Browsing by Author "Hiroyoshi, Satoshi"

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Age-related sperm production, transfer, and storage in the sweet potato weevil, cylas formicarius (fabricius) (coleoptera: Curculionidae)
(2016-11) Hiroyoshi, Satoshi; Kohama, Tsuguo; Reddy, Gadi V. P.
The relationship between sperm production, insemination rate, and sperm transfer were studied in the sweet potato weevil, Cylas formicarius. Older adult males retained more sperm in the testes-seminal vesicle complex (TSC) and thus more was ejaculated into females at first mating. Number of matings per day for males was relatively constant across different ages, and frequent mating resulted in a reduced amount of sperm transferred to females, especially in young males. Young virgin males had a relatively small ejaculate, and almost all sperm transferred to females was stored in the spermatheca, whereas older virgin males transferred a larger amount of sperm to females, in whom sperm was found in both the spermatheca and post-spermathecal organs (PSO) after mating. The number of sperm in the PSO decreased markedly within 24 h after mating, but amounts in the spermatheca remained the same. Just where the sperm in the PSO went is a point that remained undetermined. The amount of sperm in the spermatheca was reduced more rapidly in females that laid eggs than in females that did not, although sperm reduction occurred even in the latter. Insemination of this weevil corresponded with the volume of the spermatheca, and the amount of sperm stored in the TSC was determined by the age and mating history of the males.
Effects of Irradiation Dose on Sperm Production, Insemination, and Male Mating Possible Period in the Sweetpotato Weevil (Coleoptera: Brentidae)
(2018-05) Hiroyoshi, Satoshi; Mistunaga, Takayuki; Kohama, Tsuguo; Reddy, Gadi V. P.
The sterile insect technique (SIT) has been used for the control or eradication of target insect pests. To successfully apply SIT, it is very important to clarify the effect of irradiation on male reproduction in the target pest, because their mating and spermiogenesis abilities affect the success of eradication program. The sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae) is a notorious and worldwide pest of sweet potato. We investigated the effect of irradiation at five doses ranging from 0 (control) to 150 Gy on 9-d-old males. Survival rate of the control (no treatment) remained high from day 10 to 20 of adult life, whereas higher doses of irradiation reduced it, maximally by approximately 70%. Mating rates showed a similar tendency. Radiation dose neither affected sperm production nor sperm transfer at any dose, although spermiogenesis is active during the adult stage. However, radiation dose affected the lifetime total of ejaculated sperm number, likely because of fewer matings by irradiated males. These results suggest that use of a dose of 150 Gy or higher is appropriate for the final step of eradication of this weevil. At least, lower dose of irradiation may arise the inadequate sterilization, resulting in a failure of eradication program. We conclude that weekly release of sweetpotato weevil sterilized with high dose, achieving complete sterilization, could be useful for eradication program after reducing the population by male annihilation method.
Effects of juvenile hormone analogue (methoprene) and 20-hydroxyecdysone on reproduction in Polygonia c-aureum (Lepidoptera: Nymphalidae) in relation to adult diapause
(2017-05) Hiroyoshi, Satoshi; Reddy, Gadi V. P.; Mitsuhashi, Jun
We investigated the effects of juvenile hormone analogue (methoprene) and 20-hydroxyecdysone on female and male reproduction in a nymphalid butterfly, Polygonia c-aureum. This butterfly has a facultative adult diapause controlled by the corpora allata and brain. Methoprene seems to terminate reproductive diapause, although transplantation experiments indicate that the activity of the corpora allata does not affect male mating behavior Endo (Dev Growth Differ 15:1-10, 1973a), suggesting that the brain may be involved in diapause. We found that exposure to methoprene promoted the development of ovaries and of the male accessory glands and simplex. On the other hand, exposure to 20-hydroxyecdysone did not promote the development of female and male reproductive organs and eupyrene sperm movement from the testis to the duplex in the adult stage. Ecdysteroid titer in both sexes was consistently low in adults. These results suggest that imaginal diapause is largely regulated by juvenile hormone in this butterfly.
Effects of pre-overwintering conditions on eupyrene and apyrene spermatogenesis after overwintering in Polygonia c-aureum (Lepidoptera: Nymphalidae)
(2017-07) Hiroyoshi, Satoshi; Yoshimura, Jin; Iwabuchi, Kikuo; Reddy, Gadi V. P.; Mitsuhashi, Jun
Sperm polymorphism is widely known in invertebrates. In insects, Lepidoptera has two types of sperm: nucleated eupyrene (fertile) sperm and anucleated apyrene (unfertile) sperm. These sperm types are produced during post-embryogenesis, and eupyrene spermatogenesis precedes apyrene spermatogenesis. During overwintering, spermatogenesis stops and a portion of undifferentiated-stage spermatocytes degenerate. After overwintering, spermatogenesis restarts with unaffected spermatogonia. However, how new spermatozoa arise in the adult testes after overwintering is not known in Lepidoptera. In this study, we investigated the spermatogenesis events in the nymphalid butterfly Polygonia c-aureum after overwintering under various environmental conditions. Our results indicate that both eupyrene and apyrene spermatogenesis restart at any stopping stage and sperm of these types are regenerated in no particular order after adult insect overwintering. This suggests that the spermatogenesis occurring after overwintering proceeds without embryogenetic restrictions related to the developmental sequence.