Another paper in Gen.Comp.Endo. addresses the issue “Vertebrate estrogen regulates the development of female characteristics in silkworm, Bombyx mori”. While they use vertebrate estradiol to see its effect on vitellogenin expression, they also analyse whether endogenous estrogen is present. They claim that an endogenous estrogen analogue exists in B. mori.
Very strange, to be polite. Or bullshit, to be honest. The silkworm genome has been almost fully sequenced. The side-chain cleavage enzyme (cyp11a1) are definitely not present as well as the aromatase (cyp19). Without these no chance for any estradiol or analogue.
What they may have found is an estrogen receptor agonist. The literature is full of these. They are usually called endocrine disruptors since they disturb normal estrogen functions. The structures of estrogen receptor agonists are diverse and no clearcut picture has emerged to my knowledge. Such a molecule may well be present in Bombyx mori.
Caution! Not always when estrogen is claimed there is estradiol present!