Dynamics Of Moth Research Articles

Characterization of a Novel RNA Virus Discovered in the Autumnal Moth Epirrita autumnata in Sweden

A novel, 10 kb RNA virus—tentatively named ‘Abisko virus’—was discovered in the transcriptome data of a diseased autumnal moth (Epirrita autumnata) larva, as part of a search for the possible causes of the cyclical nature and mortality associated with geometrid moth dynamics and outbreaks in northern Fennoscandia. Abisko virus has a genome organization similar to that of the insect-infecting negeviruses, but phylogenetic and compositional bias analyses also reveal strong affiliations with plant-infecting viruses, such that both the primary host origin and taxonomic identity of the virus remain in doubt. In an extensive set of larval, pupal, and adult autumnal moth and winter moth (Operophtera brumata) outbreak samples, the virus was only detected in a few adult E. autumnata moths as well as the single larval transcriptome. The Abisko virus is therefore unlikely to be a factor in the Fennoscandia geometrid population dynamics.

Impact of Entomophaga maimaiga (Entomophthorales: Entomophthoraceae) on outbreak gypsy moth populations (Lepidoptera: Erebidae): the role of weather.

The fungal pathogen Entomophaga maimaiga Humber, Shimazu, and Soper is prevalent in gypsy moth [Lymantria dispar (L.)] populations throughout North America. To understand how weather-related variables influence gypsy moth-E. maimaiga interactions in the field, we measured fungal infection rates at 12 sites in central Pennsylvania over 3 yr, concurrently measuring rainfall, soil moisture, humidity, and temperature. Fungal mortality was assessed using both field-collected larvae and laboratory-reared larvae caged on the forest floor. We found significant positive effects of moisture-related variables (rainfall, soil moisture, and relative humidity) on mortality due to fungal infection in both data sets, and significant negative effects of temperature on the mortality of field-collected larvae. Lack of a clear temperature relationship with the mortality of caged larvae may be attributable to differential initiation of infection by resting spores and conidia or to microclimate effects. These relationships may be helpful in understanding how gypsy moth dynamics vary across space and time, and in forecasting how the gypsy moth and fungus will interact as they move into warmer or drier areas, or new weather conditions occur due to climate change.

Consequences of asymmetric competition between resident and invasive defoliators: A novel empirically based modelling approach

Invasive species can have profound effects on a resident community via indirect interactions among community members. While long periodic cycles in population dynamics can make the experimental observation of the indirect effects difficult, modelling the possible effects on an evolutionary time scale may provide the much needed information on the potential threats of the invasive species on the ecosystem. Using empirical data from a recent invasion in northernmost Fennoscandia, we applied adaptive dynamics theory and modelled the long term consequences of the invasion by the winter moth into the resident community. Specifically, we investigated the outcome of the observed short-term asymmetric preferences of generalist predators and specialist parasitoids on the long term population dynamics of the invasive winter moth and resident autumnal moth sharing these natural enemies. Our results indicate that coexistence after the invasion is possible. However, the outcome of the indirect interaction on the population dynamics of the moth species was variable and the dynamics might not be persistent on an evolutionary time scale. In addition, the indirect interactions between the two moth species via shared natural enemies were able to cause asynchrony in the population cycles corresponding to field observations from previous sympatric outbreak areas. Therefore, the invasion may cause drastic changes in the resident community, for example by prolonging outbreak periods of birch-feeding moths, increasing the average population densities of the moths or, alternatively, leading to extinction of the resident moth species or to equilibrium densities of the two, formerly cyclic, herbivores.

Effects of biological control on long-term population dynamics: identifying unexpected outcomes

Summary 1. Attempts to control natural systems through management have often met with success but have also led to unexpected and often undesirable outcomes. Unfortunately, the ultimate result of such management programmes may not be apparent until long after the control efforts have begun. This is particularly true for forest-defoliating species that exhibit longperiod cycles such as the invasive gypsy moth Lymantria dispar, which causes widespread damage in some years but is rare in other years. 2. We studied the effects of two commonly employed biocontrol agents on gypsy moth dynamics using a series of field-tested and empirically parameterized mathematical models, which allowed us to examine various potential control strategies and assess long-term effects. 3. In a non-spatial model, addition of either a manufactured version of the same baculovirus involved in natural epizootics, or a general bioinsecticide Bacillus thuringiensis var. kurstaki (Btk), which directly kills a fraction of the population, decreases the amplitude between boom and bust portions of the cycle. 4. However, ill-planned biocontrol applications can result in increased gypsy moth densities over the long term. Thus, control efforts may maintain pest populations at unexpectedly high numbers, which could result in constant forest defoliation. 5. In a spatial two-patch model, where one patch is sprayed and the other is left untreated, there is also considerable danger that migration between patches may drive the unsprayed population to levels that could result in constant forest defoliation. 6. Synthesis and applications: Perturbations to host–pathogen systems may have unexpected results, driving and maintaining populations at multiple levels including those far from desired management goals. It is often assumed that any control strategy that decreases pest populations in the short term is beneficial, but our results show that undesirable outcomes may often occur. The mechanisms we describe apply to many systems that undergo population cycles or outbreaks regulated by density-dependent processes, and in which disease or pesticide application is used for pest control. We suggest that successful management strategies should closely monitor population responses immediately following the control application to ensure that pest populations are not being maintained at artificially high levels compared with historic data.

Effects of climate and density-dependent factors on population dynamics of the pine processionary moth in the Southern Alps

Forest pest populations can fluctuate dramatically in relation to climate and density-dependent factors. Although the distributional range of the pine processionary moth Thaumetopoea pityocampa (Lepidoptera Notodontidae) appears to be expanding northward and upslope with climate warming, the relative importance of climate and endogenous, density-dependent factors has not been clearly documented. We analyzed the population dynamics of the moth using long-term data from two provinces in the Southern Alps (Trento: 1990–2009, Bolzano/Bozen: 1975–2011) to evaluate the relative importance of climate and density-dependent factors as regional drivers. Both summer temperatures and rainfall significantly affected population growth rate, with different outcomes depending on the local conditions. Although previous studies indicated that low winter temperatures have negative effects on insect performance, our analyses did not show any negative effect on the population dynamics. A negative density dependent feedback with a 1-year lag emerged as the most important factor driving the population dynamics in both regions. Potential mechanisms explaining the observed negative density feedback include deterioration of host quality, increased mortality caused by pathogens, and increase of prolonged diapause as an adaptive mechanism to escape adverse conditions.

An innovative multistage, physiologically structured, population model to understand the European grapevine moth dynamics

We present a multistage, physiologically structured, population model for studying the dynamics of one of the most important grapevine insect pests. Growth of the population at each stage is modeled considering the climatic variations and the grape variety. A result of existence and uniqueness of solutions is presented for this original hyperbolic system as well as simulations of experimental field data.

Spatial population structure of a specialist leaf‐mining moth

1. The spatial structure of natural populations may profoundly influence their dynamics. Depending on the frequency of movements among local populations and the consequent balance between local and regional population processes, earlier work has attempted to classify metapopulations into clear-cut categories, ranging from patchy populations to sets of remnant populations. In an alternative, dichotomous scheme, local populations have been classified as self-sustaining populations generating a surplus of individuals (sources) and those depending on immigration for persistence (sinks). 2. In this paper, we describe the spatial population structure of the leaf-mining moth Tischeria ekebladella, a specialist herbivore of the pedunculate oak Quercus robur. We relate moth dispersal to the distribution of oaks on Wattkast, a small island (5 km(2)) off the south-western coast of Finland. 3. We build a spatially realistic metapopulation model derived from assumptions concerning the behaviour of individual moths, and show that the model is able to explain part of the variation in observed patterns of occurrence and colonization. 4. While the species was always present on large trees, a considerable proportion of the local populations associated with small oaks showed extinction-recolonization dynamics. The vast majority of moth individuals occur on large trees. 5. According to model predictions, the dominance of local vs. regional processes in tree-specific moth dynamics varies drastically across the landscape. Most local populations may be defined broadly as 'sinks', as model simulations suggest that in the absence of immigration, only the largest oaks will sustain viable moth populations. Large trees in areas of high oak density will contribute most to the overall persistence of the metapopulation by acting as sources of moths colonizing other trees. 6. No single 'metapopulation type' will suffice to describe the oak-moth system. Instead, our study supports the notion that real populations are often a mix of earlier identified categories. The level to which local populations may persist after landscape modification will vary across the landscape, and sweeping classifications of metapopulations into single categories will contribute little to understanding how individual local populations contribute to the overall persistence of the system.

Green oak leaf roller moth dynamics: An application of discrete time mathematical models

Discrete mathematical model is selected for description of green oak leaf roller ( Tortrix viridana L.) population dynamics. Experimental data set from Rubtsov [Rubtsov, V.V., 1992. Models of Oscillation Processes in Forest Ecosystems, Forest Institute, Moscow, Russian Federation, p. 39 (in Russian)] is analyzed from the standpoint of phenomenological theory of forest insect population dynamics [Isaev, A.S., Khlebopros, R.G., Nedorezov, L.V., Kiselev, V.V., Kondakov, Yu. P., 1984. Dynamics of Forest Insects Populations, USSR, Nauka, Novosibirsk, p. 224 (in Russian); Isaev, A.S., Khlebopros, R.G., Nedorezov, L.V., Kiselev, V.V., Kondakov, Yu.P., Soukhovol'sky, V.G., 2001. Population Dynamics of Forest Insects, Russian Federation, Nauka, Moscow, p. 347 (in Russian)]. For checking hypotheses confidence for fitting of experimental time series, Moran–Ricker model, Maynard Smith–Slatkin model, and some others are used. Selection of statistical criteria for estimating parameter's values is discussed. In addition, probabilities of realizations of several dynamical regimes are estimated.

Cohabitation and predation by insectivorous bats on eared moths in subterranean roosts

Most regions of the world support moth species that use caves as diurnal roosts and/or as overwintering and mating sites. Although subterranean roosts are often also occupied by insectivorous bats, nothing is known about moth–bat interaction at these sites. The frequency of cohabitation and the dynamics of moth–bat interaction at roosts were examined during surveys at 30 known bat roosts in eastern Australia; 15 disused mines and 15 natural caves. Moths and bats cohabited in 20 roosts (67%); however, only two species of eared moths, Speiredonia spectans and S. mutabilis (Noctuidae), were observed. These large (wingspan up to 75 mm) species show a classic escape response to ultrasound. Moths used roosts occupied by bats with both frequency modulated (FM) (four species) and constant frequency (CF) (two species) echolocation calls. Signal frequencies of these bats had ranges of 23–25 and 44–71 kHz. Moths were absent from roosts occupied by high-frequency (>140 kHz) CF bats. Predator–prey interaction was assessed by studying a sub-sample of six roosts occupied by S. spectans and the horseshoe bat Rhinolophus megaphyllus. Speiredonia spectans and R. megaphyllus cohabited roosts throughout the year. Bats captured and consumed moths in these roosts. The numbers of moth wings on the floor of roosts were counted to assess rates of predation. Bats consumed 209 moths at the six roosts over a 12-month period, representing 19% of the moth population at the start of the study. The study establishes that moth–bat cohabitation of roosts is relatively common in eastern Australia and that bats do capture moths in these sites. Bat predation seems to be a significant source of mortality of moths that occupy subterranean roosts.

Bottom‐up and top‐down effects in a tritrophic system: the population dynamics of Plutella xylostella (L.)–Cotesia plutellae (Kurdjumov) on different host plants

Abstract. 1. The effects of host‐plant resistance on the population dynamics of the Diamondback moth, Plutella xylostella L., and its solitary parasitoid, Cotesia plutellae (Kurdjumov), were studied in replicated time‐series experiments.2. Host‐plant resistance did not affect the equilibrial abundance of the Diamondback moth, but it affected the dynamics of Diamondback moth populations.3. The mean population size of Diamondback moth showed no significant difference between Brassica rapa (a susceptible host plant) and Brassica napus (a partially resistant host plant) either in the presence or absence of the parasitoid.4. Time‐series analysis suggests that the dynamics of Diamondback moth on B. rapa were underpinned by delayed density‐dependent processes. In contrast, the dynamics of the moth on B. napus were influenced by a direct density‐dependent process.5. Although measures of short‐term parasitism showed a significantly higher rate of parasitism by C. plutellae on Diamondback moth feeding on B. napus compared with B. rapa, this individual performance does not translate into differences in the population dynamics. Analysis shows no significant difference in the persistence time of the population‐level interaction between the host and parasitoid on the two different host plants.

Identifying weather‐related covariates controlling grape berry moth dynamics*

The use of plant protection products requires precise forecasting of the susceptible larval stages of the grape berry moths Lobesia botrana and Eupoecilia ambiguella as these dynamics vary with the weather pattern of a particular year. The objective of this research has been to partition the relative influence of specific climatic factors on the dynamics of these insects. Data taken from 7 years of continuous monitoring of the flight occurrence of male adults, and of the following development stages (i.e. eggs and larvae), was analysed by a generalized Leslie process. The model type reduces the population to three probabilities: development, survival and fertility. Each probability can be modelled as a function of the associated weather factors, while the functional relationships and the model parameters are established. The analysis started with the simplest approach and, in a step‐by‐step procedure, model complexity was added until a sufficient fit to the overall data set was achieved. Within the magnitude of the model, development rates were controlled solely by temperature, but the duration of single stages (i.e. survival) was found to be affected by a combination of temperature and relative humidity. The model represents a combination of mechanisms within a season with empirical components.

What causes generation cycles in populations of stored‐product moths?

Summary 1. Populations of stored‐products moths such as the Indian meal moth (Plodia interpunctella) frequently show generation cycles, fluctuations with a period of approximately one generation. 2. Three age‐structured models of stored‐product moth dynamics were investigated to see which best accounted for the observed period and pattern of Plodia dynamics. 3. A model of Gurney, Nisbet & Lawton (1983) was modified to match Plodia biology. The model assumes uniform competition amongst larvae. It predicted generation cycles, but of too long a period and with the wrong larval cohort structure. 4. The introduction of asymmetric competition (young larvae more sensitive to resource depletion but exerting weaker competitive effects) could produce generation cycles but for parameters appropriate to Plodia predicted cycles with a period of half a generation. 5. Introducing egg cannibalism to the asymmetric competition model led to the prediction of generation cycles of the right period and cohort structure for Plodia parameters.

Forest Type Affects Predation on Gypsy Moth (Lepidoptera: Lymantriidae) Pupae in Japan

A compilation of historical defoliation data from Hokkaido, Japan confirms previous reports that plantations of Larix leptolepis Gordon are more susceptible to defoliation by the gypsy moth, Lymantria dispar (L.), than are natural forests dominated by Quercus crispula Thumb. In this study, we compared levels of predation on laboratory-reared pupae deployed at a natural Quercus stand, a plantation of Betula platyphylla Hara, and a plantation of L. leptolepis . Predation was highest in the natural Quercus stand, lowest in the Larix plantation and intermediate in the Betula plantation. Counts of small mammals in traps indicated that populations of Apodemus argenteus, Apodemus speciosus ainu , and Clethrionomys rufocanus bedfordiae were most abundant in the oak forest, least abundant in the Larix plantation, and intermediate in the Betula plantation. We hypothesize that variation in the abundance of small mammals and their predation on gypsy moth pupae during periods of low gypsy-moth densities is a partial cause of the variation among stand types in their susceptibility to defoliation by gypsy moth. We also argue that predation on gypsy moth pupae by small mammals in natural oak forests is more important to gypsy moth dynamics than previously considered and that considerable similarities may exist between gypsy moth dynamics in Japan and North America.

Does Thinning Affect Gypsy Moth Dynamics?

Abstract In northeastern U.S. forests there is considerable variation in susceptibility (defoliation potential) and vulnerability (tree mortality) to gypsy moth (Lymantria dispar [L.]). Thinning has been suggested as a way to reduce susceptibility and/or vulnerability. We evaluated how thinning affected the dynamics of gypsy moth populations by experimentally thinning half of each of eight oak-mixed hardwood stands in the Central Appalachians. Population dynamics of gypsy moth were monitored using yearly counts of egg masses, numbers of larvae hatching per mass, estimates of larval density, and weekly collections of larvae and pupae which were reared to quantify mortality due to parasitoids and disease. During the 8 yr study, three stands were heavily defoliated by outbreak populations of gypsy moth, three were sprayed with pesticides accidentally, and two were not disturbed. Egg-mass densities were slightly lower in the thinned portions of the undisturbed stands, but thinning had little or no effect on gypsy moth densities in defoliated and sprayed stands. Variation in mortality of gypsy moth caused by parasitoids and disease was related to variation in egg-mass densities in the current and/or preceding years. After adjusting for the effect of gypsy moth density, thinning had no significant effect on mortality from parasitoids or pathogens. We conclude that any reduction in egg mass densities as a result of thinning is likely related to the reduction in foliar biomass, not increased natural enemy activity. For. Sci. 44(2):239-245.

Dynamic Behavior of Douglas-Fir Tussock Moth Populations in the Pacific Northwest

Abstract Larval densities of the Douglas-fir tussock moth (Orgyia pseudotsugata [McDunnough] [Lepidoptera:Lymantriidae]) were monitored annually to construct population time series in five different forest ecosystems. The time series were generated in parts of five national forests in three geographical provinces: the northern Blue Mountains of northeastern Oregon, the southern Cascade Range of south-central Oregon, and the northern Cascade Range of north-central Washington. The five series ranged in length from 12 to 23 yr and represented the broad numerical behavior of tussock moth populations in those provinces. Time series with the most variable fluctuations were recorded in the Blue Mountains, a region with a long history of regular tussock moth outbreaks. The least variable series was in the southern Cascades, an area with no previously documented outbreaks. Characteristics of series in the Blue Mountains and the northern Cascades were significantly correlated with one another, but not with those of the series in the southern Cascades. The density-dependent structure of each time Series was examined by autocorrelation and partial autocorrelation functions, which indicated that fluctuations were quasi-periodic, even at low densities, and that the most significant autoregressive process was a second-order feedback. Each time series was fit with a linear second- order autoregressive model and a discrete nonlinear logistic model with a single time delay. The models, based on density-dependent processes associated with preceding insect generations, accounted for an average of 44.6% of the variation in the time series. The remaining 55.4% of variation was due to unknown density-independent factors related to different years in the series. The models showed that the principal dynamics of tussock moth populations are generated by direct and delayed density-dependent processes. In outbreak-prone ecosystems, like those in the Blue Mountains and the northern Cascades, the primary regulation of insect numbers is by delayed feedback processes that result in populations sometimes having extreme fluctuations in density. Conversely, in nonoutbreak ecosystems, as in the southern Cascades, feedback is more balanced between both direct and delayed processes that stabilize populations at lower densities. External factors, like weather, also may influence the numerical behavior of populations to some extent, but their specific contribution to tussock moth dynamics is largely unknown. For. Sci. 42(2):182-191.

Identifying Density-Dependent Processes: A Comment on the Regulation of Winter Moth

Long-term population studies provide the foundation against which ecological hypotheses on mechanisms of population regulation can be accepted or refuted. One of the classic long-term population studies has focused on the winter moth, Operophtera brumata (L.) (Lepidoptera: Geometridae) and its associated natural enemies. Detailed population studies have been carried out in a native area at Wytham Wood, Oxfordshire (Varley & Gradwell 1963, 1968; Varley, Gradwell & Hassell 1973) and in regions where the moth has been introduced into Canada (Embree 1965, 1991; Roland 1986, 1988). Different regulatory mechanisms have emerged from these studies. At Wytham Wood, mortality occurring in the soil, mainly due to pupal predators, acts in a density-dependent manner and seems to be the primary regulatory process (Varley et al. 1973). In Canada, however, pupal predation seemed much less important and an introduced tachinid parasitoid, Cyzenis albicans (Fall.) (Diptera: Tachinidae), was identified as the main density-dependent process (Embree 1966). More recently, Roland (1986, 1988 1990, 1994) has presented yet further interesting interpretations of the winter moth population dynamics based on his studies at Mount Tolmie Park, British Columbia, Canada. In his most recent paper (Roland 1994), data are presented on the relationships between mortality and the estimated density at different stages in the life cycle between 1982 and 1990 (Fig. 1). During this period the winter moth population declined from initial high levels to relatively low levels (for the final 7 years). In order to determine the importance of these mortalities to the winter moth dynamics, Roland selected only the final six 'equilibrium' years of data for his analysis (Fig. 2). On the basis of this, he concluded that egg and larval mortality (k fec and klarv) were not densitydependent and therefore not important in regulating the winter moth population. Pupal predation by ground beetles, however, did appear to be strongly density-dependent and was thus inferred as the primary cause of stability in the British Columbia winter moth population. In this note, we question this conclusion. In particular, we caution against looking for specific densitydependent processes from relatively stationary populations. By considering all the available data (198290), we show that egg and larval mortality (k fec and klarv), in contrast to pupal mortality (kpred), are densitydependent and could have a major impact on the winter moth population regulation.

Spatial Synchrony in the Dynamics of Moth and Aphid Populations

1. We report patterns of intraspecific spatial synchrony (cross-correlation with lag zero) in the dynamics of British moths and aphids sampled at 57 and 21 localities throughout the UK. 2. Spatial synchrony was substantially higher in aphids than in moths. In both taxa, spatial synchrony declined with increasing distance between conspecific populations, but synchrony remained positive at all distances up to 800 km. 3. Species with large slopes (>2) of the spatial variance-mean regression had spatially asynchronous dynamics, as predicted by a theoretical model. 4. In noctuid moths and in aphids, but not in geometrid moths, there was a significant positive correlation between the degree of spatial synchrony and the level of temporal variability in local populations. 5. We discuss the two main hypotheses about the causes of spatial synchrony, migration and regional stochasticity (spatially correlated weather conditions). We conclude that our results on large-scale spatial synchrony in moths and aphids are better explained by regional stochasticity than by migration.

A comparative evaluation of models of cinnabar moth dynamics.

1. A complex model of cinnabar moth dynamics proposed by Dempster and Lakhani (1979) with 23 parameters is reduced to a single equation with five parameters, and the behaviour of the reduced model shown to explain most features of the full model. 2. The efficiency of the full model is compared with the reduced model and with two even simpler models (the two parameter discrete logistic and a four parameter model based on a step-function for mortality) in their abilities to describe time series data of cinnabar moth population densities from Weeting Heath. Models with more parameters were not significantly better than few-parameter models in describing population trajectories. 3. Models that included a driving variable (in this case observed rainfall data) were no better at describing the data than simpler models without driving variables. It appears, therefore, that the routine inclusion of driving variables may be counterproductive, unless there is compelling empirical or theoretical evidence of their importance and the mode of action of the driving variables can be modelled mechanistically. For example, the regression model used to describe the relationship between rainfall and plant biomass in Dempster and Lakhani (1979), breaks down if rainfall is assumed to be constant, because there is no explicit model for the regulation of plant biomass. 4. The parameter values of the cinnabar-ragwort interaction suggest that cinnabar moth dynamics may be chaotic. Whether or not field data exhibit chaos or environmental stochasticity (or a mixture of both) is impossible to determine from inspection of time series data on population density. There is an urgent need for experimental and theoretical protocols to disentangle these two sources of population fluctuation.

THE INFLUENCE OF CONSTANT TEMPERATURES ON THE NON-DIAPAUSE DEVELOPMENT OF HYSSOPUS THYMUS (HYMENOPTERA: EULOPHIDAE)

AbstractThe influence of constant temperatures on the non-diapause development of Hyssopus thymus was studied and the results of these studies are presented. A lower threshold for development of less than 12 °C and an upper threshold of about 32 °C were determined. Mean times for and rates of development at different temperatures are presented for all developmental stages. The egg is the stage most sensitive to temperature change. Regression equations describing the relationship between the rate of development and temperature for these stages are given and a thermal constant (K) of about 190 degree-days is calculated for total development. This constant is not applicable to naturally fluctuating temperatures. The results of these studies are discussed in relation to the potential impact of H. thymus on European pine shoot moth dynamics under different climatic conditions. It is concluded that H. thymus should be more effective in warmer seasons and at lower latitudes.