Female mating receptivity inhibited by injection of male-derived extracts in Callosobruchus chinensis

A novel male accessory gland peptide reduces female post-mating receptivity in the brown planthopper

Mating in insects commonly induces a profound change in the physiology and behavior of the female that serves to secure numerous and viable offspring, and to ensure paternity for the male by reducing receptivity of the female to further mating attempts. Here, we set out to characterize the post-mating response (PMR) in a pest insect, the brown planthopper Nilaparvata lugens and to identify a functional analog of sex peptide and/or other seminal fluid factors that contribute to the PMR in Drosophila. We find that N. lugens display a distinct PMR that lasts for about 4 days and includes a change in female behavior with decreased receptivity to males and increased oviposition. Extract from male accessory glands (MAG) injected into virgin females triggers a similar PMR, lasting about 24h. Since sex peptide does not exist in N. lugens, we screened for candidate mediators by performing a transcriptional and proteomics analysis of MAG extract. We identified a novel 51 amino acid peptide present only in the MAG and not in female N. lugens. This peptide, that we designate maccessin (macc), affects the female PMR. Females mated by males with macc knockdown display receptivity to wild type males in a second mating, which does not occur in controls. However, oviposition is not affected. Injection of recombinant macc reduces female receptivity, with no effect on oviposition. Thus, macc is an important seminal fluid peptide that affects the PMR of N. lugens. Our analysis suggests that the gene encoding the macc precursor is restricted to species closely related to N. lugens.

Male seminal fluid allocation according to socio-sexual context in the South American fruit fly

During copulation male insects transfer sperm and seminal fluids, including accessory gland proteins (Acps) to females, produced in the accessory glands (AGs). These Acps influence female behavior and physiology, inhibiting sexual receptivity, promoting ovulation and/or oviposition. The theory of ejaculate allocation postulates that production is costly; therefore, males strategically allocate ejaculates based on perception of sperm competition and quality and availability of females. The objective of this study was to determine in the South American fruit fly Anastrepha fraterculus whether there is differential allocation of Acps by males under different social contexts: (i) presence or absence of males in the mating arena (male social context), (ii) presence/absence of females in the mating arena (female social context), and (iii) female condition (sugar-fed/protein-fed). This was inferred through female behavior (fecundity, fertility and remating) and the dynamics of the reduction in male AGs size and protein content after copulation. No effect was observed from the various social contexts perceived by males on female's fecundity, fertility, or remating. Mated males had less protein in their AGs compared to unmated males. Male social context affected AG size after copulation: there was a marked decrease in AG size in males which mated in the presence of rival males; moreover, males mated under competition had lower protein content in their AGs than males mating without competition, suggesting that males can adjust seminal fluid quantity depending on social-mating context, although this difference did not impact the physiology and behavior of females after copulation. Our results also indicate that AG size and protein content are correlated.

Female-limited responses in remating rate and mating duration in the experimental evolution of a beetle Callosobruchus chinensis

Mating rate optima often differ between the sexes: males may increase their fitness by multiple mating, but for females multiple mating confers little benefit and can often be costly (especially in taxa without nuptial gifts or mala parental care). Sexually antagonistic evolution is thus expected in traits related to mating rates under sexual selection. This prediction has been tested by multiple studies that applied experimental evolution technique, which is a powerful tool to directly examine the evolutionary consequences of selection. Yet, the results so far only partly support the prediction. Here, we provide another example of experimental evolution of sexual selection, by applying it for the first time to the mating behaviour of a seed beetle Callsorobruchus chinensis. We found a lower remating rate in polygamy-line females than in monogamy-line (i.e. no sexual selection) females after 21 generations of selection. Polygamy-line females also showed a longer duration of first mating than monogamy-line females. We found no effect of male evolutionary lines on the remating rate or first mating duration. Though not consistent with the original prediction, the current and previous studies collectively suggest that the observed female-limited responses may be a norm, which is also consistent with the conceptual advances in the last two decades of the advantages and limitations of experimental evolution technique.

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)

Simple Summary

In insects, it is known that the diet during the larval stage affects traits in the adult stage. However, it is still unclear how it affects reproductive traits such as ejaculation. The ejaculate contains many proteins and therefore requires much nutrition, so the larval diet strongly influences it. Males of the West Indian sweet potato weevil Euscepes postfasciatus use accessory gland substances to inhibit remating by females. Crossing experiments were conducted using lines reared on artificial diets or sweet potato tubers during the larval stage, and the refractory period was examined. The results showed that the larval stage diet had a significant effect on the refractory period of females. We also found one protein of approximately 15 kDa in size expressed only in the treatments reared on sweet potatoes. To our knowledge, this is the first study to show that larval diet qualitatively influences male ejaculate and female refractory period.

Abstract

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.

Evolution of male nuptial gift and female remating: A quantitative genetic model

In some species of separate sexes, males present a nuptial gift containing nutrition to their mate. Producing a large nuptial gift is a considerable cost to the male, but it may improve his siring success if the female reduces the likelihood to accept another male after receiving a large gift. The female may receive a direct benefit by accepting another male who provides an additional nuptial gift. Additionally, the female may receive an indirect fitness benefit via laying offspring sired by a male who is able to produce a large nuptial gift. We formalized the multivariate quantitative genetics model describing the coevolution of the size of nuptial gift produced by the male (x) and the female's propensity to engage in remating (y). We analyzed the model focusing two cases: [1] remating females receive no indirect fitness benefit, but enjoy direct benefit of nutrition; and [2] remating females receive no direct benefit, but enjoy an indirect fitness benefit due to a positive genetic correlation of x and y, which is possible if random mutations tend to make males produce small nuptial gifts. In both cases, the stable evolutionary equilibrium with neither nuptial gift nor remating (x-=y-=0) always exists. Another stable equilibrium may exist in which male produces nuptial gifts (x->0) and female engage in multiple mating (y->0). We discussed implications to the sexual conflict.

Sex peptide receptor mediates the post-mating switch in Helicoverpa armigera (Lepidoptera: Noctuidae) female reproductive behavior

BACKGROUND

In Drosophila, the sex peptide receptor (SPR) in females to detect male sex peptide (SP) and trigger changes in female behavior including mating rejection and oviposition. In moths, the SPR had been identified and investigated the limited function by using RNA interference (RNAi). However, the detailed function of SPR after a normal mating in moths, especially the role in female sexual receptivity, remains to be elucidated.

RESULTS

In this study, we use Helicoverpa armigera, an economically important pest worldwide, as a case study to verify the function of SPR in vivo by CRISPR/Cas9 gene editing system. Analyzing the post-mating behaviors in mutant females, we investigated that HarmSPR could mediate the long-term sexual receptivity (remating, sex pheromone production and calling behavior) switch in female, but not affect the short-term sexual receptivity and the duration time of remating. The oviposition of mated HarmSPR^-/- females was significantly decreased by ~70% comparing to wild-type (WT) mated females and there were more eggs staying in the ovary of mutant females. SPR also showed effect on female longevity, which is that the mated HarmSPR^-/- females showed longer longevity than mated WT females.

CONCLUSION

The results detailedly demonstrated the functional role of SPR in female post-mating behaviors and we could propose a pest control strategy in which developing an antagonist of SPR to reduce the oviposition of female. © 2021 Society of Chemical Industry.

Factors Influencing the Reproductive Ability of Male Bees: Current Knowledge and Further Directions

Simple Summary

Bumblebees and honeybees are well known as the dominant and most important pollinators in natural and agricultural ecosystems. The quality characteristics of their colonies depend greatly on the reproductive ability/quality of the parents (queens and drones). Male bees, despite their exclusive reproductive role and ability to determine colony quality, have been less considered than female bees, especially bumblebees. We reviewed the current studies on environmental factors and inherent characteristics that affect the mating success and fecundity of male honeybees and bumblebees. Temperature, nutrients, pesticides, body size, weight and age affect reproduction in male bees and consequently the progeny colony quality. However, more studies, especially in male bumblebees, are still needed to address the impacts of these factors in detail to confront the requirements of agricultural pollination and declining wild bee pollinators worldwide.

Abstract

Bumblebees and honeybees are very important pollinators and play a vital role in agricultural and natural ecosystems. The quality of their colonies is determined by the queens and the reproductive drones of mother colonies, and mated drones transmit semen, including half of the genetic materials, to queens and enhance their fertility. Therefore, factors affecting drone fecundity will also directly affect progeny at the colony level. Here, we review environmental and bee-related factors that are closely related to drone reproductive ability. The environmental factors that mainly affect the sperm count and the viability of males include temperature, nutrients and pesticides. In addition, the inherent characteristics of male bees, such as body size, weight, age, seminal fluid proteins and proteins of the spermathecal fluid, contribute to mating success, sperm quality during long-term storage in the spermathecae and the reproductive behaviors of queens. Based on the results of previous studies, we also suggest that the effects of somatotype dimorphism in bumblebee males on sperm quality and queen fecundity and the indispensable and exploitable function of gland proteins in the fecundity of males and queens should be given more attention in further studies.

Injection of seminal fluid into the hemocoel of honey bee queens (Apis mellifera) can stimulate post-mating changes

Honey bee queens undergo dramatic behavioral (e.g., reduced sexual receptivity), physiological (e.g., ovary activation, ovulation, and modulation of pheromone production) and transcriptional changes after they complete mating. To elucidate how queen post-mating changes are influenced by seminal fluid, the non-spermatozoa-containing component of semen, we injected queens with semen or seminal fluid alone. We assessed queen sexual receptivity (as measured by likelihood to take mating flights), ovary activation, worker retinue response (which is influenced by queen pheromone production), and transcriptional changes in queen abdominal fat body and brain tissues. Injection with either seminal fluid or semen resulted in decreased sexual receptivity, increased attractiveness of queens to workers, and altered expression of several genes that are also regulated by natural mating in queens. The post-mating and transcriptional changes of queens receiving seminal fluid were not significantly different from queens injected with semen, suggesting that components in seminal fluid, such as seminal fluid proteins, are largely responsible for stimulating post-mating changes in queens.

Putative Drone Copulation Factors Regulating Honey Bee (Apis mellifera) Queen Reproduction and Health: A Review

Honey bees are major pollinators of agricultural and non-agricultural landscapes. In recent years, honey bee colonies have exhibited high annual losses and commercial beekeepers frequently report poor queen quality and queen failure as the primary causes. Honey bee colonies are highly vulnerable to compromised queen fertility, as each hive is headed by one reproductive queen. Queens mate with multiple drones (male bees) during a single mating period early in life in which they obtain enough spermatozoa to fertilize their eggs for the rest of their reproductive life span. The process of mating initiates numerous behavioral, physiological, and molecular changes that shape the fertility of the queen and her influence on the colony. For example, receipt of drone semen can modulate queen ovary activation, pheromone production, and subsequent worker retinue behavior. In addition, seminal fluid is a major component of semen that is primarily derived from drone accessory glands. It also contains a complex mixture of proteins such as proteases, antioxidants, and antimicrobial proteins. Seminal fluid proteins are essential for inducing post-mating changes in other insects such as Drosophila and thus they may also impact honey bee queen fertility and health. However, the specific molecules in semen and seminal fluid that initiate post-mating changes in queens are still unidentified. Herein, we summarize the mating biology of honey bees, the changes queens undergo during and after copulation, and the role of drone semen and seminal fluid in post-mating changes in queens. We then review the effects of seminal fluid proteins in insect reproduction and potential roles for honey bee drone seminal fluid proteins in queen reproduction and health. We finish by proposing future avenues of research. Further elucidating the role of drone fertility in queen reproductive health may contribute towards reducing colony losses and advancing honey bee stock development.

Identification of novel ejaculate proteins in a seed beetle and division of labour across male accessory reproductive glands

The male ejaculate contains a multitude of seminal fluid proteins (SFPs), many of which are key reproductive molecules, as well as sperm. However, the identification of SFPs is notoriously difficult and a detailed understanding of this complex phenotype has only been achieved in a few model species. We employed a recently developed proteomic method involving whole-organism stable isotope labelling coupled with proteomic and transcriptomic analyses to characterize ejaculate proteins in the seed beetle Callosobruchus maculatus. We identified 317 proteins that were transferred to females at mating, and a great majority of these showed signals of secretion and were highly male-biased in expression in the abdomen. These male-derived proteins were enriched with proteins involved in general metabolic and catabolic processes but also with proteolytic enzymes and proteins involved in protection against oxidative stress. Thirty-seven proteins showed significant homology with SFPs previously identified in other insects. However, no less than 92 C. maculatus ejaculate proteins were entirely novel, receiving no significant blast hits and lacking homologs in extant data bases, consistent with a rapid and divergent evolution of SFPs. We used 3D micro-tomography in conjunction with proteomic methods to identify 5 distinct pairs of male accessory reproductive glands and to show that certain ejaculate proteins were only recovered in certain male glands. Finally, we provide a tentative list of 231 candidate female-derived reproductive proteins, some of which are likely important in ejaculate processing and/or sperm storage.

Male age and strain affect ejaculate quality in the Mexican fruit fly

Aging in all organisms is inevitable. Male age can have profound effects on mating success and female reproduction, yet relatively little is known on the effects of male age on different components of the ejaculate. Furthermore, in mass-reared insects used for the Sterile Insect Technique, there are often behavioral differences between mass-reared and wild males, while differences in the ejaculate have been less studied. The ejaculate in insects is composed mainly of sperm and accessory gland proteins. Here, we studied how male age and strain affected (i) protein quantity of testes and accessory glands, (ii) the biological activity of accessory gland products injected into females, (iii) sperm viability, and (iv) sperm quantity stored by females in wild and mass-reared Anastrepha ludens (Diptera: Tephritidae). We found lower protein content in testes of old wild males and lower sperm viability in females mated with old wild males. Females stored more sperm when mated to young wild males than with young mass-reared males. Accessory gland injections of old or young males did not inhibit female remating. Knowledge of how male age affects different ejaculate components will aid our understanding on investment of the ejaculate and possible postcopulatory consequences on female behavior.

The male ejaculate as inhibitor of female remating in two tephritid flies

The inhibition of female receptivity after copulation is usually related to the quality of the first mating. Males are able to modulate female receptivity through various mechanisms. Among these is the transfer of the ejaculate composed mainly by sperm and accessory gland proteins (AGPs). Here we used the South American fruit fly Anastrepha fraterculus (where AGP injections inhibit female receptivity) and the Mexican fruit fly Anastrepha ludens (where injection of AGPs failed to inhibit receptivity) as study organisms to test which mechanisms are used by males to prevent remating. In both species, neither the act of copulation without ejaculate transfer nor sperm stored inhibited female receptivity. Moreover, using multiply mated sterile and wild males in Mex flies we showed that the number of sperm stored by females varied according to male fertility status and number of previous matings, while female remating did not. We suggest female receptivity in both flies is inhibited by the mechanical and/or physiological effect of the full ejaculate. This finding brings us closer to understanding the mechanisms through which female receptivity can be modulated.

Female receptivity in Anastrepha ludens (Diptera: Tephritidae) is not modulated by male accessory gland products

In numerous insects, accessory gland products (AGPs) transferred from males to females during mating are responsible for female sexual inhibition, but these products can be affected by male condition. Here, we investigated the effect of AGPs on female receptivity of the Mexican fruit fly Anastrepha ludens (Loew), and the effect of male and female strain, male irradiation, AGP dose and sexual activity period on the effectiveness of these AGPs in inhibiting female remating. Injections of aqueous extracts of male accessory glands into the abdomen of females did not reduce their receptivity either at 0.2 or 0.8 male equivalent. Females injected with AGPs behaved like virgin females and not as mated females. Neither male origin, female origin (wild versus mass-reared), nor male irradiation (sterile versus fertile males) had an effect in inhibiting female remating. Also, injections of glands obtained during the sexual calling period of males, or obtained during the morning when males are not sexually active had no effect on female remating behavior. Mated mass-reared females were more likely to remate than wild females. We conclude that inhibition of female sexual receptivity of A. ludens is mediated by factors other than AGPs, such as the number of sperm stored by females, the stimulus of copulation per se or more probably, mediated by a combination of factors. More research is needed to elucidate the role of AGPs in this species.

[What the study of seminal fluid proteins in Drosophila tells us about the evolution of reproduction]

Decrease in male fertility observed in the past decades have involved sperm quantity and quality disorders. However, decrease in quality or quantity of seminal fluid may also trigger drastic reduction of female and also male fertility. The present paper documents on the composition of seminal fluid, the consequences on sperm cells and on the physiological and behavioral effects towards females. The work evidences the crucial role of seminal fluid in the postcopulatory interactions between the sexes and illustrates the selective effects in the male-female coevolution.

Characterization of male-derived factors inhibiting female sexual receptivity in Lygus hesperus

Newly mated females of the plant bug, Lygus hesperus Knight, enter a refractory period during which their sexual receptivity to courting males is greatly reduced for several days. This behavioral change appears to be induced by male-derived factors delivered in the spermatophore during copulation. To better understand the source of the factor(s) responsible for the inhibition, the homogenates of spermatophores, or of the individual organs that provide the constituents of the spermatophore, were injected directly into the abdomen of virgin females. The contents of the lateral and medial accessory glands both appear to produce inhibitory effects, but those of the seminal vesicle had no effect. Treatment of the homogenate also indicated that the active factor(s) is heat labile and water soluble. Several unique proteins were found in the water soluble fraction of the spermatophore, one of which is similar in size to the Drosophila melanogaster sex peptide, a male derived compound known to inhibit receptivity in female flies. In addition, spermatophores contained a substantial quantity of juvenile hormone, a key endocrine regulator of reproductive behavior and physiology in most insects. The results support the hypothesized role of males in manipulating the post-mating behavior of females, and suggest this is achieved through multiple components that act in concert to induce both short- and long-term effects.

Duration and dose-dependency of female sexual receptivity responses to seminal fluid proteins in Aedes albopictus and Ae. aegypti mosquitoes

Male mosquitoes transfer seminal fluid proteins (hereafter 'SFPs') during mating. These proteins can have profound effects on female behavior in the yellow fever mosquito Aedes aegypti and the Asian tiger mosquito Aedes albopictus. SFPs are thought to be responsible for female refractoriness to mating in both species. However, only limited information is available about the duration of induced refractoriness or the quantity of SFPs required to be effective in Ae. albopictus. Here, we tested the duration of the effect of SFPs on female refractory behavior for both Aedes species. Additionally, we determined the lowest SFP dose required to induce female refractory behavior in Ae. aegypti. Virgin females were injected intra-thoracically with doses ranging from 0.25 to 0.008 equivalents of one male's SFP amount. Our results demonstrate high sensitivity of female Ae. aegypti and Ae. albopictus to SFPs of their own species, with the majority of females becoming refractory at doses ≥ 0.031 male-equivalents after injection into the hemocoel. This effect was long-lasting in both species; none of the injected females were inseminated when presented with males of their own species 30 to 34 days post-injection, whereas most saline-injected control females mated at this time point. These results will aid future work to characterize individual SFPs involved in post-mating refractoriness in these two species. Moreover, they show that as is the situation in the mosquito Anopheles gambiae, and unlike Drosophila melanogaster, sperm are not required for the maintenance of a sexual refractoriness response in Ae. aegypti and Ae. albopictus.

Factors affecting Anastrepha fraterculus female receptivity modulation by accessory gland products

In the context of the sterile insect technique (SIT), mass-rearing and male irradiation are imperative. Post-teneral treatments such as the addition of protein in adult's male diet and male hormonal treatment are used to improve sexual performance and to accelerate sexual maturation. In this work we investigated the effect of male accessory glands products (AGPs) on female receptivity of the South American fruit fly Anastrepha fraterculus (Wiedemann), and the effect of strain rearing history, male irradiation, male diet and hormonal treatment on AGPs. Injections of aqueous extracts of male accessory glands into the abdomen of females reduced their receptivity. The AGPs from laboratory males were more effective in inhibiting female receptivity, compared to AGPs from wild males, irrespective of females' origin. The AGPs from fertile males were more effective than AGPs from sterile males. The AGPs from protein-fed males were more effective than AGPs from sugar-fed males. Finally, the AGPs of males treated with juvenile hormone were less effective in inhibiting female receptivity than AGPs of untreated males. We conclude that inhibition of sexual receptivity of A. fraterculus mated females is mediated by products in male accessory gland's and the way that these products act vary widely according to the effect of extrinsic factors. We discuss the results in the perspective of the SIT application for A. fraterculus.

Effects of male nutrition on sperm storage and remating behavior in wild and laboratory Anastrepha fraterculus (Diptera: Tephritidae) females

Male physiological condition can affect his ability to modulate female sexual receptivity. Thus, studying this aspect can have biological and practical implications. Here, we examine how male nutritional status affected the amount of sperm stored, remating rate and refractory period of the tephritid fruit fly Anastrepha fraterculus (Wiedemann) females. Both wild and laboratory flies were evaluated. We also examine female sperm storage patterns. Experiments were carried out by manipulating male adult diet and exposing these males to virgin females. Females mated with differently treated males were either dissected to count the amount of sperm stored or exposed to virgin males to determine remating rate and the length of the refractory period. We found that male nutritional status affected the amount of the sperm stored and the renewal of sexual receptivity in wild flies. For laboratory flies, male nutritional status affected the length of the refractory period but not the amount of sperm stored by females. In addition, we report that the ventral receptacle is not an important organ of sperm storage in this species. We conclude that male nutritional condition influences the ability to modulate female sexual receptivity, possibly through a combination of the quantity and quality of the ejaculate. From an applied perspective, providing males with an enriched diet will likely result in increased efficacy of the sterile insect technique.

Insect seminal fluid proteins: identification and function

Seminal fluid proteins (SFPs) produced in reproductive tract tissues of male insects and transferred to females during mating induce numerous physiological and behavioral postmating changes in females. These changes include decreasing receptivity to remating; affecting sperm storage parameters; increasing egg production; and modulating sperm competition, feeding behaviors, and mating plug formation. In addition, SFPs also have antimicrobial functions and induce expression of antimicrobial peptides in at least some insects. Here, we review recent identification of insect SFPs and discuss the multiple roles these proteins play in the postmating processes of female insects.

Induction of oviposition by injection of male-derived extracts in two Callosobruchus species

In some insect species, certain substances in the seminal fluid of males induce egg production and laying in females. We determined the effects of male-derived substances on female oviposition behaviour in two Callosobruchus species, C. chinensis and C. maculatus. Aqueous extracts of the accessory gland; testis; and seminal vesicle, including the ejaculatory duct, were prepared. The injection of these extracts into abdomen of females induced oviposition in both species. Oviposition was induced by the testis and seminal vesicle extracts in C. chinensis and by the accessory gland extracts in C. maculatus. The extracts were separated into three fractions by ultrafiltration: fractions I, molecular weight (MW) <3 kDa; fraction II, 3-14 kDa; and fraction III, >14 kDa. Fraction III induced oviposition in both species. These results suggest that in these two species, the substances that induce oviposition have similar MW but are present in different organs. Oviposition was induced by high-MW (>14 kDa) substances in the testis and seminal vesicle in C. chinensis, and by high-MW substances in accessory gland in C. maculatus. Here, we have discussed the relationship between oviposition and the abovementioned male-derived substances.

Inhibition of female mating receptivity by male-derived extracts in two Callosobruchus species: consequences for interspecific mating

We investigated the effects of injecting male-derived extracts on congeneric female receptivity in two species of Callosobruchus beetle, C. chinensis and C. maculatus. We also examined the influence of interspecific mating on female remating behaviour in these two species. Male-derived extracts reduced congeneric female receptivity in both species. As quick-acting components, extracts of C. chinensis male seminal vesicles reduced the receptivity of C. maculatus females, whereas extracts of C. maculatus male testes reduced the receptivity of C. chinensis females. As slow-acting components, extracts of male accessory glands of other species reduced the receptivity of both C. maculatus and chinensis females. After interspecific mating, the sperm of C. maculatus males were transferred to the reproductive organs of C. chinensis females, thereby reducing their receptivity. In contrast, no C. chinensis sperm were transferred to the reproductive organs of C. maculatus females; accordingly, the latter's receptivity was not reduced. Furthermore, the survival rate of C. chinensis females decreased markedly after interspecific mating. These results raise the possibility that under circumstances where populations of these two species share the same habitat, reproductive interference would occur only in the interactions between C. maculatus males and C. chinensis females.

Reduced female mating receptivity and activation of oviposition in two Callosobruchus species due to injection of biogenic amines

Analyses of proximate mechanisms that control mating and oviposition behaviours in insects are important because they link behavioural ecology and physiology. Recently, seed beetles have been used as models to study evolution of female multiple mating and cost of reproduction including mating. In the present study, we investigated the effects of biogenic amines into the abdomens of females of two Callosobruchus species, Callosobruchus chinensis and Callosobruchus maculatus, on mating receptivity and oviposition behaviour. In C. chinensis, injection of octopamine and tyramine reduced receptivity to mating and tyramine and serotonin increased the number of eggs laid. Similarly, injection of tyramine reduced the receptivity of females and increased the number of eggs laid by females of C. maculatus. These results show the possibility that biogenic amines control mating receptivity and oviposition behaviour in females of two Callosobruchus species.

Effects of temperature on mating duration, sperm transfer and remating frequency in Callosobruchus chinensis

Insect body temperature is usually determined by ambient temperature. Therefore, most biochemical and physiological processes underlying behavioural patterns are temperature dependent. Mating duration is also dependent on temperature, and therefore temperature should influence on sperm transfer and female remating frequency. In the adzuki bean beetle, Callosobruchus chinensis, we found negative relationships between ambient temperature and mating duration, sperm transfer and sperm transfer duration. Female remating frequency at lower temperature (17 degrees C) was lower than at other temperatures (25 degrees C and 33 degrees C). The physiological and behavioural significance of these results is discussed. The number of ejaculated sperm was significantly lower at 33 degrees C than at 17 degrees C; the effect of temperature on sperm transfer is discussed in relation to the intensity of female refusal behaviour directed against males.

Males of the seed bug Togo hemipterus (Heteroptera: Lygaeidae) use accessory gland substances to inhibit remating by females

In species in which females mate repeatedly, males can adopt several strategies to reduce the risk of sperm competition with future males. The refractory period of females significantly increased as the mating duration increased in the seed bug Togo hemipterus (Heteroptera: Lygaeidae). To elucidate the mechanisms by which mated females are inhibited from remating, we investigated the effects of male-derived substances on the inhibition of mating receptivity of virgin females by injecting the substances into their abdomens. The length of time from injection to mating in virgin females was significantly longer for females injected with accessory gland B solution than for those injected with seminal vesicle, accessory gland A, or control solutions. This is the first report showing that heteropteran males inhibit female remating by using substances from an accessory gland. We discuss and consider the adoption and evolution of this strategy by T. hemipterus males by focusing on female genitalia structures, oviposition habit, and paternity and comparing these traits with those of other heteropterids.

Female mating receptivity after injection of male-derived extracts in Callosobruchus maculatus

The effects of male-derived extracts on female receptivity were investigated in Callosobruchus maculatus (Coleoptera: Bruchidae). Injection of aqueous extracts of the male reproductive tract into the abdomen of females reduced receptivity. Aqueous extracts of male reproductive tracts were divided to three molecular weight (MW) fractions by ultrafiltration: Fractions: (I) MW<3 kDa, (II) 3-14 kDa, and (III)>14 kDa. Fraction II reduced female receptivity from 3h after injection, and Fraction III reduced female receptivity from 2 days after injection. On the other hand, no effect on receptivity was found for Fraction I. Furthermore, male reproductive tract organs were divided into accessory gland, testis, and seminal vesicle including the ejaculatory duct. Aqueous extracts of the seminal vesicle reduced receptivity of females immediately following injection, while aqueous extracts of the accessory gland reduced receptivity at the second day. The results suggest that the components of Fraction II existed in the seminal vesicle, and those of Fraction III in the accessory gland. The results of the present and the previous studies in Callosobruchus chinensis, a species closely related to C. maculatus, were compared and are discussed from the viewpoint of the significance of ejaculation in the two species.