University of Michigan Biological Station

Biology 442 - Biology of Insects

Lecture Notes - Social Insects

1. Levels of social organization
   1. Solitary - living alone or as mated pair; no extended contact with brood - most insects
   2. Aggregation - more than mated pair living together; no cooperation for other activities; no overlap of generations - e.g. Coccinellidae, caterpillars for feeding
   3. Presocial
      1. Subsocial - some adult care of immature stages, but not up to reproductive life - e.g. Nicrophorus, Acanthosomatidae, Belostomatidae
      2. Communal - same generation use same nest without cooperating in brood care - e.g. possibly Halictidae
      3. Quasisocial - same generation use same nest and cooperate in brood care - e.g. Halictidae
      4. Semisocial - same as quasi with reproductive division of labor (worker and reproductive castes) - e.g. Halictidae, Sphecidae?
   4. Eusocial - same as semi with overlap of generations; offspring assist parents in rearing young and do not reproduce themselves.
2. Groups showing eusociality (see table below)
   1. Wasps - about 800 spp.
   2. Bees - a few hundred spp.
   3. Ants - 12,000 spp.
   4. Termites - 2,200 spp.
   5. Beetles - 1 sp?
3. Life histories
   1. Wasps
      1. Polistes (paper wasps) - solitary or cofoundresses start nest; they raise first brood, then workers take over, may get as big as 50-80 workers in north, more southward; raise reproductives in fall, they mate and overwinter in hiding places, start new nest in spring.
      2. Dolichovespula (hornets) - same as paper wasp, but build covered nest
      3. Vespula (yellow jackets) - same as hornets and paper wasp, but build underground or cavity nest - size of colony gets larger, up to 400 or more workers; mating on flowers.
      4. Metapolybia - form colonies by swarming, 20-40 workers leave with several queens, they build nest and lay eggs, then workers reduce # of queens
   2. Bees
      1. Bombus (bumble bees) - solitary foundress starts colony; builds honey pots for storage and cells for larvae; up to 3-5 days larvae are plastic in development and may become worker or queen; queens are fed directly and workers communally after that; not perrennial colonies
      2. Apis (honey bees) - perrenial colonies; workers take care of queen, cannot mate, but occassionally lay male eggs; new colonies founded by swarming, old queen leaves with some of workers and finds new nest site, several new queens are reared and one that emerges first locates other cells and kills them; colony temp is maintained at about 30° C in winter and 35° C in summer.
         1. Division of labor - just after hatching work deep in nest; then move lower and accept nectar from field bees; then feed larvae and construct cells, may attend queen; oldest go out to forage (several weeks).
         2. All larvae fed royal jelly (worker secretion) for 2 days, then future workers are switched to pollen and future queens continue to get royal jelly.
         3. Waggle dance for recruitment - communicates quality (intensity of dance), distance (length of dance), direction (angle on the nest)
   3. Ants - started by solitary, claustral queen; she raises first brood on fat reserves and former wing muscle; the stays in cell and workers forage.
      1. Seven Wonders of the Ant World
         1. Social parasitism
            1. Temporary - queen invades, gradually usurps
            2. Dulosis - slave making, raid pupae for workers
            3. Inquilinism - no worker caste, parasitic queens live in host nest
            4. a and c probably evolved from budding where females go out and mate and then return to wrong nest; b probably evolved from predaceous species
         2. Plant/ant relationships - Acacia and Pseudomyrmex
         3. Army Ants (Eciton) and Driver ants - statory and nomadic phases
         4. Leaf cutters (Atta) - cut leaves, culture fungus
         5. Honey ants - workers become honey pots
         6. Weaver ants - use larvae to spin silk and fasten nest together
         7. Phragmotic ants - workers with large heads plug entrance hole
4. Evolution of eusociality
   1. Parasocial route - solitary to communal to quasisocial to semisocial to eusocial; aggregation of sisters of same generation then get overlap of generations and loss of reproductive capabilities.
   2. Subsocial route - solitary to subsocial to overlap of reproductive periods to evolution of sterile caste.
   3. Why give up reproduction? Accounting for sterile castes. Altruism - behavior benefitting another individual while detrimental to the performer.
   4. Hypotheses to account for sterile caste.
      1. Superorganism - colony level selection required - see workers as somatic cells, reproductives as germ cells, would use subsocial route; actually different than an individual because not genetically identical and only get benefit when system is in place; doesn't explain well how it got there.
      2. Mutualistic reciprocity - uses parasocial route through semisocial society - unrelated females cooperate in raising brood. Not well supported now - most supposed examples seem to be related females.
      3. Parental manipulation - parents force offspring to be workers - may be done by underfeeding and producing young that are not well adapted to make it on their own
      4. Kin selection - suggested first by W. D. Hamilton; based on total genetic contribution to next generation and so can be individual level selection (inclusive fitness); basically how do we pass on the most genes of your genome.
         1. Assumptions
            1. no inbreeding
            2. only 1 mating for each queen
            3. ignores differences in ability to dispense and use help (K value may be different for different individuals)
            4. no a priori difference in ability to win conflicts
         2. Haplodiploid Hymenoptera have unique genetic situation where sisters are more related to each other than to daughters given the above assumptions. See tendency because probably has evolved 12 times from 110,000 Hymenoptera and only 1 time from 23,000 Orthopteroids

Group	Metamorphosis	Genetics	Workers	Food	Colony founding
Termites	Incomplete	Diploid	Male & Female	Cellulose	Monogamous pairing & budding
Wasps	Complete	Haplo-diploid	Female	Insects	Solitary queen, cofoundresses, or swarming
Ants	Complete	Haplo-diploid	Female	Various	Solitary queen or fission
Bees	Complete	Haplo-diploid	Female	Pollen	Solitary queen; cofoundresses, or swarming

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