Expressions of juvenile hormone biosynthetic genes during presoldier differentiation in the incipient colony of Zootermopsis nevadensis (Isoptera: Archotermopsidae)

Soldier differentiations require high juvenile hormone (JH) titers in workers and two molts via a presoldier stage. However, it is still unclear when the endogenous JH titer increases in workers, because identifying an individual before it undergoes the presoldier molt is quite difficult in natural conditions. In an incipient colony of Zootermopsis nevadensis Hagen, the oldest 3rd instar larva (Νo. 1 larva) always differentiates into a presoldier and the second 3rd instar larva (Νo. 2 larva) molts into a 4th instar larva. Consequently, by focusing on the ontogeny of the Νo. 1 larva, the timing of the increase in the JH titer can be determined. Here, we compared the expression levels of JH biosynthetic genes in the heads of Νo. 1 and Νo. 2 larvae. Most genes involved in JH biosynthesis were found in a genome database, and two candidate JH epoxidase (CYP15A1) genes were identified. Expression levels of JH acid methyltransferase (JHAMT) and one candidate CYP15A1, probably involved in the final steps of the JH biosynthesis, were specifically high in Νo. 1 larvae at 2–3 and 4–5 days after the appearance, respectively. Expression patterns of these genes may be used for the prediction of endogenous JH titer changes during presoldier differentiation.