Insect Dispersal Research Articles

A Review of the Phenotypic Traits Associated with Insect Dispersal Polymorphism, and Experimental Designs for Sorting out Resident and Disperser Phenotypes.

Dispersal represents a key life-history trait with several implications for the fitness of organisms, population dynamics and resilience, local adaptation, meta-population dynamics, range shifting, and biological invasions. Plastic and evolutionary changes of dispersal traits have been intensively studied over the past decades in entomology, in particular in wing-dimorphic insects for which literature reviews are available. Importantly, dispersal polymorphism also exists in wing-monomorphic and wingless insects, and except for butterflies, fewer syntheses are available. In this perspective, by integrating the very latest research in the fast moving field of insect dispersal ecology, this review article provides an overview of our current knowledge of dispersal polymorphism in insects. In a first part, some of the most often used experimental methodologies for the separation of dispersers and residents in wing-monomorphic and wingless insects are presented. Then, the existing knowledge on the morphological and life-history trait differences between resident and disperser phenotypes is synthetized. In a last part, the effects of range expansion on dispersal traits and performance is examined, in particular for insects from range edges and invasion fronts. Finally, some research perspectives are proposed in the last part of the review.

Proximate Drivers of Migration and Dispersal in Wing-Monomorphic Insects.

Gains in our knowledge of dispersal and migration in insects have been largely limited to either wing-dimorphic species or current genetic model systems. Species belonging to these categories, however, represent only a tiny fraction of insect biodiversity, potentially making generalization problematic. In this perspective, I present three topics in which current and future research may lead to greater knowledge of these processes in wing-monomorphic insects with limited existing molecular tools. First, threshold genetic models are reviewed as testable hypotheses for the heritability of migratory traits, using the sweet potato whitefly (Bemisia tabaci) as a case study of a behaviorally-polymorphic migratory species lacking morphological or physiological differentiation. In addition, both adaptive and non-adaptive explanations for the empirically variable relationship between egg production and flight in wing-monomorphic insects are discussed. Finally, with respect to the largest order of insects (Hymenoptera), the role of sex determination mechanisms for haplodiploidy as a driver for natal dispersal (for inbreeding avoidance) versus philopatry (such as in local mate competition) is discussed.

Active dispersal in Triatoma infestans (Klug, 1834) (Hemiptera: Reduviidae: Triatominae): Effects of nutritional status, the presence of a food source and the toxicological phenotype

In Argentina, the main vector of Chagas disease is Triatoma infestans (Klug, 1834). In recent years, the presence of T. infestans was reported in human dwelling after spraying with pyrethroids in several locations in Argentina. The presence of these insects can be attributed, among other factors, to colonization by bugs from sylvatic or peridomestic populations or to the evolution of resistance to insecticides. In both cases, the dispersal of insects is a determining factor. The aim was to determinate the interaction of dispersal with feeding, food resource and resistance to insecticides. Three nutritional states were obtained with the number of feeds (NF) offered (0, 1 or 2). The resistant females were evaluated only with NF1. The experimental arena was 10 m long and contained two shelters. Groups of 30 virgin females of each NF were released in one of the shelters and were able to move during 3 days/nights. Females without possibility of dispersal were the controls. Results showed that the individuals dispersed mainly walking regardless of the number of feeds, the presence of food resource and toxicological phenotype. This type of dispersal presented energy costs in susceptible individuals but not in resistant ones. The numbers of feeds that determined low nutritional states showed greater dispersal and activity associated with the shelter. The presence of a food source had an effect on the dispersal capacity and this depended on the number of feeds. There was a decrease in the dispersal in individuals with one feeding and an absence of response in fasted individuals and with two feeds. On the other hand, a lower dispersal tendency were found in resistant females compared to susceptible females, suggesting that resistance to deltamethrin is associated with adaptive costs.

Hot water treatment: an effective method for disinfecting Castanea sativa mill. dormant scions against Dryocosmus kuriphilus Yasumatsu.

The Asian chestnut gall wasp (ACGW) Dryocosmus kuriphilus Yasumatsu is the most severe pest of the genus Castanea worldwide. After its arrival in Europe, the insect dispersed rapidly from Italy to other European countries, as well as spreading over long distances within each country because of the unintentional transport of infested chestnut material owing to the fact that infestation inside the dormant buds is visually undetectable. Hot water treatment (HWT) has been tested in terms of pest and diseases control in propagation processes with a wide range of plant material and species, including the Asian chestnut Castanea mollissima cv 'Qing'. Taking into account the different thermal tolerances of plant species, an experiment to disinfect Castanea sativa scions from ACGW by HWT was performed. The effects of the immersion of dormant scions for 10min at two water temperatures (49 and 52 °C), with and without a previous period of water hydration, were tested. A 10min soak at 49 °C was effective in killing ACGW larvae while retaining an excellent percentage of successful grafts. The pre-HWT hydration stage did not influence the success of the treatment. Positive shoot growth was also recorded after HWT. We report for the first time the effectiveness of a simple and environmentally friendly protocol based on hot water for the disinfection of European chestnut (C. sativa) scions against D. kuriphilus. This will enable nurseries to supply plants free from this pest, preventing the insect dispersion, which will have a positive socio-economic impact to the chestnut tree sector. Also positive environmental impact will be favoured as gall wasp proliferation will decrease. © 2019 Society of Chemical Industry.

Development of method to forecast soybean leaf damage by common cutworm using entomological radar and searchlight trap

To develop a method to forecast soybean leaf damage caused by larvae of the common cutworm, Spodoptera litura (Fabricius), insect dispersion was monitored with an x-band entomological radar and a searchlight trap during the summer soybean season in 2016 and 2017 in western Japan. The insect catch number in the searchlight trap and number of newly damaged leaves in a soybean field were compared to see how much soybean damage the insect's arrival caused. The 2016 results indicated that catch number peaks appeared 3–5 days before the peaks in the number of newly damaged leaves. The time lag corresponded to the egg period. Similar data were found in 2017. However, both the catch number and the number of newly damaged leaves were smaller that year, due to the lower occurrence of the insect. The radar observation showed dispersion at altitudes over the monitoring site when the peaks in insect catch number occurred. The insects often arrived under a northerly wind condition, from the mountainous area to the north. This study suggested that short-term forecasting of soybean leaf damage by radar and searchlight trap may be possible.

Human-mediated dispersal in insects.

Central to the problem of biological invasions, human activities introduce species beyond their native ranges and participate in their subsequent spread. Understanding human-mediated dispersal is therefore crucial for both predicting and preventing invasions. Here, we show that decomposing human-mediated dispersal into three temporal phases: departure, transport and arrival, allows to understand how the characteristics of human activities and the biological traits of species influence each phase of the dispersal process, and ultimately govern invasion pathways in insects. Integrating these precise mechanisms into future invasion models should increase their realism and generalization for any potential insect invader. Moreover, understanding these mechanisms can provide insight into why some invasive insects are more widely distributed than others, and to estimate risks posed by species that have not yet been introduced.

Effect of reproductive state on active dispersal in Triatoma infestans (Klug, 1834) (Hemiptera: Reduviidae: Triatominae) susceptible and resistant to deltamethrin

Triatoma infestans (Klug, 1834) is the main vector of the Chagas´ disease in Argentina. The presence of insects in the domestic environment after application of pyrethroid insecticides was reported. The colonization and the evolution of insecticide resistance are processes that can explain these control failures. In both processes, the active dispersal of insects is a determining factor. The aim of the present study was to determine whether the reproductive state modulate the dispersal capacity of females of T. infestans susceptible and resistant to deltamethrin. For this, different variables associated with active dispersal were measured in virgin and copulated females both susceptible and resistant to deltamethrin. The experimental arena was 10 m long and contained two shelters. Groups of 12 females of each experimental group were released in one of the shelters and were able to move during 3 days/nights. The results showed that the females mainly dispersed by walking regardless of the reproductive state and the toxicological phenotype. On the other hand, the copula affected the posterior dispersal capacity in females susceptible and resistant to deltamethrin. The copulated females dispersed more times, leaved more times from the shelters and showed a higher proportion of dispersed individuals than the virgin females. Finally, the insecticide resistance reduced the dispersal capacity of females. The resistant insects showed lower number of dispersal events, a lower proportion of dispersed individuals, and lower exit and entry events from/to shelter than susceptible insects. This is the first report of the effect of copula on the capacity of active dispersion in vectors of Chagas disease susceptible and resistant to insecticides.

Ethylene signaling mediates potyvirus spread by aphid vectors.

Plant pathogens can influence host characteristics such as volatile emissions, nutrient composition or plant color, modulating vector and non-vector insect dynamics in the ecosystem. While previous research has focused on insect attraction and dispersal to infected plants, little is known about mechanisms mediating these interactions. Here, we investigate the role of ethylene in green peach aphid (Myzus persicae) attraction to potyvirus-infected plants. In our experiments, we utilized two different potyviruses, Potato virus Y (PVY) and Turnip mosaic virus, in lab and field experiments. Consistent with previous studies, we show that greater numbers of aphids settle on potyvirus-infected plants in the lab and greater numbers of aphids are found in PVY-infected potato (Solanum tuberosum) fields compared to controls. In laboratory experiments, inhibition of ethylene signaling in plants either chemically or genetically prevented aphids from preferentially settling on potyvirus-infected plants. Virus spread was reduced in lab arenas by over 80% when ethylene signaling was inhibited chemically. Despite this, ethylene inhibition had no significant impact on virus spread in field mesocosms. Our results indicate that induction of ethylene signaling by potyviruses mediates aphid attraction to infected plants and virus spread; however, additional factors may contribute to plant-vector dynamics in complex communities. Specific components of ethylene signaling may be important targets for future management of vector-borne viruses and research on mechanisms mediating plant-vector-virus interactions.

A method for assessing mitochondrial physiology using mechanically permeabilized flight muscle of Aedes aegypti mosquitoes

Aedes aegypti is the most important and widespread vector of arboviruses, including dengue and zika. Insect dispersal through the flight activity is a key parameter that determines vector competence, and is energetically driven by oxidative phosphorylation in flight muscle mitochondria. Analysis of mitochondrial function is central for a better understanding of cellular metabolism, and is mostly studied using isolated organelles. However, this approach has several challenges and methods for assessment of mitochondrial function in chemically-permeabilized tissues were designed. Here, we described a reliable protocol to assess mitochondrial physiology using mechanically permeabilized flight muscle of single A. aegypti mosquitoes in combination with high-resolution respirometry. By avoiding the use of detergents, high respiratory rates were obtained indicating that substrate access to mitochondria was not limited. This was confirmed by using selective inhibitors for specific mitochondrial substrates. Additionally, mitochondria revealed highly coupled, as ATP synthase or adenine nucleotide translocator inhibition strongly impacted respiration. Finally, we determined that pyruvate and proline induced the highest respiratory rates compared to other substrates tested. This method allows the assessment of mitochondrial physiology in mosquito flight muscle at individual level, and can be used for the identification of novel targets aiming rational insect vector control.

Effects of larval density on dispersal and fecundity of western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae).

The western corn rootworm, Diabrotica virgifera virgifera (LeConte) (Coleoptera: Chrysomelidae), is an economically important pest of corn in the northern United States. Some populations have developed resistance to management strategies including transgenic corn that produces insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt). Knowledge of insect dispersal is of critical importance for models of resistance evolution. Larval density affects survival in the field, and stress from crowding often affects facultative long-distance dispersal of adult insects. In this study, we used laboratory flight mills to characterize western corn rootworm flight performance as a function of larval rearing density. Larvae were reared under three densities and the resulting adult females were either allowed to fly voluntarily for 22 h or forced to fly specified durations. For both experiments we also measured lifetime fecundity following flight. The three rearing densities placed differential levels of stress on individuals, as evidenced by decreased survival to adulthood and decreased size of adults at greater rearing density. When larvae were reared under crowded conditions the resulting females were more likely to engage in flight activity, including long uninterrupted flights lasting >10 min, than those reared under low density conditions. Flight and egg production are both energy intensive processes. However, we found no evidence in either voluntary or forced flight experiments of a tradeoff between flight activity and female fecundity. The results suggest that females emerging from high density populations in cornfields are more likely to disperse and disperse farther than those emerging from low density populations. These results are important because they imply that variation in population density in the landscape will affect dispersal, which may in turn require computer models of resistance evolution to incorporate multiple dispersal rates arising from varying larval densities among fields.

Multiple Approaches to Address Potential Risk Factors of Chagas Disease Transmission in Northeastern Brazil.

Chagas disease is one of the most significant systemic parasitosis in Latin America, caused by Trypanosoma cruzi, which is mainly transmitted by hematophagous insects, the triatomines. This research was carried out in both domestic and wild environments throughout a Northeastern rural locality. Triatomines were captured in both peridomicile and wild environments, obtaining 508 specimens of triatomines, of which 99.6% were Triatoma brasiliensis. Insects were captured in 10 (18.5%) peridomiciles with an average of 8.3 triatomines per residence. Triatoma brasiliensis nymphs and adults were found in six peridomiciles, generating a 11.1% colonization. No T. cruzi infection was detected in the 447 peridomestic insects analyzed. On the other hand, of the 55 sylvatic T. brasiliensis molecularly examined for T. cruzi, 12 (21%) were positive, all harboring T. cruzi I. The blood meal analysis by enzyme-linked immunosorbent assay from gut content revealed that both peridomestic and wild triatomine populations fed mainly on birds, refractory to the parasite, which may explain the null rate of natural infection prevalence in the domestic environment. However, infected triatomines for potential home infestation within the radius of insect dispersion capacity were registered in rock outcrops around the dwellings. Anthropogenic environmental influences are able to rapidly alter these scenarios. Therefore, to avoid disease transmission to humans, we recommend constant vector control combined with periodic serological surveillance. The associated methodology presented herein may serve as a model for early detections of risk factors for Chagas disease transmission in the Brazilian Northeast.

Effect of nutritional state and dispersal on the reproductive efficiency in Triatoma infestans (Klug, 1834) (Hemiptera: Reduviidae: Triatominae) susceptible and resistant to deltamethrin

The dispersal of insects is determinant in the colonization of new areas and the propagation of insecticide resistance. Nutritional status and reproductive characteristics determine the colonization capacity after the dispersal event. Studies about of the effects of dispersal on reproduction in triatomines are few and none in resistant insects. The aim was to determine the effects of nutritional state and dispersal on the subsequent reproductive potential in Triatoma infestans (Klug, 1834) susceptible and resistant to deltamethrin. Three nutritional states were obtained with the number of feeds (NF) offered (0, 1 or 2). The resistant females were evaluated only with NF1. The experimental arena was 10 m long and contained two shelters. Groups of 30 virgin females of each NF were released in one of the shelters and were able to move during 3 days/nights. Females without possibility of dispersal were the controls. The reproductive parameters were determined on the couples between the experimental females and males from the breeding. The results showed that most of the females dispersed by walking. The dispersal had effects on the reproduction of the deltamethrin-susceptible females and this depended on the number of feeds. Fecundity, fertility and the proportion of females that oviposited were higher in females dispersed with two feeds but was lower in females dispersed with less feeds. In addition, the effect of the dispersal on the reproduction and the life time also depended of the toxicological phenotype. The resistant insect oviposited in higher proportion and showed greater fecundity and more weeks of life when they dispersed that when they did not do it, and was opposite to that observed in susceptible ones. Finally, the resistance to insecticide had an effect on the reproduction and the life span and this effect depended on whether the insects dispersed or not.

Walking activity and dispersal on deltamethrin- and spinosad-treated grains by the maize weevil Sitophilus zeamais

The maize weevil (Sitophilus zeamais) is a serious worldwide pest of stored products frequently requiring control measures to reduce its infestation and minimize grain losses. The fumigant phosphine and insecticides including pyrethroids and organophosphates have been the most used management tools against this stored product pest, but the over-reliance on these chemical products has led to insecticide resistance in maize weevil populations. A recent alternative, the actinomycete-based insecticide spinosad, has been considered highly effective against several stored grain pests, including maize weevils, and has sparked increasing attention. Nonetheless, the sublethal effects of spinosad have yet to be studied, particularly regarding its potential effect on insect dispersal within contaminated grain masses since exposure may be either enhanced or compromised. Thus, we carried out laboratory experiments using a digital tracking system and commercial insecticide formulations with the objective to assess if deltamethrin- or spinosad-contaminated grains may affect the walking activity and dispersal movements of adult maize weevils. The overall activity of groups of weevils was enhanced with insecticide exposure. However, insecticide exposure did not affect resting time and distance walked, but velocity and number of stops were affected compromising walking in individual walking bioassays. Insecticide avoidance by either irritability and repellence were not detected. Dispersal of adult maize weevils on treated grains differed among insecticidal treatments with individuals spending more time at the edges of arenas in non-treated and deltamethrin-treated grains. In contrast, insects on spinosad-treated grains were more evenly distributed within the arena. These findings reinforce the potential of spinosad as an alternative for managing maize weevils because this insecticide minimizes the risk of dispersal away from treated grains.

Incorporating terminal velocities into Lagrangian stochastic models of particle dispersal in the atmospheric boundary layer

Lagrangian stochastic models for simulation of tracer-particle trajectories in turbulent flows can be adapted for simulation of particle trajectories. This is conventionally done by replacing the zero-mean fall speed of a tracer-particle with the terminal speed of the particle. Such models have been used widely to predict spore and pollen dispersal. Here I show that this modification predicts that particles become uniformly distributed throughout the air column, which is at variance with the seminal experimental studies of Hirst et al. (1967) that demonstrated spore concentrations (and pollen concentrations) declined exponentially with height in unstable air. This discrepancy arises because the terminal speed, which is a Lagrangian property of a particle, has always been treated as if it were an Eulerian property of an ensemble of particles. In this study models are formulated correctly. I show that the mean acceleration of a tracer-particle should be replaced by the mean acceleration of a particle. Model predictions for aerial density profiles then agreed with the observations of Hirst et al. (1967) and with observations of ground-level concentrations but differed significantly from predictions obtained using conventional models. In accordance with the results of numerical simulations, the models also predict that particles are moving downwind marginally more slowly than the wind itself. Finally, the new modelling approach can be extended to predict the dispersal of small insects with active flight behaviours.

Barriers to dispersal: The effect of a weir on stream insect drift

AbstractDams and weirs degrade river ecosystems, reducing diversity and altering the assemblage composition of aquatic biota. These structures may damage rivers by disrupting longitudinal connectivity, fragmenting rivers, and isolating populations. We tested whether a weir could impede the downstream dispersal of stream insects by comparing drift rates through natural pools and through a weir pool. For three of four of our study taxa (Offadens spp., Austrosimulium spp., and Simsonia spp.), we found the numbers of drifters were consistently reduced by the weir across multiple occasions (reduction ranging from 68 to 98%) to a higher degree than natural pools (reduction ranging from 24 to 41%). Drift of Cheumatopsyche spp. through the weir was greatly reduced in December (−95%) compared with natural pools, but the weir had little effect during April (−9%). There were size‐related patterns in drift through the weir pool for some taxa. In the weir pool, emigrating individuals of Austrosimulium spp. were significantly smaller than immigrating individuals, which was not observed in natural pools. In contrast, significant reductions of Cheumatopsyche spp. drifters through the weir only occurred when individuals were small (December). Within the weir pool, the combined effects of lower average water velocity, multiple large low velocity areas, and the weir wall were likely to be the cause of the reduction in stream insect drift through the weir. The impediment of drift of some taxa by weirs may affect dispersal and colonisation processes. This obstruction of downstream movement could undermine the outcomes of river restoration projects.

Host–Plant Relations of Gall-Inducing Insects

Galls are modified, invariably symmetrical, naturally developing plant structures that arise because of messages from certain specialist insects, mostly from the Thysanoptera, Hemiptera, Diptera, and Hymenoptera, and in a lesser frequency from the Lepidoptera and Coleoptera. Several species of the Eriophyoidea (Acari) induce galls and wherever appropriate, we have considered examples from the Eriophyoidea as well, generically referred under the term “insects”. The insects live within them, deriving nourishment and shelter. When these insects attack plant tissues, osmotic-change–related stress increases, thus stimulating alterations in gas exchange and subcellular metabolic functions. The osmotic stress alters the electrical properties of the plant-cell plasma membranes and impacts on indole-acetic acid synthesis and activity, which, in turn, affects the H+-transport. Insect action stimulates parts of host-cell wall to break down and the degenerated wall materials in the cytoplasm act as elicitors. In such contexts the susceptible plants use flexible strategies to mitigate stress, which generally manifest as galls. Inherited traits also play a role in providing specific shapes to the gall, which is coordinated by the innate correlating morphogenetic factors that operate normally in the plant. The gall-inducing Diptera (Cecidomyiidae), Hemiptera (Sternorrhyncha), and Hymenoptera (Cynipidae) induce galls of highly defined and exquisite shapes. Almost all of these insects are known for their specificity to plants. The gall-inducing insects, unlike many of their free-living relatives, discriminate between plants and choose from them. Selection of a particular plant by a gall-inducing insect is not a matter of chance, given that the insect encounters varied plant taxa in the natural environment. The gall-inducing insects preferentially feed on specific plant organs, or parts of these, and on specific plant species. One recent explanation is that the gall-inducing insects prefer certain plants or parts of those plants, because they need the lipidic materials, e.g., sterols, available in those plant parts, which the insects utilize for building hormones critically necessary for their metamorphosis. Because of the sedentary nature of the juvenile stages of the inducing insect, the gravid females endowed with specialized sensory structures play a key role in selecting the site precisely for oviposition and thus for the progeny. Although a majority of gall-inducing insects are restricted to specific plant taxa, some of them, as we presently know, are indicated to be capable of inducing galls on plant species closely related to their mostpreferred hosts, thus demonstrating some level of oligophagy. A few species of Asphondyliina and Schizomyiina (Cecidomyiidae) are presently indicated as polyphagous. Clearly demonstrated host shifts and adaptive radiation in some of the European and North-American gall-inducing Tephritidae populations explain the evolution of sympatric host races, more because of changes either in the preference of feeding and/or oviposition sites or by acquiring “new” physiological adaptations to new plants or through assortative mating. Differences in the temporally regulated flowering and leafing phenologies in the susceptible plants possibly play a role in isolating gall-inducing insect populations, which enable divergence and diversification via genetic drift. The general understanding, as of now, is that host shifts and radiation in gall-inducing insects are more complex than what is known in their non-gallinducing allies. Such a complexity is attributed to intricate relationships of gall-inducing insects with plants and the dispersal of gall-inducing insects through different biogeographical realms, mainly influenced by the abundance and variety of plant species. The gall-inducing insects, as a highly evolved group,... This abstract has been truncated. To view the complete abstract please download the PDF.

Dispersal behaviour of female stag beetles (Lucanus cervus) in a mosaic landscape: when should I stay and where should I go

Abstract Global habitat destruction is bringing species to the edge. Consequently, understanding species dispersal behaviour is becoming essential in order to safeguard vital meta‐populations. Nevertheless, dispersal is too often seen as unconditional rather than triggered by habitat cues. We applied radio telemetry on female European stag beetles [Lucanus cervus (L., 1758)] in a mosaic landscape to investigate the hypothesis that dispersal is habitat driven, in this case by canopy closure and presence of suitable dead wood, SDW. We found that the decision to disperse depended on canopy closure and that dispersal distance depended both on SDW availability and canopy closure. Long distance dispersal (by flying), in contrast to small distance dispersal (mainly walking), is shown to be a successful strategy to reach locations with lower canopy closure. We conclude that dispersal of female stag beetles is not unconditional but shaped by habitat resources. It is therefore likely that habitat also affects dispersal of other insects and should be considered in future dispersal studies. For the conservation of the European stag beetle, our results imply that it is essential to provide stepping stones of suitable dead wood, preferably every 100 m and not more than 1 km apart. These stepping stones should be provided in open to half‐shaded conditions. Management systems such as coppicing which provide periodic sun‐exposure and sufficient amounts of (underground) dead wood are good management procedures for conservation of the stag beetle but they need to be performed at small scales to ensure suitable habitat proximity.

Passive kHz lidar for the quantification of insect activity and dispersal

BackgroundIn recent years, our group has developed electro-optical remote sensing methods for the monitoring and classification of aerofauna. These methods include active lidar methods and passive, so-called dark-field methods that measure scattered sunlight. In comparison with satellite- and airborne remote sensing, our methods offer a spatiotemporal resolution several orders of magnitude higher, and unlike radar, they can be employed close to ground. Whereas passive methods are desirable due to lower power consumption and ease of use, they have until now lacked ranging capabilities.ResultsIn this work, we demonstrate how passive ranging of sparse insects transiting the probe volume can be achieved with quadrant sensors. Insects are simulated in a raytracing model of the probe volume, and a ranging equation is devised based on the simulations. The ranging equation is implemented and validated with field data, and system parameters that vary with range are investigated. A model for estimating insect flight headings with modulation spectroscopy is implemented and tested with inconclusive results. Insect fluxes are retrieved through time-lag correlation of quadrant detector segments, showing that insects flew more with than against the wind during the study period.ConclusionsThe presented method demonstrates how ranging can be achieved with quadrant sensors, and how it can be implemented with or without active illumination. A number of insect flight parameters can be extracted from the data produced by the sensor and correlated with complementary information about weather and topography. The approach has the potential to become a widespread and simple tool for monitoring abundances and fluxes of pests and disease vectors in the atmosphere.

Interrelation of mating, flight, and fecundity in navel orangeworm females

AbstractThe navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae, Phycitini), is an economically important pest of nut crops in California, USA. Improved management will require better understanding of insect dispersal, particularly relative to when mating occurs. A previous study demonstrated a more robust laboratory flight capacity compared to other orchard moth pests, but it was unclear how mating affects dispersal, and how dispersal affects fecundity. In this study, 1‐ and 2‐day‐old females were allowed to fly overnight on a flight mill either before or after mating, respectively, and were then allowed to oviposit. Data on fecundity were compared between treatments to minimally handled or tethered‐only control females. Females that mated before flight flew longer and covered a greater distance than those flying prior to mating. However, timing of flight relative to mating did not affect fecundity, nor did any measure of flight performance. There was no effect on fecundity when females were forced to fly for designated durations from 3 min to 2 h. Together, our data revealed no obvious trade‐off between flight activity and reproductive output. Distances measured on the flight mills (mean ca. 15 km for mated females) may overestimate net displacement in the field where flight tracks are often meandering. The results suggest that most females mate and oviposit in or near their natal habitat, but that some may disperse potentially long distances to oviposit elsewhere.

Dispersal limitation of saproxylic insects in a managed forest? A population genetics approach

Dispersal is a key trait of species enabling gene flow among populations. For species persistence dispersal may therefore be crucial especially in a patchy or changing environment. Tree hollows are a patchy habitat as their number is locally limited and in addition to that, habitat quality of tree hollows differs. Both factors are important for colonization by saproxylic insects as species may be specialized on a particular age or quality of a tree hollow and may be dispersal-limited. Intensive forest management may further decrease the number of tree hollows and increase distances between them, if trees with hollows are removed. However, not much is known about the dispersal abilities of most saproxylic species, even though such knowledge could improve conservation efforts. To investigate the genetic population structure of saproxylic species, we collected saproxylic organisms with emergence traps from 40 hollows in beech trees in a managed forest in Germany (approximately 14×14km). We focused on three threatened species, one coleopteran and two dipteran (Anaspis ruficollis, Scraptiidae; Criorhina floccosa, Syrphidae; Xylomya maculata, Xylomyidae) emerging from our tree hollows. Microsatellite analysis was used to assess gene flow among tree hollows and population genetic structure. In contrast to other studies reporting limited dispersal in saproxylic insects, we found no indication for restricted gene flow in all three species investigated. However, we studied relatively abundant species and our study site may not have been large enough to detect genetic substructure. This study indicates that the amount and quality of a suitable habitat may at least in some cases be more limiting than the physical ability to disperse.