Isolation and characterization of eight microsatellite loci in two morphotypes of the Southeast Asian army ant, Aenictus laeviceps

Facultative parthenogenesis in the Ryukyu drywood termite Neotermes koshunensis

Parthenogenesis is a relatively rare reproductive mode in nature compared to sex. In social insects, the evolution of parthenogenesis has a notable impact on their life histories. Some termites with parthenogenetic ability produce numerous non-dispersing supplementary queens asexually, whereas other castes are produced via sexual reproduction. This asexual queen succession (AQS) system is adaptive because hundreds of the asexual queens improve the reproductive potential of the colony and maintain the genetic diversity within the colony. However, the evolutionary process of the AQS system remains unclear because parthenogenetic species without this system are unknown. Here, we report facultative parthenogenesis in the drywood termite Neotermes koshunensis. Although the eggs produced by females isolated from males hatched, the hatching rate of those eggs was lower than that of the eggs produced by females kept with males. These parthenogenetic offspring inherited only the maternal alleles and showed high homozygosity, which indicates that the mechanism of ploidy restoration is terminal fusion. A previous study showed that most colonies of this species have a single queen or orphan; thus, the AQS system has not evolved despite their parthenogenetic ability. Further investigations of N. koshunensis will reveal how parthenogenesis evolved and its role in the insect societies.

Apomictic parthenogenesis in a parasitoid wasp Meteorus pulchricornis, uncommon in the haplodiploid order Hymenoptera

Although apomixis is the most common form of parthenogenesis in diplodiploid arthropods, it is uncommon in the haplodiploid insect order Hymenoptera. We found a new type of spontaneous apomixis in the Hymenoptera, completely lacking meiosis and the expulsion of polar bodies in egg maturation division, on the thelytokous strain of a parasitoid wasp Meteorus pulchricornis (Wesmael) (Braconidae, Euphorinae) on pest lepidopteran larvae Spodoptera litura (Fabricius) (Noctuidae). The absence of the meiotic process was consistent with a non-segregation pattern in the offspring of heterozygous females, and no positive evidence was obtained for the induction of thelytoky by any bacterial symbionts. We discuss the conditions that enable the occurrence of such rare cases of apomictic thelytoky in the Hymenoptera, suggesting the significance of fixed heterosis caused by hybridization or polyploidization, symbiosis with bacterial agents, and occasional sex. Our finding will encourage further genetic studies on parasitoid wasps to use asexual lines more wisely for biological control.

Isolation of microsatellite loci from the onion thrips, Thrips tabaci

Thrips tabaci Lindeman (Thysanoptera: Thripidae), a cosmopolitan pest insect, is subdivided into at least three genetic lineages that have different biological characters, such as reproductive mode and resistibility to insecticides. Since the lineages are discriminated only by mitochondrial DNA, there is a possibility of gene flow among lineages at the genomic level. Nine polymorphic microsatellite loci were newly isolated from the taxon. Moderate to high levels of polymorphism were observed, with numbers of alleles ranging from 6 to 12 in 51 individuals. The mean observed and expected heterozygosities ranged from 0.1373 to 0.3725 and 0.5381 to 0.7748, respectively. Contrary to the expectation under Hardy-Weinberg's equilibrium, six of the nine loci exhibited a reduction to homozygosities. However, we confirmed that alleles in all the loci were inherited as Mendeilan characteristics. These new loci will be useful to explore discrimination of lineages and population genetics in this species.