Introduction to Insects: Structure, Function, Development and Feeding Behavior Thomas J. Weissling Assistant Professor of Entomology University of Florida Fort Lauderdale Research
THE INSECTS • Fossil records indicate insects on land more than 300 million years ago - mid paleozoic
Insects are from an ancient lineage that included trilobites and crustaceans which were abundant in the oceans over 500 million years ago. Trilobites are extinct: but we are surrounded by crustaceans…most of which are aquatic. Insects shared the terrestrial habitat with various relatives such as spiders, ticks, mites, and scorpions.
Insects are in the phylum Arthropoda. This group contains animals that share the following characteristics: 1) Body segmented, the segments usually grouped in two or three rather distinct regions
4) A chitinous exoskeleton, which is periodically shed and renewed as the animal grows University of Nebraska-Lincoln, Department of Entomology, Leon Higley
6) An open circulatory system, the only blood vessel usually being a tubular structure dorsal to the alimentary canal with lateral openings in the abdominal region 7) The body cavity a blood cavity or hemocoel, the coelom reduced
8) The nervous system consisting of an anterior ganglion or brain located above the alimentary canal, a pair of connectives extending from the brain around the alimentary canal, and paired ganglionated nerve cords located below the alimentary canal
9) The skeletal muscles striated 10) Excretion usually by means of tubes (the Malpighian tubules) that empty into the alimentary canal, the excreted materials passing to the outside by way of the anus
11) Respiration by means of gills, or tracheae and spiracles 12) The sexes nearly always separate
The arthropoda is divided into 4 smaller groups called classes: Crustacea 10+ legs, 2 body regions, mandibles, 2 pairs of antennae, no wings Myriapoda 1-2 pair of legs per segment, 2 body regions, mandibles, 1 pair of antennae, no wings Arachnida (Chelicerata) 8 legs, 2 body regions, chelicerae, no antennae, no wings Insecta 6 legs, 3 body regions, mandibles, 1 pair of antennae, 0, 2, or 4 wings
The Arachnida (Chelicerata) have no antennae and the mouthparts are chelicerae which are not homologous to the mouthparts of insects. They are an 8-legged group in an evolutionary line that diverged from the insects in the mid-paleozoic
The Myriapoda (centipedes, millipedes, etc.) have antennae, mandibles, maxillae and tracheal system but have only two body regions, and they add segments as they molt (anamorphosis)
In the early myriapod lineage, certain groups appeared in which segments and legs were not added at molting (epimorphic). Legs were retained on the three segments behind the head, and the remainder of the body included only 11 segments When the three segments with legs became capable of moving the creature, the rest of the body became more specialized (for reproduction, viseral functions, etc.) Ended up with three body regions.
At least ½ of the animals currently occupying the earth are insects (approximately 1.5 million different species)
Of all insect species in the world Less than 1% Considered to be pests Beneficial or not considered to be pests (> 99%)
Eat about anything imaginable, occupy about every imaginable niche
Why are insects so successful? • Have wings…dispersive • Diverse mouthparts
Relation of insects to humans: 1. Beneficial: (Pollination, Honey, Beeswax, silk [65-75 million pounds produced annually], shellac, dyes, break down raw materials, aerate soil, biocontrol of weeds and bad bugs, human food, medicine & surgery [cantharidin (Spanish fly-blister beetle), bee venom for arthritis, blow fly larvae (maggot therapy)], research animal 2. Aesthetic Value: jewelry, pets, nice to look at 3. Injurious: plants, stored foods, woods, fabrics, humans and animals
Proper identification is essential in pest management
The Insects 1. Three, usually distinct body regions (head, thorax, and abdomen) 2. One pair of segmented antennae 3. Usually have one pair of compound eyes 4. Three pair of segmented legs, one pair on each of the three thoracic segments 5. Usually with two pair of wings, some have only one pair (i.e., flies) or no wings at all.
The Head. The insect head serves a number of functions, such as feeding and sensory perception.
The Thorax. The thorax is primarily responsible for locomotion. Made up of 3 segments, the prothorax, mesothorax, and metathorax. A pair of legs arise from each segment. Wings, if present, arise from meso-, and meta-thorax.
Metamorphosis. The process of change from egg to adult. Incomplete or gradual metamorphosis. The immatures, or “nymphs” look similar to the adults (grasshoppers, aphids, cockroaches).
Complete metamorphosis. The immatures, or larvae look nothing like the adult. The larvae pass through a pupal stage to change into the adult form (wasps, beetles, moths, butterflies, flies).
Development • Molting (and control of molting)…IGR’s (Insect Growth regulator) • Diapause/Estivation (slowing of activity) • Reproduction: sexually, parthenogenetically (A form of reproduction in which an unfertilized egg develops into a new individual, occurring commonly among insects and certain other arthropods). • Mating (mate finding) • Oviposition-process of laying eggs (fertility vs. fecundity – the ability to reproduce)
Feeding • Plant-feeders, blood-feeders, parasites, scavengers…to name a few
Types of Injury Insects Cause to Plants • 1. Stand Reducers (i.e. cutworms): produce an immediate loss • in plant biomass resulting in decreased photosynthesis. • Effects are governed by pest number, and timing of damage
2. Leaf-Mass Consumers (i.e. grasshoppers): Leaf consumption is generally thought to directly affect absolute photosynthesis of the canopy.
3. Assimilate Sappers (i.e. Aphids): Insects generally with piercing/sucking or rasping mouthparts. Tend to remove plant carbohydrates and nutrients after carbon is taken up but before it is converted to tissue.
4. Turgor Reducers (i.e. Citrus root weevil larvae): Are generally root and stem feeders that affect plants water and nutrient balance. Severe reductions in water uptake results in decreased turgor which decreases the expansion of new leaves, stems and fruit. In addition, photosynthesis can be decreased.
5. Fruit Feeders (i.e. Codling moth): feeding on fruits usually results in direct destruction of harvestable produce which affects quality, yield or both. Yield losses are not always proportional to the damage.
6. Architectural Modifiers (i.e. lodging, corn rootworm larvae): Results in morphological changes in plant architecture. Can result in reduction of physiological as well as harvestable yield. Also gall forming insects.
Author: Tom Weissling, University of Florida Photos: University of Florida University of Nebraska University of California Entomology And Nematology Department Copyright University of Florida 2000 For more detailed information see the Featured Creatures WWW site at http://creatures.ifas.ufl.edu/