(<Emphasis Type="Italic">Z</Emphasis>)-9-tricosene identified in rectal gland extracts of <Emphasis Type="Italic">Bactrocera oleae</Emphasis> males: first evidence of a male-produced female attractant in olive fruit fly

It is well-known that Bactrocera oleae (olive fruit fly) females attract conspecific males by using 1,7-dioxaspiro[5,5]undecane (1) as the main component of their sex pheromone, and that 1 is produced in the female rectal gland. Although some authors have claimed that B. oleae males also attract females, to date no male-produced female attractants have been found in this species. In this paper, we report the first identification of a substance unique to males and able to attract females. The findings of the study include the following: (1) females responded in a bioassay to hexane extracts obtained from rectal glands of 15-day-old B. oleae males, (2) the presence of (Z)-9-tricosene (2) was consistently and unambiguously identified in these extracts using gas chromatography (GC) and GC-mass spectrometry methods, (3) in preliminary bioactivity tests, low doses (equivalent to a few males) of chemically and stereoisomerically pure synthetic (Z)-9-tricosene (2) attracted olive fruit fly females. Interestingly, compound 2, commonly called muscalure, is also a well-known component of the house fly (Musca domestica) sex pheromone.     

The larval parasitoid <Emphasis Type="Italic">Microplitis croceipes</Emphasis> oviposits in conspecific adults

Microplitis croceipes (Hymenoptera: Braconidae) is a larval parasitoid of Helicoverpa/Heliothis spp. In the course of mass rearing of M. croceipes, we found that females oviposited in the conspecific adults in rearing cages. When 20 pairs of inexperienced females and males or of experienced females and males were reared in a cage, the males lived for 14–15 days and the females for 18–20 days on average. At their death, 37–42% of the males and 50–57% of the females contained conspecific eggs or first instar larvae in their abdominal cavity. When two of inexperienced females met on a host-infested leaf of soybean, they attempted to sting each other. Of the attacked females, 30% contained a conspecific egg laid in their abdomen. In abdominal cavity of the adults parasitized by a conspecific female, the majority of the parasitoid eggs laid disappeared within 1 day after oviposition. Only 10–30% of the parasitoid eggs laid in conspecific adults hatched 3–4 days after oviposition, but those larvae never molted to second instar. When the adults were stung by one or two conspecific females, their subsequent longevity was significantly shorter than that for the control adults. Oviposition in conspecific adults may be prevalent in other parasitic wasps that quickly oviposit without intensive host examination, and have cuticle and size of abdomen to be stung by conspeicifcs.     

Behavioural evidence of male volatile pheromones in the sex-role reversed wolf spiders Allocosa brasiliensis and Allocosa alticeps

The use of chemical signals in a sexual context is widespread in the animal kingdom. Most studies in spiders report the use of female pheromones that attract potential sexual partners. Allocosa brasiliensis and Allocosa alticeps are two burrowing wolf spiders that show sex-role reversal. Females locate male burrows and initiate courtship before males perform any detectable visual or vibratory signal. So, females of these species would be detecting chemical or mechanical cues left by males. Our objective was to explore the potential for male pheromones to play a role in mate detection in A. brasiliensis and A. alticeps. We designed two experiments. In Experiment 1, we tested the occurrence of male contact pheromones by evaluating female courtship when exposed to empty burrows constructed by males or females (control). In Experiment 2, we tested the existence of male volatile pheromones by evaluating female behaviour when exposed to artificial burrows connected to tubes containing males, females or empty tubes (control). Our results suggest the occurrence of male volatile pheromones that trigger female courtship in both Allocosa species. The sex-role reversal postulated for these wolf spiders could be driving the consequent reversal in typical pheromone-emitter and detector roles expected for spiders.     

No discrimination against previous mates in a sexually cannibalistic spider

In several animal species, females discriminate against previous mates in subsequent mating decisions, increasing the potential for multiple paternity. In spiders, female choice may take the form of selective sexual cannibalism, which has been shown to bias paternity in favor of particular males. If cannibalistic attacks function to restrict a male's paternity, females may have little interest to remate with males having survived such an attack. We therefore studied the possibility of female discrimination against previous mates in sexually cannibalistic Argiope bruennichi, where females almost always attack their mate at the onset of copulation. We compared mating latency and copulation duration of males having experienced a previous copulation either with the same or with a different female, but found no evidence for discrimination against previous mates. However, males copulated significantly shorter when inserting into a used, compared to a previously unused, genital pore of the female.     

Mechanics and Morphology of Silk Drawn from Anesthetized Spiders

 CO₂ and N₂ anesthetized Nephila spiders produced dragline silk with mechanical properties that differed from control silk as a function of time under anesthesia. Silk from CO₂ spiders had a significantly lower breaking strain and breaking energy, significantly higher initial modulus, and marginally lower breaking stress. At the onset of anesthesia the silk diameter became highly variable. During deep anesthesia silk either became thinner or retained cross-section but fibrillated. Received: 26 August 1999 / Accepted in revised form: 22 December 1999     

Loss of legs: is it or not a handicap for an orb-weaving spider?

Leg loss is a common phenomenon in spiders, and according to the species 5% to 40% of the adults can present at least one missing leg. There is no possibility of regeneration after adult moult and the animal must manage with its missing appendages until its death. With the loss of one or more legs, female orb-weaving spiders can be penalized twice: firstly, because the legs are necessary for web construction and secondly, the legs are essential for the control of the prey after its interception by the web. During development, spiders may be also penalized because regeneration has energetic costs that take away resources for survival, growth and reproduction. All these consequences should influence negatively the development of the spider and thus its fitness. We investigated the impact of leg loss in the orb-weaving spider, Zygiella x-notata by studying its frequency in a natural population and web building and prey capture behaviours in laboratory. In field populations, 9.5% to 13%, of the adult females presented the loss of one or more legs; the majority of individuals had lost only one leg (in 48% of cases, a first one). Leg loss seems to affect all the adult spiders, as there is no difference of mass between intact spiders and those with missing leg. Data obtained with laboratory-reared spiders, showed that the loss of legs due to the moult is rare (less than 1%). Considering changes in web design, spiders with missing legs decreased their silk investment, increased the distance between spiral turns but did not change the capture surface of the web. Under our laboratory experimental conditions, spiders with one or two lost legs did not present any difference in prey capture efficiency. In laboratory conditions, spiders with lost leg(s) did not show any difference in egg sac production or in longevity (adult lifespan) compared to intact spiders.     

Homing in the wolf spider Lycosa tarantula (Araneae, Lycosidae): the role of active locomotion and visual landmarks

Previous studies on the homing of the wolf spider Lycosa tarantula have shown that it is carried out by path integration. Animals using this mechanism must measure the distance walked and the angles turned. This study aims to understand if wolf spider L. tarantula is able to estimate the walked distance in an outward path. As this information is more likely obtained by proprioceptive mechanisms, active or passive displacements have been performed. An active locomotion was found essential to estimate distances. During passive locomotion, spiders searched for their burrows near the release point while when displaced actively the inbound journey was longer than the outbound one. The possible use of visual landmarks near the burrow was also tested as a cue to complete the inbound journey. Our results did not show that L. tarantula used these visual landmarks to find the burrow. L. tarantula seems to use only proprioceptive information obtained during the outbound path to estimate the distance traveled.     

Parasitoid-induced mortality of Araneus omnicolor (Araneae, Araneidae) by Hymenoepimecis sp. (Hymenoptera, Ichneumonidae) in southeastern Brazil

All species included in the Polysphincta genus-group develop as ectophagous parasitoids of active spiders, killing their hosts prior to pupation. However, little information regarding natural history and ovipositing behavior of most species are available. In this study we inspected 85 webs of Araneus omnicolor to evaluate the frequency of parasitism and host size preferences of the wasp Hymenoepimecis sp. We also described the web characteristics of normal and parasitized spiders and the wasp ovipositing behavior. About 41% of the adult females of A. omnicolor inspected were parasitized. The highest incidence of parasitism was observed among relatively small females while no egg or larva was found in large individuals. Araneus omnicolor builds a strong web composed of an orb and barrier threads, where the spider rests within a curled leaf. The parasitoid larva builds its cocoon within this refuge, and modified cocoon webs were not observed. The ovipositing behavior of Hymenoepimecis sp. was very similar to that of Hymenoepimecis argyraphaga parasitizing Leucauge argyra, including the position of the sting, the killing of a previously attached larva, and the expelling of the egg from the base of the ovipositor.     

Development and growth in synanthropic species: plasticity and constraints

Urbanization poses serious extinction risks, yet some species thrive in urban environments. This may be due to a pronounced developmental plasticity in these taxa, since phenotypically, plastic organisms may better adjust to unpredictable urban food resources. We studied phenotypic plasticity in Nuctenea umbratica, a common European forest and urban vegetation spider. We subjected spiderlings to low (LF), medium (MF) and high (HF) food treatments and documented their growth and developmental trajectories into adulthood. Spiders from the three treatments had comparable numbers of instars and growth ratios, but differed in developmental periods. Longest developing LF spiders (♀?=?390, ♂?=?320 days) had the smallest adults, but MF (♀?=?300, ♂?=?240 days) and HF (♀?=?240, ♂?=?210 days) spiders reached comparable adult sizes through shorter development. While males and females had comparable instar numbers, females had longer development, higher growth ratios, adult sizes and mass; and while males adjusted their moulting to food availability, female moulting depended on specific mass, not food treatment. We discussed the patterns of Nuctenea sex-specific development and compared our results with published data on two other Holarctic urban colonizers (Larinioides sclopetarius, Zygiella x-notata) exhibiting high plasticity and fast generation turn-over. We conclude that despite relatively unconstrained developmental time in the laboratory enabling Nuctenea to achieve maximal mass and size—main female fitness proxies—their relatively fixed growth ratio and long generation turn-over may explain their lower success in urban environments.     

Silk wrapping of nuptial gifts as visual signal for female attraction in a crepuscular spider

An extensive diversity of nuptial gifts is known in invertebrates, but prey wrapped in silk is a unique type of gift present in few insects and spiders. Females from spider species prefer males offering a gift accepting more and longer matings than when males offered no gift. Silk wrapping of the gift is not essential to obtain a mating, but appears to increase the chance of a mating evidencing a particularly intriguing function of this trait. Consequently, as other secondary sexual traits, silk wrapping may be an important trait under sexual selection, if it is used by females as a signal providing information on male quality. We aimed to understand whether the white color of wrapped gifts is used as visual signal during courtship in the spider Paratrechalea ornata. We studied if a patch of white paint on the males’ chelicerae is attractive to females by exposing females to males: with their chelicerae painted white; without paint; and with the sternum painted white (paint control). Females contacted males with white chelicerae more often and those males obtained higher mating success than other males. Thereafter, we explored whether silk wrapping is a condition-dependent trait and drives female visual attraction. We exposed good and poor condition males, carrying a prey, to the female silk. Males in poor condition added less silk to the prey than males in good condition, indicating that gift wrapping is an indicator of male quality and may be used by females to acquire information of the potential mate.     

Settlement decisions in blue tits: difference in the use of social information according to age and individual success

Dispersers are expected to assess breeding habitat quality before settlement. Although cues reflecting habitat quality are well studied, social cues have not been as well evaluated. In this paper, we studied breeding habitat selection during 3 years in a natural population of blue tits, Cyanistes caeruleus, breeding in nest-boxes. Our aim was to investigate if this species used conspecific density and/or reproductive success of con- and heterospecifics (i.e., social cues) in settlement decisions. The patterns observed were consistent with the idea that juveniles, when dispersing from their natal patches, did not react to any of the cues that we tested. In contrast, breeders that dispersed seemed to respond to both conspecific mean patch reproductive success (PRS) and breeding density of the settlement patch in the year of dispersal, their response differing according to their own reproductive success. Indeed, failed breeders moved to areas with high PRS and low density relative to source patches, while successful breeders behaved the opposite. The comparison between juveniles and adults might be modulated by the limited time available to juveniles to gather information on PRS and density at the end of the dispersing year. Adults lacking these time constraints, however, seemed to rely on these conspecific cues although limited by their own quality. Additionally, breeders were more likely to be immigrants in patches with relatively low breeding success and density the previous year, suggesting that settlement is influenced by multiple cues, which may reveal information on different aspects of habitat and be available at different moments. Collectively, our results support the importance of social cues for blue tits’ settlement.     

Associative learning of odor with food- or blood-meal by Culex quinquefasciatus Say (Diptera: Culicidae)

The ability of many insects to learn has been documented. However, a limited number of studies examining associative learning in medically important arthropods has been published. Investigations into the associative learning capabilities of Culex quinquefasciatus Say were conducted by adapting methods commonly used in experiments involving Hymenoptera. Male and female mosquitoes were able to learn a conditioned stimulus that consisted of an odor not normally encountered in nature (synthetic strawberry or vanilla extracts) in association with an unconditioned stimulus consisting of either a sugar (males and females) or blood (females) meal. Such information could lead to a better understanding of the ability of mosquitoes to locate and select host and food resources in nature.     

Transmission of ice-nucleating active bacteria from a prey reduces cold hardiness of a predator (Araneae: Theridiidae)

The influence of ice-nucleating active (INA) bacteria on cold hardiness of the house spider, Achaearanea tepidariorum, was determined by measuring the supercooling point (SCP) of hatchlings given either INA-bacteria-fed or bacteria-free prey (Drosophila melanogaster). Spiders that had eaten INA-bacteria-fed flies showed higher SCPs than those fed on bacteria-free flies. Through feeding, INA bacteria in the prey reduce the cold hardiness of spiders. This fact should be taken into account before using INA agents as a means of pest management.     

Nestmate recognition in ants is possible without tactile interaction

Ants of the genus Camponotus are able to discriminate recognition cues of colony members (nestmates) from recognition cues of workers of a different colony (non-nestmates) from a distance of 1 cm. Free moving, individual Camponotus floridanus workers encountered differently treated dummies on a T-bar and their behavior was recorded. Aggressive behavior was scored as mandibular threat towards dummies. Dummies were treated with hexane extracts of postpharyngeal glands (PPGs) from nestmates or non-nestmates which contain long-chain hydrocarbons in ratios comparable to what is found on the cuticle. The cuticular hydrocarbon profile bears cues which are essential for nestmate recognition. Although workers were prevented from antennating the dummies, they showed significantly less aggressive behavior towards dummies treated with nestmate PPG extracts than towards dummies treated with non-nestmate PPG extracts. In an additional experiment, we show that cis-9-tricosene, an alkene naturally not found in C. floridanus' cuticular profile, is behaviorally active and can interfere with nestmate recognition when presented together with a nestmate PPG extract. Our study demonstrates for the first time that the complex multi-component recognition cues can be perceived and discriminated by ants at close range. We conclude that contact chemosensilla are not crucial for nestmate recognition since tactile interaction is not necessary.     

Heterospecific pairing and hybridization between <Emphasis Type="Italic">Nasutitermes corniger</Emphasis> and <Emphasis Type="Italic">N. ephratae</Emphasis>

The sympatric neotropical termites Nasutitermes corniger and Nasutitermes ephratae are clearly distinguishable based on morphology, nest architecture, defensive secretion composition, and molecular markers. However, given the extensive ecological, geographical, and behavioral overlap of these closely related species, the potential for interbreeding may exist. To explore this possibility, heterospecific pairs were formed experimentally to examine courtship and colony-establishment behaviors, and reproductive potential. Courtship and nest construction behavior occurred in heterospecific pairs in a similar manner to that of conspecific pairs. Survival of pairs depended upon the species of the female partner. N. ephratae females paired with N. corniger males produced as many offspring as conspecific pairs. N. corniger females mated to N. ephratae males, however, produced significantly fewer offspring at 60 days post-establishment than the reciprocal cross or conspecific N. ephratae or N. corniger pairs. This was also the only pairing in which any aggression was observed. Heterospecific pairs and groups formed in mate choice mesocosms, suggesting that species recognition between these two termites is not an important aspect of mate choice. Overall, species mismatch tolerance and hybrid offspring viability are high. The present data, together with previous evidence from defensive secretions and isozyme analysis, suggest that hybridization may periodically occur in nature, and that reproductive barriers between these two species may be incomplete. Hybridization could provide a rare but important source of genetic diversity and may ensure mating opportunities for the more abundant sex of alates in each species.     

Body-mass-dependent cost of web-building behavior in an orb weaving spider,Zygiella x-notata

In numerous spider species, reproductive success of adult females has been shown to be positively correlated with their body mass. We suggest, however, that spiders may incur greater foraging costs as their body mass increases due to the numerous and complex locomotor bouts needed to build an orb-web. Such a body-mass-dependent cost should, in turn, affect the web-building decisions of spiders. In the laboratory, we tested the influence of body mass on energetic expenditure (measured as mass loss) during web-building behavior in Zygiella x-notata. Our results showed (1) that energetic costs associated with web-building were closely related to body mass and to web-building activity, and (2) that as their body mass increased, spiders reduced the amount of silk used per web, while their foraging effort simultaneously increased. This work gives new insights into web-building behavior and energy allocation strategies of weaving spiders.     

Female feeding regime and polyandry in the nuptially feeding nursery web spider, Pisaura mirabilis

We examined the influence of female feeding regime on polyandry in the nuptially feeding nursery web spider (Pisaura mirabilis). In this species, the nuptial gift, a dead prey item wrapped in the male’s silk, is physically separate from the ejaculate. We manipulated female feeding regime (starved or fed) and the presence or absence of a gift with three successive males to test direct-benefits hypotheses (nuptial gift or sperm supply) for the expression of polyandry. The presence of a gift was necessary for copulation, as no male without a gift successfully copulated. Female mating behavior most strongly supports polyandry due to the accumulation of gifted food items (“nuptial gift” direct-benefits hypothesis). Starved females that were presented with a gift accepted significantly more gifts and inseminations than fed females. Most starved females (74%) copulated two or more times, as opposed to only 3% of the fed females. Nearly all of the females that accepted a gift subsequently copulated. The nuptial gift item seems to function as male mating effort and females appear to receive multiple matings as part of a feeding strategy.     

The effect of female wings on male courtship behavior in the cricket Gryllus bimaculatus

Sexual dimorphism exists in the shape and the structure of the forewings of the cricket (Gryllus bimaculatus). However, the functional significance of the wings in the G. bimaculatus female has been unclear. In common blue butterflies (Polyommatus icarus), wings in females have been suggested as being important for attracting males. To test whether female crickets need wings for conspecific males to recognize them and initiate mating behavior, we removed all wings from females and observed the behavior of males towards them. Most males (87.5%) showed mating behavior towards the wingless females: they produced courtship song and transferred spermatophores to the wingless females. Similarly, 88.5% of the males showed mating behavior towards intact females. When males were placed with both a wingless female and an intact female, no significant difference was detected in male mate choice. The findings demonstrate that the wing of the G. bimaculatus female is not necessary for female recognition by conspecific males and the initiation of male mating behavior, and that it is not important in male mate choice.