Adaptation and Specialization

(A) Mouthparts - Structure and function

The generalized chewing mouthparts characteristic of the grasshopper have been modified in a number of insect groups for sucking, sponging, lapping, or siphoning liquid food. Compare the mouthparts of the grasshopper to those of other insects such as true bugs (Hemiptera), flies (Diptera), honey bees (Hymenoptera), butterflies (Lepidoptera), etc.

(B) Heads of Insects.
A. A moth. Maxillae of moths are modified into recoilable tubes. B. A mosquito. C. Cross section of mosquito mouthparts. D. Bug with piercing beak. E. Cross section through beak. F. A bug penetrating plant tissue. G. Housefly. Labium is modified into a sponge.

(C) Wings - Structure and Function

Development of wings was a key to the evolutionary success of insects, allowing them to elude predators and to colonize new habitats. Wings probably evolved from lobes of the nota (dorsal plates) of the thorax. Fossil insects show evidence of wings on all three thoracic segments. Modern insects, however, have wings restricted to the meso- and metathorax. Primitive insects, such as dragonflies, have two pairs of equal sized, membranous wings. The following two trends in wing structure are common among more advanced insects:

Toughening (sclerotizing) of the forewing to provide more protection for the soft body parts of the abdomen. This reaches it culmination in the beetles (Coleoptera). Compare the forewings of dragonflies (Odonata), grasshoppers and roaches (Orthoptera), true bugs (Hemiptera) and beetles and note the increased sclerotization.

Reduction in size of the hind wing along with evolution of coupling devices to attach the wings together. This has resulted in faster more efficient flight and has frequently been associated with streamlining of the body as well. This trend reaches its zenith in the flies (Diptera) where the hind wings have been reduced to a pair of gyroscopic balancing organs, the halteres.

Take the time to observe and record the differences in size, structure, and number of wings present among the insects on display in lab.

(D) Ecology - Radiation of Insects into different habitats

Terrestrial Insects. The vast majority of insect species are adapted to a terrestrial life style. A rigid exoskeleton is often accompanied by a body surface that is resistant to water loss. The evolution of wings and the elaborate development of legs has afforded numerous options for locomotion on land.

1) Aquatic Insects. Although only about 5% of the insect species are aquatic, those that are represent an array of taxonomic groups. Aquatic insects may be predators, herbivores, or scavengers. Adaptations of aquatic insects are also varied, enhancing the likelihood of survival in various aquatic habitats. Various structures, such as suckers, claws and hooks, have been modified from legs and body parts to allow insects to cling to an underwater substrate in moving streams. Insects that inhabit still water are often physiologically adapted to an environment with reduced oxygen. Some insects have their legs adapted to swimming organs.

2) Soil Insects. There are numerous species of insects that have become specialized to inhabit soil. Springtails, beetles, termites, ants, and fly larvae are notable groups with soil-inhabiting members. Insects may ingest organic material near the soil surface and defecate organic remains deeper into the soil, thereby contributing to the process by which litter is transformed. Excavation by soil insects also alters the soil, mixing layers and creating pores where oxygen can be present.

Structural features of soil insects include reduction of wings (why?) and presence of a body that is round in cross section (why?). Sometimes the forelegs are modified for digging. Mating often occurs above the ground during brief periods. Eyes and antennae may be reduced or absent (why?).

Insects inhabit almost every imaginable habitat, including plants, wood, stored food products, and living animal tissue (parasitic insects).

Examine the material on display to become familiar with examples of adaptation and radiation of insects into different habitats.

(E) Larval vs Adult stages: Advantages/constraints of each life style

One feature of many species of insects is that the adult and larval forms are very dissimilar, and occupy very different habitats and ecological situations. Examine the display of insect larvae versus their adult forms and make a list of features that indicate adaptation to various habitats. Review the Animal Life Cycles lab in terms of elaborations of insect life cycle patterns.