Sexual dimorphism in scale insects is so extreme that if you find a male and a female on a plant, you wouldn’t know they are from the same species unless you see them mating!
Although the life cycle of scale insects has been studied in the past, little is known about the mechanisms underlying the progressive differentiation between sexes that leads to such a dimorphism. Scale insects undergo two types of metamorphosis specific to each sex: neometaboly in males with quiescent non-feeding stages reminiscent to metamorphosis, and successive molting in females resulting in neoteny.
My postdoctoral research project in Japan focused on establishing whether the Juvenile Hormone (JH), an insect growth hormone essential in metamorphosis, was linked to the diverging development pathways seen in scale insects. This study found that JH levels are different during male and female post-embryonic development and although males seem to have JH variations similar to other insects that undergo the same type of metamorphosis, females JH levels remain low at the end of their development, leading to reproductively mature females with neotenic features.
We also identified and investigated the expression of Doublesex gene, a gene that generates sex-specific isoforms and responsible for sex differentiation in other insects.
Additional funding for these projects
Juvenile hormone regulation in the flour beetle and mealybugs
Vea IM, Minakuchi C. (2021)Atypical Insects: Molecular mechanisms of unusual life history strategies. Current Opinion in Insect Science. 3 : 46-53
Muramatsu M, Tsuji T, Tanaka S, Shiotsuki T, Jouraku A, Miura K, Vea IM, Minakuchi C. (2020) Sex-specific expression profiles of ecdysteroid biosynthesis and ecdysone response genes in extreme sexual dimorphism of the mealybug Planococcus kraunhiae (Kuwana). PloS one, 15(4):e0231451.
Vea IM, Tanaka S, Tsuji., Shiotsuki T, Jouraku A, and Minakuchi C. (2019) E93 expression and links to the juvenile hormone in hemipteran mealybugs with insights on female neoteny. Insect Biochemistry and Molecular Biology, 104, 65-72. https://doi.org/10.1016/j.ibmb.2018.11.008
Vea IM, Tanaka S, Shiotsuki T, Jouraku A, Tanaka T, and Minakuchi C. (2016) Differential juvenile hormone variations in scale insect extreme sexual dimorphism. PLOS ONE 11(2): e0149459. https://doi.org/10.1371/journal.pone.0149459