) of each tree, measured from monthly hemispherical photographs, revealed that infested trees were completely defoliated in September and the slope of the GC-to-measurement dates relationship (named GC decrease index) was positively related to the number of mines per leaf. Anatomical observations showed that infested trees produced more wood per year than controls through more false rings with wider xylem conduits and, hence, with higher conductive area and theoretical flow. In fact, the theoretical flow was positively related to the defoliation intensity. In contrast, the allocation of photosynthates to seeds was strongly reduced in infested trees with respect to controls (up to 50% less). The hypothesis was advanced that horse chestnut trees reacted to C. ohridella attacks by increasing the hydraulic efficiency of the wood, thus ameliorating the water and nutrient supply to leaves between the spring and mid-summer and, therefore, compensating, at least partly, the reduced leaf lifespan.

Parasitism of different larval stages of Cameraria ohridella

About 20 species of parasitic Hymenoptera havebeen reported from the horse chestnutleafminer, Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae). Generally,parasitism is low compared to other closelyrelated leafminers and the parasitism levelvaries considerably. Among other reasons,parasitism rates depend on the developmentalstage of the moth and therefore vary with thesampling date. In the current study,investigations on the parasitism of the moth'sfirst generation were carried out in order todetermine which preimaginal stages areparasitized by the most abundant parasiticwasps. Minotetrastichus frontalis (Nees),Pnigalio agraules (Walker) and Chrysocharis nephereus (Walker) (allHymenoptera: Eulophidae) developed as larval orpupal parasitoids and preferred later larvalinstars of the moth. Egg parasitism did notoccur. Overall, the last two of the six larvalinstars (the spinning instars) of the leafminersuffered the heaviest attack. In concordancewith the fairly low parasitism rates, theeffect of the four most abundant chalcidoids onthe leafminer population was negligible, havingno significant influence on the mortality ofC. ohridella. Although the speciescomposition of the parasitoid complex of C. ohridella shows similarities with thesituation found in other closely relatedleafmining moths, it is unlikely that thenaturally occurring chalcidoids will be able toprevent the horse chestnut leafminer fromdeveloping epidemic population densities in thenear future.

Sex pheromone of horse-chestnut leafminer Camneraria ohridella and its use in a pheromone-based monitoring system.

Gas chromatography combined with electroantennographic detection (GC-EAD), electroantennography (EAG), and wind-tunnel and field experiments were used to reinvestigate the composition of Cameraria ohridella (Lepidoptera, Gracillariidae, Lithocolletinae) sex pheromone. The GC-EAD experiments showed one EAD-active area corresponding to the major pheromone component. (8E,10Z)-tetradeca-8,10-dienal. The EAG experiments proved that (9E)-tetracedecenal and stereoisomers of (8E,10Z)-tetradeca-8,10-dienal exhibited significant electrophysiological activity and could, therefore, be considered as possible minor pheromone components. However, wind-tunnel and field experiments demonstrated that none of these compounds affect the efficacy of the main pheromone component. A monitoring system based on (8E,10Z)tetradeca-8,10-dienal was developed and used to study the flight activity of C. ohridella.

Acute spread in France of an invasive pest, the horse chestnut leafminer Cameraria ohridellaDeschka & Dimic (Lep., Gracillariidae)

AbstractThe horse chestnut leafminer, Cameraria ohridella Deschka & Dimic (Lepidoptera, Gracillariidae) spread over the last 10 years from central Europe to western Europe and was observed for the first time in 2000 in the east of France and near Paris. This study presents the results of surveys carried out in France in 2001 to investigate the distribution and infestation level of the leafminer. One year after its first discovery, the moth was present in a large part of the country and for the first time has been observed in Paris. The spread of the moth is due mainly to natural dispersal and to passive dispersal by human activities.

Parasitism of the horse chestnut leaf miner, Cameraria ohridellaDeschka and Dimic (Lep., Gracillariidae), in Serbia and Macedonia

AbstractA study concerning the parasitism of Cameraria ohridella, a pest of Aesculus hippocastanum invading Europe, has been carried out in Serbia and Macedonia in 1998 and 1999. From C. ohridella 14 species of parasitoids were reared, which are polyphagous and occur in the whole of Europe. Twelve of the species found belong to the Chalcidoidean family Eulophidae. The rates of parasitism at different sampling dates did not exceed 25 %. The results, when compared with data from central Europe, showed that C. ohridella most certainly does not originate from Serbia or Macedonia – the regions in which C. ohridella was observed for the first time – as an indigenous leaf miner on A. hippocastanum.

Monitoring the population dynamics of the horse chestnut leafminer Cameraria ohridella with a synthetic pheromone in Europe

A monitoring system for Cameraria ohridella males based on a synthetic sex pheromone was tested in the Czech Republic, Germany, France and Greece. From the obtained data on the insect phenology we concluded that in Central Europe C. ohridella typically has three generations per year. The pheromone monitoring can be used to detect the pest when it appears in uninfested areas and is also suitable to determine population densities.

Female sex pheromone of Cameraria ohridella Desch. and Dim. (Lepidoptera: Gracillariidae): structure confirmation, synthesis and biological activity of (8E,10Z)-8,10-tetradecadienal and some analogues.

Mass spectrometric investigations confirmed the structure of the female produced sex pheromone of the horse-chestnut leafminer Cameraria ohridella Desch. and Dim. to be (8E,IOZ)-8,10-tetradecadienal. Pure samples, prepared in a straightforward synthesis, were highly attractive in field tests and proved to be suitable for monitoring of flight activities and population dynamics. In mixtures with the synthetic pheromone, analogues like 9-tridecynal and 7-dodecynyl formate were shown to reduce trap catches. In electroantennographic experiments, pheromone analogues were less active than the pheromone. 9-Tridecynal was the most EAG active analogue tested, followed by 7-dodecyn-1-yl formate and 7-undecyn-1-yl formate.

ChemInform Abstract: Synthesis of (8E,10Z)-Tetradeca-8,10-dienal, Sex Pheromone of Horse Chestnut Leafminer (Cameraria ohridella), and All Its Geometrical Isomers.

(8 E ,10 Z )-Tetradeca-8,10-dienal ( 1a ), sex pheromone of the horse chestnut leafminer ( Cameraria ohridella ; Lepidoptera, Gracillariidae), and its geometrical isomers ( 1b - 1d ) were efficiently synthesized using tetrakis(triphenylphosphine)palladium catalyzed cross-coupling reactions of alk-1-ynes or alkenyl alanes with corresponding vinyl iodides. The stereoisomeric purity of obtained tetradecadienals 1a - 1d was higher than 95% (GC). Relative electroantennographic (EAG) activities of the prepared compounds 1a - 1d elicited on male antennae supported the previously published identification of the C. ohridella sex pheromone.

Die Verbreitung der Roßkastanien‐Miniermotte Cameraria ohridellaDesch. & Dimic (Lepid., Gracillariidae) in der Region Südtirol‐Trentino

Abstract: A survey on the present distribution of the horse chestnut leafmining moth, Cameraria ohridella Desch. & Dimic 1986, in Europe and in Italy is given: In Europe, within a period of 15 years, the leafminer – recently introduced into Central Europe – has settled in an area that spreads over 13 latitudinal and about 20 longitudinal degrees; in Northern Italy, an area of approximately 50,000 km2 has been afflicted in the 5 years since the leafminer’s introduction in South Tyrol and Julian Venetia in 1993.The development of the distribution in the region of South Tyrol and Trentino is shown: In the province of Bozen‐South Tyrol, between 1995 and 1999 the moth has spread in all the three principal valleys (Eisacktal, Pustertal, Etschtal); in the Trentino province, first local attacks began only in 1998, near Trento and Riva, but spread over the entire Etschtal/Adige Valley in 1999. While in South Tyrol C. ohridella was introduced from the North (North Tyrol), the introduction into the Trentino occured from the South (Verona).At present the attacks in Trentino province are preponderantly low (resulting heavy only in the city of Trento and in Riva del Garda) and limited to altitudes ranging from 70 to 700 in. In South Tyrol, attacks are mainly heavy in altitudes ranging from 250 to 900/950 m, while they are low in the increasingly affected higher altitudes of 1,000 to 1,230 m. Numeric attack parameters are given to show attack intensities.The number of generations per year depends on the respective climatic conditions: in lower‐altitudes, usually three generations develop in a year, but in higher altitudes (800 to 1,100 m) only two generations; in the climatically favoured area around the Lake Garda a (partial) fourth generation appears possible.The question of host plants (Aesculus sp., Acer sp.) and the larval parasitism of C. ohridella is discussed. The parasitism of the larvae, principally by Eulophidae (Hym., Chalcidoidea), was ascertained already in the first years of attack: In South Tyrol, 16 species of parasitoids appeared, and 8 in the Trentino province, but only two species were dominant: Minotetrastichus sp. and Pnigalio sp. The level of parasitism reached was low, comparable to other Central European countries.

Synthesis of (8E,10Z)-Tetradeca-8,10-dienal, Sex Pheromone of Horse Chestnut Leafminer (Cameraria ohridella), and All Its Geometrical Isomers

(8E,10Z)-Tetradeca-8,10-dienal (1a), sex pheromone of the horse chestnut leafminer (Cameraria ohridella; Lepidoptera, Gracillariidae), and its geometrical isomers (1b-1d) were efficiently synthesized using tetrakis(triphenylphosphine)palladium catalyzed cross-coupling reactions of alk-1-ynes or alkenyl alanes with corresponding vinyl iodides. The stereoisomeric purity of obtained tetradecadienals1a-1dwas higher than 95% (GC). Relative electroantennographic (EAG) activities of the prepared compounds1a-1delicited on male antennae supported the previously published identification of theC. ohridellasex pheromone.

OCCURRENCE OF CAMERARIA OHRIDELLA Deschka & Dimic IN BOSNIA-HERZEGOVINA

The horse-chestnut leafminer Cameraria ohridella Deschka & Dimic, is a new speciesin Bosnia-Herzegovina, discovered in 1993 and distributed throughout almost thewhole of the country today. The insect has spread from Macedonia (discovered for thefirst time in 1985) to other parts of Europe. This paper deals with the distribution ofthe leafminer in the country and the symptoms found on the attacked trees.

Identification of a new lepidopteran sex pheromone in picogram quantities using an antennal biodetector: (8 E,10 Z)-tetradeca-8,10-dienal from Cameraria ohridella

A major sex attractant released by the virgin female of the horse-chestnut leafminer Cameraria ohridella Deschka et Dimić (Lepidoptera: Gracillariidae) which devastates horse-chestnut trees in Europe, was identified in picogram quantities as (8 E,10 Z)-tetradeca-8,10-dienal without using spectral methods. The identification solely relied on gas chromatography with electroantennographic detection (GC-EAD), calculation of Kovats' indices of the active principle on different GC phases, and construction of antennal response spectra (EAG response profiles) to C 12 and C 14 saturated and unsaturated standards with different functional groups. The dienal was prepared by a stereospecific synthesis and shown to be highly active for conspecific males in pg amounts and fully comparable to the natural substance.