Picture Of Three Solitary Bees

An Introduction to the Solitary Bees

(Hymenoptera, Apoidea)

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Introduction Mating and Nesting Foraging Weather
Parasites Anthophora plumipes Pictures Book Reviews

Introduction,

Bees have probably been around since just after the first flowering plants appeared and fossils date back to the Cenozoic. Bees are not only cute, but are extremely important to the ecology of most habitats as they are the primary pollinators of entomophilous plants (entomophilous plants are plants pollinated by insects, in comparison with anemophilous plants which are pollinated by the wind.) They are therefore of inestimable economic importance as well, in America millions of solitary bees of the family Megachile are farmed and looked after every year because of their pollination services. They have biting chewing mouth parts and two pairs of wings of which the hind pair are generally smaller.

 

 

Of Bees and Wasps

The main difference between Bees and Wasps is that Bees feed their larvae on 'honey' a mixture of pollen and nectar which they have collected from flowers, whereas Wasps feed their larvae on meat, mostly paralysed arthropods (the exception to this rule is a small family of wasps called the Masarinae who feed their larvae on a pollen nectar mixture). If you get to look at them under a microscope you will see another difference, i.e. Bees always have some, often many, 'plumose' or 'feather-like' hairs, these help in collecting pollen; Wasps always have only un-branched hairs like you and me. Bees originated from hunting wasps (Sphecoidea).

Solitariness

There are more than 20,000 known species of Bee in the world, by far the greatest portion of these are solitary. By solitary we mean that a single female, after she emerges from her pupae and is mated by a male, constructs, provisions and lays an egg in each cell in a nest by herself. This in comparison with social (called eusocial) bees like the Bumble Bees, Honey Bees, Sweat Bees and Stingless Bees, all of whom have a Queen who lays eggs and a number of workers who look after them. Like everything else in life this is not the end of the story, these are two nice neat descriptions which are really opposing ends of a continuum, i.e. there are some bees that not purely solitary but not really eusocial either. These are given various names such as, communal (i.e. Dialictus sp.) and semisocial (i.e. Augochlorella sp.) and quasisocial (i.e. Euplusia sp.) depending on how close they get to being 'eusocial'. Some bees nest in living or dead wood, sandstone and or soil, while others construct nests in existing hollows using other materials such as soil or plant material.

Communal Nesting.

Though both Solitary Bees and Wasps build their nest individually you still often find lots of the soil nesting species nesting together in a small area. This is because they are often very fussy about where they build their nests and if there is only a small area available that is suitable for nesting in, in any one neighbourhood, then everyone will want to nest there. Hence you often get loads of Solitary Bees and or Wasps nesting side by side in one place. The largest recorded aggregation is 423,000 female bees in an area of 1300 m2. Aggregations can continue of over 20 years or can become extinct. 15% of bee genera and sub-genera contain cleptoparasitic species.

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Mating and Nesting Habits

protandry i.e. males emerge before females is the norm in solitary bees and it means the males are waiting for the females when they emerge. Males live much shorter lives than females on average, and can often only be found at the beginning of a species' season. Male and female bees often look quite different.

Many bees produce specific pheromones, and these are often important in bringing the two sexes together. In some species such as Centris adani the males deposit the marking pheromones on the female during copulation and this makes them unattractive to other males. In some cleptoparasite genera such as Nomada the males produce a pheromone in their mandibular glands which mimics the substances produced by the hosts Dufour's gland, this is sprayed over the female during mating, presumably making it easier for the female to gain entry into the hosts nest.

Orchids of the genus Ophrys emit mimic pheromones which attract male bees of which ever species is being mimicked, males of Andrena, Anthophora, Colletes, Eucera and Tetralonia amongst others fall for these lures. The males attempt to mate with the flowers and end up pollinating them. Females of most species only mate once. However in a few other species the females are receptive all season, e.g. Panurgus spp. In some species of Nomadopsis and Perdita the male remains coupled with the female while she forages, thus preventing other males from mating with her. Males look for females at flowers, at the nest site where they emerged, and at other non-resource sites which are called 'encounter sites', In any one area there may be one lone male patrolling from one encounter site to another or there may be hundreds. When the number of males is very large they may form swarms and patrol synchronously from site to site. In some species such as Osmia rufa the males may have home ranges which represent only a part of the total encounter sites available.

In some species males mark the flowers that mark the boundaries of their range with pheromones. In some non-aggressive bees such as Andrena, Nomada and Triepeolus males may sent mark non-flowering plants to mark the edges of the patrol routes, these markings may be attractive to other males which then join in the patrol. When a receptive female is encountered by one male he will attempt to mate with her, if more than one male is present the others will probably also attempt to mate with her and a large mass of bees, all but one being male, will tumble to the ground. Otherwise non-aggressive males may well fight when a receptive female is present.

In some more aggressive species e.g. Anthidium manicatum and Hoplitis anthocopoides the males are territorial. Territorial males then either patrol their territory , e.g. Megachile and Callanthidium, or they can wait at a single encounter site which they defend from other males, e.g. species of Xylocopa. As always in nature there are variants and some Anthidium males patrol along a route when few other males are around but switch to defending a single flower clump when other males are numerous. The size of male territories ranges from about 0.5m2 to 6m2. Males probably never hold a territory for an entire breeding season and in some cases territories change owners after relatively short times. This is partly controlled by the density of resources and the amount of competition. In Anthidium manicatum it has been shown that the best territories are held by the largest males. and that territory holding males forage more and copulate more than do non-territory holding males. In circumstances like this you get selection for large males and males tend to be larger than females.

Copulation is normally brief and often involves the mating pair getting mobbed by all the nearby males, the exception to this is the Panurgines. Nomadopsis males may either find the female at a flower and fly with her 'in copula' to the nest or vice versa, depending on the species.

In some gregarious nesters such as Anthophorines and Panurgines, mating takes place over the nesting site, or else it can take place inside the burrow, as in some Andrena and Paracolletes. However, mating normally takes place at, or in a flower being visited by the female for pollen, or as in the case of Nomia melanderi it occurs both at flowers and/or at the nest. Males of some species of Andrena have been observed patrolling along hedgerows, presumably in order to maximise their chances of meeting and mating with a female.

Many solitary bees nest near where they emerged, especially soil, wood and wall nesting species. There may sometimes be hundreds of thousands nesting in one area. Most nest in the ground, in well drained soils of varying degrees of slope, however Megalopta ipomoeae is a nocturnal bee which nests in damp soil in tropical forests. Most of the Bees which nest in plants use plants with pithy stems, i.e. bramble, raspberry, elder, maple or bamboo, whilst only a few, like Xylocopa sp. gnaw out holes in solid wood, and Megachile sp. and Osmia sp. use many different cavities, from holes made in wood or soil by other insects to snail shells and man-made objects.

Many ground nesting species pile the soil from the burrows up in a little volcano hillock around the nest (e.g. Andrena haemorrhoidalis), whilst others build entrance tubes or turrets. The depth of the burrow depends on the species and soil type, those that nest in very dry soil lend to dig deeper holes. The Xylocopines, most Anthophorines, Megachilids and some Colletids construct their nest cells end on end.

In most of the solitary bees the cells are lined with wax or varnish-like waterproofing material and sometimes the tunnels of the Colletids are lined with a thin, cellophane-like material. These substances are secreted by the salivary glands in Andrenids, Colletids and Hallictids, but are abdominally secreted in the Anthophorines. However Megachilids, the leaf cutters, use bits of leaf or petals, while some use mud and/or pebbles.

Bee genera and cell lining materials
Trachusa leaf sections
Heteranthidium sand cemented with resin
Dianthidium pebbles
Serapista plant fibres stuck to trees

The cells are provisioned with pollen and usually some nectar in species of Andrena. The pollen is generally made into a dough-like ball with the nectar but in Lithurge sp. it is left quite dry, whilst in many Colletids and Anthophorines the food may be a semi-liquid gruel. In most Anthophorines about half the food is liquid and this portion is eaten first.

A few species lay their egg part way through provisioning the nest (e.g. Lithurge fuscipennis) but by far the most common procedure is to fully provision the nest then lay the egg and close the cell. Most lay the egg on the food but the Emphorines insert the egg under the food. Species of Colletes, Melecta and Nomada stick the egg onto the cell wall.

Development is usually quick, taking only a few weeks to pupation. The bee may then remain a pupa until a suitable emergence time. In species with more than one generation per year this may be quite soon after pupation is finished, but in the many univoltine (having one generation per year) species it will mean over-wintering as a pupa. over-wintering may be extended to several years when the weather is poor. Alternatively species like Andrena and Osmia emerge from the pupa and overwinter as inactive adults in the cell, or in some species of Xylocopa and Ceratina may emerge in the fall and then overwinter gregariously in old burrows or other suitable places. Most do not form a cocoon, the exception to this is the Megachilids.

Nesting females normally nest/sleep in their burrows while many males and not yet nesting females may gather into groups, often containing a mixture of species consisting of up to several hundreds of bees for the night. Some bees, like some Sphecid wasps, grasp the stem of a plant with their mandibles and let the rest of the body relax, either head up, or as in Coelioxys sp. with the head facing down. Others hold the stem with their legs as well, either head down (Melissodes obliqua and M. perplexa), or head up as in M. bimaculata. Nocturnal bees sleep in flowers during the day.




Foraging

All bees are dependent on flowers. Most bees show flower constancy to some extent when collecting pollen either as individuals collecting from flowers of one species, in this case individuals of one bee species may use different species of flowers, and individuals may change species of flower. This is common among social bees such as Apis sp., Bombus sp. and Melipona sp. as well as semi-social bees such as Halictus sp. and many solitary bees such as Anthophora sp., Andrena sp. and Megachile sp.. Many solitary bees however are species specific to one or only a few species of flower. Those which visit one species are called 'monolectic', those that visit a few species as 'oligolectic' and the rest, those that visit many different species as 'polylectic'. Oligolecty tends to occur more in temperate zones rather than in tropical regions. Because plants tend to flower at certain times of the year monolectic bees must relate to this i.e. Andrena sp. on Salix are active only in early spring. In some cases at least it is now known that monlectic or oligolectic bees are more efficient at foraging on the chosen flowers than polylectic bees i.e. Hoplitis anthocopoides is more efficient at foraging on Echium vulgare than several of the polylectic bees which also forage on it . Some bees simply show colour preferences i.e. Megachile brevis prefers blue or purple flowers. Xylocopa virginica texana marks flowers it has visited with a short-lived repellent. This helps it avoid visiting the same flower twice.

Besides nectar and pollen, some flowers secrete oils from special floral glands called elaiophores. The bees that collect this oil have special morphological adaptations to their pollen gathering apparatus to assist them.

Monolectic Bees and their Flowers
Megachile strophostyles Strophostyles helvola
Andrena nothoscordi Nothaxadum striatum
Andrena florea Bryony alba
Cemolobus ipomoeae Ipomoea pendurata
Colletes brevicornis Specularia perfoliata
Oligolectic Bees and their Flower Groups
Colletes armatus Asteraceae
Megachile generosa Leguminosae
Andrena macoupinensis Salix
Pseudopanurgus labrosiformis Heliantheae
Emphor bombiformis Hibiscus

Nocturnal bees in the genera Perdita, and the sub-genera Sphecodogastra and Evylaeus, all collect pollen from Evening Primroses and other Oenothera and related Onagraceae. Xenoglossa sp. forage at Curcubita (cucumber family) flowers before dawn. This is called matinal foraging, as opposed to crepuscular foraging, foraging after sunset. Nocturnal foragng bees tend to be large and dark, and to possess large ocelli.

Morphalogical Adaptations

Bees pollen apparatus is adapted to the flowers they use. Bees which collect from flowers with large pollen grains have loose, more open scopae (pollen baskets) whilst those that specialise in the compositae have dense scopae to hold the smaller pollen grains, while Verbenapsis sp. have special hairs on their front tarsi to allow them to collect pollen from the tube protected anthers of Verbena. You will often here bees referred to as long and short tounged, this reflects the flowers they have adapted to specialise in. The tongue lengths relate to the lengths of the corolla. Many Anthophorines are long-tongued and visit deep flowers such as Ipomea sp. whereas short-tongued bees for instance are more likely to visit compositae.

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Weather

Weather conditions affect both flowering plants and solitary bees. Ironically the sort of late winter early spring weather which is good for flowering plants is bad for bees while the dry weather which the bees prefer reduces the number of blooms on the flowers. This is possibly because moisture favours the growth of fungi which attack the bees in the nest cells. Bees, particularly species of Lasioglossum will often remain in the nest burrows when the weather is cold or overcast, and sometimes will even remain there when the weather appears perfect for foraging, this is probably a result of attempts to maximise reproductive success over more than one year in those species which live to participate in two or more breeding seasons. Some may remain as a pupa for a whole season if the weather is not suitable and leave emerging until the next year.

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Parasites

Bees have many enemies including 'parasitic bees' which are bees which lay their eggs in completed but unsealed cells of other bees that are referred to as there hosts in the classical parasitological terminology. The table below gives a few examples, giving you some idea of how common this occurrance is. Having said that, the number of parasites must always remain far smaller than the number of hosts in the same way that predators are always less frequent than their prey. Though there are many facultative cleptoparasites, cleptoparasitism can also occur on an opportunistic basis with many normally foraging bees.

It is interesting to note that in harmony with Emery's rule which states that cleptoparasitic species tend to be closely related to their hosts, that long-tongued cleptoparasitic bees usually have long-tongued bees as their hosts etc, however some long-tongued bee cleptoparasites have learned to use short-tongued bees hosts, but no short-tongued bee cleptoparasites have learned to use long-tongued bee hosts.

Parasitic Bees and their known Hosts
The Parasite The Host
Sphecodes Halictus
Stelis Heriades
Stelis Hoplitis
Chelynia Anthidium
Chelynia Heriades
Chelynia Hoplitis
Chelynia Osmia
Dioxys Anthidium
Dioxys Megachile
Dioxys Osmia
Coelioxys Megachile
Nomada Andrena
Nomada Nomia
Holcopasites Pseudopanurgus
Neopasites Dufourea
Oreopasites Nomadopsis
Townsendiella Conanthalictus
Epeolus Colletes
Triepeolus Melissodes
Epeoloides Macropis
Melecta Anthophora
Xeromelecta Anthophora
Zacosmia Anthophora
Ericrocis Anthophora

Parasitic bees are not a solitary bees only problems though, there are quite a number of other invertebrates who are willing to take advantage the solitary bees work. These include Oil Beetles, Bee Flies, Velvet Ants (Mutilidae), Rubytailed Wasps (Chrysididae), Sapygids, and various Ichneumons and other parastic wasps. Oil beetles (Melloidae) and Bee Flies (Bombyliidea) are similar in the way they attack the solitary bees, They lay their eggs at ground level near the bees nest or near flowers likely to be visited by certain solitary bees, The larvae are fast moving lice like creatures in their first instar and either find their own way quickly to the bees nest or climb up to a flower to wait for a bee. The then catch a lift to the bees nest from her whilst she visits the flower. On arriving a the nest the little parasite first eats several of the hosts eggs and then starts feeding on the nectar and pollen stores. In Europe nearly all the Meloe are parasites on solitary bees, however in other parts of the world their more common prey are grasshoppers. Apart from all these problems many solitary bees die in their cells as lavae having fallen prey to one of a number of fungi which like to grow on them

In a study of two populations of Anthophora busleyi, Linlsey and MacSwain in 1942 found 22 different organisms in the bees nests of which at least 18 would cause the death of the bee larvae or pupa.

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A closer look at Anthophora plumipes

Anthophora plumipes is the Plume-legged Bee, and like many solitary bees it is usual for the males to be seen first, it was nearly two weeks after the first males emerged before I saw any females this year. This is because the female makes her nest in a long hole with the cells that contain the eggs placed one after another, this means that the egg she lays first is the last bee to leave the nest next spring, and visa-versa, i.e. that the last egg she lays is the first bee to leave the nest. In all Hymenopterans the sex of an adult insect is controlled by whether or not the egg is fertilised before it is laid, fertilised eggs produce females and unfertilised eggs produce males. Therefore, because, she can control whether or not to let the sperm she received from the male fertilise any given egg before she lays it, and because she always lays fertilised eggs first and unfertilised eggs last the female Anthophora plumipes ensures that next spring it is always the males that we see first.

Anthophora plumipes are lovely bees, they are the size of a small bumble bee and make a sound that is similar but higher in pitch. The male is a tawny/orange colour with a patch of plumose hairs on the tarsi of his middle legs and a yellow face, both sexes have very long tongues which you can easily see as the bee hovers in front of a flower. In South-West Europe including Britain, the female is an all black bee with orange hairs making up her pollen basket on her hind legs, but in South-East Europe, the Middle East and beyond she is the same colour as the male, nobody seems to know why the female is a different colour here. A. plumipes is a low very fast flying bee, and in the hotter places where it lives such as the Sinai Desert in Israel it uses its fast flight to keep cool. It does this by pumping all its blood into its abdomen so that as much of it as possible will be cooled by the quickly passing air.

The females are very cautious and tend to fly off at the slightest sign of trouble, besides making them hard to catch, this makes it difficult for the males to get them to sit still long enough to mate. To solve this problem the male uses the plumes on his middle legs to cover the eyes of the females during mating, so that she won't get spooked and fly off half way through.

The males are territorial and tend to guard a home range which contains either, the sorts of flowers the females like to visit, or a site suitable for nesting. (They nest in the holes between the stones in the walls of the 14th century Manor House at North Wyke where I work, but they also like cliff faces and will even nest in the ground if that is all they can find, though they prefer vertical surfaces.) The male patrols around his home range spending time at each patch of flowers and or nest site chasing off intruders. He is very serious about this and defends his chosen resources from all comers whether they are a competing male bee or not. To drive intruders away from his range he accelerates straight at them very quickly and rams them with his head, he can knock out insects much larger than himself this way. If you have a lot of A. plumipes around you may well find another rather attractive bee with nasty habits hanging around the nest holes. This is Melecta armata, which is a brood parasite, or Cuckoo bee, it lays its eggs in the nest of A. plumipes, after she has stocked them and layed her egg. The M. armata larvae hatches first, then procedes to eat the Anthophora's egg before devouring its store of food as well. Bees like this can be recognised because they do not collect pollen and therefore have no pollen baskets.

Anthophora bees are very successful and though we only have four species in Britain there many in warmer parts of the world, for instance there are over 100 in Israel.

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Picture Parade

These paintings were painted at or before the turn of the century and my favourites are those from a group of manuscripts smuggled out of Russia at the start of the revolution, the rest come from Saunders 1896 monograph on the Aculeates of Britain, as the artist is unfortuneately not honoured in the book there is little I can do here but be grateful for his past efforts. I have cut and pasted the individual images after scanning in the relevent pages and I apologise for the background and contrast discrepencies this has caused, still the pictures are beautiful and I hope you enjoy them. All the pictures are in JPG format.


Plate 5. 66K Showing :- Andrena fulva, Andrena angustior, Andrena fucata, Andrena ferox, Andrena bucephala, Andrena nigriceps, Andrena fulvicrus, Andrena albicrus, Andrena hattorfiana, Andrena fasciata, Andrena cettii.
Plate 6. 61K Showing :- Andrena ferghanica, Andrena semiaenea, Andrena turkestanica, Andrena fedtshenkoi.
Plate 7. 55K Showing :- Anthidium fedtshenkoi, Anthidium unicum, Anthidium callosum.
Plate 8. 73K Showing :- Anthidium manicatum, Osmia leucomelana, Stelis aterrima.
Plate 9. 41K Showing :- Osmia bicolour, Osmia parietina, Osmia xanthomelana, Osmia rufa, Osmia coerulescens, Osmia aurulenta, Osmia pilicornus.
Plate 10. 76K Showing :- Anthophora freimuthi, Anthophora stschurowskyi, Anthophora kaufmanni, Anthophora bifasciata, Anthophora olgae, Anthophora semperi.
Plate 11. 37K Showing :- Halictus quadricinctus, Halictus maculatus, Halictus cylindricus, Halictus breviceps, Halictus xanthopus, Halictus gramineus.
Plate 12. 71K Showing :- Anthophora abramowi, Anthophora melanapyga, Plistotrichia compacta, Tetralonia rufescens, Eucera sogdiana, Eucera melaleuca.
Plate 13. 59K Showing :- Camptopoeum miribile, Rophites orobinus, Rophites clavator, Megachile desertorum, Osmia fedtshenkoi.
Plate 14. 77K Halictus funarius, Dioxys formosa, Coelioxys sogdiana, Melicta, fuscipennis, Crocisa aberrans.
Plate 15. 66K Showing :- Colletes dariesana, Colletes succincta, Prosopis brevicornis, Prosopis cornuta, Prosopis dilatata. Sphecodes gibbus, Halictus rubicundis, Dasypoda hirtipes.
Plate 16. 66K Showing :- Panurgus ursinus, Epeolus, rufipes, Ceratina cynea, Chelostoma florisomne, Ceolioxys acuminata, Ceolioxys quadridentata, Melecta acuminata, Melecta luctuosa, Megachile ligniseca, Megachile maritima, Megachile, argentata.
Plate 17. 59K Showing :- Anthophora retusa, Anthophora pilipes, Anthophora quadrimaculata, Sarapoda bimaculata, Eucera longicornis.
Plate 18. 81K Showing :- Nomada fedtshenkoi, Nomada strigicollis, Nomada obburdinensis, Nomada ruficollis.
Plate 19. 60K Showing :- Nomada fucata, Nomada solidaginis, Nomada lateralis, Nomada lathburiniana, Nomada alboguttata, Nomada sexfasciata, Nomada ruficornis, Nomada ochrostoma.

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Book Reviews


Provisional Atlas of the aculeate Hymenoptera of Britain and Ireland Parts 1.and 2. , by Robin Edwards (Ed.)
The Conservation of Bees, by Andrew Matheson, Stephen L. Buchmann, Christopher O’Toole, Paul Westrich and Ingrid H. Williams (Editors)
The Evolution of Social Behaviour in Insects and Arachnids, by Jae C. Choe and Bernard J. Crespi (Eds).
The Ecology and Natural History of Tropical Bees, by D.W.Roubik

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Solitary Bees on the Web

Alternative Pollinators, links.

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