Juvenile hormones (JHs) and completion of oöcyte development in the African migratory locust: A comparative and quantitative study

Abstract

The effect of juvenile hormones (JHs) I and III on induction and completion of oöcyte development in allatectomized adult Locusta migratoria migratorioides females was studied. Whenever possible, oviposition rate served as a parameter, though, necessarily, oöcyte length was employed when no laying occurred. In the latter instance, oöcytes were usually measured twice, at laparotomy (special operation of the living female) and later at dissection. Normal (unoperated), allatectomized, allatectomized and later corpora allata (CA)-implanted females, as well as allatectomized females receiving solvents without hormone, constituted the controls. Allatectomy prevented oöcyte development, but reimplantation of CA led to its completion (laying). Injection or topical application of solvent(s) alone did not induce oöcyte development in allatectomized females. Topical application of JHI in methanol induced small, though distinct, vitellogenetic growth of the oöcytes. A more marked effect was obtained with JHI topically applied in olive oil. Injection of JHI greatly improved the effect, and only this method led to completion of oöcyte development. Hormone concentration in olive oil between 0.075 and 0.5% ( w v ), single or repeated (up to four) injections, did not influence oviposition rate for a 40-μg cumulative dose of JHI, though duration of laying was affected. Increasing cumulative doses of JHI, or JHIII, increased oviposition rate, furnishing well-defined dose-response curves. ED 50 (effective dose 50%, defined as 0.5 oviposition rate, that is, number of pods laid is equal to half the number of females) was about 30 μg per female for JHI and about 44 μg per female for JHIII. Thus, JHI was about 1.4–1.5 times more efficacious than JHIII. Ten micrograms of JHI did not induce completion of oöcyte development; 60 μg did so more than once in a portion of the females. Surprisingly, dosage and cumulative dose did not affect the number of eggs per pod, which always remained considerably lower than in normal (unoperated) controls. Pods laid by allatectomized and JH-injected females were viable, hatched reasonably, and the progeny achieved normal adult stage and sexual maturation. Injected JHI restored the secretory functioning of the oviduct. Unreliability of oöcyte length for assaying JH in adult female locusts, mode of JH administration, lack of difference in the results for single and repeated injections (of the same cumulative dose), and the crucial effect of the cumulative dose are discussed. Effective doses are considered as unphysiologically high, and some hypotheses are forwarded in explanation. The lack of effect of the cumulative dose on number of eggs per pod is also discussed and related to nutritional and/or metabolic factors, especially female-specific protein (=vitellogenin) synthesis.