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, we knew nothing about the mechanisms underlying the progressive differentiation between sexes that leads to such a dimorphism. Scale insects actually 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 remains low at the end of their development, leading them to have neotenic features as adults.
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.