Entomological Science最新文献

Lithosiini (Lepidoptera: Erebidae: Arctiinae) is distinctive in having some species that feed on lichens, whereas the majority of moths feed on vascular plants. However, the larval diet of most Lithosiini species is poorly known. This study examines whether Lithosiini species, collected in a tropical rainforest of Borneo (nine species) and a temperate forest of Japan (eight species), feed on lichens as larvae, based on stable isotope analyses. As a result, the δ¹⁵N values for eight of nine Lithosiini species collected from Borneo were notably lower than those of nine co-occurring herbivorous non-Lithosiini species, and were similar to those of sympatric, lichen-feeding termites; however, δ¹³C and δ¹⁵N values of one Lithosiini species (Adites sp.) were significantly higher than those of the other moth species and similar to those of humus-feeding termites and predatory insects occurring at the same site. These results have suggested that the Lithosiini in the Southeast Asian tropical rainforests contain some species that feed on lichens as their larval main diet and at least one species whose larvae feed on humus or animal-derived materials. In contrast, the δ¹³C and δ¹⁵N values of all examined Lithosiini species (eight species) in the temperate forest have suggested that their larvae fed on plants and not on lichens. Our stable isotope ratio analysis presented quantitative evidence suggesting lichen-feeding by Lithosiini moths in a tropical rainforest without observation of feeding behavior during the larval stages.

The Japanese species of the genera Norellisoma Hendel, 1910 and Milania Šifner, 2010 of the Scathophagidae are reviewed. Of the three species of Norellisoma, N. ezoensis sp. nov. is described as new to science from Hokkaido, northern Japan. Generic redefinition of Milania and redescriptions of M. agrion (Séguy) and M. longiabdomina (Sun) are presented together with figures of diagnostic characteristics. A key to the Japanese species of Norellisoma and Milania is also provided.

Investigating the well-established relationships between insects and novel host plants will shed light on numerous aspects of evolution and ecology of phytophagous insects. However, in these systems, it is not always clear which plants were originally used as insect hosts, and how the focal insects adapted to the original host(s), before establishing the novel insect–host relationships. Henosepilachna vigintioctomaculata (Motschulsky) (Coleoptera: Coccinellidae) is a well-known pest of the potato Solanum tuberosum (Solanaceae), however its original host in Honshu, the main island of Japan, before the potato introduction is uncertain. A wild solanaceous weed, So. megacarpum, is the most likely candidate for the original host, although the use of this plant by H. vigintioctomaculata has never been recorded in Honshu. This study reports the occurrence of a H. vigintioctomaculata population depending almost solely on So. megacarpum at Yamagata, northern Honshu. Additionally, the host-use ability of this population was compared to that of a pest population under laboratory conditions. Based on the results obtained, it is discussed how the properties of beetles on So. megacarpum facilitated the use of the potato, assuming that So. megacarpum was the original host of H. vigintioctomaculata in Honshu.

The population of the diving beetle Cybister rugosus (Macleay, 1825) has been declining in recent years, and it is designated as “Vulnerable” (VU) in the Red List of Japan. However, there have been no quantitative studies on the feeding habits of the larval stage of this beetle. Revealing the feeding habits is indispensable for understanding the life history of C. rugosus. In the current study, we reared C. rugosus larvae on different prey taxa (Odonata nymph, fish, tadpole, and shrimp) and evaluated their growth and survival rates. Previous studies have shown that three congeneric Cybister species larvae feed mainly on invertebrates. However, all larval instars of C. rugosus were able to feed on invertebrates and vertebrates and grow. Thus, we considered C. rugosus to be a generalist compared to the other Cybister species. The larval periods were shorter for C. rugosus that fed on Odonata nymphs than on any other prey. Feeding different prey taxa had no significant effect on the body length of newly emerged adult males. However, the body length of newly emerged adult females was larger when the larvae fed on Odonata nymphs than when the larvae fed on fish. As in other Cybister species, we concluded that the Odonata nymph is an appropriate food from the viewpoint of increased growth rate in C. rugosus.

Dytiscidae are the largest aquatic group belonging to the order Coleoptera. However, approximately 40% of Dytiscidae members have been threatened with extinction in Japan, and Laccophilus is one of the genera with considerable decline. A description of the life history of these species and their ecological information will contribute to their conservation. In this study, I described the life history of Laccophilus lewisioides Brancucci, 1983 (Coleoptera: Dytiscidae: Laccophilinae) using rearing-based methods under laboratory conditions. I then compared the biology of the larval stages of this species to four Laccophilus species, L. vagelineatus Zimmermann, 1922, L. hebusuensis Watanabe & Kamite, 2020, L. yoshitomii Watanabe & Kamite, 2018, and L. kobensis Sharp, 1873. The developmental period for each immature stage at 26°C was as follows: first instar larva, 4–12 days (n = 16); second instar larva, 5–9 days (n = 15); third instar larva, 5–10 days (n = 15); landing to pupation, 2–3 days (n = 2); pupation to adult emergence, 4 days (n = 1); and landing to escape, 8–9 days (n = 14). The total larval period was significantly longer for L. lewisioides than for the other four Laccophilus species. The duration of larval period could be strongly related to the duration of stable water level in the reproductive habitat. The coloration of the larval stage varied between species groups, suggesting that the larvae adapt to the surrounding environment and show a camouflage effect. This is the first report on the immature stages in the life cycle of L. lewisioides.

Amphiops mater Sharp, 1873, live on the water surface from the egg stage to the pupal stage. Pupae are usually attached to floating objects and normally hatch even when removed from the objects and allowed to float on the water. The pupal period lasts 2–3 days (mean 2.4 days). Interestingly, the pupae are not easily preyed upon by water striders, Gerris latiabdominis Miyamoto, 1958, and their inconspicuous shape and short pupal duration may allow them to escape predation. Most Hydrophilidae species pupate on land, but A. mater can complete its life stages in an aquatic environment.

Diving beetles (Dytiscidae) play an important ecological role in most aquatic water habitats. However, approximately 40% of dytiscids in Japan have been classified as threatened, and further knowledge on their life history is necessary to support conservation efforts. In this study, we collected adult Copelatus zimmermanni (Coleoptera: Dytiscidae) from an ephemeral rain pool and raised a generation under laboratory conditions. We then compared the larval period with two Copelatus species, C. parallelus and C. masculinus. Complete development (egg to adult) occurred in 39–61 days (n = 10) and comprised the following stages: egg (3–6 days, n = 20), first instar (3–8 days, n = 20), second instar (3–12 days, n = 15), third instar larvae (4–13 days, n = 14), and landing to escape (11–36 days, n = 10). The third instar and total larval periods of C. zimmermanni were significantly shorter than those of C. parallelus and C. masculinus. The differences in the duration of larval periods may be related to the permanence of water sources used as reproductive sites for each species. We suggest that the shorter developmental period of C. zimmermanni allows it to complete entire lifecycles even in highly ephemeral aquatic habitats. This is the first report on the immature stages of a species within the C. nigrolineatus species group.

There are two pollination-mutualistic systems between Colocasiomyia flies and Alocasia odora. The two systems are different in the number of fly species involved. One is a two-to-one system, where C. xenalocasiae and C. alocasiae share inflorescences/infructescences of A. odora in the Ryukyu Islands (Japan), Taiwan, Guangdong, and Guangxi (China). The other system, which additionally involves the third species, C. grandis, is seen from southern Yunnan (China) to northern Vietnam. To reveal coexistence mechanisms in these systems, we compared breeding habits of the component species between the two- and three-species systems in natural conditions, and undertook a field experiment to test a hypothesis whether oviposition sites of the component species are affected by interference competition between them. The observations under natural conditions confirmed the breeding niche separation of component species in the two-species system: C. xenalocasiae uses mostly the pistillate region of spadix, whereas C. alocasiae uses mostly the staminate region, with partial overlap of their oviposition sites in the lower intermediate region. In the three-species system, however, these two species separated their oviposition sites nearly completely from each other, suggesting that they are excluded from the lower intermediate region by the third species, C. grandis, which monopolizes there. The result of field experiments did not support this hypothesis: neither C. xenalocasiae nor C. alocasiae changed oviposition behavior regardless of the absence or the presence of C. grandis. Therefore, we propose an alternative hypothesis that the oviposition site segregation among the three species has evolved as a consequence of the past and/or ongoing competition of larvae.

Some insects use multiple defensive methods, although little research exists on the complementary effects of these strategies on their predators. For example, Megacrania tsudai uses crypsis to blend with its background and when threatened it uses a chemical spray. However, the effectiveness of the spraying defense is unclear, although some potential predators were known. This study aimed to reveal the effect of the secondary defenses of M. tsudai. Although the liquid chemical amount changes with growth stages, neither geckos, frogs, spiders nor insects could predate M. tsudai when it grew to a certain size, regardless of the spray effectiveness. Therefore, at the fifth instar or older growth stages of M. tsudai, its predators were limited to birds. Megacrania tsudai that did not spray their liquid chemicals were attacked by predators (other than birds) more than species that sprayed the chemicals. Birds predated all instars regardless of the amount of liquid spray. In conclusion, M. tsudai mainly uses cryptic coloration for predators using visual sense such as diurnal birds, and body size and chemical defenses for other predators, as its defensive measure. The defensive strategy of M. tsudai could relate to its life history.