Ryukyu Sankei Corporation

Tomigusuku, Japan

Ryukyu Sankei Corporation

Tomigusuku, Japan
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Teruya K.,Okinawa Prefectural Plant Protection Center | Ohishi T.,Okinawa Prefectural Plant Protection Center | Turui K.,Ryukyu Sankei Co. | Turui K.,University of Ryukyus
Japanese Journal of Applied Entomology and Zoology | Year: 2017

Prevention or reduction of infection by the neogregarine parasite Farinocystis sp. is indispensable for effective mass-production of the West Indian sweet potato weevil Euscepes postfasciatus (Fairmaire). The established method of weevil collection, coercively drawing weevils from the larval rearing cage, was suspected to increase the risk of breaking infected individuals, which causes horizontal transmission of the parasite to uninfected individuals. Here, we developed a novel collection method in which the weevils were permitted to spontaneously leave the larval rearing cage. The significant decrease in infection rate and the significant increase in the fecundity of weevils collected by the novel method suggested that this method may improve the mass-production of weevils.


Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Co. | Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Co. | 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.


Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Co. | Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Co. | 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.


Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Co. | Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Co. | 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.


Kuriwada T.,Okinawa Prefectoral Plant Protection Center | Kuriwada T.,Ryukyu Sankei Co. | Kumano N.,Okinawa Prefectoral Plant Protection Center | Kumano N.,Ryukyu Sankei Co. | And 3 more authors.
Journal of Economic Entomology | Year: 2010

Inadvertent selection is an important genetic process that frequently occurs during laboratory culture and maintenance of biological control agents and other beneficial organisms used in procedures such as the sterile insect technique (SIT). We investigated effects of mass rearing and inbreeding depression on life history traits (number of progeny emerging from host plants, body weight, developmental period, and starvation tolerance) in the sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Brentidae). The effect of inbreeding was measured by comparing the results obtained from the full-sib crosses with those obtained from nonkin crosses in both wild and mass-reared strains. The mass-reared strain had more progeny than the wild strain. The developmental period of mass-reared strain was shorter than that of the wild strain. Other traits did not differ significantly between strains. We detected inbreeding depression effects on numbers of progeny, and the effects were more pronounced in the mass-reared strain. Hence, laboratory adaptation to mass rearing can produce changes in important biological attributes of sweetpotato weevils. © 2010 Entomological Society of America.


Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Co. | Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Co. | 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.


Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Co. | Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Co. | And 3 more authors.
Journal of Pest Science | Year: 2011

In sterile insect technique (SIT) programs, the released sterile males are important for their effectiveness. The use of sex pheromones to collect males is economical; however, pre-exposure to sex pheromones may affect male mating behavior, and would thus reduce the effectiveness of the SIT programs. Males exposed to sex pheromone may become attractive to other males due to pheromone adsorption on their body impregnation, prevent mating and reduce the dispersal of sterile males. We examined the effect of pre-exposure to sex pheromone on the mating behavior of male sweetpotato weevil Cylas formicarius. Pre-exposure to high-dose sex pheromone for 24 h did not affect the male mating behavior of C. formicarius, and the exposed males did not attract other males. These results suggest that male C. formicarius that were collected from a mass-rearing facility using sex pheromone can be effectively used in SIT programs. © 2010 Springer-Verlag.


Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Co. | Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Co. | And 3 more authors.
Applied Entomology and Zoology | Year: 2012

The effectiveness of the sterile insect technique (SIT) depends on the ability of released sterile males to mate with and inseminate wild females, but the use of gamma radiation to induce sterility negatively affects both somatic and reproductive cells of the sterilized insects. Recently, the effectiveness of fractionated-dose irradiation (FI), in which a sterilizing dose is delivered over time in a series of small irradiations, has been demonstrated in the West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire). FI improves male mating propensity compared with acute irradiation; however, this renewed technique takes a long time (72 h in the present circumstances) compared with the traditional technique (approximately 20 min) using single-dose irradiation (150 Gy) to fully sterilize this weevil. The extra time required by FI might negatively affect the quality of released sterile males, because weevils expend limited resources, such as metabolic energy or sperm, in mating freely in this period. We evaluated whether the temporal storage of weevils at low temperature (5°C and 15°C) improves the quality of sterile males compared with the normal condition (25°C). Temporal storage at low temperature in FI improves male mating propensity. For example, the sexually active phase of males exposed to 15°C was 18 days at least after irradiation. This period was longer than that of normal males (14 days). Meanwhile, this manner delayed male reproductive development and temporarily reduced mating competitiveness ability. If considering the long active phase of sterile males exposed to 15°C, these disadvantage would be cancelled out. We discuss the advantage of FI with temporal storage at low temperature in the eradication program using SIT for E. postfasciatus. © 2011 The Japanese Society of Applied Entomology and Zoology.


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.


Kuriwada T.,Okinawa Prefectural Plant Protection Center | Kuriwada T.,Ryukyu Sankei Co. | Kumano N.,Okinawa Prefectural Plant Protection Center | Kumano N.,Ryukyu Sankei Co. | And 3 more authors.
Journal of Applied Entomology | Year: 2010

The aim of our study was to examine the effect of mass-rearing, in which there is no exposure to predators, on antipredator traits of insects for improving sterile insect technique programs. The duration of death-feigning (antipredator behaviour) in sweet potato weevil Cylas formicarius (Summers) (Coleoptera: Brentidae) after mass-rearing for 71 generations were compared with those in wild strain. There was no significant difference in the duration of death-feigning between wild and mass-reared strains. This indicated that the death-feigning behaviour of mass-reared strain was maintained for 71 generations even in the absence of predators. We discuss the reasons why death-feigning behaviour is maintained after mass-rearing. © 2009 Blackwell Verlag, GmbH.

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