Effects of larval diapause and the juvenile hormone analog, fenoxycarb, on testis development and spermatogenesis in the wax moth, Galleria mellonella (Lepidoptera: Pyralidae)

Piotr Bebas,Bronislaw Cymborowski,Michalina Kazek,Marta Anna Polanska

doi:10.14411/eje.2018.040

Piotr Bebas, Bronislaw Cymborowski + Show 2 more

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https://doi.org/10.14411/eje.2018.040

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Abstract

Facultative diapause in the wax moth, Galleria mellonella, occurs in the final larval instar. Application of juvenile hormone analogs (JHAs) to the larvae of this species has similar effects to diapause, in terms of prolonged development of the larval stages and the arrest in the metamorphosis of internal organs. Here, we focus on testes development and spermatogenesis at the end of larval development in G. mellonella, how they are affected by diapause induced by an environmental decrease in temperature to 18°C and the application of a JHA (fenoxycarb) to larvae. Because neither testis development nor spermatogenesis are described in detail for this species, we examined them in individuals not in diapause during the period from the last larval instar to the newly emerged adult and present a timetable of changes that occur in the development of testes in this species. These observations have increased the very limited data on the course of spermatogenesis in pyralid insects. We then used these data for comparative analysis of testes in larvae from two experimental groups: individuals in diapause and those treated with fenoxycarb. The results on the general morphology testes revealed obvious degenerative changes caused by fenoxycarb (but not by diapause), including testicular wall hypertrophy and disarrangement of testicular follicles. Moreover, treatment with fenoxycarb finally resulted in the disintegration of nearly all testicular cyst-containing germ cells at different stages of spermatogenesis, a situation never previously described in the literature. In contrast, the main effect of diapause on testes was merely the degeneration of spermatocytes in the proximal regions of the testicular follicles. Finally, the TUNEL analyses, revealed that the degenerative changes in germ cells were apoptotic in character in the testes of both individuals in diapause and fenoxycarb-treated males.

Highlights

In Lepidoptera, the most intensive testicular growth, caused by an increase in the frequency of mitotic divisions of the primary germ cells, occurs during the last larval instar (Friedländer et al, 2005)
The upper-median zone of the follicles is occupied by bipotential spermatocytes that arise from spermatogonia (Figs 1B and 2E)
These cells are closely packed in the cysts and differentiate into primary apyrene spermatocytes and primary eupyrene spermatocytes, which are visible in sections of testes at different stages of maturation (Figs 1B and 2F, G)

Summary

Introduction

In Lepidoptera, the most intensive testicular growth, caused by an increase in the frequency of mitotic divisions of the primary germ cells, occurs during the last larval instar (Friedländer et al, 2005). In most Lepidoptera, at the end of their larval development (pre-pupal stage), the paired kidney-shaped testes fuse into a single organ that undergoes torsion such that pupae and adult males possess a single gonad consisting of eight twisted chambers, known as testicular follicles (TF), (Cholodkovsky, 1880; Drecktrah, 1966; Jones, 1973; LaChance & Olstad, 1988; Pereira & Santos, 2015) It has been clearly shown, at least in some species, that simultaneously with the testis fusion-torsion process, spermiogenesis of developmentally advanced spermatids is initiated, leading to the appearance of mature spermatozoa bundles that increase in number with the progression of metamorphosis (Chaudhury & Raun, 1966; Nowock, 1972, 1973; Jones et al, 1984; Corsato-Alvarenga et al, 1987). In Lepidoptera, spermatogenesis is dichotomous because the spermatocytes undergo differ-

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