Haplodiploidy is the sex system in which males are haploid (one chromosome set, from an unfertilised egg) and females diploid. Two-spotted spider mites, western flower thrips 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 is exposed to selection, so a recessive 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.
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.
A diploid organism carries two complete sets of chromosomes, one from each parent; normal cannabis is diploid with 2n = 20.Tetranychus urticae, the commonest cannabis mite indoors: a 0.5 mm sap-feeder that stipples leaves pale and spins webbing, breeding fastest in hot, dry rooms.Slender insects about 1-2 mm long, chiefly western flower thrips (Frankliniella occidentalis), that rasp leaf surfaces, leaving silvery streaks dotted with black frass.A gene is a stretch of DNA that carries the instructions for one functional product, usually a protein such as an enzyme, and is the basic unit of inheritance.A recessive allele only shows its effect when a plant carries two copies of it; in a single copy it is masked by a dominant allele and carried silently.How a pesticide kills its target, grouped by IRAC into numbered classes; rotating between groups across pest generations slows resistance.Reproduction in which unmated females lay unfertilised eggs that become males, while mated females make both sexes. Typical of spider mites and thrips.Reproduction without mating. Indoor aphids are all-female and give live birth to daughters that already carry developing embryos.The share of offspring that are female; because only females lay eggs, a female-biased ratio speeds population growth.The inherited ability of a pest population to survive doses of a pesticide that once controlled it, selected by repeated use of one mode of action.
