The B chromosome of Pseudococcus viburni: a selfish chromosome that exploits whole-genome meiotic drive

Meiosis, the key process underlying sexual reproduction, is generally a fair process: each chromosome has a 50% chance of being included into each gamete. However in some organisms meiosis has become highly aberrant with some chromosomes having a higher chance of making it into gametes than others. Yet why and how such systems evolve remains unclear. Here we study the unusual reproductive genetics of mealybugs, in which only maternal-origin chromosomes are included into the gametes during male meiosis, while paternally-derived chromosomes degrade. This whole genome meiotic drive occurs in all males and is evolutionarily conserved. However one species - the obscure mealybug Pseudococcus viburni - has a segregating B chromosome that increases in frequency by escaping paternal genome elimination. Here we present whole-genome and gene expression data from laboratory lines with and without B chromosomes. These data allow us to identify B-linked sequences including >70 protein-coding genes as well as a B-specific satellite repeat that makes up a significant proportion of the chromosome. We also used these data to investigate the evolutionary origin of the B chromosome. The few paralogs between the B and the core genome are distributed throughout the genome, showing that it is unlikely that the B originated through a simple duplication of one of the autosomes. We also find that while many of the B-linked genes do not have paralogs within the P.viburni genome, but they do show orthology with genes in other hemipteran insects suggesting that the B might have originated from fission of one of the autosomes, possibly followed by further translocations of individual genes. Finally in order to understand the mechanisms by which the B is able to escape elimination when paternally-derived we generated gene expression data for males and females with and without B chromosomes. We find that at the developmental stage when meiosis is taking place only a small number of B-linked genes show significant expression. Only one gene was significantly over-expressed during male meiosis, which is when the drive occurs: a acetyltransferase involved in H3K56Ac, which has a putative role in meiosis and is therefore a promising candidate for further studies. Together, these results form a promising foundation for studying the mechanisms of meiotic drive in a system that is uniquely suited for this approach.

The Anagyrus (Hymenoptera: Encyrtidae) parasitoids of the obscure mealybug Pseudococcus viburni (Hemiptera: Pseudococcidae) in Spain, with description of a new species

The presence of three species of the genus Anagyrus Howard (Hymenoptera: Encyrtidae) parasitizing the obscure mealybug Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae) in agricultural ecosystems of citrus, persimmon and ornamental plants from Eastern Spain is recorded. Anagyrus aligarhensis Agarwal & Alam is recorded for the first time as parasitoid on this mealybug. Anagyrus fusciventris (Girault) is a new record for Spain. Anagyrus borrianensis sp. nov., reared as a specific primary parasitoid of this mealybug, is described and illustrated. The joint presence of Anagyrus pseudococci (Girault) and Anagyrus vladimiri Triapitsyn on citrus crops is confirmed. A key to species of Anagyrus parasitoids of Planococcus and Pseudococcus mealybugs in Eastern Spain is provided

Pseudococcus viburni (obscure mealybug).

P. viburni, commonly known as obscure mealybug, is an unarmoured scale insect and a common pest in the UK, Netherlands, Australia, New Zealand, the French Riviera, Iran, California and Chile. It can affect a number of fruit and nursery plants including apples, tomatoes, orchids and cacti and cause substantial damage to fruit orchards and vineyards. The degree of polyphagy of P. viburni, combined with its numerous economically important host-plants, have meant that it began to be carried on infested plant material between countries from an early date. The species was first recorded outside South America, in France by Signoret (1875), and its subsequent spread followed the trade routes between Europe and the rest of the world; the species is still increasing its geographical range. While obscure mealybug does not spread widely by its own means, human transport of infested plant material disseminates it over long distances very effectively. It has successfully adapted to life in a variety of ecological conditions and in the higher latitudes where it cannot survive winter outdoors, it thrives in greenhouses (Schoen and Martin, 1999).

Pseudococcidae (Hemiptera: Coccomorpha) in Uruguay: morphological identification and molecular characterization, with descriptions of two new species

Mealybugs (Hemiptera: Coccomorpha: Pseudococcidae) are important pests in fruit production in Uruguay; however, very little is known about the species involved. A survey of mealybugs associated especially with fruit crops (apple, citrus, figs, grapes, pears, quince and strawberry), and other crops like vegetables and sugar cane, ornamentals and weeds was performed between 2017 and 2019 in Uruguay, using integrated taxonomy (morphology and DNA analyses) for their identification. A total of 19 mealybug species were identified. The most common species were Planococcus ficus (Signoret), Pseudococcus scatoterrae Granara de Willink and Pseudococcus viburni (Signoret) on fruits, and Phenacoccus madeirensis Green, Phenacoccus peruvianus Granara de Willink and Planococcus citri (Risso) on ornamental plants, all of them causing damage to their hosts. This study presents nine new species records for Uruguay, besides the description of two new species. An identification key to the mealybugs in Uruguay is provided.

New data on the fauna of mealybugs (Hemiptera; Pseudococcidae) inhabiting subtropical plants in the Lankaran-Astara Region of Azerbaijan

Invasive insect species enter new environment mainly with their host plants and spread rapidly in new conditions due to the absence of natural entomophages that can effectively limit their numbers. Comprehensive studies of the invaders, including crop pest, are of great importance for agricultural practice. In this regard, we investigated mealybugs (Pseudococcidae) in the orchards of five subtropical species, viz. lemon (Citrus limon) mandarin (Citrus reticulate), orange (Citrus sinensis), persimmon (Diospyros kaki), and pomegranate (Punica granatum) in the Lankaran-Astara Region of Azerbaijan. The research was conducted in 2016‒2019 in various seasons. Three mealybug species were recorded from the area in question: Pseudococcus comstocki Kuwana 1902, Pseudococcus viburni Signoret 1875, Pseudococcus calceolariae (Maskell, 1879). An annotated list of species provides collecting localities, their geographical coordinates, dates of collection, and the number of individuals found. We obtained data on species distribution, biology, host plants and signs of infestation. Ps. viburni was registered in the fauna of Azerbaijan for the first time; a developement period of its larvae and imagoes is provided. The highest infestation of the vegetative organs was observed on the citrus plants: on average, 30 % of trees were damaged by Ps. comstocki, 27 % by Ps. viburni, and 21 % by Ps. calceolariae. Two mealybug species (Ps. comstocki, Ps. viburni) were found on the persimmon and only one species (Ps. comstocki) on the pomegranate. Ps. comstocki population density was the highest in the study area (3–5 larvae per 10 cm of branches, and 4–5 colonies per 100 leaves during flowering). All three species were found together on the stems and leaves of citrus crops; Ps. comstocki was observed on the fruits of mandarin and persimmon, and Ps. viburni was only on the persimmon. Based on the data obtained, the degree of harmfulness of the above species was determined: for Ps. comstocki – 3–5 larvae per 10 cm of branches, and 4–5 colonies per 100 leaves during flowering; for Ps. viburni – 2–3 larvae per 10 cm of branches, and 3–4 colonies per 100 leaves during flowering; and for Ps. calceolariae – 2–3 larvae per 10 cm of branches, and 2–3 colonies per 100 leaves during flowering.

A Survey of Virginia Vineyards Revealed High Incidences of Grapevine Rupestris Stem Pitting-Associated Virus, Grapevine Red Blotch Virus, and Two Mealybug Species

We investigated the prevalence of viruses infecting grapevines in Virginia, identity of disease vectors, and potential factors affecting virus incidence. Tested viruses were grapevine leafroll-associated virus (GLRaV-1 and -4), grapevine fleck virus (GFkV), grapevine virus A (GVA), grapevine virus B (GVB), grapevine rupestris stem pitting-associated virus (GRSPaV), tomato ringspot virus (ToRSV), grapevine vein clearing virus (GVCV), grapevine red blotch virus (GRBV), and grapevine Pinot gris virus (GPGV). We documented wide distributions of GRSPaV (54%) and GRBV (24%) and common occurrences of grape (Pseudococcus maritimus) and Gill’s (Ferrisia gilli) mealybugs among vineyards. This is the first report of GLRaV-1, GLRaV-4, GVA, GVB, GRSPaV, and obscure mealybug (Pseudococcus viburni) in Virginia. We also documented significant association (P ≤ 0.05) of the presence of mealybugs and GVA and GVB. With younger vines, significantly lower incidences were found for viruses that were listed (i.e., tested for a certification) by the Foundation Planting Service’s and the National Clean Plant Network’s grape programs. On the other hand, there was a lack of the age effect on incidence of GRSPaV and GRBV, which were not listed until recently. These results suggest the importance of clean plant material and vector management for grapevine virus disease management in Virginia.