Female mate choice in the carpenter bee Xylocopa varipuncta (Hymenoptera: Anthophoridae)

Females of the carpenter bee Xylocopa (Neoxylocopa) varipuncta Patton exhibit highly active mate choice. During the spring in central Arizona, males of this species hover at shrubs and trees on or near ridgelines in late afternoons. Occasionally, females fly to and closely approach pheromone-releasing males on their territories, but in 65 of 85 approaches the female left without copulating. Some females visited several males in a few minutes. Copulation only occurred when the female landed on a spot that the resident male rubbed with his body upon the female's arrival. Males did not attempt to disrupt courtship or copulation by other males. In 1988 one creosote bush proved especially attractive to males, as measured by the frequency with which the site was occupied simultaneously by more than one male. The majority of close approaches by females occurred in this one bush. Simultaneous occupation of hovering sites was very rare in 1989. In this year, there was a weak but significant correlation between the frequency with which different sites were visited by intruder males and by females. These results support the hypothesis that males are able to identify locations most likely to attract potential mates.     

Bioassay evidence for a sex attractant pheromone in the large carpenter bee, Xylocopa varipuncta (Anthophoridae: Hymenoptera)

A field bioassay was conducted to test i˜hethercompoundsp roduced in the thoracic gland of male X. varipuncta are involved in long-range mate attraction. Filter paper impregnated with the two most abundant compounds of the male gland was placed in sites comparable to those used by territorial males during the time of day when mating activity occurs. Females visited these filter paper 'lures' as often as they visited unmanipulated males in the study area. Males with the chemical mixture added to their territories did not receive more matings than males at territories where we had not added the chemical mixture. These findings and other studies, summarized herein, support the hypothesis that the male gland produces a pheromone which functions as a long-range sex attractant.     

Hilltopping, leks and female choice in the Carpenter bee Xylocopa (Neoxylocopa) varipuncta

The mating system of the Carpenter bee, Xylocopa (Neoxylocopa) varipuncta Patton, closely resembles the leks of certain vertebrates. Males defend hovering stations at small creosote bushes on ridgetops in the Sonoran Desert, as well as at large ironwood trees in dry washes. Ridgetops, like washes, may provide orientation guides for dispersing females, channelling potential mates to waiting males. During the height of the two month flight season, both males and females were more concentrated on the ridge than in the wash. Males were particularly densely aggregated at or near two prominent peaks on the study ridge. At times, two or more males occupied the same creosote bush. Females visited hovering males infrequently, and exhibited a high degree of freedom in mate choice, usually rejecting males after a close inspection.
The reduction in territorial intolerance exhibited by some males at ridgetop sites may occur: (1) because of the costs of repelling many intruders and (2) because females may choose among males through direct analysis of male phenotype, rather than by selecting a male on the basis of territory position.     

Observations on Male Territories in a Carpenter Bee,Xylocopa (Neoxylocopa) hirsutissima Maidl (Hymenoptera,Anthophoridae)

Observations were made on territoriality of ♂♂ of the Brazilian carpenter bee Xylocopa hirsutissima. These territories are found on mountain tops where the ♂♂ hover from 4–6 p.m. in close vicinity of an optical beacon, being a protruding shrub or little tree. Territories are defended against other ♂♂Production of a pheromone by the mandibular glands is supposed. This territoriality as well as that of other species of the genus is considered to be an important aspect of the mating biology.     

Thermoregulatory physiology of the carpenter bee,Xylocopa varipuncta

Summary The carpenter beesXylocopa varipuncta maintain thoracic temperatures of 33.0°C to 46.5°C during continuous free flight from 12°C to 40°C. Since the thoracic temperature excess is not constant (decreasing from 24°C at low air temperatures to 6°C at high) the bees are thermoregulating. We document physiological transfer of relatively large amounts of heat to the abdomen and to the head during pre-flight warm-up and during artificial thoracic heating. Most of the temperature increase of the head is due to passive conduction, while that of the abdomen is due to active physiological heat transfer despite a series of convolutions of the aorta in the petiole that anatomically conform to a counter-current heat exchanger. Although the thermoregulatory mechanisms during flight are far from clarified, our data suggest that thermoregulation involves a strong reliance on active convective cooling through increased flight speed.     

Sex ratio and maternal investment in the multivoltine large carpenter bee Xylocopa sulcatipes (Apoideh: Anthophoridae)

Abstract. 1. Females of the multivoltine carpenter bee Xylocopa sulcutipes (Maa) (Hymenoptera: Anthophoridae) usually excavate a straight tunnel in dead twigs and mass provision a linear array of up to ten brood cells with pollen and nectar. An egg is deposited upon each food mass within one cell.
2. Female offspring generally receive a higher provisioning mass (0.180 ± 0.048 g) than males, a significant difference ( P > 0.001). There are, however, male larvae that receive as much food or more as their sisters or female larvae reared in another nest.
3. There is a close positive association between the size of a mother and the weight of provisions for individual daughters, but not for sons.
4. Female offspring are positioned in the innermost brood cells (Gositions 1, 2 and 3). The sex ratio of the outer cells is either significantly male biased (positions 4–6) or skewed towards males (positions 8 and 9). Positions 7 and 10 are in equilibrium.
5. Solitary females produce a significantly female biased sex ratio ( P < 0.01). Sex ratio in social nests is skewed toward females, but not significantly so ( P < 0.2). There is no significant difference between the sex ratio of solitary and social nests ( P = 0.361). The population sex ratio (pooled sex ratio of all broods produced) is significantly female biased ( P = 0.003).
6. Females kept in the laboratory produced female biased sex ratios whilst unmated females produced all-male broods indicating that insemination and ovarian development are not causally related.
7. The expected sex ratio (ESR) under equal investment, calculated as 1/CR (CR = mean male provision weight/mean female provision weight), is 137.5:117.5 (males:females), and differs significantly from that observed, 104:151 (males:females) ( P < 0.001). The 'Local Resource Enhlancement' hypothesis best explains the female biased sex ratio found in X.sulcatipes and its maintenance in the population.     

木蜂的巢内行为和交配策略

木蜂Xylocopa作为蜜蜂科的一个重要类群, 用来研究昆虫社会进化早期阶段具有重要意义。本文综述了近年来木蜂的营巢习性、 社会性行为和交配策略的研究进展。木蜂巢的建筑与巢内巢室的分布、 巢室的大小、 贮备蜂粮的效率和被寄生的敏感性等均有一定的关系。在筑巢地点, 随着木蜂种群数量的增加, 同种雌蜂之间的资源存在着竞争, 木蜂对巢室的守卫加强, 更多地表现为对同种雌蜂的守卫以及防御其他的天敌入侵。其社会多态性由独栖性向社会性演化, 主要表现为独栖性、 亚社会性、 半社会性、 共生性和准社会性等方式, 甚至同一种群内会出现不同的社会性行为。在交配策略上, 木蜂的雄蜂在外部形态特征上具有适应交配和寻找雌蜂的进化特征, 并且具有复杂的领地行为。这些研究理论对于我们深刻理解木蜂的行为生物学具有重要意义, 同时也有助于进行更深层次的社会性蜂类演化进程的探索。     

Social Behaviour of the Carpenter Bee Xylocopa pubescens (Spinola)

The development of about 20 relatively small nests of Xylocopa pubescens was studied. After the first offspring had become adult, these nests reached a social stage in which there was only one egg-layer per nest. Freshly emerged (teneral) adults eat a lot of food, collected by a forager, before they fly out of the nest. This food appears to be of major importance to these bees in that it makes them fully agile. It seems therefore, that part of the food needed for the development of a young bee is not given at the larval stage, via the beebread, but at the teneral adult stage. As a result of this, a necessary overlap of generations is accomplished. Besides, less pollen has to be collected for the provision of a brood cell, so more cells can be constructed within a short period of time. There is a high degree of nest competition. Many nests were taken over by conspecific individuals (or by females of X. sulcatipes) that were searching for nesting sites within the study area. However, although more than 50% of the solitary nests were taken over sooner or later, strangers hardly ever intruded into social nests, with more than one adult. This illustrates how important it is for a reproducing female to tolerate the presence of nestmates which guard the nest in her absence. Although in most cases the foundress of a nest proceeded to produce new brood in the presence of her offspring, it happened that a daughter took over reproduction from her mother. In two of these cases, it could be observed that a mother started a new nest elsewhere after having been thrown out by her own daughter. At least in these cases, nest competition between mother and daughter started long before the mother had reached the end of her reproductive capacities. Since nesting possibilities are scarce, it seems a logical strategy to stay in the maternal nest and wait for a chance to become the egg-layer if the mother dies or if she loses her dominance. The occurrence of several social interactions among nestmates is discussed: — trophallaxis was observed often, not only under ‘forced’ conditions, but also as a form of ‘voluntary’ feeding; — nestmates were observed to groom each other.     

Location before emergence of the female bee, Centris pallida, by its male (Hymenoptera: Anthophoridae)

Large numbers of males of the bee Centris pallida Fox have been observed patrolling areas in which females are emerging. Males locate specific sites at which a buried bee is about to emerge and dig down to meet the other individual, male or female. If it is a female, mating is initiated when she scrambles into the excavation pit created by the male. Males fight intensely with one another for possession of digging sites and for unburied virgin females. Experiments indicate that males locate conspecifics beneath the surface on the basis of extremely non-specific olfactory cues; they are capable of locating buried honey bees and other insects. The evolution of digging behaviour is traced to selection favouring males that are first to reach a virgin female which will mate just once in her lifetime. A number of examples are given of other insects that have evolved similar abilities, apparently in response to similar selection pressures.     

Some cytological features of follicle cells in an ovariole of the carpenter bee (Xylocopa virginica virginica) (L) (Hymenoptera: Apidae)

In an attempt to provide some essential basic data, currently very sparse, on the ultrastructure of solitary bees, the histology, cytology and ultrastructure of thin and ultrathin sections of ovarioles of the adult carpenter beeXylocopa virginica virginica were studied with the light and transmission electron microscopes. The work revealed an apparently previously unreported occurrence of intracellular paired membrane configurations in follicle cells of an ovariole and confirmed the presence in follicle cells of somatic intercellular bridges previously reported in follicle cells in a variety of bees, but not in the carpenter bee. Microtubules and bacteroids were also seen in the follicle cells.     

Foraging and courtship behaviour in males of the solitary bee Anthophora plumipes (Hymenoptera: Anthophoridae): thermal physiology and the roles of body size

Abstract.

• 1 The effects of climate and body size on male behaviour were examined in the solitary bee Anthophora plumipes (Hymenoptera: Anthophoridae), which shows resource-based polygyny at floral food sources in Britain in spring.
• 2 Larger males are able to fly at lower temperatures than smaller males, and can therefore court females under conditions in which smaller males cannot fly. This is predicted from patterns of endothermic ability at low temperatures already demonstrated within this species.
• 3 Video analysis of male competition for opportunities to initiate courtship with tethered females showed that larger males are also competitively superior, and can displace smaller males from favoured flight positions immediately behind females.
• 4 The mating system shown by male A plumipes is strongly dependent on male density. At low densities, males show exclusive territoriality at floral sources. As male density increases, this strategy is abandoned in favour of patrolling with considerable spatial overlap between males, and opportunistic Polygyny.
• 5 Despite high endothermic abilities, male behaviour is highly dependent on weather, and particularly ambient temperature. Males bask in the early morning and maintain high thoracic temperatures. Temperature data from freshly killed bees show that thoracic warming from solar sources effectively doubles the thermogenic power generated by the bee alone at low ambient temperatures.
• 6 Male strategies in A.plumipes are compared to female responses to climate. Having controlled for differences in body size there is no difference in endothermic abilities between the sexes. Males do not, however, fly under conditions in which females of the same size would remain active. These results are discussed in the light of differential dependence of reproductive success on flight activity for the two sexes.

     

Male territoriality and mating tactics in the wool-carder bee,Anthidium septemspinosum Lepeletier (Hymenoptera: Megachilidae)

Mate-seeking behaviours in males ofAnthidium septemspinosum are described. Mating occurred at the females' food plant patches, as in other congeneric species previously studied. Males were behaviourally classified either as territorial or non-territorial. Territorial males were generally larger, and superior in mating. Smaller males were forced to be non-territorial, adopting a different mating tactic of creeping into the territories to intercept females. This compensated for their physical inferiority in mating competition. The adaptive significance of this tactic is discussed.     

Behavioural specialization in pre-reproductive colonies of the allodapine beeExoneura bicolor (Hymenoptera: Anthophoridae)

Summary Exoneura bicolor is a univoltine allodapine bee common in montane forests of southern Australia, where it exhibits a semisocial/quasisocial colony organization. Within-nest behaviour in postemergence autumn nests ofExoneura bicolor was recorded with the aim of studying behavioural specialization in pre-reproductive colonies. Ten complete colonies were transferred to purpose-built observation nests shortly before brood eclosion in late summer. Behaviour within observation nests was recorded for periods of up to 44 days after establishment, covering a period when colonies are preparing for overwintering. Dispersal of females and brood rearing do not occur at this time, although some females may become inseminated. Analyses of data using multivariate techniques indicated four distinguishable behavioural castes, designated here as Guards, Nest Absenters, Nest Modifiers and Non-recruits. This represents a higher degree of behavioural specialization than recorded to date for other allodapines. Behaviours performed by Guards and Nest Absenters are likely to involve considerable risks, but benefit the colony as a whole, so that some nestmates in prereproductive colonies exhibit altruism that frequently aids adult siblings or cousins. The males in our study were fed by females via trophallaxis and two of the males participated in nest maintenance tasks. Our results suggest that autumn colonies ofE. bicolor form well-integrated behavioural units even though brood rearing does not commence until the following spring.     

Neutral sterols and ecdysteroids of the solitary cactus bee Diadasia rinconis cockerell (hymenoptera: Anthophoridae)

Using high performance liquid chromatography in conjunction with radioimmunoassay and mass spectrometry, the major ecdysteroid of the solitary cactus bee, Diadasia rinconis, was determined to be 20-hydroxyecdysone, with lesser amounts of makisterone A. Another 28-carbon ecdysteroid thought to be the 24-epimer of makisterone A was also detected. The neutral sterols of Diadasia consisted primarily of 24-methylenecholesterol (92.2%) with lesser amounts of other C₂₈ and C₂₉ sterols. Cholesterol accounted for less than 0.1% of the total tissue sterols. The occurrence of 20-hydroxyecdysone in a phytophagous hymenopteran is discussed in relation to the low level of cholesterol encountered. © 1993 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Carpenter Bee (Xylocopa micans) Risk Indifference and a Review of Nectarivore Risk-sensitivity Studies

This paper presents new results of risk-sensitive foraging studiesof the carpenter bee, Xylocopa micans, and reviews the workto date on risk sensitivity in nectarivores. In the field, nectarivoreschoose among alternative food sources (flowers) that differin the variabilities of their nectar rewards. In the lab, theforaging situation for carpenter bees was experimentally simplifiedby offering the bees a choice between either "low variance"or "high variance" artificial flowers. The two flower typesdiffered in their variabilities but offered the same expectedshortterm rates of net energy gain to test the predictions ofthe short-term rate maximization mechanism. Foragers were testedunder two energy budget conditions, hungry and well-fed, totest the predictions of the z-score model. Individual carpenterbees were indifferent to variability in both nectar volume andnectar sugar concentrations, and their risk-indifference wasunaffected by energy budget. These findings of risk indifferencesupport neither the variance discounting nor the z-score modelof risk sensitivity. Since the low and high variance flowertypes are equivalent for carpenter bees in short-term rate ofenergy gain, there can be no selection on carpenter bees tobe sensitive to variability based on differences in rate ofgain. Studies of risk sensitivity in honey bees and bumble beesusing variance in nectar concentration support this contention.These findings are compared with other nectarivore risk sensitivitystudies in order to highlight the most likely mechanisms underlyingaversion to variation in nectar rewards (short-term rate maximizing,the Weber-Fechner law of perception and learning non-empty flowers)and to suggest future research in the interplay of these threemechanisms.     

Phylogeny of the bee genus Agapostemon (Hymenoptera: Halictidae)

Abstract. A phylogeny for genus Agapostemon (Hymenoptera: Halictidae) is reconstructed from morphological characters, using all species, with four representatives of Agapostemonini as outgroup taxa. Parsimony analysis using 150 unordered characters resulted in eighteen equally parsimonious trees, a strict consensus of which is highly resolved for Agapostemon. Based on this analysis, Agapostemonoides Roberts & Brooks is returned to generic status, and a new subgenus is described: Notagapostemon, which includes the rhopalocerus, heterurus, atrocaeruleus, erebus, kohliellus, nasutus and intermedius groups of Moure & Hurd. Species groups are proposed for Notagapostemon and revised in A. (Agapostemon). Agapostemon cockerelli Crawford is synonymized with A. obliquus (Provancher), A. epichryseus (Morelos) with A. leunculus Vachal, A. inca Roberts with A. heterurus Cockerell, A. hispaniolicus Roberts female with A. centratus (Vachal) and A. hispaniolicus Roberts male with A. alayoi Roberts. Optimization of known behaviours suggests communal ancestry for the genus and infers the prevalence of this behaviour in Agapostemon. Optimization of geographical range suggests a Central American or Caribbean origin of Agapostemon, with one invasion of North America and multiple invasions of South America and the Caribbean. One invasion of the Caribbean suggests arrival from North America via Florida.