Phylum Arthropoda Class Insecta

Class Insecta – Characteristics Approximately 1 million species – more than all other animals combined Order World North America Coleoptera (Beetles) 290,000 29,000 Lepidoptera (Moths, butterflies) 180,000 14,000 Hymenoptera (bees, ants, wasp) 103,000 17,500 Diptera (flies, gnats, mosquitoes) 85,000 16,000

Class Insecta – Characteristics 3 distinct somites Head, thorax, abdomen 1 pair antennae 3 pair jointed legs attached to thorax – “hexapods” 2 pair of wings usually attached to thorax

Class Insecta – Characteristics Mouth parts adapted for chewing, piercing, & sucking Digestive -- complete; salivary glands & “gastric caeca” aid in digestion 3 regions: foregut, midgut, & hindgut Circulatory – open; consists of slender, dorsal heart Hemolymph collects in sinuses in hemocoel

Class Insecta – Characteristics Respiration – Air is drawn in from sides of abdomen through “spiracles” Trachea branches into smaller “tracheoles” where gas exchange takes place Excretion – “Malpighian tubules” function similar to kidneys, located in anterior portion of the hindgut Insects can have as few as 2 or as many as 100 Malpighian tubules

Marcello Malpighi, 1628-1694 Rest his dearly departed soul :-(

Class Insecta – Characteristics Nervous system – Double ventral nerve cord Several pairs of ganglia per segment Well developed sense organs

Class Insecta – Characteristics Sensory reception Simple eyes (ocelli) and compound eyes Antennae – Single pair; chemoreceptors, “tactile hairs” Sound reception – tympanic membrane on each side of body

Class Insecta – Characteristics Reproduction – Sexes separate, “dioecious” “Viviparous”, internal fertilization with internal development. Eggs develop with a yolk & thin protective shell Eggs can be deposited with an “ovipositor” Two types of development Complete & incomplete metamorphosis

Complete Metamorphosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Complete Metamorphosis

Incomplete Metamorphosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Incomplete Metamorphosis This stage involves a series of “molts”

Reasons insects are so successful… Exoskeleton for protection Mobility – wings and legs Small body size Efficient energy use High reproductive success Short life cycle – leads to adaptive changes Metamorphosis is controlled by hormones

Reasons insects are so successful… Protective coloration Mimicry Defensive chemicals