Western Orchard Predatory Mite Genome Project

Western orchard predatory mite
Western Orchard Predatory Mite

Image Source:
Jack Kelly Clark, University of California Statewide Integrated Pest Management Program

About the Project

In collaboration with Dr. Marjorie Hoy at the University of Florida at Gainesville, we sequenced the western orchard predatory mite (Metaseiulus occidentalis). The M. occidentalis genome sequence and its analysis has been published in Genome Biology and Evolution, "Genome Sequencing of the Phytoseiid Predatory Mite Metaseiulus occidentalis Reveals Completely Atomized Hox Genes and Superdynamic Intron Evolution."

Metaseiulus occidentalis is an effective predator of spider mite, eriophyoid mite, and tarsonemid mite pests in almonds, apples, pears, grapes, cotton, and strawberries in the western USA. It was purposefully introduced into Australia and New Zealand to control pest mites in apple and peach orchards, and is commercially mass reared and released to control spider mite pests in strawberries and other agricultural crops in the USA.

M. occidentalis kills pest mites by sucking out the partially digested contents of its prey, leaving behind only shriveled eggs or carcasses of the active stages. This tiny predator, about the size of a period at the end of this sentence, can reduce pest mite populations to low densities over long periods of time because it has a rapid development time (ca. one week) and high reproductive rate.

This species has 3 and 6 small chromosomes in male and female adults, respectively, which appear to be acrocentric. Initially, M. occidentalis was assumed to be arrhenotokous. However, because females need to mate before ovipositing it was determined, through experiment and cytology, that the genetic system of M. occidentalis is parahaploidy.

All females are 2n and mated females typically produce one male for each 2.5 females. Males initially are derived from fertilized eggs in which homologous chromosomes pair half way through embryonic development. The paternally derived chromosomes are heterochromatinized and lost from the nuclear genome. Male larvae and all subsequent active stages are haploid (n=3).

M. occidentalis tolerates inbreeding well and commonly sib mates. Parahaploidy and sibmating allows this predator to respond rapidly to selection for resistance to pesticides; selection can act on the haploid active stages of males and sibmating allows a rapid consolidation of resistance alleles.

This work was funded by Dr. Hoy’s research funds.

Genomic Resources

Additional Resources

Western Predatory Mite page at UC IPM Online.

Updates about the western orchard predatory mite genome are being posted to mite genomics listserv. Please contact Stephen Richards with your email address to sign up.