Midori Tuda

A New Species Megabruchidius sophorae (Coleoptera, Bruchidae), Feeding on Seeds of Styphnolobium (Fabaceae) New to Bruchidae

Abstract A new species Megabruchidius sophorae (Insecta, Coleoptera) is described from Japan (Honshu). The larval host of this bruchid is the seeds of the tree legume ‘enju’, or chinese scholar tree, Styphnolobium japonicum (a senior synonym of Sophora japonica), which is a new host genus to Bruchidae. Styphnolobium is positioned basally in molecular phylogeny of the leguminous subfamily Papilionoideae. Other members of Megabruchidius are known to feed on Gleditsia, the tree legumes that belong to the most ancestral subfamily Caesalpinioideae. Therefore, Megabruchidius utilizes ancestral groups of legumes as its host plants. Megabruchidius has been inferred to be ancestral, based on its behavior. The character state of the host for this third Megabruchidius species supports that the genus is ancestral, at least in the subfamily Bruchinae. We also reviewed the genera closely related to Megabruchidius, i.e., Bruchidius and Sulcobruchus in Bruchidini, and wrote a key to the species in the genus Megabruchidius.

GENETIC ARCHITECTURE OF METABOLIC RATE: ENVIRONMENT SPECIFIC EPISTASIS BETWEEN MITOCHONDRIAL AND NUCLEAR GENES IN AN INSECT

The extent to which mitochondrial DNA (mtDNA) variation is involved in adaptive evolutionary change is currently being reevaluated. In particular, emerging evidence suggests that mtDNA genes coevolve with the nuclear genes with which they interact to form the energy producing enzyme complexes in the mitochondria. This suggests that intergenomic epistasis between mitochondrial and nuclear genes may affect whole‐organism metabolic phenotypes. Here, we use crossed combinations of mitochondrial and nuclear lineages of the seed beetle Callosobruchus maculatus and assay metabolic rate under two different temperature regimes. Metabolic rate was affected by an interaction between the mitochondrial and nuclear lineages and the temperature regime. Sequence data suggests that mitochondrial genetic variation has a role in determining the outcome of this interaction. Our genetic dissection of metabolic rate reveals a high level of complexity, encompassing genetic interactions over two genomes, and genotype × genotype × environment interactions. The evolutionary implications of these results are twofold. First, because metabolic rate is at the root of life histories, our results provide insights into the complexity of life‐history evolution in general, and thermal adaptation in particular. Second, our results suggest a mechanism that could contribute to the maintenance of nonneutral mtDNA polymorphism.

Evolutionary diversification of the bean beetle genus Callosobruchus (Coleoptera : Bruchidae) : traits associated with stored-product pest status

Despite the fact that many plant‐feeding insects are pests, little effort has been made to identify key evolutionary trait transitions that allow taxa to acquire or lose pest status. A large proportion of species in the genus Callosobruchus are economically important pests of stored, dry postharvest beans of the tribe Phaseoleae. However, the evolution of this feeding habit is poorly understood. Here, we present a reconstruction of the phylogeny of the Asian and African Callosobruchus based on three mitochondrial genes, and assess which traits have been associated with the evolutionary origin or loss of ability to reproduce on dry beans. Our phylogenetic analysis showed that species group into the chinensis and the maculatus clades, which are also supported by genital morphology, and an additional paraphyletic group. Ancestral ability to use dry beans has been lost in the chinensis clade but acquired again in C. chinensis. Dry‐bean use and host‐plant use were both phylogenetically constrained and transitions in the two were significantly correlated. Host shifts from the subtribe Phaseolinae to Cajaninae were more common than the reverse and were more likely in species using young beans. The ability to use dry beans was more likely gained when using Phaseolinae hosts and promoted habitat shifts from tropical to temperate regions. Adaptation to arid climate was also associated with the ability to reproduce on dry beans and on Phaseolinae. Thus, our analysis suggests that physiological adaptations to an arid climate and to Phaseolinae hosts both render beetles predisposed to become pests of cultivated beans.

Description of the soybean pod gall midge, Asphondylia yushimai sp. n. (Diptera: Cecidomyiidae), a major pest of soybean and findings of host alternation

The soybean pod gall midge is an important pest of soybean in Japan and is known to occur also in Indonesia and China. This gall midge is described from Japan as Asphondylia yushimai sp. n. and is clearly distinguished from its congeners by the arrangement of the lower frontal horns of the pupa and the sequence of the mtDNA COI region. It is concluded that Prunus zippeliana Miquel is a winter host of the soybean pod gall midge since haplotypes of the soybean pod gall midge coincide with those of the Prunus fruit gall midge that produces fruit galls on P. zippeliana. In addition, phenological and distributional information on the two gall midges and on their host plants supports the identification of the winter host. In Japan, the soybean pod gall midge overwinters as a first instar in the fruit galls on P. zippeliana and emerges as an adult from the galls in May. In summer and autumn, the soybean pod gall midge has two or more generations in the pods of soybean, Glycine max (L.) Merrill or wild fabaceous and caesalpiniaceous plants. Thus host alternation by A. yushimai is confirmed. This is the second finding of host alternation by a species of Asphondylia, the first instance being that of Asphondylia gennadii (Marchal) in Cyprus.

Sexual conflict and the gender load: correlated evolution between population fitness and sexual dimorphism in seed beetles

Although males and females share much of the same genome, selection is often distinct in the two sexes. Sexually antagonistic loci will in theory cause a gender load in populations, because sex-specific selection on a given trait in one sex will compromise the adaptive evolution of the same trait in the other sex. However, it is currently not clear whether such intralocus sexual conflict (ISC) represents a transient evolutionary state, where conflict is rapidly resolved by the evolution of sexual dimorphism (SD), or whether it is a more chronic impediment to adaptation. All else being equal, ISC should manifest itself as correlated evolution between population fitness and SD in traits expressed in both sexes. However, comparative tests of this prediction are problematic and have been unfeasible. Here, we assess the effects of ISC by comparing fitness and SD across distinct laboratory populations of seed beetles that should be well adapted to a shared environment. We show that SD in juvenile development time, a key life-history trait with a history of sexually antagonistic selection in this model system, is positively related to fitness. This effect is due to a correlated evolution between population fitness and development time that is positive in females but negative in males. Loosening the genetic bind between the sexes has evidently allowed the sexes to approach their distinct adaptive peaks.

Evolution of contest competition and its effect on host-parasitoid dynamics.

In experimental populations of the cowpea bean weevil Callosobruchus maculatus (Coleoptera: Bruchidae) and a parasitic wasp Heterospilus prosopidis (Hymenoptera: Braconidae), large changes in the abundances and the fluctuations of both species occurred after approximately 20 generations. In this paper, we examine the hypothesis that this observed change in the dynamics may have been caused by an evolutionary shift in the mode of competition among the bean weevils. A Nicholson-Bailey type model is developed using parameters measured from the experiments. The host larvae can differ in the type of competitive behaviour that they exhibit, which can be either of a contest type or of a scramble type. If a bean contains one or more larvae of the contest type, only one of these will survive and any scramble-type larvae in the bean will be killed. If no contest-type larvae are present within a bean, multiple individuals of the scramble type can emerge from a single bea n. The model assumes many genotypes, differing in the fraction of offspring of the two types. If a high per capita resource availability is maintained, then the scramble type is selected for, but if resources are limited, then the contest type is selected for. The host population at the start of the experiment, taken from a stock culture, was composed mostly of the scramble type. The model is successful in explaining the initial quick increase in the hosts abundance, followed by the evolutionary increase in the fraction of the contest type among hosts, resulting in the more stable population dynamics of the host–parasitoid system, as observed in the experiments. However, it predicts a parasitoid abundance much higher than that observed. We discuss alternative hypotheses to explain the observed evolutionary shift in the population dynamics. We also examine the effect of the difference in size of the beans in the stock culture and those used in the experiments.

Global legume diversity assessment : concepts, key indicators, and strategies

While many plant species are considered threatened under anthropogenic pressure, it remains uncertain how rapidly we are losing plant species diversity. To fill this gap, we propose a Global Legume Diversity Assessment (GLDA) as the first step of a global plant diversity assessment. Here we describe the concept of GLDA and its feasibility by reviewing relevant approaches and data availability. We conclude that Fabaceae is a good proxy for overall angiosperm diversity in many habitats and that much relevant data for GLDA are available. As indicators of states, we propose comparison of species richness with phylogenetic and functional diversity to obtain an integrated picture of diversity. As indicators of trends, species loss rate and extinction risks should be assessed. Specimen records and plot data provide key resources for assessing legume diversity at a global scale, and distribution modeling based on these records provide key methods for assessing states and trends of legume diversity. GLDA has started in Asia, and we call for a truly global legume diversity assessment by wider geographic collabora- tions among various scientists.

A novel host shift and invaded range of a seed predator, Acanthoscelides macrophthalmus (Coleoptera: Chrysomelidae: Bruchinae), of an invasive weed, Leucaena leucocephala

An endophagous seed predator, Acanthoscelides macrophthalmus (Coleoptera: Chrysomelidae: Bruchinae), utilizes Neotropical Leucaena (Fabaceae: Mimosoideae). One of its hosts, Leucaena leucocephala, is a fast‐growing nitrogen‐fixing tree that serves as a multipurpose beneficial plant but eventually becomes an aggressive invader where it was introduced. Herein, we report A. macrophthalmus invasion of the Far East, South Asian tropics and subtropics (Japanese Pacific Islands, Taiwan, Southern China, Northern Thailand and Southern India). Of other field‐collected mimosoid legumes, an introduced tree, Falcataria moluccana, in Taiwan was found to be used by the seed predator. Conversely, our published work review revealed that the seed predator had retained high host specificity to Leucaena species in its native and introduced regions. Acanthoscelides macrophthalmus was able to utilize aphagously postharvest mature seeds for oviposition and larval development, which is a trait of post‐dispersal seed predators. We confirmed that A. macrophthalmus that was reared on L. leucocephala was able to utilize F. moluccana as well. Although the relatively high host specificity of the oligophagous beetle is suitable for controlling the weedy L. leucocephala, the potential host range expansion confirmed by this study must be cautioned.

Habitat-related mtDNA polymorphism in the stored-bean pest Callosobruchus chinensis (Coleoptera: Bruchidae)

The genetic diversity of populations of the azuki bean beetle, Callosobruchus chinensis (Linnaeus) from natural, pre-harvest and post-harvest sites, was investigated to understand population structure and gene flow. A 522-bp fragment of the mitochondrial gene COI was sequenced for eight populations of C. chinensisfrom Japan, Korea and Taiwan collected from different habitats. Six haplotypes were detected, one of which, U1, occurred most frequently and widely. The following hypotheses were tested as a cause of the wide distribution of haplotype U1; (i) topographical separation (by national boundaries), (ii) host plant species, and (iii) habitat type (natural, pre-harvest crop, or post-harvest storage). Categorization of collection sites by country or by host species did not yield differences in the occurrence of haplotype U1, but habitat type did. Populations utilizing cultivated post-harvest hosts that were mass stored were highly likely to be the common haplotype, whereas host plants in natural habitats away from agriculture were utilized by populations with locally characteristic haplotypes. Sampling of commercial beans for quarantine and export purposes indicated that gene flow in C. chinensis was largely unidirectional into Japan at the present time.

Relative importance of weather and density dependence on the dispersal and on-plant activity of the predator Orius minutus

Abstract The present study evaluated the relative effects of abiotic (weather: temperature, wind speed, and rain) and biotic (intra- and intertrophic density dependence: densities of conspecifics, prey per predator individual and leaves on plants) factors on the dispersal and on-plant activity (foraging and oviposition) of the predatory bug, Orius minutus, under seminatural field conditions. Experiments were conducted at plots, each comprising 25 potted azuki bean plants, placed symmetrically in concentric circles, in 1998 and 1999. At the central pot within each plot, 5 marked females of O. minutus (with a male in 1998) were released, and their location and activity were recorded hourly up to 24 h. A total of 78 individuals were released. Stepwise multiple logistic regression was used to select among weather, density dependence, and time variables. Hourly dispersal probability of individuals was positively correlated with temperature and negatively with time since release and with prey density per individual O. minutus. Hourly probability of individuals being active was positively correlated with temperature and negatively with number of leaves of visited plants and conspecific density per leaf. Between-year difference was observed in the probability of individuals being active, which was higher in 1998 than in 1999, probably generated by hunger and higher age. By contrast, diffusion rate was estimated to be lower in 1998, suggesting a trade-off between foraging/oviposition and dispersal by flight. The results indicate that dispersal is affected by temperature and intra-/intertrophic-level density dependence within and between trophic levels, as are foraging/oviposition. The importance of incorporating both abiotic and biotic factors should be stressed when modeling predator–prey metapopulation dynamics on a greenhouse scale.