Lecture 6 Predation, Parasitism, Parasitoids, and Scavengers PDF

Predation, parasitism, parasitoids, and scavengers Ent 104 Johnson Outline of Lecture Some general principles Taxonomic overview – Who does what Case histories – Army ants Predation Insects as predators – Predators kill and consume other animals Two main classes of predators in insects Traditional p...

Predation, parasitism, parasitoids, and scavengers Ent 104 Johnson Outline of Lecture Some general principles Taxonomic overview – Who does what Case histories – Army ants Predation Insects as predators – Predators kill and consume other animals Two main classes of predators in insects Traditional predators – Solitary and group hunters Parasitoids – They also kill and consume animals, but They do so slowly in a manner reminiscent of a parasite that runs amuck Who are the predators? About 25% of insect species are predators or parasites Which orders? – Almost every order has at least some predatory species Even caterpillars – Orders that are exclusively predatory Odonates, Mantodea, MantoPhasmatodea, Neuropterans, Mecoptera Predation strategies Sit and wait – leopards Trap – spiders Active search – wolves Sit and wait Sit and wait predators are often camouflaged – Many mantids They are often fast once they identify prey – Robber flies, odonates Traps Active search predators Random searches – Predacious larva Active searches – Chemical Chemicals released by plants after attack by herbivorous insects – Visual Fire flies are a classic example Parasitoid basics Parasitoids find their hosts – Some are generalists – Some are very specific Parasitoids lay an egg in or on their hosts – Most Parasitoids discriminate against already parasitized hosts Pheromones can be internal or external Development of egg into larva kills host Larva pupates, mates, then searches for new host Anti-Parasitoid Physiology Encapsulation response – Insects have the ability to encapsulate a foreign body with a impenetrable layer of tissue that kills it Immune cells surround the parasite Cells are then melanized to thicken them Toxic compounds can also be secreted by the immune cells Photo by Dan Hultmark How do parasitoids avoid encapsulation? – Avoidance Hangout in a tissue that cannot allow encapsulation – Evasion Parasitoid mimics the hosts proteins and encapsulation is not triggered – Destruction Host is severely weakened by feeding and cannot encapsulate – Suppression Viruses associated with parasitoid interfere with the encapsulation response – Subversion The parasitoid is encapsulated but tolerates it From NC State Biological Control center Who are the parasitoids? Hymenoptera – Many families – Female finds the host – Stinger is often used to immobilize the host – Viruses often injected Diptera – Fewer families – Larva sometimes finds the host – 1st instar larva sometimes has morphological modifications for host finding Why are they important? Selective agents – Involved in evolutionary arms races with their hosts Population control – Predator prey dynamics Biocontrol – Raised and released to control pests Hyperparasitoids A second parasitoid develops at the expense of the first parasitoid Development can occur inside or outside the primary parasitoid larva Usually the hyperparasitoid feeds on the pupa of the first parasitoid Occurs in dipterans, coleopterans, and hymenopterans Who are the parasites? Many orders have some (or many) parasitic species – Dipterans, Hymenoptera, Coleoptera Orders that are exclusively or mostly parasites: – Strepsiptera, fleas, lice Strepsiptera Male is a weird looking bug – Develops inside host, but leaves when it pupates Females remain as larva-like insect inside the host – Never pupate – Signals to flying males with pheromones Females lay larva that search for new hosts – Jump off host on flowers and wait for new hosts Credit: Michael Hrabar Strepsipteran emergence Scavengers Dead wood – termites Carrion & Dung – beetles General – Crickets, silverfish From ambrosiasymbiosis.org Ants Social insects are ecologically dominant Social insects are the most complex animal societies Social insects have a lot of very derived traits – Armies, farming, herding, slave making, etc Predatory case history: Army ants Army ants are both group hunting and migratory Lots of ants are either group hunters or migratory It’s the two together that make army ants Army ant colonies are some of the largest of all ant colonies – 20,000,000 workers in driver ants Major classes of army ants Eciton sp – Latin America – Hundreds of thousands of workers – fixed life cycle – Sometimes called legionary ants – Specialize on either social insects or generalist insects Dorylus sp – Africa – Millions of workers – More flexible than Eciton in life cycle – Driver ants (safari ants in Africa) – Generalist feeders Nest Eciton bivouacs on the ground in a solid mass of ants – Queen, males, and brood in the center Driver ants bivouac in the ground in a large quickly constructed nest Foraging Bivouac dissolves in the morning into one or many foraging columns – Column or swarm raid Media and minima do the hunting and transporting Soldiers stand at the side and guard the columns – Mainly from vertebrates Foraging columns Swarm – Classic army ant strategy – Takes anything that gets in the path of the advancing front Column – Going somewhere in particular – Usually to attack a social insect nest Bees, wasps, ants, termites Wasp prey Ant prey Everything Paper wasps and army ants Reproduction Reproduction is by fission (as in honey bees) Each year one brood cycle produces sexual brood – Many males and a few queens When the new queen matures the colony splits in two and each goes its separate way Males look nothing like the females and were initially thought to be separate species – They have to fly to another new column to find a mate Nomadism (migratory) Colonies are so large that they quickly deplete the supply of insects around their nest The colony therefore has to move often – Eciton has two phases Nomadic: colony moves every day Stationary: colony stays in the same place for a time – Dorylus with a more flexible period Queen morphs Queens lay all their eggs in a short burst – Hundreds of thousands or even millions of eggs in one bout of a few days to a week Interesting facts Driver ants are blind – Communication is entirely pheromone based Driver ants can kill even vertebrates if they can’t get away Ant birds, 10 species in Panama, follow army ant raids and eat the flying insects that are scared up by the ants Dorylus queens are the largest of all ants (up to 5 cm) Driver ants