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Scenario analysis has emerged as a key tool to analyze complex and uncertain future socio-ecological developments. However, currently existing global scenarios (narratives of how the world may develop) have neglected biological invasions, a major threat to biodiversity and the economy. Here, we use a novel participatory process to develop a diverse set of global biological invasion scenarios spanning a wide range of plausible global futures through to 2050. We adapted the widely used “two axes” scenario analysis approach to develop four families of four scenarios each, resulting in 16 scenarios that were later clustered into four contrasting sets of futures. Our analysis highlights that socioeconomic developments and technological innovation have the potential to shape biological invasions, in addition to well-known drivers, such as climate and human land use change and global trade. Our scenarios partially align with the shared socioeconomic pathways created by the climate change research community. Several factors that drive differences in biological invasions were underrepresented in the shared socioeconomic pathways; in particular, the implementation of biosecurity policies. We argue that including factors related to public environmental awareness and technological and trade development in global scenarios and models is essential to adequately consider biological invasions in global environmental assessments and thereby obtain a more integrative picture of future social–ecological developments.

•Human activities increasingly disperse insect species beyond their historical ranges.•Understanding human-mediated dispersal is crucial for predicting future invasions.•Three phases of dispersal uniquely affect the dynamics and geography of invasions.•Human activities influencing dispersal phases vary in frequency, scale and direction.•Different sets of species traits are selected by the three dispersal phases.

Invasions by insects introduced via international trade continue to cause worldwide impacts. Surveillance programs using traps baited with host volatiles and pheromones can detect incursions of nonnative species. We report on two experiments executed to determine if attractants for several insect species can be combined without compromising trap catches and detection ability of target species. In the first experiment, we tested the effect of bark beetle pheromones (plus α-pinene) and trap contact with foliage on trap catches of the brown marmorated stink bug Halyomorpha halysStål (Hemiptera: Pentatomidae) in traps baited with a mixture of bisabolenes and methyl (E,E,Z)-2,4,6-decatrienoate. Trap capture of H. halysadults was greater in traps not in contact with foliage, and the bark beetle pheromones ipsenol and ipsdienol did not affect trap capture of H. halys. In the second experiment, we tested the effects of multi-lure interactions among the primary host attractants α-pinene and ethanol, and the pheromones monochamol, ipsenol, ipsdienol, lanierone, and the H. halyscompounds, on trap captures of various forest and agricultural insect pests. Specifically, we targeted Monochamusspp. (Coleoptera: Cerambycidae), Ipsspp. (Coleoptera: Scolytinae) and H. halys. We found that a combination of all lures did not catch significantly lower numbers of Monochamus carolinensisOlivier, Monochamus scutellatusSay (Coleoptera: Cerambycidae), and Ips piniSay (Coleoptera: Scolytidae) than lure combinations missing components although removal of both lanierone and ipsdienol somewhat increased catches of Ips grandicollisEichhoff (Coleoptera: Curculionidae). Our results support the use of traps baited with a full combination of these attractants in surveillance programs. This should reduce costs and increase detection rates of a wider range of conifer forest pests and H. halys.

Like most pines, radiata pine (Pinus radiataD.Don) is conventionally considered resistant to defoliation by European gypsy moth, i.e. it is only consumed by late larval stages, or when susceptible species are not available or are scarce. The ability of this moth to complete development on this host in field conditions has never been reported. A gypsy moth outbreak in a pure radiata pine plantation was observed in north-western Spain, where this insect is endemic. During the 2 years of outbreak culmination (2012 and 2013), approximately 46 ha of radiata pine were severely defoliated (>75 % of leaf area removed) and no defoliation was evident in nearby stands of susceptible species. Large numbers of egg masses were present on stems of pine trees. Larvae were observed feeding exclusively on radiata pine needles beginning with the first instar and continuing to pupation. Nearly 100 % tree mortality occurred in stands severely defoliated. The occurrence of a European gypsy moth outbreak in a pure radiata pine plantation contradicts previous observations that larvae of this species cannot complete development in stands comprised entirely of pines. These results suggest that European strains of the gypsy moth hold great potential for damage to commercial radiata pine plantations where this species is utilised in plantation forestry, such as in New Zealand or Australia.

The ecological impacts of modern global climate change are detectable in a wide variety of phenomena, ranging from shifts in species ranges to changes in community composition and human disease dynamics. So far, however, little attention has been given to temporal changes in spatial synchrony—the coincident change in abundance or value across the landscape—despite the importance of environmental synchrony as a driver of population trends and the central role of environmental variability in population rescue and extinction. Here we demonstrate that across North America, spatial synchrony of a significant proportion of 49 widespread North American wintering bird species has increased over the past 50 years—the period encompassing particularly intense anthropogenic effects in climate—paralleling significant increases in spatial synchrony of mean maximum air temperature. These results suggest the potential for increased spatial synchrony in environmental factors to be affecting a wide range of ecological phenomena. These effects are likely to vary, but for North American wildlife species, increased spatial synchrony driven by environmental factors may be the basis for a previously unrecognized threat to their long-term persistence in the form of more synchronized population dynamics reducing the potential for demographic rescue among interacting subpopulations.

Despite the substantial impacts of nonindigenous plant pests and weeds, relatively little is known about the pathways by which these organisms arrive in the U.S. One source of such information is the Port Information Network (PIN) database, maintained by the U.S. Department of Agriculture, Animal and Plant Health Inspection Service (APHIS) since 1984. The PIN database is comprised of records of pests intercepted by APHIS personnel during inspections of travelers’ baggage, cargo, conveyances and related items arriving at U.S. ports of entry and border crossings. Each record typically includes the taxonomic identify of the pest, its country of origin, and information related to the commodity and interception site. We summarized more than 725,000 pest interceptions recorded in PIN from 1984 to 2000 to examine origins, interception sites and modes of transport for nonindigenous insects, mites, mollusks, nematodes, plant pathogens and weeds. Roughly 62% of intercepted pests were associated with baggage, 30% were associated with cargo and 7% were associated with plant propagative material. Pest interceptions occurred most commonly at airports (73%), U.S.-Mexico land border crossings (13%) and marine ports (9%). Insects dominated the database, comprising 73 to 84% of the records annually, with the orders Homoptera, Lepidoptera and Diptera collectively accounting for over 75% of the insect records. Plant pathogens, weeds and mollusks accounted for 13, 7 and 1.5% of all pest records, respectively, while mites and nematodes comprised less than 1% of the records. Pests were intercepted from at least 259 different locations. Common origins included Mexico, Central and South American countries, the Caribbean and Asia. Within specific commodity pathways, richness of the pest taxa generally increased linearly with the number of interceptions. Application of PIN data for statistically robust predictions is limited by nonrandom sampling protocols, but the data provide a valuable historical record of the array of nonindigenous organisms transported to the U.S. through international trade and travel.Despite the substantial impacts of nonindigenous plant pests and weeds, relatively little is known about the pathways by which these organisms arrive in the U.S. One source of such information is the Port Information Network (PIN) database, maintained by the U.S. Department of Agriculture, Animal and Plant Health Inspection Service (APHIS) since 1984. The PIN database is comprised of records of pests intercepted by APHIS personnel during inspections of travelers’ baggage, cargo, conveyances and related items arriving at U.S. ports of entry and border crossings. Each record typically includes the taxonomic identify of the pest, its country of origin, and information related to the commodity and interception site. We summarized more than 725,000 pest interceptions recorded in PIN from 1984 to 2000 to examine origins, interception sites and modes of transport for nonindigenous insects, mites, mollusks, nematodes, plant pathogens and weeds. Roughly 62% of intercepted pests were associated with baggage, 30% were associated with cargo and 7% were associated with plant propagative material. Pest interceptions occurred most commonly at airports (73%), U.S.-Mexico land border crossings (13%) and marine ports (9%). Insects dominated the database, comprising 73 to 84% of the records annually, with the orders Homoptera, Lepidoptera and Diptera collectively accounting for over 75% of the insect records. Plant pathogens, weeds and mollusks accounted for 13, 7 and 1.5% of all pest records, respectively, while mites and nematodes comprised less than 1% of the records. Pests were intercepted from at least 259 different locations. Common origins included Mexico, Central and South American countries, the Caribbean and Asia. Within specific commodity pathways, richness of the pest taxa generally increased linearly with the number of interceptions. Application of PIN data for statistically robust predictions is limited by nonrandom sampling protocols, but the data provide a valuable historical record of the array of nonindigenous organisms transported to the U.S. through international trade and travel.

Historical records of the incidence of defoliation caused by the beech caterpillar, Quadricalcarifera punctatella(Motschulsky) in northern Japanese prefectures from 1910–1993 were used to characterize the cyclicity and synchrony of outbreaks. Cyclicity and synchrony were quantified using standard Box-Jenkins time series methods as well as spectral analysis and simple Markov models. Statistical analysis of these records indicated the presence of quasi-periodic behavior with 8–11 yr between outbreaks. Outbreaks tended to occur synchronously among different prefectures, though the onset of outbreaks was typically lagged. This study illustrates the use of specific statistical methods for characterizing cyclicity and synchrony from crude records of the presence/absence of outbreaks.

AbstractLarval color morph frequencies were observed in the offspring of hybrid and backcross matings between pure Choristoneura occidentalisFreeman and C. retiniana(Walsingham) laboratory lines. Offspring of hybrid matings were mostly brown larval forms but intermediate and green larvae also occurred. Progeny of backcrosses to C. occidentaliswere almost entirely brown larvae. Backcrosses to C. retinianayielded mostly green larvae but a substantial number of intermediate and brown larvae also were in the progeny. There was no evidence that larval color is sex-linked or sex-limited.

AbstractAn analysis of the times to emergence in three sparse populations of Choristoneuraspp. in western North America indicates that there was considerable variation in the calculated threshold of development among populations. Also, the number of heat units required to effect the emergence of any specified proportion of the population varied considerably among populations. The pattern of intra-population variation in times to emergence is such that the within-family variation was much larger than the among-family variation in the two populations from areas in which white fir is the only host. In the other population, from an area with a mixed stand of Douglas-fir and white fir, the pattern is reversed. This pattern remains even after an accounting is made for the parental host and larval color morph. It is hypothesized that the pattern of variation in the times to emergence may be due to the presence, in the latter population, of physiological morphs which cannot be recognized either by their appearance or their host of origin. These results have clear implications for pest management procedures which attempt to schedule activities related to the emergence of these insects in the spring.

Pheromone-baited traps located close to both host and nonhost crowns were more attractive than traps located between crowns for bothC. occidentalis Freeman andC. retiniana (Walsingham) at both 10 m and at 1.5 m above the ground. At 10 m height, traps located in host foliage were more attractive than those located in nonhost foliage, but at 1.5m height there was no significant difference. These results were obtained for both dense and sparse populations ofC. occidentalis and sparse populations ofC. retiniana. We conclude that the tree species on which a virgin female is located is not an important factor restricting mating between closely relatedChoristoneura spp. Also, the tree species on which a trap is located may not be an important factor that must be standardized in developing pheromone monitoring systems forC. occidentalis andC. retiniana.

A series of cellular transition probability models that predict the spatial dynamics of gypsy moth (Lymantria disparL.) defoliation were developed. The models consisted of four classes: Simple Markov chains, Rook's and Queen's move neighborhood models, and distance weighted neighborhood models. Historical maps of gypsy moth defoliation across Massachusetts from 1961 to 1991 were digitized into a binary raster matrix and used to estimate transition probabilities. Results indicated that the distance weighted neighborhood model performed better then the other neighborhood models and the simple Markov chain. Incorporation of interpolated counts of overwintering egg mass counts taken throughout the state and incorporation of historical defoliation frequencies increased the performance of the transition models.

AbstractEmergence from hibernacula of 2nd instars of Choristoneura occidentaliswas more variable but later than that of C. retiniana. However, early-instar development was faster in C. occidentalisand compensated for the difference in emergence times so that both species entered the 6th instar simultaneously. There were no species-related differences in development beyond the 6th instar. Though they have different resource-tracking patterns early in their life cycle, temporal isolation between these species is unlikely. No developmental morphs were found in either species but there were several instances where individuals that developed at an increased (or decreased) rate in one stage developed slower (or faster) than the mean rate in a substantial stage. Negative correlations between development times were indicative of this. These correlations reduced variation in adult eclosion times induced by extended spring emergence and are indicative of homeostasis in development within populations. Negative correlation coefficients between development periods were more common in C. occidentalis, which also had the more variable spring-emergence pattern. Hybrids were intermediate in almost all development traits.

AbstractAttraction of male Choristoneuraspp. to various mixtures of the pheromone components of C. occidentalisFreeman and C. retiniana(Walsingham) released at various rates was evaluated at several sites in western North America. At all but 1 location, male trap capture increased with progressively greater release rates of a 92:8 mixture of (E)- and (Z)-11-tetradecenals (TDALs), previously identified as active components of the attractant pheromone of C. occidentalis. Similarly, trap catch was positively correlated with release rate of an 84:7:8:1 mixture of (E)- and (Z)-11-tetradecenyl acetates and (E)- and (Z)-11-tetradecenols (1:0.1 TDACs:TDOLs), previously identified as active components of the attractant pheromone of C. retiniana. All release rates of TDALs attracted only C. carnana(C. occidentalisand C. carnanaprobably are subspecies of the same species) in the central Sierra Nevada, but in the southern Cascades all but the lowest release rate of TDALs attracted significant numbers of males classified as C. retinianain addition to those classified as C. occidentalis. At all locations, 1:0.1 TDACs: TDOLs exhibited complete species specificity, attracting only C. retinianaat all release rates tested. The 1:0.1 ratio of TDACs: TDOLs was the most attractive mixture of these components to C. retiniana. Addition of 1:0.1 TDACs: TDOLs did not significantly affect attraction of C. carnanato TDALs. However addition of TDALs significantly decreased attraction of C. retinianato 1:0.1 TDACs:TDOLs.

AbstractThe seasonal distributions of Choristoneura occidentalisFreeman and C. retiniana(Walsingham) males attracted to pheromone sources overlapped considerably at two sites in south-central Oregon. Bimodality in the seasonal distributions of trapped males of both species was associated with a period of cool weather. The daily periods of female calling, and attraction of males to female-baited traps and to chemically baited traps overlapped greatly between the two species. However, these three aspects of C. occidentalismating behavior began 1–2 h before those of C. retiniana. Under laboratory conditions, there was also considerable overlap in the calling periods of the two species; but again, C. occidentalisfemales initiated calling slightly earlier than did female C. retiniana. Females of both species continued to call many hours past the cessation of male attraction to pheromones in the field. Male attraction to pheromones occurred earlier on cool evenings than on warm evenings. Laboratory studies indicated a similar effect of temperature on timing of female calling. Little intraspecific variation in calling periodicity was observed among field-collected populations of each species. However, a C. occidentalislaboratory colony appeared to have partially lost its circadian rhythm of calling.

AbstractThe pheromone specificity of female Choristoneura occcidentalisFreeman and C. retiniana(Walsingham) from several locales, laboratory colonies, and interspecific matings was determined by observing the numbers and wing maculations of males attracted at several sites in southern Oregon. Pheromone specificity of females reared from field-collected brown (typical of C. occidentalis) and green (typical of C. retiniana) larval morphs differed considerably but differed little among sites of origin. Field-collected females attracted more males than conspecific individuals from laboratory colonies. F1and F2interspecific hybrids most closely resembled C. occidentalisin the numbers and types of males attracted. As a group, progeny of backcrosses to C. retinianaappeared intermediate between pure lines of the species in their pheromone specificity. Females reared from intermediate-colored field-collected larvae varied considerably in attractiveness. Most attracted groups of males similar to those attracted to female C. retiniana, but others attracted males most similar to those attracted to female progeny of C. retinianahybrid backcrosses. These findings support the conclusion that hybrid matings occur between these species at a low frequency in nature.

AbstractBrown larval morphs, diagnostic of Choristoneura occidentalisFreeman, and green larval morphs, diagnostic of C. retiniana(Walsingham), were found on both Douglas-fir and white fir in mixed stands in south-central Oregon. The rank proportion of brown morphs in stands was strongly correlated with the rank proportion of Douglas-fir in host species basal area component. Despite considerable overlap in most phenotypic characters, differences in phenotypic frequencies between sympatric green and brown morphs were found in larval head capsule pigmentation, thoracic shield pigmentation, pupal coloration, and adult forewing ground color. In laboratory matings, neither larval host nor larval color morph influenced the mating success, as assessed by the production of viable eggs. Crosses between females reared from brown larval morphs and males from green morphs produced a slightly lower proportion of viable eggs when compared with intramorph matings. Larval host had little effect on either the fecundity of females or the viability of their progeny. Females reared from brown larval morphs produced significantly more eggs than their green counterparts from the same stand. The occurrence of intermediates in all mixed stands and the production of families with anomalous morph frequencies indicate that these two species hybridize in nature. The lack of much structural differentiation and varying efficacy of reproductive barriers indicate that relatively little differentiation of the regulatory genome has occurred between these two species.

The article discusses the benefits of timing in preventing invasive species.

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.

The article focuses on a study which was published in the existing issue of the journal "Diversity and Distributions" revealed the presence of Emerald Ash Borer (Agrilus planipennis) on ash trees in southeast Michigan in the 1990s. Topics discussed include professor of forest entomology Deb McCullough of Michigan State University (MSU), the borers have infested at least 22 states in the U.S. And two provinces in Canada, and ash trees throughout the state were dead or dying.

Invasions by non-indigenous species are a problem of increasing magnitude and threaten the stability of the world's ecosystems and economies. Despite the enormity of this problem, relatively little is known about the importance of various invasion pathways. Using historical records of interceptions of alien insects in air passenger baggage by USDA inspectors, we characterize baggage as an invasion pathway. The most commonly infested commodity intercepted by inspectors was fruit (mainly tropical fruits), and the most commonly intercepted insects were Homoptera and Diptera. Numbers of interceptions from passengers originating in various countries were positively related to the volume of air traffic from that country and negatively associated with the gross national product of the country. In a more detailed case history, we used port inspection data to characterize baggage as a pathway for entry of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Our analysis indicated that contrary to an earlier report, this insect has arrived at a sustained level in Los Angeles (and elsewhere); and these regulatory incidents can be used to explain the repeated detection of the species in California in years following eradication campaigns.

Pheromone traps can be used for evaluating the success of treatments that are applied to either eradicate or delay the growth of isolated low-density populations of the gypsy moth, Lymantria dispar (L.). We developed an index of treatment success, T, that measures the reduction in moth counts in the block treated adjusted by the change in moth counts in the reference area around it. This index was used to analyze the effectiveness of treatments that were conducted as part of the USDA Forest Service Slow-the-Spread of the gypsy moth project from 1993 to 2001. Out of 556 treatments that were applied during this period, 266 (188,064 ha) were selected for the analysis based on several criteria. They included 173 blocks treated with Bacillus thuringiensis (Berliner) variety kurstaki and 93 blocks treated with racemic disparlure. Analysis using general linear models indicated that disparlure treatments were significantly more effective than B. thuringiensis treatments in reducing moth captures. The frequency of repeated treatments in the same area was higher after B. thuringiensis than after disparlure applications. Treatments were more successful if the pretreatment moth counts outside of the block treated were low compared with moth counts inside the block.

Pheromone traps can be used for evaluating the success of treatments that are applied to either eradicate or delay the growth of isolated low-density populations of the gypsy moth, Lymantria dispar (L.). We developed an index of treatment success, T, that measures the reduction in moth counts in the block treated adjusted by the change in moth counts in the reference area around it. This index was used to analyze the effectiveness of treatments that were conducted as part of the USDA Forest Service Slow-the-Spread of the gypsy moth project from 1993 to 2001. Out of 556 treatments that were applied during this period, 266 (188,064 ha) were selected for the analysis based on several criteria. They included 173 blocks treated with Bacillus thuringiensis (Berliner) variety kurstaki and 93 blocks treated with racemic disparlure. Analysis using general linear models indicated that disparlure treatments were significantly more effective than B. thuringiensis treatments in reducing moth captures. The frequency of repeated treatments in the same area was higher after B. thuringiensis than after disparlure applications. Treatments were more successful if the pretreatment moth counts outside of the block treated were low compared with moth counts inside the block.

Mesoscale weather data was input to a gypsy moth, Lymantria dispar L., phenological model to provide a landscape description of gypsy moth phenology. Mesoscale climatological (30-yr average) and single-season (1990) data were spatially interpolated by regressing station temperature as a function of geophysical data (longitude, latitude, and elevation). The interpolated, high-resolution (1 by 1 km pixels) minimum and maximum temperatures were input into a previously developed gypsy moth phenology model to predict egg hatch dates for a single season and for an average season as defined by climatological data. The single-season and climatological predictions were compared statistically to observed egg hatch dates at 15 sites in two states. The single-season predictions and the observed dates were only 2.1 ± 0.2 (mean (± SE) d apart when averaged over all sites, indicating that mesoscale data can successfully be used as input into gypsy moth phenology models. Although the results of the single-year simulation were mostly accurate, the mesoscale climatic predictions of egg hatch averaged 24.3 ± 0.7 d after the observed date in the field. This difference was caused by the unusually warm spring in 1990 compared with a climatological (average) season. The comparison of the singleseason and climatic predictions in 1990 indicate the importance of using mesoscale data from a current season to update the phenological predictions used in long-range planning.

The correlation of various preseason field measurements with subsequent defoliation by the gypsy moth, Lymantria dispar (L.), was examined from a series of forest stands in central Pennsylvania. These measurements included preseason egg-mass density, density of old egg masses (residual egg masses from previous generations), fecundity, number of larvae hatching per mass, egg-mass length, and host-tree basal area. Egg density (product of fecundity and egg-mass density) was the best single variable for predicting defoliation. The product of egg-mass density and mean egg-mass length provided predictions of defoliation nearly as well as egg density, reflecting the previously observed linear relationship between egg-mass length and fecundity. The addition of the ratio of new-old egg masses to the model significantly increased the model fit. Parameters of these and other parameters in linear and nonlinear (Weibull) models are provided. These results indicate that recording one or two additional field measurements (egg-mass length or counts of old egg masses) increases the precision in the prediction of defoliation when densities range from 100 to 10,000 egg masses per acre (250 to 25,000 egg massesper ha).

The effectiveness of aerial applications of Bacillus thuringiensis and diflubenzon (Dimilin) in a gypsy moth, Lymantria dispar (L.), management program was evaluated using a geographic information system. System data included counts of overwintering egg mass densities, defoliation maps, and treatment block boundaries collected by the Appalachian Integrated Pest Management Program in Virginia and West Virginia from 1989 to 1992. Diflubenzuron treatments resulted in greater foliage protection and population reduction than did applications of B. thuringiensis except when egg mass densities before treatment were < 1,000 egg masses per hectare. Generally, neither treatment provided foliage protection in the year following treatment, especially when treatment blocks were small or near to defoliating populations, or both.

Timed walks are widely used by pest managers for estimating gypsy moth, Lymantria dispar (L.), egg mass densities. According to this method, an individual(s) walks through a woodlot for a fixed length of time (typically 5 min) and counts all egg masses observed. These counts are then used in one of several previously developed linear regression equations to estimate egg masses per unit area. In this study, we evaluated the statistical properties of these estimates. At several 25-ha woodlots, we estimated true egg mass densities by counting egg masses in multiple fixed-radius plots. Two observers then made four 5-min walks through each woodlot. These counts were more highly correlated with estimated density when expressed as numbers per walk than as number per distance walked. Analysis of variance indicated that timed counts varied significantly among observers. For individual observers, counts of egg masses per walk were used to develop linear regressions for predicting egg mass densities. These regressions were characterized to determine the confidence intervals associated with density estimates obtained from a given number of samples. Results indicate that even if separate regression equations were developed for each observer, the timed-walk method provides imprecise estimates. Lack of precision and observer effects indicate that fixed-time and fixed-distance methods of estimating gypsy moth egg mass densities should be discontinued. Analyses indicated that even one O.OI-ha fixed-radius plot per woodlot will usually provide a more precise estimate of density than four or more 5-min walks.

Geostatistics were used to quantify spatial variation in captures of adult male gypsy moths, Lymantria dispar (L.), in pheromone-baited traps in the central Appalachians. Spatial variationwas analyzed in the infested zone, where yearly total capture was >300 moths per trap; the transition zone, where moth capture ranged from 1 to 300 moths per trap: and the uninfested zone, where moth capture was <1 moth per trap. The trend associated with gypsy moth spread was removed in each zone using linear and nonlinear regression. Spatial correlation among trap captures in the transition zone (correlogram sill, 0.544; range, 31.2 km) was much stronger than in the infested (sill, 0.269; range, 23.9 km) and uninfested (sill, 0.222; range, 19.7 km) zones. Additional short-range correlation (range, 1.4 km) was detected in the uninfested zone. Differences in the spatial distribution of male moth populations among the 3 zones may be caused by different dominating population processes in each zone. Other factors, such as trap saturation, also may contribute to the difference in the patterns of moth captures. Obtained zone-specific geostatistical parameters can be used for interpolation of moth captures at unsampled locations and for improving gypsy moth monitoring.

Since its introduction near Boston in 1869, the gypsy moth, Lymantria dispar (L.), has spread over 1,000 km to the southwest. To measure its current rate of spread through the central Appalachian Mountains we estimated population boundaries, which are lines that separate areas with population densities generally above and below a specific threshold. Population boundaries were estimated in northwestern Virginia and southeastern West Virginia using male moth counts (1988–1994), egg mass counts (1988–1991), and defoliation maps (1988–1994). The boundary of 1 moth per trap was on average no km from the boundary of defoliation, and the male moth capture rate increased 10 times per 29 km perpendicular to the population front. Approximately 11 yr separated the time when traps caught 1 moth per trap until defoliation first occurred in the same area. The rates of gypsy moth spread estimated using different census methods and from different population thresholds changed almost synchronously from year to year. Only spread rates estimated from defoliation data had a different temporal pattern. Gypsy moth spread rate declined from 1988 to 1994 by 35%, as measured from time series of spread rates and boundary compression (reduction of the distance between adjacent boundaries). Reduction in gypsy moth spread rate may have been the result of intensive population management in the area.

Within 1-ha plots, gypsy moth, Lymantria dispar L., densities were artificially elevated from low densities (about 20 egg masses/ha) to high densities (8,000 egg masses/ ha) using field-collected eggs and F1 sterile laboratory-reared eggs. At all sites, including the feral and sterile release areas, densities decreased to undetectable levels (less than 10 egg masses/ha). In the sterile and feral release areas, parasitism by Cotesia melanoscela (Ratzeburg) was the largest source of identified mortality and was significantly greater than in the surrounding area or in untreated plots. Within the feral release area, parasitism by Compsilura concinnata (Meigen) and Parasetigena silvestris (Robineau-Desvoidy) was substantial and was greater than in the surrounding area. This pattern was not observed in the sterile release area. This difference may have been caused by differences in gypsy moth phenologies between the two populations. Spatially density-dependent mortality caused by parasitoids is hypothesized to be important in the regulation of low-density populations. Furthermore, this mortality may have profound effects on attempts to suppress populations using releases of induced- inherited sterile insects.

The influence of the position of egg masses of the gypsy moth, Lymantria dispar (L.), on a tree bole on hatching time was investigated at field sites in Ontario and Pennsylvania. Although eggs were deposited predominantly on the eastern sides of tree boles, egg hatch was most advanced in masses located on southern sides. There was no strong relationship between height on the tree bole and rate of egg hatch, especially for the lower portion (<2m) of the bole. Eggs deposited under bark flaps experienced a significant delay in hatching compared with eggs deposited on the bark surface. Within egg masses, eggs from the bottom third of the mass hatched slightly later than those from the middle or top thirds of the mass. Understanding the microclimatic variables that influence hatch times will improve the accuracy of prediction of the phenology of this forest pest.

Previous studies indicate that North American gypsy moth, Lymantria dispar (L.), populations are driven by a numerically bimodal replacement rate model: Nt+1/Nt = f(N), where f(N) is bimodal, resulting in two equilibrium densities. Under this theory, populations are regulated about a low density equilibrium for many years until some perturbation (usually mass immigration) elevates populations to high densities, where they are regulated about a high-density equilibrium until crashing. In this paper, the evidence for and against numerical bimodality in gypsy moth populations is reviewed. The Melrose Highlands data (egg mass densities at 83 plots in New England from 1910 to 1931) were reexamined. These analyses indicated bimodality in f(N) when data were expressed as yearly means of several plots in a zone ˜30 km in diameter, but there was no clear evidence of bimodality in the dynamics at individual plots. Density fluctuations in these relatively small plots (0.07 ha) were instead dominated by apparently random effects. It is hypothesized that short-range dispersal dominates the dynamics of populations at these spatial scales. These results illustrate the importance of spatial scale in the characterization of ecological processes.

Slowing the expansion of the range of the gypsy moth, Lymantria dispar (L.), in North America will reduce the area affected by gypsy moth populations in the future and hence may be economically justified. The rate of range expansion can be reduced by eradication of isolated gypsy moth infestations in a barrier zone that is located just beyond the expanding population front and is slowly shifted in the direction of population spread. We developed a model to optimize the allocation of resources for monitoring and treatment of isolated colonies in a barrier zone. Model parameters were estimated using data collected in the central Appalachian Mountains. The model predicted that the cost of slowing population spread is minimized when the density of pheromone traps and eradication activity within the barrier zone decrease with increasing distance from the population front. Sensitivity analysis indicated that the output was most sensitive to the change of the maximum distance from the population front at which colonies can become established. The present value of predicted costs of all monitoring and treatment in the barrier zone were <1/4 the present value of expected benefits from slowing the spread of the gypsy moth over 25 yr.

Maps of defoliation caused by the gypsy moth, Lymantria dispar (L.), as well as point estimates of egg mass density and counts of male moths captured in pheromone-baited traps collected from the Shenandoah National Park and George Washington National Forest from 1989- 1992 were assembled in a geographic information system. A maximum likelihood estimation procedure was used to fit 15 logistic regression models that predicted the probability of noticeable defoliation in 1-ha grid cells from various combinations of egg mass densities, counts of males in pheromone traps, presence of defoliation in the previous year, and distance to the expanding gypsy moth population front. Models that incorporated egg mass density estimates and distance to the infested front provided the most reliable predictions of defoliation probability. The performance of these models was comparable with decision errors encountered using various egg mass density thresholds alone. The errors associated with application of egg mass density thresholds and the various models were high and highlighted the need for improved methods for predicting defoliation.

Gypsy moth, Lymantria dispar (L.), is gradually spreading in North America from New England to the west and south. Monitoring this expansion is important for evaluating effects of population management on the rate of gypsy moth spread, for planning areas regulated by domestic quarantine, and for accurate timing of preventive silvicultural measures. Spread rate was measured as the distance between population boundaries in consecutive years. Gypsy moth population boundaries from 1988 to 1995 were estimated in northwestern Virginia and southeastern West Virginia using counts of male moths in pheromone-baited traps. Population boundaries estimated using the 10 moths per trap threshold were most stable in space and time compared with the boundaries estimated for other thresholds ranging from 1to 300 moths per trap. Thus, the 10 moths per trap threshold is reliable for the monitoring of gypsy moth spread. Local spread rates were significantly autocorrelated in space (range, 80 km) but not in time. The rate of gypsy moth spread decreased from 16.9 km/yr in 1984-1990 to 8.8 km/yr in 1991-1996. An 8-km intertrap distance was adequate for detecting this decline in the rate of gypsy moth spread.

Outbreaks of the gypsy moth, Lymantria dispar (L.), typically occur over large areas but are difficult to predict. Previously developed models forecast defoliation from preseason counts of egg masses in a given stand. In this study, we take a different approach to defoliation prediction: forecasts are based upon the statistical autocorrelation of defoliation through space and time. Spatial and temporal autocorrelation of defoliation in historical data was quantified at a variety of scales using variograms. We used a 30-yr time series of aerial sketch maps of gypsy moth defoliation in Massachusetts to calculate these variograms. The variograms were then used to parameterize a geostatistical estimation technique: three-dimensional simple kriging. Kriged estimates are weighed averages of values from nearby locations and are typically used to interpolate two-dimensional data. In this study, we used kriging to extrapolate future defoliation maps into a third dimension, time. Kriged estimates were expressed as probabilities of detectable defoliation. Predicted probabilities were estimated for each year of the time series and were compared with actual defoliation maps for that year. The kriging procedure usually performed well in predicting the spatial distribution of outbreaks in a given year, but the magnitude of regionwide outbreaks generally lagged a year behind actual values. Though this approachis not currently suitable for operational use, it represents a novel approach to landscape level forecasting of insect outbreaks. These models may ultimately outperform current forecasting systems.

Oak leaf area index (LAI) was estimated using wide-angle photographs of the forest canopy taken from the ground at grid points throughout three sites on Cape Cod, Mass. Confidence intervals for these estimates and optimal sample sizes were calculated. Oak LAI estimates leveled off by early June when no defoliation was present. Within-plot two-dimensional spatial distribution of oak LAI was very similar to the spatial distribution of oak basal area. Consequently, there was a positive correlation between local oak leaf area and local basal area. Comparison of LAI estimates taken before and after gypsy moth, Lymantria dispar (L.), defoliation allowed the estimation of oak leaf area consumed. Leaf area loss was similar in areas of high and low host foliage densities. The correlation of leaf area lost with local density of early instars was greater than the correlation with the density of late instars.

A technique was developed for estimating larval gypsy moth, Lymantria dispar (L.), densities using simultaneous measurements of the amount of frass produced per larva (frass yield) and the amount of frass falling in the forest per unit area (frass drop). The technique was tested in a postseason experiment in which 6,000 larvae were released in a stand. Frass yield was measured by individually caging several larvae in the field on cut host foliage. The most reliable and efficient method of measuring frass drop was the deployment of several large funnel-shaped frass traps near the forest floor. Number of pellets was found to be superior to frass weight as a unit for quantifying frass yield and drop, because it was not strongly influenced by instar distribution. Density estimates obtained using this method closely matched those expected from the number of larvae released. Frass width measurements provided a method of estimating instar distributions.

At three sites on Cape Cod, Mass., successive gypsy moth, Lymantria dispar (L.), larval densities were estimated using simultaneous measurements of the number of frass pellets produced per larva (frass yield) and the number of frass pellets falling in the forest per unit area (frass drop). Estimated larval densities declined through the period of larval development at all sites. Frass yield was positively correlated with ambient temperature. Frass drop was positively correlated with the basal area of host trees immediately around the frass trap. At a low-density population, rate of frass drop exhibited a diel periodicity similar to that of larval feeding. Mean-variance relationships of frass drop measurements and density estimates indicated that frass pellets and larvae were spatially aggregated within stands. The optimal ratio of drop to yield samples and the number of replicates of each sample necessary to obtain a given level of precision decreased with increasing density.

Estimation of the boundary of the geographic distribution of gypsy moth, Lymantria dispar (L.), populations is important for monitoring and controlling the spread of this species in North America. In this study, gypsy moth population boundaries were estimated from male moths counts in pheromone–baited traps and from egg mass counts in a 5.18– million–ha area in northwestern Virginia and southeastern West Virginia.Population boundaries were estimated for 5 yr (1988–1992) and for different population density thresholds using the following 3 methods: (1) best classification(minimizing the number of grid cell misclassifications),(2) 1st occurrence method, and (3) logistic regression of log population counts versus distance perpendicular to population boundary.All 3 methods generated similar boundaries for male moth counts, and boundaries obtained with the first 2 methods were most correlated. The regression method failed to estimate boundaries of egg mass populations because of their irregular spatial distribution. However,the 2 other methods were successful and yielded similar results. The average gypsy moth spread rate estimated using male counts was 10.7–11.9 km/yr.The minimum spread rate was 3.8–4.9 km in 1991, and the maximum rate was 19.4–22.6 Km in 1989.

Outbreaks of the gypsy moth, Lymantria dispar (L.), were partially synchronous across the New England states (Massachusetts, Maine, New Hampshire, and Vermont) from 1938 to 1992. To explain this synchrony, we investigated the Moran effect, a hypothesis that local population oscillations, which result from similar density-dependent mechanisms operating at time lags, may be synchronized over wide areas by exposure to common weather patterns. We also investigated the theory of climatic release, which postulates that outbreaks are triggered by climatic factors favorable for population growth. Time series analysis revealed defoliation series in 2 states as 1st-order autoregressive processes and the other 2 as periodic 2nd-order autoregressive processes. Defoliation residuals series computed using the autoregressive models for each state were cross correlated with series of weather variables recorded in the respective states. The weather variables significantly correlated with defoliation residuals in all 4 states were minimum temperature and precipitation in mid-December in the same gypsy moth generation and minimum temperature in mid- to late July of the previous generation. These weather variables also were correlated strongly among the 4 states. The analyses support the predictions of the Moran effect and suggest that common weather may synchronize local populations so as to produce pest outbreaks over wide areas. We did not find convincing evidence to support the theory of climatic release.

Mating success of tethered gypsy moth, Lymantria dispar (L.), females was measured in 9 newly established, low-density populations in Virginia and West Virginia in 1993–1994. Mating success was correlated with male moth capture rate in milk carton pheromone-baited traps located at the same sites. The instantaneous mating probability for virgin females averaged 0.15 times the mean male capture rate. Average mortality of tethered females caused by predation was 52% per day. Counts of males in pheromone traps combined with expectations of population growth can be used to predict likelihood of persistence (versus extinction) of isolated gypsy moth populations.