The female Euscepes postfasciatus refractory period is induced by the male but length is determined by the female.

Females of many animals mate multiple times during their lives (i.e., polyandry). The period between matings (mating interval) is called the refractory period (RP). In the West Indian sweet potato weevil (Euscepes postfasciatus), males use the ejaculate to induce the RP in females to prevent re-mating. By measuring the RP, a large variation of 1-49 days was observed. This variation may be due to the males (ejaculate quantity and quality) and females (ejaculate sensitivity/degradation ability and body size) and their interactions, but the exact mechanisms are currently unclear. Here, we investigated a tendency towards a particular female RP duration and the associated traits of males and females to test the following three factors responsible for variation in the length of the RP: male manipulation of ejaculate volume, individual differences in male ejaculation substances, and ejaculate sensitivity/degradation ability in females. We prepared virgin males and females to create mating pairs. The following day, another mate was introduced to the females, and the first RP was measured. The same procedure was used for measuring the second RP. The males were also provided with another female (second female), mated, and then the RP of the second female was measured. In addition, the relationship between the length of the RP and female fitness was investigated. The results showed that there was a significant positive correlation between the first and second RP in the focal females, while no significant correlation was observed between the RP of the first and second females induced by the same male. It was also found that the length of the RP did not affect female fitness. This indicated that the males did not adaptively manipulate ejaculation volume depending on the quality of the females, and variance in the length of the RP may be explained by variation in the female physiological ability against ejaculate.

Effects of Larval Diet on the Male Reproductive Traits in the West Indian Sweet Potato Weevils Euscepes postfasciatus (Coleoptera: Curculionidae).

Larval diet significantly affects adult traits, although less is known about how they affect reproductive traits. Males of West Indian sweet potato weevil Euscepes postfasciatus deliver a remating inhibitor along with sperm to their mates during mating, leading to a refractory period (the period before females mate again). Crossing experiments were conducted using lines reared on artificial diets, including sweet potato powder (AD) or sweet potato tubers (SP) during the larval stage, and the refractory period was examined. We also examined whether the larval diet qualitatively or quantitatively altered male ejaculate. The results showed that the refractory period was significantly longer in the SP treatment than in the AD treatment for males and females. There was no significant difference in ejaculate volume. However, the number of sperm in the testes-seminal vesicles complex was significantly higher in the SP treatment. Additionally, SDS-PAGE revealed that the ejaculate was qualitatively different depending on the larval diet, and one protein of approximately 15 kDa in size was expressed only in the SP treatments. Revealing how larval diet affects reproductive traits in adult males will help shed light on the diverse evolution of insect mating systems and reproductive behavior.

Reproduction-related interactions and loads induce continuous turn alternation leading to linearity in a terrestrial isopod.

Turn alternation (TA) is the tendency to turn in the opposite direction of an immediately preceding turn when moving forward, resulting in an overall linear trajectory. TA has been observed in many animals, and terrestrial isopods are considered model organisms for studying TA. Optimizing their fleeing speed and trajectory helps isopods efficiently escape from predatory threats. However, since reproduction induces morphological and physiological changes, individuals might adjust their trajectories depending on their altered mobility. In this study, we investigated the effect of reproduction-related factors on the frequency of TA, which enables linearity, in the common rough woodlouse Porcellio scaber. The results showed that breeding females enhanced their linearity more than nonbreeding females and males. Furthermore, females without access to a potential mate enhanced their linearity more than females and males with access to a potential mate and maintained a high linearity for approximately 40 days. In terrestrial isopods, continuous TA for linearity may be used to avoid reproductive failure because of lack of encounters with the potential mate or to compensate for low running ability due to physical or physiological loads. Conversely, individuals that do not need to worry about reproductive failures or individuals with small loads could perform the random turn that does not require learning or memory. This is the first study to show that the events involved in reproduction affect the linearity shown by continuous TA in terrestrial isopods.

Female Marking via Rubidium-Labeled Ejaculates in the West Indian Sweetpotato Weevil (Coleoptera: Curculionidae).

The West Indian sweetpotato weevil, Euscepes postfasciatus (Fairmaire), is one of the pests of the sweet potato, Ipomoea batatas, in tropical and subtropical countries. Although an eradication program using the sterile insect technique (SIT) for this weevil is now underway in Japan, the lack of potent attractants such as sex pheromones for this weevil species prevents effective monitoring and hampers pest control operations. New methods to monitor the performance of sterile males using trapped wild females are needed. In this study, we tested whether the ejaculate of the labeled males that were fed an artificial diet labeled with the trace element, rubidium (Rb), is detectable in the fertilized females. We fed an artificial diet treated with Rb (1.00, 0.50, 0.25, and 0.00%) to adult male weevils for 14 d after emerging and quantified the rubidium content in inseminated females. We also examined the side effects of the artificial diet on mating performance and longevity. The advantages of monitoring the spatial level of sterility using data from females labeled with ejaculate of Rb-fed males in an SIT eradication program are discussed.

When a male perceives a female: the effect of waxy components on the body surface on decision-making in the invasive pest weevil.

Insects use various semiochemicals for sexual communication and mate recognition; these can therefore be used to govern the behaviours of harmful pest species, and several candidate chemicals have been explored for this purpose. For the West Indian sweet potato weevil, Euscepes postfasciatus, which is one of the most serious pests of sweet potato, no effective capture techniques, such as sex pheromone lures, exist. Toward exploring promising procedures for monitoring these weevils, we assessed the effect of secretions on the body surface on the recognition of congeners and on courtship behaviour in the weevils. Our study clearly demonstrated that weevils responded to extracts from the body surface, and the behaviour adopted by the weevils varied significantly depending on the condition of the extracts. Furthermore, we found a significantly prolonged retention time for males on glass beads covered with extracts of females based on survival analysis. These findings are, as far as we are aware, the first to show the effect of lipid components of the body surface on decision-making in these economically important pest weevils.

Killing two bugs with one stone: a perspective for targeting multiple pest species by incorporating reproductive interference into sterile insect technique.

The sterile insect technique is an environmentally friendly method to control and even eradicate agricultural and veterinary insect pests without using chemical pesticides in excess. However, the continuous production and release of sterile insects is economically costly and eradication programs using sterile insects have not always been successful owing to the incomplete mating ability of the sterile insects. Here we focus on the theory and empirical findings of interspecific negative mating interaction, known as reproductive interference, to develop a more cost-effective and value-added pest management program. We suggest that sterile insects can be used for simultaneous control of both wild-type conspecifics and closely related pest species by taking advantage of the fact that, when species recognition abilities are incomplete, courtship and mating are often misdirected toward heterospecies. This new approach might help mitigate economic damage and human health crises caused by pest insects. © 2018 Society of Chemical Industry.

The complete mitochondrial genome of the bumblebee, Bombus hypocrita sapporensis (Insecta: Hymenoptera: Apidae) from Hokkaido Island, Japan.

The complete is mitochondrial genome of the Japanese bumblebee Bombus hypocrita sapporensis from Hokkaido Island, Japan is analysed using next generation sequencing. The mitochondrial genome of B. h. sapporensis was observed to be a circular molecule of 15,835 bp. The average AT content in the B. h. sapporensis mitochondrial genome was 85.53%. It was predicted to contain 13 protein-coding genes (PCGs), 22 tRNA genes, and two rRNA genes, along with one A + T-rich control region. The PCGs had ATA, ATG, or ATT as the initiation codon and were terminated by the typical stop codon TAA, except for Cytb. All the tRNA genes typically formed a cloverleaf secondary structure, except for trnE, trnF, and trnS1. The molecular phylogenetic analysis indicated that the B. h. sapporensis from Hokkaido Island population was most similar to that of the geographically isolated B. h. sapporensis from Rebun Island.

Is elytral color polymorphism in sweetpotato weevil (Coleoptera: Brentidae) a visible marker for sterile insect technique? Comparison of male mating behavior.

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.

Biological role of Nardonella endosymbiont in its weevil host.

Weevils constitute the most species-rich animal group with over 60,000 described species, many of which possess specialized symbiotic organs and harbor bacterial endosymbionts. Among the diverse microbial associates of weevils, Nardonella spp. represent the most ancient and widespread endosymbiont lineage, having co-speciated with the host weevils for over 125 million years. Thus far, however, no empirical work on the role of Nardonella for weevil biology has been reported. Here we investigated the biological role of the Nardonella endosymbiont for the West Indian sweet potato weevil, Euscepes postfasciatus. This insect is an experimentally tractable pest insect that can easily be reared on a natural diet of sweet potato root as well as on an agar-based artificial diet. By larval feeding on an antibiotic-containing artificial diet, Nardonella infection was effectively eliminated from the treated insects. The antibiotic-treated insects exhibited significantly lighter body weight and lower growth rate than the control insects. Then, the antibiotic-treated insects and the control insects were respectively allowed to mate and oviposit on fresh sweet potatoes without the antibiotic. The offspring of the antibiotic-treated insects, which were all Nardonella-negative, exhibited significantly lighter body weight, smaller body size, lower growth rate and paler body color in comparison with the offspring of the control insects, which were all Nardonella-positive. In conclusion, the Nardonella endosymbiont is involved in normal growth and development of the host weevil. The biological role of the endosymbiont probably underlies the long-lasting host-symbiont co-speciation in the evolutionary course of weevils.

The neogregarine protozoan Farinocystis sp. reduces longevity and fecundity in the West Indian sweet potato weevil, Euscepes postfasciatus (Fairmaire).

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.

Sperm storage and viability within females of Euscepes postfasciatus: effect of irradiation on sperm abundance and viability within female.

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.

Effect of irradiation on dispersal ability of male sweetpotato weevils (Coleoptera: Brentidae) in the field.

We used the mark-and-recapture method in the field to test the effect of gamma radiation on the dispersal ability of the male sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Brentidae), a serious sweetpotato pest in Japan. To evaluate the dispersal ability of male sweetpotato weevil, we released 27,218 males (13,302 males irradiated with a dose of 200 Gy and 13,916 nonirradiated males) in two replications (September and October 2005). Each replication lasted 5 d from the release of weevils to the removal of traps, and male weevils were released twice (1 and 3 d before trap setting). Forty pheromone traps were placed in lines corresponding to eight compass directions and five distance classes (20, 50,100, 200, and 500 m) in each replication. We captured 2,263 irradiated males (17.0%) and 2,007 nonirradiated males (14.4%) in the two replications. Six irradiated and eight nonirradiated males were captured in the traps 500 m far from the release point. All parameters to evaluate the dispersal ability of irradiated male sweetpotato weevil (recapture rate, dispersal distance, and dispersal direction) were similar to nonirradiated males in three of the four trials. However, parameters were different between irradiated males and nonirradiated males in one trial. Because the majority of parameters consistently show that the similarity of the dispersal ability, we considered that male sweetpotato weevil irradiated with a dose of 200 Gy possessed equal dispersal ability to that of nonirradiated males in the field.