Archive for insects

Pea Aphid Genome Annotation Workshop

I’m now at Princeton, attending Pea Aphid Genome Annotation Workshop I.

Actually I am neither a genomicist nor a bioinformatist. However, I’ve been engaged in aphid studies for many years using some molecular techniques, so that I am a bit interested in a genomics.

I am not good at dealing large amount of information like genomic informations, but I think these genomics studies largely help us to understand the complicated biology of many organisms.

To use genome information in a smart manner, the annotation of genes seems to be important.

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Genome sizes of termites

One of our papers on the genome sizes of termites and related insects (i.e. cockroaches) was recently accepted and the article is now available on line.

Koshikawa S, Miyazaki S, Cornette R, Matsumoto T, Miura T. 2008. Genome size of termites (Insecta, Dictyoptera, Isoptera) and wood roaches (Insecta, Dictyoptera, Cryptocercidae). Naturwissenschaften: in press. [doi: 10.1007/s00114-008-0395-7]

ABSTRACT – The evolution of genome size has been discussed in relation to the evolution of various biological traits. In the present study, the genome sizes of 22 dictyopteran species were estimated by Feulgen image analysis densitometry and 6-diamidino-2-phenylindole (DAPI)-based flow cytometry. The haploid genome sizes (C-values) of termites (Isoptera) ranged from 0.58 to 1.90 pg, and those of Cryptocercus wood roaches (Cryptocercidae) were 1.16 to 1.32 pg. Compared to known values of other cockroaches (Blattaria) and mantids (Mantodea), these values are low. A relatively small genome size appears to be a (syn)apomorphy of Isoptera + Cryptocercus, together with their sociality. In some phylogenetic groups, genome size evolution is thought to be influenced by selective pressure on a particular trait, such as cell size or rate of development. The present results raise the possibility that genome size is influenced by selective pressures on traits associated with the evolution of sociality.

Parasitoid wasp

Last week, one of my colleague sent me this photo.

His son collected a lepidopteran worm to observe. Some days after that, the worm died with lots of weird stuffs.

I’m sure this is because of parasitoid wasp, which probably belongs to the family Braconidae. These parasitic wasps are really fascinating! The host insect species are diverse and the parasites adapt the life history and physiology of host species. 

I am not familiar with the parasitic wasps but the some wasps show phenotypic plasticity depending on host insect species. This sounds very interesting to me, so I will talk about this some time.

Papua golden stag beetle

Papua golden stag beetle

One of my lab members is so-called “stag-beetle freak”. He is keeping various species of stag beetles, among which a species is conspicuous because of its color. It is the Papua golden stag beetle. Here, three female individuals which have fantastic colors are shown. We do not know little about the proximate and ultimate mechanism of the color, but we really are addicted to them. (Photo by RC)

Madagascar hissing cockroach

Hissing Cockroach

Recently, one of my colleagues Dr. KM gave me this fascinating cockroach. I’ve got two pairs of adult roaches and several juveniles (nymphs). This belongs to the Madagascar hissing cockroach Gromphadrina portentosa.

Unfortunately, one of the two adult females escaped from the container, and probably hide somewhere in my room…

Mayfly imaginal molt

mayfly
At night, at the window of my lab, a subimago of mayfly came and preceeded the imaginal molt to become imago. The left insect is the cast-off exoskeleton of subimago. the adult mayfly possess very large compound eyes.

In comparison with the other hemimetabolous insects, the subimago stage is unusual and mysterious stage, because wings are normaly formed in adult stage in most of hemi- and holometabolous insects.

Dynastid Beetle

Now it is the season for the pupation of the Japanese dynastid beetles Allomyrina dichotoma. Most of the larvae in our lab has pupated, and some of them have already eclosed to become adult beetles, although all of the adults were female.
dynastid beetles

I am very much interested in this insect, because the male horn is a polyphenic trait, that shows dimorphism among males in addition to the sexual dimorphism. Even in the female pupae, there is a horn-like structures in head and thorax although there are no horns in adults. I guess there may be some disc-like structure in the larval epithelium in both sexes.

Caste determination in Diacamma

Diacamma sp.

Most of ant species possess several types of female individuals even in a single colony, namely reproductive individual (queen) and one or more types of helpers (workers). But some ant species exhibit only one type of female individuals, among which reproductives and helpers are determined behaviorally.

The above picture is Diacamma sp. that belongs to the subfamily Ponerinae. This species produces only a single type of female adults, that are wingless. Instead of wings, they possess vestigial wings called “gemmae”. They perform very peculiar behavior when a new adult emerges from cocoon.

If a new female individual is mutilated with her gemmae by other colony members (workers), she becomes workers. While, if a new female is not mutilated, she becomes reproductive, called “gamergate”. Thus, this vestigial wings function as “caste-determination switch”. This type of behaviorally-determined caste system provides us a key system for understanding behavioral basis of sociality seen in various social insects.

Juvenile hormone

juvenile hormone III

Juvenile hormone (JH), one of the important insect hormones, plays various important roles in the physiological regulations in insects. In our study on insect polyphenism, for example, JH triggers various morphological changes such as phase polyphenism in locusts and aphids, caste differentiation in social insects etc. Many of the insects use juvenile hormone III (JHIII), which is the simplest form of JH. JHI and JHII are also known, but only in Lepidopteran insects.

However, the mechanisms of reception of this hormone remains to be unsolved. No one knows the receptor for JH. Many works suggested that the threshold for JH must be the important regulatory mechanism of polyphenic traits.

Interestingly, various types of analogues for this molecule (JHA) can mimic the function. For example, in termites, we can induce soldier differentiation by the artificial applicaiton of JHA. We often use this method to investigate the developmental mechanism of soldier differentiation.

Arboreal termite nest

Nest of Nasutitermes takasagoensis

Many termite species construct well-designed nests. Especially, higher termites that belong to the family Termitidae, make various types of nests such as large mound nests or arboreal carton nests. There are only one species of termite that construct arboreal nests, i.e. Nasutitermes takasagoensis. This species belongs to the subfamily Nasutitermitinae, same as Hospitalitermes.

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