A field study of mating between two species of bedbug in northern KwaZulu, South Africa

The interspecific cross-mating of female Cimex lectularius Linnaeus with male Cimex hemipterus (Fabricius) results in a visible mark developing in the female ectospermalege. This mark has been used to record the frequency of mating between female C.lectularius and male C.hemipterus in sympatric wild populations in a DDT-sprayed area of northern KwaZulu, South Africa. A high percentage (11/16 = 69%) of C.lectularius females were marked, showing that these two species mate in nature.     

Production of a hybrid between the bedbugs Cimex hemipterus and Cimex lectularius

Of 479 eggs laid by female Cimex lectularius Linnaeus and C.hemipterus (Fabricius) mated by males of the other species, one was fertile and gave rise to a first stage nymph. The egg showed sculpturing typical of C.hemipterus, the female parent, and the nymph conformed to the narrow pronotum and abdomen of this species, being significantly different from C.lectularius in the width of the abdomen. Because the orientation and lengths of the bristles on the sides of the abdomen were distinctly different from C.hemipterus and closely resembled C.lectularius, the single nymph obtained from the cross C.hemipterus x lectularius was interpreted as being a hybrid rather than a product of parthenogenesis.     

Alarm pheromones and chemical communication in nymphs of the tropical bed bug Cimex hemipterus (Hemiptera: Cimicidae)

The recent resurge of bed bug infestations (Cimex spp.; Cimicidae) and their resistance to commonly used pesticides calls for alternative methods of control. Pheromones play an important role in environmentally sustainable methods for the management of many pest insects and may therefore be applicable for the control of bed bugs. The tropical bed bug, Cimex hemipterus, is a temporary ectoparasite on humans and causes severe discomfort. Compared to the common bed bug, Cimex lectularius, little is known about the chemical signalling and pheromone-based behaviour of the tropical species. Here, we show that the antennal morphology and volatile emission of C. hemipterus closely resembles those of C. lectularius and we test their behavioural responses to conspecific odour emissions. Two major volatiles are emitted by male, female and nymph C. hemipterus under stress, (E)-2-hexenal and (E)-2-octenal. Notably, nymph emissions show contrasting ratios of these compounds to adults and are further characterized by the addition of 4-oxo-(E)-2-hexenal and 4-oxo-(E)-2-octenal. The discovery of this nymph pheromone in C. hemipterus is potentially the cause of a repellent effect observed in the bio-tests, where nymph odours induce a significantly stronger repellent reaction in conspecifics than adult odours. Our results suggest that pheromone-based pest control methods developed for C. lectularius could be applicable to C. hemipterus, with the unique nymph blend showing promising practical properties.     

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.     

Situation exploitation: higher male mating success when female resistance is reduced by feeding

Optimal male and female mating rates rarely coincide. Males often shift the rate in their favor by either increased signaling and by overcoming female resistance to copulation. The concept of sensory exploitation posits that males produce signals that mimic naturally selected benefits and so deceitfully attract females. However, males also have to overcome female resistance to actual copulation. Males may do so by copulating during situations when the female's ability to resist is decreased because of competing naturally selected demands. Males of the common bedbug, Cimex lectularius , an obligate blood feeder, mate at a rate, and in a manner that is harmful to females. Females have to feed regularly to produce eggs, and during feeding female body volume increases by 300%. Choice trials using unfed and either fed or experimentally enlarged but unfed females showed that the increased postfeeding body volume of females attracted more male mating attempts, strongly reduced female resistance to male mating attempts and resulted in a net increase in female mating rate. Our results, therefore, suggest that males have increased mating success in a situation that females cannot avoid because it is naturally selected. Such "situation exploitation" of low resistance may be a common phenomenon.     

Trauma, disease and collateral damage: conflict in cimicids

The bed bugs and bat bugs (Hemiptera: Cimicidae) are unusual in being a gonochorist (separate male and female genders) taxon with obligate traumatic insemination. Males of all the species in this family have a lanceolate paramere (intromittent organ) which they use to pierce the female's body wall and inseminate directly into her haemocoel, despite the presence of a functional female genital tract. Mating is tightly linked to the feeding cycle in Cimex lectularius, the common bed bug. In this paper, I examine key aspects of the reproductive anatomy and behaviour of C. lectularius that underpin the nature of the conflict over mating rate in this species. I then examine the consequences of traumatic insemination for female fitness and examine potential mechanisms that might underpin those costs. Finally, the collateral consequences of the male reproductive tactic on other males of C. lectularius and the African bat bug, Afrocimex constrictus are examined.     

聚四氟乙烯对温带臭虫爬行能力的影响

温带臭虫Cimex lectularius L.是一种重要的卫生害虫,严重影响人们的生活和健康。目前有关该虫的防治措施主要以喷洒化学杀虫剂为主,而杀虫剂的使用不当极易导致该虫抗药性的产生或进一步加重,还将对人身安全构成极大的威胁。因此,探索高效、安全的防治方法成为当前温带臭虫防治过程中亟待解决的问题。本研究在实验室条件下采用行为观察法评估了高分子聚合物-聚四氟乙烯对温带臭虫垂直和水平爬行能力的影响。结果表明,随着聚四氟乙烯涂层宽度的增加,温带臭虫的垂直攀爬能力逐渐降低,当涂层宽度为6 cm时可100%阻隔温带臭虫垂直攀爬,且涂层的持效期可达112 d以上。而聚四氟乙烯涂层无法阻止温带臭虫的水平扩散。研究结果可为温带臭虫的高效、安全物理预防提供理论依据和技术支持。     

A matter of taste: direct detection of female mating status in the bedbug

Males of the bedbug, Cimex lectularius, traumatically inseminate females by inserting a needle-like intromittent organ (penis) through the female's abdominal wall after she has fed. We demonstrate that: (i) mating duration determines ejaculate size; (ii) a female's first copulation in a bout of copulations always lasts longer than subsequent copulations; (iii) the intromittent organ bears sensillae; (iv) males use their intromittent organ to 'taste' whether their current mate has recently copulated; and (v) the consequence of detecting female mating status is the reduction of copulation duration and ejaculate size. We discuss why male bedbugs might show this pattern of ejaculate-size adjustment.     

No genetic correlation between the sexes in mating frequency in the bean beetle, Callosobruchus chinensis

Female multiple mating, which is common in animals, may have evolved not in response to fitness advantages to females but as a genetic corollary to selection on males to mate frequently. This nonadaptive hypothesis assumes a genetic correlation between females and males in mating frequency, which has received a few empirical investigations. We tested this hypothesis by observing the correlated response in male mating frequency in the adzuki bean beetle, Callosobruchus chinensis to artificial selection on female propensity to remate. Compared to control females, females from lines selected for increased or decreased female propensity to remate had, respectively, higher or lower mating frequency measured by the number of mating within a given period. This indicates that female receptivity to remating is genetically correlated with female mating frequency, and thus the artificial selection for female propensity to remate influenced female mating frequency. In contrast, males from the selected lines that diverged in female mating frequency did not vary significantly in their mating frequency. These results indicate that there is no genetic correlation between the sexes in mating frequency in C. chinensis. This study shows that the reason why females in C. chinensis remate despite suffering fitness costs cannot be explained by indirect selection resulting from selection on males to mate multiple times.     

Effects of mating patterns on reproductive performance and offspring fitness in Cryptolaemus montrouzieri

We examined the female mating choice of Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) when exposed to a male with which she had mated before vs. a novel male which she never encountered. After first mating, most females chose to remate with the same male and showed a shorter mating latency period to copulation with the familiar male as compared to a new male. Then, we allowed a female to mate once, 5× with the same, or 5× with different males to evaluate how different mating patterns influence the females’ reproductive performance and offspring fitness. Mating 5× with the same male or different males improved female egg production, but had no effect on hatching rate or offspring fitness. Our findings suggest that female C. montrouzieri are able to distinguish between familiar and unfamiliar males and prefer to mate with the former. Further, multiple mating appears to offer material benefits to female C. montrouzieri specifically by increasing fecundity.     

Effect of male and female multiple mating on the fecundity, fertility, and longevity of diamondback moth, Plutella xylostella (L.)

Abstract:  The effect of diamondback moth (DBM), Plutella xylostella (Lep., Plutellidae) male and female multiple mating on fecundity, fertility, and longevity was studied. Males could mate for five times with virgin females during scotophase. The successful copulation rates, fecundity of female, and longevity of both females and males decreased when male mating times increased, whereas copulation duration increased. Correlation coefficient between copulation duration and male mating times was significant ( r  = 0.7358, P = 0.0001, spearman rank-order correlation). There were linear relationships between mating history of males and longevities of males and females, and regression relationships between them were significant. Mated females had similar daily reproductive pattern, which laid the most eggs on the first day after mating in spite of their mates' mating history. Virgin females laid some infertile eggs before they died. Most of the females mated once during their lifespan but 19.9% of females mated twice when one female kept with one male during scotophase. There were no significant differences in the fecundity, fertility and longevity between the single- and twice-mated females. Correlation coefficient between copulation duration and female mating times was not significant ( r  = 0.0860, P = 0.8575). Results suggested that DBM females may be monandrous. Multiple mating did not increase male or female mating fitness.     

Delayed mating and its cost to female reproduction in the butterfly,Eurema hecabe

The timing of mating of females under semi-natural condition, male ejaculate production and their effects on female fecundity were examined inEurema hecabe. Age of the first mating of females varied, and the number of matings increased with age. Male spermatophore production depended on age and body mass. The spermatophore mass at the second mating depended only on the interval between the first and second matings. The timing of the first mating and the spermatophore mass did not affect female fecundity. The timing of mating of females relative to the role of male spermatophores in female fecundity and male mating strategy are discussed.     

The evolution of optimal female mating rate changes the coevolutionary dynamics of female resistance and male persistence

Mating decisions usually involve conflict of interests between sexes. Accordingly, males benefit from increased number of matings, whereas costs of mating favour a lower mating rate for females. The resulting sexual conflict underlies the coevolution of male traits that affect male mating success ('persistence') and female traits that affect female mating patterns ('resistance'). Theoretical studies on the coevolutionary dynamics of male persistence and female resistance assumed that costs of mating and, consequently, the optimal female mating rate are evolutionarily constant. Costs of mating, however, are often caused by male 'persistence' traits that determine mating success. Here, we present a model where the magnitude of costs of mating depend on, and evolve with, male persistence. We find that allowing costs of mating to depend on male persistence results in qualitatively different coevolutionary dynamics. Specifically, we find that male traits such as penis spikes that harm females are not predicted to exhibit runaway selection with female resistance, in contrast to previous theory that predicts indefinite escalation. We argue that it is essential to determine when and to what extent costs of mating are caused by male persistence in order to understand and accurately predict coevolutionary dynamics of traits involved in mating decisions.     

The Effects of Age and Previous Mating Experience on Pre- and Post-copulatory Mate Choice in Female House Crickets (<Emphasis Type="Italic">Acheta domesticus</Emphasis> L.)

Although females’ mating preferences are influenced by male characteristics, there are a number of factors intrinsic to females and unrelated to male phenotype that can modulate female choice. We assessed the effects of age and mating experience on mechanisms of pre- and post-copulatory mate choice in female house crickets, Acheta domesticus L., by randomly assigning males to females, but independently varying the age and number of previous matings of females at the time of experimental matings. Latency to mating, a measure of a female’s pre-copulatory preference, was influenced by female age at the time of mating, with older females mating sooner than younger females. The reduced selectivity of older females appears consistent with life-history theory, which predicts that the reproductive value of females should decline with age. The length of time that females retained the spermatophore after mating, a measure of a female’s post-copulatory mating preference, was not influenced by female age at the time of mating, the number of previous matings, or any interaction between the two main effects. Contrary to previous reports, male mass had no effect on either the latency to mating or female retention of the spermatophore in A. domesticus. We conclude that female age and mating experience can moderate female selectivity, but that their impact varies according to the mechanism by which females favor particular sires.     

Assortative preferences and discrimination by females against hybrid male song in the grasshoppers Chorthippus brunneus and Chorthippus jacobsi (Orthoptera: Acrididae)

The grasshoppers Chorthippus brunneus and Chorthippus jacobsi are highly differentiated for male mating signals, and form a mosaic hybrid zone in northern Spain. At some sites within this zone, many hybrids are observed. At others, few hybrids are observed. Such bimodal sites may reflect recent contacts between parental genotypes, or local variation in levels of assortative mating or selection against hybrids. Playback of 12 parental and F1 male songs to 296 parental and hybrid females revealed positive assortative preferences in C. brunneus and C. jacobsi females, supporting a direct role of male mating signals in female choice. However, all female genotypic classes showed reduced responsiveness to F1 male songs. Such sexual selection against hybrids is consistent with the narrow cline width observed in the field for song characters relative to morphology. These results have implications for the genetic structure of the hybrid zone and for models of speciation by reinforcement.     

The Effect of Abdominal Spines on Female Mating Frequency and Fecundity in a Water Strider

Conflict between the sexes over mating decision may result in antagonistic coevolution in structures that increase control over copulation. In Aquarius paludum both females and males have long abdominal spines. We tested the hypothesis that abdominal spines increase female ability to resist male mating attempts and reduce the costs of mating in A. paludum. We manipulated female spine length and observed female mating and egg-production rate in two different studies. We found that females with intact spines succeeded to reject male mating attempt more often than females with removed spines. Intact females also mated less often than females with removed or shortened spines. Male presence and mating rate increased female egg number. Our results thus support the hypothesis that abdominal spines help female to reject male mating attempts but contrary to predictions, we found that A. paludum females somehow benefit from multiple matings in spite of the sexual conflict.     

Opportunities for female choice in the bed bug Cimex lectularius

Bed bugs are cited as exemplars of sexual conflict because mating can only occur via traumatic insemination. However, past antagonistic coevolution between the sexes does not necessarily preclude current female choice. Here, we investigate opportunities for precopulatory female choice in bed bugs. We examined whether females seek out mating opportunities when they gain the most benefit: when females are virgin and/or have recently fed. But, we found that female mating and feeding status had little effect on female attraction to males and male odor. To determine whether females approach male harborages (home crevices) to seek matings in nature, we investigated where matings occurred among unfamiliar pairs of bed bugs. We found that, despite female attraction to male odor, matings were most likely to take place in the female's harborage rather than the male's harborage. We also examined the effect of feeding on male and female ability to mate. Whereas previous research reported that engorgement impaired female ability to refuse matings, we found that male feeding status had a larger effect on the success of mating encounters than female feeding status. Fed males had poor mating success, suggesting that males may be faced with a trade‐off between mating and feeding.     

Intra-specific variation in female remating in Callosobruchus chinensis and C. maculatus

The effects of mating duration on female remating (exp. 1) and under different male densities (exp. 2) were examined in two strains of the adzuki bean beetle, Callosobruchus chinensis and in one strain of the bruchid beetle, C. maculatus. In experiment 1, the frequency of female remating was markedly different between the two strains of C. chinensis. Females of the jC strain, reared long-term in the laboratory, did not remate after being allowed to mate freely (=monogamy), whereas females of the isC strain, recently established from the field, showed high remating frequencies (=polyandry). In both strains, the frequency of female remating increased after the duration of the first mating was deliberately shortened. The relation between mating duration and remating frequency was significantly different, however, between the two strains. In a closely related species, C. maculatus, which manifests polyandry, this relation was more similar to that of the field-derived (=isC) than to that of the laboratory-derived (=jC) strain of C. chinensis. The reasons for the inter-strain variation observed in the remating frequencies of C. chinensis are also discussed. In experiment 2, the mating duration of the three strains was compared under different male densities. Only the lab-derived strain demonstrated a significantly shorter mating duration when one female was placed together with five males than when paired with one male. The shorter mating duration (approximately 26 s) was similar to that of females allowed to remate in the monogamous strain in experiment 1.     

The role of female dominance hierarchies in the mating behaviour of mosquitofish

While studies of sexual selection focus primarily on female choice and male-male competition, males should also exert mate choice in order to maximize their reproductive success. We examined male mate choice in mosquitofish, Gambusia holbrooki, with respect to female size and female dominance. We found that the number of mating attempts made by a male was predicted by the dominance rank of females in a group, with dominant females attracting more mating attempts than subordinates. The number of mating attempts made by males was independent of the female size. The observed bias in the number of mating attempts towards dominant females may be driven either by straightforward male mate choice, since dominance and female fecundity are often closely related, or via the dominant females mediating male mating behaviour by restricting their access to subordinate females.     

Validation of a Method for Quantifying Male Mating Preferences in the Guppy (Poecilia reticulata)

Male and female mating preferences are commonly inferred from association times spent with potential mates in a dichotomous‐choice test. However, this assessment method is rarely validated, particularly so for male mating preferences. Using the Trinidadian guppy (Poecilia reticulata), an important model species in the study of sexual selection, we tested whether a male’s mating preference for either of two stimulus females in a dichotomous‐choice test predicted his mating behaviours directed at the preferred female when he was allowed to swim freely with both females. First, we presented individual males with two females that differed in body length in a dichotomous‐choice apparatus in which the male could only use visual cues to assess the paired females. We quantified male mating preference as the duration of time a focal male spent associating with each female. Immediately following this test, the focal male was allowed to swim freely with both females, and we quantified the time he spent sexually pursuing each female and the number of courtship sigmoid displays and copulation attempts he directed at each female. On average, males did not significantly prefer either of the two stimulus females in either of the two tests; however, the magnitude of male preference for the larger female tended to increase as the size difference between the paired females increased. More importantly, there was a significant positive relationship between male association time in the dichotomous‐choice test and both the time spent sexually pursuing and the number of courtship sigmoid displays directed at the same female initially preferred in the dichotomous‐choice test. Collectively, these results confirm that association time measured in a dichotomous‐choice test is a reliable predictor of male mating preferences in the Trinidadian guppy.