A highly contiguous genome assembly of a polyphagous predatory mite Stratiolaelaps scimitus (Womersley) (Acari: Laelapidae)

As a polyphagous soil-dwelling predatory mite, Stratiolaelaps scimitus (Womersley) (Acari: Laelapidae), formerly known as Stratiolaelaps miles (Berlese), is native to the Northern hemisphere and preys on soil invertebrates, including fungus gnats, springtails, thrips nymphs, nematodes, and other species of mites. Already mass-produced and commercialized in North America and Europe, S. scimitus is now introduced in China as a biocontrol agent for field crop. The introduction, however, can lead to unexpected genetic changes within populations of biological control agents, which might decrease the efficacy of pest management or increase the risks to local environments. To better understand the genetic basis of its biology and behavior, we sequenced and assembled the draft genome of S. scimitus using the PacBio Sequel platform II. We generated ∼150 × (64.81 Gb) PacBio long reads with an average read length of 12.60 kb. Reads longer than 5 kb were assembled into contigs, resulting in the final assembly of 158 contigs with a N50 length of 7.66 Mb, and captured 93.1% of the BUSCO gene set (n = 1,066). We identified 16.39% (69.91 Mb) repetitive elements, 1,686 non-coding RNAs, and 13,305 protein-coding genes, which represented 95.8% BUSCO completeness. Combining analyses of genome family evolution and function enrichment of gene ontology and pathway, a total of 135 families experienced significant expansions, which were mainly involved in digestion, detoxification, immunity and venom. Major expansions of the detoxification enzymes, i.e., P450s and carboxylesterases, suggest a possible genetic mechanism underlying polyphagy and ecological adaptions. Our high-quality genome assembly and annotation provide new insights on the evolutionary biology, soil ecology and biological control for predaceous mites.

Late Cretaceous domatia reveal the antiquity of plant–mite mutualisms in flowering plants

Mite houses, or acarodomatia, are found on the leaves of over 2000 living species of flowering plants today. These structures facilitate tri-trophic interactions between the host plant, its fungi or herbivore adversaries, and fungivorous or predaceous mites by providing shelter for the mite consumers. Previously, the oldest acarodomatia were described on a Cenozoic Era fossil leaf dating to 49 Myr in age. Here, we report the first occurrence of Mesozoic Era acarodomatia in the fossil record from leaves discovered in the Upper Cretaceous Kaiparowits Formation (76.6–74.5 Ma) in southern UT, USA. This discovery extends the origin of acarodomatia by greater than 25 Myr, and the antiquity of this plant–mite mutualism provides important constraints for the evolutionary history of acarodomatia on angiosperms.

Functional response of the predaceous mites Amblyseius largoensis and Euseius concordis when feeding on eggs of the cashew tree giant whitefly Aleurodicus cocois

The giant whitefly, Aleurodicus cocois, is one of the main pests of cashew trees around the world. In the present study we evaluated the biological potential of the predaceous mites Amblyseius largoensis and Euseius concordis against A. cocois. The consumption and functional responses to prey egg densities of A. largoensis and E. concordis were investigated in laboratory experiments. Logistic regression indicated that both predators exhibited a type II response to prey eggs, and the eggs consumption increased with egg density up to a maximum, after which it slowly decreased. The value of the attack rate (a') was higher for A. largoensis than that for E. concordis, but the handling time (Th) did not differ between the two predators. The predicted maximum daily consumption was 35 eggs for A. largoensis and 32 eggs for E. concordis. Our results indicate that A. largoensis and E. concordis could be effective biocontrol agents of the cashew tree giant whitefly, especially in conditions of low pest population density.