Entomological Science最新文献

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.

Female fritillary butterflies (Lepidoptera: Nymphalidae: Argynnini) are known to have diversified genital structures, especially at the entrance of the bursa copulatrix. However, the origin and function of such elaborated structures are poorly known to date. We examined the male and female genital structures of six Japanese species selected from five genera/subgenera [Argynnis (Argynnis), Argynnis (Damora), Argynnis (Argyronome), Fabriciana, and Speyeria] of the Argynnini tribe and found that traumatic copulation is widespread in Argynnini. Various male genital structures, such as the uncus, valva, and phallus, can cause wounds to the female genitalia. The eighth venter of the female, where the highest morphological diversity in female genitalia was detected, is hooked and held by the male uncus during copulation. It is very likely that the diversified female genital structure coevolved with the male uncus as a counterpart for traumatic coupling.

As differences in sex pheromones usually act as a barrier against interspecific mating, the fact that the closely related moths Xylena fumosa (Butler) and X. formosa (Butler) (Lepidoptera: Noctuidae: Xyleninae) are commonly attracted to the sex pheromone lure for Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae: Heliothinae) seems unlikely, suggesting that some mechanisms exist between them to mitigate a potential reproductive interference in pheromone communications. Thus, we examined the overlaps in ecological niches of the two species, and their attractiveness to commercial pheromone lures for other moths, through pheromone trap surveys and published reports. Long-term field surveys using traps baited with five to six types of artificial sex pheromone lures including those designed for H. armigera, and information in published works revealed that there was a nonnegligible overlap between the two species in terms of seasonal timing of captures, geographic habitats and host plants. These factors, therefore, did not appear to provide conclusive evidence mitigating reproductive interference. However, there was a slight but significant difference between them in the trends of attraction to different artificial pheromone lures; X. formosa was attracted albeit in a small number to the lures for Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), whereas X. fumosa was only attracted to those for H. armigera. This suggests that differences in pheromone composition, rather than differences in temporal and spatial distributions, between the two species could play a more significant role in premating reproductive isolations.