[The effect of farnesyl methyl ether on molting rhythm and testes development inEphestia kühniella. Studies in vivo and in vitro]

Abstract

Oral application of farnesyl methyl ether (FME), which allows for a continuous supply, inhibited the pupal differentiations of the integument. Animals fed during the course of the last larval instar reached the stage of grown-up feeding larvae, but did not enter the pharate pupal phase. By this way pupation could practically be delayed for any length of time. When the FME was administered from the first day of this instar a supernumerary larval molt occurred in some animals. A further molt, however, did not take place. An earlier treatment increased the number of superlarvae. Beginning the exposure to FME at the end of the last larval instar, some larval-pupal intermediates could be obtained with predominantly larval characteristics.When the continuous application was discontinued and the animals were transferred to FME-free food, a normal pupation took place.In the testes the metamorphosis changes of fusion and torsion were similarly inhibited by the juvenile hormone analogue.Furthermore, FME influenced testis growth. A dilution series was tested on two age groups (1- or 7-day-old last instar larvae). On transforming the data into the logarithms, two negative linear dose-response relationships were obtained. The regression analysis showed that both sets of data fitted simple straight-line models. The regression curves could be regarded as parallel whereby the older animals had higher testis size values at a given dose. However, compared with the size at the beginning of the FME-application, in the older animals a real decrease in volume took place.When the animals were transferred to untreated food, their testes became normal in size, fused and twisted.The dose-response relationship could be verified in vitro. Here too, a negative linear regresion of the log (testis size) on the log (FME-dose) was found. The regression coefficient did not differ significantly from that calculated from the in vivo data. Hence, FME acts directly on the testis sheath and does not control the organ size by alterations of the hemolymph.Testes will fuse autonomously if they have passed the critical period of this process. Culturing organs after this period on a FME-containing medium, they fused after one day despite the presence of the juvenile hormone analogue. However, with further incubation these fused partners separated. Testes which were already fused at the beginning of the incubation remained together. This indicates that there is a period of modifiable surface properties of the testes during which a fusion can be reversed by FME.The process of torsion does not show such a reversibility.