The Effect of Abiotic Factors on the Male Mate Searching Behavior and the Mating Success of Aphidius ervi (Hymenoptera: Aphidiidae)

The effect of wind speed and distance from the source on the male response of the aphid parasitoid, Aphidius ervi (Hymenoptera: Aphidiidae), to a pheromone source was studied in a wind tunnel. The number of males taking flight, entering the plume and successfully reaching the source, decreased at wind speeds >50 cm/s. Furthermore, the proportion of those attempting upwind flight that fell to the ground increased with increasing wind speed. In contrast, distance from the source had no significant effect on any of the parameters examined. While male flight behavior was significantly reduced at 70 cm/s, some males walked to the source when there was a bridge connecting the pheromone source and the release platform. This suggests that ambulatory behavior could be a significant component of male mate searching in A. ervi when wind conditions are too strong for upwind flight. The possible effects of variation in atmospheric pressure on male flight behavior to the long distance pheromone, as well as to the short distance one, were also investigated. No significant effects of atmospheric pressure were observed. These findings differ significantly from those previously reported for another aphid parasitoid, A. nigripes, and the reasons for such differences are discussed.     

Experimental Examination of Intraspecific Density-Dependent Competition during the Breeding Period in Monarch Butterflies (Danaus plexippus)

A central goal of population ecology is to identify the factors that regulate population growth. Monarch butterflies (Danaus plexippus) in eastern North America re-colonize the breeding range over several generations that result in population densities that vary across space and time during the breeding season. We used laboratory experiments to measure the strength of density-dependent intraspecific competition on egg laying rate and larval survival and then applied our results to density estimates of wild monarch populations to model the strength of density dependence during the breeding season. Egg laying rates did not change with density but larvae at high densities were smaller, had lower survival, and weighed less as adults compared to lower densities. Using mean larval densities from field surveys resulted in conservative estimates of density-dependent population reduction that varied between breeding regions and different phases of the breeding season. Our results suggest the highest levels of population reduction due to density-dependent intraspecific competition occur early in the breeding season in the southern portion of the breeding range. However, we also found that the strength of density dependence could be almost five times higher depending on how many life-stages were used as part of field estimates. Our study is the first to link experimental results of a density-dependent reduction in vital rates to observed monarch densities in the wild and show that the effects of density dependent competition in monarchs varies across space and time, providing valuable information for developing robust, year-round population models in this migratory organism.     

Effect of photoperiod and temperature on reproduction of the monarch butterfly,Danaus plexippus

Optimal posteclosion ovarian development in monarch butterflies occurs at about 28°C. Higher and lower temperatures appear progressively inhibitory. Reproductive gland development in males follows a similar pattern. Juvenile hormone injections stimulate oöcyte maturation in animals held at 20 and 35°C but are most effective at the higher temperature. Juvenile hormone injections are ineffective at 10 and 15°C. The stimulatory effect of increasing photophase on ovarian development was most apparent at optimal temperature. The possible significance of our findings to monarch migration is discussed.     

Differential Postalightment Oviposition Behavior of Monarch Butterflies on Asclepias Species

The monarch butterfly, Danaus plexippus L., oviposits mainly on plants in the Asclepiadaceae, particularly within the genus Asclepias. We studied postalightment oviposition behavior of monarch females on three host species—Asclepias curassavica, A. incarnata , and A. tuberosa. After landing on the host, they used their forelegs, midlegs, and antennae to assess plant suitability. When these appendages were examined by scanning electron microscopy, contact chemoreceptor sensilla were found. In choice tests, A. incarnata was most preferred, while A. tuberosa was least preferred. However, the use of appendages varied for the different host species. Antennae were most frequently used during post-alightment behavior on A. curassavica, whereas forelegs were used more often on A. incarnata, and all three appendages were used extensively on A. tuberosa. Use of the midlegs was generally followed by use of the antennae. Tasting with either forelegs or antennae apparently may lead to egg laying on some host species. Rupture of the plant surface by midleg spines was also observed. The behavior and host preference of individual females varied significantly and may reflect differences in receptor sensitivity.     

Mating Behavior and Reproductive Potential in the Turnip Moth Agrotis segetum (Lepidoptera: Noctuidae)

We investigated the lifetime mating potential and the reproductive behavior of male and female turnip moths Agrotis segetum (Schiff.) under field and laboratory conditions. The sex ratio was 1 : 1 in a lab-reared population as well as in two wild populations. Males were capable of mating repetitively a relatively large number of times (mean of 6.7 ± 2.7 matings) when given access to new virgin females throughout their lifetimes. Females seldom mated more than once (mean ± 1.3 ± 0.6 matings), indicating a male-biased operational sex ratio. The mean potential lifetime mating was five times higher in males, while the coefficient of variance was lower in males. There was no differences in longevity between animals that were allowed to mate and animals not allowed to mate, indicating no direct costs or benefits of mating in physiological terms. In males, the number of matings was positively correlated with longevity, but this was not the case in females. Nor was there a correlation between the number of female matings and the number of fertilized eggs. There was a negative correlation between the number of eggs fertilized and the number of times males had previously mated, indicating that male ejaculates were limited. Male spermatophore size also decreased with number of achieved matings. Laboratory-reared females attracted males in the field throughout their lifetimes, with a peak at 3–7 days of age. Wild males, allowed to choose between pairs of caged females in the field, were attracted in equal numbers to females of different ages. Females did not show any mate-rejection behavior in the field. They mated with the first male that courted them. No incidence of mate replacement by males arriving later to already courted females were recorded.     

Reversal Learning and Risk‐Averse Foraging Behavior in the Monarch Butterfly,Danaus plexippus (Lepidoptera: Nymphalidae)

Learning ability allows insects to respond to a variable environment, and to adjust their behaviors in response to positive or negative experiences. Pollinating insects readily learn to associate floral characteristics, such as color, shape, or pattern, with appetitive stimuli, such as the presence of a nectar reward. However, in nature pollinators may also encounter flowers that contain distasteful or toxic nectar, or offer highly variable nectar volumes, providing opportunities for aversive learning or risk‐averse foraging behavior. Whereas some bees learn to avoid flowers with unpalatable or unreliable nectar rewards, little is known about how Lepidoptera respond to such stimuli. We used a reversal learning paradigm to establish that monarch butterflies learn to discriminate against colored artificial flowers that contain salt solution, decreasing both number of probes and probing time on flowers of a preferred color and altogether avoiding artificial flowers of a non‐preferred color. In addition, when we offered butterflies artificial flowers of two different colors, both of which contained the same mean nectar volume but which differed in variance, the monarchs exhibited risk‐averse foraging: they probed the constant flowers significantly more than the variable ones, regardless of flower color or butterfly sex. Our results add to our understanding of butterfly foraging behavior, as they demonstrate that monarchs can respond to aversive as well as appetitive stimuli, and can also adjust their foraging behavior to avoid floral resources with high variance rewards.     

Male Mating History Influences Female Mate Choice in the Trinidadian Guppy (Poecilia reticulata)

Based on the phenotype‐linked fertility hypothesis, sexual selection should favour females that can accurately assess the recent mating history of available sexual partners and preferentially avoid mating with recently‐mated males [who may be sperm depleted (SD)] so as to minimize the risk of their eggs not being fertilized. This hypothesis has received to date only limited attention and empirical support. Therefore, in the current study, we investigated experimentally whether females of a vertebrate species, the Trinidadian guppy (Poecilia reticulata), are able to assess the recent mating history of males, and thus potentially their functional fertility, and choose to avoid mating with males that appear to have recently mated and who may be sperm limited. Individual virgin females were first given a dichotomous choice between a male that had not been recently observed to interact sexually with another female (i.e. not sperm‐depleted) and another male that had been observed to interact sexually with a female (i.e. potentially sperm‐depleted) as sexual partners. Paired males were matched for body length and coloration. Immediately following this test, the focal females were subjected to a free‐swimming mate‐choice test using the same paired stimulus males. As predicted, on average, female guppies avoided the apparently recently‐mated (and potentially sperm‐depleted) male and exhibited a significant preference for the other male not recently observed mating (and thus not likely sperm limited) during both tests. We do not yet fully understand the underlying mechanisms of this preference. Therefore, further research on the particular cues that females use to assess the recent mating history and fertility status of males is required.     

No Correlation Between Ectoparasitism and Male Mating Success in a Damselfly: Why Parasite Behavior Matters

The mating success of individually marked male damselflies parasitized by water mites was closely followed. The number of ectoparasites could be determined exactly from knowledge of the parasite's life cycle. In contrast to previous studies, no correlation between water mite infestation and male mating success was revealed. The reasons for this discrepancy may be explained by the inclusion of the parasite's behavior. The body fat content of the males was negatively correlated with the mite load, indicating that parasitism reduces host's condition. It is hypothesised that the water mites damselfly system is not valuable for testing the Hamilton and Zuk hypothesis. Furthermore, selection exerted or mediated by parasites should act during the teneral phase.     

Size Assortative Mating and Reproductive Success of the Funnel-Web Spider, Agelena limbata (Araneae; Agelenidae)

Field observations and laboratory experiments were conducted to assess the relation between male size and reproductive success in the funnel-web spider, Agelena limbata Thorell (Agelenidae), in 2 years. In this species, the body size of males is similar to that of females. In the field, size assortative mating occurred in both years. In 1 year, partial correlation coefficient analysis indicates that male cephalothorax width is a beter predictor of the copulated female cephalothorax width than of the date of pairing. In laboratory experiments, females tended to reject courting males that were smaller in relative body size, and males that were larger in relative body size had greater copulation success. Consequently female rejection of smaller courting males has some contribution to size assortative mating. Since larger females deposited more numerous eggs in the field, larger males are expected to have a higher reproductive success.     

Oviposition preference and larval performance of monarch butterflies (Danaus plexippus) on two invasive swallow-wort species

The potential of two invasive herbaceous vines Vincetoxicum nigrum (L.) Moench and Vincetoxicum rossicum (Kleopow) Barbar. (Asclepiadaceae) to reduce monarch butterfly (Danaus plexippus L.) (Lepidoptera: Nymphalidae, Danainae) populations was investigated by evaluating oviposition selection in adult monarch butterflies and larval feeding preference in choice tests comparing the native host plant of monarch butterflies, Asclepias syriaca L. (Asclepiadaceae) and the two non‐indigenous Vincetoxicum species. In both choice and no‐choice tests, no eggs were oviposited on either of the two Vincetoxicum species whereas over 66 eggs per female were oviposited on A. syriaca plants. All first instar larvae allowed to feed on A. syriaca for 48 h survived while a significantly lower proportion survived on V. rossicum (44%) and V. nigrum (14%). Mean weight of larvae that did survive on the Vincetoxicum species was significantly lower than the mean weight of larvae that fed on A. syriaca. The mean weight of surviving larvae, however, did not differ between the two Vincetoxicum species. The mean proportion of leaves consumed by larvae feeding on A. syriaca was significantly greater than the mean proportion of leaves consumed by larvae feeding on either Vincetoxicum species. Findings from this research indicate that V. rossicum and V. nigrum are not viable hosts of monarch butterflies and are likely to pose little direct threat to their populations as oviposition sinks. The ability of these highly aggressive plants, however, to out‐compete and displace the native host of monarchs, A. syriaca, may pose a more serious threat. The potential of monarch populations to adapt to the two Vincetoxicum species as host plants over the long‐term is discussed.     

Ultraviolet Ornamentation and Male Mating Success in a High-Density Assemblage of the Butterfly Colias eurytheme

Ultraviolet (UV) colour patterns, particularly those deriving from surface structures, serve a role in sexual signalling and mate choice in a range of animal groups. In the butterfly Colias eurytheme (Pieridae), male-limited iridescent UV functions in species recognition, and has potential as an intraspecific sexual signal of mate quality. I compared the dorsal colouration and body size of males discovered ‘in-copula’ (N = 95) with a random sample of free-flying individuals (N = 129), both collected from a high density agricultural population located in Chandler, U.S.A. Despite reasonable variance in each trait, I found no among-group differences in UV characters (brightness, hue and angular visibility) or in the coincident pigmentary yellowish-orange (brightness and saturation). Statistical power was sufficient to detect all but the smallest among-group differences, and there was a marginally significant tendency for in-copula males to be larger. These data do not support the hypothesis for intraspecific female choice upon male dorsal colouration. However, I discuss how the density and apparently very young age of individuals in the sampling population may have pre-disposed this result, and thus, how sexual selection on male colouration may operate in a density dependent manner.     

Sneaky Monkeys: An Audience Effect of Male Rhesus Macaques (Macaca mulatta) on Sexual Behavior

Males and females have different sexual interests and subsequently may show conflicting sexual strategies. While dominant males try to monopolize females, promiscuity benefits females and subordinate males. One way to escape monopolization by dominant males is to copulate in their absence. We tested this inhibitory effect of males on the sexual behavior of their group members in captive group‐living Rhesus macaques. Copulations between females and nonalpha males almost exclusively took place when the alpha male was out of sight. Furthermore, the inhibiting effect was not unique for the alpha male. An upcoming nonalpha male also inhibited copulations of its group members, and three other nonalpha males inhibited female copulation solicitations. Females adjusted their behavior to the presence of bystander males, as they initiated and accepted initiations more often in absence than in presence of bystander males. Although not significant, in males, a similar pattern was found. The observed reduction in mating behavior in presence of bystander males is in accordance with an “audience effect,” in which the behavior is modulated in relation to the presence or absence of third parties. This audience effect may serve as an important mechanism to reduce (aggressive) interruptions of subordinate male copulations.     

Mating behavior of male deer ticksIxodes dammini (Acari: Ixodidae)

To analyze the sexual behavior of male black-legged deer ticks Ixodes dammini,we collected ticks infesting 202 white-tailed deer. On average, 17.7 males and 8.8 females infested each deer. Field-collected males copulated with a mean of 2.25 females, and virgin males mated with 2.4 females. On experimental hosts, males established sexual contact with feeding females and repelled other males, and about half remained paired after their mate detached. Engorged females continue to be receptive, and males mate more readily with them than with nonfed females. We conclude that male I. damminiare endowed with a repertoire of behaviors which favor an opportunistic mating before seeking a host and a preference for mating with feeding females on the host accompanied by tenacious mate guarding.     

Male Mating Success and the Effect of Mating History on Ejaculate Traits in a Facultatively Parthenogenic Insect (Extatosoma tiaratum)

Males can typically increase their lifetime reproductive success by mating with multiple females. However, recent studies across a broad range of species have demonstrated physiological constraints on male multiple mating. In this study, we investigate male mating capacity in Extatosoma tiaratum, a facultative parthenogenetic phasmatid. Sperm limitation is thought to be one factor favouring the evolution and maintenance of parthenogenetic reproduction, but studies on male mating ability in facultative parthenogenetic species are extremely rare. To explore whether male mating success varies with mating history, we provided males with weekly mating opportunities with different females throughout their lives. We then observed mating success, and the variation in ejaculate size and quality within each mating. We showed that most, but not all, males can mate multiply, however the amount of ejaculate produced is variable and depends upon male body mass and mating history.     

Fluctuating Asymmetry and Male Mating Success in a Sphragis-Bearing Butterfly Luehdorfia japonica (Lepidoptera: Papilionidae)

The relationship between fluctuating asymmetry (FA) and mating success was studied within males of the sphragis-baring butterfly Luehdorfia japonica, which were collected at various periods during their mating season. FA was measured on the forewing and hindwing radius lengths of male butterflies. Mating frequency of males was estimated by assessing the degree of scale loss from their claspers. Males consume scales and use them to form sphragis on the female abdomen during copulation, sealing the ostium bursa for life. Age of males was scored as wing age 0 to 4 according to the wearing of the wing. FA was negatively correlated with mating frequency but positively correlated with wing age, and average FA decreased with mating season. As females have little chance to express mate choice, it is likely that FA is an indicator of male viability: symmetrical males live longer and/or fly more actively, resulting in a higher lifetime mating success compared to asymmetrical males.     

Pyrazines as warning odour components in the Monarch butterfly, Danaus plexippus, and in moths of the genera Zygaena and Amata (Lepidoptera)

2-Methoxy-3-alkylpyrazines have been identified as odour components in Danaus plexippus, Zygaena lonicerae and an Australian Amata species, by means of coupled gas chromatography/mass spectrometry, with selected ion monitoring. Wide variability in pyrazine content was observed with D. plexippus and this was correlated with similar variability in the larval food-plants, Asclepias spp., which are presumed to be the odour sources for this butterfly. The importance of pyrazines in the biology of aposematic insects and their role as ingredients of a generalized warning system are discussed.     

Multiple Mating and Reproductive Success of Male and Female Apple Maggot Flies, Rhagoletis pomonella (Diptera: Tephritidae)

Mature male and female apple maggot flies mated frequently on a field-caged host tree during a 14-day study. Each sex averaged one mating per day (mean of 1.0 ± 0.1), but some females mated up to eight times per day and some males up to six times per day. Reproductive success was estimated based both on observed numbers of matings in the field cage and on previous work relating fecundity and fertility to female mating status. Male and female flies did not differ in mean or variance in reproductive success, indicating that this is a polygamous mating system consisting of both polygyny and polyandry. We discuss the significance of this with regard to the framework of insect mating control and frequency proposed by others. We also discuss behaviors (such as movements, agonistic encounters, occurrences on fruit, and ovipositions) that do and do not show correlations with mating success in apple maggot flies.     

Male Demography,Female Mating Behavior,and Infanticide in Wild Patas Monkeys (Erythrocebus patas)

Infanticide by males has been hypothesized to be a naturally selected behavioral strategy that increases the infanticidal male's reproductive success. The sexual selection hypothesis has been challenged via alternative, nonadaptive hypotheses that dispute its empirical and theoretical bases. Two of the most widely recognized alternatives are the social pathology hypothesis, in which infanticide results from overcrowding or recent human disturbance, and the generalized aggression hypothesis, in which infanticide is an epiphenomenon of increased male aggression. We report the first case of infanticide in wild, seasonally breeding patas monkeys (Erythrocebus patas) living at a low population density in a stable habitat, conditions which do not support the social pathology hypothesis. Its exceptional occurrence is consistent with the sexual selection hypothesis: over a 7-year period the infanticidal male was the only one of 13 resident males that was not present during the actual conception season but was present during the following birth season. Also consistent with this hypothesis, mothers were differentially targeted for male aggression, which increased sevenfold during the days surrounding the infanticide and then decreased to baseline levels after the infanticide. Aggression targeted at mothers does not support the generalized aggression hypothesis. As predicted by the sexual selection hypothesis, females began soliciting mating immediately after the infanticide, despite its occurrence in the nonconceptive season.     

The Effect of Limb Loss on the Courtship and Mating Behavior of the Wolf Spider Pardosa milvina (Araneae: Lycosidae)

Limb loss is common in the wolf spider Pardosa milvina, appearing in nearly one third of adult males but occurring less frequently among adult females and juveniles. Since males wave their first pair of legs during courtship displays, the reproductive consequences of limb loss may be significant. We measured the courtship and mating effects of the loss of one, two, or four legs among adult male P. milvina. Missing one or two legs did not significantly reduce a male's ability to mate, but missing four legs was detrimental to mating success, reduced both courtship intensity and copulation duration, and increased cannibalism frequency. Results suggest behavioral flexibility in compensating for limited leg loss and a defensive function of the anteriormost legs to thwart female cannibalism attempts.