# Haplodiploidy

> A sex-determination system where males develop from unfertilised eggs with one chromosome set and females from fertilised eggs with two; found in mites, thrips and whiteflies.

- Canonical: https://genetixbay.com/knowledge/glossary/haplodiploidy.html
- Also written: haplodiploid, haplo-diploid
- Glossary category: Pests and diseases · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Haplodiploidy is the sex system in which males are haploid (one chromosome set, from an unfertilised egg) and females [diploid](https://genetixbay.com/knowledge/glossary/diploid.md). [Two-spotted spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [western flower thrips](https://genetixbay.com/knowledge/glossary/thrips.md) and whiteflies all use it. The spider mite genome paper discusses it as part of the biology that makes the species such an adaptable pest.

## In practice

Haplodiploidy speeds up pesticide resistance. In haploid males every [gene](https://genetixbay.com/knowledge/glossary/gene.md) is exposed to selection, so a [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) resistance gene cannot hide in carriers the way it does in diploid species; resistant males survive and pass it to all their daughters. Combine that with a generation of about a week at 25-30 C and resistance can appear within one season of repeating one [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md).

## Don't confuse with

- **Arrhenotoky**: the reproduction mode that follows from haplodiploidy (unmated females make sons).
- **Parthenogenesis in aphids**: females make daughters without males, a different system.

## Related terms

[Arrhenotoky](https://genetixbay.com/knowledge/glossary/arrhenotoky.md), [Sex ratio](https://genetixbay.com/knowledge/glossary/sex-ratio.md), [Pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md)

## Read more

- [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md)
- [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md)
- [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md)

## Sources

1. Grbic, M. et al., 2011. The genome of Tetranychus urticae reveals herbivorous pest adaptations. Nature 479:487-492. https://doi.org/10.1038/nature10640
2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html