Morphology

I. Morphology

A. Major body regions

• head, vision, brain, antennae, mouth, esophagus, glands

• thorax, muscle for heat-generation and locomotion

• petiole is constriction between thorax and abdomen

• abdomen, digestion and reproduction

B. The head

• 2 compound eyes, three auxiliary eyes called ocelli which cannot focus and form images are used solely for determining light intensity or to regulate diurnal activities and orientation

• one pair antennae, smell (olfactory acuity of bees is about same to man, but bees are 10-100X more sensitive to odors of wax and flowers). Antennae also can determine direction of smell. There may be sensors for carbon dioxide, taste, humidity, and possibly temperature. The Johnston’s organs, inside antennae, are sensitive to minute changes in antennal bending which measures flight speed.

• genae, region between mandibles and bottom of eye, useful in diagnosing families.

• mandibles + internal mandibular glands—brood food gland for workers, mandibular gland for queen, mandibles used for biting, carrying, chewing, and molding wax

• tongue or proboscis, used to suck up fluids, feed each other (trophallaxis), and receive pheromones. Tongue length often dictates what types of flowers bee can visit.

C. The thorax

• Notum is dorsal plate for thorax

• Sternum is ventral plate for thorax

• prothorax ~ pronotum (Snodgrass handout: N1, L1, spl = pronotal lobe of lecture 1) Note that there’s no S1; this is one of the defining characters of a bee as in lecture 1. It is the pronotum that wraps around and joins on the venter without a distinct ventral sclerite.

• mesothorax (N2, S2, L2, Tg)

• metathorax (N3, S3, L3)

• the propodeum (IT) is actually the anterior-most abdominal segment. During pupation it crowds against the thorax and becomes superficially a part of it. Note the abdominal spiracle on the “thorax.”

• 3 pair legs, one on each section of thorax

• 2 pair wings

• heavily tracheated

• thoracic muscles are also involved in heat production

D. The legs

• coxa

• trochanter(s)

• femur

• tibia (broadened on hind legs to constitute the corbiculum)

• tarsus, 5 segments first of which is basitarsus

• basitarsus (is broadened on hind leg to form pollen brushes)

See Snodgrass pp. 109-110. Pollen is raked off front of body by front legs, passed to mid legs, and mid legs are raked between the combs on inner side of rear basitarsi. Opposing basitarsi rub against each other and the rakes (ras) on the distal end of pollen scrape pollen onto the pollen press; the bee then flexes the pollen press and it pushes the pollen load up into the corbiculum on the broadened outer side of the tibium.

• antenna cleaner (on basitarsus of foreleg)

E. The wings

• forewing

• hindwing

• hamuli

• submarginal cells

• basal vein

• first and second recurrent veins

• indirect flight—longitudinal and dorso-ventral muscles cause thorax to flex. Wing base pivots on a fulcrum. Secondary muscles pivot wing to allow side-ways flight. Indirect musculature is much more efficient than direct musculature. The hindwings have muscles to raise them, but are pulled down only by their attachment to the forewings via the hamuli. Other muscles allow wings to fold back. Wings can be “unhooked” to allow shivering.

F. The abdomen

• reproductive system, emphasize female system. Ovaries are poorly developed in workers, well developed in queens. Ovaries joined by lateral oviducts to a common middle oviduct where there is a spermatheca. Workers and queens both have spermathecae, but workers’ are poorly developed. Queen has muscular control of releasing sperm.

• gut—esophagus, crop (muscular for nectar transport), proventriculus (contains “teeth” [proventricular valve] for straining out pollen from crop contents), midgut (absorption), kidneys (excretory or malpighian tubules) permeate throughout abdominal tissues, rectal pads (H2O reclamation?), and rectum (reservoir)

G. Other systems

• dorsal blood vessel, an open system in which blood flows freely in body cavity. Blood enters heart in one-way valves called ostia and muscle contractions push it forward down the aorta and dumps it on brain. The loops at the petiole in bumble bees serve to heat the abdomen for incubating brood clump

• ventral nerve cord, a brain (cerebrum), concentrated around compound eyes with seven ganglia down a ventral nerve cord

• respiratory system, invaginations of cuticle at outer openings called spiracles that make tubules or sacs. Inactive gas exchange until bee gets active, then it actively pumps its abdomen to increase air exchange.

II. Classification

A. Higher taxa

• Phylum Arthropoda—’’jointed foot”, segmented body.

• Class Hexapoda (or Insecta)—”six-legged”

• Order Hymenoptera—”membranous wings” of “marriage” of hind and fore wing. Includes ants, wasps, and bees.

• Suborder Apocrita—slender wasted

• Subgroup Aculeata—”stinging” Hymenopterans

• Superfamily Apoidea—bees and sphecoid wasps

B. Families of bees. There are 7-11. The latest authority, Michener (2000) says 7. We will mention only six.

• Colletidae—digger bees, polyester bees, includes common Georgia species Colletes thoracicus, short tongued and bilobed, second recurrent vein sigmoid

• Andrenidae—digger bees, short tongued, second recurrent vein straight

• Halictidae—sweat bees, basal vein strongly arched

• Megachilidae—leafcutting bees, mason bees, orchard bees, long tongued, 2 submarginal cells

• Anthophoridae—some are digger bees, includes carpenter bees; a 1993 paper lumped anthoporids into Apidae, long tongued, 3 submarginal cells, narrow genae

• Apidae—includes bumble bees (Bombus) and honey bees (Apis mellifera), long tongued, 3 submarginal cells, genae broad

• Mimicry—”bees” that aren’t bees

III. Immature development

• egg hatches after a few days (3 in Apis), shell disintegrates

• Larvae are eating machines, no eyes, antennae, legs. Fed pollen+nectar or glandular secretions. Molts 4-5 times; each stage called an instar. Midgut is not connected to hindgut during feeding phase. Defecation and molt to prepupa. Fecal pellets may be incorporated into cocoon. In Apis the cocoon is greatly minimized.

• prepupa—an elongated larva; very common overwintering stage in solitary bees. Last larval skin then sheds to reveal the pupa.

• Pupa—reorganization of internal tissues. Wing buds are apparent. Colorless pupal skin is shed when the adult cuticle has hardened to reveal complete wings. Wings are expanded by pumping blood into their veins; the cuticle hardens and the bee emerges.

• development time is highly variable depending largely on the life history of the species. In solitary species in which there is no temperature regulation the development of each stage can speed up or slow down according to ambient conditions. In well-developed societies, however, temperature is closely controlled and development time is very programmed, rigid, and predictable.

• 2 divergent pathways: (1) fertilized or not and (2) (in social bees) well-fed or not.