High level of novelty under the hood of convergent evolution

Little is known about the extent to which species use homologous regulatory architectures to achieve phenotypic convergence. By characterizing chromatin accessibility and gene expression in developing wing tissues, we compared the regulatory architecture of convergence between a pair of mimetic butterfly species. Although a handful of color pattern genes are known to be involved in their convergence, our data suggest that different mutational paths underlie the integration of these genes into wing pattern development. This is supported by a large fraction of accessible chromatin being exclusive to each species, including the de novo lineage-specific evolution of a modular optix enhancer. These findings may be explained by a high level of developmental drift and evolutionary contingency that occurs during the independent evolution of mimicry.

Pyrethroid Exposure Reduces Growth and Development of Monarch Butterfly (Lepidoptera: Nymphalidae) Caterpillars

Insecticide exposure has been identified as a contributing stressor to the decline in the North American monarch butterfly Danaus plexippus L. (Lepidoptera: Nymphalidae) population. Monarch toxicity data are currently limited and available data focuses on lethal endpoints. This study examined the 72-h toxicity of two pyrethroid insecticides, bifenthrin and β-cyfluthrin, and their effects on growth and diet consumption. The toxicity of bifenthrin to caterpillars was lower than β-cyfluthrin after 72 h. Survival was the most sensitive endpoint for bifenthrin, but diet consumption and caterpillar growth were significantly reduced at sublethal levels of β-cyfluthrin. Using AgDRIFT spray drift assessment, the aerial application of bifenthrin or β-cyfluthrin is predicted to pose the greatest risk to fifth-instar caterpillars, with lethal insecticide deposition up to 28 m for bifenthrin and up to 23 m for β-cyfluthrin from treated edges of fields. Low boom ground applications are predicted to reduce distances of lethal insecticide exposure to 2 m from the treated field edge for bifenthrin and β-cyfluthrin. Growth and survival of fifth-instar monarch caterpillars developing within the margins of a treated field may be significantly impacted following foliar applications of bifenthrin or β-cyfluthrin. These findings provide evidence that pyrethroid insecticides commonly used for soybean pest control are a potential risk to monarch caterpillars in agricultural landscapes.

How do moth and butterfly taste?-Molecular basis of gustatory receptors in Lepidoptera

Insect gustatory system plays a central role in guiding insect feeding behaviors, insect-plant interactions and coevolutions. Gustatory receptors (GRs) form the interface between the insect taste system and their environment. Previously, most studies on insect GRs are focused on Drosophila; much less attention has been paid to Lepidoptera species, which consist of a large number of serious agricultural crop pests. With the exceptional advances in the next generation sequencing (NGS), cellular biology, RNA interference (RNAi), and clustered regularly interspaced short palindromic repeats (CRISPR) technologies in recent years, extraordinary progresses have been achieved elucidating the molecular mechanisms of Lepidopteran GRs. In this review, we highlighted these advances, discussed what these advances have revealed and provide our new insights into this field.

Genetic Variation Influences Tolerance to a Neonicotinoid Insecticide in 3 Butterfly Species

Neonicotinoid pesticides harm nontarget insects, but their sublethal effects on butterflies are understudied. We exposed larvae of 3 butterfly species (Pieris rapae, Colias philodice, and Danaus plexippus) to low levels of the neonicotinoid imidacloprid in their host plants and followed individuals to adulthood. Imidacloprid altered adult body size, especially in female monarchs, but its effects varied across maternal families, highlighting the importance of considering genetic variation in ecotoxicological testing. Environ Toxicol Chem 2020;39:2228-2236. © 2020 SETAC.

Distance Diminishes the Effect of Deltamethrin Exposure on the Monarch Butterfly, Danaus plexippus

The monarch butterfly, Danaus plexippus (Lepidoptera: Nymphalidae), is threatened by substantial loss of habitat, extreme weather events linked to global climate change, and nontarget impacts of broad-spectrum insecticides. To investigate the impact of chronic ingestion of pyrethroids on monarchs, wild-type Florida D. plexippus were reared on milkweed (Asclepias curassavica) that was exposed to ultra-low volume applications of DeltaGard by a truck-mounted fogger, at distances of 25 and 50 m. We observed significant negative impacts on monarchs reared on milkweed at 25 m from the DeltaGard spray route, including significant decreases in survival, and significantly longer development times, compared with untreated controls. Larvae reared on host plants closest to the truck spray route were 3 times more likely to experience a mortality event than the control cohort in trial 1 and 6 times in trial 2. Survival of monarch caterpillars reared on milkweed sprayed at 50 m was not significantly different from controls. For monarchs that survived to adulthood, we did not observe statistically significant differences among cohorts for variables measured. These data demonstrate that ultra-low volume treatments of pyrethroids can result in significant mortality in monarchs, but that the effects diminish with distance from the spray route.

Host Plant Choice Determined by Reproductive Interference between Closely Related Butterflies

AbstractA number of empirical studies have concluded that reproductive interference (RI) contributes to parapatric species distributions or sexual exclusion. However, the possibility that divergent host plant use in phytophagous insects is due to sexual exclusion has seldom been considered. Here, we present evidence that RI is responsible for different host plant use by two Pierid butterfly species, Pieris napi and Pieris melete. When a novel host species was introduced about 50 years ago, two Pierid butterfly species at first used both the ancestral host species and the novel one. Subsequently, P. napi shifted to use only the novel host, while P. melete shifted to specialize on the ancestral host. To explain these patterns, we investigated whether the two host species differ in suitability for larval growth and survival. Additionally, we tested whether RI occurred between the two butterfly species using large outdoor field cages. Courtship of females by conspecific and heterospecific males reduces the number of eggs laid by approximately half. However, RI is asymmetric and would generate selection on P. melete females to evolve to avoid the more suitable host species preferred by P. napi. Thus, our study suggests that sexual exclusion can explain the shift in host plant use by these two butterfly species.

Eradicating the large white butterfly from New Zealand eliminates a threat to endemic Brassicaceae

In May 2010 the large white butterfly, Pieris brassicae L. (Lepidoptera: Pieridae), was discovered to have established in New Zealand. It is a Palearctic species that-due to its wide host plant range within the Brassicaceae-was regarded as a risk to New Zealand's native brassicas. New Zealand has 83 native species of Brassicaceae including 81 that are endemic, and many are threatened by both habitat loss and herbivory by other organisms. Initially a program was implemented to slow its spread, then an eradication attempt commenced in November 2012. The P. brassicae population was distributed over an area of approximately 100 km2 primarily in urban residential gardens. The eradication attempt involved promoting public engagement and reports of sightings, including offering a bounty for a two week period, systematically searching gardens for P. brassicae and its host plants, removing host plants, ground-based spraying of insecticide to kill eggs and larvae, searching for pupae, capturing adults with nets, and augmenting natural enemy populations. The attempt was supported by research that helped to progressively refine the eradication strategy and evaluate its performance. The last New Zealand detection of P. brassicae occurred on 16 December 2014, the eradication program ceased on 4 June 2016 and P. brassicae was officially declared eradicated from New Zealand on 22 November 2016, 6.5 years after it was first detected and 4 years after the eradication attempt commenced. This is the first species of butterfly ever to have been eradicated worldwide.

Legacy of a Butterfly's Parental Microbiome in Offspring Performance

An insect's phenotype can be influenced by the experiences of the parental generation. However, the effects of the parental symbiotic microbiome and host plant use on the offspring are unclear. We addressed this gap of knowledge by studying Pieris brassicae, a multivoltine butterfly species feeding on different brassicaceous plants across generations. We investigated how disturbance of the parental bacterial community by antibiotic treatment affects F1 larval traits. We tested the effects depending on whether F1 larvae are feeding on the same plant species as their parents or on a different one. The parental treatment alone had no impact on the biomass of F1 larvae feeding on the parental plant species. However, the parental treatment had a detrimental effect on F1 larval biomass when F1 larvae had a different host plant than their parents. This effect was linked to higher larval prophenoloxidase activity and greater downregulation of the major allergen gene (MA), a glucosinolate detoxification gene of P. brassicae Bacterial abundance in untreated adult parents was high, while it was very low in F1 larvae from either parental type, and thus unlikely to directly influence larval traits. Our results suggest that transgenerational effects of the parental microbiome on the offspring's phenotype become evident when the offspring is exposed to a transgenerational host plant shift.IMPORTANCE Resident bacterial communities are almost absent in larvae of butterflies and thus are unlikely to affect their host. In contrast, adult butterflies contain conspicuous amounts of bacteria. While the host plant and immune state of adult parental butterflies are known to affect offspring traits, it has been unclear whether also the parental microbiome imposes direct effects on the offspring. Here, we show that disturbance of the bacterial community in parental butterflies by an antibiotic treatment has a detrimental effect on those offspring larvae feeding on a different host plant than their parents. Hence, the study indicates that disturbance of an insect's parental microbiome by an antibiotic treatment shapes how the offspring individuals can adjust themselves to a novel host plant.

Seasonal phenotype-specific expression of microRNAs during metamorphosis in the European map butterfly Araschnia levana

The European map butterfly (Araschnia levana) is a well-known example of seasonal polyphenism because the spring and summer imagoes exhibit distinct morphological phenotypes. The day length and temperature during larval and prepupal development determine whether spring or summer imagoes emerge after metamorphosis. Inspired by the fundamentally different transcriptomic profiles in prepupae developing from larvae exposed to long days or short days, we postulate that posttranscriptional epigenetic regulators such as microRNAs (miRNAs) may contribute to the epigenetic control of seasonal polyphenism in A. levana. To test this hypothesis, we used microarrays containing over 2,000 insect miRNAs to identify candidate regulators that are differentially expressed in last-instar larvae or pupae developing under long-day or short-day conditions. We used our transcriptomic database to identify potential 3'-untranslated regions of messenger RNAs to predict miRNA targets by considering both base pair complementarity and minimum free energy hybridization. This approach resulted in the identification of multiple targets of miRNAs that were differentially regulated in polyphenic morphs of A. levana including a candidate (miR-2856-3p) regulating the previously identified diapause bioclock protein gene. In conclusion, the expression profiling of miRNAs provided insights into their possible involvement in seasonal polyphenism of A. levana and offer an important resource for further studies.

Variation in Below-to Aboveground Systemic Induction of Glucosinolates Mediates Plant Fitness Consequences under Herbivore Attack

Plants defend themselves against herbivore attack by constitutively producing toxic secondary metabolites, as well as by inducing them in response to herbivore feeding. Induction of secondary metabolites can cross plant tissue boundaries, such as from root to shoot. However, whether the potential for plants to systemically induce secondary metabolites from roots to shoots shows genetic variability, and thus, potentially, is under selection conferring fitness benefits to the plants is an open question. To address this question, we induced 26 maternal plant families of the wild species Cardamine hirsuta belowground (BG) using the wound-mimicking phytohormone jasmonic acid (JA). We measured resistance against a generalist (Spodoptera littoralis) and a specialist (Pieris brassicae) herbivore species, as well as the production of glucosinolates (GSLs) in plants. We showed that BG induction increased AG resistance against the generalist but not against the specialist, and found substantial plant family-level variation for resistance and GSL induction. We further found that the systemic induction of several GSLs tempered the negative effects of herbivory on total seed set production. Using a widespread natural system, we thus confirm that BG to AG induction has a strong genetic component, and can be under positive selection by increasing plant fitness. We suggest that natural variation in systemic induction is in part dictated by allocation trade-offs between constitutive and inducible GSL production, as well as natural variation in AG and BG herbivore attack in nature.

Tolerance of Novel Toxins through Generalized Mechanisms: Simulating Gradual Host Shifts of Butterflies

Organisms encounter a wide range of toxic compounds in their environments, from chemicals that serve anticonsumption or anticompetition functions to pollutants and pesticides. Although we understand many detoxification mechanisms that allow organisms to consume toxins typical of their diet, we know little about why organisms vary in their ability to tolerate entirely novel toxins. We tested whether variation in generalized stress responses, such as antioxidant pathways, may underlie variation in reactions to novel toxins and, if so, their associated costs. We used an artificial diet to present cabbage white butterfly caterpillars (Pieris rapae) with plant material containing toxins not experienced in their evolutionary history. Families that maintained high performance (e.g., high survival, fast development time, large body size) on diets containing one novel toxic plant also performed well when exposed to two other novel toxic plants, consistent with a generalized response. Variation in constitutive (but not induced) expression of genes involved in oxidative stress responses was positively related to performance on the novel diets. While we did not detect reproductive trade-offs of this generalized response, there was a tendency to have less melanin investment in the wings, consistent with the role of melanin in oxidative stress responses. Taken together, our results support the hypothesis that variation in generalized stress responses, such as genes involved in oxidative stress responses, may explain the variation in tolerance to entirely novel toxins and may facilitate colonization of novel hosts and environments.

Parasite-host specificity: A cross-infection study of the parasite Ophryocystis elektroscirrha

Many parasites are constrained to only one or a few hosts, showing host specificity. It remains unclear why some parasites are specialists and other parasites are generalists. The parasite Ophryocystis elektroscirrha (OE) is a neogregarine protozoan thought to be restricted to monarch butterflies, Danaus plexippus (Nymphaliae) and D. gilippus. Recently, we found OE-like spores in other Lepidoptera, specifically in three noctuid moths: Helicoverpa armigera, H. assulta and H. punctigera, as well as another nymphalid, Parthenos sylvia. To our knowledge, this is the first report of OE-like parasite infections in species other than the genus Danaus. In sequencing 558 bp of 18S rRNA, we found the genetic similarity between OE from D. plexippus and OE-like parasite from the moths H. armigera and H. punctigera to be 95.2%. When we conducted cross-species infection experiments, we could not infect the moths with OE from D. plexippus, but OE-like parasite from H. armigera did infect D. plexippus and a closely related moth species Heliothis virescens. Interestingly, we did not find the OE-like parasite in the H. armigera population from Spain. Inter-population infection experiments with H. armigera demonstrated a higher sensitivity to OE-like infection in the population from Spain compared to the populations from Australia and China. These results suggest geographic variation in OE-like susceptibility and coevolution between parasite and host. Our findings give important new insights into the prevalence and host specificity of OE and OE-like parasites, and provide opportunities to study parasite transmission over spatial and temporal scales.

The dynamics of cyanide defences in the life cycle of an aposematic butterfly: Biosynthesis versus sequestration

Heliconius butterflies are highly specialized in Passiflora plants, laying eggs and feeding as larvae only on them. Interestingly, both Heliconius butterflies and Passiflora plants contain cyanogenic glucosides (CNglcs). While feeding on specific Passiflora species, Heliconius melpomene larvae are able to sequester simple cyclopentenyl CNglcs, the most common CNglcs in this plant genus. Yet, aromatic, aliphatic, and modified CNglcs have been reported in Passiflora species and they were never tested for sequestration by heliconiine larvae. As other cyanogenic lepidopterans, H. melpomene also biosynthesize the aliphatic CNglcs linamarin and lotaustralin, and their toxicity does not rely exclusively on sequestration. Although the genes encoding the enzymes in the CNglc biosynthesis have not yet been biochemically characterized in butterflies, the cytochromes P450 CYP405A4, CYP405A5, CYP405A6 and CYP332A1 have been hypothesized to be involved in this pathway in H. melpomene. In this study, we determine how the CNglc composition and expression of the putative P450s involved in the biosynthesis of these compounds vary at different developmental stages of Heliconius butterflies. We also establish which kind of CNglcs H. melpomene larvae can sequester from Passiflora. By analysing the chemical composition of the haemolymph from larvae fed with different Passiflora diets, we show that H. melpomene is able to sequestered prunasin, an aromatic CNglcs, from P. platyloba. They are also able to sequester amygdalin, gynocardin, [C¹³/C¹⁴]linamarin and [C¹³/C¹⁴]lotaustralin painted on the plant leaves. The CNglc tetraphyllin B-sulphate from P. caerulea is not detected in the larval haemolymph, suggesting that such modified CNglcs cannot be sequestered by Heliconius. Although pupae and virgin adults contain dihydrogynocardin resulting from larval sequestration, this compound was metabolized during adulthood, and not used as nuptial gift or transferred to the offspring. Thus, we speculate that dihydrogynocardin is catabolized to recycle nitrogen and glucose, and/or to produce fitness signals during courtship. Mature adults have a higher concentration of CNglcs than any other developmental stages due to increased de novo biosynthesis of linamarin and lotaustralin. Accordingly, all CYP405As are expressed in adults, whereas larvae mostly express CYP405A4. Our results shed light on the importance of CNglcs for Heliconius biology and their coevolution with Passiflora.

The extremely low energy cost of biosynthesis in holometabolous insect larvae

The metabolic cost of growth, which quantifies the amount of energy required to synthesize a unit of biomass, is an important component of an animal's ontogenetic energy budget. Here we investigated this quantity as well as other energy budget variables of the larvae of a holometabolous insect species, Vanessa cardui (painted lady). We found that the high growth rate of this caterpillar cannot be explained by its metabolic rate and the percentage of the metabolic energy allocated to growth; the key to understanding its fast growth is the extremely low cost of growth, 336 Joules/gram of dry mass. The metabolic cost of growth in caterpillars is 15-65 times lower than that of the endothermic and ectothermic species investigated in previous studies. Our results suggest that the low cost cannot be attributed to its body composition, diet composition, or body size. To explain the "cheap price" of growth in caterpillars, we assumed that a high metabolic cost for biosynthesis resulted in a high "quality" of cells, which have fewer errors during biosynthesis and higher resistance to stressors. Considering the life history of the caterpillars, i.e., tissue disintegration during metamorphosis and a short developmental period and lifespan, we hypothesized that an energy budget that allocates a large amount of energy to biosynthesizing high quality cells would be selected against in this species. As a preliminary test of this hypothesis, we estimated the metabolic cost of growth in larvae of Manduca sexta (tobacco hornworm) and nymphs of Blatta lateralis (Turkestan cockroach). The preliminary data supported our hypothesis.

Disrupting butterfly caterpillar microbiomes does not impact their survival and development

Associations with gut microbes are believed to play crucial roles in the physiology, immune function, development and behaviour of insects. However, microbiome sequencing has recently suggested that butterflies are an anomaly, because their microbiomes do not show strong host- and developmental stage-specific associations. We experimentally manipulated butterfly larval gut microbiota and found that disrupting gut microbes had little influence on larval survival and development. Larvae of the butterflies Danaus chrysippus and Ariadne merione that fed on chemically sterilized or antibiotic-treated host plant leaves had significantly reduced bacterial loads, and their gut bacterial communities were disrupted substantially. However, neither host species treated this way suffered a significant fitness cost: across multiple experimental blocks, treated and control larvae had similar survival, growth and development. Furthermore, re-introducing microbes from the excreta of control larvae did not improve larval growth and survival. Thus, these butterfly larvae did not appear to rely on specialized gut bacteria for digestion, detoxification, biomass accumulation and metamorphosis. Our experiments thus show that dependence on gut bacteria for growth and survival is not a universal phenomenon across insects. Our findings also caution that strategies which target gut microbiomes may not always succeed in controlling Lepidopteran pests.

Toxicity of Agrochemicals Among Larval Painted Lady Butterflies (Vanessa cardui)

In the Southern High Plains of the United States, beef cattle feed yards and row crop agriculture are predominant sources of agrochemical usage. Beef cattle feed yards use large quantities of veterinary pharmaceuticals to promote cattle growth and health, along with insecticides to control insect pests, whereas row crop-based agriculture relies on herbicides, fungicides, and insecticides to increase yields. Previous studies have documented the occurrence of agrochemicals beyond feed yard and row crop agriculture boundaries in uncultivated, marginal areas, raising concern that migratory pollinators and pollinators indigenous to the Southern High Plains frequenting these remaining habitat corridors may become exposed to toxic agrochemicals. Larvae of the painted lady butterfly (Vanessa cardui) were used to investigate the potential toxicity of agrochemicals used on feed yards and in row crop agriculture among pollinators. Moxidectin, an antiparasiticide used on beef cattle feed yards, was determined to be extremely toxic to V. cardui larvae, with a lethal dose at which 50% of larvae died of 2.1 ± 0.1 ng/g. Pyraclostrobin, clothianidin, and permethrin all delayed V. cardui development. However, moxidectin was the only chemical that produced significant toxic effects at environmentally relevant concentrations. These results indicate that agrochemicals originating from feed yards have the potential to adversely impact the development of pollinator larvae occurring in the Southern High Plains. Environ Toxicol Chem 2019;38:2629-2636. © 2019 SETAC.

Gene duplication and subsequent functional diversification of sucrose hydrolase in Papilio xuthus

Sucrose is the main product of photosynthesis in plants, providing a rich carbon and energy source for the physiological growth and development of insects. In a previous study, we identified a novel sucrose hydrolase (SUH) in the larval midgut of moths. Intriguingly, there are two copies of Suh, namely Suh1 and Suh2, in several species of butterflies. However, the biochemical characteristics of SUHs in butterflies remain unclear. In this study, we found that this duplication and subsequent diversification produced two Suh genes in Papilio xuthus. These two PxSuh genes were significantly divergent in terms of their expression pattern and enzyme properties. PxSuh messenger RNA expression was highest during the larval stage, reduced in the prepupal and pupal stages and, for PxSuh1, slightly increased again in the adult. The observed levels of PxSuh2 were overall below those of PxSuh1 amongst the development stages examined. Compared with PxSUH2, which has maintained the original gene function of maltose hydrolysis, PxSUH1 exhibits substrate specificity for sucrose with an optimum enzyme activity occurring at an alkaline pH. The data show that PxSuh1 is evolutionarily adapted for effective functioning in an alkaline digestive system. Furthermore, we find that functional diversification of Suh facilitates P. xuthus to digestive carbohydrate of host plants. Thus, our findings offer new insights into the ecological and evolutionary adaptation of digestive enzymes in butterflies.

A digestive tract expressing α-amylase influences the adult lifespan of Pteromalus puparum revealed through RNAi and rescue analyses

BACKGROUND

Midgut and salivary gland α-amylases are digestive enzymes required for the development of insects and have been investigated in some insect species. However, α-amylases in the endoparasitioid wasps have not been reported. Pteromalus puparum (Hymenoptera: Pteromalidae) is a dominant endoparasitioid wasp that parasitizes many butterfly species, including the Brassicaceae pest Pieris rapae (Lepidoptera: Pieridae). Here, we studied the characteristics and functions of three α-amylases in P. puparum.

RESULTS

We cloned three genes encoding α-amylases in P. puparum, PpAmy1, PpAmy2 and PpAmy3. The full length of the PpAmy1 cDNA is 1872 bp, encoding 496 amino acids, the PpAmy2 cDNA is 1863 bp long, encoding 518 amino acids, and PpAmy3 cDNA consists of 1802 bp encoding 521 amino acids. PpAmys are highly similar in amino acid sequences, but they have separate tissue distributions. Phylogenetic results show that gene duplications may occur between PpAmy2 and PpAmy3. PpAmy1 and PpAmy3 are most highly expressed in the digestive tract and the venom apparatus, respectively, while PpAmy2 is broadly expressed in all tissues. We report that PpAmy1 acts in the digestive tract, where it influences lifespan as demonstrated using RNAi and α-amylase rescue analyses, and there is no significant difference in longevity when PpAmy2 and PpAmy3 are knocked down.

CONCLUSION

PpAmys probably have roles in carbohydrate metabolism of P. puparum and its host/parasitoid relationships. The characterization and functional study of PpAmys lays the foundation for the protection and utilization of parasitoid resources, and the biological control of agricultural pests. © 2019 Society of Chemical Industry.

Reproducible phenotype alteration due to prolonged cooling of the pupae of Polyommatus icarus butterflies

The phenotypic changes induced by prolonged cooling (2-12 weeks at 5 °C in the dark) of freshly formed Polyommatus icarus pupae were investigated. Cooling halted the imaginal development of pupae collected shortly after transformation from the larval stage. After cooling, the pupae were allowed to continue their developmental cycle. The wings of the eclosed specimens were investigated by optical microscopy, scanning and cross-sectional transmission electron microscopy, UV-VIS spectroscopy and microspectroscopy. The eclosed adults presented phenotypic alterations that reproduced results that we published previously for smaller groups of individuals remarkably well; these changes included i) a linear increase in the magnitude of quantified deviation from normal ventral wing patterns with increasing cooling time; ii) slight alteration of the blue coloration of males; and iii) an increasing number of blue scales on the dorsal wing surface of females with increasing cooling time. Several independent factors, including disordering of regular scale rows in males, the number of blue scales in females, eclosion probability and the probability of defect-free eclosion, showed that the cooling time can be divided into three periods: 0-4 weeks, 4-8 weeks, and 8-12 weeks, each of which is characterized by specific changes. The shift from brown female scales to first blue scales with a female-specific shape and then to blue scales with a male-specific shape with longer cooling times suggests slow decomposition of a substance governing scale formation.

Nutritional stress reduces flight performance and exploratory behavior in a butterfly

Anthropogenic global change, including agricultural intensification and climate change, poses a substantial challenge to many herbivores due to a reduced availability of feeding resources. The concomitant food stress is expected to detrimentally affect performance, amongst others in dispersal-related traits. Thus, while dispersal is of utmost importance to escape from deteriorating habitat conditions, such conditions may negatively feedback on the ability to do so. Therefore, we here investigate the impact of larval and adult food stress on traits related to dispersal ability, including morphology, physiology, flight performance, and exploratory behavior, in a butterfly. We show that inadequate nutrition during development and in the adult stage diminishes flight performance, despite some re-allocation of somatic resources. Detrimental effects of food stress on flight performance were mainly caused by reductions in body mass and storage reserves. Similar results were found for exploratory behavior. Furthermore, exploratory behavior was found to be (moderately) repeatable at the individual level, which might indicate the existence of a personality trait. This notion is further supported by the fact that flight performance and exploratory behavior were positively correlated, potentially suggesting the existence of a dispersal syndrome. In summary, our findings may have important implications for dispersal in natural environments, as the conditions requiring dispersal the most impair flight ability and thereby likely dispersal rates.

Drift and Directional Selection Are the Evolutionary Forces Driving Gene Expression Divergence in Eye and Brain Tissue of Heliconius Butterflies

Investigating gene expression evolution over micro- and macroevolutionary timescales will expand our understanding of the role of gene expression in adaptation and speciation. In this study, we characterized the evolutionary forces acting on gene expression levels in eye and brain tissue of five Heliconius butterflies with divergence times of ∼5-12 MYA. We developed and applied Brownian motion (BM) and Ornstein-Uhlenbeck (OU) models to identify genes whose expression levels are evolving through drift, stabilizing selection, or a lineage-specific shift. We found that 81% of the genes evolve under genetic drift. When testing for branch-specific shifts in gene expression, we detected 368 (16%) shift events. Genes showing a shift toward upregulation have significantly lower gene expression variance than those genes showing a shift leading toward downregulation. We hypothesize that directional selection is acting in shifts causing upregulation, since transcription is costly. We further uncovered through simulations that parameter estimation of OU models is biased when using small phylogenies and only becomes reliable with phylogenies having ≥ 50 taxa. Therefore, we developed a new statistical test based on BM to identify highly conserved genes (i.e., evolving under strong stabilizing selection), which comprised 3% of the orthoclusters. In conclusion, we found that drift is the dominant evolutionary force driving gene expression evolution in eye and brain tissue in Heliconius Nevertheless, the higher proportion of genes evolving under directional than under stabilizing selection might reflect species-specific selective pressures on vision and the brain that are necessary to fulfill species-specific requirements.

Plasticity and divergence in ultraviolet reflecting structures on Dogface butterfly wings

The vast diversity of animal coloration is generated through a combination of pigment and structural colors. These colors can greatly influence the fitness and life history of an organism. Butterflies and their wing colors are an excellent model to study how these colors can impact the development and success of an organism. In this study, we explore species differences in structurally-based ultraviolet coloration in the Zerene butterfly. We show clear species differences in ultraviolet (UV) pattern and reflectance spectra. By varying larval diet, we show evidence for developmental plasticity in the structure and organization of UV reflecting scales in Zerene cesonia. We further show that feeding the larval host plant of Zerene eurydice to Z. cesonia does not result in greater similarity in scale structure or UV coloration to the sister species. These results not only demonstrate a connection between plasticity in a male ornamentation, UV wing pattern, and larval resource acquisition, but also identify candidate structural and organizational changes in wing scales responsible for the trait variation.

A biotrophic fungal infection of the great burnet Sanguisorba officinalis indirectly affects caterpillar performance of the endangered scarce large blue butterfly Phengaris teleius

Interactions between ecological communities of herbivores and microbes are commonly mediated by a shared plant. A tripartite interaction between a pathogenic fungus-host plant-herbivorous insect is an example of such mutual influences. In such a system a fungal pathogen commonly has a negative influence on the morphology and biochemistry of the host plant, with consequences for insect herbivore performance. Here we studied whether the biotrophic fungus Podosphaera ferruginea, attacking the great burnet Sanguisorba officinalis, affects caterpillar performance of the endangered scarce large blue butterfly Phengaris teleius. Our results showed that the pathogenic fungus affected the number and size of inflorescences produced by food-plants and, more importantly, had indirect, plant-mediated effects on the abundance, body mass and immune response of caterpillars. Specifically, we found the relationship between caterpillar abundance and variability in inflorescence size on a plant to be positive among healthy food-plants, and negative among infected food-plants. Caterpillars that fed on healthy food-plants were smaller than those that fed on infected food-plants in one studied season, while there was no such difference in the other season. We observed the relationship between caterpillar immune response and the proportion of infected great burnets within a habitat patch to be positive when caterpillars fed on healthy food-plants, and negative when caterpillars fed on infected food-plants. Our results suggest that this biotrophic fungal infection of the great burnet may impose a significant indirect influence on P. teleius caterpillar performance with potential consequences for the population dynamics and structure of this endangered butterfly.

Interspecific Differences in the Larval Performance of Pieris Butterflies (Lepidoptera: Pieridae) Are Associated with Differences in the Glucosinolate Profiles of Host Plants

The tremendous diversity of plants and herbivores has arisen from a coevolutionary relationship characterized by plant defense and herbivore counter adaptation. Pierid butterfly species feed on Brassicales plants that produce glucosinolates as a chemical deterrent against herbivory. In turn, the larvae of pierids have nitrile specifier proteins (NSPs) that are expressed in their gut and disarm glucosinolates. Pierid butterflies are known to have diversified in response to glucosinolate diversification in Brassicales. Therefore, each pierid species is expected to have a spectrum of host plants characterized by specific glucosinolate profiles. In this study, we tested whether the larval performance of different Pieris species, a genus in Pieridae (Lepidoptera: Pieridae), was associated with plant defense traits of putative host plants. We conducted feeding assays using larvae of three Pieris species and 10 species of the Brassicaceae family possessing different leaf physical traits and glucosinolate profile measurements. The larvae of Pieris rapae responded differently in the feeding assays compared with the other two Pieris species. This difference was associated with differences in glucosinolate profiles but not with variations in physical traits of the host plants. This result suggests that individual Pieris species are adapted to a subset of glucosinolate profiles within the Brassicaceae. Our results support the idea that the host ranges of Pieris species depend on larval responses to glucosinolate diversification in the host species, supporting the hypothesis of coevolution between butterflies and host plants mediated by the chemical arms race.

Insights into eyespot color-pattern formation mechanisms from color gradients, boundary scales, and rudimentary eyespots in butterfly wings

Butterfly eyespot color patterns are traditionally explained by the gradient model, where positional information is stably provided by a morphogen gradient from a single organizer and its output is a set of non-graded (or graded) colors based on pre-determined threshold levels. An alternative model is the induction model, in which the outer black ring and the inner black core disk of an eyespot are specified by graded signals from the primary and secondary organizers that also involve lateral induction. To examine the feasibility of these models, we analyzed eyespot color gradients, boundary scales, and rudimentary eyespots in various nymphalid butterflies. Most parts of eyespots showed color gradients with gradual or fluctuating changes with sharp boundaries in many species, but some species had eyespots that were composed of a constant color within a given part. Thus, a plausible model should be flexible enough to incorporate this diversity. Some boundary scales appeared to have two kinds of pigments, and others had "misplaced" colors, suggesting an overlapping of two signals and a difficulty in assuming sharp threshold boundaries. Rudimentary eyespots of three Junonia species revealed that the outer black ring is likely determined first and the inner yellow or red ring is laterally induced. This outside-to-inside determination together with the lateral induction may favor the induction model, in which dynamic signal interactions play a major role. The implications of these results for the ploidy hypothesis and color-pattern rules are discussed.

Prepatterning of Papilio xuthus caterpillar camouflage is controlled by three homeobox genes: clawless, abdominal-A, and Abdominal-B

Color patterns often function as camouflage to protect insects from predators. In most swallowtail butterflies, younger larvae mimic bird droppings but change their pattern to mimic their host plants during their final molt. This pattern change is determined during the early fourth instar by juvenile hormone (JH-sensitive period), but it remains unclear how the prepatterning process is controlled. Using Papilio xuthus larvae, we performed transcriptome comparisons to identify three camouflage pattern-associated homeobox genes [clawless, abdominal-A, and Abdominal-B (Abd-B)] that are up-regulated during the JH-sensitive period in a region-specific manner. Electroporation-mediated knockdown of each gene at the third instar caused loss or change of original fifth instar patterns, but not the fourth instar mimetic pattern, and knockdown of Abd-B after the JH-sensitive period had no effect on fifth instar patterns. These results indicate the role of these genes during the JH-sensitive period and in the control of the prepatterning gene network.

Insect egg deposition renders plant defence against hatching larvae more effective in a salicylic acid-dependent manner

Plants can improve their antiherbivore defence by taking insect egg deposition as cue of impending feeding damage. Previous studies showed that Pieris brassicae larvae feeding upon egg-deposited Brassicaceae perform worse and gain less weight than larvae on egg-free plants. We investigated how P. brassicae oviposition on Arabidopsis thaliana affects the plant's molecular and chemical responses to larvae. A transcriptome comparison of feeding-damaged leaves without and with prior oviposition revealed about 200 differently expressed genes, including enhanced expression of PR5, which is involved in salicylic acid (SA)-signalling. SA levels were induced by larval feeding to a slightly greater extent in egg-deposited than egg-free plants. The adverse effect of egg-deposited wild-type (WT) plants on larval weight was absent in an egg-deposited PR5-deficient mutant or other mutants impaired in SA-mediated signalling, that is, sid2/ics1, ald1, and pad4. In contrast, the adverse effect of egg-deposited WT plants on larvae was retained in egg-deposited npr1 and wrky70 mutants impaired further downstream in SA-signalling. Oviposition induced accumulation of flavonols in WT plants with and without feeding damage, but not in the PR5-deficient mutant. We demonstrated that egg-mediated improvement of A. thaliana's antiherbivore defence involves SA-signalling in an NPR1-independent manner and is associated with accumulation of flavonols.

Cardenolide Intake, Sequestration, and Excretion by the Monarch Butterfly along Gradients of Plant Toxicity and Larval Ontogeny

Monarch butterflies, Danaus plexippus, migrate long distances over which they encounter host plants that vary broadly in toxic cardenolides. Remarkably little is understood about the mechanisms of sequestration in Lepidoptera that lay eggs on host plants ranging in such toxins. Using closely-related milkweed host plants that differ more than ten-fold in cardenolide concentrations, we mechanistically address the intake, sequestration, and excretion of cardenolides by monarchs. We show that on high cardenolide plant species, adult butterflies saturate in cardenolides, resulting in lower concentrations than in leaves, while on low cardenolide plants, butterflies concentrate toxins. Butterflies appear to focus their sequestration on particular compounds, as the diversity of cardenolides is highest in plant leaves, lower in frass, and least in adult butterflies. Among the variety of cardenolides produced by the plant, sequestered compounds may be less toxic to the butterflies themselves, as they are more polar on average than those in leaves. In accordance with this, results from an in vitro assay based on inhibition of Na⁺/K⁺ ATPase (the physiological target of cardenolides) showed that on two milkweed species, including the high cardenolide A. perennis, extracts from butterflies have lower inhibitory effects than leaves when standardized by cardenolide concentration, indicating selective sequestration of less toxic compounds from these host plants. To understand how ontogeny shapes sequestration, we examined cardenolide concentrations in caterpillar body tissues and hemolymph over the course of development. Caterpillars sequestered higher concentrations of cardenolides as early instars than as late instars, but within the fifth instar, concentration increased with body mass. Although it appears that large amounts of sequestration occurs in early instars, a host switching experiment revealed that caterpillars can compensate for feeding on low cardenolide host plants with substantial sequestration in the fifth instar. We highlight commonalities and striking differences in the mechanisms of sequestration depending on host plant chemistry and developmental stage, which have important implications for monarch defense.

Moderate plant water stress improves larval development, and impacts immunity and gut microbiota of a specialist herbivore

While host plant drought is generally viewed as a negative phenomenon, its impact on insect herbivores can vary largely depending on the species involved and on the intensity of the drought. Extreme drought killing host plants can clearly reduce herbivore fitness, but the impact of moderate host plant water stress on insect herbivores can vary, and may even be beneficial. The populations of the Finnish Glanville fritillary butterfly (Melitaea cinxia) have faced reduced precipitation in recent years, with impacts even on population dynamics. Whether the negative effects of low precipitation are solely due to extreme desiccation killing the host plant or whether moderate drought reduces plant quality for the larvae remains unknown. We assessed the performance of larvae fed on moderately water-stressed Plantago lanceolata in terms of growth, survival, and immune response, and additionally were interested to assess whether the gut microbial composition of the larvae changed due to modification of the host plant. We found that larvae fed on water-stressed plants had increased growth, with no impact on survival, up-regulated the expression of one candidate immune gene (pelle), and had a more heterogeneous bacterial community and a shifted fungal community in the gut. Most of the measured traits showed considerable variation due to family structure. Our data suggest that in temperate regions moderate host plant water stress can positively shape resource acquisition of this specialized insect herbivore, potentially by increasing nutrient accessibility or concentration. Potentially, the better larval performance may be mediated by a shift of the microbiota on water-stressed plants, calling for further research especially on the understudied gut fungal community.

Taste sensitivity and divergence in host plant acceptance between adult females and larvae of Papilio hospiton

On the island of Sardinia the lepidopteran Papilio hospiton uses Ferula communis as exclusive host plant. However, on the small island of Tavolara, adult females lay eggs on Seseli tortuosum, a plant confined to the island. When raised in captivity on Seseli only few larvae grew beyond the first-second instar. Host specificity of lepidopterans is determined by female oviposition preferences, but also by larval food acceptance, and adult and larval taste sensitivity may be related to host selection in both cases. Aim of this work was: (i) to study the taste sensitivity of larvae and ovipositing females to saps of Ferula and Seseli; (ii) to cross-compare the spike activity of gustatory receptor neurons (GRNs) to both taste stimuli; (iii) to evaluate the discriminating capability between the two saps and determine which neural code/s is/are used. The results show that: (i) the spike responses of the tarsal GRNs of adult females to both plant saps are not different and therefore they cannot discriminate the two plants; (ii) larval L-lat GRN shows a higher activity in response to Seseli than Ferula, while the opposite occurs for the phagostimulant neurons, and larvae may discriminate between the two saps by means of multiple neural codes; (iii) the number of eggs laid on the two plants is the same, but the larval growth performance is better on Ferula than Seseli. Taste sensitivity differences may explain the absence of a positive relationship between oviposition preferences by adult females and plant acceptance and growth performance by larvae.

Molecular Characterization and Expression Analysis of Two Acetylcholinesterase Genes From the Small White Butterfly Pieris rapae (Lepidoptera: Pieridae)

Acetylcholinesterases (AChEs) are essential for the hydrolysis of the neurotransmitter acetylcholine and play crucial roles in the termination of neurotransmission. AChEs are encoded by the ace genes. However, the ace genes from the small white butterfly, Pieris rapae (L.) (Lepidoptera: Pieridae), remained uncharacterized. In this study, two aces (Prace1 and Prace2) were identified from P. rapae. Prace1 encoded a PrAChE1 protein consisting of 694 amino acid residues, and Prace2 encoded the 638-amino-acid PrAChE2. The two identified PrAChEs both had features typical of AChEs, including the catalytic triad, choline-binding sites, an oxyanion hole, an acyl pocket, a peripheral anionic subsite, an FGESAG motif and 14 conserved aromatic amino acids. Phylogenetic analysis showed that Prace1 and Prace2 were clustered into two distinct groups: ace1 and ace2, respectively. The two Praces were distributed on different genomic scaffolds: Prace1 on scaffold 156 and Prace2 on scaffold 430. Additionally, Prace1 consisted of three exons and two introns, whereas Prace2 consisted of six exons and five introns. One amino acid mutation (Gly324Ala) in PrAChE1 and two (Ser291Gly and Ser431Phe) in PrAChE2 were consistent with mutations in other insect AChEs that are associated with insecticide insensitivity. Both Prace1 and Prace2 were highly expressed at the fifth-instar larval stage and in the larval head, and the transcriptional levels of Prace1 were significantly higher than those of Prace2 in all of the tested life stages and tissues. This is the first report characterizing two ace genes in P. rapae. The results pave the way for functional study of these genes.

Metapopulation dynamics in a changing climate: Increasing spatial synchrony in weather conditions drives metapopulation synchrony of a butterfly inhabiting a fragmented landscape

Habitat fragmentation and climate change are both prominent manifestations of global change, but there is little knowledge on the specific mechanisms of how climate change may modify the effects of habitat fragmentation, for example, by altering dynamics of spatially structured populations. The long-term viability of metapopulations is dependent on independent dynamics of local populations, because it mitigates fluctuations in the size of the metapopulation as a whole. Metapopulation viability will be compromised if climate change increases spatial synchrony in weather conditions associated with population growth rates. We studied a recently reported increase in metapopulation synchrony of the Glanville fritillary butterfly (Melitaea cinxia) in the Finnish archipelago, to see if it could be explained by an increase in synchrony of weather conditions. For this, we used 23 years of butterfly survey data together with monthly weather records for the same period. We first examined the associations between population growth rates within different regions of the metapopulation and weather conditions during different life-history stages of the butterfly. We then examined the association between the trends in the synchrony of the weather conditions and the synchrony of the butterfly metapopulation dynamics. We found that precipitation from spring to late summer are associated with the M. cinxia per capita growth rate, with early summer conditions being most important. We further found that the increase in metapopulation synchrony is paralleled by an increase in the synchrony of weather conditions. Alternative explanations for spatial synchrony, such as increased dispersal or trophic interactions with a specialist parasitoid, did not show paralleled trends and are not supported. The climate driven increase in M. cinxia metapopulation synchrony suggests that climate change can increase extinction risk of spatially structured populations living in fragmented landscapes by altering their dynamics.

Evaluation of the potential exposure of butterflies to genetically modified maize pollen in protected areas in Italy

Environmental impacts of genetically modified crops are mandatorily assessed during their premarket phase. One of the areas of concern is the possible impact on nontarget organisms. Crops expressing Cry toxins might affect Lepidoptera larvae living outside cultivated fields, through pollen deposition on wild plants, which constitute their food source. While pollen toxicity varies among different events, possible exposure of nontarget species depends on the agro-environmental conditions. This study was conducted in two protected areas in Italy, characterized by different climatic conditions, where many Lepidoptera species thrive in proximity to maize cultivations. To estimate the possible exposure in absence of the actual stressor (e.g., Cry1-expressing maize plants), we conducted a two-year field survey of butterflies and weeds. Indicator species were selected-Aglais (Inachis) io in the Northern site and Vanessa cardui in the Southern site-and their phenology was investigated. Pollen dispersal from maize fields was measured by collection in Petri dishes. Duration and frequency of exposure was defined by the overlap between pollen emission and presence of larvae on host plants. Different risk scenarios are expected in the two regions: highest exposure is foreseen for A. io in the Northern site, while minimal exposure is estimated for V. cardui in the Southern site. In the latter case, locally grown maize cultivars flower in mid-summer in coincidence with an aestivation period for several butterfly species due to hot and dry conditions. Moreover, host plants of V. cardui are at the end of their life cycle thus limiting food availability.

Molecular identification and characterization of rhodaneses from the insect herbivore Pieris rapae

The association of cabbage white butterflies (Pieris spec., Lepidoptera: Pieridae) with their glucosinolate-containing host plants represents a well-investigated example of the sequential evolution of plant defenses and insect herbivore counteradaptations. The defensive potential of glucosinolates, a group of amino acid-derived thioglucosides present in plants of the Brassicales order, arises mainly from their rapid breakdown upon tissue disruption resulting in formation of toxic isothiocyanates. Larvae of P. rapae are able to feed exclusively on glucosinolate-containing plants due to expression of a nitrile-specifier protein in their gut which redirects glucosinolate breakdown to the formation of nitriles. The release of equimolar amounts of cyanide upon further metabolism of the benzylglucosinolate-derived nitrile suggests that the larvae are also equipped with efficient means of cyanide detoxification such as β-cyanoalanine synthases or rhodaneses. While insect β-cyanoalanine synthases have recently been identified at the molecular level, no sequence information was available of characterized insect rhodaneses. Here, we identify and characterize two single-domain rhodaneses from P. rapae, PrTST1 and PrTST2. The enzymes differ in their kinetic properties, predicted subcellular localization and expression in P. rapae indicating different physiological roles. Phylogenetic analysis together with putative lepidopteran rhodanese sequences indicates an expansion of the rhodanese family in Pieridae.

Inhibitory effects of an extract from non-host plants on physiological characteristics of two major cabbage pests

The diamondback moth (Plutella xylostella) and small white cabbage butterfly (Pieris rapae) are the two main serious pests of cruciferous crops (Brassicaceae) that have developed resistance to chemical control methods. In order to avoid such resistance and also the adverse effects of chemical pesticides on the environment, alternative methods have usually been suggested, including the use of plant enzyme inhibitors. Here, the inhibitory effects of proteinaceous inhibitors extracted from wheat, canola, sesame, bean and triticale were evaluated against the digestive α-amylases, larval growth, development and nutritional indecs of the diamondback moth and small white cabbage butterfly. Our results indicated that triticale and wheat extracts inhibited α-amylolytic activity in an alkaline pH, which is in accordance with the moth and butterfly gut α-amylase optimum pH. Dose-dependent inhibition of two crucifer pests by triticale and wheat was observed using spectrophotometry and gel electrophoresis. Implementation of specificity studies showed that wheat and triticale-proteinaceous extract were inactive against Chinese and purple cabbage amylase. Triticale and wheat were resistant against insects' gut proteases. Results of the feeding bioassay indicated that triticale-proteinaceous extract could cause a significant reduction in survival and larval body mass. The results of the nutritional indecs also showed larvae of both species that fed on a Triticale proteinaceous inhibitor-treated diet had the lowest values for the efficiency of conversion of ingested food and relative growth rate. Our observations suggested that triticale shows promise for use in the management of crucifer pests.

Taste receptor plasticity in relation to feeding history in two congeneric species of Papilionidae (Lepidoptera)

In the peripheral taste system of insects, the responsiveness of gustatory receptor neurons (GRNs) depends on several factors, such as larval instar, feeding history, physiological state and time of day. To study the role of the feeding history, the spike activity of the maxillary taste chemosensilla in the larvae of two related species of Lepidoptera (Papilio machaon L. and Papilio hospiton Géné) raised on different host plants, was recorded with electrophysiological techniques after stimulation with simple stimuli (sugars, bitters and inorganic salt) and host plant saps, with the aim of cross-comparing their response patterns and evaluating any effects of different feeding histories. For this purpose the larvae were raised each on their preferential host plant and, in addition, P. machaon larvae was also raised on Ferula communis, the host plant preferred by P. hospiton. The GRN spike activity of the lateral and medial sensilla of each test group was measured in response to simple and complex stimuli. The taste discrimination capabilities and modalities of the two species were measured and cross-compared with the aim of studying convergence and/or divergence linked to the insect feeding history. The results show that: a) the GRN responsiveness of both sensilla in P. machaon raised on Fe. communis differs significantly from that of P. machaon on Foeniculum vulgare, but is not different from P. hospiton on Fe. communis; b) P. machaon larvae raised on Fe. communis exhibit response spectra somewhat intermediate between those of P. machaon on fennel and of P. hospiton on Fe. communis, the latter two exhibiting a wider difference from each other; c) the pattern of GRNs activity generated by each plant sap in both sensilla of P. machaon raised on Fe. communis is different from that generated when raised on Fo. vulgare, while no difference is observed with P. hospiton. The data support the hypothesis that diet-related factors may influence peripheral chemosensitivity in lepidopterous larvae.

Do juvenile developmental and adult body characteristics differ among genotypes at the doublesex locus that controls female-limited Batesian mimicry polymorphism in Papilio memnon?: A test for the "cost of mimicry" hypothesis

Female-limited Batesian mimicry may have evolved because of stronger predation pressure on females than on males, but some physiological costs of mimicry may also hinder the evolution of mimicry in males. In Papilio memnon, which possesses a female-limited Batesian mimicry polymorphism, two alleles at the doublesex (dsx) locus strictly control female phenotypes. To examine whether there are physiological costs associated with mimetic genotypes in the juvenile stage, we compered mortality, juvenile growth and development, and the resultant adult characteristics among three dsx genotypes (HH, Hh, hh) at a constant temperature (25 °C) and two differing day lengths (LD 14:10 and LD 12:12; the latter might induce pupal diapause) by crossing individuals heterozygous (Hh) for the dsx allele. All pupae emerged directly without diapause irrespective of day length. The genotype frequencies of the emerged individuals were consistent with the expected 1:2:1 ratio of HH:Hh:hh. The sex ratio was significantly male-biased in one of two families, but not in the other. We found no effect of genotype on any developmental or adult characteristic, although there were sex differences in most traits. The larval development time was longer and growth rate higher in females than in males; pupal weight, forewing length, and total dry mass of the thorax and abdomen were greater in females, whereas the thoracic mass/abdominal mass ratio was greater in males. We also found that the growth rate was higher and pupal period longer with a short day than with a long day. Overall, we found no evidence for physiological costs associated with the mimetic genotypes. However, it is too early to conclude that no physiological cost of mimicry affects the evolution and maintenance of this female-limited Batesian mimicry polymorphism because we have not studied the adults of different genotypes.

Viral exposure effects on life-history, flight-related traits, and wing melanisation in the Glanville fritillary butterfly

Infections represent a constant threat for organisms and can lead to substantial fitness losses. Understanding how individuals, especially from natural populations, respond towards infections is thus of great importance. Little is known about immunity in the Glanville fritillary butterfly (Melitaea cinxia). As the larvae live gregariously in family groups, vertical and horizontal transmission of infections could have tremendous effects on individuals and consequently impact population dynamics in nature. We used the Alphabaculovirus type strain Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and demonstrated that positive concentration-dependent baculovirus exposure leads to prolonged developmental time and decreased survival during larval and pupal development, with no sex specific differences. Viral exposure did not influence relative thorax mass or wing morphometric traits often related to flight ability, yet melanisation of the wings increased with viral exposure, potentially influencing disease resistance or flight capacity via thermal regulation. Further research is needed to explore effects under sub-optimal conditions, determine effects on fitness-related traits, and investigate a potential adaptive response of increased melanisation in the wings due to baculovirus exposure.

Comparative transcriptome analysis provides insights of anti-insect molecular mechanism of Cassia obtusifolia trypsin inhibitor against Pieris rapae

Pieris rapae, a serious Lepidoptera pest of cultivated crucifers, utilizes midgut enzymes to digest food and detoxify secondary metabolites from host plants. A recombinant trypsin inhibitor (COTI) from nonhost plant, Cassia obtusifolia, significantly decreased activities of trypsin-like proteases in the larval midgut on Pieris rapae and could suppress the growth of larvae. In order to know how COTI took effect, transcriptional profiles of P. rapae midgut in response to COTI was studied. A total of 51,544 unigenes were generated and 45.86% of which had homologs in public databases. Most of the regulated genes associated with digestion, detoxification, homeostasis, and resistance were downregulated after ingestion of COTI. Meanwhile, several unigenes in the integrin signaling pathway might be involved in response to COTI. Furthermore, using comparative transcriptome analysis, we detected differently expressing genes and identified a new reference gene, UPF3, by qRT-polymerase chain reaction (PCR). Therefore, it was suggested that not only proteolysis inhibition, but also suppression of expression of genes involved in metabolism, development, signaling, and defense might account for the anti-insect resistance of COTI.

Wolbachia in the Genus Bicyclus: a Forgotten Player

Bicyclus butterflies are key species for studies of wing pattern development, phenotypic plasticity, speciation and the genetics of Lepidoptera. One of the key endosymbionts in butterflies, the alpha-Proteobacterium Wolbachia pipientis, is affecting many of these biological processes; however, Bicyclus butterflies have not been investigated systematically as hosts to Wolbachia. In this study, we screen for Wolbachia infection in several Bicyclus species from natural populations across Africa as well as two laboratory populations. Out of the 24 species tested, 19 were found to be infected, and no double infection was found, but both A- and B-supergroup strains colonise this butterfly group. We also show that many of the Wolbachia strains identified in Bicyclus butterflies belong to the ST19 clonal complex. We discuss the importance of our results in regard to routinely screening for Wolbachia when using Bicyclus butterflies as the study organism of research in eco-evolutionary biology.

Toxicity and residual effects of insecticides on Ascia monuste and predator Solenopsis saevissima

BACKGROUND

Investigating the impact of pesticides on non-target organisms is essential for sustainable integrated pest management programs. We therefore assessed the toxicity of ten insecticides to the brassica caterpillar Ascia monuste and its ant predator Solenopsis saevissima and examined the effect that the insecticide synergists had on toxicity to the predator. We also assessed the residual period of control and impact of the insecticides during the brassica growing cycle.

RESULTS

All insecticides except flubendiamide exhibited mortality above the threshold required by Brazilian legislation (80%). Chlorantraniliprole, cyantraniliprole, indoxacarb and spinosad exhibited lower toxicity to the ant predator than they did to the brassica caterpillar. The results obtained for synergized insecticides suggest that selectivity to the predator was due the involvement of cytochrome P450-dependent monooxygenases. Chlorfenapyr and cyantraniliprole exhibited the highest residual periods of control to the brassica caterpillar, whereas malathion had the greatest impact on the predator.

CONCLUSION

Most of the insecticides efficiently controlled the brassica caterpillar, but not all exhibited selectivity to the predator. Therefore, due to the distinctive responses of organisms with respect to residual periods of control and the impact of the insecticides, spraying frequency must be strongly considered in integrated pest management programs. © 2017 Society of Chemical Industry.

Divergence in cryptic leaf colour provides local camouflage in an alpine plant

The efficacy of camouflage through background matching is highly environment-dependent, often resulting in intraspecific colour divergence in animals to optimize crypsis in different visual environments. This phenomenon is largely unexplored in plants, although several lines of evidence suggest they do use crypsis to avoid damage by herbivores. Using Corydalis hemidicentra, an alpine plant with cryptic leaf colour, we quantified background matching between leaves and surrounding rocks in five populations based on an approximate model of their butterfly enemy's colour perception. We also investigated the pigment basis of leaf colour variation and the association between feeding risk and camouflage efficacy. We show that plants exhibit remarkable colour divergence between populations, consistent with differences in rock appearances. Leaf colour varies because of a different quantitative combination of two basic pigments-chlorophyll and anthocyanin-plus different air spaces. As expected, leaf colours are better matched against their native backgrounds than against foreign ones in the eyes of the butterfly. Furthermore, improved crypsis tends to be associated with a higher level of feeding risk. These results suggest that divergent cryptic leaf colour may have evolved to optimize local camouflage in various visual environments, extending our understanding of colour evolution and intraspecific phenotype diversity in plants.

Milkweed Matters: Monarch Butterfly (Lepidoptera: Nymphalidae) Survival and Development on Nine Midwestern Milkweed Species

The population of monarch butterflies east of the Rocky Mountains has experienced a significant decline over the past 20 yr. In order to increase monarch numbers in the breeding range, habitat restoration that includes planting milkweed plants is essential. Milkweeds in the genus Asclepias and Cynanchum are the only host plants for larval monarch butterflies in North America, but larval performance and survival across nine milkweeds native to the Midwest is not well documented. We examined development and survival of monarchs from first-instar larval stages to adulthood on nine milkweed species native to Iowa. The milkweeds included Asclepias exaltata (poke milkweed) (Gentianales: Apocynaceae), Asclepias hirtella (tall green milkweed) (Gentianales: Apocynaceae), Asclepias incarnata (swamp milkweed) (Gentianales: Apocynaceae), Asclepias speciosa (showy milkweed) (Gentianales: Apocynaceae), Asclepias sullivantii (prairie milkweed) (Gentianales: Apocynaceae), Asclepias syriaca (common milkweed) (Gentianales: Apocynaceae), Asclepias tuberosa (butterfly milkweed) (Gentianales: Apocynaceae), Asclepias verticillata (whorled milkweed) (Gentianales: Apocynaceae), and Cynanchum laeve (honey vine milkweed) (Gentianales: Apocynaceae). In greenhouse experiments, fewer larvae that fed on Asclepias hirtella and Asclepias sullivantii reached adulthood compared with larvae that fed on the other milkweed species. Monarch pupal width and adult dry mass differed among milkweeds, but larval duration (days), pupal duration (days), pupal mass, pupal length, and adult wet mass were not significantly different. Both the absolute and relative adult lipids were different among milkweed treatments; these differences are not fully explained by differences in adult dry mass. Monarch butterflies can survive on all nine milkweed species, but the expected survival probability varied from 30 to 75% among the nine milkweed species.

Larvicidal activity of synthetic tropane alkaloids against Ascia monuste orseis (Lepidoptera: Pieridae)

BACKGROUND

Tropane alkaloids are known to play a role in plant defence. By blocking acetylcholine receptors, they exert insecticidal and deterrent effects against herbivore insects. Carbamates are an important class of chemical insecticides that also inhibit acetyl cholinesterase. The objective of this work was to synthesise a series of tropane alkaloids bearing a carbamate group, and to evaluate their effects against the pest Ascia monuste. The effects of the most active compounds were evaluated on the A. monuste predator Solenopsis saevissima and on the pollinator Tetragonisca angustula.

RESULTS

The synthesis of carbamate-tropane alkaloids was accomplished in 4-5 steps from commercially available ketones. Results from bioassays showed that compounds 6a, 10a and 14a presented higher activities against second-instar larvae of A. monuste, with LD₅₀ values of 1.01, 3.76 and 1.92 µg substance mg^-1 insect, and TL₅₀ values of 7.0, 15.0 and 5.0 h respectively. These compounds were also tested for their selectivity in favour of S. saevissima and T. angustula. Compound 6a, which showed the highest activity against A. monuste, also showed lower toxicity against S. saevissima.

CONCLUSION

Tropane alkaloid derivatives bearing a carbamate group show potential for the development of novel insecticides against A. monuste. © 2017 Society of Chemical Industry.

Carried over: Heat stress in the egg stage reduces subsequent performance in a butterfly

Increasing heat stress caused by anthropogenic climate change may pose a substantial challenge to biodiversity due to associated detrimental effects on survival and reproduction. Therefore, heat tolerance has recently received substantial attention, but its variation throughout ontogeny and effects carried over from one developmental stage to another remained largely neglected. To explore to what extent stress experienced early in life affects later life stages, we here investigate effects of heat stress experienced in the egg stage throughout ontogeny in the tropical butterfly Bicyclus anynana. We found that detrimental effects of heat stress in the egg stage were detectable in hatchlings, larvae and even resulting adults, as evidenced by decreased survival, growth, and body mass. This study shows that even in holometabalous insects with discrete life stages effects of stress experienced early in life are carried over to later stages, substantially reducing subsequent fitness. We argue that such effects need to be considered when trying to forecast species responses to climate change.

Idiosyncratic development of sensory structures in brains of diapausing butterfly pupae: implications for information processing

Diapause is an important escape mechanism from seasonal stress in many insects. A certain minimum amount of time in diapause is generally needed in order for it to terminate. The mechanisms of time-keeping in diapause are poorly understood, but it can be hypothesized that a well-developed neural system is required. However, because neural tissue is metabolically costly to maintain, there might exist conflicting selective pressures on overall brain development during diapause, on the one hand to save energy and on the other hand to provide reliable information processing during diapause. We performed the first ever investigation of neural development during diapause and non-diapause (direct) development in pupae of the butterfly Pieris napi from a population whose diapause duration is known. The brain grew in size similarly in pupae of both pathways up to 3 days after pupation, when development in the diapause brain was arrested. While development in the brain of direct pupae continued steadily after this point, no further development occurred during diapause until temperatures increased far after diapause termination. Interestingly, sensory structures related to vision were remarkably well developed in pupae from both pathways, in contrast with neuropils related to olfaction, which only developed in direct pupae. The results suggest that a well-developed visual system might be important for normal diapause development.

Comparative morphology of the prothoracic leg in heliconian butterflies: Tracing size allometry, podite fusions and losses in ontogeny and phylogeny

Prothoracic legs of heliconian butterflies (Nymphalidae, Heliconiinae, Heliconiini) are reduced in size compared to mesothoracic and metathoracic legs. They have no apparent function in males, but are used by females for drumming on host plants, a behavior related to oviposition site selection. Here, taking into account all recognized lineages of heliconian butterflies, we described their tarsi using optical and scanning electron microscopy and searched for podite fusions and losses, and analyzed allometry at the static, ontogenetic and phylogenetic levels. Female tarsi were similar, club-shaped, showing from four to five tarsomeres, each bearing sensilla chaetica and trichodea. Male tarsi were cylindrical, formed from five (early diverging lineages) to one (descendant lineages) either partially or totally fused tarsomeres, all deprived of sensilla. Pretarsi were reduced in both sexes, in some species being either vestigial or absent. Tarsal lengths were smaller for males in almost all species. An abrupt decrease in size was detected for the prothoracic legs during molting to the last larval instar at both histological and morphometric levels. In both sexes, most allometric coefficients found at the population level for the prothoracic legs were negative compared to the mesothoracic leg and also to wings. Prothoracic tarsi decreased proportionally in size over evolutionary time; the largest and smallest values being found for nodes of the oldest and youngest lineages, respectively. Our results demonstrate that evolution of the prothoracic leg in heliconian butterflies has been based on losses and fusions of podites, in association with negative size allometry at static, ontogenetic and phylogenetic levels. These processes have been more pronounced in males. Our study provided further support to the hypothesis that evolution of these leg structures is driven by females, by changing their use from walking to drumming during oviposition site selection. In males the leg would have been selected against due to absence of function and thus progressively reduced in size, in association with podites fusions and lost.

Livestock Grazing Shapes the Vegetation Structure and Subsequent Habitat Use by the Endangered Skipper Pyrgus ruralis lagunae (Lepidoptera: Hesperiidae)

Many species adapted to alpine and montane meadow ecosystems are at risk of extinction. The skipper Pyrgus ruralis lagunae Scott is a mountaintop butterfly restricted to San Diego County, CA, a federally listed endangered species, and is in imminent risk of extinction. Historically, P. r. lagunae was found in the Laguna and Palomar mountains. We did not detect the skipper in the Laguna Mountains, and the species has likely been extirpated from this area, which represents half of its historical range and is the type locality. We studied three populations on Palomar Mountain. Skippers primarily occupied areas close to creeks or in adjacent ravines at two nongrazed sites. The third site is grazed by cattle, and skippers were found close to the forest edge. At nongrazed locations, creek areas had higher cover of intermediate-height vegetation, more bare ground, and more flowers compared with unoccupied areas of the same meadow. The vegetation at occupied and unoccupied areas within the grazed meadow were similar. Even so, skippers occupied areas with more bare ground as well as greater species richness of flowering plants. A grazing exclosure was previously installed in an attempt to protect and enhance skipper habitat, but skippers did not use the dense grasslands that developed inside the exclosures. Contrary to the prevailing theory, protection from grazing did not improve skipper habitat. This illustrates how management based on inadequate biological information can hinder well-intentioned conservation efforts.

Chemosensory basis of larval performance of Papilio hospiton on different host plants

Papilio hospiton Géné is an oligophagous species, endemic of the islands of Corsica and Sardinia, using various Apiaceae and Rutaceae as host plants, such as Ferula communis, Ferula arrigonii, Peucedanum paniculatum, Ruta lamarmorae and Pastinaca latifolia. We previously found that the lateral maxillary styloconic sensillum in the larva has two deterrent neurons, one phagostimulant and one salt specific, while the medial sensillum has two phagostimulant neurons, one deterrent and one salt specific. In this work we studied the sensitivity of gustatory receptor neurons (GRNs) to saps of F. communis, F. arrigonii, P. paniculatum, P. latifolia and R. lamarmorae and evaluated the relationship between taste sensitivity to different host-plants and larval growth rate on each of them. The spike activity was recorded from medial and lateral taste sensilla stimulated with plant saps, and GRN response patterns were cross compared in the light of a different feeding acceptance. The phagodeterrent GRNs show a higher activity in response to F. arrigonii and R. lamarmorae than to F. communis, P. paniculatum and P. latifolia. Behavioral trials showed that the time to pupation is significantly longer when larvae are reared on F. arrigonii and R. lamarmorae than on the other host-plants. These results suggest that the different activity of the phagodeterrent GRNs may inhibit food acceptance and extend the duration of the larval stage.

Conserved patterns of integrated developmental plasticity in a group of polyphenic tropical butterflies

BACKGROUND

Developmental plasticity is thought to have profound macro-evolutionary effects, for example, by increasing the probability of establishment in new environments and subsequent divergence into independently evolving lineages. In contrast to plasticity optimized for individual traits, phenotypic integration, which enables a concerted response of plastic traits to environmental variability, may affect the rate of local adaptation by constraining independent responses of traits to selection. Using a comparative framework, this study explores the evolution of reaction norms for a variety of life history and morphological traits across five related species of mycalesine butterflies from the Old World tropics.

RESULTS

Our data indicate that an integrated response of a suite of key traits is shared amongst these species. Interestingly, the traits that make up the functional suite are all known to be regulated by ecdysteroid signalling in Bicyclus anynana, one of the species included in this study, suggesting the same underlying hormonal regulator may be conserved within this group of polyphenic butterflies. We also detect developmental thresholds for the expression of alternative morphs.

CONCLUSIONS

The phenotypic plasticity of a broad suite of morphological and life history traits is integrated and shared among species from three geographically independent lineages of mycalesine butterflies, despite considerable periods of independent evolution and exposure to disparate environments. At the same time, we have detected examples of evolutionary change where independent traits show different patterns of reaction norms. We argue that the expression of more robust phenotypes may occur by shifting developmental thresholds beyond the boundaries of the typical environmental variation.