Contribution of habitat type to residency and dispersal choices by overwintered and summer adult Colorado potato beetles

The walking and flight dispersal of marked overwintered and summer Colorado potato beetles (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), released in field box‐plots was monitored simultaneously in six habitats over a period of 4 days. The emigration out of plots by walking beetles was calculated from the catch in linear pitfall traps completely surrounding each box‐plot and emigration flight was estimated from the number of beetles missing from the plot or captured by the trap. Overwintered beetles dispersed sooner after release than summer beetles. Overall, the mean number of beetles retained by the habitat was significantly higher in the host habitat (potato) than in any non‐host habitat tested (soybean, pasture, bare ground, water, woodland). Unexpectedly, there was no or little difference in overall beetle retention between non‐host habitats except for higher retention in the water habitat. No difference in the ratio of flight over walking could be detected by the study between overwintered and summer CPB except in the water and woodland habitats. Twenty‐four hours after release, the highest ratios were obtained in the water and woodland habitats and the lowest in the bare‐ground habitat, but ratios were similar for all habitats, except water, after 96 h. As a population, under these experimental conditions, 96 h after release, it seems that CPB displayed a slight preference for flight over walking, with walking as a default mode. A fed and starved pre‐release treatment had no effect on dispersal rates or mode of dispersal. Essentially, our results showed that over a 96‐h period, northeastern North American CPB emigrated at similar rates from the various non‐host habitats encountered, except for water, using walking as much as flight. The host habitat retained CPB significantly longer than non‐host habitats but with a mode of dispersal ratio similar to that in non‐host habitats. The impact on dispersal of the various habitats encountered by CPB in the agro‐ecosystem was less important than expected suggesting that the interaction of environmental parameters is likely to have the most significant impact in determining dispersal rates and dispersal modes.     

Non-Density Dependent Pollen Dispersal of Shorea maxwelliana (Dipterocarpaceae) Revealed by a Bayesian Mating Model Based on Paternity Analysis in Two Synchronized Flowering Seasons

Pollinator syndrome is one of the most important determinants regulating pollen dispersal in tropical tree species. It has been widely accepted that the reproduction of tropical forest species, especially dipterocarps that rely on insects with weak flight for their pollination, is positively density-dependent. However differences in pollinator syndrome should affect pollen dispersal patterns and, consequently, influence genetic diversity via the mating process. We examined the pollen dispersal pattern and mating system of Shorea maxwelliana, the flowers of which are larger than those of Shorea species belonging to section Mutica which are thought to be pollinated by thrips (weak flyers). A Bayesian mating model based on the paternity of seeds collected from mother trees during sporadic and mass flowering events revealed that the estimated pollen dispersal kernel and average pollen dispersal distance were similar for both flowering events. This evidence suggests that the putative pollinators – small beetles and weevils – effectively contribute to pollen dispersal and help to maintain a high outcrossing rate even during sporadic flowering events. However, the reduction in pollen donors during a sporadic event results in a reduction in effective pollen donors, which should lead to lower genetic diversity in the next generation derived from seeds produced during such an event. Although sporadic flowering has been considered less effective for outcrossing in Shorea species that depend on thrips for their pollination, effective pollen dispersal by the small beetles and weevils ensures outcrossing during periods of low flowering tree density, as occurs in a sporadic flowering event.     

Field estimates of fitness costs of the pace‐of‐life in an endangered damselfly

Theory predicts that within‐population differences in the pace‐of‐life can lead to cohort splitting and produce marked intraspecific variation in body size. Although many studies showed that body size is positively correlated with fitness, many argue that selection for the larger body is counterbalanced by opposing physiological and ecological selective mechanisms that favour smaller body. When a population split into cohorts with different paces of life (slow or fast cohort), one would expect to detect the fitness–size relationship among and within cohorts, that is, (a) slower‐developing cohort has larger body size and higher fitness than faster‐developing cohort, and (b) larger individuals within each cohort show higher fitness than smaller individuals. Here, we test these hypotheses in capture–mark–recapture field surveys that assess body size, lifespan, survival and lifetime mating success in two consecutive generations of a partially bivoltine aquatic insect, Coenagrion mercuriale, where the spring cohort is slower‐developing than the autumn cohort. As expected, body size was larger in the slow‐developing cohort, which is consistent with the temperature‐size rule and also with the duration of development. Body size seasonal variation was greater in slow‐developing cohort most likely because of the higher variation in age at maturity. Concordant with theory, survival probability, lifespan and lifetime mating success were higher in the slow‐developing cohort. Moreover, individual body size was positively correlated with survival and mating success in both cohorts. Our study confirms the fitness costs of fast pace‐of‐life and the benefits of larger body size to adult fitness.     

CLINAL VARIATION IN SEED TRAITS INFLUENCING LIFE CYCLE TIMING IN ARABIDOPSIS THALIANA

Early life‐history transitions are crucial determinants of lifetime survival and fecundity. Adaptive evolution in early life‐history traits involves a complex interplay between the developing plant and its current and future environments. We examined the plant's earliest life‐history traits, dissecting an integrated suite of pregermination processes: primary dormancy, thermal induction of secondary dormancy, and seasonal germination response. We examined genetic variation in the three processes, genetic correlations among the processes, and the scaling of germination phenology with the source populations’ climates. A spring annual life history was associated with genetic propensities toward both strong primary dormancy and heat‐induced secondary dormancy, alone or in combination. Lineages with similar proportions of winter and spring annual life history have both weak primary dormancy and weak thermal dormancy induction. A genetic bias to adopt a spring annual strategy, mediated by rapid loss of primary dormancy and high thermal dormancy induction, is associated with a climatic gradient characterized by increasing temperature in summer and rainfall in winter. This study highlights the importance of considering combinations of multiple genetically based traits along a climatic gradient as adaptive strategies differentiating annual plant life‐history strategies. Despite the genetic‐climatic cline, there is polymorphism for life‐history strategies within populations, classically interpreted as bet hedging in an unpredictable world.     

Host plant effects on the behavioural phenotype of a Chrysomelid

1. The food plant quality influences feeding preferences and various life history traits of herbivorous insects. However, the effects of different host plant qualities on the behavioural phenotype have rarely been studied in behavioural ecology, especially in a pest‐crop‐framework. 2. Behavioural phenotypes of insects may not only be affected by external environmental factors, such as the host plant quality but are also shaped by internal factors, such as the sex and the age of individuals. 3. To study host plant effects on behavioural phenotypes, we reared mustard leaf beetles (Phaedon cochleariae Fabricius) either on their natural host watercress or on the crop cabbage, on which this beetle can be a pest. The behavioural phenotype was characterised twice in the adult lifetime by measuring six behavioural traits tested in distinct contexts. 4. Depending on the context, different behavioural traits were specifically affected by the host plant, the sex and/or the age. Beetles fed on cabbage became more active with age. Furthermore, the boldness tested in an unprotected environment context was influenced by the host, with beetles fed on cabbage being bolder, whereas the boldness in a hiding or predator attack context was affected by the age and/or the interaction of host plant × sex. 5. In conclusion, beetles fed on the crop cabbage develop a different behavioural phenotype compared to beetles fed on watercress. Previous results showed that beetles reared on cabbage have a higher reproductive output. Thus, beetles fed on the crop potentially express a faster pace‐of‐life.     

An alternative hibernation strategy involving sun-exposed 'hotspots', dispersal by flight, and host plant finding by olfaction in an alpine leaf beetle

Oreina cacaliae (Schrank) (Coleoptera: Chrysomelidae) has a 2‐year life cycle that it has to complete within the short warm seasons of the harsh alpine environment. Three years of field observations and experiments revealed that not all beetles overwintered in the soil next to their principal host Adenostyles alliariae (Asteraceae), as was previously assumed, but that many O. cacaliae left their host in autumn and flew to overwintering sites that were extensively sun‐exposed. In spring, these individuals became active 2 months earlier than their conspecifics that had remained in the soil close to the host plant. These early beetles flew from their hibernation sites against the direction of the prevailing wind. After a random landing in snow, they walked to the spring host Petasites paradoxus (Asteraceae) and fed on its floral stalks, the only plant parts present at that time. A few weeks later, they took flight again to locate newly emerging A. alliariae on which they would feed and deposit larvae as did individuals that had overwintered close to A. alliariae. Leaves of A. alliariae contain pyrrolizidine alkaloids (PAs), which the beetles sequester for their own defence. The dominating PA (seneciphylline) was also found to be present in the floral stalks of P. paradoxus. With additional behavioural assays in the field and laboratory, we demonstrated the importance of plant odours in the short‐range host location process. This study reveals a unique hibernation behaviour in which part of the beetle population uses exceptionally warm locations from which they emerge in spring, long before all the snow has melted. This early, but risky emergence allows them to exploit a second, highly suitable host plant, which they locate first by wind‐guided flight and then by odour‐guided walking. The well‐fed beetles then use odour again to move to their principal host plant, on which they reproduce.     

Experimentally induced host‐shift changes life‐history strategy in a seed beetle

Expansion of the host range in phytophagous insects depends on their ability to form an association with a novel plant through changes in host‐related traits. Phenotypic plasticity has important effects on initial survival of individuals faced with a new plant, as well as on the courses of evolutionary change during long‐term adaptation to novel conditions. Using experimental populations of the seed beetle that evolved on ancestral (common bean) or novel (chickpea) host and applying reciprocal transplant at both larval and adult stage on the alternative host plant, we studied the relationship between the initial (plastic) phases of host‐shift and the subsequent stages of evolutionary divergence in life‐history strategies between populations exposed to the host‐shift process. After 48 generations, populations became well adapted to chickpea by evolving the life‐history strategy with prolonged larval development, increased body mass, earlier reproduction, shorter lifespan and decreased plasticity of all traits compared with ancestral conditions. In chickpea‐adapted beetles, negative fitness consequences of low plasticity of pre‐adult development (revealed as severe decrease in egg‐to‐adult viability on beans) exhibited mismatch with positive effects of low plasticity (i.e. low host sensitivity) in oviposition and fecundity. In contrast, beetles adapted to the ancestral host showed high plasticity of developmental process, which enabled high larval survival on chickpea, whereas elevated plasticity in adult behaviour (i.e. high host sensitivity) resulted in delayed reproduction and decreased fecundity on chickpea. The analysis of population growth parameters revealed significant fluctuation during successive phases of the host‐shift process in A. obtectus.     

Phenotypic Plasticity and Repeatability in the Mating Signals of Enchenopa Treehoppers, with Implications for Reduced Gene Flow among Host-Shifted Populations

Mate signaling systems, because of their role in assortative mating, have often been implicated in the origins of evolutionary independence between lineages. We investigated three sources of phenotypic plasticity in mating signals with potential relevance to assortative mating in a species in the Enchenopa binotata complex of treehoppers. This group has been a model for speciation in sympatry through shifts to novel host plants. Host shifts result in partial reproductive isolation in Enchenopa binotata because of their effects on life history timing, but interbreeding is still possible if there is dispersal and some overlap of mating periods. Courtship in these plant‐feeding insects is mediated by plant‐borne vibrational signals. We asked whether variation in male mate signaling behavior is influenced by plant substrate, age, or size, each of which may play a role in interactions among host‐shifted populations. Males produced fewer, shorter signals when on non‐hosts than when on hosts. However, there were no effects of age or size on signal variation. Significant repeatability of some signal features (carrier frequency and the number of signals produced in a signaling bout) is consistent with the presence of genetic variation and thus the potential to respond to selection. Our results suggest that plasticity in mate signaling systems, and in particular in male mate searching behavior on hosts and non‐hosts, may have the potential to reduce interbreeding between populations that use different species of host plant.     

Partial bivoltinism in a gregarious endoparasitoid: larval diapause as influenced by season and sharing a host

The yearly timing of the life cycle of a parasitoid is a key element of its life‐history strategy. I examine here factors influencing the expression of partial bivoltinism in Tetrastichus julis Walker (Hymenoptera: Eulophidae), a specialist parasitoid introduced to North America to attack its univoltine host, the cereal leaf beetle, Oulema melanopus (L.) (Coleoptera: Chrysomelidae). The varying tendency was assessed of individuals of this gregarious larval parasitoid to either emerge as adults in the same summer they mature, or to enter diapause to emerge the following year. Parasitized hosts were obtained by rearing cereal leaf beetles collected as mature larvae from grain fields in northern Utah (western USA) throughout the growing seasons in 2013 and 2014. Cocoons spun by these beetles were held to determine patterns over the spring and summer in the tendency of the parasitoid to forgo larval diapause. A high percentage (nearly 90% in 2013) of parasitoid individuals were found to forgo diapause and emerge in the same summer from earliest maturing hosts. This percentage rapidly declined to 20% or less of individuals forgoing diapause and emerging from cocoons as the summer advanced. The percentage of parasitoid individuals forgoing diapause increased significantly at a given time of season (early or late) as the number of conspecifics with which an individual shared a host larva increased. These results may reflect a trade‐off for individual parasitoids in which greater success in finding – and ovipositing in – host larvae the following spring vs. in summer, is countered by reduced survivorship in diapausing over the winter vs. emerging in the same summer in which the parasitoid matures. Expression of partial bivoltinism of T. julis, as affected strongly by both season and within‐host density, results in high rates of parasitism of cereal leaf beetles both early and late in the season.     

Variation in singing behaviour among morphs of the sand field cricket,Gryllus firmus

1. Trade‐offs play a fundamental role in the evolution of many traits. 2. In wing‐polymorphic field crickets, the long‐winged morph can disperse from unfavourable environments, but has lower reproductive success than the short‐winged morph, because of costs associated with flight capability. 3. However, long‐winged individuals may minimise costs in favourable environments by histolysing their flight muscles and becoming flightless. 4. Few studies have examined how flight‐muscle histolysis affects male signalling and mate attraction. 5. We examined differences in singing activity and song characteristics among the flightless (short‐winged and histolysed long‐winged) and the flight‐capable male morphs, and female preferences for male song, in the sand field cricket. 6. We found: (i) both flightless morphs sang more than the flight‐capable morph, (ii) song characteristics varied among the three morphs, and (iii) females preferred songs characteristic of the long‐winged morphs. 7. Histolysis should increase mating success of long‐winged males because it increases singing activity. 8. Histolysed long‐winged males may have higher mating success than short‐winged males as they sing as frequently but produce more attractive songs. 9. Therefore, plasticity within the long‐winged morph may reduce costs of maturing in environments from which dispersal is not advantageous; non‐flying morphs may be pursuing different reproductive tactics.     

Limited dispersal and its effect on population structure in the milkweed beetle Tetraopes tetraophthalmus

Summary The movement patterns of adult milkweed beetles, Tetraopes tetraphthalmus, were monitored via a mark-recapture technique. Movement or dispersal patterns were studied in two natural populations, one in which the host plant, Asclepias syriaca, was nearly continuously distributed over a 250×90 m area and another where Asclepias was distributed in 17 small discrete patches. In both populations dispersal distances resulting from the flight patterns of the adult beetles were quite short, averaging less than 40 m from the point of first encounter 10 days after marking. Males were shown to be more vagile than females. The distribution of dispersal distances collected from one of the populations was fit to three statistical distributions cited in the literature as expected from dispersal by many small-scale movements or observed in other species. It was found that an equation describing an exponential decay gave the best statistical fit to the data collected here for milkweed beetles. The data is discussed in the context of the effects of the limited dispersal power of the beetles and the distribution of suitable habitat on the population structure of Tetraopes.     

Heritability of and strong single gene (Pgi) effects on life‐history traits in the Glanville fritillary butterfly

We estimated broad‐sense heritabilities (H²) of 13 female and seven male life‐history traits of the Glanville fritillary butterfly (Melitaea cinxia) under semi‐natural conditions in a large outdoor population cage. The analysis was based on full‐sib families collected as young larvae in the field and reared under common garden conditions. We found significant genetic variance in female lifespan, fecundity, number of matings and host‐plant preference as well as in male body mass and mobility. Apart from host‐plant preference, female traits that were more strongly correlated with lifetime reproductive success (LRS; measured as total number of eggs laid) had higher H². LRS itself exhibited significant heritability. Host‐plant preference had very high H², consistent with a previously reported genetically determined geographical cline in host‐plant preference in the study area. Lifespan and egg hatching rate were significantly associated with a SNP in the coding region of the Pgi gene, for which there is previous evidence for balancing selection. Selection on Pgi, which furthermore shows spatial and temporal variation, may maintain genetic variance in fitness‐related life‐history traits. In contrast, we found no strong evidence for life‐history trade‐offs.     

Biased dispersal of Metrioptera bicolor,a wing dimorphic bush‐cricket

In the highly fragmented landscape of central Europe, dispersal is of particular importance as it determines the long‐term survival of animal populations. Dispersal not only secures the recolonization of patches where populations went extinct, it may also rescue small populations and thus prevent local extinction events. As dispersal involves different individual fitness costs, the decision to disperse should not be random but context‐dependent and often will be biased toward a certain group of individuals (e.g., sex‐ and wing morph‐biased dispersal). Although biased dispersal has far‐reaching consequences for animal populations, immediate studies of sex‐ and wing morph‐biased dispersal in orthopterans are very rare. Here, we used a combined approach of morphological and genetic analyses to investigate biased dispersal of Metrioptera bicolor, a wing dimorphic bush‐cricket. Our results clearly show wing morph‐biased dispersal for both sexes of M. bicolor. In addition, we found sex‐biased dispersal for macropterous individuals, but not for micropters. Both, morphological and genetic data, favor macropterous males as dispersal unit of this bush‐cricket species. To get an idea of the flight ability of M. bicolor, we compared our morphological data with that of Locusta migratoria and Schistocerca gregaria, which are very good flyers. Based on our morphological data, we suggest a good flight ability for macropters of M. bicolor, although flying individuals of this species are seldom observed.     

The role of olfactory cues in the sequential radiation of a gall‐boring beetle,Mordellistena convicta

1. Herbivorous insects often have close associations with specific host plants, and their preferences for mating and ovipositing on a specific host‐plant species can reproductively isolate populations, facilitating ecological speciation. Volatile emissions from host plants can play a major role in assisting herbivores to locate their natal host plants and thus facilitate assortative mating and host‐specific oviposition. 2. The present study investigated the role of host‐plant volatiles in host fidelity and oviposition preference of the gall‐boring, inquiline beetle, Mordellistena convicta LeConte (Coleoptera: Mordellidae), using Y‐tube olfactometers. Previous studies suggest that the gall‐boring beetle is undergoing sequential host‐associated divergence by utilising the resources that are created by the diverging populations of the gall fly, Eurosta solidaginis Fitch (Diptera: Tephritidae), which induces galls on the stems of goldenrods including Solidago altissima L. (Asteraceae) and Solidago gigantea Ait. 3. Our results show that M. convicta adults are attracted to galls on their natal host plant, avoid the alternate host galls, and do not respond to volatile emissions from their host‐plant stems. 4. These findings suggest that the gall‐boring beetles can orient to the volatile chemicals from host galls, and that beetles can use them to identify suitable sites for mating and/or oviposition. Host‐associated mating and oviposition likely play a role in the sequential radiation of the gall‐boring beetle.     

Seasonal dispersal of water beetles (Coleoptera) in an agricultural landscape: a study using Moericke traps in northwest Spain

Information on flight dispersal in water beetles in the Iberian Peninsula is scarce. This study provides new data on the dispersion flight phenology of 21 species captured using Moericke traps in an agricultural system in León province (NW Spain) during two annual cycles (1992 and 1993). The species captured form part of the assemblage of aquatic Coleoptera commonly found in stagnant environments in the centre of the Iberian Peninsula. Most of them are good flyers and colonisers. These flights are related to two environmental variables: mean atmospheric temperature and rainfall. The results show a clear relation between temperature and the flight period as most of the specimens dispersed during peaks of high mean daily temperatures, and a negative relation with rainfall. With regard to phenology, two types of dispersion strategy were identified: flights in the middle of summer to escape from drought and flights in spring and autumn for colonising new habitats. The first group includes Hydroglyphus geminus (Fabricius) and, in particular, Helophorus brevipalpis Bedel, whose great abundance in the dispersal stage is related to parthenogenetic reproduction and the rapid production of a large number of colonising females. The second strategy corresponds to univoltine species with overwintering adults such as Helophorus alternans Gené or species from the genus Hydroporus Clairville.     

Random movement pattern of fed and unfed adult Colorado potato beetles in bare‐ground habitat

• 1 Although the successful management of the Colorado potato beetle Leptinotarsa decemlineata (Say) depends on the prevention of its dispersal, its walking pattern in the landscape remains poorly understood. In the present study, post‐diapause, early summer, late summer and colony adult beetles, both fed and unfed before release, were tracked with a harmonic radar to establish their walking movement pattern in a bare‐ground field.
• 2 The random walk model successfully described the dispersal of all beetle types, whether fed or unfed.
• 3 The diverse life history of this species was manifested by an increased distance travelled and deviations of individual paths from the random model. Starved post‐diapause beetles travelled furthest and individual paths deviating from random were both local and directed, probably aiming to maximize opportunities for host colonization. Starved early summer beetles also travelled further than fed beetles but relied more on random movement to disperse in the habitat. Starving had little impact on the distance travelled or the path deviations of late summer beetles that are searching for overwintering site rather than hosts.
• 4 The increased displacement of starving beetles over fed beetles corresponded with an increased walking step and index of straightness.
• 5 The impact of starvation on travel distance was greater than expected from laboratory tests.
• 6 In conclusion, the results obtained in the present study suggest a random walking pattern to search arable land until host volatile or visual impulses trigger a more directed walk or flight.

     

Reproductive status and flight activity of the overwintered Colorado potato beetle

Mating behavior of post-diapause Colorado potato beetles, Leptinotarsa decemlineata (Say), was observed within an overwintering site, a rotated potato field, newly colonized potato plants, and under laboratory conditions. The influence of spring mating on beetle flight in the presence and in the absence of host plants was investigated using a computer-linked flight mill system. Diapause was terminated simultaneously in male and female beetles, and the first matings were observed as early as within the first 24 h after the beetles emerged from the soil (60–90 DD accumulated). The beetles mated within the overwintering site, the potato field, and the fields rotated out of potatoes. Mating status did not affect flight behavior of overwintered beetles; however, unfed beetles displayed higher flight activity than fed beetles. Most flight activity took place soon after flight muscle regeneration, and then declined sharply by the 5th day after flight initiation. Mating in or near overwintering sites soon after diapause termination might be an important factor in providing gene flow between insecticide-resistant and insecticide-susceptible Colorado potato beetle populations, and should be considered in designing resistance management plans.     

Lifetime inbreeding depression in a leaf beetle

Ongoing habitat loss and fragmentation result in rapid population size reductions, which can increase the levels of inbreeding. Consequently, many species are threatened by inbreeding depression, a loss of individual fitness following the mating of close relatives. Here, we investigated inbreeding effects on fitness‐related traits throughout the lifetime of the mustard leaf beetle (Phaedon cochleariae) and mechanisms for the avoidance of inbreeding. Previously, we found that these beetles have family‐specific cuticular hydrocarbon profiles, which are likely not used as recognition cue for precopulatory inbreeding avoidance. Thus, we examined whether adult beetles show postcopulatory inbreeding avoidance instead. For this purpose, we determined the larval hatching rate of eggs laid by females mated sequentially with two nonsiblings, two siblings, a nonsibling, and a sibling or vice versa. The beetles suffered from inbreeding depression throughout their entire ontogeny, as evinced by a prolonged larval development, a decreased larval and adult survival and a decreased reproductive output of inbred compared to outbred individuals. The highest larval hatching rates were detected when females were mated with two nonsiblings or first with a sibling and second with a nonsibling. Significantly lower hatching rates were measured in the treatments with a sibling as second male. Thus, the results do not support the existence of postcopulatory inbreeding avoidance in P. cochleariae, but revealed evidence for second male sperm precedence. Consequently, an alternative strategy to avoid inbreeding costs might exist in this beetle, such as a polyandrous mating system, potentially coupled with a specific dispersal behavior.     

Population structure of a vector‐borne plant parasite

Parasites are among the most diverse groups of life on Earth, yet complex natural histories often preclude studies of their speciation processes. The biology of parasitic plants facilitates in situ collection of data on both genetic structure and the mechanisms responsible for that structure. Here, we studied the role of mating, dispersal and establishment in host race formation of a parasitic plant. We investigated the population genetics of a vector‐borne desert mistletoe (Phoradendron californicum) across two legume host tree species (Senegalia greggii and Prosopis velutina) in the Sonoran desert using microsatellites. Consistent with host race formation, we found strong host‐associated genetic structure in sympatry, little genetic variation due to geographic site and weak isolation by distance. We hypothesize that genetic differentiation results from differences in the timing of mistletoe flowering by host species, as we found initial flowering date of individual mistletoes correlated with genetic ancestry. Hybrids with intermediate ancestry were detected genetically. Individuals likely resulting from recent, successful establishment events following dispersal between the host species were detected at frequencies similar to hybrids between host races. Therefore, barriers to gene flow between the host races may have been stronger at mating than at dispersal. We also found higher inbreeding and within‐host individual relatedness values for mistletoes on the more rare and isolated host species (S. greggii). Our study spanned spatial scales to address how interactions with both vectors and hosts influence parasitic plant structure with implications for parasite virulence evolution and speciation.     

Effect of food deprivation on the ambulatory movement of the Colorado potato beetle,Leptinotarsa decemlineata

Modification of dispersal behaviour is a common response of insects to food and water deprivation. The literature suggests that different insects respond with different strategies: changing walking parameters, switching dispersal mode (walking to flight or vice versa), or changing the host searching path. The goal of this study was to add to the limited literature on the subject by investigating, whether the walking parameters of adult male Colorado potato beetles, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), change in response to food and water deprivation. Observations on the distance walked, the travel speed, and the frequency of walking bouts were carried out in laboratory arenas using motion monitoring equipment. Summer and overwintered beetles were exposed to short starvation periods (2, 4, 8, 24 h) and two ranges of long starvation periods (1, 2, 4, 8 days and 1, 2, 4, 8, 16, and 32 days). Only the longest food deprivation periods of 16 and 32 days significantly reduced the walking distance, speed, and frequency of walking bouts of summer beetles. No changes were observed with overwintered beetles. The tolerance of the beetles without access to water to the different periods of food deprivation was similar to that for beetles with water except after a starvation period of 32 days, when the travel speed of summer beetles was significantly reduced by 33%. The absence of increased walking parameters found in this study and earlier observations of increased flight frequency suggest that the strategy of summer beetles will be to change the dispersal mode from walking to flight and/or to change the walking host searching path. The same results of this study and earlier observations of a decrease in the mean frequency of daily flights suggest that the strategy of overwintered L. decemlineata, exposed to food deprivation, will be to change the host search walking path rather than the walking parameters themselves.