Ent1LectInsectDefense2008

Ent1LectInsectDefense2008 - Staying Alive: Insect Defense...

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Unformatted text preview: Staying Alive: Insect Defense in a Hostile World Lecture Topics Selection pressures that drive evolution of defense mechanisms in the insect world Defenses: Sensory awareness Mechanical M h i l Protective resemblance & camouflage Chemical Warning coloration Mimicry What is the driving force behind evolution of defense mechanisms in the insect world? 1 Sensory Awareness Compound Eye of a Fly Compound Eye of a Mosquito AVOIDANCE OF PREDATORS Acute eyesight and rapid responses (e.g. flies) . Hawk Moth Katydid AVOIDANCE OF PREDATORS Acute hearing and rapid responses, e.g. sensitivity to the ultraultrasonic frequencies emitted by insect-eating bats. When the insectinsect senses that it is on the bat’s radar, it drops to the ground out of radar range. 2 Mechanical Defense StilletoStilleto-like mouthparts combined with burning digestive juices (above), spiny raptorial legs (right), threatening displays, armour-like armourspiny exoskeleton. Protective Resemblance & Camouflage: How Not To Be Seen Resembling inanimate objects, or from a primary predator’s point of view inedible objects. A caterpillar of an unnamed moth resembles a bird dropping (left). This katydid (right) resembles a living green leaf. Its behavior involves swaying, much as a leaf on tree sways in the breeze. Resemblance to Inanimate Objects or Inedible Objects Left: grasshopper resembling quartzite stone in the desert of South Africa. Right: Treehoppers arranged on a stem capitalizing on their resemblance to thorns. 3 Protective Resemblance & Camouflage: How Not To Be Seen Left: Caterpillar of the peppered moth avoids being eaten by birds by resembling a twig. Right: A thornbug next to a rose thorn which it resembles. Protective Resemblance & Camouflage: How Not To Be Seen A grasshopper that uses camouflage and protective resemblance. Camouflage Artistry: Orchid with Praying Mantis 4 Camouflage Left: Immature of a Praying Mantis escapes predators by resembling a dead leaf. Right: An arctic moth is camouflaged from predators by blending into the lichens on which it feeds. The Influence of Humans and Environmental Change In 1848, trees in the countryside of Victorian England were covered with pale lichens. The pale form of the common peppered was most common, with only rare occurences of the dark form. In 1855, air pollution caused the death of the lichens and the bark was dark. The black or melanic form of the common peppered moth increased to 98% and the pale form became quite rare. 5 As air pollution was reduced, what outcome do you predict for the moth populations? The Decoy Approach: False Head Markings This moth has false head markings on the tips of its hind wings to direct the pecks of hungry birds to a non-vital part nonof the body. Startle Tactics and Eyespots Eyespots deter birds, especially if they are widely separated (mimicking a large animal). They are often on the hind wings allowing wide separation. Eyespots are frequently combined with camouflage to enhance the startle effect. Fulgorid 6 Chemical Defense Left: The black swallowtail butterfly caterpillar has a gland that emits an unpleasant scent. The gland is brightly colored, thus it can serve to startle a predator, as well as repelling it with an nasty smell. Right: Caterpillar of a moth uses defensive spines that contain a stinging fluid to discourage predators. Chemical Defense The bombadier beetle carries chemicals in separate chambers in its abdomen. When disturbed the chemicals are combined in a single chamber and exploded at a would-be predator. would- Chemical Defense and Warning Coloration Red and black, yellow and black, orange and black all serve as signals to predators that an animal is poisonous. In the case of the monarch butterfly, the caterpillars feed on milkweed plants and sequester a chemical that causes birds to vomit violently. A bird will generally only try to eat one of these insects once! 7 Chemical Defense and Warning Coloration Top: Larvae of the sawfly are brightly colored, use a startle defense and emit a foul secretion to discourage predators. Bottom: The lubber grasshopper defends itself by exuding a foul smelling, toxic foam. Some birds, such as the loggerhead shrike have overcome this defense. Chemical Defense, Warning Coloration and Living Gregariously Many insects enhance the impact of their warning coloration by living gregariously. Models and Mimics: Batesian Mimicry Model = oil beetle with its black and yellow coloration. Sequesters toxins and makes predators that feed upon it ill. j , Mimic = jewel beetle, NOT toxic, but broadcasts a false message on the same wavelength, thus avoiding predators without investing in sequestering noxious chemicals. What must this system rely upon to work? 8 Common Cause: Mullerian Mimicry Many distasteful insects mimic the same colors and patterns. 9 ...
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