POLYPLOIDY AND PREVITELLOGENIC FOLLICULAR ATRESIA DURING OOGENESIS IN THE EUROPEAN EARWIG FORFICULA AURICULARIA (DERMAPTERA: FORFICULIDAE)

Abstract

The Canadian Entomologist 131: 323 -334 (1999) Oogenesis and associated ovarian development were studied from the onset of adult eclosion to oviposition in the European earwig, Forjicula auricularia L., by examining histological sections of ovarioles and whole mounts of ovaries. Each pair of ovaries contains a mean of 85.4 ovarioles. Chronologically, oogenesis has been divided into four phases, adult emergence, previtellogenesis, vitellogenesis, and choriogenesis, each described here in detail. The mean size of the basal follicle increases from 15 y m at time of adult emergence to 0.9 mm at time of choriogenesis, and the oocyte to trophocyte ratio increases from 1.0 to 4, with a minimum of 0.5 at the onset of previtellogenesis. The oocyte to trophocyte ratio of 0.7 marks the onset of vitellogenesis, which lasts about three times (60 days) as long as previtellogenesis. The extended vitellogenesis is still under way when females bury themselves in the ground, in October, in the MontrCal area. Tourneur J-C. 1999. Ovogenese imaginale du Forficule commun Forficula auricularia (Dermaptera: Forficulidae). The Canadian Entomologist 131 : 323-334. L'ovogenbse du Forficule commun Forjicula auricularia L. et les modifications ovariennes qui les accompagnent ont Ct C suivies de la mue imaginale A la ponte en observant des coupes histologiques d'ovarioles et des ovaires montCs in toto. Chaque paire d'ovaires prCsente un nombre moyen d'ovarioles de 85,4. Chronologiquement, l'ovogenbse a Ct C scindCe en quatre phases, Cmergence de l'adulte, prCvitellogenbse, vitellogenkse et choriogenkse et chacune d'elles a fait l'objet d'une description dCtaillCe. La taille moyenne du follicule basal passe de 15 p m a1'Cmergence de l'adulte a 0,9 mm a la choriogenbse, pendant que le rapport ovocyte B trophocyte passe de 1 a 4, avec un minimum de 0,5 en dCbut de prCvitellogenkse. La valeur 0,7 du ratio ovocyte a trophocyte marque le debut de la vitellogenbse qui requiert trois fois plus de temps (60 jours) que la prCvitellogenbse. La longue vitellogenbse est toujours en cours quand les femelles entrent dans le sol, en Octobre, dans la rCgion de MontrCal.

Factors affecting the egg-laying pattern of Forficula auricularia (Dermaptera: Forficulidae) in three climatologically different zones of North America

“…Previtellogenic follicular atresia occurs in both the Vancouver and San Francisco populations, as previously observed in the Montréal population (Tourneur 1999b). This observation also suggests that previtellogenic follicular atresia occurs at the same rate of two nuclear fusions per reproductive cycle, hence the need of a minimum of three oocytes per egg produced.…”

“…The fixed number of oocytes sets the maximum number of broods that can be produced (Vancassel 1984). In the case of the Montréal population, this limit is 6.1±1.1 (Tourneur 1999b).…”

“…During each reproductive cycle, previtellogenic follicular atresia due to trophocyte nuclear fusion (two fusions during a reproductive cycle) use up three oocytes for each egg produced. This decreases the number of broods than can be produced by each female (Tourneur 1999b). Therefore, at most two broods can be produced in the Montréal area.…”