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Tomigusuku, Japan

Teruya K.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Corporation | Kumano N.,The University of Okinawa
Japanese Journal of Applied Entomology and Zoology | Year: 2015

A lot of sterile males need to be released continuously in the target area in the sterile insect technique (SIT). Therefore, mass-rearing of the target pest insects is indispensable for SIT programs. The West Indian sweet potato weevil, Euscepes postfasciatus, has been maintained for over 44 generations (~ 8 years) for its eradication program in the Okinawa Prefectural Plant Protection Center (Naha, Okinawa, Japan). The selective pressures under mass-rearing conditions are likely to be very different from those of wild ones. The specific selective pressures over many generations under mass-rearing conditions would adversely affect the reproductive capacity of mass-reared insects. Therefore, evaluation of the mating performance of mass-reared males compared with that of wild ones is indispensable in SIT eradication programs. Although we compared mating performance with respect to four reproductive characteristics (duration of mating behavior, mating success, mating competitiveness ability and number of transferred sperm in female spermatheca during copulation) between mass-reared and wild males in E. postfasciatus, there was no evidence that the mass-reared males were inferior to the wild males in terms of mating performance. Thus, we considered that the mass-rearing procedure for at least 44 generations did not adversely influence the male mating activity in E. postfasciatus. Source


Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Corporation | Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Corporation | And 4 more authors.
Entomologia Experimentalis et Applicata | Year: 2011

The sterile insect technique (SIT), based on the principles of population and behavioral ecology, is widely used to suppress or eradicate target pest insect populations. The effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females; however, the use of gamma radiation to induce sterility negatively affects both somatic cells as well as reproductive cells. Consequently, sterilization by irradiation drastically diminishes mating performance over time. It is well known that fractionated-dose irradiation, in which a sterilizing dose is delivered via a series of smaller irradiations, reduces radiation damage. In the present study, we evaluated the effect of fractionated-dose irradiation on fertility, longevity, and mating propensity in Cylas formicarius (Summers) (Coleoptera: Brentidae) for 16days after irradiation. Fractionated-dose irradiation with 200Gy induced full sterility regardless of the number of radiation doses. Although the mating propensity of males sterilized by a single 200Gy dose (the current standard of the Okinawa Prefecture SIT program) was equal to that of non-irradiated weevils for the first 6days, the mating propensity of males sterilized by a series of three doses was maintained for at least the first 12days. These results demonstrated that fractionated-dose irradiation can be highly advantageous in C. formicarius eradication programs. © 2011 The Authors. Entomologia Experimentalis et Applicata © 2011 The Netherlands Entomological Society. Source


Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Corporation | Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Corporation | And 4 more authors.
Population Ecology | Year: 2011

Persistent mating attempts by males (sexual harassment) are frequently observed among animals. For females, resisting persistent males can be costly because vigorous resistance increases both energy expenditure and the possibility of injury. Although one tactic for coping with male harassment is to cease resistance and mate with the persistent partner, the females of several species are able to prevent the fertilization of their egg(s) despite copulation. In this study, we used three different sex ratios to investigate whether a male's mating persistence affects his mating success in the West Indian sweet potato weevil Euscepes postfasciatus, in which males mount females both before and after copulation. Consistent with our predictions, we found that female weevils resist and manipulate sperm transfer either before or during copulation according to their preferences. Female weevils were able to reject the sperm of persistent males despite having copulated with them. However, neither copulation and/or post-copulatory mounting affected insemination success. We speculate that the intensive resistance shown by females before copulation may induce mechanical sterility in E. postfasciatus. © 2010 The Society of Population Ecology and Springer. Source


Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Corporation | Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Corporation | And 4 more authors.
Entomologia Experimentalis et Applicata | Year: 2010

Male body size is considered to be one of the major determinants of mating success among many insect species. Because the effectiveness of the sterile insect technique (SIT) depends on the ability of released sterile males to mate with and inseminate wild females, it is indispensable to understand the effect of male body size on the mating behavior of both sexes for the progress of the SIT program. We investigated how male body size and the presence of other rival males affect the guarding and copulatory durations of the West Indian sweetpotato weevil, . Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae). In this species, males guard females before and after copulation. By observing the mating behavior under two sex-ratio conditions (male-to-female ratios of 1:1 and 2:1), we found that small males hastened to court females when rival males were present, but the females rejected these small males as mates. Therefore, we consider that female weevils adopt a counter-adaptation for mate preference in response to this male mating strategy. Body size did not affect the durations of copulation and post-copulatory guarding. Although we found a conditional mating strategy for body size in . E. postfasciatus, it is unlikely to have a large influence on the weevil-eradication program using SIT. © 2010 The Authors. Journal compilation © 2010 The Netherlands Entomological Society. Source


Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Corporation | Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Corporation | And 3 more authors.
Behavioral Ecology and Sociobiology | Year: 2011

Inadvertent selection is an important genetic process that frequently occurs during laboratory culture. The mass-reared strain of the sweet potato weevil Cylas formicarius exhibits stronger inbreeding depression than the wild strain does. When inbreeding depression occurs in a population, mating with a close relative is often considered maladaptive; however, in some contexts, the inclusive fitness benefits of inbreeding may outweigh the costs, favoring individuals that tolerate a low level of inbreeding depression. Theory predicts that mass-reared strain weevils will avoid inbreeding while wild strain weevils will tolerate inbreeding. To examine this prediction, we compared the effect of relatedness on the mating and insemination successes in mass-reared and wild strains of C. formicarius. While close relative pairs of the wild strain copulated less frequently than non-kin pairs, almost all mass-reared strain pairs copulated irrespective of relatedness. The results showed that the strain with weak inbreeding depression (wild strain) avoided inbreeding, whereas the strain with strong inbreeding depression (mass-reared strain) tolerated inbreeding. The contradiction between the theoretical prediction and our results is discussed from the perspective of laboratory adaptation, mating systems, and life history of C. formicarius. © 2011 Springer-Verlag. Source

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