Definition of a juvenile hormone-sensitive period in Rhodnius prolixus

This paper is an attempt to establish the times of onset and termination of the juvenile hormone-sensitive period for metamorphosis in fifth-instar larvae of Rhodnius. Small regions of the abdominal integument were exposed to discrete pulses of the juvenile hormone analogue ZR-515 (methoprene) by applying small drops of a mixture in paraffin to the dorsum at various times after a bloodmeal and removing these drops after different time intervals. The diffusion coefficient of the analogue in the integument was estimated and used together with estimates of its metabolism to determine the lag times between application of the analogue and its rise to above threshold concentration in the epidermis, and between removal of the analogue source and its fall to below threshold concentration in the epidermis. These lag times were estimated to be 1.5 and 24h, respectively. Knowledge of the lag times makes it possible to establish the limits of the juvenile hormone-sensitive period or metamorphosis from the responses of larvae to variously-timed pulses of the analogue. The juvenile hormone-sensitive period has the following properties. For the population as a whole it lasts from about day 3 to about day 9 after a bloodmeal. Any individual in that population, however, only requires the presence of juvenile hormone during a 2 to 4-day period. The exact duration of an individual's sensitive period within these limits is a stochastic event. Surprisingly, for any individual, a pulse of juvenile hormone is equally effective when experienced early as when experienced late during its juvenile hormone-sensitive period.