Parthenogenetic Insect Research Articles

Host-associated differentiation in a highly polyphagous, sexually reproducing insect herbivore.

Insect herbivores may undergo genetic divergence on their host plants through host-associated differentiation (HAD). Much of what we know about HAD involves insect species with narrow host ranges (i.e., specialists) that spend part or all their life cycle inside their hosts, and/or reproduce asexually (e.g., parthenogenetic insects), all of which are thought to facilitate HAD. However, sexually reproducing polyphagous insects can also exhibit HAD. Few sexually reproducing insects have been tested for HAD, and when they have insects from only a handful of potential host-plant populations have been tested, making it difficult to predict how common HAD is when one considers the entire species’ host range. This question is particularly relevant when considering insect pests, as host-associated populations may differ in traits relevant to their control. Here, we tested for HAD in a cotton (Gossypium hirsutum) pest, the cotton fleahopper (CFH) (Pseudatomoscelis seriatus), a sexually reproducing, highly polyphagous hemipteran insect. A previous study detected one incidence of HAD among three of its host plants. We used Amplified fragment length polymorphism (AFLP) markers to assess HAD in CFH collected from an expanded array of 13 host-plant species belonging to seven families. Overall, four genetically distinct populations were found. One genetically distinct genotype was exclusively associated with one of the host-plant species while the other three were observed across more than one host-plant species. The relatively low degree of HAD in CFH compared to the pea aphid, another hemipteran insect, stresses the likely importance of sexual recombination as a factor increasing the likelihood of HAD.

Bridging developmental boundaries: lifelong dietary patterns modulate life histories in a parthenogenetic insect.

Determining the effects of lifelong intake patterns on performance is challenging for many species, primarily because of methodological constraints. Here, we used a parthenogenetic insect (Carausius morosus) to determine the effects of limited and unlimited food availability across multiple life-history stages. Using a parthenogen allowed us to quantify intake by juvenile and adult females and to evaluate the morphological, physiological, and life-history responses to intake, all without the confounding influences of pair-housing, mating, and male behavior. In our study, growth rate prior to reproductive maturity was positively correlated with both adult and reproductive lifespans but negatively correlated with total lifespan. Food limitation had opposing effects on lifespan depending on when it was imposed, as it protracted development in juveniles but hastened death in adults. Food limitation also constrained reproduction regardless of when food was limited, although decreased fecundity was especially pronounced in individuals that were food-limited as late juveniles and adults. Additional carry-over effects of juvenile food limitation included smaller adult size and decreased body condition at the adult molt, but these effects were largely mitigated in insects that were switched to ad libitum feeding as late juveniles. Our data provide little support for the existence of a trade-off between longevity and fecundity, perhaps because these functions were fueled by different nutrient pools. However, insects that experienced a switch to the limited diet at reproductive maturity seem to have fueled egg production by drawing down body stores, thus providing some evidence for a life-history trade-off. Our results provide important insights into the effects of food limitation and indicate that performance is modulated by intake both within and across life-history stages.

Sex produces as numerous and long-lived offspring as parthenogenesis in a new parthenogenetic insect

Sex is a costly form of reproduction compared with parthenogenesis, but sex persists because of the more resistant and competitive descendants that it produces. We obtained thelytokous offspring from unmated female Doru lineare (Eschscholtz, 1822) earwigs, a species of insect in which parthenogenesis has never before been reported, and found that their number and survival rate did not differ from offspring of mated females. Current hypotheses support advantages of sex or parthenogenesis, but never equilibrium between them like the one reported in this paper. We suggest that parthenogenesis is how females multiply their entire genome and renew themselves.

When one is not necessarily a lonely number: initial colonization dynamics of Adelges tsugae on eastern hemlock, Tsuga canadensis

The ability to establish successfully in a new area can vary considerably among species. In addition to the well-recognized importance of propagule pressure in driving the rates of establishment of biological invaders, the life history strategy of a species can also affect establishment success, such as in the extent to which Allee effects (positive density-dependence), and environmental and demographic stochasticity manifest themselves. We quantified the establishment success of Adelges tsugae, a non-native insect currently invading North American hemlock. We inoculated eastern hemlock host trees with varying densities of this parthenogenetic insect, from 1 to >500 progrediens ovisacs. The number of settled sistens (the subsequent generation) was positively related to the initial density. More interesting, however, was that we recorded successful establishment from released progrediens ovisacs, and the subsequent initiation of the next generation (sistens), in ≈39 % of host trees inoculated with 1 ovisac. The observation that successful establishment can be accomplished by a single ovisac produced by a single individual has important implications in the invasion dynamics and management of A. tsugae.

Transgenerational Behavioral Plasticity in a Parthenogenetic Insect in Response to Increased Predation Risk

Reliable cues of increased predation risk can induce phenotypic changes in an organism’s offspring (i.e. transgenerational phenotypic plasticity). While induction of defensive morphologies in naive offspring in response to maternal predation risk is widespread, little is known about transgenerational changes in offspring behavior. Here we provide evidence for transgenerational behavioral plasticity in the pea aphid, Acyrthosiphon pisum. When pre-reproductive individuals of two genotypes (“pink” and “green”) were exposed to the alarm pheromone (E)-β-Farnesene (EBF), a reliable cue of increased predation risk, next-generation offspring altered their feeding site choices relative to the location of the maternal aphids. Offspring of EBF-treated aphids occupied “safer” feeding sites: green offspring occupied “safer” feeding sites in the natal colony, while pink offspring dispersed to occupy sites on neighboring plant leaves.

Light- induced electron transfer and ATP synthesis in a carotene synthesizing insect

A singular adaptive phenotype of a parthenogenetic insect species (Acyrthosiphon pisum) was selected in cold conditions and is characterized by a remarkable apparition of a greenish colour. The aphid pigments involve carotenoid genes well defined in chloroplasts and cyanobacteria and amazingly present in the aphid genome, likely by lateral transfer during evolution. The abundant carotenoid synthesis in aphids suggests strongly that a major and unknown physiological role is related to these compounds beyond their canonical anti-oxidant properties. We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules. The redox potentials of molecules involved in this process would be compatible with the reduction of the NAD+ coenzyme. This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules.

Host-associated genetic differentiation in pecan leaf phylloxera

Host-associated differentiation (HAD) is the formation of genetically distinct host-associated populations. One of the genotypic signatures of HAD is that populations exhibit stronger differentiation by host-plant species than by geographic isolation. HAD, as a mechanism promoting ecological speciation, has been invoked to explain phytophagous insect diversity. Two traits proposed to promote HAD are endophagy and parthenogenesis. Using amplified fragment length polymorphisms (AFLPs), we tested for the presence of HAD in pecan leaf phylloxera, Phylloxera notabilis Pergande (Hemiptera: Phylloxeridae), an endophagous, gall inducing, and cyclically parthenogenetic insect on sympatric pecan and water hickory at a geographic mesoscale. This species shows strong HAD. Whereas the effect of collecting site was significant, accounting for 7.3% of molecular variation, host-plant species identity accounted for 63.5%. In addition, a choice test indicated that pecan leaf phylloxera originating from water hickory showed weak but significant preference for leaflets of the natal host, whereas pecan leaf phylloxera originating from pecan did not. This is the first such study of a species of arboreal Phylloxeridae, a poorly known insect group. This is also the first endophage and the second parthenogen shared by these two hickory species to show evidence of HAD. This hickory system could be a good parthenogen-rich counterpoint to the goldenrod system in the study of HAD in insect communities.

Genetic mechanism and evolutionary significance of the origin of parthenogenetic insects

There is a high proportion of parthenogenesis in insecta, and the parthenogenetic potential of insects is an important but often ignored threaten factor for the agricultural and forestry production. The maintenance of parthenogenetic species is a puzzling issue in evolutionary biology. In recent years, although the cellular mechanisms during parthenogenesis in some species have been well studied, the underlying genetic mechanisms that cause the switch from sexual reproduction to parthenogenesis have not been defined. While, understanding the genetic mechanism and evolutionary significance of the origin of parthenogenetic insects is crucial for preventing the pests in agricultural and forestry production. Here we summarized recent studies aimed at identifying the underlying genetic mechanism of parthenogenesis in insects, and briefly discussed its potential application in this filed.

Comparing the refuge strategy for managing the evolution of insect resistance under different reproductive strategies

Genetically modified (GM) crops are used extensively worldwide to control diploid agricultural insect pests that reproduce sexually. However, future GM crops will likely soon target haplodiploid and parthenogenetic insects. As rapid pest adaptation could compromise these novel crops, strategies to manage resistance in haplodiploid and parthenogenetic pests are urgently needed. Here, we developed models to characterize factors that could delay or prevent the evolution of resistance to GM crops in diploid, haplodiploid, and parthenogenetic insect pests. The standard strategy for managing resistance in diploid pests relies on refuges of non-GM host plants and GM crops that produce high toxin concentrations. Although the tenets of the standard refuge strategy apply to all pests, this strategy does not greatly delay the evolution of resistance in haplodiploid or parthenogenetic pests. Two additional factors are needed to effectively delay or prevent the evolution of resistance in such pests, large recessive or smaller non-recessive fitness costs must reduce the fitness of resistance individuals in refuges (and ideally also on GM crops), and resistant individuals must have lower fitness on GM compared to non-GM crops (incomplete resistance). Recent research indicates that the magnitude and dominance of fitness costs could be increased by using specific host–plants, natural enemies, or pathogens. Furthermore, incomplete resistance could be enhanced by engineering desirable traits into novel GM crops. Thus, the sustainability of GM crops that target haplodiploid or parthenogenetic pests will require careful consideration of the effects of reproductive mode, fitness costs, and incomplete resistance.

Metabolic rate depression is induced by caloric restriction and correlates with rate of development and lifespan in a parthenogenetic insect

Caloric restriction (CR) extends lifespan in most animals, but the mechanisms underlying this phenomenon are the subject of much debate. We investigated the association between longevity and resting metabolic rate (RMR) in Indian stick insects ( Carausius morosus) by (i) determining the appropriate scaling coefficient for calculating mass-corrected RMR of insects throughout development, (ii) quantifying the response of RMR to diet history, and (iii) correlating RMR in multiple life-history stages with adult and total lifespan. Over a range of body sizes, whole-body RMR (measured as oxygen consumption rate) scaled linearly with body mass. Mass-specific RMR decreased in response to CR, particularly when food was restricted during juvenile stages. With one exception, RMR of insects in different life-history stages matched current feeding level and was not substantially affected by intake history. Total lifespan was affected by intake, with insects that experienced CR early in development living longer than insects that were fed ad libitum. Although CR was associated with extended total lifespan and decreased RMR, it was also associated with shortened adult lifespan. Thus, we found limited evidence that decreased RMR plays a causative role in determining longevity. Instead, CR and decreased RMR were associated with slower progression through pre-reproductive life-history stages.

Biological Control of Alfalfa Snout Beetle with a multi-species application of locally adapted persistent entomopathogenic nematodes: The first success

Alfalfa snout beetle (ASB), Otiorhynchus ligustici (L.), is a very severe pest of alfalfa, grown in areas of northern New York and southeastern Ontario, Canada, bordering Lake Ontario and the St. Lawrence River. ASB often kills out entire fields in a single year from larval root feeding when populations are high. This parthenogenetic insect was first reported in North America in 1896 in Oswego Co., NY, where it was introduced by the dumping of sailing ballast between 1848 and 1896. ASB was identified as an alfalfa pest when alfalfa was introduced into the area in the 1920's. With ASB adults and larvae spending all of their 2-year life cycle in close association with soil, a biological control strategy focused on the use of locally adapted persistent entomopathogenic nematodes (EPNs) appeared to be a logical research direction. Research was initiated in 1989 and these studies were conducted primarily on a single farm (the John Peck Farm, located in Great Bend, Jefferson Co., New York) that historically contained extremely high populations of ASB. In 2002, the Peck Farm experienced an unexpected and sudden collapse of the ASB infestation. Subsequent studies on the Peck Farm revealed that the combination of two locally adapted nematodes had dispersed throughout the entire Peck Farm. We believe that the coexistence and soil residence partitioning of H. bacteriophora 'Oswego' with the native S. carpocapsae 'NY001' together exposed a wider range of life stages of ASB to nematode attack and subsequently applied enough biological control pressure on snout beetle to reduce the population to sub-economic levels. This research suggests that using locally adapted EPNs in a multi-species application provides a more effective approach to the biological control of ASB and potentially that of other soil pests.

Using the pea aphid Acrythociphon pisum as a tool for screening biological responses to chemicals and drugs

BackgroundThough the biological process of aphid feeding is well documented, no one to date has sought to apply it as a tool to screen the biological responses to chemicals and drugs, in ecotoxicology, genotoxicology and/or for interactions in the cascade of sequential molecular events of embryogenesis. Parthenogenetic insect species present the advantage of an anatomical system composed of multiple germarium/ovarioles in the same mother with all the intermediate maturation stages of embryos from oocyte to first instar larva birth. This could be used as an interesting model to visualize at which step drugs interact with the cell signalling pathway during the ordered developmental process.FindingsWe designed a simple test for screening drugs by investigating simultaneously zygote mitotic division, the progression of embryo development, cell differentiation at early developmental stages and finally organogenesis and population growth rate. We aimed to analyze the toxicology effects of compounds and/or their interference on cellular signalling by examining at which step of the cascade, from zygote to mature embryo, the developmental process is perturbed. We reasoned that a parthenogenetic founder insect, in which the ovarioles shelter numerous embryos at different developmental stages, would allow us to precisely pinpoint the step of embryogenesis in which chemicals act through specific molecular targets as the known ordered homeobox genes.ConclusionUsing this method we report the results of a genotoxicological and demographic analysis of three compound models bearing in common a bromo group: one is integrated as a base analog in DNA synthesis, two others activate permanently kinases. We report that one compound (Br-du) altered drastically embryogenesis, which argues in favor of this simple technique as a cheap first screening of chemicals or drugs to be used in a number of genotoxicology applications.

Involvement of Mos–MEK–MAPK pathway in cytostatic factor (CSF) arrest in eggs of the parthenogenetic insect, Athalia rosae

Extensive survey of meiotic metaphase II arrest during oocyte maturation in vertebrates revealed that the mitogen-activated protein kinase (MAPK) pathway regulated by the c-mos proto-oncogene product, Mos, has an essential role in cytostatic activity, termed cytostatic factor (CSF). In contrast, little is known in invertebrates in which meiotic arrest occurs in most cases at metaphase I (MI arrest). A parthenogenetic insect, the sawfly Athalia rosae, in which artificial egg activation is practicable, has advantages to investigate the mechanisms of MI arrest. Both the MAPK/extracellular signal-regulated protein kinase kinase (MEK) and MAPK were phosphorylated and maintained active in MI-arrested sawfly eggs, whereas they were dephosphorylated soon after egg activation. Treatment of MI-arrested eggs with U0126, an inhibitor of MEK, resulted in dephosphorylation of MAPK and MI arrest was resumed. The sawfly c-mos gene orthologue encoding a serine/threonine kinase was cloned and analyzed. It was expressed in nurse cells in the ovaries. To examine CSF activity of the sawfly Mos, synthesized glutathione S-transferase (GST)-fusion sawfly Mos protein was injected into MI-resumed eggs in which MEK and MAPK were dephosphorylated. Both MEK and MAPK were phosphorylated again upon injection. In these GST-fusion sawfly Mos-injected eggs subsequent mitotic (syncytial) divisions were blocked and embryonic development was ceased. These results demonstrated that the MEK–MAPK pathway was involved in maintaining CSF arrest in sawfly eggs and Mos functioned as its upstream regulatory molecule.

The phylogenetic relationships betweenDryocosmus,Chilaspisand allied genera of oak gallwasps (Hymenoptera, Cynipidae: Cynipini)

AbstractOak gallwasps (Hymenoptera; Cynipidae, tribe Cynipini) are cyclically parthenogenetic insects that induce galls on specific plant hosts in the family Fagaceae. Understanding the processes underlying the evolution of specific oak associations requires knowledge of the phylogenetic relationships among oak gallwasp genera. Although three major lineages of oak gallwasps have been identified, the status and relationships of several species‐poor but biologically significant genera remain unresolved. Two such genera areChilaspisandDryocosmus, whose western palaearctic species all gall oaks in the sectionCerris.Dryocosmusis particularly significant biologically because it includes: (a) the only palaearctic gallwasp to gall chestnuts,Castanea, and (b) nearctic species. The oak sectionCerrisis wholly absent from the nearctic, and the relationship between palaearctic and nearcticDryocosmusis significant for patterns of host plant evolution in the tribe as a whole. We examined the relationships betweenChilaspis,Dryocosmusand other oak cynipid genera using cladograms from sequence data for two mitochondrial loci (cytochromecoxidase subunit I and cytochromeb) and two nuclear loci (the 28S ribosomal gene regions D2 and D3–5). Our analyses support the following conclusions: (1) palaearcticChilaspisandDryocosmusspecies form an intermingled monophyletic group. (2) We propose thatChilaspisMayr, 1881 is asyn.n.ofDryocosmusGiraud, 1859 and propose the nameD. mayrias acomb.rev.for the species previously namedC. mayri, andD. nitidusandD. israeliascomb.n.ofC. nitidaandC. israeli, respectively. (3) We reassess the utility of morphological characters previously regarded as diagnostic for these genera. (4) Two species previously known only from a single generation represent two halves of a single species lifecycle.Dryocosmus nervosusis here designated asyn.n.ofD. cerriphilus. (5) The nearctic speciesD. favuslies outside the palaearcticChilaspis/Dryocosmusclade, andDryocosmusas currently recognized is not a monophyletic group. (6)Dryocosmus/Chilaspisis closely related to the other oak gallwasp taxa (Aphelonyx,Plagiotrochus,Pseudoneuroterus,Trichagalma, and someNeuroterusspecies) galling sectionCerrisoaks. This implies an early branching evolution of this oak association within this group, and supports previous work showing the rarity of oak gallwasp host shifts.

Clone Diversity in the Polyploid Weevil Otiorhynchus Scaber

Parthenogenetic insects are in general polyploid. These polyploid parthenogenetic forms seem to be superior competitors compared to their diploid and sexual relatives. Numerous studies have shown a surprisingly high clonal diversity in parthenogeinetic insects. We have studied Otiorhynchus scaiber, a common flightless weevil. O. scaber consists of three forms: one diploid sexually reproducing form with a very limited distribution and two widely distributed polyploid parthenogenetic forms. All forms, diploids and polyploids, coexist within the central area of distribution where both genetic and clonal diversity are highest. Diversity and degree of ploidy decrease towards the margin of distribution, so that only tetraploids inhabit the margins. This geographical pattern of distribution is a common phenomenon in parthenogenetic animals with different ploidy levels. We suggest that the high clonal diversity in populations of O. scaber is due to a continuous transition from diploid sexuality to triploid and finally to tetraploid parthenogenesis. We propose that the transition is caused by chance fertilisations of unreduced eggs.

Lifecycle closure, lineage sorting, and hybridization revealed in a phylogenetic analysis of European oak gallwasps (Hymenoptera: Cynipidae: Cynipini) using mitochondrial sequence data

Oak gallwasps are cyclically parthenogenetic insects that induce a wide diversity of highly complex species- and generation-specific galls on oaks and other Fagaceae. Phylogenetic relationships within oak gallwasps remain to be established, while sexual and parthenogenetic generations of many species remain unpaired. Previous work on oak gallwasps has revealed substantial intra-specific variation, particularly between regions known to represent discrete Pleistocene glacial refuges. Here we use statistical phylogenetic inference methods on sequence data for a fragment of the mitochondrial cytochrome b gene to reconstruct the relationships among 62 oak gallwasp species. For 16 of these we also include 23 additional cytochrome b haplotype sequences from different Pleistocene refuge areas to test the effect of intra-specific variation on inter-specific phylogeny reconstruction. The reconstructed phylogenies show good intra-generic resolution and identify several conserved clades, but fail to reconstruct either very recent or very ancient divergences. Nine of the 16 species represented by multiple haplotypes are not monophyletic. The apparent discordance between the recovered gene tree and the current taxonomic classification can be explained through: (a) collapsing of some species currently known only from either a sexual or a parthenogenetic generation into a single cyclically parthenogenetic entity; (b) sorting of ancestral polymorphism in diverging lineages, and (c) horizontal transfer of haplotypes, perhaps due to hybridization within glacial refuges. Our conclusions emphasise the need for careful intra-specific sampling when reconstructing phylogenies for radiations of closely related species and imply that for certain taxonomic groups full phylogenetic resolution (using molecular markers) may not be attainable.

High Fecundity and Low Fertility in Parthenogenetic Planarians

High Fecundity and Low Fertility in Parthenogenetic Planarians

QUANTITATIVE VARIATION IN FINITE PARTHENOGENETIC POPULATIONS: WHAT STOPS MULLER'S RATCHET IN THE ABSENCE OF RECOMBINATION?

Finite parthenogenetic populations with high genomic mutation rates accumulate deleterious mutations if back mutations are rare. This mechanism, known as Muller's ratchet, can explain the rarity of parthenogenetic species among so called higher organisms. However, estimates of genomic mutation rates for deleterious alleles and their average effect in the diploid condition in Drosophila suggest that Muller's ratchet should eliminate parthenogenetic insect populations within several hundred generations, provided all mutations are unconditionally deleterious. This fact is inconsistent with the existence of obligatory parthenogenetic insect species. In this paper an analysis of the extent to which compensatory mutations can counter Muller's ratchet is presented. Compensatory mutations are defined as all mutations that compensate for the phenotypic effects of a deleterious mutation. In the case of quantitative traits under stabilizing selection, the rate of compensatory mutations is easily predicted. It is shown that there is a strong analogy between the Muller's ratchet model of Felsenstein (1974) and the quantitative genetic model considered here, except for the frequency of compensatory mutations. If the intensity of stabilizing selection is too small or the mutation rate too high, the optimal genotype becomes extinct and the population mean drifts from the optimum but still reaches a stationary distribution. This distance is essentially the same as predicted for sexually reproducing populations under the same circumstances. Hence, at least in the short run, compensatory mutations for quantitative characters are as effective as recombination in halting the decline of mean fitness otherwise caused by Muller's ratchet. However, it is questionable whether compensatory mutations can prevent Muller's ratchet in the long run because there might be a limit to the capacity of the genome to provide compensatory mutations without eliminating deleterious mutations at least during occasional episodes of sex.

Meiotic mechanisms in a parthenogenetic grasshopper species and its hybrids with related bisexual species

The genetic system of the all-female Australian grasshopper species Warramaba virgo is of a type which is now familiar in parthenogenetic vertebrates (Parker & Selander, 1976, Uzzell, 1970, Uzzell & Darevski, 1975, CueUar 1971), but is very uncommon in parthenogenetic insects. Having originated by hybridization between two bisexual species, lCarramaba virgo reproduces by a form of automictic parthenogenesis in which a premeiotic doubling of the karyotype in the oocyte (from 2n = 15 to 4n = 30 in individuals having the standard karyotype) is followed by a synapsis which is restricted to sister chromosomes. The ensuing meiosis proceeds normally, with 15 chiasmate bivalents, except that there are approximately twice as many bivalents as in related bisexual species (Fig. 2A). The mechanism automatically ensures that all the offspring of a given female are genetically identical to one another and to their mother. No genetic recombination occurs, the chiasmata being without genetic consequences, since they are formed between chromosomes that are molecular copies of one another (White, Cheney & Key, 1963). Although, as mentioned above, this mechanism is now known in parthenogenetic Fu~hes, salamanders and lizards, and also in many earthworms (Omodeo 1952; 1955) it is not known with certainty in other parthenogenetic insects, most of which are either apomictic (lacking meiosis in the oocyte) or if automictic compensate their meiosis by a postmeiotic doubling process of some kind. In the lizards, earthworms etc., which possess what we may call the lCarramaba mechanism, it is not quite certain that synapsis is restricted to sister chromosomes, although this appears probable on general grounds. We do not know how long ago Warramaba virgo arose by hybridization. The fact that it exists in two distinct areas of Australia separated by a gap of 1600 km argues for a respectable antiquity (extinction of populations in the middle of its range probably occurred during the 'great arid' period 6000-3000 y B.P.). On the other hand, the fact that the species which hybridized to give rise to it still exist, with essentially unmodified karyotypes, is evidence against a very remote antiquity. Tentatively, one might suggest that W. virgo arose at least half a million years ago and perhaps even earlier (White 1980). The modem representatives of the species which hybridized to give rise to I4/. virgo are the unnamed

Genetic polymorphism and evolution in parthenogenetic animals. V. Triploid Adoxus obscurus (Coleoptera: Chrysomelidae).

SUMMARYThe genetic variability at 16 enzyme loci in 52 Scandinavian triploid parthenogenetic populations of the beetleAdoxus obscurushas been studied by starch-gel electrophoresis. The overall genotypes of different beetles have been compared with each other and with a sample from a diploid bisexual population from Canada. Eighty per cent of the parthenogenetic beetles have the same overall genotype. The remainder belong to six genotypes, three of which are found in only one population. The variability within and between parthenogenetic populations ofA. obscurusis much lower than in other comparable parthenogenetic insects studied by us. This is interpreted to be a consequence of the efficient migration of the genotypes with the highest fitness, leading to a replacement of less-adapted genotypes.A. obscurusis a flying insect, whereas the other parthenogenetic insects studied by us are sluggish flightless forms.