Search

A series of 3-oxygenated α-ionone analogs have been developed as highly specific male lures for the solanaceous fruit fly Bactrocera latifrons, a pest of solanaceous fruits. We compared the attractant and phagostimulant activities of analogs with or without (i) unsaturations at the 4,5- and/or 7,8-positions and (ii) oxygen moieties at the 3- and/or 9-positions of the ionone molecule. Since naturally occurring vomifoliol (V2) was found to induce a highly potent phagostimulant activity in B. latifrons males, related analogs including dehydrovomifoliol (V1), 6-hydroxy-α-ionone (U1), and 6-hydroxy-α-ionol (U2) were synthesized to evaluate their attractant and phagostimulant activities. Synthetic V1, V2, U1, and U2 exhibited low attractant activity, but their phagostimulant activity was relatively high. Optical isomers of 3-oxo-7,8-dihydro-α-ionone (P3) and V1 were prepared to examine the stereochemical specificity of attractants. (+)-(6R)-P3 and (+)-(6S)-V1 exhibited the corresponding activities, while their respective antipodal enantiomers were found entirely inactive.

application/pdf, Gamma radiation from isotopic sources has been used in sterile insect technique (SIT) programs worldwide, but it might be difficult to continue using these sources in future SIT programs because of social issues. Therefore, an alternative sterilization source to gamma rays, such as X-rays, needs to be developed. The physical properties of radiation are different between gamma rays and X-rays: for example, X-rays have a shorter penetration depth than gamma rays. Therefore, X-rays may not fully confer male sterility, depending on the target pest insects. The present study investigated whether the West-Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) and the sweetpotato weevil Cylas formicarius (Fabricius) are sterilized by X-rays generated in a low-energy X-ray irradiator, without deterioration of male mating ability, at the doses currently used in the eradication programs for E. postfasciatus (150Gy) and C. formicarius (200Gy) using gamma rays at Okinawa, Japan. The results demonstrated that it is possible to use X-rays in future SIT programs for E. postfasciatus and C. formicarius, because X-ray irradiated males were almost completely sterilized without deterioration of their mating ability. © 2018, The Japanese Society of Applied Entomology and Zoology.

Euscepes postfasciatus (Fairmaire) is an invasive pest of the sweet potato (Ipomoea batatas) and is also parasitic to other wild host plants of the Ipomoea genus. The population density of E. postfasciatus is sometimes greater in Ipomoea pes-caprae L. than in Ipomoea indica (Burm. f.). We investigated the desirability of I. pes-caprae as a host plant for E. postfasciatus in terms of reproductive and developmental potential. Females laid fewer eggs on I. pes-caprae, and the eclosion of their larvae was delayed compared with on I. indica. Furthermore, the larval growth rate was slower on I. pes-caprae than on I. indica. These results suggest that I. pes-caprae is not always the preferred host for egg laying and growth rate in the early developmental stages. However, the larval survival rate after the initial period of development was markedly better on I. pes-caprae than on I. indica. The present simulation study demonstrated that the population density of E. postfasciatus on I. pes-caprae overwhelmed that on I. indica over generations. Comparing the two wild host plant species, I. pes-caprae outweighs I. indica with respect to total population growth, but reproduction on I. indica may be advantageous for the colonization of the new habitat.

The oriental fruit fly and its relatives, Bactrocera dorsalis complex Hendel (Diptera: Tephritidae) were eradicated from the islands of Okinawa Prefecture, southwestern Japan, in 1986. Since just after the eradication, however, re-invasion of B. dorsalis complex has been continuing to date, and the cause of the re-invasion has not been fully analyzed yet. It is believed that there are two possible routes of the re-invasion: wind-borne immigration and importation of infested fruits. This study analyzed the former natural factor by calculating backward trajectories for B. dorsalis complex males caught in monitoring traps from 1986 to 2012. In 65.8 % of the total re-invasion events, trajectories could be traced to at least one of the insect’s native regions: Taiwan (71.8 %), the Philippines (24.3 %) and southern China (3.9 %). In these possible immigration events, the influencing meteorological factors were found to be fronts (44.6 %), typhoons (36.0 %), high-pressure system ridges (12.0 %) and tropical depressions (7.5 %). The number of insects caught per trap was found to greater on the islands near the estimated sources than those further from the sources, supporting the hypothesis of wind-borne immigration of B. dorsalis complex into Okinawa.

Sterile insect technique (SIT) is widely used to eradicate target pest species. Its effectiveness depends on the ability of released sterile males to mate with wild females. In pest species with a female choice mating system, there is potential for female preference to evolve in the wild population in view of the resulting zero-fitness in females that mate with sterile males. The evolution of female preference against sterile males can, therefore, reduce the efficiency of the SIT as the likelihood decreases that sterile males will mate with wild females. We examined this experimentally by using the solanaceous fruit fly Bactrocera latifrons, a serious pest of solanaceous crops, by allowing female preference in mass-reared fruit flies to select between fertile and sterile males over 12 generations. However, this did not generate a rapid evolutionary response. Also the remating rate of females did not increase, even when the first mating partner was a sterile male. We discuss the implication of the results ...

Selection for genetic adaptation might occur whenever an animal colony is maintained in the laboratory. The laboratory adaptation of behavior such as foraging, dispersal ability, and mating competitiveness often causes difficulties in the maintenance of biological control agents and other beneficial organisms used in procedures such as the sterile insect technique (SIT). Sweet potato weevil, Cylas formicarius (Summers) (Coleoptera: Brentidae), is an important pest in sub-tropical and tropical regions. An eradication program targeting C. formicarius using SIT was initiated in Japan with weevils being mass-reared for 95 generations to obtain sufficient sterile males. The mass-reared strain of C. formicarius exhibits weaker female resistance to male mating attempts compared with the wild strain. This could affect the success of SIT programs because mating persistence of mass-reared males might be expected to decrease in response to weak female resistance. We show that high success of sperm transfer to mass-reared females was due to weak female resistance to male mating attempts. However, the mating behavior of mass-reared males did not change. In C. formicarius, the trait of male persistence to mate was not correlated with the female resistance traits. Our results suggest that mass-rearing conditions do not have negative effects on the mating ability of the sterile males of this species, and thus that the current mass-rearing procedures are suitable for production of sterile males for the weevil eradication program.

For ensuring the effectiveness of sterile insect technique (SIT) programmes, maintaining the reproductive competitiveness and dispersal ability of mass-reared sterile males is essential. Inadvertent selection is an important genetic process that frequently occurs during mass rearing to produce sterile males. We investigated the effect of mass-rearing conditions on the responsiveness to sex pheromones and spontaneous flight activity of males of the sweetpotato weevil Cylas formicarius (Coleoptera: Brentidae). There were no significant differences in the responsiveness to sex pheromones and spontaneous flight activity between wild and mass-reared strains. These results indicate that mass-reared strains of C. formicarius might not cause serious problems for implementing SIT programmes.

Behaviour during copulation can alter the fate of sperm of the mating males. This behaviour may exert selective pressure, resulting in the evolution of diverse reproductive behaviour, morphology, and physiology. This study examined the role of female copulatory behaviour on sperm fate in the sweet potato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae). In this species, males mount the female during copulation. The female frequently walks during copulation, carrying the male on her back. Here, we describe and quantify the copulatory behaviour of mating pairs and examine the sperm fate. Insemination success, as determined by the presence of sperm in the spermatheca, was lower when females walked for longer periods during copulation. This result emphasizes the value of studying variation in female copulatory behaviour in order to understand the factors that influence sperm fate. We discuss the implications of these results on sexual selection and utility in programs applying sterile insect techniques.

The West Indian sweet potato weevil Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) is a major pest of sweet potato Ipomoea batatas (L.) in the tropical and subtropical regions. The sterile insect technique (SIT) could be used as one of the most effective methods for suppression or eradication of the weevil. The effectiveness of SIT depends on the ability of the released sterile males to mate with and inseminate wild females. However, the effect of sterile weevils on the fitness of E. postfasciatus has not been evaluated on natural density. Here, we investigated the effect of gamma-irradiated weevil density on the number of weevil progeny. When irradiated weevils were released in numbers equal to those of non-irradiated weevils, the number of progeny was reduced by half of that in the control treatment, and it remained at this state for 2 weeks. Our results show that irradiated weevils ensure adequate and efficient suppression of wild weevils. We conclude that the SIT programs will be employed as effective eradication method for E. postfasciatus.

The sweetpotato weevil Cylas formicarius (Fabricius) (Coleoptera: Brentidae) and West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) are major pests of sweet potato Ipomoea batatas (L.) Lam., in tropical and subtropical regions. Effects of intra- and inter-specific competition on the number of progeny (fecundity), body weight and developmental time of C. formicarius and E. postfasciatus were examined in single- and mixed-species treatments under laboratory conditions. Cylas formicarius tended to outcompete E. postfasciatus, whereas E. postfasciatus rather than C. formicarius tolerated higher conspecific densities. We discuss the implications of the results for pest management and resource partitioning of pestiferous weevils.

The West Indian sweet potato weevil Euscepes postfasciatus (Fairmaire) is a troublesome pest insect of sweet potato that originally came from the Caribbean, but is now expanding its distribution into the Pacific Islands. Although sterile insect techniques have been used against this pest in a demonstration experiment on Kume Island [Ohno et al. (2006) Kontyu to Shizen 41:25–30], effective methods of monitoring E. postfasciatus are scarce. It is necessary to detect the weevils at an early stage of invasion in uninvaded areas, and an attractant trap can be used to achieve this. Thus, we developed an ultraviolet (UV) light-emitting diode trap, invented a method for diffusing the light to attract more insects, and investigated the attractiveness of the light trap to E. postfasciatus under laboratory conditions. Our results indicate that diffused UV light has a higher potential to attract E. postfasciatus than direct UV light. Furthermore, sweet potato is an effective bait to use to capture the weevils attracted by UV light. Thus, E. postfasciatus can be trapped using diffused UV light and sweet potato bait.

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.

When there is an inbreeding depression, mating with a kin individual is generally considered maladaptive behaviour. However, in some conditions, the inclusive fitness benefits from inbreeding may outweigh the costs of inbreeding depression, and thus, inbreeding tolerance is often adaptive. Inbreeding depression and the effect of relatedness on mating behaviour in the West Indian sweet potato weevil Euscepes postfasciatus were examined. No significant inbreeding depression was detected as indicated by body weight and number of progeny emerging from sweet potato roots. Male mating performance (i.e. number of mating occurrences per night) was adversely affected by inbreeding depression, but the effect was low (fitness loss was 6.3%). Although there were no significant differences in latency to mounting, pre-copulatory guarding, copulation and post-copulatory guarding duration between full-sib and non-kin pairs, the copulation rate of full-sib pairs was significantly higher than that of non-kin pairs. These results support the theoretical prediction that when inbreeding depression is weak, copulation with close relative individuals is favoured.

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.

Because life-history theory predicts that risky behaviours such as mating should increase as life expectancy decreases, predatory avoidance is expected to decrease with age. However, this prediction has not been examined. In the present study, the effect of age on death-feigning behaviour, a form of predatory avoidance behaviour in the sweetpotato weevil Cylas formicarius (Summers) (Coleoptera: Brentidae), is investigated by performing a longitudinal study. Because the effects of mating history and age usually cannot be distinguished, mating history is controlled. The results show that only female weevils decrease the investment in death-feigning behaviour with age, whereas male weevils do not show any age-related change. In addition, death-feigning behaviour of mated females is longer than that of virgin females, possibly because additional mating partners would be not needed by mated females.

The sterile insect technique (SIT) is widely used to suppress or eradicate target pest insect populations. Although the effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females, the use of gamma radiation to induce sterility negatively impacts reproductive cells as well as somatic cells. Consequently, sterilization by irradiation drastically diminishes mating performance over time. In the current study, we evaluated the effect of irradiation dose intensity on fertility, mating propensity, and mating competitiveness in sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae), for 16 d after irradiation. Although the mating propensity of males irradiated with 200 Gy, the dose currently used to induce complete sterility of C. f. elegantulus in the SIT program in Okinawa Prefecture, was equal to that of nonirradiated weevils for the first 6 d, the mating propensity of males irradiated with doses between of 75 and 150 Gy was maintained for the first 12 d. The potential fertilization ability of weevils was highly depressed compared with the control weevils, even in those treated with 75 Gy. Mating performance was severely compromised in weevils that were irradiated with a dose of 100 Gy or more. These results demonstrate that partial sterilization can be highly advantageous in eradication programs for the sweetpotato weevil. We discuss the advantages of the application of partial irradiation in insect eradication programs.

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.

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.

The sterile insect technique (SIT) is based on population and behavioral ecology and is widely used to suppress or eradicate target pest insect populations. The effectiveness of SIT depends on the ability of the released sterile males to mate with and inseminate wild females. The use of gamma-radiation to induce sterility is, however, associated with negative impacts not only on reproductive cells but also on somatic cells. Consequently, irradiation for sterilization diminishes mating performance over time. In this study, we evaluated the balance between the irradiation dose and both fertility and mating propensity in Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) for 22 days following irradiation. The mating propensity of males irradiated with a 150-Gy dose, as currently used to induce complete sterility of E. postfasciatus in the SIT program in Okinawa Prefecture, was equal to that of non-irradiated weevils for up to 6 days, and the mating propensity of males irradiated with a dose of 125 Gy was equal to that of non-irradiated weevils for twice this period (12 days). The fertilization ability of weevils irradiated with a dose of 125 Gy was reduced by 4.6% in males and 0.6% in females, compared to the potential fertilization ability. We also discuss the possibility of the application of partially sterilized insects in eradication programs.

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.

The West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) is a major pest of the sweet potato Ipomoea batatas (L.) Lam. and this weevil is a target of an eradication program using the Sterile Insect Technique in Okinawa Prefecture, Japan. Understanding the population ecology is essential in the planning of an eradication program; hence, a host-plant infestation survey and light trap survey have been conducted to monitor the population dynamics of the weevil on Kume Island (Okinawa Prefecture), which is the target area of the trial weevil eradication project. Seasonal tendencies of weevil density were found in these field surveys, but the tendency found in the host-plant infestation survey was not seen every year, and the effectiveness of the light trap is somewhat suspect. To confirm the reliability of the tendency observed in these field surveys, the present study attempted to explain the tendency by a seasonal temperature change using a temperature-based model of weevil population dynamics. The seasonal changes of weevil density differed according to host plants and host-plant fields. The seasonal changes of weevil density inside the host plant Ipomoea indica and outside the host plants in I. indica fields were consistent with those predicted by the model. However, those inside the host plant Ipomoea pes-caprae in the host-plant infestation survey were contrary to the predicted ones, and those observed outside host plants in I. pes-caprae fields by the light trap survey were not in good agreement with the predicted ones. It was concluded that the seasonal change of the weevil density observed in I. indica and I. indica fields can be explained by a seasonal temperature change, but factors other than seasonal temperature change are needed to explain those in I. pes-caprae and I. pes-caprae fields.

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.

The sterile insect technique (SIT) is widely used to suppress or eradicate target insect pest populations. The effectiveness of SIT depends on the ability of the released sterile males to mate with and inseminate wild females. Irradiation is effective for sterilizing mass-reared insects, and the negative impacts of this procedure are not limited to reproductive cell damage. In this study, we evaluated the death-feigning that is considered as an antipredator behavior of male Cylas formicarius (Summers) (Coleoptera: Blentidae) irradiated with 200 Gy, which is the dose used in the SIT program in Okinawa Prefecture. Irradiated male insects were observed in the laboratory for 10 d after irradiation. On d 0, fewer irradiated males feigned death than nonirradiated males. The number of irradiated and nonirradiated males who feigned death and the duration of their death-feigning were about the same from 2 d after irradiation. On the basis of our results, we discuss the optimal release time of irradiated m...

A single distinct EAG-active compound was found in the extract of virgin females of the sweetpotato vine borer moth, Omphisa anastomosalis (Guenee) (Lepidoptera: Crambidae), and was identified as (10E,14E)-10,14-hexadecadienal (E10E14-16:Ald) at ca. 20 ng/female. Minor related compounds were also identified as hexadecanal (16:Ald), (10E)-10-hexadecenal (E10-16:Ald) and (14E)-14-hexadecenal (E14-16:Ald) at 3.1%, 3.0% and 0.7% amounts relative to the EAG-active component, respectively. In the field, more male moths were captured with traps baited with high amounts of E10E14-16:Ald, which confirmed that this compound is a sex pheromone component. The attractiveness was, however, significantly inferior to that of virgin females. The attractiveness did not increase when minor related compounds were added to the compound. Nevertheless, synthetic E10E14-16:Ald should be useful for monitoring field populations of O. anastomosalis.

The species composition of spider mites on crops in Okinawa is peculiar in that Tetranychus okinawanus and T. piercei are dominant on most islands, whereas T. urticae (green form) and T. kanzawai are not. To determine the source plants of Tetranychus species infesting crops, as well as to contribute to our understanding of the cause of this peculiar mite fauna, we collected Tetranychus mites on non-crop plants throughout Okinawa (more than 450 sites on 15 islands) and identified them. Except in the case of T. parakanzawai, the species frequently found on crops tended to occur frequently on non-crop plants, suggesting that the peculiar species composition on crops reflects that also on non-crop plants. T. parakanzawai has been rarely found on crops but frequently found on particular non-crop plants, possibly due to the narrower host range of this species. The type of host plants varied among mite species; for example, T. okinawanus was frequently found on indigenous plants inhabiting the seashore and invasive weeds, T. piercei and T. parakanzawai on inland indigenous plants, T. urticae (green form) on invasive weeds, and T. neocaledonicus on introduced trees. These results are of great significance when considering vegetation control as a tactic for the integrated management of spider mites.

Although there have been numerous studies on the effects of mating history on mating behaviour, few studies have reported the relationship between mating history and other contextual behaviours such as foraging and predator avoidance. We examined the effect of mating history on death-feigning behaviour (an antipredator behaviour) in the sweetpotato weevil. Because mating behaviour can be divided into phases, we examined the effects of encounters with the opposite sex, copulation and insemination success on death-feigning behaviour. For females after copulation and males after multiple copulations the duration of death-feigning behaviour was reduced, whereas encounters with the opposite sex had no effect. Insemination success did not affect the duration of death feigning in males, but inseminated females reduced the duration of death feigning. We discuss the implications of these results for the effect of mating history on this antipredator behaviour.

Irradiation has been widely used in suppression or eradication programs that use the sterile insect technique (SIT) or in studying sperm competition. Although it is well known that irradiation has negative impacts on reproductive (sperm) cells, previous studies have assumed that sperm from irradiated males behave identically to normal sperm in the female reproductive tract after mating. In this study, we used the West Indian sweetpotato weevil Euscepes postfasciatus to investigate the effect of irradiation on the abundance and viability of sperm in female spermatheca for 14 days after copulation. The abundance of sperm in females did not change throughout the experimental period, and sperm viability gradually decreased regardless of irradiation. In this weevil, irradiated sperm appear to behave identically to normal sperm in females for 14 days following irradiation/copulation. Therefore, the effect of irradiation on sperm viability within the female spermatheca is considered to be insignificant.

The West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) is a major pest of sweetpotato Ipomoea batatas (L.) Lam (Solanales: Convolvulaceae) in some countries. In order to improve mass-rearing for an eradication program employing the sterile insect technique (SIT), optimal population density of E. postfasciatus in an artificial diet was examined. Six population densities (1000, 4000, 7000, 10000, 13000, and 16000 individuals per container with 200 g of artificial diet) were compared for effect on the number of eggs collected and hatchability. The total number of eggs collected after 24 d increased with an increase in population density and reached a saturation level at 13,000 individuals, whereas hatchability was not affected by population density. The results indicated that optimal population density in mass rearing was 13,000 individuals on 200 g of artificial diet. Furthermore, we examined cannibalism by adult weevils in the presence of other diets. The...

Because multiple mating by females encourages sperm competition, the assessment of female mating status before insemination is important for males in order to avoid the risk of sperm competition or to intensify sperm competition. When interacting with females before sperm transfer, males can alter their mating tactics according to the risk or intensity of sperm competition. Information on how mating systems are associated with sperm competition is essential for sterile insect technique eradication programs, which depend on successful mating of released sterile males with wild females. We tested whether males of the West Indian sweetpotato weevil, Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae), adjusted their mating behavior in response to female mating experience and/or age. As virgin/young female weevils accepted males more easily than non-virgin/old females, assessing females before insemination can be adaptive for male weevils. We found that E. postfasciatus males were unable to adjust their mating tactics in response to female mating status. Although this mating strategy would be costly for individual male weevils, the ability in males to discriminate female mating status can prevent the chance of mating with already-mated females containing the sperm of wild male(s). Therefore, the mating tactics of male E. postfasciatus are advantageous for sterile insect technique eradication programs.

The effect of irradiation on the dispersal ability of males and females of the flightless West Indian sweetpotato weevil, Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae), a major sweet potato pest, was examined in the field using mark–release–recapture techniques. To evaluate the dispersal ability of the weevil, we released 7 619 weevils in two replicates (July and August 2007). Each replicate lasted 5 days from release to sampling and consisted of one weevil release and two weevil samplings. Thirty-two traps were placed in lines corresponding to eight compass directions and in four distance classes (8, 12, 16, and 20 m) in each replicate. We captured 709 (9.3%) weevils in the two replicates. Weevils dispersed at least 20 m from the release point in 2 days, regardless of sex or irradiation. Dispersal was strongly affected by wind direction, and in both replicates most weevils were recaptured in upwind directions. The mean dispersal distance for non-irradiated weevils was about 11 m per 2 days. Although there were some differences between sexes in recapture rate and dispersal distance, there was no consistent difference between irradiated and non-irradiated weevils in dispersal distance. We conclude that irradiation does not affect the dispersal ability of flightless E. postfasciatus in the field.

To establish a simple method for discriminating Okinawa and Ogasawara strains of the sweet potato weevil, Cylas formicarius, about 560 bp of the internal transcribed spacer-1 (ITS-1) region of the ribosomal DNA (rDNA) of C. formicarius was collected from several islands of Okinawa Prefecture and Ogasawara Islands and analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The 345 weevils collected in Okinawa and Ogasawara were discriminated correctly by the RFLP patterns with the restriction enzyme RsaI. The results suggest that C. formicarius originating from Ogasawara Islands is an effective genetic marking strain for an eradication project using the sterile insect technique implemented by the Okinawa prefectural government.

The re-invasion of Okinawa by the Bactrocera dorsalis complex (oriental fruit fly and its relatives) after its eradication was comprehensively documented for the first time. From 1987 to 2008, more than 300 adult flies were captured by monitoring traps baited with methyl eugenol, showing frequent re-invasion. During this period, re-colonization (detection of infested fruits) occurred six times; in all cases the flies were successfully re-eradicated by countermeasures (mainly male annihilation method). This indicates that the oriental fruit fly problem in Japan has not been resolved and that the flies should be monitored and counteracted continuously. By summarizing the re-invasion data, we found interesting geographical patterns. Adults were more frequently trapped in the southern area (Sakishima Islands, SI), while colonization occurred more frequently in the northern area (Okinawa Islands, OI). Annual trap catches increased in SI, but not in OI. In SI, adults were trapped most frequently in summer, whereas peak catches in OI were observed in autumn. These results demonstrate that the invasion pattern in OI is independent from that in SI. One possible explanation for the observed geographical differences is that it reflects the difference in invasion causes.

To use elytral color morphs of Cylas formicarius as a genetic marker in its eradication using the sterile insect technique, the geographic distribution of the morphs was examined in the three main infested areas of Japan (Central Ryukyus, Southern Ryukyus, and Ogasawara Islands). In addition to the two known color morphs in Japan (bluish elytra (BE) and greenish elytra (GE)), the piceous elytra (PE) was found mainly in the Southern Ryukyus at low frequency. The color morph frequencies varied between the Central and Southern Ryukyus and between locations within the two areas, while only BE was found in the Ogasawara Islands. PE would be useful for genetically marking sterile weevils to be released. Similarly, GE would be useful in some islands where GE is rarely or not found. BE frequencies on two islands in the Central Ryukyus (Amami and Okinawa) and two islands in the Southern Ryukyus (Miyako and Ishigaki) in 2006–2007 were higher than in 2002–2003.

The sterile insect technique (SIT) is widely used for suppressing or eradicating target pest insect populations. The effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females. Irradiation not only damages the reproductive cells but the somatic cells as well. The mating behavior of irradiated males may be altered over time due to the depressed metabolic activity brought about by sterilization. In this study, we evaluated the mating behavior (copulation behavior, mating performance, and ability of sperm transfer) of irradiated males in Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) for 16 days after irradiation in the laboratory. The mating performance of males irradiated with a 150 Gy dose, as currently used in the SIT program in Okinawa prefecture for E. postfasciatus, decreased compared to that of control after day 7. As a result, we considered that irradiation had no major effect on male mating behavior for approximately 1 week after irradiation.

In 1998, several males of Bactrocera tau, a common pest fruit fly in Asia, were captured on Ishigaki Island, Okinawa, by a trap set for monitoring the melon fly (B. cucurbitae) invasion. In 2003, one male was trapped again. We collected vast amounts of host fruit of B. tau on Ishigaki, but could not confirm infestation by this species. These results indicated that B. tau had invaded Ishigaki at least twice but failed to colonize. B. tau may have come from Taiwan, considering its geographic proximity to Ishigaki and the abundance of the species in Taiwan. The invasions could not be fully explained by natural factors alone; it was possible that human-induced means were also involved. We believe that this species can colonize Okinawa, since the host plants are abundant year-round, a potential competitor, B. cucurbitae, is not currently present, and Okinawa is located south of the northern limit of B. tau. Since B. tau has a host range and population growth capacity similar to B. cucurbitae, the species could cause severe damage to crops in Okinawa, much like that caused by B. cucurbitae in the past. We must remain alert for possible re-invasion by B. tau.

In the mass rearing of Euscepes postfasciatus using artificial diets, a method for estimating the number of eggs is essential for monitoring egg-collection efficiency and controlling egg-seeding density on the diets. To develop a simple method, we first analyzed the relationship between the volumes of eggs aspirated into a 1- or 2-ml measuring pipette and the number of eggs in it. A significant difference in the pattern of increase in egg number, along with the increase of volume, was found between the two pipette types. Linear and quadratic regressions fitted well for the 1- and 2-ml pipette data, respectively (R2>0.97). To extend the egg-number estimation to a larger quantity of eggs, we performed similar analyses using a 5-ml measuring cylinder. Here, the number of eggs contained was determined using the above measuring pipettes and regressions. A linear regression of the estimated number of eggs on volume fitted well (R2=0.99). The results show that the number of E. postfasciatus eggs can be estimated precisely using measuring pipettes or cylinders. This study also showed that the pattern of increase in egg number differs depending on the measuring equipment, which should be considered for establishing egg-number estimation methods for other insects.

The West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) is a major pest of the sweet potato Ipomoea batatas (L.) Lam (Solanales: Convolvulaceae) in some countries. In order to improve the mass-rearing systems involved in an eradication program employing the sterile insect technique (SIT), we improved the efficiency of the method used for collecting adult weevils from artificial larval diets; this was done by using the combination of a sieve and Tullgren apparatus. Using this combination, we could collect 95.4% of weevils from artificial diets. Furthermore, the time spent in collection with this method was approximately one-fifth of that spent with the existing hand-sorting method. These results showed that this new collection method will improve the efficiency of mass rearing of West Indian sweetpotato weevils.

The mating success of mass-reared and individually marked melon flies, Bactrocera cucurbitae (Coquillett), was observed during 7 d under 2 different densities in the laboratory. Frequency distribution of mating success of individual males under the low density was clumpy, but that of males under the high density was random. This difference seemed to result from disturbance among individuals under high density, where males could not make their territories. As mating frequency of females showed random or repulsed distributions in the 2 densities, all females seemed to mate at similar frequencies. Adult size was not related to mating success in either sex under the 2 densities. The characteristics of mating success in mass-reared melon flies for sterile insect techniques were considered to be related to extremely high adult rearing density.

The sterile insect technique (SIT) is widely used for suppressing or eradicating target pest insect populations. In the eradication programs using the SIT, a large number of sterile insects are marked and released in the field. In Japan, Cylas fonnrmicarius (F.) group (Coleoptera: Brentidae) weevils are marked with a fluorescent powder dye to monitor the progress of such programs. However, this monitoring technique is not fully effective because of the disappearance or contamination of the dye. Therefore, an alternative marking method is required. Currently, a rare color morph such as piceous elytra (PE) is used for visible marking of C. formicarius group weevils. A PE-monomorphic strain has previously been established by artificial selection from a small locally distributed population; this can lead to reduced survival and genetic changes in behavioral traits due to inbreeding depression. In this study, we evaluated the survival rate and mating behavior of PE males of C. formicarius group. The characteristics of the PE males were similar to those of the wild strain (WS) males. Thus, we considered that PE males were suitable for visible marking in the eradication programs using the SIT.

The number of West Indian sweet potato weevils, Euscepes postfasciatus, being mass-reared in a facility for use in sterile insect technique (SIT) eradication programs has undergone a drastic reduction. A neogregarine protozoan pathogen Farinocystis sp. (an undescribed species) was detected in vivo in the mass-reared E. postfasciatus. We investigated the effects of this disease on the longevity and fecundity of host weevils and the incubation time of the disease in the host body under mass-rearing conditions. Our results demonstrated that infection by this Farinocystis sp. decreased both longevity and fecundity in E. postfasciatus. In particular, the pathogen severely limited the production of progeny by infected females compared to healthy females. Therefore, we consider this protozoan infection to be the major cause of the decreased E. postfasciatus production in the mass-rearing facility.