Entomological Science最新文献

Oviposition preference for spherical substrates has been reported in some insects but not in Drosophila species until the recent finding that Drosophila suzukii preferentially lays eggs on spherical surfaces with a smaller radius, whereas D. melanogaster does not. This finding raised two questions: (i) Was this trait specifically acquired in D. suzukii or lost in D. melanogaster? (ii) In the latter case, is it due to the long-term laboratory culture using oviposition substrates with flat surfaces? To answer these questions, we examined the oviposition preference of three Drosophila species using the stocks recently established from wild individuals. As with D. suzukii, D. simulans and D. takahashii showed significant preference for spherical surfaces with a smaller radius, suggesting that this trait is shared by multiple Drosophila species. In contrast, D. melanogaster did not show any preference for either smaller or larger radii, showing that the preference already has been lost in the natural population of D. melanogaster. It may be possible that the loss of oviposition preference for spherical surfaces is involved in the evolutionary process of D. melanogaster becoming a human commensal.

Adelges (Cholodkovskya) viridanus (Cholodkovsky 1896) (Hemiptera: Adelgidae) is found throughout Eurasia where it is understood to be anholocyclic, feeding on species of larch (Larix), without host alternation. For the first time, we report this species in North America, outside of its native range, from specimens collected in an arboretum in Ohio, USA. Molecular phylogenetic analysis was inconclusive as to whether it was introduced from Europe or Asia. In addition, specimens collected from Picea jezoensis in Japan were confirmed for the first time as A. (C.) viridanus by matching DNA sequences to specimens collected on Larix. Therefore, A. (C.) viridanus is either capable of completing a host-alternating holocycle in Japan, or includes very recently diverged anholocyclic populations on Picea. Finally, we describe the adult fundatrix form, which was previously unknown.

In ants, workers of different sizes may perform various tasks, even in so-called monomorphic species with relatively low body size variation. However, it is unclear if the body size diversity of monomorphic workers correlates with task efficiency, especially in stressful contingencies. Here we tested if the body size variation of workers corresponds with its efficiency in transferring pupae. Transferring brood is a pre-set behavioral response to stress, e.g. suboptimal temperature. Here we applied a laboratory experiment simulating nest damage. The study was performed on the common garden ant (Lasius niger (Linnaeus, 1758)) – a species with no distinct worker subcastes. The efficiency of workers was measured as the latency of transferring pupae from a lit part of the experimental colony to a darkened part, while the body size diversity was expressed as the within-colony coefficient of variation in head width. We did not find any significant correlation between efficiency and body size variation. Summarizing the existing studies and the present results, we propose the hypothesis that the body size diversity of L. niger may have implications for workers’ division of labor but not for their task efficiency in a stressful contingency.

Insects usually have cryptic colors to avoid detection by visually hunting predators. However, if the insects acquire toxic or repellent substances against predators, some of them develop conspicuous coloration to exhibit their unpalatability. Such warning colors allow insects to survive. In the nine-spotted diurnal moths (Erebidae: Arctiinae: Syntomini), we found the above-ground pupating species to have conspicuous colored pupae, but the ground-surface pupating species to have cryptic colored pupae. In this study, the relationships between unpalatability and coloration of these pupae are examined among three species of Amata and one species of Syntomoides. Pupae of the two species (A. germana and A. flava) are conspicuous in their color pattern with seven black dotted lines longitudinally on their pale-yellow bodies. These pupae are exposed to the aerial predators in a coarse silk mesh hanging from leaves and/or branches. The other two species (A. fortunei and S. imaon) pupate in spaces under stones, fallen twigs and leaves on the ground surface, and the pupae in a coarse silk cocoon is cryptic dark brown. Their pupation site selections are reproduced in the rearing glass vessels. Palatability assessment using lizards as a potential predator suggests that pupae of A. germana, A. flava and A. fortunei are unpalatable and the lizard's feeding response decreases with experience. However, pupae of S. imaon are all eaten (palatable). Finally, the possible evolutionary scenario of pupal colors of these four species is discussed in relation to pupation site selection and palatability.

Giant water bugs (Hemiptera: Belostomatidae) are key predators in freshwater ecosystems and have been reported to feed on several species of vertebrates, including fishes, amphibians and reptiles. Here, we report the opportunistic predation of an adult female vesper bat (Afronycteris nana) by a giant water bug (Lethocerus cordofanus) in a temporary pond in a rice paddy in Guinea-Bissau, West Africa. To our best knowledge, this is the first instance of natural predation upon a mammal by a giant water bug to be documented in a scientific report.

Mimicry with warning colors includes Batesian and Müllerian mimicries. If we divide mimicry by sex, there are theoretically four types of mimicry: unimodal, female-limited, male-limited and dual mimicry. The latter three cases cause sexual dimorphism in body color and marking pattern but are rarely reported. In this study, we show that the tussock moth Numenes albofascia is possibly a dual mimic. The wing color and marking pattern of male and female N. albofascia are completely different, with the male's pattern resembling that of the smoky moth Pidorus atratus, while the female pattern resembles that of the tiger moth Arctia caja. Body size also differs greatly between the sexes of N. albofascia, matching the mimicry model species of each sex. These moths are distributed sympatrically in Japan, and their adult seasons overlap with each other. According to lizard feeding experiments, N. albofascia is palatable, while both male and female model species are unpalatable. Actograms in the laboratory and the light trapping in the field suggest that females of N. albofascia fly actively from sunset to midnight, while males fly during the twilight period around dawn. Therefore, male and female N. albofascia might be Batesian mimics of diurnally active P. atratus and nocturnally active A. caja, respectively, and the great sexual dimorphism of this moth could be caused by dual mimicry.

Cymbella janischii, an invasive species of diatom, has been broadening its geographical range in Japan since 2004, flourishing in substantial colonies in river beds. As thick and mucilaginous colonies of this diatom often cover large areas of river beds, this elicits concerns regarding the potential alteration of sedimentary bottom structures and resultant effects on the native ecosystems. The presence of the diatoms growing on the body surface of two aquatic beetles, Grouvellinus nitidus (Elmidae) and Ectopria opaca (Psephenidae) in a Japanese river was confirmed. This constitutes the inaugural documentation of invasive diatoms having a specific relationship with native aquatic insects at an individual level.

Females of many acanthosomatid shield bugs attend eggs and young nymphs by covering them with their bodies. Although such form of maternal care has been suggested to have evolved independently in four genera, Elasmucha, Sastragala, Acanthosoma and Sinopla, previous studies exploring its adaptive function have solely focused on species of Elasmucha. This study pioneered an experimental examination of maternal care in the Japanese species Sastragala esakii. Field experiments demonstrated that unattended egg masses suffered intense predation, whereas egg masses attended by their mothers were rarely preyed upon. The ant Crematogaster sp. was the most common egg predator, while two other insect species were also observed to prey on eggs. The exclusion of ant workers and other walking predators from accessing egg masses through the utilization of a sticky trap resulted in a remarkably improved egg survival rate in orphaned egg masses, suggesting that, at least in our study site, maternal care of S. esakii primarily functions to protect eggs from walking predators. Laboratory observations revealed that egg protection against predators was achieved through at least two distinctive defensive behaviors shown by egg-tending females: (i) tilting their bodies when approached by predators; and (ii) fanning their wings when in contact with predators. However, females displayed a limited response to predators approaching from the posterior direction, suggesting that visual cues play a significant role in predator recognition. These results indicate a similarity in the maternal care functions between Elasmucha and Sastragala, and suggest the parallel evolution of female defensive behaviors.

Holometabolous insects dramatically change their morphology via molt, both from larva to pupa and from pupa to adult. In nonmodel insects, RNA interference (RNAi) is a strong tool for analyzing gene function during postembryonic development. In many cases, larval RNAi is effective for analyzing genes involved in morphogenesis via metamorphosis. However, RNAi of genes involved in development sometimes results in lethality before animals metamorphose to pupae and/or adults, making it impossible to analyze their function during the pupal period. In this study, we establish a pupal RNAi system in the stag beetle Dorcus rectus. We selected the genes white and scarlet for RNAi knockdown to investigate appropriate injection timing and position. Both genes are known to be involved in eye pigmentation. By using these candidate genes, we demonstrate the potential of pupal RNAi in this experimental system. This method will be useful for analyzing pupal-specific morphogenesis including fine-shaping of the enlarged male mandible in this species.

Our knowledge on how the local distribution pattern of ordinary and novel hosts promotes or hinders the progress of adaptation to the novel hosts by phytophagous insects is limited. The herbivorous ladybird beetle Henosepilachna vigintioctopunctata (Coleoptera: Coccinellidae) depends mainly on solanaceous plants as hosts; the major wild host of this beetle species in Java, Indonesia, is Solanum torvum. However, in several regions of Southeast Asia, including Java, H. vigintioctopunctata also occurs on the introduced fabaceous weed, Centrosema molle. Circumstantial evidence indicates that the use of C. molle by beetles became frequent in the very early 2000s in East Java. In the present study, based on laboratory and field data obtained from 2003 to 2005, we evaluated the degree of adaptation to C. molle by H. vigintioctopunctata populations from East Java and documented the geographic pattern of host-plant distribution in East Java. Laboratory experiments revealed that the beetles from East Java possessed the highest degree of adaptation to C. molle among the beetle populations thus far investigated, suggesting that the adaptation to C. molle by beetles proceeded quite rapidly in East Java in the early 2000s. Meanwhile, field surveys showed that the habitats in East Java consisted of mosaics with sites where only C. molle was distributed and sites where C. molle and solanaceous plants co-occurred. We discussed the role of such geographical structure of habitats in promoting the rapid adaptation of H. vigintioctopunctata to C. molle in East Java.