Population ecology of insect invasions and their management

Citizen science provides a reliable and scalable tool to track disease-carrying mosquitoes

Recent outbreaks of Zika, chikungunya and dengue highlight the importance of better understanding the spread of disease-carrying mosquitoes across multiple spatio-temporal scales. Traditional surveillance tools are limited by jurisdictional boundaries and cost constraints. Here we show how a scalable citizen science system can solve this problem by combining citizen scientists' observations with expert validation and correcting for sampling effort. Our system provides accurate early warning information about the Asian tiger mosquito (Aedes albopictus) invasion in Spain, well beyond that available from traditional methods, and vital for public health services. It also provides estimates of tiger mosquito risk comparable to those from traditional methods but more directly related to the human-mosquito encounters that are relevant for epidemiological modelling and scalable enough to cover the entire country. These results illustrate how powerful public participation in science can be and suggest citizen science is positioned to revolutionize mosquito-borne disease surveillance worldwide.

Evaluation of predicted Medfly ( Ceratitis capitata) quarantine length in the United States utilizing degree-day and agent-based models

Invasions by pest insects pose a significant threat to agriculture worldwide. In the case of Ceratitis capitata incursions on the US mainland, where it is not officially established, repeated detections are followed by quarantines and treatments to eliminate the invading population. However, it is difficult to accurately set quarantine duration because non-detection may not mean the pest is eliminated. Most programs extend quarantine lengths past the last fly detection by calculating the amount of time required for 3 generations to elapse under a thermal unit accumulation development model (“degree day”). A newer approach is to use an Agent-Based Simulation (ABS) to explicitly simulate population demographics and elimination. Here, predicted quarantine lengths for 11 sites in the continental United States are evaluated using both approaches. Results indicate a strong seasonality in quarantine length, with longer predictions in the second half of the year compared with the first; this pattern is more extreme in degree day predictions compared with ABS. Geographically, quarantine lengths increased with latitude, though this was less pronounced under the ABS. Variation in quarantine lengths for particular times and places was dramatically larger for degree day than ABS, generally spiking in the middle of the year for degree day and peaking in second half of the year for ABS. Analysis of 34 C. capitata quarantines from 1975 to 2017 in California shows that, for all but two, quarantines were started in the second half of the year, when degree day quarantine lengths are longest and have the highest uncertainty. For a set of hypothetical outbreaks based on these historical quarantines, the ABS produced significantly shorter quarantines than degree day calculations. Overall, ABS quarantine lengths were more consistent than degree day predictions, avoided unrealistically long values, and captured effects of rare events such as cold snaps.

Description of an establishment event by the invasive Asian longhorned beetle (Anoplophora glabripennis) in a suburban landscape in the northeastern United States

The establishment of non-native species is commonly described as occurring in three phases: arrival, establishment, and dispersal. Both arrival and dispersal by the Asian longhorned beetle (Anoplophora glabripennis Motschulsky), a xylophagous Cerambycid native to China and the Korean peninsula, has been documented for multiple locations in both North America and Europe, however the transitional phase, establishment, is not well understood for this species due to the need to rapidly remove populations to prevent dispersal and assist eradication, and the evident variation in the behavior of populations. Here we describe the dynamics of an establishment event for the Asian longhorned beetle in a small, isolated population within the regulated quarantine zone near Worcester, Massachusetts, USA. These data were collected during an opportunity afforded by logistical limits on the Cooperative Asian Longhorned Beetle Eradication Program administered by state, federal, and local government partners. Seventy-one infested red maple (Acer rubrum) trees and 456 interspersed un-infested trees were surveyed in an isolated, recently established population within a ~0.29 ha stand in a suburban wetland conservation area in which nearly 90% of the trees were host species, and nearly 80% were Acer rubrum. Tree-ring analyses show that within this establishing population, Asian longhorned beetles initially infested one or two A. rubrum, before moving through the stand to infest additional A. rubrum based not on distance or direction, but on tree size, with infestation biased towards trees with larger trunk diameters. Survey data from the larger landscape suggest this population may have generated long-distance dispersers (~1400 m), and that these dispersal events occurred before the originally infested host trees were fully exploited by the beetle. The distribution and intensity of damage documented in this population suggest dispersal here may have been spatially more rapid and diffuse than in other documented infestations. Dispersal at these larger spatial scales also implies that when beetles move beyond the closed canopy of the stand, the direction of dispersal may be linked to prevailing winds.

Assessing Flight Potential of the Invasive Asian Longhorned Beetle (Coleoptera: Cerambycidae) With Computerized Flight Mills

The Asian longhorned beetle, Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae: Lamiinae), is an invasive woodborer that poses a serious threat to urban and natural landscapes. In North America, this beetle is a quarantine pest, and populations are subject to eradication efforts that consist of the identification, removal, and destruction of infested host material, and removal or prophylactic treatment of high-risk host plant species. To enhance Asian longhorned beetle eradication protocols in landscapes with extensive host availability, we assessed the dispersal potential of male and female adults of varying age, mating, and nutritional status using computerized flight mills. In total, 162 individuals were tethered to computerized flight mills for a 24-h trial period to collect information on total distance flown, flight times and velocities, and number and duration of flight bouts. Adult Asian longhorned beetles (in all treatments) flew an average of 2,272 m within a 24-h period, but are capable of flying up to 13,667 m (8.5 miles). Nutrition and age had the greatest impacts on flight, with Asian longhorned beetle adults >5 d of age that had fed having greater overall flight performance than any other group. However, mating status, sex, and body size (pre-flight weight and elytron length) had a minimal effect on flight performance. This information will be useful for refining quarantine zones surrounding areas of infestation, and for providing greater specificity as to the risk the Asian longhorned beetle poses within invaded regions.

First Report of Mating Disruption With an Aggregation Pheromone: A Case Study With Tetropium fuscum (Coleoptera: Cerambycidae)

Tetropium fuscum (F.), native to Europe and established in Nova Scotia, Canada, since at least 1990, is considered a low-to-moderate threat to spruce (Picea spp.) forests in North America and regulated as a quarantine pest by the Canadian Food Inspection Agency. We tested broadcast applications of the aggregation pheromone racemic (5E)-6,10-dimethyl-5,9-undecadien-2-ol (fuscumol), formulated at 10% concentration in Hercon Bio-Flakes (Hercon International, Emigsville, PA), for efficacy in disrupting T. fuscum mating and suppressing populations. Two applications of 2.5-2.75 kg Bio-Flakes (250-275 g a.i.) per ha per season significantly reduced trap catches and mating success (2009, 2010, 2012): about 30% of females trapped in treated plots had mated compared with 60% of females trapped in untreated plots. Similar reductions in mating success were observed in 2011 with one or two 4.5 kg/ha applications of Bio-Flakes. Mean densities of T. fuscum colonizing sentinel bait logs or girdled trees were 36% lower in pheromone-treated plots than in untreated plots, but the difference was not statistically significant. Lack of population suppression may have been because mated females immigrated into treated plots or because populations were so high that despite a 50% reduction in mating success, absolute numbers of mated females were sufficient to infest our bait logs or trees. This is the first demonstration of insect mating disruption via broadcast application of an aggregation pheromone. Pheromone-mediated mating disruption has potential to slow the spread of invasive cerambycids by targeting low-density outlier populations near or beyond the leading edge of an infestation.

Flight Capacity of the Walnut Twig Beetle (Coleoptera: Scolytidae) on a Laboratory Flight Mill

The walnut twig beetle, Pityophthorus juglandis Blackman, and associated fungus Geosmithia morbida Kolařík, Freeland, Utley, & Tisserat constitute the insect-fungal complex that causes thousand cankers disease in walnut, Juglans spp., and wingnut, Pterocarya spp. Thousand cankers disease is responsible for the decline of Juglans species throughout the western United States and more recently, the eastern United States and northern Italy. We examined the flight capacity of P. juglandis over 24-h trials on a flight mill in the laboratory. The maximum total flight distance observed was ∼3.6 km in 24 h; however, the mean and median distances flown by beetles that initiated flight were ∼372 m and ∼158 m, respectively. Beetles flew for 34 min on average within a 24-h flight trial. Male and female flight capacities were similar, even though males were larger than females (0.64 vs. 0.57 mm pronotal width). Age postemergence had no effect on flight distance, flight time, or mean flight velocity. The propensity to fly, however, decreased with age. We integrated results of flight distance with propensity to fly as beetles aged in a Monte Carlo simulation to estimate the maximum dispersal capacity over 5 d, assuming no mortality. Only 1% of the insects would be expected to fly >2 km, whereas one-third of the insects were estimated to fly <100 m. These results suggest that nascent establishments remain relatively localized without anthropogenic transport or wind-aided dispersal, which has implications for management and sampling of this hardwood pest.

Correlations in the degeneracy of structurally controllable topologies for networks

Many dynamic systems display complex emergent phenomena. By directly controlling a subset of system components (nodes) via external intervention it is possible to indirectly control every other component in the system. When the system is linear or can be approximated sufficiently well by a linear model, methods exist to identify the number and connectivity of a minimum set of external inputs (constituting a so-called minimal control topology, or MCT). In general, many MCTs exist for a given network; here we characterize a broad ensemble of empirical networks in terms of the fraction of nodes and edges that are always, sometimes, or never a part of an MCT. We study the relationships between the measures, and apply the methodology to the T-LGL leukemia signaling network as a case study. We show that the properties introduced in this report can be used to predict key components of biological networks, with potentially broad applications to network medicine.

Population Distribution and Range Expansion of the Invasive Mexican Rice Borer (Lepidoptera: Crambidae) in Louisiana

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is an invasive pest that was first introduced into southern Texas in 1980 and has been expanding its range eastward along the United States Gulf Coast. The pest attacks rice (Oryza sativa L.), sugarcane (Saccharum spp.), corn (Zea mays L.), and other graminaceous crops, and its establishment in Louisiana is expected to have severe economic impacts on crop production. Range expansion and population distribution of E. loftini were monitored with a network of 77 pheromone traps throughout southwestern Louisiana from 2013 to 2015. Eoreuma loftini was ubiquitous throughout the study region, with male moths captured in every habitat sampled. Spatial analysis revealed the population is characterized by high and low density clusters, with the greatest trap captures occurring in southeastern Calcasieu Parish and southern Jefferson Davis Parish. Trap captures in more northern regions of the study were lower than in southern parishes. Trap captures in areas where the pest has been established for >3 yr were greatest in rice habitats. The weighted mean population center moved eastward at a rate of ∼11 km per year. Human-aided movement of E. loftini was probably not involved in the eastward expansion documented during this study. Seasonal population peaks were detected in March-April, July-August, and October-November. This study indicates this species is continuing its spread eastward along the United States Gulf Coast and will likely become established throughout Louisiana within the next 20 yr.

Spatiotemporal dynamics of the Southern California Asian citrus psyllid (Diaphorina citri) invasion

Biological invasions are governed by spatial processes that tend to be distributed in non-random ways across landscapes. Characterizing the spatial and temporal heterogeneities of the introduction, establishment, and spread of non-native insect species is a key aspect of effectively managing their geographic expansion. The Asian citrus psyllid (Diaphorina citri), a vector of the bacterium associated with huanglongbing (HLB), poses a serious threat to commercial and residential citrus trees. In 2008, D. citri first began expanding northward from Mexico into parts of Southern California. Using georeferenced D. citri occurrence data from 2008-2014, we sought to better understand the extent of the geographic expansion of this invasive vector species. Our objectives were to: 1) describe the spatial and temporal distribution of D. citri in Southern California, 2) identify the locations of statistically significant D. citri hotspots, and 3) quantify the dynamics of anisotropic spread. We found clear evidence that the spatial and temporal distribution of D. citri in Southern California is non-random. Further, we identified the existence of statistically significant hotspots of D. citri occurrence and described the anisotropic dispersion across the Southern California landscape. For example, the dominant hotspot surrounding Los Angeles showed rapid and strongly asymmetric spread to the south and east. Our study demonstrates the feasibility of quantitative invasive insect risk assessment with the application of a spatial epidemiology framework.

Predicting North American Scolytinae invasions in the Southern Hemisphere

Scolytinae species are recognized as one of the most important tree mortality agents in coniferous forests worldwide, and many are known invaders because they are easily transported in wood products. Nonnative trees planted in novel habitats often exhibit exceptional growth, in part because they escape herbivore (such as Scolytinae) pressure from their native range. Increasing accidental introductions of forest pest species as a consequence of international trade, however, is expected to diminish enemy release of nonnative forest trees. In this context, there is need to characterize patterns of forest herbivore species invasion risks at global scales. In this study, we analyze the establishment potential of 64 North American Scolytinae species in the Southern Hemisphere. We use climate-based ecological niche models (MaxEnt) to spatially define the potential distribution of these Scolytinae species in regions of the Southern Hemisphere were pines are planted. Our model predicts that all of the pine-growing regions of the Southern Hemisphere are capable of supporting some species of North American Scolytinae, but there are certain "hotspot" regions, southeastern Argentina, Bolivia, Chile, Peru and southwestern Australia, that appear to be suitable for a particularly large number of species. The species with the highest predicted risk of establishment were Dendroctonus valens, Xyleborus intrusus, Hylastes tenuis, Ips grandicollis, Gnathotrichus sulcatus, and Ips calligraphus. Given that global commerce is anticipated to continue to increase, we can expect that more Scolytinae species will continue to establish outside their range. Our results provide information useful for identifying a global list of potential invasive species in pine plantations, and may assist in the design of comprehensive strategies aimed at reducing pest establishment in Southern Hemisphere forest plantations.

Aggregation and a strong Allee effect in a cooperative outbreak insect

Most species that are negatively impacted when their densities are low aggregate to minimize this effect. Aggregation has the potential to change how Allee effects are expressed at the population level. We studied the interplay between aggregation and Allee effects in the mountain pine beetle (Dendroctonus ponderosae Hopkins), an irruptive bark beetle that aggregates to overcome tree defenses. By cooperating to surpass a critical number of attacks per tree, the mountain pine beetle is able to breach host defenses, oviposit, and reproduce. Mountain pine beetles and Hymenopteran parasitoids share some biological features, the most notable of which is obligatory host death as a consequence of parasitoid attack and development. We developed spatiotemporal models of mountain pine beetle dynamics that were based on the Nicholson-Bailey framework but which featured beetle aggregation and a tree-level attack threshold. By fitting our models to data from a local mountain pine beetle outbreak, we demonstrate that due to aggregation, attack thresholds at the tree level can be overcome by a surprisingly low ratio of beetles per susceptible tree at the stand level. This results confirms the importance of considering aggregation in models of organisms that are subject to strong Allee effects.

Olfactory Cues, Visual Cues, and Semiochemical Diversity Interact During Host Location by Invasive Forest Beetles

Plant-feeding insects use visual and olfactory cues (shape, color, plant volatiles) for host location, but the relative importance of different cues and interactions with non-host-plant volatiles in ecosystems of varying plant biodiversity is unclear for most species. We studied invasive bark beetles and wood borers associated with pine trees to characterize interactions among color, host and non-host volatiles, by employing traps that mimic tree trunks. Cross-vane flight intercept traps (black, green, red, white, yellow, clear) and black funnel traps were used with and without attractants (α-pinene + ethanol), repellents (non-host green leaf volatiles, 'GLV'), and attractant/repellent combinations in four pine forests in New Zealand. We trapped 274,594 Hylurgus ligniperda, 7842 Hylastes ater, and 16,301 Arhopalus ferus. Trap color, attractant, and color × attractant effects were highly significant. Overall, black and red traps had the highest catches, irrespective of the presence of attractants. Alpha-pinene plus ethanol increased trap catch of H. ligniperda 200-fold but only 6-fold for H. ater and 2-fold for A. ferus. Green leaf volatiles had a substantial repellent effect on trap catch of H. ligniperda but less on H. ater and A. ferus. Attack by H. ligniperda was halved when logs were treated with GLV, and a similar effect was observed when logs were placed among broadleaved understory shrubs emitting GLV. Overall, H. ligniperda was most strongly affected by the olfactory cues used, whereas H. ater and A. ferus were more strongly affected by visual cues. Collectively, the results support the semiochemical diversity hypothesis, indicating that non-host plant volatiles from diverse plant communities or artificial dispensers can contribute to resistance against herbivores by partly disrupting host location.

Co-Infestation and Spatial Distribution of Bactrocera carambolae and Anastrepha spp. (Diptera: Tephritidae) in Common Guava in the Eastern Amazon

Field infestation and spatial distribution of introduced Bactrocera carambolae Drew and Hancock and native species of Anastrepha in common guavas [Psidium guajava (L.)] were investigated in the eastern Amazon. Fruit sampling was carried out in the municipalities of Calçoene and Oiapoque in the state of Amapá, Brazil. The frequency distribution of larvae in fruit was fitted to the negative binomial distribution. Anastrepha striata was more abundant in both sampled areas in comparison to Anastrepha fraterculus (Wiedemann) and B. carambolae The frequency distribution analysis of adults revealed an aggregated pattern for B. carambolae as well as for A. fraterculus and Anastrepha striata Schiner, described by the negative binomial distribution. Although the populations of Anastrepha spp. may have suffered some impact due to the presence of B. carambolae, the results are still not robust enough to indicate effective reduction in the abundance of Anastrepha spp. caused by B. carambolae in a general sense. The high degree of aggregation observed for both species suggests interspecific co-occurrence with the simultaneous presence of both species in the analysed fruit. Moreover, a significant fraction of uninfested guavas also indicated absence of competitive displacement.

Bark and Ambrosia Beetles Show Different Invasion Patterns in the USA

Non-native bark and ambrosia beetles represent a threat to forests worldwide. Their invasion patterns are, however, still unclear. Here we investigated first, if the spread of non-native bark and ambrosia beetles is a gradual or a discontinuous process; second, which are the main correlates of their community structure; third, whether those correlates correspond to those of native species. We used data on species distribution of non-native and native scolytines in the continental 48 USA states. These data were analyzed through a beta-diversity index, partitioned into species richness differences and species replacement, using Mantel correlograms and non-metric multidimensional scaling (NMDS) ordination for identifying spatial patterns, and regression on distance matrices to test the association of climate (temperature, rainfall), forest (cover area, composition), geographical (distance), and human-related (import) variables with β-diversity components. For both non-native bark and ambrosia beetles, β-diversity was mainly composed of species richness difference than species replacement. For non-native bark beetles, a discontinuous invasion process composed of long distance jumps or multiple introduction events was apparent. Species richness differences were primarily correlated with differences in import values while temperature was the main correlate of species replacement. For non-native ambrosia beetles, a more continuous invasion process was apparent, with the pool of non-native species arriving in the coastal areas that tended to be filtered as they spread to interior portions of the continental USA. Species richness differences were mainly correlated with differences in rainfall among states, while rainfall and temperature were the main correlates of species replacement. Our study suggests that the different ecology of bark and ambrosia beetles influences their invasion process in new environments. The lower dependency that bark beetles have on climate allowed them to potentially colonize more areas within the USA, while non-native ambrosia beetles, being dependent on rainfall, are typically filtered by the environment.

How much is a pheromone worth?

Pheromone-baited traps have been widely used in integrated pest management programs, but their economic value for growers has never been reported.  We analyzed the economic benefits of long-term use of traps baited with the citrus fruit borer Gymnandrosoma aurantianum sex pheromone in Central-Southern Brazil. Our analysis show that from 2001 to 2013 citrus growers avoided accumulated pest losses of 132.7 million to 1.32 billion USD in gross revenues, considering potential crop losses in the range of 5 to 50%. The area analyzed, 56,600 to 79,100 hectares of citrus (20.4 to 29.4 million trees), corresponds to 9.7 to 13.5% of the total area planted with citrus in the state of São Paulo. The data show a benefit-to-cost ratio of US$ 2,655 to US$ 26,548 per dollar spent on research with estimated yield loss prevented in the range of 5-50%, respectively. This study demonstrates that, in addition to the priceless benefits for the environment, sex pheromones are invaluable tools for growers as their use for monitoring populations allows rational and reduced use of insecticides, a win-win situation.

Dilution of Fluon Before Trap Surface Treatment Has No Effect on Longhorned Beetle (Coleoptera: Cerambycidae) Captures

Several studies have observed that trap captures of longhorned beetles (Coleoptera: Cerambycidae) can be increased by treating the surface of intercept traps with a lubricant. In addition to being expensive, these treatments can alter the spectral properties of intercept traps when applied neat. These surface treatments, particularly Fluon, are commonly used diluted as a low friction coating to prevent insects from climbing out of rearing containers. The purpose of this study was to examine the effect of diluting Fluon on the spectral properties of treated corrugated plastic traps and the capture of longhorned beetles including Monochamus scutellatus (Say), Monochamus mutator (LeConte), and Monochamus notatus (Drury). Intercept panel traps were baited with attractant semiochemicals and treated with either undiluted (i.e., 100%) Fluon, a 1:1 mixture of Fluon and water (50%), a 1:9 mixture of Fluon and water (10%), or untreated. There were no obvious differences in the relative reflectance of untreated black Coroplast plastic or black Coroplast plastic treated with 50 or 10% Fluon. Traps treated with 100% Fluon had similar patterns of peak reflectance to the other treatments but overall had higher relative reflectance. In general, no effect of diluting the Fluon was observed for male or female M. scutellatus or M. mutator , but an effect of treating traps with Fluon was observed. Similar results were observed for the combined captures of Clytus ruricola Olivier, Cyrtophorus verrucosus Olivier, Megacyllene caryae (Gahan), Xylotrechus colonus (F.), Neoclytus acuminatus (F.), Neoclytus mucronatus (F.), and Phymatodes testaceus (L.). No treatment effect was observed for M. notatus .

How Far Can the Palm Weevil, Rhynchophorus vulneratus (Coleoptera: Curculionidae), Fly?

The palm weevil, Rhynchophorus vulneratus, is native to Southeast Asia and was recovered from an infested Canary Islands date palm in Laguna Beach, California, USA, in 2010. The detection of this potentially destructive palm pest initiated a detection, containment, and eradication program that was reliant, in part, on the deployment of bucket traps loaded with aggregation pheromone and baited with fermenting fruit. A key question that pertained to the deployment of traps was “how far can R. vulneratus fly?” This question could not be answered and in response to this knowledge deficit, computerized flight mill studies were conducted with field-captured R. vulneratus in an outdoor screen house in Sumatra, Indonesia. Of the 63 weevils tethered to flight mills, ∼27% failed to fly >1 km in 24 h and were excluded from analyses. In total, 46 weevils (35 females and 11 males) flew >1 km on flight mills and of these adults, the average total distance flown in 24 h was significantly greater for females (∼32 km) when compared with males (∼15 km). A small proportion of females (∼16%) flew 50-80 km, and one female flew 100.1 km in 24 h. Flying weevils exhibited an average weight loss of ∼13–17% and non-flying control weevils (n=27) lost 10–13% body weight in 24 h. The distribution of flight distances for female and male weevils combined was leptokurtic, which suggests that faster than expected spread by R. vulneratus may be possible in invaded areas.

Ancient and modern colonization of North America by hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), an invasive insect from East Asia

Hemlock woolly adelgid, Adelges tsugae, is an invasive pest of hemlock trees (Tsuga) in eastern North America. We used 14 microsatellites and mitochondrial COI sequences to assess its worldwide genetic structure and reconstruct its colonization history. The resulting information about its life cycle, biogeography and host specialization could help predict invasion by insect herbivores. We identified eight endemic lineages of hemlock adelgids in central China, western China, Ulleung Island (South Korea), western North America, and two each in Taiwan and Japan, with the Japanese lineages specializing on different Tsuga species. Adelgid life cycles varied at local and continental scales with different sexual, obligately asexual and facultatively asexual lineages. Adelgids in western North America exhibited very high microsatellite heterozygosity, which suggests ancient asexuality. The earliest lineages diverged in Asia during Pleistocene glacial periods, as estimated using approximate Bayesian computation. Colonization of western North America was estimated to have occurred prior to the last glacial period by adelgids directly ancestral to those in southern Japan, perhaps carried by birds. The modern invasion from southern Japan to eastern North America caused an extreme genetic bottleneck with just two closely related clones detected throughout the introduced range. Both colonization events to North America involved host shifts to unrelated hemlock species. These results suggest that genetic diversity, host specialization and host phylogeny are not predictive of adelgid invasion. Monitoring non-native sentinel host trees and focusing on invasion pathways might be more effective methods of preventing invasion than making predictions using species traits or evolutionary history.

Direction of interaction between mountain pine beetle (Dendroctonus ponderosae) and resource-sharing wood-boring beetles depends on plant parasite infection

Plant pathogens can have cascading consequences on insect herbivores, though whether they alter competition among resource-sharing insect herbivores is unknown. We experimentally tested whether the infection of a plant pathogen, the parasitic plant dwarf mistletoe (Arceuthobium americanum), on jack pine (Pinus banksiana) altered the competitive interactions among two groups of beetles sharing the same resources: wood-boring beetles (Coleoptera: Cerambycidae) and the invasive mountain pine beetle (Dendroctonus ponderosae) (Coleoptera: Curculionidae). We were particularly interested in identifying potential mechanisms governing the direction of interactions (from competition to facilitation) between the two beetle groups. At the lowest and highest disease severity, wood-boring beetles increased their consumption rate relative to feeding levels at moderate severity. The performance (brood production and feeding) of mountain pine beetle was negatively associated with wood-boring beetle feeding and disease severity when they were reared separately. However, when both wood-boring beetles and high severity of plant pathogen infection occurred together, mountain pine beetle escaped from competition and improved its performance (increased brood production and feeding). Species-specific responses to changes in tree defense compounds and quality of resources (available phloem) were likely mechanisms driving this change of interactions between the two beetle groups. This is the first study demonstrating that a parasitic plant can be an important force in mediating competition among resource-sharing subcortical insect herbivores.

Eradication of Invading Insect Populations: From Concepts to Applications

Eradication is the deliberate elimination of a species from an area. Given that international quarantine measures can never be 100% effective, surveillance for newly arrived populations of nonnative species coupled with their eradication represents an important strategy for excluding potentially damaging insect species. Historically, eradication efforts have not always been successful and have sometimes been met with public opposition. But new developments in our understanding of the dynamics of low-density populations, the availability of highly effective treatment tactics, and bioeconomic analyses of eradication strategies offer new opportunities for developing more effective surveillance and eradication programs. A key component that connects these new developments is the harnessing of Allee effects, which naturally promote localized species extinction. Here we review these developments and suggest how research might enhance eradication strategies.

Comparative analysis of development and survival of two Natal fruit fly Ceratitis rosa Karsch (Diptera, Tephritidae) populations from Kenya and South Africa

Comparative analysis of development and survivorship of two geographically divergent populations of the Natal fruit fly Ceratitis rosa Karsch designated as Ceratitis rosa R1 and Ceratitis rosa R2 from Kenya and South Africa were studied at seven constant temperatures (10, 15, 20, 25, 30, 33, 35 °C). Temperature range for development and survival of both populations was 15-35 °C. The developmental duration was found to significantly decrease with increasing temperature for Ceratitis rosa R1 and Ceratitis rosa R2 from both countries. Survivorship of all the immature stages of Ceratitis rosa R1 and Ceratitis rosa R2 from Kenya was highest over the range of 20-30 °C (87-95%) and lowest at 15 and 35 °C (61-76%). Survivorship of larvae of Ceratitis rosa R1 and Ceratitis rosa R2 from South Africa was lowest at 35 °C (22%) and 33 °C (0.33%), respectively. Results from temperature summation models showed that Ceratitis rosa R2 (egg, larva and pupa) from both countries were better adapted to low temperatures than R1, based on lower developmental threshold. Minimum larval temperature threshold for Kenyan populations were 11.27 °C and 6.34 °C (R1 and R2, respectively) compared to 8.99 °C and 7.74 °C (R1 and R2, respectively) for the South African populations. Total degree-day (DD) accumulation for the Kenyan populations were estimated at 302.75 (Ceratitis rosa R1) and 413.53 (Ceratitis rosa R2) compared to 287.35 (Ceratitis rosa R1) and 344.3 (Ceratitis rosa R2) for the South African populations. These results demonstrate that Ceratitis rosa R1 and Ceratitis rosa R2 from both countries were physiologically distinct in their response to different temperature regimes and support the existence of two genetically distinct populations of Ceratitis rosa. It also suggests the need for taxonomic revision of Ceratitis rosa, however, additional information on morphological characterization of Ceratitis rosa R1 and Ceratitis rosa R2 is needed.

The Wide Potential Trophic Niche of the Asiatic Fruit Fly Drosophila suzukii: The Key of Its Invasion Success in Temperate Europe?

The Asiatic fruit fly Drosophila suzukii has recently invaded Europe and North and South America, causing severe damage to fruit production systems. Although agronomic host plants of that fly are now well documented, little is known about the suitability of wild and ornamental hosts in its exotic area. In order to study the potential trophic niche of D. suzukii with relation to fruit characteristics, fleshy fruits from 67 plant species were sampled in natural and anthropic ecosystems (forests, hedgerows, grasslands, coastal areas, gardens and urban areas) of the north of France and submitted to experimental infestations. A set of fruit traits (structure, colour, shape, skin texture, diameter and weight, phenology) potentially interacting with oviposition choices and development success of D. suzukii was measured. Almost half of the tested plant species belonging to 17 plant families allowed the full development of D. suzukii. This suggests that the extreme polyphagy of the fly and the very large reservoir of hosts producing fruits all year round ensure temporal continuity in resource availability and contribute to the persistence and the exceptional invasion success of D. suzukii in natural habitats and neighbouring cultivated systems. Nevertheless, this very plastic trophic niche is not systematically beneficial to the fly. Some of the tested plants attractive to D. suzukii gravid females stimulate oviposition but do not allow full larval development. Planted near sensitive crops, these "trap plants" may attract and lure D. suzukii, therefore contributing to the control of the invasive fly.

Do Native Insects and Associated Fungi Limit Non-Native Woodwasp, Sirex noctilio, Survival in a Newly Invaded Environment?

Sirex noctilio F. (Hymenoptera: Siricidae) is an introduced pest of pines (Pinus spp.) in several countries in the Southern Hemisphere. Although S. noctilio is established in North America (first discovered in 2004), it has not been a destructive pest there so far, where forest communities more closely resemble those in its native Eurasian range—where it is not a pest. To investigate the influence of the existing community of associated insects (competitors + natural enemies) and fungi (vectored by insects) on S. noctilio survival in North America, we examined stage-specific mortality factors and their relative importance, generating life tables drawn from experimentally-manipulated and natural cohorts of Sirex spp. (mostly S. noctilio, but some native S. nigricornis F.). For both natural and experimentally-manipulated cohorts, factors which acted during the earliest Sirex life stages, most likely tree resistance and/or competition among fungal associates, were paramount in dictating woodwasp survival. Experimentally-manipulated life tables revealed that protection from the community of associates resulted in a significantly, and substantially larger (>15x) S. noctilio F1 generation than exposure to it. Seventy percent of generation mortality in the exposed cohort was due to tree resistance or unknown causes early in larval development, which could have included competition among other bark- or wood-inhabiting insects and/or their fungal associates. Only 46% of generation mortality in the protected cohort was due to tree resistance and/or unknown causes. Parasitoids, particularly endoparasitoids (Ibalia spp.), showed limited ability to control S. noctilio, and reduced the experimentally-established cohort by only 11%, and natural cohorts an average of 3.4%. The relative importance of tree resistance vs. competition with bark- and wood-borers in reducing S. noctilio survival remains unclear. Tree resistance and/or competition likely contribute more than natural enemies in maintaining the S. noctilio population in North America below damaging levels.