Distribution of the entomopathogenic fungus Entomophaga maimaiga (Entomophthorales: Entomophthoraceae) at the northern edge of its range in Europe

The gypsy moth Lymantria dispar is a serious economic pest in European broadleaf forests. However, the entomopathogenic fungus Entomophaga maimaiga, which has a great potential to regulate gypsy moth numbers, has recently spread in the Central and Eastern European area of the moth's range. In the current study, 39 plots in oak forests in the Slovak Republic and the Czech Republic were monitored for E. maimaiga from 2014 to 2016. These plots were located along the northern edge of the E. maimaiga range where gypsy moth outbreaks have occurred in the past. The fungus was detected in 16 of the 39 plots. The results thus confirm that E. maimaiga is quite widespread along the northern edge of its range in Europe and can be considered to be established in that area.     

The potential for Entomophaga maimaiga to regulate gypsy moth Lymantria dispar (L.) (Lepidoptera: Erebidae) in Europe

Gypsy moth, Lymantria dispar L., is one of the most important pests of deciduous trees in Europe. In regular cycles, it causes large‐scale defoliation mostly of oak, Quercus spp., forests. Government authorities in the most infested countries in Europe conduct large‐scale applications of pesticides against gypsy moth. In 1999, a new natural enemy, the entomopathogenic fungus Entomophaga maimaiga, was successfully introduced into a gypsy moth population in Bulgaria. Recent investigations suggest that now E. maimaiga is quickly spreading in Europe. Herein, past studies are reviewed regarding this fungus with special emphasis on its potential for becoming an important factor regulating gypsy moth populations in Europe, focusing on the host's population dynamics in relation to the fungus, the influence of environmental conditions on fungal activity, the influence of E. maimaiga on the native entomofauna, including other gypsy moth natural enemies, and spread of the fungus. Based on this analysis, the potential of E. maimaiga for providing control in European gypsy moth populations is estimated.     

Different susceptibility of indigenous populations of Lymantria dispar to the exotic entomopathogen Entomophaga maimaiga

The recovery of the host‐specific entomopathogen Entomophaga maimaiga is still limited to certain world areas, although it is recently spreading to Eastern Europe. This study evaluated the effectiveness and fitness of an E. maimaiga isolate from Balkans against Lymantria dispar populations collected along the Italian peninsula and main islands, where the fungus has never been reported. As a result of different bioassays, the pathogenicity against gypsy moth larvae was generally confirmed, although significant differences among insects feeding upon diverse forest plant species were observed. The lack of significant susceptibility of other lepidopteran species from the same areas is also reported.     

Lepidoptera‐specific insecticide used to suppress gypsy moth outbreaks may benefit non‐target forest Lepidoptera

相似文献   

Spatial analysis of gypsy moth populations in Sardinia using geostatistical and climate models

• 1 Spatial fluctuations of the Sardinian population of the gypsy moth Lymantria dispar (L.) (Lepidoptera: Lymantriidae) were characterized using geostatistical and climate models. Data on gypsy moth egg mass abundance recorded at 282 permanent monitoring sites from 1980 to 2004 were incorporated in a geographic information system with the vegetational, geomorphological and pedological features of the sites.
• 2 Statistical analyses revealed that the relative outbreak frequency was related to the predominant host tree, slope and elevation of the monitoring sites, whereas there was no correlation between outbreak frequency and exposure and soil type.
• 3 By using bioclimatic modelling, probability maps of gypsy moth outbreaks were generated. The model identified a probability surface with climatic conditions favourable to gypsy moth outbreaks and thus potentially subject to defoliation. The maps included 92 sites where outbreaks never occurred, suggesting that the Sardinian climate may not be a determinant factor for gypsy moth outbreaks.
• 4 The geostatistical method cokriging with outbreak frequency as a covariate was found to be the most suitable technique to estimate gypsy moth egg mass abundance. Semivariograms showed spatial correlation of egg mass abundance within the range 18.5–53 km. The results obtained were used to create regional gypsy moth distribution maps by cokriging, which demonstrated the outbreak foci and different infestation levels at each monitoring area. These results can help to delimit the treatment areas and develop rational gypsy moth management programmes.

     

Extensive gypsy moth defoliation in Southern New England characterized using Landsat satellite observations

Southern New England is currently experiencing the first major gypsy moth (Lymantria dispar) defoliation event in nearly 30 years. Using a novel approach based on time series of Landsat satellite observations, we generated consistent maps of gypsy moth defoliation for 2015 (first year of the outbreak), 2016 (second year of outbreak), and 2017 (third year of outbreak). Our mapped results demonstrate that the defoliation event continued through the 2017 growing season. Moreover, the affected area more than doubled in extent each year and expanded radially to encompass 4386 km² of forested area in Rhode Island, eastern Connecticut, and central Massachusetts. The current gypsy moth outbreak is believed to be the result of a series of unusually dry springs in 2014, 2015, and 2016, which suppressed Entomophaga maimaiga, a fungal mortality agent that has historically reduced gypsy moth impacts in this region. The continuation and marked expansion of the outbreak in 2017 despite average spring rainfall suggests that caterpillars were active early in the growing season, and mortality from the fungus likely peaked after significant defoliation had already occurred. Our Landsat time series approach represents an important new source of data on spatial and temporal patterns in gypsy moth defoliation, and continued satellite-based monitoring will be essential for tracking the progress of this and other gypsy moth outbreaks.     

Modeling the Influence of Rainfall and Temperature on the Phenology of Infection of Gypsy Moth, Lymantria dispar, Larvae by the Fungus Entomophaga maimaiga

A computer model driven by daily maximum-minimum temperature and rainfall records was developed to investigate the influence of weather on times when gypsy moth larvae, Lymantria dispar, can become infected by the fungal pathogen Entomophaga maimaiga. In the model, gypsy moth eggs are hatched and neonates are exposed primarily to germinating resting spores in the soil during the spring. Risk of infection is related to forest floor moisture. Larval and fungal development follows a degree-day model. When larvae become 4th instars, they can again become infected by resting spores because they hide in the litter during daylight hours. If rain falls when infected caterpillars die, the fungus sporulates, producing conidia. The number of conidia produced is assumed to directly influence the probability of infection of other larvae. The model was run using weather records from 1990 through 1992. Predicted times of infection were compatible with estimated fungal recruitment rates and changes in field disease prevalence rates. Assumptions about infection mechanisms in the model are discussed as they relate to the real world.     

Detection and quantification of Entomophaga maimaiga resting spores in forest soil using real-time PCR

Environmental sampling to monitor entomopathogen titre in forest soil, a known reservoir of insect pathogens such as fungi and viruses, is important in the evaluation of conditions that could trigger epizootics and in the development of strategies for insect pest management. Molecular or PCR-based analysis of environmental samples provides a sensitive method for strain- or species-based detection, and real-time PCR, in particular, allows quantification of the organism of interest. In this study we developed a DNA extraction method and a real-time PCR assay for detection and quantification of Entomophaga maimaiga (Zygomycetes: Entomophthorales), a fungal pathogen of the gypsy moth, in the organic layer of forest soil. DNA from fungal resting spores (azygospores) in soil was extracted using a detergent and bead mill homogenization treatment followed by purification of the crude DNA extract using Sephadex–polyvinylpolypyrrolidone microcolumns. The purification step eliminated most of the environmental contaminants commonly co-extracted with genomic DNA from soil samples but detection assays still required the addition of bovine serum albumin to relieve PCR inhibition. The real-time PCR assay used primers and probe based on sequence analysis of the nuclear ribosomal ITS region of several E. maimaiga and two E. aulicae strains. Comparison of threshold cycle values from different soil samples spiked with E. maimaiga DNA showed that soil background DNA and remaining co-extracted contaminants are critical factors determining detection sensitivity. Based on our results from comparisons of resting spore titres among different forest soils, estimates were best for organic soils with comparatively high densities of resting spores.     

Effect of conidial dispersal of the fungal pathogen Entomophaga maimaiga (Zygomycetes: Entomophthorales) on survival of its gypsy moth (Lepidoptera: Lymantriidae) host

Several researchers have developed a one-generational computer model that simulates infection prevalence of gypsy moth, Lymantria dispar, caterpillars by its fungal pathogen, Entomophaga maimaiga. Inputs required are temperature, humidity, and rainfall records, a measure of fungus resting spore load in the soil, and an estimate of gypsy moth larval density. In a previous study, the model accurately tracked fungal-induced host mortality as long as airborne fungal conidia were allowed to disperse freely over a local area. In 2002, dispersal of conidia and its influence on the impact of the fungus on the gypsy moth was investigated. Gypsy moth densities and fungus resting spore loads were measured in 15 plots within a 3 km area. In 7 of the plots, prevalence of fungal disease was determined weekly by collecting and rearing gypsy moth larvae. Different strategies were used to disperse conidia within the model, and resulting simulated prevalence rates were compared to actual data. Model output was most accurate when airborne conidia were permitted to disperse equally to all plots. Thus, to accurately assess the impact of the fungus in one location, it is necessary to take into account fungal activity throughout the local area.     

Diurnal pattern of death and sporulation in Entomophaga maimaiga-infected Lymantria dispar

Entomophaga maimaiga Humber, Shimazu, et Soper (Zygomycotina: Entomophthoraceae) is a naturally occurring obligate fungal pathogen specific to gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae) larvae. This fungus is considered the most important natural enemy of this pest insect in North America and Asia. A critically important step for the development of E. maimaiga epizootics is the transmission of propagules to healthy larvae, a process known to require high humidity. Some pathogens are known to manipulate the time of day that hosts die so that propagules are produced to maximize chances of survival and thus enhance transmission. The objective of this study was to assess whether E. maimaiga manipulates L. dispar to die at a certain time of day. Laboratory bioassays were conducted at 15 and 20 °C to record the 24‐h activity pattern of death and sporulation exhibited under an L14:D10 photoperiod and 100% r.h. by four isolates of E. maimaiga in its host L. dispar. Events were recorded every 4 h. Our results clearly demonstrate that E. maimaiga‐infected L. dispar larvae die mainly in the afternoon and that the fungus sporulates during the night. The rhythm was independent of the fungal isolate tested and type of spores produced after larval death. By raising the temperature from 15 to 20 °C, the peak death time narrowed and sporulation was initiated earlier at night.     

Location of a lepidopteran specificity region in insecticidal crystal protein CryllA from Bacillus thuringiensis

The Bacilius thuringiensis insecticidal crystal protein CryllA has both high mosquito activity and gypsy moth activity; in contrast CryllB, which is 87% homologous, displays no mosquito activity and has a threefold lower gypsy moth activity. The regions responsible for specificity against gypsy moth (Lymantria dispar) and mosquito (Aedes aegypti) larvae were located by introducing Mlul and Xhol sites into homologous positions within the putative domain ii of both cryllA and cryllB genes, which divided almost equally the respective second domains into three regions. Taking advantage of naturally occurring Nhel and Narl sites that border the putative domain II, a set of seven chimeric proteins were produced by exchanging all combinations of those regions Isetween CryllA and CryllB. Analysis of the toxicity of these chimeric proteins demonstrated that the lepidopteran and dipteran specificity regions of CryllA were not collnear. While the specificity region of CryllA against mosquito larvae involved region 1 and probably also region 2, the specificity region of CryllA against gypsy moth larvae was located within region 2.     

Mechanical thinning to restore oak savanna promoted predator assemblages of gypsy moth pupae in Michigan

相似文献   

Rapid identification of the Asian gypsy moth and its related species based on mitochondrial DNA

The gypsy moth—Lymantria dispar (Linnaeus)—is a worldwide forest defoliator and is of two types: the European gypsy moth and the Asian gypsy moth. Because of multiple invasions of the Asian gypsy moth, the North American Plant Protection Organization officially approved Regional Standards for Phytosanitary Measures No. 33. Accordingly, special quarantine measures have been implemented for 30 special focused ports in the epidemic areas of the Asian gypsy moth, including China, which has imposed great inconvenience on export trade. The Asian gypsy moth and its related species (i.e., Lymantria monocha and Lymantria xylina) intercepted at ports are usually at different life stages, making their identification difficult. Furthermore, Port quarantine requires speedy clearance. As such, it is difficult to identify the Asian gypsy moth and its related species only by their morphological characteristics in a speedy measure. Therefore, this study aimed to use molecular biology technology to rapidly identify the Asian gypsy moth and its related species based on the consistency of mitochondrial DNA in different life stages. We designed 10 pairs of specific primers from different fragments of the Asian gypsy moth and its related species, and their detection sensitivity met the need for rapid identification. In addition, we determined the optimal polymerase chain reaction amplification temperature of the 10 pairs of specific primers, including three pairs of specific primers for the Asian gypsy moth (L. dispar asiatic), four pairs of specific primers for the nun moth (L. monocha), and three pairs of specific primers for the casuarina moth (L. xylina). In conclusion, using our designed primers, direct rapid identification of the Asian gypsy moth and its related species is possible, and this advancement can help improve export trade in China.     

Interpopulation quality in gypsy moths with implications for success of two pupal parasitoids: Brachymeria intermedia (Nees) and Coccygomimus turionellae (L.)*

Abstract.

• 1 Gypsy moth egg masses were collected from innocuous, release and outbreak populations and reared in the laboratory on synthetic diet under identical conditions.
• 2 Outbreak population gypsy moths hatched sooner, were smaller and less fecund than innocuous or release gypsy moths, but had a higher concentration of total carbohydrates in their haemolymph.
• 3 Pupae from each population source were submitted to parasitization by two pupal parasitoids. Emerging B.intermedia, an established parasitoid of the gypsy moth associated with outbreak populations, were largest on outbreak source gypsy moths. C. turionellae, not a usual parasitoid of the gypsy moth, were largest when emerging from innocuous or release population gypsy moths. Implications for population dynamics of the gypsy moth are discussed.

     

Orientation of field populations ofBrachymeria intermedia [Hym.: Chalcididae], to host and host-habitat cues

Brachymeria intermedia (Nees), a pupal parasitoid of the gypsy moth, was caught in the field using plexiglas traps coated with Tangletrap (2). Significantly greater numbers of females were collected in traps baited with gypsy moth pupae than in traps with male or femaleB. intermedia or traps painted yellow.B. intermedia collected in traps during the first 3 weeks of native gypsy moth pupation were primarily female. A preponderance of males were caught during the fourth week. The hyperparasite,Brachymeria compsilurae (Cwfd) was also trapped in small numbers. Gypsy moth pupae were hung in interior and exterior areas of woodland sites. A greater number ofB. intermedia emerged from pupae in woodland edge sites than from pupae in interior woodland sites.     

Comparing two methods for quantifying soil-borne Entomophaga maimaiga resting spores

To improve usability of methods for quantifying environmentally persistent entomophthoralean resting spores in soil, we modified and tested two methods using resting spores (azygospores) of the gypsy moth pathogen Entomophaga maimaiga. Both methods were effective for recovering resting spores at concentrations >100 resting spores/g dry soil. While a modification of a method originally described by Weseloh and Andreadis (2002) recovered more resting spores than a modified method based on Percoll density gradients, the ability to estimate true densities from counts was similar for both methods. Regression equations are provided for predicting true resting spore densities from counts, with R² values for both methods ?0.90.     

Parasitoid complex of the Asian gypsy moth (Lymantria dispar) (Lepidoptera: Lymantriidae) in Primorye Territory,Russian Far East

A study of the moth parasitoid complex attacking gypsy moth, Lymantria dispar (L.) was carried out in Primorye territory, Russia Far East. Season-long collections at three sites in the Vladivostok area and collections at seven sites of central region of Primorye revealed the 18 primary parasites: one egg parasitoid, 11 larval parasitoids, one larval-pupal parasitoid, one parasitic nematode, one ectoparasitoid, and three diseases including NPV (nuclear polyhedrosis virus) and Entomophaga maimaiga. Phobocampe species (Ichneumonidae) dominated the parasitoid complex, parasitizing 5.5% of the larvae in the Vladivostok area and 9.3% in central Primorye, rates which are much higher than those detected from other Asiatic regions of Russia and Northeastern Asia. The insect parasitoid complex was found to be somewhat depauperate. The 11.8% average total parasitism in eastern Russian is similar to the 12% recorded in the US. Both regions have large gypsy moth outbreaks, but other factors including diseases have compensated for the rather low mortality exerted by the parasitoid complex in the Russian Far East.     

Estimating the susceptibility of tree species to attack by the gypsy moth, Lymantria dispar

ABSTRACT.

• 1 Numbers of gypsy moth larvae feeding on each of 922 randomly sampled trees in a Quercus—Acer—Fraxinus forest in southwestern Quebec, Canada were counted in 1979 and in 1980 to quantify the larval feeding preferences as observed in the field for eighteen deciduous and one coniferous tree species at the northern range limit of the gypsy moth.
• 2 Both the diameter at breast height (dbh) and the estimated foliage biomass of the sampled trees were used to calculate the relative proportions of foliage represented by each of the nineteen tree species in the forest canopy. With these data on availability and utilization of the tree species by the gypsy moth larvae an Ivlev-type electivity index was used to quantify the larval feeding preferences. These preferences observed in the field define the susceptibility of a tree species to attack by the gypsy moth.
• 3 The feeding preferences calculated using estimated foliage biomass were comparable to the simpler calculation based on dbh (Spearman's rho = 0.79; P= 0.0001). The dbh-based feeding preferences remained almost unchanged in 1979 and 1980 (Spearman's rho = 0.83; P= 0.0001).
• 4 The composite 1979—80, dbh-based feeding preferences show Quercus rubra, Populus grandidentata, Ostrya virginiana, Amelanchier spp. and Acer saccharum were preferentially attacked by gypsy moth. Prunus serotina, Betula lutea, Acer rubrum, A. pensylvanicum, Fraxinus americana, Ulmus rubra, P. pensylvanicum and B. papyrifera were avoided. All nineteen tree species were, however, utilized to at least some degree by gypsy moth larvae.
• 5 These results quantitatively affirm and clarify earlier reports of gypsy moth feeding preferences in North America and Eurasia. The advantages and limitations of using an electivity index to estimate the susceptibility of different tree species to attack by folivores like the gypsy moth are discussed.

     

Variation in the ability of larvae of phytophagous insects to develop on evolutionarily unfamiliar plants: a study with gypsy moth Lymantria dispar and Eucalyptus

• 1 By examining variation in the abilities of polyphagous insects to develop on host plants with secondary metabolites that they have never encountered previously, we may be able to gain some insights into the nature of evolution of biochemical mechanisms to process plant secondary metabolites by phytophagous insects.
• 2 The present study aimed to examine variation in the ability of gypsy moth larvae Lymantria dispar (Lymantriidae) to complete development on different species of the plant genus Eucalyptus (Myrtaceae). Leaves of at least some Eucalyptus species contain formylated phloroglucinol derivatives. These are secondary metabolites that are evolutionarily unfamiliar to the gypsy moth.
• 3 Larvae of gypsy moth showed extremely variable responses in larval performance between Eucalyptus species, between individual trees within host plant species, between moth populations, and between individuals within moth populations.
• 4 Larval survivorship was in the range 0–94%, depending on the host. Failure of at least some larvae to complete development on some Eucalyptus species indicates that gypsy moth larvae have a limited ability to process secondary metabolites in eucalypt leaves.
• 5 At least some individuals, however, appear to already possess biochemical mechanisms that process the secondary metabolites in leaves of Eucalyptus species, and therefore the abilities of larvae to complete development on phylogenetically and chemically unfamiliar hosts are already present before the gypsy moth encounters these potential hosts.