Biodiversity – Nov. 5/12
- Order Hymenoptera – Wasps: Hymen means membrane and ptera means wing, so these are
- This is the last order of the big four. There are many common names for the Order Hymenoptera
including wasps, bees, ants, sawflies, velvet ants, stinging wasps, parasitoid wasps, parasitic wasps,
mud wasps, hornets, and yellow jackets. Bees and ants are derived monophyletic groups within the
Hymenoptera. All Hymenoptera are wasps. A synapomorphy for this order is two pairs of
membranous wings with hamuli. Many have secondarily lost their wings (ex. worker ants).
Reproductive ants still have their wings. The hind wings are smaller than the front wings. The wings
are clear and membranous. A synapomorphy for this order is hamuli, which are a series of tiny hooks
on the leading edge of the hind wings. They attach to the trailing edge of the front wings. The hamuli
allow the wings to hook together during flight and presumably aids in flight. Hymenoptera are
excellent fliers. Insects in this order undergo complete metamorphosis with the stages egg, larva,
pupa, and adult. The larvae are called larvae (no special name for them). Larvae spin silk from labial
silk glands and they pupate within a silken cocoon. Some groups have secondarily lost the ability to
produce silk. There is haplo-diploid sex determination. Females have well-developed ovipositors.
Only females of one derived clade (Aculeata) can sting. There are 150,000 described species
worldwide in this order. Most are parasitoids (probably close to 100,000). Estimates show that there
are large numbers of parasitoid species undescribed in the tropics. While beetles and moths are
relatively well-studied, flies and wasps are under-studied. Eric Grissell coined the term hyperdiverse
in 1999 referring to the fact that so many parasitoid wasps are undescribed in the tropics.
- Haplo-diploid sex determination (haplodiploidy): Females mate and can store sperm in her body.
They can decide whether or not to fertilize their egg. Fertilized eggs develop into females. Females
are diploid. Unfertilized eggs develop into males. Males are haploid. The sex of the offspring is
controlled by fertilization of the egg. The sex of the individual is determined by the number of sets of
- Ovipositor: Ovi means egg. An ovipositor is an egg-depositing device. It is a spear-like structure on
females that is used to lay eggs into a substrate (could be plant, animal, soil, etc.). It has a sheath that
protects it when it is not being used. It is modified into a stinger in Aculeata.
- Basal/primitive Hymenopterans: They are commonly called sawflies. The females have a saw-like
ovipositor that is used to cut into plants to deposit her eggs. The thorax is broadly joined to the
abdomen (no wasp waist/constriction between the two segments). Most larvae are phytophagous
(feed on plants). Sawfly larvae resemble caterpillars. The main differences are that they have more
prolegs than caterpillars (more than 5) and they lack crochets on the prolegs. They are found in
- Apocrita is a monophyletic group of wasp-waisted hymenopterans. Most hymenopterans belong to
the Apocrita group. A synapomorphy for this group is a wasp waist, which is a constriction between
the thorax and abdomen. All have well-developed ovipositors with protective sheaths.
- Phylogeny: The order Hymenoptera consists of the basal sawfly groups and Apocrita. Apocrita
comprises the advanced Hymenopterans with a wasp waist, including all the parasitoids plus the
Aculeata (stinging hymenoptera including stinging wasps, bees, and ants). The parasitoids consist of
50 families (not a clade). The parasitoids are not a monophyletic group. The sawflies are not a
- Parasitoids: A parasitoid is an organism that uses only one individual as food (the host) and
eventually kills that host organism (usually another insect or other arthropod such as a spider).
Parasitoids differ from predators and parasites. Predators typically eat many prey items, but parasitoids consume only one individual. Parasites typically do not kill their hosts (ex. fleas), but
parasitoids kill their hosts. Some flies (ex. tachinids), many wasps, and a very few other insects are
parasitoids. Sometimes the terminology is not very good. For example, the terms parasitic fly or
parasitic wasp both mean parasitoid. We say “the fly parasitized the host larva” when we are