Abstract Synchronous hatching is widespread in insects and may confer adaptive advantages such as predator avoidance and aggregation of hatchlings. In Locusta migratoria , two mechanisms have been proposed to underlie hatching synchrony within egg pods: maternal phase effects and embryo–embryo interactions. This study examined whether maternal phase influences within‐pod hatching synchrony when embryo–embryo communication is experimentally manipulated. Eggs from solitarious and gregarious females were maintained either in contact (clumped) or individually separated and incubated at 30°C under continuous illumination. Mean hatching time, within‐batch variance in hatching time, and the duration from 10 to 90% hatching were analyzed. Gregarious eggs laid by crowd‐reared adults were slightly larger and hatched earlier on average than solitarious eggs laid by isolation‐reared adults under both egg conditions, confirming a phase‐dependent difference in embryonic developmental rate. In contrast, hatching synchrony was strongly influenced by egg condition: Most clumped eggs hatched within a few hours, whereas separated eggs hatched later and over a much broader time span. No significant phase‐dependent differences were detected in either the variance of hatching time or the 10–90% hatching period. These findings indicate that maternal phase primarily influences embryonic developmental rate, whereas physical contact among eggs is essential for the final synchronization of hatching within an egg pod. The results highlight the importance of distinguishing embryonic developmental timing from within‐pod hatching synchrony.
Abstract Sympetrum frequens , a common yet regionally declining dragonfly in Japan, is likely to use forests as seasonal habitats during the adult stage. After emerging from lowland wetlands in early summer, adults move to montane forests to avoid summer heat, and they return to the lowlands for reproduction in autumn, where they roost and forage in nearby forests. However, the spatial patterns of forest habitats remain unclear, probably because detecting individuals within forests is difficult. In contrast, after leaving forests, they become observable in foothills in late summer and in lowland paddy fields during autumn, where their distribution may retain the spatial legacies of recent forest use. This study analyzed the relationships between adult abundance observed during these periods and the surrounding forest landscapes across multiple spatial scales and elevation bands in central Japan to infer the forest habitats they previously occupied. In late summer, a significant positive effect of forest area at elevations of 400–600 m (average summer temperature range: 23.8–25.4°C) within 5 km best explained the number of adults at foothills. In autumn, adult abundance in the lowland paddy fields was best explained by a significant hump‐shaped relationship with forest area within 5 km, peaking at approximately 40% forest cover. These results suggest spatial and climatic structuring of their seasonal forest habitats, which may advance our ecological understanding and inform conservation planning for this species. Furthermore, this study underscores the value of landscape analysis that uses the outside‐forest abundance of multi‐habitat species to identify forest habitats.
Abstract Desiccation resistance is an important physiological trait in insects, but how seasonal cues jointly affect this trait remains poorly understood in gerrid water striders. This study examined how temperature and photoperiod from the nymphal stage through early adulthood influence desiccation resistance in Aquarius paludum amamiensis (Miyamoto). First‐instar nymphs were reared under four combinations of high or low temperature and long‐ or short‐day photoperiod. Desiccation resistance was evaluated 30 days after adult emergence by measuring survival time, water loss at death, water loss rate and initial body water content. Survival time was significantly affected by temperature, photoperiod and their interaction, with the shortest survival under high‐temperature–long‐day conditions. Water loss rate also showed a significant interaction and was higher under high‐temperature–long‐day than high‐temperature–short‐day conditions. Initial body water content was generally lower at high than low temperature. Reproductive activity was strongly affected by temperature: Nearly all females reared at high temperature oviposited, and total egg production was substantially greater than at low temperature. Including wing morph as an explanatory variable did not alter the principal interactions. These results indicate that the effect of photoperiod on desiccation resistance depends strongly on temperature, with long‐day conditions reducing survival primarily at high temperature. Because reproductive activity was affected mainly by temperature, the interaction in desiccation resistance may involve photoperiod‐dependent regulation of water balance beyond reproductive maturation alone.
Abstract Approximately 75% of lycaenid butterfly species in the world associate with ants during their larval stages to gain protection against natural enemies such as parasitoids. Despite intensive studies on lycaenid–ant interactions, parasitoids exploiting myrmecophilous hosts remain poorly understood, thereby limiting our understanding of the eco‐evolutionary dynamics of parasitoid–host interactions. Here, three sibling species of Cotesia Cameron (Hymenoptera: Braconidae) parasitising ant‐associated lycaenid larvae in Japan were identified, and their ecological differentiation within this parasitoid group was investigated. We propose the Cotesia inducta complex, comprising Cotesia inducta (Papp), Co . sp. aff. inducta and Co. suzukii sp. nov. Co. inducta is recorded from Japan (Honshu) for the first time, and Co. suzukii sp. nov. is described and illustrated from Japan (Honshu and Kyushu). Co. suzukii sp. nov. is a specialist parasitoid of Arhopala japonica (Murray) (Theclinae) on Quercus spp., whereas Co. inducta exhibits a broad host range across multiple lycaenid subfamilies (Curetinae, Polyommatinae and Theclinae) in Europe and Japan. Mitochondrial DNA analyses reveal the monophyly of the Co. inducta complex, as well as that of Co. inducta and Co. suzukii sp. nov. Both species are multivoltine; however, Co. inducta exploits different host species seasonally, whereas Co. suzukii sp. nov. consistently utilises Ar. japonica . Moreover, Co. inducta primarily parasitises flower‐feeding hosts, whereas Co. suzukii sp. nov. only uses leaf‐feeding hosts, indicating that host‐feeding habitat contributes to diversification within the Co. inducta complex. These findings provide fundamental ecological information on parasitoids associated with myrmecophilous butterflies.
Genetic disturbance represents a critical threat to species conservation by eroding evolutionary history and compromising population fitness. A geographically isolated population of Luehdorfia japonica (Lepidoptera: Papilionidae) resides on Mt. Ishizare within the Kanto Mountains of Kanagawa Prefecture, Japan. Historical documentation of butterfly releases suggested a risk of genetic disturbance within this population. This study utilized genome-wide single-nucleotide polymorphism (SNP) analysis of 67 individuals using 581 SNPs to quantify the extent of genetic disturbance. While the results showed genetic disturbance had occurred, the proportion of exotic genetic clusters was remarkably low, ranging from 1.6% to 2.4%. Thus, the impact of genetic disturbance at Mt. Ishizare, Kanagawa Prefecture, was found to be slight. These findings indicated that the risk of genetically disturbed individuals migrating to neighboring areas where individuals have become established is also low. Consequently, the conservation value of the Mt. Ishizare population remains substantially intact, warranting continued protection of this unique evolutionary lineage.
In Lepidoptera, extremely long adult proboscises have evolved in several lineages, enabling access to nectar deep within long-tubed flowers. However, such elongation likely incurs biomechanical costs during nectar uptake due to increased fluid resistance. To extract nectar, adult lepidopterans are thought to use a suction pump within the head capsule, which generates negative pressure through the contraction of dilator muscles attached to the pump chamber. The development of these muscles may help compensate for the functional costs associated with proboscis elongation, but the relationship between dilator muscle volume and other morphological traits remains poorly understood. In this study, we examined 35 species of hawkmoths (Sphingidae: Macroglossinae, 19 species; Smerinthinae, 8 species; Sphinginae, 7 species; and Langiinae, 1 species) collected in Japan, encompassing a wide range of proboscis lengths (3.2-75.9 mm). Using X-ray micro-computed tomography (micro-CT), we quantified the volume of the dilator muscles associated with the suction pump. We then investigated how proboscis length and other morphological traits (head width, body length, and forewing length) influence dilator muscle volume using phylogenetic generalized least squares (PGLS) models. Our results showed that the dilator muscle volume increased with both proboscis length and head width even after accounting for phylogeny. These findings suggest that the evolution of long proboscises in hawkmoths has been accompanied by the development of enlarged dilator muscles, likely as a compensatory adaptation to overcome increased resistance during nectar uptake. Moreover, the observed association with head width indicates that cranial dimensions may constrain and/or facilitate the evolution of suction musculature.
Male dimorphism, the presence of two different forms of males within a population, has been observed in several species and is often accompanied by distinct reproductive strategies. Among arachnids, harvestmen are known to frequently exhibit this phenomenon. However, previous research has largely focused on species of the suborder Laniatores from the Neotropical region. In order to address this issue, an investigation was conducted into the male morphology and reproductive behavior of Phalangium opilio (suborder Eupnoi), a species of harvestman that is widely distributed throughout the northern hemisphere and New Zealand. We identified male dimorphism for the first time in P. opilio, specifically in the chelicerae and pedipalpal femurs. Furthermore, we found the presence of mate guarding behavior after mating, a behavior that had not been previously reported in this species. It is noteworthy that this behavior was more prevalent in males with large chelicerae or pedipalpal femurs, but minor males also exhibited guarding behavior when the opponent's traits were smaller. This pattern suggests that the relative size, rather than the absolute size, of these traits may be crucial in determining guarding behavior. Furthermore, we reported the first instances of cannibalism caused by lethal aggression in this species.
Understanding how ecological communities are assembled requires disentangling the relative roles of deterministic and stochastic processes across heterogeneous environments. Tropical freshwater ecosystems remain underrepresented in this context, despite their high biodiversity and vulnerability to anthropogenic pressures. We investigated community assembly mechanisms in predaceous diving beetles (Coleoptera: Dytiscidae) across three ecologically distinct freshwater habitats in Uganda-a papyrus-dominated wetland, a montane stream-pond system, and a human-modified wetland. Using standardized activity trapping, functional trait data (body size), multivariate ordination, generalized linear models (GLMs), and null model co-occurrence analyses, we evaluated patterns of species composition, abundance, and assembly structure. Assemblages showed remarkably similar species richness, diversity indices, and rank-abundance distributions across sites. Detrended Correspondence Analysis revealed moderate compositional turnover (2.3 SD units), indicating partial but not complete species replacement along the primary environmental gradient. A negative binomial GLM indicated that site identity influenced abundance, whereas body size and its interaction with site were not significant predictors, suggesting weakly negative and consistent size-abundance relationships across habitats. Null model analyses rejected competition-driven exclusion and instead supported species aggregation consistent with habitat filtering, facilitation, or shared environmental responses. Together, these results indicate that Ugandan Dytiscidae assemblages are structured by a combination of broad-scale dispersal, habitat filtering, and stochastic processes, resulting in resilient community structures across heterogeneous freshwater environments. Our findings highlight the value of functional traits and null models for understanding tropical freshwater community assembly and inform conservation and biomonitoring strategies in rapidly changing landscapes.
Butterflies locate flowers while flying and find nectar after landing, which is time and energy-intensive. Butterflies rely on visual cues such as flower color, which they can learn through experience to optimize foraging efficiency. While many studies have focused on color in butterfly foraging behavior, flowers also have other potential visual signals that may facilitate localization, such as the petal angle and shadows cast inside the flower by petal inclination. However, these traits have not been widely considered as floral signals utilized by insects. This study investigated whether Papilio xuthus uses petal angle and floral shadows to improve foraging efficiency. First, we conducted choice tests using non-angled flowers and angled small flowers. Adult P. xuthus visited angled small flowers more frequently than non-angled flowers, indicating that when flowers of different shapes are in the same place, na & iuml;ve P. xuthus preferentially visits flowers with angled petals. Second, we compared the success rates of feeding behavior between angled and non-angled flowers. Female adults exhibited higher success rates of foraging behavior on angled flowers than on non-angled flowers, implying that petal inclination facilitated nectar acquisition. Finally, we conducted choice tests between brightly colored flowers and flowers that mimicked the presence of shadows. Both males and females tend to visit shadow-mimicking flowers more frequently than uniformly bright flowers, suggesting that centrally located shadow-like patterns can influence flower choice. This study underscores the criticality of previously overlooked floral traits (petal angles and shadows) in butterfly foraging and provides new insights into butterfly behavioral ecology.
Urbanization imposes a range of abiotic stressors on organisms, with artificial light at night (ALAN) among the most significant. Although numerous studies have shown that ALAN disrupts circadian rhythms and consequently affects a wide range of traits, its impacts on male reproductive capacity and survival, as well as their wavelength dependence, remain largely unknown. To examine how different wavelengths of ALAN affect male reproductive capacity and survival, and whether urban-derived lines have evolved mechanisms to mitigate such effects, we compared genetically distinct isofemale lines derived from multiple urban and rural source populations of Drosophila suzukii to evaluate the impacts of each wavelength of ALAN on emergence time, wing length and sperm head size. Flies were reared under controlled conditions with red, green or blue light exposure at night. Blue light delayed emergence in individuals from both populations, while red light led to an increase in wing length. Sperm head size decreased under blue light in urban flies and under all wavelength treatments in rural flies. Notably, individuals from urban-derived lines showed greater variation in emergence time but tended to show reduced variability in wing length and sperm size, suggesting an adaptive strategy to buffer morphological traits while adjusting developmental timing. These findings reveal that the biological impact of ALAN is not limited to blue wavelengths, as even red light, which is generally assumed to have little or no effect on insects due to their limited sensitivity to long wavelengths, can alter reproduction and development, highlighting the complex ecological consequences of urban light pollution.
We present the first records of Spalangia crassicornis Bou & ccaron;ek, 1963 (Hymenoptera: Spalangiidae) from Japan. This species was observed at three localities in Hokkaido, where it was found in association with nests of Lasius capitatus (Kuznetsov-Ugamsky, 1928) and Lasius fuji Radchenko, 2005 sensu lato (Hymenoptera: Formicidae). Spalangia crassicornis was frequently observed entering and leaving Lasius ant nests and walking among workers without eliciting aggressive responses, and these interactions were documented using both photographic and video records. These observations suggest that S. crassicornis may have evolved traits that allow it to avoid aggression from host ants. Consistent with these observations, analyses of cuticular hydrocarbons indicated that S. crassicornis does not employ chemical mimicry but instead exhibits a markedly reduced cuticular hydrocarbon profile, which may avoid ant aggression. Furthermore, rearing and DNA analyses revealed that Milichia sp. near ludens represents a new host record for S. crassicornis. Ant workers of L. capitatus briefly antennated a larva of Milichia sp. near ludens upon contact but showed no aggressive behavior. Based on this observation, the larva may possess adaptive traits enabling it to avoid attacks by host ants.
Sandy beaches are a globally threatened habitat, and endemic taxa are at risk of extinction. The soil-dwelling fauna of natural sandy beaches in Japan is poorly known. We deployed 60 pitfall traps along ten transects from the high tideline to a coastal pine forest, on a natural sandy beach in Tottori during the summer. Traps caught 5,923 invertebrates belonging to 16 taxonomic groups, dominated by Coleoptera and Orthoptera. Zonation patterns of soil-dwelling invertebrates are described at high (order or class) and low (species of Coleoptera) taxonomic levels using nonmetric multidimensional scaling and nonhierarchical clustering. At the high taxonomic level, invertebrates formed three groups of taxa extending from the tideline to the coastal forest. Tidal habitat was characterized by crustaceans (Amphipoda and Decapoda) and that of the forest edge by common forest soil-dwelling taxa (e.g. Oligochaeta, Diplopoda, Isopoda). Vegetated dunes were characterized by taxa in the insect orders Dermaptera, Orthoptera, Hemiptera and Coleoptera. Two distinct groups of Coleoptera taxa were apparent: at the tideline, and at the dune-forest edge; tideline Coleoptera were characterized by Idisia ornata Pascoe, 1866, Hypocaccus varians varians (Schmidt, 1890), Eopachylopus ripae (Lewis, 1885), Suzukielater babai (Kishi & & Ocirc;hira, 1956), Phaleria atriceps (Lewis, 1894), and dune-forest edge Coleoptera by Phelopatrum scaphoides (Marseul, 1876), Craspedonotus tibialis Schaum, 1863, Paracardiophorus sequens sequens (Cand & egrave;ze, 1873), Meristhus niponensis Lewis, 1894, Scarites sulcatus sulcatus Olivier, 1795. Given the naturalness of the study site, we consider the distributions of taxa in this region to be characteristic of undisturbed sandy beaches in Japan.
Snow scorpionflies (Boreus; Mecoptera: Boreidae) are cold-adapted insects that are active on snow, yet basic ecological and phylogenetic information remains scarce for species from East Asia and the Russian Far East. In the Japanese archipelago, Boreus jezoensis Hori and Morimoto (1996) is the only recorded species of the genus and has been known solely from its type locality, Mt. Hirayama (Hokkaido), with no subsequent confirmed records. We conducted field surveys in montane areas of Hokkaido, including the type locality; 26 adult Boreus individuals were identified from exposed moss patches adjacent to snow. Morphological examinations confirmed that specimens from both mountains are B. jezoensis, representing the second record of the species and providing a new locality record approximately 170 km from the type locality. We also generated the first mitochondrial cytochrome c oxidase subunit I (COI) sequences for B. jezoensis and reconstructed a preliminary COI phylogeny of Boreus. The B. jezoensis samples formed a strongly supported clade with low genetic divergence between the two populations. Together, these findings extend the known distribution of B. jezoensis, provide foundational DNA barcode resources for East Asian Boreus, and offer basic ecological information for this poorly known species.
Invasive species often exert substantial impacts on native ecosystems and may provide native parasites-including potentially even specialist parasites-with opportunities to encounter novel hosts. Here, we show that a native host-specific social parasite can occur within colonies of an invasive ant. We surveyed nests of the Argentine ant Linepithema humile (Hymenoptera: Formicidae) in Osaka, Japan, and collected the ant cricket Myrmecophilus tetramorii (Orthoptera: Myrmecophilidae) and the silverfish Nipponatelurina kurosai (Zygentoma, Ateluridae). Notably, M. tetramorii is a specialist parasite known to exclusively exploit the native ant Tetramorium tsushimae (Hymenoptera: Formicidae), and its occurrence in a L. humile colony represents, to our knowledge, the first documented record of a specialist social parasite occurring in a colony of an invasive ant. Whether these parasites are able to reproduce or establish stable populations within L. humile colonies requires further investigation. However, our study demonstrates that direct ecological contact with a novel host is occurring in the field. This report provides important implications for understanding the initial stage of host-range expansion not only in generalist parasites but also in parasites with strong host specificity under biological invasions.
Giant water bugs (Hemiptera: Belostomatidae) are predatory aquatic insects that mainly prey on other aquatic insects, anurans (juveniles and adults), small fishes, and occasionally reptiles (snakes and turtles), birds, and small mammals (bats). Although species of the belostomatid genus Lethocerus have been reported preying on snakes and turtles in the Nearctic region, there are no reports of lizards and turtles being consumed by nymphs and adults of this genus in the Neotropics. Here, we report the opportunistic predation of a juvenile tropidurid lizard (Tropidurus torquatus) and a hatchling chelid turtle (Phrynops geoffroanus) by a nymph and an adult female giant water bug (Lethocerus delpontei) in a disused swimming pool on a farm in the municipality of Concei & ccedil;& atilde;o do Par & aacute;, Minas Gerais State, Southeast Brazil. To our knowledge, this represents not only the first record of lizard and turtle predation by L. delpontei, but also the first record of T. torquatus and P. geoffroanus as prey items of belostomatids.
We analyzed metaphase chromosomes of 13 herbivorous drosophilid species representing six genera of the tribe Drosophilini, including the first chromosomal description for Styloptera. Chromosome numbers ranged from 2n = 6 in Liodrosophila aerea, the lowest yet reported in Drosophilidae, to 2n = 14 in Scaptomyza hexasticha, the highest known. The so-called "standard karyotype" (2n = 8: 1R, 2V, 1D; X = R), long associated with Drosophila melanogaster, was also observed in five independent herbivorous genera: Dichaetophora, Liodrosophila, Microdrosophila, Scaptomyza, and Styloptera. All species exhibited an XX/XY sex chromosome system, with a telocentric X except in Lo. chaolipinga and Lo. porrecta, where it was metacentric. The number of major chromosome arms was conserved within two genera, 14 in Lordiphosa and 10 in Scaptomyza. These results suggest that, despite interspecific variation in chromosome number, fundamental chromosomal elements have been repeatedly conserved as a common karyotype framework across herbivorous drosophilids, implying the presence of evolutionary constraints acting on karyotype organization within Drosophilini.
Species introduced outside their native range can directly affect native fauna through predation or mating interference, especially when ecologically similar species overlap in distribution. Although Hierodula chinensis Werner, 1929, has recently been reported from western Japan and is suspected to be an introduced species, little is known about its interactions with the native mantis Hierodula patellifera Serville, 1839. We conducted laboratory trials to assess the antagonistic interactions between these species. In intraguild predation trials, both species preyed on each other as nymphs; however, H. chinensis tended to win when larger in size. Reproductive interference was also observed. Males of H. chinensis copulated with H. patellifera females, often resulting in female death. However, no copulation was observed during the reverse pairing. These findings suggest that both intraguild predation and reproductive interference negatively affect H. patellifera, with body size and developmental timing possibly mediating the outcomes. Overall, this study demonstrates the potential asymmetric interactions between closely related mantid species, highlighting the need for further ecological studies in natural environments.
Releasing sexually sterile male insects to reduce mating success of wild females and wild males is known as a control strategy of serious insect pests. In this strategy, sexually sterile males are expected to be able to mate with wild females in the field where wild males are also present. Competitiveness of sterile males is thus critical in this strategy. In this study, we investigated the effects of infection of Mesenetia, bacterial symbionts that induce cytoplasmic incompatibility, on male competitiveness in the coconut hispine beetle Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae). First, we investigated the mating competitiveness of B. longissima males infected with Mesenetia through a process of releasing infected and uninfected males into a plastic cup with uninfected females. Egg hatch rates in different I/U ratios (ratio of infected males to uninfected males)-0.2, 0.5, 1, 2 and 5-were then recorded. Results showed that hatch rates decreased with the increasing I/U ratio. The model assuming equal mating competitiveness fit well to observed hatch rates. We then investigated sperm utilization in females under sequential mating with infected and uninfected males. Results showed that hatch rates drastically decreased after second mating when females mated with uninfected males first and infected males second. These suggest that B. longissima males infected with Mesenetia have comparable mating and sperm competitiveness with that of uninfected males.
Strepsipterans are endoparasitic insects that parasitize hosts belonging to seven insect orders. They develop inside the host body, and adult males emerge to become free-living. To date, male emergence has been observed only in the families Mengenillidae, Xenidae and Elenchidae (Order Strepsiptera), which parasitize silverfishes, hornets and planthoppers, respectively. In these cases, emergence sites on host bodies are exposed. However, in some strepsipterans, males emerge from the arthrodial membrane on the dorsal side of the abdomen, which is covered by the host's wings. Such emergence behavior has not been reported previously. Here, we report how Blissoxenos esakii (Strepsiptera: Corioxenidae) emerges from this covered site. Blissoxenos esakii was collected from nine locations in Tsukuba City, Japan, and reared in the laboratory until male emergence. Ten males successfully emerged from their hosts, and emergence was observed in four cases, including one case in which a host was parasitized by two male B. esakii. In all four cases, hosts raised their wings during male emergence, a behavior not observed in unparasitized hosts, thereby enabling B. esakii to emerge. Further investigation is needed considering the possibility that this behavior constitutes host manipulation and a common action among the hosts parasitized by corioxenids, which emergence site is covered by the host's wings.
Two Anterhynchium species, A. flavomarginatum and A. gibbifrons, are solitary tube-renting eumenine wasps that occur sympatrically in Japan. The latter may be a non-native species that potentially affects native ecosystems through interactions with their parasites. In this study, we observed the parasitic behavior of the miltogrammine fly Amobia distorta, a major parasite of these two species and investigated whether its hosts exhibited defensive behaviors. Among the observed insect parasites, Am. distorta showed the highest parasitism rate on both Anterhynchium species. The parasitic behavior of Am. distorta did not significantly differ between the two host species. Both host species showed similar defensive flight behaviors when the parasite fly approached the host's nest. However, there was no difference in the number of brood cells or intercalary cells per nest between parasitized and unparasitized nests in either species. Differences in the number of brood and empty cells per nest were only observed between host species, suggesting that differences in host nest-building behavior may be involved.
