arrhenotoky

Arrhenotoky is a form of haplodiploidy in which unfertilized eggs develop into males and fertilized eggs develop into females. It is common in many Hymenoptera (bees, wasps, and ants) and is observed in some mites and thrips.

In arrhenotokous species, a female typically lays eggs that may or may not be fertilized. An unfertilized egg undergoes development as a haploid embryo, producing a male. A fertilized egg receives paternal and maternal genomes and develops into a diploid female. In many Hymenoptera, the sex of offspring is thus tied to the fertilization status of the egg.

Many Hymenoptera also exhibit a complementary sex-determination (CSD) system, in which sex is determined by the number of paternal gene copies. Haploid individuals are always male; diploid individuals can be female or, if homozygous at the sex locus, may become sterile diploid males. Arrhenotoky and CSD together can influence population dynamics, especially in small or inbred populations where diploid males may arise.

Arrhenotoky has ecological and evolutionary implications: it enables reproduction without mating, supports rapid population growth and colonization, and interacts with social structure in eusocial species by influencing sex ratios and worker control over reproduction. Some species may exhibit facultative arrhenotoky, with males arising from unfertilized eggs under certain environmental or physiological conditions. A well-known example is the honey bee, where fertilized eggs become female workers or queens, and unfertilized eggs become drones.