Biodiversity – Nov. 7/12
- The order Hymenoptera contains the basal sawfly groups and the Apocrita. The Apocrita comprises
the advanced hymenopterans with a wasp waist, including all the parasitoids (50 families) and the
Aculeata (stinging hymenoptera including stinging wasps, bees, and ants). A synapomorphy of the
Apocrita is a wasp waist.
- Parasitoids can be ectoparasitoids or endoparasitoids. Ectoparasitoid – The wasp larva (the
parasitoid) feeds on the outside of the host body. Endoparasitoid – The wasp larva (the parasitoid)
feeds on the inside of the host body. Oviposition – The act of ovipositing, or laying eggs. Venom –
Parasitoids have venom, or substances injected through the ovipositor, that paralyze or subdue the
host before or during oviposition. These are not defensive venoms, but in some groups (stinging
wasps) the venom has evolved to become defensive.
- Parasitoids come out at night because their hosts are nocturnal. They have aggressive behaviour only
when they’re being threatened and they can use their ovipositor as a defensive mechanism.
- Parasitoids can also be divided into idiobiosis and koinobiosis. Idiobiosis (the basal condition) – The
female wasp paralyzes the host at the time of oviposition. The female wasp then lays an egg on or
inside the paralyzed host. Wasp larva consumes the living but paralyzed host. The host eventually
dies. The host is paralyzed but alive. It is not feeding or developing, but it eventually dies. Koinobiosis
(derived, independently evolved in multiple lineages) – The female wasp temporarily paralyzes the
host or not at the time of oviposition. The female wasp lays egg(s) on or inside the non-paralyzed or
temporarily paralyzed host. The host eventually resumes feeding and developing (venom wears off)
while the wasp larva is feeding and developing on/in it. The host eventually dies.
- Parasitoid biology: Both idiobionts and koinobionts can be either ectoparasitic or endoparasitic,
depending on the taxon. There are four types – ectoparasitic idiobiont, endoparasitic idiobiont,
ectoparasitic koinobiont, and endoparasitic koinobiont (ex. family Braconidae). Most idiobionts are
ectoparasitoids. Most koinobionts are endoparasitoids. Adult parasitoids have fast oviposition. This
is because they parasitize adults and adult insects can defend themselves well compared to a host
larva (ex. adult parasitoids from Family Braconidae).
- Endoparasitic idiobiont – ex. egg parasitoid, Family Encyrtidae. Endoparasitic Koinobiont – ex. larval-
larval parasitoid, Family Braconidae. Larvae host continues to develop with larvae wasps inside.
- Ectoparasitic idiobiont (basal condition): Hosts tend to be mature, and need to be appropriate size to
feed larva at the time of oviposition. Mature hosts are harder to find than younger hosts. Most of
these parasitoids are generalists and they use a wider variety of host species. They can’t depend on
always finding the same species of host because mature hosts are less abundant.
- Endoparasitic koinobiont (derived condition): Female wasps can oviposit in smaller/younger and
more abundant hosts. Younger hosts are also more vulnerable hosts – are easier to parasitize
because they don’t have fully developed defense mechanisms (ex. young caterpillars don’t have
osmeterium). Wasp larvae are highly adapted to overcome host defenses/immune system. Most are
specialists (are very host specific).
- Aculeata – Stinging Wasps: Wasp waist is a constriction between the thorax and abdomen. It is a
symplesiomorphy for Aculeata since all Apocrita have it. A synapomorphy for Aculeata is a modified
ovipositor. Eggs are laid from near the base. The tip delivers a potent venom that will
paralyze/subdue/cause pain in larger animals such as tarantul