Entomological Science最新文献

Water striders (Hemiptera: Gerridae) are sucking predators that inhabit freshwater and marine environments. They prey mainly on insects that fall on the water surface, but they are also known to feed on amphibian eggs. Here, we report on the predation of egg sacs of Hynobius nigrescens (Caudata: Hynobiidae) by Gerris (Macrogerris) insularis. We observed predation on egg sacs of H. nigrescens by G. insularis at a pond in a mountainous area of Nagano City, Nagano Prefecture, Japan. We also found egg sacs with predation marks probably made by water striders at a pond in the mountainous area of Nishimeya Village, Aomori Prefecture, Japan. Five water striders collected around the preyed egg sacs were identified as G. insularis. We filled three tanks with water and an egg sac, and three water striders that were collected at the site in Nishimeya Village were placed together in each tank. In two tanks, the jelly layer of the egg sac was partially cut in a horizontal manner, while in another tank, the jelly layer was removed on the part of the egg sac exposed on the water surface. Notably, the water striders exhibited predatory behavior only when the jelly layers were removed. Considering the results of the rearing experiment and the predation marks observed in the field, G. insularis is also likely to prey on egg sacs at the site in Nishimeya Village. Our study suggested that predation by G. insularis occurs when eggs are accidentally exposed due to disturbance of the jelly layer.

It is widely recognized that heterogeneous environments promote biodiversity. Consequently, we investigated whether heterogeneous environments influence the diversity of ground-dwelling beetles within a well-managed conifer plantation forest. We collected carabid beetles, and necrophagous silphid and dung beetles (necrophagous beetles) using pitfall traps at 37 sites with or without fish meat bait. The result of a two-dimensional principal component analysis (PCA) utilizing environmental indices measured at each site suggested that the environmental heterogeneity depended on the survival density of planted conifers, serving as an indicator of historical gap formation levels. Gaps populated by invading broadleaved trees exhibited low canopy opening percentages and understory cover degrees, while those filled by the growth of planted conifers displayed the opposite conditions. The presence of bait had a negligible impact on carabid beetles but significantly influenced necrophagous beetles. No significant relationships were found between the scores of PCA components and the beetle species richness, suggesting that a heterogeneous environment does not increase the beetle species diversities. However, significant relationships were observed with the scores on nonmetric multidimensional scaling axes, indicating that a heterogeneous environment contributes to the complexity of beetle assemblages. The most dominant carabid, Synuchus cycloderus, was abundant in areas where historical gap formation was thought to be more prevalent. Among necrophagous beetles, Pherotrupes laevistriatus and Panelus parvulus preferred habitats with darker environments, in contrast to Onthophagus fodiens and O. nitidus. This study will aid in developing forestry practices aimed at conserving specific ground-dwelling beetle species within conifer plantations.

There are approximately 850 species of Ficus (Moraceae). However, few species of gall midges (Diptera: Cecidomyiidae) inhabiting syconia and leaves of fig trees are known. In field surveys, gall midges were found in syconia of Ficus caulocarpa and Ficus subpisocarpa. Here, we examined adults, pupae and larvae of the gall midge species, describe the morphology, and provide information on distribution, behavior and genetic data. A new genus, Ficidiplosis Yukawa and Arimoto, gen. nov., is established in the supertribe Cecidomyiidi for two new species, Ficidiplosis subpisocarpae Yukawa and Arimoto, sp. nov. and Ficidiplosis caulocarpae Yukawa and Arimoto, sp. nov., which emerged from syconia of Ficus subpisocarpa and Ficus caulocarpa, respectively, in Japan and Taiwan. The larvae of Ficidiplosis species feed on the parenchyma of the fig wall and pupate there without making galls. The mitochondrial cytochrome c oxidase subunit I (COI)-based neighbor-joining tree using samples from Japan and Taiwan supported the existence of two separate species.

Mushrooms produce a great variety of defense chemical compounds to protect themselves from fungivores. Alpha-amanitin is one of such compounds found in some Amanita mushrooms. The present study focuses on the effect of α-amanitin on adult survival in 17 drosophilid species including mycophagous ones from the subgenus Drosophila and the genus Hirtodrosophila and nonmycophagous ones of the subgenera Drosophila, Siphlodora and Sophophora. The results showed that all the essential fungivores and some partially mycophagous species from different lineages are tolerant to this lethal toxin at a concentration of 50 μg/mL, suggesting that the α-amanitin tolerance may have been acquired more or less independently of the evolution of mycophagy in the family Drosophilidae.

Drosophila subobscura is an excellent model species for testing genetic variation in thermal adaptation due to its rich inversion chromosomal polymorphism. In Palearctic populations, the inversions of this species can be classified as “cold”, “warm” or “nonthermal” adapted. Based on this classification the Chromosomal Thermal Index (CTI) was developed, which allows measuring the thermal adaptation of populations and monitoring changes over time. Here, we aim to use this index in American colonizing populations of D. subobscura for the first time to obtain new information on the species thermal adaptation. Thus, thermal adapted inversions (“cold” and “warm”) were defined for the American continent and CTI was computed in South American (1981 and 1999 samples) and North American (1985 and 2004 samples) populations of D. subobscura. In general, both American populations showed an inverse relationship between CTI values and latitude, with CTI values decreasing when latitude increases. When comparing populations sampled in different years, an increase in CTI values was detected in four out of six temporal comparisons (only one was significant) of South America (1981 and 1999) and in six out of seven populations of North America (1985 and 2004). A global analysis using a one-way repeated measures anova of CTI values in both American hemispheres showed a trend of increase for “warm” adapted inversions in Chile and North America, but this increase was only significant for the latter. Overall, these results are in agreement with global warming expectations, although natural selection acted differently in the colonized hemispheres.

Insect community structures and biological interactions vary with the distance from the mainland to islands. Gall inducers are key organisms in local arthropod communities because their galls harbor diverse arthropods. We investigated the parasitoid community of a gall-inducing cecidomyiid Schizomyia sasakii on the Izu Peninsula and the Izu Islands, Japan. We examined relationships between parasitism by Inostemma sp. and Torymus hirtipennis, and gall characteristics, and analyzed the directional selection on gall characteristics induced by S. sasakii in each locality. The species richness of parasitoids on the Izu Islands decreased with the distance from the Izu Peninsula to each island, and area of respective islands. Inostemma sp. preferably attacked large galls on Ohshima Island, and T. hirtipennis tended to attack relatively small galls in the Izu Peninsula. Directional selection on gall characteristics of S. sasakii favored the induction of larger galls and thicker tissues by S. sasakii on Ohshima Island. In contrast, no directional selection was detected in the gall characteristics on Hachijojima Island. The number of alternative host species of parasitoid may affect variation in parasitoid richness of S. sasakii on distant and small islands, because the species richness of gall midges is necessary to maintain local parasitoid populations. Our study supported the ovipositor limitation hypothesis for the torymid species, related to gall size. The directional selection of parasitoid attacks on the Izu Islands may act to favor the induction of large and hypertrophic galls by S. sasakii to avoid the parasitoids.

One of the characteristics of the adult eclosion rhythm in Drosophila melanogaster is that adult emergence time differs greatly between the first and second eclosion days. The emergence time is in the middle of the light period on the first eclosion day, but immediately after light-on on the second day. We hypothesized that incomplete entrainment of the endogenous pacemaker to the light–dark (LD) cycle is responsible for the daily variation. Due to the very short pupal period of this species, adult emergence may occur before complete synchronization of the pacemaker with the external cycle on the first eclosion day. Therefore, the peak time on the first eclosion day may differ significantly from that on the second day. To verify this hypothesis, using pupae that had pupariated within 24 h, the time difference between the first and second peaks was compared in LD 12:12 or constant darkness at five different temperatures from 30 to 15°C. In both light regimes, the time difference decreased with decreasing temperature and extended pupal duration. The interval between the eclosion peaks approached 24 h, supporting this hypothesis. These results can be interpreted by using a two-oscillator model.

Estimating parasitism rates in the field is essential for developing and evaluating biocontrol strategies using parasitoids. In this study, we developed a simple polymerase chain reaction (PCR)-based method for detecting parasitism of the cassava mealybug Phenacoccus manihoti Matile-Ferrero (Hemiptera: Pseudococcidae) by the primary parasitoid Anagyrus lopezi De Santis (Hymenoptera: Encyrtidae) and its hyperparasitoid Prochiloneurus pulchellus Silvestri (Hymenoptera: Encyrtidae). Primers were designed to amplify partial cytochrome c oxidase subunit I genes of each species, and their sensitivity was evaluated with mealybugs that had been parasitized by A. lopezi 0, 3, and 6 days earlier, and mummified mealybugs containing A. lopezi pupae that had been parasitized by P. pulchellus 0, 3, 6, 9, and 12 days earlier. The detection rate of parasitism by A. lopezi was 100% for all ages of A. lopezi. The detection rate of parasitism by P. pulchellus ranged from 94.1% to 100%, depending on its developmental stage. For P. pulchellus, template DNA was diluted 10 times before PCR because PCR with the original concentration showed low detection rates, presumably due to the presence of PCR inhibitors. Overall, our primers can be considered sufficiently sensitive to be used for detecting each species.