Social Insects

1. Social Insects • Sociality evolved multiple times in insects • Much of Earth’s fauna consists of social insects • They play major roles in entire ecosystems • Proliferation of ants and termites associated with change from solitary to social lifestyle

2. Subsocial • More widespread • 13 orders of insects • no reproductive division of labor

3. Eusocial • Three traits • Some individuals in colony reproduce, others sacrifice reproduction • Cooperation in tending young • Overlap of generations within colonies • Ants, termites, some bees and wasps

4. Aggregations as subsocial behavior • Food exploitation • bark beetles • Roosting • Aposematism • monarch butterflies • ladybird beetles • Chemical defenses • Sawflies • Parental care

5. Aggregations as subsocial behavior • Food exploitation • bark beetles • Roosting • Aposematism • monarch butterflies • ladybird beetles • Chemical defenses • sawflies • Parental care

6. Parental care • What parental care do all insects provide? • Post hatching attention, provision and protection of food • Without nesting • Tending eggs and young • Care of nest • Can involve feeding • Blattodea, Orthoptera, Dermaptera, Hemiptera, Coleoptera and Hymenoptera

7. Membracid nannies • Parental care by ants. • Ants obtain honeydew from treehoppers

8. Nesting as social behavior • Eggs laid in structure and parents tend young • Types of nests • New construction • Pre-existing • Types of care • Vigilence • Nutrition

9. Nesting as social behavior • Solitary nesting • No reproductive division of labor • Examples: ground nesting crickets, earwigs, some beetles, Hymenoptera • What orders? Nesting is not known in other orders.

10. Nesting as social behavior Most nesting subsocial Hymenoptera are parasitoid wasps.

11. Communal nesting • Nests shared among individuals • Parents clean, provision, defend nests • Conflicts among nest mates common • Halictinae, Megachilinae, Andreninae

12. Subsocial aphids & thrips • Aphids • Behavioral and morphological differences • Soldiers • All first instar • molt into normal feeding individuals • Reproduction delayed if molt is delayed • Special caste of soldiers

13. Subsocial aphids & thrips • Aphids • Behavioral and morphological differences • Soldiers • All first instar • molt into normal feeding individuals • Reproduction delayed if molt is delayed • Special caste of soldiers

14. Subsocial aphids Soldier nymphs Remain at 2nd instar without molting and growing. Sclerotized cuticle Sterile Attack natural enemies & competitors Perform housekeeping. Adults Differences likely attributable to differences in gene expression between the castes POLYPHENISM Genetically identical clones by parthenogenesis Molt and grow. Soft cuticle. Contribute to reproduction. Perform neither defense nor house-keeping. Reproductive (normal) nymphs

15. Subsocial aphids Soldiers injecting venom into predatory lacewing larva

16. Subsocial aphids & thrips • Thrips • Behavioral and morphological differences • Dispersers & soldiers in colony in gall • Soldiers defend gall against other thrips species and usually reproduce less than dispersers

17. Subsocial thrips Dispersers are highly fecund, participate in extensive brood care, and are adept and initiating and growing new galls. Soldiers have low fecundity and are involved primarily in defense of the gall from kleptoparasites. They cannot initiate or grow galls.

18. Quasisociality & Semisociality • Communal nest- Members of same generation cooperate in brood care • Quasisociality- All females can reproduce • Semisociality • Division of reproductive labor • Workers are sisters to queens • No morphological difference between queen and workers

19. Eusociality • Multigenerational colonies • Polyphenism: morphological differences between queen and workers • Polyethism: behavioral differences • Caste system • Reproductives • Workers • Soldiers • Subcastes • Found only in Hymenoptera and ALL Isoptera

20. Natural selection & Eusociality • Why would some individuals NOT be involved in reproduction?

21. Natural selection & Eusociality • W.D. Hamilton gave us the tools to solve one of Darwin’s greatest challenges. • The evolution of altruism.

22. Eusocial Hymenoptera • Why are there so many origins of Eusociality in the Hymenoptera? • How are ‘r’ and ‘B’ maximized with respect to ‘C’?

23. Super-relatedness in Hymenoptera • What sex-determination system do all Hymenoptera have? • So, what is the genetic relatedness between sisters? • How could this result in a maximization of ‘r’? • What benefits might there be of this extensive social behavior?

24. Eusocial Hymenoptera • Which is/are the male(s) in the above figure? • Which is/are the female(s) in the above figure? • Feeding quality + substance yields polyphenism in diploids, which are all ____________.

25. Hymenoptera • Numerous origins of eusociality from subsociality. • Primitively eusocial • Females morphogically similar • Colonies usually annual • Advanced eusocial • Ants, some wasps, many bees • Behavioral and morphological differentiation • Workers different than queens

26. Primitive eusocial Hymenoptera • Numerous transitional lineages, e.g.: • Polistine Wasps, a few others • >1 female forms colony • Colony lasts 1 yr • Variable # reproductives • Bumblebees, Halictinae • >1 female forms colony • ‘winning’ female reproduces and is aggressive • Sexual retardation reversed if queen dies

27. Bumblebees • Colony foundation by one or more females • Pheromones used to modify worker behavior • Ovarian development in late season workers • Queen may be driven from nest • Workers produce male offspring parthenogenetically

28. Advanced eusocial Hymenoptera • Many bees and some wasps, ants • Females dimorphic • Specialization of workers • Wasps • Queen founds first brood of workers • Subsequent generations include males, then reproductive females

29. Eusocial honeybees (Apidae) • Colony develops and may found new colonies during summer • Nest made of wax secreted by bees • Castes: queen (larger), worker (smaller), drone • Old workers: hive; Young workers: field

30. Extreme eusociality: ants (Formicidae) Amblyopone are specialist predators of centipedes • All ants are eusocial • Workers may be polyphenic • Trophogenic • Feeding • Predatory • Seed and grain harvesters • Mutualists with plants • Honey dew specialists • Fungus harvesters • Parasites (slave-makers & usurpers)

31. Extreme eusociality: ants (Formicidae) • All ants are eusocial • Workers may be polyphenic • Trophogenic • Feeding • Predatory • Seed and grain harvesters • Mutualists with plants • Honey dew specialists • Fungus harvesters • Parasites (slave-makers & usurpers)

32. Extreme eusociality: ants (Formicidae) • All ants are eusocial • Workers may be polyphenic • Trophogenic • Feeding • Predatory • Seed and grain harvesters • Mutualists with plants • Honey dew specialists • Fungus harvesters • Parasites (slave-makers & usurpers)

35. Eusocial Isoptera • What sex determination system do termites have? • Uh-oh, ‘zup? • Perhaps something about maximizing ‘B’ when feeding on wood? • What else happens to wood-feeding insects in their population structure (remember Normark paper)?

36. Eusocial Isoptera • In what way does this caste determination structure differ from Hymenoptera?

37. Termites • Lower termites • Wood-digesting endosymbionts • Loose castes, all workers immature • Morphology and caste may change after molting • Queen similar to workers

38. Termites • Higher termites: Termitidae • No symbiotic flagellates • How do they digest wood? • Rigid caste system • Queen differs from workers

39. Termite mounds