• Mouthparts 1 • Mouthparts 2 • Thorax and Abdomen 1 • Thorax And

• HeadHead •• MouthpartsMouthparts 11 •• MouthpartsMouthparts 22 •• ThoraxThorax andand abdomenabdomen 11 •• ThoraxThorax andand abdomenabdomen 22 •• CockroachCockroach dissectiondissection

© 1997 B.K. Mitchell & J.S. Scott, Department of Biological Sciences, University of Alberta The compound eyes are often the most COCKROACH BRAIN - dorsal aspect The inside of the prominent structures on the insect head. Drawing of dissected cockroach head contains more The Insect Head Adult holometabolous insects,as well as head showing brain and related than the brain, of immatures and adults of hemimetabolous Insects are strongly cephalized animals, that is, many of the important nerves. Frontal and hypocerebral course. There are insects have them. Insect compound ganglia are part of the stomatogas- many muscles that functions are moved anteriorly with a high degree of merging or eyes have thousands of more or less tric nervous system, while the cor- operate the various condensing of segments, sensory structures and neural ganglia. This equivalent sensory cartridges called om- pora cardiaca and corpora allata are appendages - the module illustrates the preceding statement. Additional information on matidia. Each ommatidium has a hexago- mouthpart muscles the insect head can be found in the mouthpart module. nal lens (hundreds in focus in this picture) being particularly and six to eight light-sensitive cells. Sin- complex. Six or seven segments are condensed to form the head capsule. This gle homologous sensory cells from nu- strong structure provides protection for the brain, support for eyes, oesophagus frontal ganglion merous adjacent ommatidia respond to This cleared whole ocelli, antennae and mouthparts. The strongest muscles in the head light in their limited field of view and send mount reveals an- serve the mandibles in chewing insects and the sucking pump in the information to the same place in the recurrent nerve other aspect of the piercing-sucking insects. optic lobe of the brain. The image formed head that is often in the insect brain is not as detailed as antennal nerve The hard exoskeleton that is a common feature of arthropods is overlooked - the ours but insects can be exquisitely sensi- optic lobe tentorium (red ar- particularly well illustrated in the head. The lesser appreciated internal tive to movement in the visual field. They rows). cuticular support structures are also well represented by the cross- also can see in colour. corpus cardiacum bracing tentorium. corpus allatum The tentorium is the “internal skeleton” which gives strength to the head capsule and provides a place for muscle attachment. It is formed by tube-shaped inward ex- Supported in part by B.K.Mitchell and J.S.Scott Academic Technologies for Learning © Department of Biological Sciences hypocerebral tensions of the exoskeleton. The mandibles, maxillary and labial palpi are all and Faculty of Science, University of Alberta University of Alberta 4 ganglion 8 visible in this frontal view. 13 Grasshoppers and cockroaches This section through a compound This is a scanning (drawings) are often used to illus- retinular layer eye shows some of the features. electron micro- trate the most basic form of the in- The lens layer is in red, the eye graph of the right sect head. The eye is often promi- lens retinular layer in black and gray side of a bug em- nent and the mouthparts can seem layer and the first of three parts of the bryo. strange to us. The evolutionary optic lobe in blue-gray. flexibility of the four mouthpart seg- Can you find the mental appendages is the theme of The retinular layer contains the following seg- the mouthpart segment of this se- sensory cells (six to eight per om- ments? ries. matidium). The dark layer just un- der the lens layer contains pig- In cockroaches, the head ments that help reduce light scat- • labial Back View is very flexibly attached to tering during the day. the thorax via an exten- • labral sive neck membrane (arrow). The oesophagus, optic • mandibular * heart, tracheal system, lobe and nervous system all •maxillary pass through the foramen at the back of the head The green arrow marks the boundary between the head and thorax. ( asterisk ). The eye is the bulge on the side of the head. Ventral is down and anterior is to the right. This is a dark adapted eye so the pigments are all at one end. This increases 1 light scattering (decreases resolution) but it increases sensitivity. 5 9

Insect heads take many shapes reflecting the characteristic feeding habits of the Jake Remple, a Cana- The sub- species concerned. For example, predaceous insects have forward directed dian entomologist, HEAD OF INSECT oesophagus oesophageal mouthparts with a corresponding forward protrusion of the head. The predators summarized this inter- Acron + 6 segments ganglion (SOG) pretation of insect of all insects head segmentation serves the major 1 1 - labral based on a careful ex- 2 mouthparts and 2 - antennal amination of develop- it’s therefore 4 3 - intercalary ing embryos of the much involved 5 4 - mandibular blister beetle Lytta. with feeding. stalkfly 6 5 - maxillary This picture is of The last three seg- a frontal section antlion larva 6 - labial ments are easy to see scorpion 3 through the SOG fly at all stages of devel- of a fly. acron opment (mandibular, neuropil maxillary and labial) because they bear ob- nerve labellar vious bi-lateral ap- tract nerve pendages.

The three anterior segments required developmental analysis to confirm their pres- A typical ganglion (functional concentration of nerve cells) is composed of a periph- eral region of cell bodies (nerve and glial cells - red) and a region of nerve to nerve tsetse fly ence. The acron is homologous with the front part of the body of bi-laterally sym- cicada metrical animals such as the earthworm and is not considered a true segment connections called the neuropil. water 10 beetle 2 because it lacks a pair of appendages. larva 6

The three most prominent arrangements of the head have been given the names Prognathous, Hypognathous and Opisthorhynchous. This unusual view of the 1 suboesophageal ganglion (SOG) Plant bug of a fleshfly shows the brain and corpus pedunculatum SOG in the same orientation as archicerebrum the previous picture. Use the oe- 2 prosocerebrum sophagus as a reference point. Tiger 3 deutocerebrum 1 Here a single neuron has been beetle tritocerebrum 2 commisure filled with a fluorescent dye to re- brain labral nerve 3 veal its extensive branching pat- nervus connectivus tern in the SOG and in the brain. Prognathous 4 nervus recurrens commisure The cell body of this neuron is the frontal ganglion oesophagus bright dot just above the cell body nervus procurrens 5 4 label. This neuron is one of many 6 5 6 that process taste input from the labellar sensilla.

Leaf Opisthorhynchous beetle The largest structure in the head-neck region is the brain and sub-oesophageal gan- suboesophageal glion complex. The oesophagus passes between these two major masses of nerv- cell ous tissue. These are dorsal and lateral views respectively. The numbers corre- body ganglion spond to the segmentation numbers of the previous slide. 11 7 Hypognathous 3 This frontal view of a cock- Dipteran mouthpart modifications roach head gives a better idea Mouthparts of Insects eye of what the mouthparts look labellum like in situ. The tentorium is REVIEW maxillary palp Insects owe their great success to their abilities to adapt to a antenna also visible (see module on the wide variety of habitats. Adaptations have occurred, indeed head in this series). Can you recognize the following? continue to occur, at every level of organization from the Note the well sclerotized man- molecular to the ecological. The comparative study of insect dibular “teeth” (black ridges in • antennae Horsefly adult- mouthparts is first and foremost a study of adaptation. We mandible lower center) and the protrud- Dissected ing galeae/lacinia and para- clypeus mouthparts single out mouthparts and the gross morphological level of • (ex. Micro-slide) maxillary organization in introductory courses because the variety of glossa. The mandibles appear palp to be at the front since the lab- • eye labrum adaptations is so great that we can address vast landscapes rum which largely covers them lacinia lacinia of insect evolution by looking at mouthparts alone. Also, they is transparent in this cleared • frons are relatively easy to see and appreciate and, perhaps most specimen. mandible hypopharynx mandible important, the mouthparts are entral to insect trophic • labial palpi behaviour cfood gathering behaviour). Horseflies (Tabanidae) have the same kinds of mouthpart modifications as labial maxillary • labrum blackflies, but since they are larger, are easier for us to study (their bite also causes more physical damage). All of the basic parts can be seen here and Supported in part by B.K.Mitchell and J.S.Scott palp palp mandible Academic Technologies for Learning © Department of Biological Sciences • don’t resemble the mouthparts of the cockroach. Nevertheless these are the and Faculty of Science, University of Alberta University of Alberta hypopharynx 4 8 appendages of the same segments - the result of the same basic develop- maxillary palpi mental plan. • 12 This detailed view of a Dipteran mouthpart modifications cockroach maxilla clearly cardo Mosquitoes have carried the business of piercing and shows the sclerites that The American cockroach sucking to a fine art. The stylets are modified labrum, make up this complex REVIEW (Periplaneta americana) has stipes maxillae and mandibles, just as in horseflies and appendage. The darker “generalized” mouthparts. Here’s a better challenge. This is a blackflies, but the cross section size is markedly re- the cuticle the heavier This insect is omnivorous and lateral view of a cockroach head with duced making for a much stealthier approach to feed- the tanning and usually its mouthparts are well suited the mouthparts extruded. Which of ing. e to chewing on a wide variety the heavier the scleroti- the following can you recognize? of food items. zation. Thus, the lightest cuticle is membranous- pharyngeal Only female mosqui- maxilla antennae pump toes take blood. Males The mouthparts are well de- like and semi- transpar- • antennal base mandibles veloped in cockroaches. Each ent while the darkest cu- do not possess the labium necessary m.pts. The mouthpart pair comprise the lacinia ticle is hard. • clypeus antenna galea maxillary e mosquito shown has two bi-lateral appendages of galea labrum their segment. The blue arrow shows • eye palpi all m.pts hence is a mandible labial where the maxilla at- female. Both sexes labrum palp The mouthpart-bearing seg- taches to the head. • galea suck nectar, and pos- maxillary ments are the labral, man- sess the large label- laciniae palp dibular, maxillary and labial. • hypopharynx tentorium lum. Two of the segments (mx and maxillary palp salivary hypopharynx duct • labial palp labium 5 • labium 13 1 • labrum This posterior view of the cock- This labium was taken from the 9 Dipteran mouthpart modifications foramen roach head shows additional same specimen as the maxilla in magnum features as well as the various the previous slide. Note that much This completes our review of basic insect mouthparts mouthpart appendages. sub- of the cuticle is thin, so much so Note the complexity of the max- mentum that the muscles operating the la- as found in the American cockroach (Periplaneta antenna illa and labium. bial palpi are visible (blue arrow- americana). Make sure that you understand this basic See next slide for additional de- heads ). eye plan before proceeding. tails. Compare the tips of the galea and cardo lacinia in the previous slide with the The rest of this module on mouthparts shows how vari- glossae and paraglossae in this labium stipes mentum photo. All are dark indicating hard- ous insect groups have used the basic mandibulate maxilla pre- ened cuticle. These structures are ground plan to produce highly modified mouthparts ex- mentum used to manipulate food. x.s. prementum quisitely adapted to their own way of obtaining food. By contrast, the tips of the palpi in Maxillary stylets- green both appendages are covered with Labral stylet - blue labial palp labellum membranous cuticle and, as we will ( not seen in X.S.) Mandibular stylets - yellow galea see later, with many sensory pegs. Food canal - red paraglossa Salivary canal - pink prestomen maxillary palp glossa labial Hypopharynx - black paraglossa palp Mosquito head and mouthparts - Labium - tan 2 6 10 frontal view 14 Hidden among the maxil- You may be Dipteran mouthpart modifications Dipteran mouthpart modifications lae and labium is the asked to dissect glossa paraglossa Blackflies (Simulidae) are small in- “tongue” or hypopharynx. the mouthparts of labium antenna sects but their mouthparts are rela- labial palp It has very thin a cockroach in the maxillary tively large. All of the parts are pres- (membranous) cuticle and maxilla laboratory and this palp ent in adults but they are greatly rostrum contains the opening of is what your final modified from the basic plan. The prementum the salivary gland duct. dissection should maxilla eye labellum is used for nectar feeding mentum look like. The but the labrum, lacinia, and mandi- The labium is the most parts are ar- submentum bles are modified as piercing struc- labrum complex of the cockroach ranged in the or- tures for blood feeding. The rela- maxillary mouthparts and exists as der of segmenta- tively large wound and the antigenic palpi a single piece rather than tion from anterior labium lacinia properties of the salivary proteins haustellum as two distinct, mirror im- to posterior. The hypopharynx lead to ugly skin reactions. stipes age parts as in the maxil- hypopharynx is lae. This single labium is the only part that cardo The higher flies (houseflies and relatives) clearly formed from a fu- is not a true seg- labellum maxilla maxilla have lost the mandibles and maxillae, ex- pseudotracheae sion of bi-lateral append- mandible mental append- cept for the maxillary palpi. They special- ages as the paired palpi, mandible age but rather a labrum ize in modifications of the labial append- The fly labellum is a complex sen- glossae and paraglossae modified part of labrum ages only to produce sophisticated lap- sory organ and feeding structure hypopharynx reveal. the prostomium labellum ping, probing, scraping and piercing looking something like a sock. It’s (foregut). maxillary palp labrum mouthparts. Most of them cannot pierce dexterous being controlled by nu- mandible mandible host skin but some, like the tsetse fly merous small muscles. 3 7 11 15 (later slide) can. Dipteran mouthpart modifications Hymenopteran mouthpart modifications These three drawings summarize the structure of a typical insect taste haustellum This SEM (Scanning Electron Micro- hair or sensillum. There are usually scope) micrograph of a fleshfly label- four cells projecting to the pore tip lum shows the sensory hairs that and these taste different chemicals cover the surface of the oral surface with some overlap in sensitivity. A µ of the lobes. These sensory hairs 10 mechanosensory cell (not shown) taste sugars, salts, amino acids, wa- 1µ usually terminates at the base of the ter and other chemicals as well as sensillum. Supporting cells (brown, conferring a delicate sense of touch blue and green) are important to the on the whole organ. maxillary physiology of the entire system but palp they are not sensory. The numbers indicate the length of the scale bar mandible in micrometers. labellum The sawflies, bees and wasps have vari- ous arrangements of mouthparts, the labial most complex being those of bees (photo palp at right). Like lepidopterans, bees use a tube to suck nectar but it is a modified glossa flabellum Galeae of leaf beetles have specialized taste hairs with rounded tips (red ar- glossa (part of the labium). Mandibles are rowheads). These are used to taste leaves before a decision is made to take 27 retained primarily for handling wax - in a meal. Leaves of poor host plants don’t taste right to the beetle so small front fact, the structure of the mandibles gives 16 20 meals are taken. Leaves of host plants are assessed quickly and extended 23 100µ rise to the precise hexagonal arrangement feeding occurs.

Dipteran mouthpart modifications These two examples of taste hairs were taken from leaf bee- antenna Hemipteran tle galea. The pore in the tip is where the leaf juice enters in antenna order to be tasted. The sensil- eye lum with the little fingers in the right hand picture does not maxillary palpi have much of a pore and is probably used to sense tem- haustellum perature and humidity. labellum dilating muscles maxillary palp Inside the large taste hairs we find the sen- Tsetse flies have carried labellar sory cells, as this electron microscope cross modification to an extreme un- maxilla mandible labium mandible maxilla section through the base of the larger sen- matched by any other insect. The sillum at top right shows. The four num- fine labellum with its tooth bearing 1 haustellum Insects with incomplete metamorphosis also 2 bered cells are chemosensory while the one tip makes a needle-like penetration use highly modified mouthparts as shown in marked with a yellow arrowhead is mecha- labrum of the host skin. the true bugs and their relatives. These are salivary 3 nosensory. Most taste hairs in insects can duct used for piercing and sucking and are similar 4 also sense movement. labellum { in some ways to the modifications seen in hypopharynx 17 mosquitoes. Note the large dilating muscles of 24 the sucking pump - the largest muscle in the 21 bug head. Lepidopteran mouthpart modifications This series of increasing magnifications are taken antenna This concludes our survey of mouthpart modifications. In from the inside of the labrum cardo ocellus several places we mentioned that sensory structures (epipharynx) of a leaf beetle. The epipharynx forms the were present on certain mouthparts, such as palp tips. anterior surface of the buccal In fact, one of the greatest concentrations of chemosen- cavity (roof of the mouth so eye to speak) and it also bears stipes silla is found on the mouthparts - the other major site food maxillary taste-sensitive structures. canal palp pilifer being the antennae. These sensillae are not hair- like but take the shape of epipharynx short pegs-in-pits. They too In the next section, we look in detail at some sensory have pores. labial palp structures and comment briefly on their function. The study of sense organs has major implications for phero- galea labrum galea mone biology, insect-plant interactions and the chemical modification of feeding by the use of antifeedants.

In moths and butterflies the sucking mouthpart is largely the modified maxillary galea. The area along the food canal is lined with taste pegs. The maxillary palpi are much reduced and mandibles are absent. 25 18

Lepidopteran mouthpart modifications labial mandible maxillary maxillary palp palp antenna The real thing looks different palp from the previous drawing of course. For one thing, moths eye and butterflies are covered with scales (modified cuticular hairs), as seen in this cleared lepidop- teran head. The large labial palpi are sensory, in fact, in some specialized nocturnal moths the organs of hearing are also on the palpi. The galeae are separated in this prepara- If you have been studying this module carefully, you will likely be tion. During feeding, they are labial able to quickly make sense of this ventral view of the head and palp held close together to form a mouthparts of a leaf beetle (Chrysomelidae). Leaf beetles chew sucking tube. leaves hence have strong mandibles. The palpi are well devel- The most obvious of the mouthpart sensory structures are the palpi (maxillary oped for sensory purposes as are parts of the labrum and the and labial). In leaf beetles, the palp tips provide four surfaces that are covered galeae galea. with small sensory pegs - some for taste and some for smell. 19 22 26 The Insect Thorax and Abdomen Mesothorax of spruce budworm moth - lateral view In the simplest terms, the thorax is the locomotory centre of the insect tergum since all six legs and the wings are found there. The largest muscles are also found in the thorax. The thorax is a box-like structure with extensive internal cuticular cross bracing. It also sports numerous dorsoventral The Wing Base flight muscle cuticular plates (sclerites) that are intimately involved in locomotion. basalar subalar To conserve mass, some of the thoracic muscles are involved in both The wing must move with great dexterity if walking and flying. This works because these are mutually exclusive muscles to alary sclerites the insect is to fly properly. The axillary scle- rites (red arrows) provide a major part of this behaviours and the motor nervous system plays the appropriate motor prothoracic complex attachment and the muscles that program at the appropriate time. The abdomen is simple in its anterior pleuron subalar muscle insert on them are responsible for small but region getting quite complex in the last three segments where the (wing supination) crucial movements of the wing in flight. This sclerites of the external reproductive system are found. Both male and sclerite/muscle system is also involved in Respiration in insects is mediated by a complex, multi-branched tracheal sys- female insects have extensive cuticular modifications for reproduction, wing folding. tem. The tracheal tubes (tracheae) are epidermal in origin and so are lined with thin cuticle. They communicate with the outside via segmental openings called females particularly for oviposition (egg laying) and males for sperm basalar muscle spiracles found on the thorax and abdomen. When present, there are two spira- insertion. Many insects can be identified at the species level only by (wing pronation) trochanter muscle cles per segment. Not all segments have spiracles, for example, compare the looking carefully at the male genitalia. coxa spiracles in an adult cockroach and an adult fly. These photos show examples Supported in part by B.K.Mitchell and J.S.Scott trochanter of spiracles and associated tracheae. The spiracle on the right has a filter sys- Academic Technologies for Learning Department of Biological Sciences tem to prevent entry of dust. Many spiracles have complex opening/closing and Faculty of Science, University of Alberta © 4 University of Alberta 8 mechanisms. 12 part of cuticular Ventral View of Periplaneta Thorax Mating behav- cross bracing Most insects have four wings flight muscle which either beat quite independ- iour in insects neck region ently as in dragonflies or with is often a com- haemocoel varying degrees of unity. The front plex business pronotum and hind wings of moths are that is a critical prothoracic strongly linked together and the part of the hind wing has a strong structure species isolat- sternum called the frenulum (red arrow) ing mecha- that is part of the linking appara- nism. Thus, mesothoracic tus. It hooks into a process on the intricate be- front wing called a jugum (in ju- haviours cor- pleuron gate moths in any case). rectly per- mesothoracic formed signal tergum femur species iden- tity. mesothoracic gut trochanter leg muscle ventral nerve cord In addition to behaviour, the structure of the last few abdominal segments plays membranous In the honeybee (not shown), the hind wing has little hooks a major role in species recognition. Here two craneflies are locked in copula. metathoracic that look very much like the hooks in a Velcro strip and the cuticle Specialized sclerites of the last three abdominal sclerites (terminalia) allow only coxa Cross section through the thorax of a cockroach showing some major internal fore wing has a corresponding surface for attachment. structures. Note the size of the muscles and that some are cut in longitudinal members of the same species to proceed this far. 1 section while others are cut in cross section. 5 9 13

Meso- and Metathoracic Seg- ments of Periplaneta - ventral view seg ix male( ) anal style male mesopleuron abdomen seg vii female ( ) anal cercus mesosternum coxal suranal cavity plate haltere

Diptera, as you can see from the name, have two wings instead of four. In flies, metapleuron As with most insects, the cockroach abdomen is composed of a series of similar the hind wings take the form of dumbell shaped structures that act as balancing metasternum segments until the terminal end when sex complicates things. Mating behaviour, organs during flight. These highly modified and specialized hind wings are called pheromone production, egg production and release are all handled largely by the halteres In the Odonata the male actually grabs the female by the back of the neck coxal abdomen and particularly by modifications of the last abdominal segments. The during mating and as they fly or perch, the female reaches around with her cavity male and female cockroach abdominal tips shown here clearly reveal some ob- abdomen and takes sperm from a specialized holding pouch near the junc- 2 vious differences. 6 10 tion of the male thorax and abdomen. 14

Grasshoppers are much stronger flyers than cockroaches and this is clearly reflected in the structure of the thorax. Note the greater fusion of the ventral femur tibia thoracic sclerites to form a Insect legs have numerous strong pterothoracic “box” to adaptations that depend on support flight. tarsus the insect’s lifestyle. Here are trochanter two examples. At top, a leg coxa from an aquatic insect (note mesothorax the numerous fine hairs that Wing veins provide support for the thin, delicate membranous cuticle that make spread for swimming) it is up the rest of the wing, as shown here by these two wings from a fly. Many veins also used to name the basic also house tracheae and provide a passage for haemolymph (blood). Numerous leg parts. At bottom, raptorial sense organs are found on the wings, especially wind sensitive hairs, and the spinasternum testis forelegs from a mantispid cells in these organs must respire and receive nutrients. Accessory hearts at the Insects often have rather as- metathorax (mantidfly) used for seizing base of the wing provide a sometimes complex flow of haemolymph in the veins. tonishing reproductive struc- prey then clamping during Wing veins can also be important taxonomic characters at the Family level. tures, especially the male in- accessory aedeagus feeding. tromittent organ or aedeagus. gland In this flour beetle the aedeagus is withdrawn into 3 7 11 the abdomen when not in use. 15 exocuticle mesocuticle This is a section of bending cuticle. As you can see, it is tergite8 not exactly like the previous stylus drawing. Not all cuticle looks tergite10 alike. Some is very thick, oth- tergite9 ers thin. Some cuticle has well developed mesocuticle, as shown here. The blue en- o snakefly o cranefly endocuticle docuticle is elastic, so this 1 2 coxopodium cuticle is highly bendable. coxopodium 2 gonapophysis As the functional skeleton of arthropods, the cuticle is the primary place for muscle Male and female abdomens are also attachment. This section shows how inti- variously modified, mostly for, in the tonofibrillae 1 gonapophysis mate is the connection between muscle case of the male, holding the female cuticle and cuticle. Muscle extensions called to- in position during copulation and in gonangium muscles nofibrillae make the actual link. At moult- the female accepting the male dur- ing, these connections must remain func- ing copulation and also for oviposi- tional until the last moment when new This drawing shows, in generalized form, the way female abdominal seg- tion (egg laying). connections are established with the new ments 8, 9 and 10 are modified for egg laying. Along with mating, egg lay- o waterbug cuticle developing beneath the old. 16 20 ing requires extensive modification of sclerites. 24

exocuticle In these views of actual specimens you can identify mainstream flow some of the cuticular parts endocuticle shown in the drawing of the generalized female ab- boundary layer domen. This specimen is a leafhopper. vortex bending cuticle

laminar sublayer substrate Parasitic wasps take the busi- ness of ovipositor modification to an extreme but all of the basic parts are there. 50% of The entire abdomen can also serve important functions in arthropods. The tail all wasps are parasitic on flick that is part of the escape response of the crayfish is perhaps the best other insects and need to lay known (it’s part of the reason that lobster tails are such good eating). Here is The spectacular picture of a wing base of a moth, shows a top view of bend- their eggs with great precision another use of the whole abdomen displayed by blackfly larvae. They twist their ing cuticle. The yellow ovals are the cones of mesocuticle protruding down since many are quite host abdomen 180 degrees so that their feeding fans can be properly oriented in the into the blue endocuticle, so this particular sclerite is very flexible. The specific. mainstream water flow. large areas of yellow cuticle are exocuticle and are relatively hard. 17 21 25

Many aquatic insects use special adap- tations of the last abdominal segments for orienting in the stream or for breath- ing. Notice how this mayfly nymph uses its caudal filaments for orientation.

Requirements of internal organs also influence the shape of the abdomen. The crop of this mosquito is so full of blood that the abdomen is swollen to Flies, such as this housefly, have a different version of the ovipositor. near maximum size (cuticle does not The last few abdominal segments telescope into the larger anterior stretch). A large egg load can also swell abdominal segments except when the fly is laying eggs. Then these the abdomen like this. segments are extended as shown here. 18 22

poison gonangium sac trichoid sensillum

tergite9 epicuticle dermal gland duct sheath 2 coxopodium 2 gonapophysis exocuticle bulb (hard) epicuticle gland 1 gonapophysis In bees, the ovipositor function is endocuticle subsumed by the sting which is (soft) exocuticle served by a poison gland. Ovi- position is through a simple epidermis opening. dermal gland trichogen basement epidermal oenocyte cell membrane cell

The head, thorax and abdomen are covered with cuticle as are the foregut, hindgut and tracheal system. These are the basic components of insect cuticle that you should be familiar with. The epicuticle provides a continuous wax cov- sting ering to prevent desiccation. The exocuticle is a mix of chitin (like cellulose) and 19 tanned protein. You can see why it won’t stretch. The endocuticle, including mesocuticle is flexible and elastic. 23 DISSECTION OF COCKROACH - GENERAL DISSECTION OF COCKROACH - NERVOUS SYSTEM Cockroach Dissection antenna HEAD While it is impossible to chose an insect species that truly represents Recently killed male cockroach, HEAD the morphology of all, the cockroach has gained a commanding with legs removed and partially position as the insect of choice for illustrating the ‘basic’ insect body mesothoracic suboesophageal imbedded (dorsal side up) in black ganglion ganglion plan. Another strong contender for this role is the grasshopper. Even composite wax, in a dissecting tray. THORAX terms like ‘the cockroach’ and ‘the grasshopper’ are terribly Distilled water or Ringer’s solution misleading, since there are many species of each with sometimes interganglionic is added to the dish before the interganglionic connective marked differences in various structures. Nevertheless, cockroaches connective and grasshoppers are good representatives of insects with chewing dissection begins. abdominal mandibles and lacking extreme morphological specializations of the ganglion major body parts. interganglionic Here we address the major external and internal parts of the fat body connective American cockroach, Periplaneta americana. Some of the terms will metathoracic ABDOMEN ganglion be new but many will be strikingly familiar for they are named after cockroach mounted in black composite wax their, sometimes very approximate, counterparts in vertebrates. abdominal muscles

Supported in part by B.K.Mitchell and J.S.Scott Academic Technologies for Learning Department of Biological Sciences and Faculty of Science, University of Alberta © University of Alberta cercus

DISSECTION OF DISSECTION OF COCKROACH - GENERAL DISSECTION OF COCKROACH - O REPRODUCTIVE SYSTEM Abdomen of male cockroach. testis dorsal Wings and abdominal tergites vessel removed exposing fat body, testis crop tracheae, dorsal vessel and underlying alimentary organs. tracheae vas deferens fat vesicula testis lies dorsal seminalis vessel within this stomach fat body

fat body anal cercus tracheae

fat body anal styles O external features Lateral view of

DISSECTIONDISSECTION OFOF COCKROACHCOCKROACH -- MOUTHPARTSMOUTHPARTS DISSECTIONDISSECTION OFOF COCKROACHCOCKROACH -- RESPIRATORYRESPIRATORY SYSTEMSYSTEM DISSECTIONDISSECTION OFOF COCKROACHCOCKROACH -- O REPRODUCTIVEREPRODUCTIVE SYSTEMSYSTEM

ovarioles

maxilla labrum

mandibles cellular sheath colleterial hypopharynx tracheae surrounding gland ovarioles separated ovarioles from cellular sheath labium terminal egg

aperture frontal view spiracle operculum } anal frontal view of entire head, cercus O insect pin external features of entire head stained and cleared to tracheae placed through tracheal supply around stomach showing position show underlying spiracle opening into of mouthparts mouthparts connecting trachea

DISSECTIONDISSECTION OFOF COCKROACHCOCKROACH -- MOUTHPARTSMOUTHPARTS DISSECTION OF COCKROACH - ALIMENTARY SYSTEM

clypeus mandibles (6) (5) labrum (1) labium (4) oesophagus

crop

maxilla (3)

enteric caeca labium testis gizzard (4) hypopharynx (2) stomach

maxilla (3) mandibles (5) ileum Malpighian vas tubules hypopharynx deferens (2) colon labrum (1) rectum (1) - (6) order of removal from head