Entomology: April 17, 2006
I. Neopterous exopterygotes (cont.) **NOTE: The “How to know the insects” key combines the Hemiptera and Homoptera together into the Order Hemiptera. You should still consider them as separate orders. If keyed to the Suborder Heteroptera, it is Order Hemiptera If keyed to the Suborder Homoptera, it is Order Homoptera A. Order Homoptera (“homo”= same): aphids, leafhoppers, cicadas, and others 1. Adult characteristics a) Head (note eyes, ocelli-if present, mouthparts, other structures of note) Have piercing-sucking mouthparts that arise further back (more posterior, ventral) and cannot be project as far forward as for the Hemiptera. b) Thorax Triangular-shaped scutellum on mesothorax (in both the Hemiptera and the Homoptera) The two pair of wings are similar, held tent-like over abdomen Enlarged pronotum in treehoppers and planthoppers: function? c) Abdomen No cerci Some groups with distinctive ovipositors. 2. Distinctive larval features a) In most, “normal” incomplete metamorphosis b) In some, the final nymphal instar is dormant and pupa-like. 3. Groups a) Suborder Auchenorrhynca: rostrum arises from the posterior portion of the head; antennae are short and bristle-like. treehoppers, spittlebugs, planthoppers (small, common), cicadas b) Suborder Sternorrhynca: proboscis appears to arise from between the coxae of the forelegs aphids and scale insects 4. Habitat a) Terrestrial; found in a variety of terrestrial habitats 5. Food/Feeding behavior a) Almost exclusively herbivorous, sucking juices out of plants 6. Locomotion/flight a) Some are average/good fliers; some w/o wings 7. Selected aspects of reproduction a) Periodical Cicadas: Nymph habitat and food source? How long as nymphs? Adults emerge synchronously Males make very loud mating calls with the tymbal organ on the first abdominal segment How does the tymbal organ work? Why is the egg-laying process damaging to the host plant? b) Aphids have incredibly complex life histories [Fig. 12.33] Alternation of 2 or more plant species “Typical” yearly cycle:
Page 1 of 3 Overwinter as eggs on their woody host plant. Eggs hatch in spring and develop into wingless females. Females give birth via parthenogenesis to live, nymphs that also develop into wingless females. (May do this for a few generations) As the season progresses increasing number of winged females Why produce winged individuals at this time? These produce more wingless females (parthenogenesis) As the summer ends, winged individuals of both genders are produced. Why produce winged individuals at this time? What genders are the winged forms? Do the winged individuals mate directly with each other? Explain… 8. Other a) Many homopterans are plant pests. In what three ways do they cause damage? Which groups are the most problematic? b) Spittlebugs: How do they produce the froth, and what is its role? c) Symbiotic relationship between some homopterans (aphids, plantlice) and ants What do the aphids provide? What do the ants provide? II. (Neopterous) Endopterygotes **Most diverse of the insect orders (40% of all insects, 25% of all animals) A. Order Coleoptera (“coleo” = sheath): beetles 1. Adult characteristics a) Head (note eyes, ocelli-if present, mouthparts, other structures of note) b) Thorax Hardened pronotum (notal sclerite) Forewings are called “elytra”—hardened (scleratized); usually meet in a central, vertical line. Protective functions? Role of space under the elytra? Hindwings membranous c) Abdomen No cerci 2. Distinctive larval features a) The larvae usually have three pairs of legs, although some have no legs 3. Habitats a) Both aquatic and terrestrial (variety of habitats) 4. Food/feeding behavior a) A majority are herbivorous, many are predaceous, but very few are parasitic. 5. Locomotion/flight a) Generally weak fliers. 6. Selected aspects of reproduction (see below, in “groups”) 7. Other
Page 2 of 3 a) Many are agricultural pests: destructive to crops and/or vectors for plant disease 8. Groups (some examples of more common and/or unique groups) a) Curculionidae (weevils or “snout beetles”) Largest family in the animal kingdom Note distinctively long rostrum; antennae occur on the rostrum and are often elbowed. Role of long snout for females? Often infest important crops (i.e. boll weevil on cotton) b) Buprestidae (jewel beetles) Metallic, wood-boring beetles Eggs are laid in wood. Our local species, the golden jewel beetle (Buprestis aurulenta) lays its eggs in dead or dying conifers The larvae tunnel through the wood Some with heat sensors. Adaptive value? Adults feed on flowers, nectar and pollen c) Carabidae (ground beetles) Ground dwellers Primarily active hunters: well-developed legs, large mandibles How do larval carabid beetles feed? Why are the “bombardier” beetles so named? d) Cerambycidae (longhorn beetles) Distinctively long antennae, 2/3-4 times the body length. Dull or bright. Brightly colored ones often aposematic. Overall habits similar to Buprestidae e) Scarabidae Size, shape and color variable; distinctive antennae. The dung beetles are in this group. Why do females roll balls of dung? Do these beetles actually feed on dung? f) Many others…learn about them as you find them!
Study questions
1. See question 1 on April 7 as well as questions imbedded in the outline.
2. Describe the generalized life cycle of periodical cicadas to the level described in lecture.
3. Describe the generalized life cycle of aphids to the level described in lecture. Be sure you understand the adaptive value of various aspects, such as having >1 plant host, winged and wingless forms, parthenogenetic vs. sexually produced forms.
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