1. Insect Societies
Lecture 21

2. 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)

3. Subsociality in insects
Aggregation
Often aposematic

4. Subsociality in insects
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

5. Parental care without nesting
Giant water bugs (Belostomatidae) exhibit paternal egg-tending

6. Parental care with solitary nesting
Carrion beetles (Silphidae: Nicrophorus) display extended biparental care of young and reproductive cooperation between the sexes

7. Parental care with communal nesting
Digger wasps (Sphecidae) share nest with others and females remain in the nest and guard

8. Subsociality in insects
Sterile soldier caste
Subsocial aphids (Pseudoregma sp.)

9. Eusociality in insects
Division of labor, with a caste system involving sterile or non-reproductive individuals assisting reproductive individuals
Co-operation among colony members in tending the young
Overlap of generations capable of contributing to colony functioning
Eusociality is only known from Hymenoptera (bees, wasps, ants) and Termitoidae (Blattodea)

10. 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

11. Haplodiploidy: a precursor to eusociality?

12. SOL: Solitary
SUB: Subsocial
EU: Eusocial

13. 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

14. Wasp Nest building

15. 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)

16. Honey bee (Apis mellifera)

17. Ants (Formicidae)
Two major female castes: reproductive queen and workers
Some species have polymorphic workers: minor, media, major workers
Caste determination trophogenic

18. 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

19. Role of JH in caste differentiation
Physogastry: termite queen’s abdomen being distended to % of its original size

20. 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