We provide objective criteria for assessing the taxonomic status of genera, especially those that are monotypic, using the coccid genus Taiwansaissetia Tao, Wong & Chang. This genus contains only the type species, Lecanium formicarii Green [currently Taiwansaissetia formicarii (Green)], known from the Afrotropical and Oriental regions. Here, Taiwansaissetia is synonymised (syn.nov.) with Coccus Linnaeus (Hemiptera: Coccidae) on the basis of phylogenetic analyses of DNA sequence data and morphological examination. All analyses (maximum parsimony, neighbour-joining and Bayesian inference) of four gene regions (18S, 28S, COI and EF-1α), and a concatenation of these regions, placed the clade including T. formicarii and three unidentified Coccus specimens as sister to the type species of Coccus, C. hesperidum Linnaeus, with high support. Taiwansaissetia formicarii is more closely related to C. hesperidum than C. hesperidum is to C. viridis (Green), which is considered to be a 'typical' species of Coccus, and several other current members of Coccus [C. longulus (Douglas), C. penangensis Morrison and C. pseudomagnoliarum (Kuwana)]. Explicit criteria, including monophyly, diagnosability, sister taxa being of equal rank, and the level of genetic divergence between T. formicarii and C. hesperidum relative to within-genus divergence of other scale insects, were used to assess the taxonomic status of Taiwansaissetia. The autapomorphic features of Taiwansaissetia that differentiate it from typical species of Coccus might be due to its myrmecophilous habit and adaptation to living inside ant nests -most other species of Coccus live externally on their host plants. Since its description in 1896, T. formicarii has been placed in four different genera: here we transfer it back to Coccus as C. formicarii (Green) stat.rev. We rediagnose the genus Coccus to accommodate the features of C. formicarii. This study also found that Coccus might not be monophyletic, warranting further study of the group.Correspondence: Yen-Po Lin,

1. The megadiverse herbivores and their host plants are a major component of biodiversity, and their interactions have been hypothesised to drive the diversification of both.2. If plant diversity influences the diversity of insects, there is an expectation that insect species richness will be strongly correlated with host-plant species richness. This should be observable at two levels (i) more diverse host-plant groups should harbour more species of insects, and (ii) the species richness of a group of insects should correlate with the richness of the host groups it uses. However, such a correlation is also consistent with a hypothesis of random host use, in which insects encounter and use hosts in proportion to the diversity of host plants. Neither of these expectations has been widely tested.3. These expectations were tested using data from a species-rich group of insects -the Coccidae (Hemiptera).4. Significant positive correlations were found between the species richness of coccid clades (genera) and the species richness of the host-plant family or families upon which the clades occur. On a global scale, more closely related plant families have more similar communities of coccid genera but the correlation is weak. 5. Random host use could not be rejected for many coccids but randomisation tests and similarity of coccid communities on closely related plant families show that there is non-random host use in some taxa. Overall, our results support the idea that plant diversity is a driver of species richness of herbivorous insects, probably via escape-and-radiate or oscillation-type processes.

Asexual lineages provide a challenge to species delimitation because species concepts either have little biological meaning for them or are arbitrary, since every individual is monophyletic and reproductively isolated from all other individuals. However, recognition and naming of asexual species is important to conservation and economic applications. Some scale insects are widespread and polyphagous pests of plants, and several species have been found to comprise cryptic species complexes. Parasaissetia nigra (Nietner, 1861) (Hemiptera: Coccidae) is a parthenogenetic, cosmopolitan and polyphagous pest that feeds on plant species from more than 80 families. Here, we implement multiple approaches to assess the species status of P. nigra, including coalescence-based analyses of mitochondrial and nuclear genes, and ecological niche modelling. Our results indicate that the sampled specimens of P. nigra should be considered to comprise at least two ecotypes (or "species") that are ecologically differentiated, particularly in relation to temperature and moisture. The presence of more than one ecotype under the current concept of P. nigra has implications for biosecurity because the geographic extent of each type is not fully known: some countries may currently have only one of the biotypes. Introduction of additional lineages could expand the geographic extent of damage by the pest in some countries.