Insect Societies

Lecture 21

Insect sociality

• Co-operative behaviors– Eusocial: co-operate in

reproduction and have division of reproductive effort (bees, wasps, ants, termites)

– Subsocial: less developed social habits (many insects)

– Solitary: no social behaviors (most insects)

Subsociality in insects

• Aggregation– Often aposematic

• Parental care– Without nesting (Belostomatidae example)– With solitary nesting (Silphidae example)– With communal nesting (Sphecidae example)

• Nesting: eggs are laid in a pre-existing or newly constructed structure to which the parents being food supplies for the young

Subsociality in insects

Parental care without nesting• Giant water bugs (Belostomatidae) exhibit

paternal egg-tending

Parental care with solitary nesting

• Carrion beetles (Silphidae: Nicrophorus) display extended biparental care of young and reproductive cooperation between the sexes

Parental care with communal nesting

• Digger wasps (Sphecidae) share nest with others and females remain in the nest and guard

Subsociality in insects

• Sterile soldier caste– Subsocial aphids (Pseudoregma sp.)

Eusociality in insects

1. Division of labor, with a caste system involving sterile or non-reproductive individuals assisting reproductive individuals

2. Co-operation among colony members in tending the young

3. Overlap of generations capable of contributing to colony functioning

Eusociality is only known from Hymenoptera (bees, wasps, ants) and Termitoidae (Blattodea)

Eusociality in Hymenoptera

• Queen, drones, worker, soldiers• Haplodiploid genetic system in which queens

control the sex of their offspring– Males develop from unfertilized eggs, thus haploid– Females develop from fertilized eggs, thus diploid– Behavioral and chemical maintenance of monarchy

• Division of labor by polyphenism or polyethism

Haplodiploidy: a precursor to eusociality?

SOL: SolitarySUB: SubsocialEU: Eusocial

Wasp (Vespula sp.)

• Female caste dimorphic (queen and worker)

• Age polyethism– Newly emerged workers

involve in nest construction and food distribution

– Middle-aged workers involve in foraging

– Old-aged workers involved in guarding

Wasp Nest building

Honey bee (Apis mellifera)

• Female dimorphism: queen and worker

• Workers have wax glands and pollen-collecting apparatus (corbicula and combs), barbed stinger

• Workers exhibit polyethism• Caste differentiation

trophogenic (determined by food)

Honey bee (Apis mellifera)

Ants (Formicidae)

• Two major female castes: reproductive queen and workers

• Some species have polymorphic workers: minor, media, major workers

• Caste determination trophogenic

Termites (Termitoidae)

• Primary reproductives: queen and king

• Supplementary reproductives: potentially reproductive, but with arrested development

• Sterile termites: workers and soldiers (nasus)

• Nymphs: developmental instars of reproductives

• Larvae: instars of sterile lineages

Physogastry: termite queen’s abdomen being distended to 500-1000% of its original size

Role of JH in caste differentiation

Evolution of eusociality

• Kin selection: evolutionary strategy that favors the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction– rB > C where r = coefficient of relatedness, B =

benefit gained by the recipient of altruism, C = cost suffered by the donor of altruism

• Subsociality might be a precursor to eusociality