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.