In Hymenoptera, thanks to its haplodiploid sex determination, arrhenotokous parasitoid females are able to control offspring sex ratio by determining whether to use sperm or not at the time of oviposition. However, the offspring sex ratio may also be influenced by the mating behavior of a male. When a male searches females, he will have more chances to encounter with other males in a high male density population than low male density population. If the male is competitive, the male can find females faster and may have longer copulation time, and eventually transfer more sperm than other males. In this study, we investigated mate searching time, copulation duration and offspring sex ratio as a function of the male density. Although the results show difference between searching time and copulation duration, they are not statistically significant. We will discuss the statistical consequence, male density dependent offspring sex ratio and its evolutionary implications.

In Korea, twelve species in genus Myrmica have been described. Some of them are morphologically similar and this makes their identification difficult. For this reason, we collected several Myrmica species in question and inferred their phylogenetic relationship using the 418bp partial COI (cytochrome C oxidase 1) region from a total of 33 individuals. We found that the CO1 haplotypes are effectively grouped into three clusters that match well to their external morphological characters. Although this three species could be distinguished by the only small part of the COI region, the two individual sample of the M. kotokuii and one sample of the M. carinata are included in the M. kurokii group. The results indicate that the morphological identification could be obscure in the three species and it requires a close examination for this phenomenon.

Wolbachia is one of the most common endosymbionts best known to induce several reproductive alterations in its insect hosts. In some cases, the insect hosts harbor more than two strains of the bacterium. The Vollenhovia emeryi ant lives in dead trees and is morphologically subdivided into the long-winged and the short-winged. Interestingly the short-winged morph is free of Wolbachia, but only the long-winged morph is multiple- infected with the Wolbachia bacterium. We sampled four populations of the long-winged morph in Korea and performed pyrosequencing in Multilocus Sequence Typing (MLST), to determine the bacterial strain diversity. Six different gene regions (coxA, fbpA, ftsZ, gatB, hcpA and wsp gene) were targeted and amplified. However, the result shows that diversity of haplotypes is very high. The pyrosequencing approach in MLST, a new method of discriminating Wolbachia strains, is promising to effectively detect multiple infections and rare haplotypes.

The hologenome theory of evolution proposes that an organism is simply not an individual but the totality of numerous microbial symbionts to the host. In fact, the evidence of biochemical and physiological associations between the symbionts and the host has been growing fast in all major taxa. The Vollenhovia emeryi ant is tiny and found nationwide in Korea. The ant can be further categorized by its wing morphology, eg. long-winged and short-winged. Our initial screening process showed that the microbial reproductive manipulator, the Wolbachia bacterium, only infected the long-winged morph. This gave us a good opportunity to investigate the effect of the Wolbachia infection on the bacterial community diversity using the next generation sequencing technique. We find that there are about 180 bacterial symbionts in the short-winged morph. On the other hand, the long-winged morph has only about 20 bacterial symbionts. This implies that the bacterial community diversity may be subject to the existence of Wolbachia. Furthermore, the Wolbachia strain diversity is unexpectedly high. In addition, the bacterial structure difference among castes indicates that there may be labour division even between queens. The results and future research direction will be discussed from the hologenome theory perspective.

The α-proteobacterium Wolbachia is maternally inherited and is known to induce reproductive distortions in a wide range of insect taxa such as cytoplasmic incompatibility, feminization, male killing and parthenogenesis (PI). When a female is infected with PI-Wolbachia, she does not need a male to produce female offspring, because the female can produce female offspring via gamete duplication without the aid of sperm. However, in the parasitoid wasp Trichogramma kaykai species, Wolbachia infected parthenogenetic females still produce a fraction of male offspring. Offspring sex ratio for 10 days are different according to each T. kaykai isofemale line that is infected with PI- Wolbachia. This may be caused by complex interactions between Wolbachia and the host genetic backgrounds on converting sex of infected eggs.

The α-proteobacterium Wolbachia pipientis infects a wide range of arthropods and filarial nematodes. Wolbachia is maternally inherited and is known to induce reproductive anomalies such as cytoplasmic incompatibility, feminization, male killing and parthenogenesis induction (PI). Trichogramma kaykai is a tiny wasp that parasitizes on lepidopteran eggs. When a female of the wasp is infected with PI-Wolbachia, the female produces female offspring via gamete duplication without the aid of sperm. As she ages, however, the fraction of male offspring increases. In this study, we investigated the effect of host genetic background on the expression of sex ratio between isofemale lines. Virgin females of six isofemale lines were allowed to lay eggs individually for 10 days. There was the positive relationship between female age and the offspring sex ratio. Furthermore, the sex ratio was significantly different among isofemale lines, implying that the host genetic background had an effect on the sex ratio. Based on the results, evolution of symbiosis in terms of sex ratio and future experimental design are discussed.