Tuesday, October 31, 2017

Arthro-Pod Episode 33: The Horror of Parasitoid Insects!

Hi there bug lovers and welcome to our Halloween special! Today, Jody and Jonathan are featuring parasitoids, one of the most fascinating groups of insects! Their life cycles lend themselves to Halloween discussion as they are often reminiscent of the Alien in Alien, devouring victims from the inside out. 

Aphid mummies caused by a parasitoid braconid wasp (Photo Jody Green; UNL)

In the show we discuss the differences between parasites and parasitoids but here are some easy definitions if you are curious: 

Parasites: lives off another’s (host) benefits by deriving nutrients at host’s expense giving nothing in return

Some examples
External: leech, lice, fleas, ticks, mites
Internal: tapeworm, protozoan that transmits Malaria via mosquito vector, horsehair worms

Here is a horsehair worm leaving a mantis

Parasitoid: Usually insects that undergo complete metamorphosis such as wasps and flies, where the female lays eggs in or on the host and the larvae behaves like an internal parasite, developing using the host’s body for nutrients, but eventually kills the host by through the developmental process. 

Some examples
Braconid wasp
Sphingid caterpillar (Spingidae)

Eggs laid & free living in side hemolymph, emerge & spin cocoon on outside of caterpillar
Hornworm caterpillar has hundreds of larvae or cocoons on the outside of its body. Wasp is very small.
Aphidius sp.
Aphids (Aphididae)
Eggs laid on aphid, grows inside, killing it, pupation creates the mummy form, chews hole out of the rear end
In the same place where aphids are found, aphid mummies are swollen, tan, papery spheres with cornicles. Tiny wasps among aphids.
Emerald wasp/Jewel wasp (Ampulicidae)

American cockroach
Sting thoracic ganglion to paralyze, then sting head to disarm escape reflex, chews off half of each antenna, guides cockroach to burrow
Wasp is found in Asia & Africa. Metallic blue color, 2nd & 3rd pair of legs are bright red & enlarged
Scolioidea (Scoliidae)
Scarab beetles/white grubs, Japanese beetles (Scarabaeidae)
Burrows in ground to look for larvae, spins cocoon underground, locates host by kairomones like hydrocarbons, feces
Wasp has stout body, bright colors, black & yellow.
Cicada killer wasps (Crabronidae)
Catch cicada using sounds, provision burrows with paralyzed cicadas, overwinter as larvae, pupate in spring, emerge as adults in summer (no adults overwinter)
Largest wasp, often close to wooded area where cicadas can be found, females are very large solitary, males territorial but only has pseudo stinger.
Velvet ant
Cicada killer
Lay egg in nest cell of cicada killer when larvae pupates it consumes pupae (Hyperparasite)
Bright colors, females lack wings, coarse hair
Ichneumonid wasp
Coleoptera, Lepidoptera, Hymenoptera  grub, larva or pupae
Inject eggs into hosts bodies or in larvae of other icheunmonids (Hyperparasite). Can use ovipositor to inject into wood boring larvae below bark
Slender waist, lots of antennal segments, some have long threadlike ovipositors
Tachinid fly
Caterpillars and other insect hosts

Robust fly with shiny or very hairy butt, feeds on flowers as adult

Emblemasoma sp. (Sarcophagidae)
Locates host by acoustically hunting male cicadas, drops 1-6 maggots at base of wings that burrow into body to feed, larvae use “oral hooks” to chew their way out to pupate in soil.
Flesh fly with red eyes, 3 dark stripes on thorax

Cicada killer wasp with hapless cicada victim (Photo Jody Green; UNL)

Not all parasitoids are wasps! Flies and beetles can parasitize as well! (Photo Jody Green; UNL)

Questions? Comments? 

Follow the hosts on Twitter @JLarson_UNL@JodyBugsmeUNL, and @MSkvarla36

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This episode is freely available on archive.org and is licensed under Creative Commons: By Attribution 3.0. http://creativecommons.org/licenses/by/3.0/

Beginning/ending theme: "There It Is" by Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0