First molecular genetic evidence for automictic parthenogenesis in cockroaches

Apomixis for no bacteria-induced thelytoky in Diglyphus wani (Hymenoptera: Eulophidae)

In Hymenoptera species, the reproductive mode is usually arrhenotoky, where haploid males arise from unfertilized eggs and diploid females from fertilized eggs. In addition, a few species reproduce by thelytoky, where diploid females arise from unfertilized eggs. Diploid females can be derived through various cytological mechanisms in thelytokous Hymenoptera species. Hitherto, these mechanisms were revealed mainly in endosymbiont-induced thelytokous Hymenoptera species. In contrast, thelytokous Hymenoptera species in which a reproductive manipulator has not been verified or several common endosymbionts have been excluded were paid less attention in their cytological mechanisms, for instance, Diglyphus wani (Hymenoptera: Eulophidae). Here, we investigated the cytological mechanism of D. wani using cytological methods and genetic markers. Our observations indicated that the diploid karyotypes of two strains of D. wani consist of four pairs of relatively large metacentric chromosomes and one pair of short submetacentric chromosomes (2n = 10). The arrhenotokous strains could complete normal meiosis, whereas the thelytokous strain lacked meiosis and did not expulse any polar bodies. This reproductive type of lacking meiosis is classified as apomictic thelytoky. Moreover, a total of 636 microsatellite sequences were obtained from thelytokous D. wani, dominated by dinucleotide repeats. Genetic markers results showed all three generations of offspring from thelytokous strain maintained the same genotype as their parents. Our results revealed that D. wani is the first eulophid parasitoid wasp in Hymenoptera whose thelytoky was not induced by bacteria to form an apomictic thelytoky. These findings provide a baseline for future inner molecular genetic studies of ameiotic thelytoky.

Life-History Traits from Embryonic Development to Reproduction in the American Cockroach

Simple Summary

The American cockroach is a widely distributed sanitary pest closely related to human life. The American cockroach is not only a hygienic pest that we all know but also beneficial to humans as its extract can be used medicinally and could be a model organism for physiology and neuroscience studies. In this study, we provide a life table of the American cockroach in a stable environment, including embryonic development, nymphal instars, and adult reproduction. Newly laid eggs hatch into nymphs after about 35 days of embryonic development. Under sufficient materials and space, gregarious nymphs undergo 14 molts before transforming into adults. Adult females can produce fertile offspring whether they have mated or not. On average, mated females produce an ootheca every 4 days, while unmated females produce an ootheca every 10 days. Each ootheca contains 12–16 eggs. Additionally, group living seems to improve the survival rate of offspring of unmated females.

Abstract

The American cockroach, Periplaneta americana (Insecta: Blattodea: Solumblattodea: Blattidae), is an urban hygiene pest but also a model organism for physiology and neuroscience study. However, the current description of the developmental process of the American cockroach is insufficient. In this study, we provide a life table of the American cockroach in a stable environment, including embryonic development, nymphal instars and adult reproduction. Our results show that there are 14 nymphal instars of the American cockroach in groups with sufficient living materials and space. The secondary sexual characteristics are evident in last-instar nymphs and adults, namely, the complete absence of the anal stylus in females. The entire embryonic development process was divided into 20 stages on the basis of lateral-view observations of the embryos. The formation of the embryo involves the fusion of paired blastoderm regions with higher cellular density, similar to that in other insects of Polyneoptera. With respect to reproduction, the gamogenetic females produced their first ootheca earlier than the parthenogenic females, and the frequency of oviposition was higher for the former throughout adulthood. Interestingly, group living seems to improve the parthenogenesis success rate in the American cockroach.

Chromosome Unipolar Division and Low Expression of Tws May Cause Parthenogenesis of Rice Water Weevil (Lissorhoptrus oryzophilus Kuschel)

Rice water weevil (RWW) is divided into two types of population, triploid parthenogenesis and diploid bisexual reproduction. In this study, we explored the meiosis of triploid parthenogenesis RWW (Shangzhuang Town, Haidian District, Beijing, China) by marking the chromosomes and microtubules of parthenogenetic RWW oocytes via immunostaining. The immunostaining results show that there is a canonical meiotic spindle formed in the triploid parthenogenetic RWW oocytes, but chromosomes segregate at only one pole, which means that there is a chromosomal unipolar division during the oogenesis of the parthenogenetic RWW. Furthermore, we cloned the conserved sequences of parthenogenetic RWW REC8 and Tws, and designed primers based on the parthenogenetic RWW sequence to detect expression patterns by quantitative PCR (Q-PCR). Q-PCR results indicate that the expression of REC8 and Tws in ovarian tissue of bisexual Drosophila melanogaster is 0.98 and 10,000.00 times parthenogenetic RWW, respectively (p < 0.01). The results show that Tws had low expression in parthenogenetic RWW ovarian tissue, and REC8 was expressed normally. Our study suggests that the chromosomal unipolar division and deletion of Tws may cause parthenogenesis in RWW.

New Insights into Cockroach Control: Using Functional Diversity of Blattella germanica Symbionts

Simple Summary

Insect hosts have close relationships with microbial symbionts. The limited metabolic networks of most insects are enhanced by these symbiotic relationships. Using symbiotic microorganisms for biological control of insects and insect-borne diseases has become an important research topic and shows potential for the development of applicable control approaches. Blattella germanica (L.) is public health pest worldwide; it is difficult to control because of its strong reproductive ability, adaptability, and resistance to insecticides. In this paper, the diverse biological functions (nutrition metabolism, reproductive regulation, insecticide resistance, defense, and behavior management) of symbionts, their interaction mechanism with hosts, and the research progress in the control of B. germanica are reviewed and discussed.

Abstract

Insects have close symbiotic relationships with several microbes, which extends the limited metabolic networks of most insects. Using symbiotic microorganisms for the biological control of pests and insect-borne diseases has become a promising direction. Blattella germanica (L.) (Blattaria: Blattidae) is a public health pest worldwide, which is difficult to control because of its strong reproductive ability, adaptability, and resistance to insecticides. In this paper, the diverse biological functions (nutrition, reproductive regulation, insecticide resistance, defense, and behavior) of symbionts were reviewed, and new biological control strategies on the basis of insect–symbiont interaction were proposed. We highlight new directions in B. germanica control, such as suppressing cockroach population using Wolbachia or paratransgenes, and combining fungal insecticides with synergistic agents to enhance insecticidal efficacy.

Widespread occurrence of asexual reproduction in higher termites of the Termes group (Termitidae: Termitinae)

BACKGROUND

A decade ago, the mixed reproductive strategy Asexual Queen Succession (AQS) was first described in termites. In AQS species, the workers, soldiers and dispersing reproductives are produced through sexual reproduction, while non-dispersing (neotenic) queens arise through automictic thelytokous parthenogenesis, replace the founding queen and mate with the founding king. As yet, AQS has been documented in six species from three lineages of lower (Rhinotermitidae) and higher (Termitinae: Termes group and Syntermitinae) termites. Independent evolution of the capacity of thelytoky as a preadaptation to AQS is supported by different mechanisms of automixis in each of the three clades. These pioneering discoveries prompt the question on the extent of thelytoky and AQS in the diversified family of higher termites.

RESULTS

Here, we investigated the capacity of thelytoky and occurrence of AQS in three species from the phylogenetic proximity of the neotropical AQS species Cavitermes tuberosus (Termitinae: Termes group): Palmitermes impostor, Spinitermes trispinosus, and Inquilinitermes inquilinus. We show that queens of all three species are able to lay unfertilized eggs, which undergo thelytokous parthenogenesis (via gamete duplication as in C. tuberosus) and develop through the transitional stage of aspirants into replacement neotenic queens.

CONCLUSIONS

The breeding system in P. impostor is very reminiscent of that described in C. tuberosus and can be characterized as AQS. In the remaining two species, our limited data do not allow classifying the breeding system as AQS; yet, also in these species the thelytokous production of neotenic females appears to be a systematic element of reproductive strategies. It appears likely that the capacity of thelytokous parthenogenesis evolved once in the Termes group, and may ultimately be found more widely, well beyond these Neotropical species.