Effects of familiarity and nestmate number on social interactions in two communal bees, Andrena scotica and Panurgus calcaratus (Hymenoptera, Andrenidae)

Summary: Communality is considered a widespread form of social organization in bees and wasps, one in which two or more females of the same generation share a common nest and amongst whom there is no reproductive division of labor. The evolution and maintenance of egalitarian communal societies poses theoretical difficulties where 'cheating' amongst nestmates is practised. Yet there is little knowledge of the intranidal social interactions among communal conspecifics that allow an understanding of the degree of cooperation versus exploitation amongst nestmates in such societies. Using a circle-tube arena, we staged interactions in the laboratory among pairs of female conspecifics using two communal andrenid species, Andrena scotica and Panurgus calcaratus, to score their cooperative and aggressive behaviors. For both species, females did not discriminate between familiar (nestmate) and unfamiliar (non-nestmate) conspecifics in their cooperative and aggressive behaviors, suggesting that there is universal acceptance of conspecifics. Levels of cooperation and aggression did not vary with the number of nestmates in the nest of origin for either species. In addition, frequencies of social interactions did not vary with body size, wing wear or ovarian development in P. calcaratus. Interspecific comparisons were made with published data on social interactions of other bee species at varying levels of social organization (solitary to eusocial) derived from analogous circle-tube experiments. Panurgus calcaratus displayed highly cooperative behavior, similar to that of a previously studied communal bee, Lasioglossum hemichalceum (Kukuk, 1992a). Andrena scotica displayed lower levels of cooperation, and was in this sense more similar to solitary species and to interactions amongst non-nestmate individuals of eusocial species. Both A. scotica and P. calcaratus displayed very low levels of aggressive behavior, again similar to L. hemichalceum. As a working hypothesis, we suggest the existence of a communal behavioral syndrome comprising high levels of intranidal cooperation and low aggression, both directed indiscriminately at conspecifics.     

Spatial Nest‐Settlement Decisions in Digger Wasps: Conspecifics Matter more than Heterospecifics and Previous Experience

Research into the driving forces behind spatial arrangement of wasp nests has considered abiotic environmental factors, but seldom investigated attraction or repulsion towards conspecifics or heterospecifics. Solitary female digger wasps (Hymenoptera) often nest in dense aggregations, making these insects good models to study this topic. Here, we analysed the nesting patterns in an area shared by three species of the genus Bembix, in a novel study to discover whether female wasps are attracted to or repulsed by conspecific nests, heterospecific nests or their own previously established nests when choosing nest‐digging locations. Early in the season, each species showed a clumping pattern of nests, but later in the season, a random distribution of nests was more common, suggesting an early conspecific attraction. Such behaviour was confirmed by the fact that females started building their nests more frequently where other females of their species were simultaneously digging. The distances between subsequent nests dug by individual females were shorter than those obtained by random simulations. However, this pattern seemed to depend on the tendency to dig close to conspecifics rather than remain in the vicinity of previous nests, suggesting that females' experience matters to future decisions only on a large scale. Nesting patches within nest aggregations largely overlapped between species, but the nests of each species were generally not closer to heterospecific nests than expected by chance, suggesting that females are neither repulsed by, nor attracted to, congenerics within nest aggregations. A role of the spatial distribution of natural enemies on the observed nesting patterns seemed unlikely. Bembix digger wasp nest aggregations seem thus to be primarily the result of female–female attraction during nest‐settlement decisions, in accordance with the ‘copying’ mechanisms suggested for nesting vertebrates.     

Group nesting and individual variation in behavior and physiology in the orchid bee <Emphasis Type="Italic">Euglossa nigropilosa</Emphasis> Moure (Hymenoptera,Apidae)

The Euglossini are a key group for studying the traits that promote or hinder highly social behavior in bees because it is the only tribe in the Apine clade without large colonies or females with distinct life histories, e.g. queens and workers. There have been few studies on behavior of orchid bee females in nests because these nests are not found easily. Taking advantage of the relatively high abundance of Eg. nigropilosa nests at Reserva Natural La Planada, Colombia, we examined social behavior of Eg. nigropilosa individuals in five nests (3 original and 2 reused) for nine months. We report this species to have the largest colonies known for Euglossa, with nests reaching up to 22 individuals, and all nests containing more than one female bee from the same generation. These nests presented many traits that correspond to communal insect colonies. No generational overlap and no cooperative brood care were detected. We examined natural enemies and resource limitation as important factors for group nesting. We examined parasitoid attacks to cells in a nest with females and one without females. We also searched for nesting locations and examined nest re-use as indicators of nest site limitation. Lastly, we examined behavioral and physiological differences among females in the same nest. Such differences could be the bases for evolution of alternative life histories among group living females. We examined extent of ovary development and oviposition rates in similarly aged females in the same nest. We found large variation in reproductive effort of young females. We also examined differences in resin foraging and cell usurpation behaviors. Behavioral specialization was observed, with some individuals bringing only resin to the nest. Inside the nests, bees had territories in which they constructed and defended cells. This territoriality may be a defense against usurpation of provisioned cells by nest mates. Received 10 December 2007; revised 2 May 2008; accepted 7 May 2008.     

Kin Recognition in the largely Solitary Bee,Manuelia postica (Apidae: Xylocopinae)

The recognition of conspecifics is a central issue to social behaviour. In eusocial hymenopterans, kin recognition has been clearly demonstrated. Manuelia postica is a largely solitary bee species in which larvae develop inside individual cells within a nest and remain isolated from conspecifics until the destruction of partitions by adults. Nestmate recognition in M. postica has been previously demonstrated under experimental conditions. Isolation between individuals during development and nestmate recognition ability in adult females make M. postica an ideal species for testing the occurrence of kin recognition capacity in females. Kin recognition was demonstrated through cross‐fostering field experiments involving the single transfer of recently enclosed larvae, and subsequent laboratory recognition bioassays with emerging females. Results suggest kin recognition occurs through self‐referent phenotype matching. Given the basal position of Manuelia in the phylogeny of the Apidae, kin recognition may represent an ancestral recognition mechanism in Apidae species phylogenetically more derived than M. postica.     

Floating and fidelity in nest visitation byCrawfordapis luctuosa (Hymenoptera: Colletidae)

We studied nest visitation behavior of the ground-nesting beeCrawfordapis luctuosa (Colletidae) at the Monteverde Cloud Forest Preserve, Puntarenas Province, Costa Rica. Some females entered many nests, while others consistently entered only one nest. Multiple nest entry was exhibited by bees we called floaters, and those bees that consistently entered only one nest were provisioning bees. Provisioning bees abandoned their old nests after provisioning periods and became nonprovisioning bees that floated over the nesting area. Floating behavior was a nest-searching behavior typified by oscillating flights just above the ground (<15 cm). Floaters investigated available nests and were not observed to interact aggressively with nest owners. Upon establishing a new nest, floaters became provisioning bees.     

Effects of Fungicide and Adjuvant Sprays on Nesting Behavior in Two Managed Solitary Bees,Osmia lignaria and Megachile rotundata

There is a growing body of empirical evidence showing that wild and managed bees are negatively impacted by various pesticides that are applied in agroecosystems around the world. The lethal and sublethal effects of two widely used fungicides and one adjuvant were assessed in cage studies in California on blue orchard bees, Osmia lignaria, and in cage studies in Utah on alfalfa leafcutting bees, Megachile rotundata. The fungicides tested were Rovral 4F (iprodione) and Pristine (mixture of pyraclostrobin + boscalid), and the adjuvant tested was N-90, a non-ionic wetting agent (90% polyethoxylated nonylphenol) added to certain tank mixtures of fungicides to improve the distribution and contact of sprays to plants. In separate trials, we erected screened cages and released 20 paint-marked females plus 30–50 males per cage to document the behavior of nesting bees under treated and control conditions. For all females in each cage, we recorded pollen-collecting trip times, nest substrate-collecting trip times (i.e., mud for O. lignaria and cut leaf pieces for M. rotundata), cell production rate, and the number of attempts each female made to enter her own or to enter other nest entrances upon returning from a foraging trip. No lethal effects of treatments were observed on adults, nor were there effects on time spent foraging for pollen and nest substrates and on cell production rate. However, Rovral 4F, Pristine, and N-90 disrupted the nest recognition abilities of O. lignaria females. Pristine, N-90, and Pristine + N-90 disrupted nest recognition ability of M. rotundata females. Electroantennogram responses of antennae of O. lignaria females maintained in the laboratory did not differ significantly between the fungicide-exposed and control bees. Our results provide the first empirical evidence that two commonly used fungicides and a non-ionic adjuvant can disrupt nest recognition in two managed solitary bee species.     

Behavioral mechanisms preventing filial ovicide in house wrens

Because unmated house wrens (Troglodytes aedon) regularly destroyclutches of conspecifics, we examined mechanisms that preventbreeding individuals from destroying eggs in their own nests.Results of our experimental field study indicate that the egg-destroyingbehavior of males is partially suppressed after mating and thatthe suppression may prevent filial ovicide in some individuals.At least 35% of males continue to destroy conspecific eggs duringthe incubation period of their mates. Because filial ovicideby males is prevented independently of female presence at thenest, we conclude, after eliminating alternative hypotheses,that filial ovicide by males is prevented through their recognitionof nest locations. Egg-destroying behavior of females is alsosuppressed during the incubation. The suppression is strongerthan in males because fewer females than males destroy foreigneggs over a comparable time period. Females respond to experimentallychanged nest location and nest structure, but not egg coloration.We conclude that filial ovicide by females is prevented throughthe suppression of their eggdestroying behavior and throughtheir recognition of nest location and structure.     

Female‐biased sleeping aggregations of Amegilla florea urens (Hymenoptera: Apidae)

Although male bees and wasps aggregate in specific sites overnight, few studies have addressed the behaviors of female hymenopterans during the night. It is generally understood that they spend the night in a burrow or nest structure. We found female‐biased sleeping aggregations of Amegilla florea urens in populations on Iriomote Island. The sex ratio and number of sleeping individuals in the sex‐mixed aggregations changed daily. This species used dead branches as its main sleeping places, and the maximum number of individuals observed per place was 15. Females arrived at the aggregation place later and left it earlier in the morning than did males. Our result suggests that females used the sleeping place regularly but avoided a long stay with males. The use of the same sleeping place by the two sexes may be due to a limited number of sites suitable for sleeping in the forest.     

Lack of social preference between unfamiliar and familiar juvenile Port Jackson sharks Heterodontus portusjacksoni

This study investigated whether captive-reared juvenile Port Jackson sharks Heterodontus portusjacksoni choose to aggregate and if familiarity is one of the mechanisms driving social preference. In a controlled binary-choice experiment, juvenile sharks were given the option to associate or not with unfamiliar conspecifics, or to associate or not with familiar conspecifics. In neither group did juvenile H. portusjacksoni actively choose to associate with conspecifics, but familiarity decreased the proportion of time spent near a conspecific only during the initial phase of the experiment. Treatment (1 or 3 shoal mates), sex and size had no effect on aggregation behaviour. These findings suggest that familiarity is not a driver of social preferences in juvenile H. portusjacksoni, contrary to results in another shark species. Additionally, adult H. portusjacksoni form large aggregations during the breeding season and actively associate with familiar sex and size-matched individuals, thus our results suggest the species undergoes an ontogenetic shift in social behaviour.     

Conspecific Attraction Drives Intraspecific Aggregations by Nephila clavipes Spiders

Aggregation behavior is common throughout the animal world, although it is rare in spiders (Araneae). Nephila clavipes spiders are frequently found both in solitary webs and in aggregations of conspecifics. N. clavipes aggregations are not considered social, because these spiders do not engage in food sharing or group parental care. The currently accepted explanation for N. clavipes aggregations is that they form passively, as spiders aggregate in response to the patchy distribution of food resources in the environment. Here, we show instead that N. clavipes females actively seek out conspecifics and, therefore, that aggregations arise from conspecific attraction. We experimentally established that (1) N. clavipes females actively follow the trails left by conspecifics and (2) aggregations are formed independently of prey density in a particular area. These results suggest that while aggregations in high food patches increase encounter rates of conspecific spiders and support the nutritional needs of multiple large spiders, this potential benefit is not the proximate mechanism for aggregation. Thus, we hypothesize that N. clavipes females likely acquire fitness benefits from aggregating with conspecifics.     

Nesting biology of tropical solitary and social sweat bees,Lasioglossum (Dialictus) figueresi Wcislo andL. (D.) aeneiventre (Friese) (Hymenoptera: Halictidae)

Summary The nesting biology of a mainly solitary bee,Lasioglossum (Dialictus) figueresi, is compared with that of a possible relative and mainly eusocial bee,L. (D.) aeneiventre. These bees nest in the ground in highly disturbed areas in the Meseta Central of Costa Rica. Information is provided on social organization, male production, diel and seasonal activity patterns, pollen utilization, natural enemies and nest architecture. L. (D.) figueresi nests within aggregations in vertical earthen banks, and 80–90 % of females are solitary during the nest-provisioning phase. Social nests contain two (or rarely three) females which may be either equal or unequal in reproductive status (i.e. mated with developed ovaries or not). Solitary nests and two-female nests do not experience different rates of parasitism. Mid-way through the dry season, females cease provisioning at a time when otherL. (Dialictus) remain active. Females typically remain within their nests, although they occasionally forage for nectar. This behavior is similar of that of spring gynes of temperate eusocial species. The egg-to-adult developmental rate ofL. (D.) figueresi is unusually slow for halictine bees, however, so that all the adult females die before their brood eclose in April and May, precluding overlap of generations. The eclosed offspring remain in open cells within their natal nests until mid-June, when both males and females emerge to mate. These newly mated females either establish new nests or re-use old ones. L. (D.) aeneiventre nests within aggregations in horizontal ground or in vertical banks. A foundress female digs a nest at the beginning of the dry season, although some re-activate old nests. Foundress nests develop into colonies with various kinds of social organization. In contrast toL. (D.) figueresi, L. (D.) aeneiventre is active nearly all year round, except during periods of heavy rain, and produces up to three broods per year.Sweat bees (Hymenoptera: Halictinae) are a socially heterogeneous group of mainly ground-nesting bees which are abundant world-wide. Intra-specific variation in social behavior is prevalent both within and among populations, presumably indicating social and environmental control of behavioral modifications (see e.g. Sakagami and Munakata, 1972; Eickwort, 1986; Packer, 1990; Yanega, 1988; reviewed in Michener, 1990). The initial stages of hymenopteran social evolution are represented by solitary individuals and those in undifferentiated societies, yet their biology is not well known, as is true for the numerous tropical halictine species or populations (see Michener, 1990).The subgenusDialictus ofLasioglossum is a primarily New World group of several hundred species (Moure and Kurd, 1987). These bees are monotonously similar in structure and appearance, yet diverse in social behavior. FemaleLasioglossum (Dialictus) figueresi are usually solitary, and structurally are very similar to their social relativeL. (D.) aeneiventre (Wcislo, 1990 a). The systematic placement of these species with respect to otherL. (Dialictus) is uncertain, but they have no obvious affinities to other recognized species groups (G. C. Eickwort, pers. comm.). Unusual morphological features, such as large size, yellowish wings and pubescence, and features of the genital organs, may indicate thatL. (D.) figueresi is the more derived of the pair, and may therefore be secondarily solitary, as is known for other sweat bees (Packer, 1991).     

Nest Entrance Marking with Colony Specific Odors by the Bumble Bee Bombus occidentalis (Hymenoptera: Apidae)

We investigated the ability of naturally foraging female bumble bees (Bombus occidentalis) to recognize their nest entrance in the field. In a blind binary-choice paradigm, females discriminated between nest entrances tipped with caps from their own nest entrances and entrances tipped with caps previously associated with foreign heterospecific or foreign conspecific colonies. Washing caps in organic solvents eliminated the manifestation of this nest-entrance recognition and significantly decreased the episodes of antennating caps. These results indicate that bees deposit colony-specific chemicals on nest entrances that are later perceived via contact chemoreception. Females treated foreign heterospecific and foreign conspecific caps similarly, suggesting that bees may not assess or respond to the degree of similarity between their own colony odor and a foreign colony odor.     

Mixed colonies of two species of congeneric stingless bees (Hymenoptera: Apinae,Meliponini) display environmentally‐acquired and endogenously‐produced recognition signals

Nestmate recognition is fundamental for the maintenance of social organization in insect nests. It is becoming well recognized that cuticle hydrocarbons mediate the recognition process, although the origin of recognition cues in stingless bees remains poorly explored. The present study investigates the effects of endogenously‐produced and environmentally‐acquired components in cuticular hydrocarbons in stingless bees. The tests are conducted using colonies of Plebeia droryana Friese and Plebeia remota Holmberg. Recognition tests are performed with four different groups: conspecific nestmates, conspecific non‐nestmates, heterospecifics and conspecific, genetically‐related individuals that emerge in a heterospecific nest. This last group is produced by introducing brood cells of P. droryana into a P. remota colony, and the resulting adult bees are tested for acceptance 10 days after emergence. For all groups, 15 individuals are sampled for chemical analysis. The results show the acceptance of all conspecific nestmates, and the rejection of almost every conspecific non‐nestmate and every heterospecific bee. Genetically‐related individuals emerging from heterospecific nests present intermediate rejection (66.7% rejection). Chemical analysis shows that P. droryana individuals emerging in a P. remota nest have small amounts of alkene and diene isomers found in P. remota cuticle that are not found in workers from the natal nest. The data clearly show that the majority of the compounds present in P. droryana cuticle are endogenously produced, although a few unsaturated compounds are acquired from the environment, increasing the chemical differences and, consequently, the rejection percentages.     

Not all who wander are lost: nest fidelity in <Emphasis Type="Italic">Xylocopa virginica</Emphasis> examined by mark recapture

Relocation to novel nests (sometimes called drifting) in flying Hymenoptera is often interpreted as the result of navigation error and guard bees erroneously admitting foreign individuals into the nest. We studied nest fidelity and nest relocation of both females and males in a nesting aggregation of Xylocopa virginica in southern Ontario, Canada, where females can nest either solitarily or socially. Adult female and male bees were trapped at nest entrances, individually paint marked, and then released. Subsequent recapture patterns were used to assess nest fidelity: that is, how faithful individuals were to their home nest and how often they moved to another nest. Bees were considered to have relocated if they were recaptured in a nest different from the one in which they were initially trapped, indicating that they had spent at least one night in a new nest. Some females were only captured in one nest, some occasionally moved to new nests, temporarily or permanently, and a few were never caught in the same nest twice. In addition, females relocated to nests that were further away in 2007 when population density was low, suggesting that they seek out and claim nesting spaces when they are available. Males relocated more frequently than females, with most drifting from nest to nest in no obvious pattern. This indicates that males spend the night wherever space is available or in nests nearest to their territories. This study reveals that for both female and male X. virginica, nest membership is not as stable as once thought.     

Population structure and survival in a solitary wasp (Microbembex cubana: Hymenoptera,Sphecidae, Nyssoninae)

Summary This paper documents population structure in a solitary wasp, Microbembex cubana (Hymenoptera, Sphecidae, Nyssoninae), on a small (15 km²) Bahamian island. A relatively isolated portion of this population was studied April–June 1985. The population comprised small aggregations of territorial males and nesting females. Individuals of both sexes were with rare exceptions faithful to a home aggregation during their one- to two-month adult lifespans, conducting all reproductive activities there. Individuals from different aggregations, however, mixed daily during these activities: feeding on nectar, hunting for provisions and retiring to clustered sleeping burrows. Significant variation occurred among the nine breeding aggregations in size, density, sex-ratio (which was on average 2:1 in favor of males) and survival (which was 0.93–0.99 per individual/per day and which was not higher for females than for males). Aggregations retained the same characteristics for longer than the life expectancies of individuals in them.Factors affecting reproductive success and survivorship in M. cubana are complex: they are apparently only partially overlapping between males and females and subject to spatial variation. Patterns in the data suggest several hypotheses about how behavior, morphology and habitat interact to shape population processes. I propose that aggregations arise and are characterized by considerable behavioral inertia because individual M. cubana use conspecifics as sources of information on resource quality. Because M. cubana occurs in secondary habitats, individuals retain flexibility in responding to better opportunities for reproduction, but this population exhibits more viscosity than reported for other ground-nesting solitary Hymenoptera.     

Incubation failure and nest abandonment by Leach's Storm‐Petrels detected using PIT tags and temperature loggers

ABSTRACT The nocturnal activity of burrow‐nesting seabirds, such as storm‐petrels and shearwaters, makes it difficult to study their incubation behavior. In particular, little is known about possible differences in the incubation behavior of adults at successful and unsuccessful nests. We combined the use of passive integrated transponder (PIT) technology and nest‐temperature data loggers to monitor the incubation behavior of 10 pairs of Leach's Storm‐Petrels (Oceanodroma leucorhoa). The mean incubation bout length was 3.31 ± 0.59 (SD) days for individual adults at successful nests (N= 4) and 1.84 ± 1.16 d for individuals at unsuccessful nests (N= 6). Mean bout length for pairs in successful burrows (3.51 ± 0.56 d) did not differ significantly (P= 0.07) from that for pairs in unsuccessful burrows (1.80 ± 1.20 d), perhaps due to one failed nest with a high mean bout length (4.15 d). The total number of incubation bouts per parent (4.3 ± 1.9 bouts) did not differ with hatching success. Adults whose nests failed repeatedly exhibited truncated incubation bouts (< 12 h) prior to complete nest failure and were more likely than successful parents to make brief visits to nearby, occupied nesting burrows. Our results suggest that the decision by Leach's Storm‐Petrels to abandon a nest is not an abrupt one. Rather, failed nesting attempts may be characterized by truncated incubation bouts where individuals pay the energetic cost of travel to and from the burrow, but do not remain long enough to successfully incubate the egg.     

Interannual Variation in Nut Abundance Is Related to Agonistic Interactions of Foraging Female Japanese Macaques (Macaca fuscata)

The importance of dominance status to foraging and ultimately survival or reproductive success in wild primates is known; however, few studies have addressed these variables simultaneously. We investigated foraging and social behavior among 17 adult female Japanese macaques (Macaca fuscata) on Kinkazan Island, northern Japan, from September to November in 2 consecutive years (2004 and 2005) to determine whether interannual variation in food availability was related to variation in agonistic interactions over food resources and the feeding behavior of individuals of different dominance rank. We compared energy obtained with daily energy requirements and also examined the effect of variation in feeding behavior on female survival and reproductive success. Fruiting conditions differed considerably between the 2 yr: of four nut-producing species, the nuts of only Torreya nucifera fruited in 2004, whereas all four species, particularly Fagus crenata, produced nuts in abundance in 2005. The abundance and average crown size of trees of Torreya nucifera were smaller than those of Fagus crenata, and there was a higher frequency of agonistic interactions during 2004, when dominant, but not subordinate, individuals were able to satisfy daily energy requirements from nut feeding alone through longer nut feeding bouts. In contrast, all macaques, regardless of their dominance rank, were able to satisfy their energy requirements by feeding on nuts in 2005. Subordinate macaques appeared to counter their disadvantage in 2004 by moving and searching for food more and maintaining larger interindividual distances. Several lower-ranking females died during the food-scarce season of 2004, and only one dominant female gave birth the following birth season. In contrast, none of the adult females died during the food-scarce season of 2005, and 12 females gave birth the following birth season. These findings suggest that an interaction between dominance rank and interannual variation in food availability are related to macaque behavior, survival, and reproduction.     

Alarm signals in Daphnia?

Daphnia magna can respond to chemical cues from freshly crushed conspecifics with various behavioural reactions. A shift in vertical distribution towards the bottom, the formation of aggregations and direct escape responses can all be induced by water-borne signals released from crushed Daphnia. The pattern and strength of the first two behavioural responses (i.e. the persistent tendency to occupy deeper strata in the experimental columns and to stay within patches) indicate that Daphnia perceive the signal from crushed conspecifics as nonspecific information, not necessarily associated with any particular kind of danger from either vertebrate or invertebrate predators. The adaptive value and possible costs associated with performing these two behavioural reactions are discussed. The adaptive value of the induced escape response was directly tested: Daphnia which had experienced the presence of a cue from crushed conspecifics avoided attacks by common bream more efficiently than naive Daphnia. The recognition of the signal originating from crushed conspecifics can be especially adaptive in encounters with unfamiliar predators and with predators that undergo ontogenetic shifts in their diet. Under natural conditions, the combination of such a signal with a predator cue can, very reliably, advertise the local scale of the predatory impact. Received: 10 October 1996 / Accepted: 20 May 1997     

Nestmate recognition in Parischnogaster striatula (Hymenoptera Stenogastrinae), visual and olfactory recognition cues

The recognition of nestmates from alien individuals is a well known phenomenon in social insects. In the stenogastrine wasp Parischnogaster striatula, we investigated the ability of females to recognize nestmates and the cues on which such recognition is based. Recognition of nestmates was observed in naturally occurring interactions between wasps approaching a nest and the resident females on that nest. This recognition was confirmed in experiments in which nestmates or alien conspecifics were presented to resident females. In naturally occurring interactions, nestmates generally approach their nest with a direct flight, while aliens usually hover in front of the nest before landing. In experiments in which the presented wasps were placed close to the nest in a direct manner, antennation of the presented wasp generally occurred, indicating that chemical cues are involved. Experiments in which dead alien individuals, previously washed in hexane, and then reapplied with extracts were recognized by colonies giving further evidence that chemical cues mediate nestmate recognition. Epicuticular lipids, known to be nestmate recognition cues in social insects, were chemically analysed by GC-MS for 44 P. striatula females from two different populations (13 different colonies). Discriminant analysis was performed on the data for the lipid mixture composition. The discriminant model showed that, in the samples from these two populations, 68.2% and 81.9% of the specimens could be correctly assigned to their colony.     

Major benefits of guarding behavior in subsocial bees: implications for social evolution

Parental care is a behavior that increases the growth and survival of offspring, often at a cost to the parents' own survival and/or future reproduction. In this study, we focused on nest guarding, which is one of the most important types of extended parental care; we studied this behavior in two solitary bee species of the genus Ceratina with social ancestors. We performed the experiment of removing the laying female, who usually guards the nest after completing its provisioning, to test the effects of nest guarding on the offspring survival and nest fate. By dissecting natural nests, we found that Ceratina cucurbitina females always guarded their offspring until the offspring reached adulthood. In addition, the females of this species were able to crawl across the nest partitions and inspect the offspring in the brood cells. In contrast, several Ceratina chalybea females guarded their nests until the offspring reached adulthood, but others closed the nest entrance with a plug and deserted the nest. Nests with a low number of provisioned cells were more likely to be plugged and abandoned than nests with a higher number of cells. The female removal experiment had a significantly negative effect on offspring survival in both species. These nests frequently failed due to the attacks of natural enemies (e.g., ants, chalcidoid wasps, and other competing Ceratina bees). Increased offspring survival is the most important benefit of the guarding strategy. The abandonment of a potentially unsuccessful brood might constitute a benefit of the nest plugging behavior. The facultative nest desertion strategy is a derived behavior in the studied bees and constitutes an example of an evolutionary reduction in the extent of parental care.