Flightless Females Research Articles

Puliciphora Dahl (Diptera: Phoridae) in Wales

A male of the scuttle fly genus Puliciphora Dahl was found in a sample from a flight interception trap at Dinefwr Estate NNR, Llandeilo, Wales. This is only the fourth Puliciphora record for Britain and the first outside the Oxford area. Dispersal of members of this genus is limited by the flightless females, which are carried by males a few metres to oviposition sites. It seems likely, therefore, that the Welsh occurrence involved transportation by human activity from another source.

Resource allocation strategies and mechanical constraints drive the diversification of stick and leaf insect eggs

The diversity of insect eggs is astounding but still largely unexplained. Here, we apply phylogenetic analyses to 208 species of stick and leaf insects, coupled with physiological measurements of metabolic rate and water loss on five species, to evaluate classes of factors that may drive egg morphological diversification: life history constraints, material costs, mechanical constraints, and ecological circumstances. We show support for all three classes, but egg size is primarily influenced by female body size and strongly trades off with egg number. Females that lay relatively fewer but larger eggs, which develop more slowly because of disproportionately low metabolic rates, also tend to bury or glue them in specific locations instead of simply dropping them from the foliage (ancestral state). This form of parental care then directly favors relatively elongated eggs, which may facilitate their placement and allow easier passage through the oviducts in slender species. In addition, flightless females display a higher reproductive output and consequently lay relatively more and larger eggs compared with flight-capable females. Surprisingly, local climatic conditions had only weak effects on egg traits. Overall, our results suggest that morphological diversification of stick insect eggs is driven by a complex web of causal relationships among traits, with dominant effects of resource allocation and oviposition strategies, and of mechanical constraints.

Larval polyphagy of Cataspilatesmarceloi (Lepidoptera, Geometridae), a Neotropical geometrid moth with flightless females.

Surveys in the arid shrubland of the central Andes revealed larval polyphagy for Cataspilatesmarceloi Vargas, 2022 (Lepidoptera, Geometridae, Ennominae, Boarmiini), a geometrid moth with flightless females. This discovery suggests that, as well as in the Holarctic fauna, larval polyphagy would have been important for the evolution of flightlessness among Neotropical geometrid moths of the tribe Boarmiini.

Ectoparasitism of the Flightless Drosophila melanogaster and D. hydei by the Mite Blattisocius mali (Acari: Blattisociidae).

Predatory mites dispersing by means of insects are often ectoparasites and may use various tactics to get onto the host, counteract its defenses, and diminish its survival. Blattisocius mali is a promising biological control agent which has been reported as transported by several drosophilid species. Our goal was to determine the type of relationship between this mite and fruit flies. We used flightless females of Drosophila melanogaster and D. hydei, which were commercially raised as live pet food. The predatory females mostly attacked the tarsi of the flies and then preferentially moved to the cervix or close to coxa III, where they eventually drilled their chelicerae and started feeding. Although both fly species used similar defensive tactics, more B. mali females did not attack D. hydei or did so with a delay, and a higher percentage of mites fell off the D. hydei tarsi during the first hour of observation. After 24 h, we noted the increased mortality of flies exposed to the presence of mites. Our study indicates the ectoparasitic relationship of B. mali with drosophilids. However, further research is needed to confirm the transport of this mite on wild D. hydei and D. melanogaster, both in the laboratory and under natural conditions.

Flightless Females in the Neotropical Moth Genus Cataspilates Warren (Lepidoptera: Geometridae) †.

Although adults are winged and able to fly in most Lepidoptera species, they are apterous or brachypterous and unable to fly in others, such as the flightless females of some geometrid moths. Records of flightless females in the highly diverse and widespread tribe Boarmiini (Geometridae: Ennominae) are mainly restricted to some Nearctic and Palearctic genera. The aim of this study is to provide the first record of flightless females for Cataspilates Warren, 1897, a Boarmiini genus endemic to the Neotropical Region, through the description of Cataspilates marceloi sp. nov. from the arid highlands of the western slopes of the Andes of northern Chile. DNA barcodes confirmed the conspecificity of brachypterous females and winged males reared from larvae collected on the native shrub Adesmia spinosissima (Fabaceae). This contribution represents the first female description for Cataspilates and provides a new opportunity to improve the understanding of the evolution of flightlessness in geometrid moths.

Wings make queens of Indian jumping ants

Families are complicated – ask any ant. Embarking on a new life, the females of many ant species take to the wing before establishing themselves as queen of their own colony populated with their worker offspring, which provide care and labour. But these hierarchical divisions are not so clear cut in all ant species. ‘The association of some behaviours with the queen and others with the worker morph is not universal’, says Benjamin Pyenson from Arizona State University, USA, explaining that Indian jumping ant (Harpegnathos saltator) queens can take on roles usually associated with workers, while the workers are also capable of producing eggs – usually the preserve of ant queens – in specific situations. Pyenson, Christopher Albin-Brooks and Jürgen Liebig, also from Arizona State University, wondered whether the loss of the queen's wings might have something to do with their ability to straddle the boundaries that usually differentiate queens from their worker offspring.However, as Indian jumping ant founding queens naturally perform many of the duties of workers – foraging and caring for brood and defending the nest – simply monitoring the caring responsibilities of the queen ants after they had lost their wings was not going to be sufficient to determine whether wingless queens transition to behaving like workers. Fortunately, winged queens never duel with workers to establish where they reside in the colony's two-tier hierarchy, whereas wingless queens do. So, Pyenson, Albin-Brooks and Corinne Burhyte (Arizona State University), set out to discover whether queen ants that had lost their wings tussled more with their colony mates than queens that still had their wings. Sure enough, after watching hours of ant interactions, the researchers saw that queens that had naturally shed their wings duelled more than winged queens and Pyenson says, ‘One clue that the queen and worker ants might not be all that different was that the stings I received from both of them seemed equally painful!’. In addition, all the colony residents duelled more when the researchers removed some queen's wings.The team also kept track of the fertility of several queens, discovering that the wingless queens produced fewer yolky eggs – which could go on to produce young. The wingless queens were becoming more like worker ants, losing their fertility. Also, some of the females whose wings had been removed by the scientists mated with males from their own colony, something that winged and naturally wingless queens never do, to avoid inbreeding and ensure that they find new nests with unrelated males. Finally, the researchers checked the oily waterproof coating covering the ants’ exterior to find out how appealing the winged and wingless queens smelled to mates, as winged females produce more alluring oily scents to attract males. However, 2 months after losing their wings, the now flightless females had lost their attractive aroma. Without wings, Indian jumping ant queen ants shift to behaving like workers and their bodies also adjust to become more worker-like.The discovery that Indian jumping ant workers and queens are equally capable of taking on each other's roles could help scientists understand how the sophisticated hierarchical colony structures favoured by other ant species have evolved. ‘Our results tell us that the ant queen's ability to fly away from the nest probably evolved before the ability to lay a lot of eggs, because in some species the workers can also lay eggs and the queens and workers are similar sizes’, Pyenson explains.

A novel method for assessing the threat to oak stands from geometrid defoliators

Oak forests are of great ecological and socioeconomic values but are declining in many regions due to abiotic and biotic factors, including crown damage by defoliating insects. In Europe, several geometrid species reach outbreak densities and are then able to cause severe oak defoliation. Prior to control measures, the threat posed by defoliators must be reliably assessed to limit the treated area and consequently to minimize the negative environmental impacts and the costs of the insecticide application. Few methods have been developed so far to assess the threat to oak forests from geometrids, most of which have proven to be unreliable and/or labour-consuming. In this paper, we present a new method for predicting crown damage from geometrid defoliators based on the density of their flightless females assessed with the use of collar traps installed on tree trunks. The studies were conducted in 2014–2020 in 68 oak stands in Poland. Using beta regression, we estimated the relationship between the density of geometrid females (from genera: Operophtera, Erannis, Agriopis, Alsophila and Apocheima) in collar traps and subsequent defoliation caused by their progeny (i.e. larvae). We then proposed threshold numbers of female density to predict different levels of defoliation and calculated the numbers of collar traps that would be required to detect the threshold density of geometrid females indicating expected defoliation >30%. The new method allows forest managers to monitor populations of different species and phenological groups of geometrids and predict the threat (expected defoliation) to oak forests from these insects.

Size-dependent flight capacity and propensity in a range-expanding invasive insect.

For capital-breeding insects, all resources available for adult metabolic needs are accumulated during larval feeding. Therefore, body size at adult eclosion represents the total energetic capacity of the individual. For female capital breeders, body size is strongly correlated with lifetime fecundity, while in males, body size, which correlates with fitness, is less understood. In capital-breeding species with wingless, flightless, or dispersal-limited females, flight potential for male Lepidoptera has important implications for mate-finding and may be correlated with body size. At low population densities, failure to mate has been identified as an important Allee effect and can drive the success or failure of invasive species at range edges and in species of conservation concern. Th capital-breeding European subspecies of Lymantria dispar (L.), was introduced to North America in 1869 and now ranges across much of eastern North America. In L. dispar, females are flightless and mate-finding is entirely performed by males. We quantified male L. dispar flight capacity and propensity relative to morphological and physiological characteristics using fixed-arm flight mills. A range of male body sizes was produced by varying the protein content of standard artificial diets while holding other dietary components constant. Wing length, a proxy for body size, relative thorax mass, and forewing aspect were all important predictors of total flight distance and maximum speed. These results have important implications for mate-finding and invasion dynamics in L. dispar and may apply broadly to other capital-breeding insects.

Dispersal and Migration Patterns of Freshwater Semiaquatic Bugs.

Simple SummarySemiaquatic bugs have colonized the water surface of most aquatic habitats, from small and temporary puddles and streams to the open ocean. Most semiaquatic bugs are wing-polymorphic, as some individuals have fully developed wings (macropterous) and others have shortened wings (brachypterous) or are wingless (apterous). This is characteristic for most temperate water striders, common on lakes, fishponds, and pools around the world. The report presented here is based on the collection of more than 23,000 individuals of nine species of semiaquatic bugs that were individually marked by a unique code and released. The recaptures revealed several distinct dispersal strategies, with differences among individual species. Collection of the marked bugs also helped to describe dispersal via the water surface by flightless individuals. Using the results of the presented survey, our knowledge of these interesting insects is considerably extended, and it can help us to understand the general dispersal patterns of aquatic insects.Semiaquatic bugs (Hemiptera: Heteroptera: Gerromorpha) are mostly wing-polymorphic species with flight dispersal as an important life history trait, but the specific flight ability and dispersal pattern remain unexplored in most species. This report presents the results of a long-term survey based on the individual marking of more than 23,000 specimens of eight water striders (Gerridae) and a water cricket Velia caprai (Veliidae). Three distinct lentic habitats were sampled (solitary fishponds, systems of nearby fishponds and systems of small, often temporary pools) and one lotic habitat—a small forest stream. Recaptures revealed that three gerrid species tend to stay at the breeding site, but can differ in dispersal via the water surface. Reproductive flightless females disperse most actively via the water surface, possibly bypassing the trade-off between dispersal and reproduction. One species has a sex-dependent dispersal pattern, with females being rather philopatric, whereas males often disperse. Three other gerrid species are highly dispersive and tend to change breeding site. V. caprai, the only lotic species included in this survey, tend to move upstream and possibly compensate for the downstream drift.

Suppressing mosquito populations with precision guided sterile males

The mosquito Aedes aegypti is the principal vector for arboviruses including dengue/yellow fever, chikungunya, and Zika virus, infecting hundreds of millions of people annually. Unfortunately, traditional control methodologies are insufficient, so innovative control methods are needed. To complement existing measures, here we develop a molecular genetic control system termed precision-guided sterile insect technique (pgSIT) in Aedes aegypti. PgSIT uses a simple CRISPR-based approach to generate flightless females and sterile males that are deployable at any life stage. Supported by mathematical models, we empirically demonstrate that released pgSIT males can compete, suppress, and even eliminate mosquito populations. This platform technology could be used in the field, and adapted to many vectors, for controlling wild populations to curtail disease in a safe, confinable, and reversible manner.

Morph-specific life-history correlations in a wing-dimorphic water strider.

Life-history theory predicts a negative correlation between reproduction and survival because individuals differ in their investment in early reproduction at the expense of survival. However, life-history trade-offs can be masked when individual differences in resource allocation are smaller than those in resource acquisition. In polymorphic species, as distinct morphs exhibit differences in intrinsic physiology, the relative effects of resource acquisition and allocation on life-history traits will differ between morphs, contributing to morph-specific life-history correlations. Here, in the wing-dimorphic water strider Aquarius paludum, we found that wing morphs differed in within-morph individual-level life-history correlations. Longer-lived flight-capable long-winged females produced fewer eggs per day and matured later, whereas life-history trade-offs were not observed in short-winged flightless females. The survival-reproduction trade-off observed in long-winged females may be a result of individual differences in the timing of wing muscle histolysis. Individuals that underwent wing histolysis early would have increased reproduction at the expense of a shorter life, whereas individuals with late wing histolysis would have reduced reproduction but a longer life. Short-winged females, who never develop wings, effectively have more resources to allocate to both survival and reproduction, masking any life-history trade-offs. Thus, we suggest that morph-specific effects of resource allocation trade-offs can shape the morph-specific extent of individual variation in life-history strategies, which may contribute to the evolution and maintenance of within-species polymorphism.

Reproductive Systems, Transfer and Digestion of Spermatophores in Two Asian Luciolinae Fireflies (Coleoptera: Lampyridae).

Simple SummaryDuring mating, fireflies may transfer sperm to the female wrapped in food materials (spermatophores). We investigate in two firefly species structures in both male and female that indicate production and receipt of spermatophores. Their structure, how they attach and discharge the sperm inside the female, and how long they persist might indicate if these fireflies mate only once or more. Potential differences between males and females of both fully winged and species with flightless females are determined. An overview of present knowledge of female reproductive anatomy is given. An argument is mounted suggesting direct observation of biological structures like spermatophores might be the only reliable way of determining their presence.The internal reproductive anatomy of males and females of two Asian Luciolinae fireflies Emeia pseudosauteri (Geisthardt, 2004) and Abscondita chinensis (L., 1767) is described, and the time course for spermatophore transfer and digestion examined. E. pseudosauteri is sexually dimorphic, with a flightless female, and Abs. chinensis is sexually monomorphic, with the female flighted. Both are monandrous. Possible female accessory glands are described for the first time for both species. An overview of present knowledge of female reproductive anatomy in the Luciolinae reveals males of 18 species in 10 genera may produce spermatophores and permits speculation about spermatophore production in another 16 genera.

Potential Differences and Methods of Determining Gypsy Moth Female Flight Capabilities: Implications for the Establishment and Spread in Novel Habitats

The introduction of the Asian gypsy moth into novel environments continues with frequent interceptions in North America. There is a concern that these subspecies will pose a greater threat to the forests and urban environments of North America than the established gypsy moths (Lymantria dispardispar L.), due to their greater capacity for female flight. Asian gypsy moth populations vary in many key traits, including female flight capabilities. The potential impacts of female flight, in combination with the other key traits, on the ecology and spread of this insect are first discussed in this communication. This also provides the first review of most of the current literature on the variations in flight capability and flight distance of gypsy moth populations, as well as variation in other traits of concern and the potential methods of identification, with special attention paid to the Asian subspecies Lymantria dispar japonica Motschulsky and Lymantria dispar asiatica Vinkovskij. There are currently good tools for identifying the general origin of introduced gypsy moth populations, but these do not provide enough information to effectively manage introductions. Gypsy moth key traits differ among populations, even within each subspecies of the gypsy moth, so introduction of gypsy moths from other world areas into locations where the gypsy moth is already present could result in unwanted changes in gypsy moth biology. It also appears that the introduction of flight-capable females could enhance a population’s dispersal capability and require modifications to management protocols used for flightless females. Therefore, rapid tools to assess key traits in introduced populations are needed to adequately plan for, or deal with, new introductions into novel habitats.

Review of North American Dascillidae (Coleoptera: Dascilloidea), with Descriptions of Dramatic Female Wing Reduction

The species of Dascillidae are reviewed for North America. Anorus arizonicusBlaisdell, 1934 is proposed as a new synonym of Anorus parvicollisHorn, 1894; Dascillus plumbeusHorn, 1880 is proposed as a new synonym of Dascillus davidsoni LeConte, 1859. The termitiform, flightless female of A. parvicollis, with extremely reduced elytra, is described and illustrated for the first time. A key is provided for adults of all three valid species of North American Dascillidae, which includes newly described and illustrated characters for all species. Adult females of all three species are described and compared. All have hind wings at least somewhat reduced compared to their fully winged male counterparts and display a grade of elytral development from complete (D. davidsoni) to tiny and scalelike (A. parvicollis). A distributional checklist of New World Dascillidae is provided. Pleolobus fuscescensPhilippi and Philippi, 1864 is designated as the type species for the Chilean genus PleolobusPhilippi and Philippi, 1864. We also provide distribution maps for all North American species and discuss some higher classification issues within Dascillidae.

CRISPR/Cas9 knockout of female-biased genes AeAct-4 or myo-fem in Ae. aegypti results in a flightless phenotype in female, but not male mosquitoes.

Aedes aegypti is a vector of dengue, chikungunya, and Zika viruses. Current vector control strategies such as community engagement, source reduction, and insecticides have not been sufficient to prevent viral outbreaks. Thus, interest in novel strategies involving genetic engineering is growing. Female mosquitoes rely on flight to mate with males and obtain a bloodmeal from a host. We hypothesized that knockout of genes specifically expressed in female mosquitoes associated with the indirect flight muscles would result in a flightless female mosquito. Using CRISPR-Cas9 we generated loss-of-function mutations in several genes hypothesized to control flight in mosquitoes, including actin (AeAct-4) and myosin (myo-fem) genes expressed specifically in the female flight muscle. Genetic knockout of these genes resulted in 100% flightless females, with homozygous males able to fly, mate, and produce offspring, albeit at a reduced rate when compared to wild type males. Interestingly, we found that while AeAct-4 was haplosufficient, with most heterozygous individuals capable of flight, this was not the case for myo-fem, where about half of individuals carrying only one intact copy could not fly. These findings lay the groundwork for developing novel mechanisms of controlling Ae. aegypti populations, and our results suggest that this mechanism could be applicable to other vector species of mosquito.

Tools for monitoring oak defoliating geometrids – traps for catching males and females

ABSTRACT Several insect species, including those belonging to Geometridae, pose serious threats to oak stands, primarily by causing cyclic defoliation and increasing the vulnerability of trees to adverse secondary factors. Our major study goal was to compare the effectiveness of two types of pheromone traps, funnel vs. bucket traps, for capturing Operophtera brumata males, and the effectiveness of two types of barrier traps, glue bands vs. collar traps, installed on tree trunks for capturing flightless geometrid females that climb host trees to mate and oviposit. The relationship between catches of O. brumata males and females captured using the funnel and collar traps, respectively, was also assessed. The numbers of males in the two types of pheromone traps did not differ significantly, and the practical use of these traps is discussed. Among the traps targeting females, the collar traps showed much higher effectiveness than the glue bands. The relationship between the O. brumata male and female catches was significant and was described by an exponential function, which can be used for estimating female density using male catches and vice versa. Our study found significant advantages of collar traps over glue bands for monitoring oak defoliating geometrid species.

Phylogenomics reveals conservation challenges and opportunities for cryptic endangered species in a rapidly disappearing desert ecosystem

There is growing evidence for the decline of cryptic species across the planet as a result of human activities. Accurate data regarding patterns of poorly known or hard-to-find species diversity is essential for the recognition and conservation of threatened species and ecosystems. Casey’s June beetle Dinacoma caseyi is a federally listed endangered species restricted to the Coachella Valley in southern California, where rapid development is leading to habitat fragmentation. This fragmentation may be disproportionately impacting a wide-range of poorly-dispersing, cryptic species, including Casey’s June beetle, which has flightless females. We characterized 1876 single nucleotide polymorphisms from across the genome along with 1480 bp of mitochondrial DNA of all confirmed extant Dinacoma populations. We found that Dinacoma is isolated into three distinct species, including evidence for a previously undescribed species revealed during this study. Each is restricted to a small part of the inland desert region. Our results suggest unappreciated and fine scale diversity, which may be reflected in the other cryptic species of the region. Patterns of diversity in non-vagile species should guide ongoing conservation planning in the region. These results show that genetic exchange within the one remaining island of beetle habitat (Palm Canyon Wash) is not limited. However, non-vagile species, such as Casey’s June beetle, may not colonize suitable but fragmented habitat islands which presents risks to the species due to habitat loss and periodic natural events that may put the single population at risk of extirpation.

A highly secure method for rearing Aedes aegypti mosquitoes

BackgroundVector-borne infectious diseases are caused by pathogenic microorganisms transmitted mainly by blood-sucking arthropod vectors. In laboratories, the handling of insects carrying human pathogens requires extra caution because of safety concerns over their escape risk. Based on standard insect containment practices, there have been cases where costly enhancements were required to definitely protect laboratory workers and neighbors from potential infection through mosquito bites. Here, we developed a mosquito rearing method that provides a reliable and cost-effective means to securely contain pathogen-infected females of the yellow fever mosquito Aedes aegypti.ResultsTo debilitate the motility of A. aegypti females, mosquitoes were rendered completely flightless by ablation of either wing. The “single-winged” mosquitoes exhibited a severe defect in flying ability and were incubated in a container with inside surfaces covered with a net stretched to approximately 1-mm mesh, which helped the mosquitoes hold on and climb up the wall. In this container, flightless females consistently showed similar blood feeding and egg laying activities to intact females. Eighty-five percent of the flightless mosquitoes survived at 1 week after wing ablation, ensuring feasibility of the use of these mosquitoes for studying pathogen dynamics.ConclusionsThis mosquito rearing method, with a detailed protocol, is presented here and can be readily implemented as a highly secure insectary for vectors carrying human pathogens. For researchers in an environment where highly strict containment practices are mandatory, this method could offer appropriate opportunities to perform research on pathogen–mosquito interactions in vivo.

Comparing the Expression of Olfaction-Related Genes in Gypsy Moth (Lymantria dispar) Adult Females and Larvae from One Flightless and Two Flight-Capable Populations

In insects, flight and sophisticated olfactory systems go hand in hand and are essential to survival and evolutionary success. Females of many Lepidopteran species have secondarily lost their flight ability, which may lead to changes in the olfactory capabilities of both larval and adult stages. The gypsy moth, Lymantria dispar, an important forest pest worldwide, is currently undergoing a diversification process with three recognized subspecies: the Asian gypsy moth (AGM) L. dispar asiatica, the Japanese gypsy moth L. dispar japonica (JGM) and the European gypsy moth (EGM) L. dispar dispar. Females of EGM populations from North America have lost their flight capacity whereas the JGM and AGM females are flight capable, making this an ideal system to investigate the relationship between flight and olfaction. We used next-generation sequencing to obtain female antennal and larval head capsule transcriptomes in order to (i) investigate the differences in expression of olfaction-related genes among populations; (ii) identify the most similar protein sequences reported for other organisms through a BLAST search, and (iii) establish the phylogenetic relationships of these sequences with respect to other insect species. Using this approach, we identified 115 putative chemosensory genes belonging to five families of olfaction-related genes. A principal component analysis revealed that the gene expression patterns of female antennal transcriptomes from different subspecies were more similar among them than to the larval head capsules of their respective subspecies supporting strong chemosensory differences between the two developmental stages. An analysis of the shared and exclusively expressed genes for three populations shows no evidence that loss of flight affects the number or type of genes being expressed. These results indicate either that (a) loss of flight does not impact the olfactory gene repertoire or that (b) the secondary loss of flight in the American EGM populations may be too recent to have caused major changes in the genes being expressed. However, we found higher expression values for IRs, OBPs GRs and ORs in EGM females, suggesting that differences in transcription rates could be an adaptation of flightless females to their chemical environment. Differences in olfactory genes and their expression in the

The thoracic anatomy of the male and female winter moth Nyssiodes lefuarius (Lepidoptera: Geometridae) and evolutionary changes in the thorax of moths and butterflies

The thoraces of males and flightless females of the geometrid winter moth Nyssiodes lefuarius are described, documented in detail, and compared. Morphological, functional, and evolutionary aspects of the female phenotype are discussed. The flightlessness of female N. lefuarius is linked not only with complex modifications of the skeletomuscular structure, especially elements of the flight apparatus, but also with greatly enlarged ovaries and a reduced gut. Compared with other flightless female lepidopterans, females of N. lefuarius display a specific thoracic skeletomuscular configuration, which strongly suggests independent evolution, in agreement with the phylogenetic pattern. The evolutionary scenario of flight ability enhancement in Lepidoptera is demonstrated using a combined phylogeny from recent studies based on molecular data. Thoracic skeletomuscular characters are compiled and mapped, mainly using extensive information from the literature, but also including the new morphological data obtained from the male N. lefuarius. Important changes in the thoracic character system are linked with the rise of Coelolepida, Heteroneura, and Ditrysia. Only minor changes take place in the character system in more advanced groups of Lepidoptera. A highly unusual feature is the secondarily stiff wing type in some groups of Ditrysia without the neopteran basal folding mechanism. The morphological background of the secondarily evolved “palaeopteran” condition is a complex of different character changes. Major problems in the reconstruction of the phylogeny are a high degree of homoplasy and missing detailed data for several crucial taxa emerging close to the root of the order.