WEEK 3: SENSORY SYSTEMS AND BEHAVIOR

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WEEK 3: SENSORY SYSTEMS AND BEHAVIOR INSECTS DETECT THE OUTSIDE WORLD VIA SENSILLA Sensilla receive some form of stimulus from the environment and translate it into a nerve impulse, called

1 WEEK 3: SENSORY SYSTEMS AND BEHAVIOR INSECTS DETECT THE OUTSIDE WORLD VIA SENSILLA Sensilla receive some form of stimulus from the environment and translate it into a nerve impulse, called transduction. The energy can be detected in many forms. MECHANORECEPTION sense mechanical changes like the bending of a hair, or stretching of part of the body, and even molecular movements associated with the propagation of a sound wave. CHEMORECEPTION sense energy released by the chemical reaction of a target molecule binding to a specific receptor. PHOTORECEPTION detecting energy from electromagnetic waves photons. THERMORECEPTION - detecting kinetic energy/heat. Most insect receptors are made up of 2 cell types 1) Receptor cells: bipolar neurons which actually detect the stimulus and send the signal, and 2) Accessory cells: surround the receptor cells and determine the property of the receptor via the structures they secrete (e.g. setae). The major receptor types are 1) Trichoid sensillum. This is a hair sensilla, or setae. 2) Coeloconic pits and ampullaceous pits. These are sunken pits in the cuticle without hairs. 3) Campaniform sensilla or placoid sensilla are pits covered over with a cuticular dome. 4) Chordotonal organs are stretch receptors. They detect movements of the animal and growth in size. *Key point: these are the major types of receptors (not counting photoreceptors) described based on their structure (e.g. hair, dome, pit), not on their function. Some sensillum can have lots of types of receptors. For example a trichoid sensillum can have a mechanoreceptor and chemoreceptors. Stretch receptors at the base of antennae (between 2 nd and 3 rd segments) are called JOHNSTON S ORGAN. They tell the insect about movements of the antennae in honeybees these tell the bee about the strength and direction of the air stream flowing over the insect. The bees can use this information to control how fast they are flying. Diving beetles trap an air bubble against their body and antennae. As the beetle twists and rotates under water, the bubble slides around (always going up). The Johnston s organ detects the movement of the air bubble, and beetles use this information to control posture during dives. Image on the left: (Dipera: Culicidae), p=pedicel, containing Johnston s organ, and s=scape. Sound perception occurs using mechanoreceptors that detect vibrations from the air or substrate. e.g. Male mosquitoes have modified antennae with flagellum hairs which are tuned (via length) to pick up vibrations emitted by wing beats of females.

Subgenal organs are stretch receptors located in the end of tibiae (legs).

Tympanal organs detect air-borne vibrations (what we think of as sound).

air space. It is wired too stretch receptors.

detected. Note: Insects cannot perceive a range of frequencies i.e. they are tone deaf!

So, unlike birds, insects are much closer to using a sort of Morse code.

To the left, some insectss have their tympanal organs on their legs, such as

Chemoreception The detection of chemicals plays a huge role in insects smell

Chemoreceptors are modifiedd hair sensilla with nerve dendrites in the center

These pores trap molecules, which bind to receptors on dendrites and initiate

Chemoreceptors are usually concentrated on mouthparts (to taset food), on

feed (taste suitability of foodd plants, oviposition sites, etc.).

and locate females. Antennae can have awesome surface areas and tons of pores.

hairs, and each hair has ~3,000 pores, resulting in over 45 million pores per

2 Subgenal organs are stretch receptors located in the end of tibiae (legs). They are sensitive to vibrations underfoot. Tympanal organs detect air-borne vibrations (what we think of as sound). They involve a thin, tight cuticle, the Tympanum, stretched over an internal air space. It is wired too stretch receptors. The size and shape of the air space affect which frequencies of sound are detected. Note: Insects cannot perceive a range of frequencies i.e. they are tone deaf! The Tympanum either vibratess or not. So, unlike birds, insects are much closer to using a sort of Morse code. Information is coded in the temporal pattern of bursts. To the left, some insectss have their tympanal organs on their legs, such as this Orthopteran. Chemoreception The detection of chemicals plays a huge role in insects smell is everything! Chemoreceptors are modifiedd hair sensilla with nerve dendrites in the center and lotss of pores to the outside. These pores trap molecules, which bind to receptors on dendrites and initiate nerve impulses. Chemoreceptors are usually concentrated on mouthparts (to taset food), on antennae (these are the true smelling organss of insects), and on the pads of feed (taste suitability of foodd plants, oviposition sites, etc.). Some antennae are extremely sensitive with huge, filamentous branches covered with hairs. They are often most developed in male insects that use pheromones to detect and locate females. Antennae can have awesome surface areas and tons of pores. E.g. male silk worm moths, each plumose antenna has up to 17,000 chemosensory hairs, and each hair has ~3,000 pores, resulting in over 45 million pores per male moth! Some antennae can detect and respond (with an action potential) to single molecules. On the right, Trictena atripalpis (Lepidoptera: Helialidae), showing chemosensory hairs on antennae. Antennae are used to find mates, to find food, and to find places to lay eggs. Many parasitoids use volatiles emitted by chewed plant tissues or by frass to findd hosts in which they lay eggs. Aquatic locomotion Includes material from the intro. entomology course taughtt by Dr. Douglas Emlen and from Thee Insects, Authors: Gullan & Cranston.

Many insects rely on the surface tension of water molecules

They use pads of hydrophobic hairs as floats.

(e.g. whirligig beetles), 2) use undulations of body (e.g.

dragonfly nymphs), 4) Sink and actually walk along the river

Insect Flight The capacity for flight is perhaps the single

Insects were the first flying organisms thus, flight was a

It is not clear from the fossil record how, exactly, wings

Insect wings are not segmented appendages like legs (or like

Paranotal flap hypothesis : Wings arose from flap-like

The idea is that even small flaps (i.e. intermediate stages) would have been beneficial.

The muscles are already there: flapping pulls water across

can be aphrodisiac chemicals, as seen in the queen butterfly

The males have brushes coming off of their abdomen, and they

3 Many insects rely on the surface tension of water molecules tiny, lightweight insects literally walk onn water (e.g.water striders). They use pads of hydrophobic hairs as floats. They generally use the outside four legs for support and middle two legs like paddles. To swim below the surface they 1) use appendages like oars (e.g. whirligig beetles), 2) use undulations of body (e.g. legless aquatic larvae), 3) Use jet-propulsion of water through the anus (e.g. dragonfly nymphs), 4) Sink and actually walk along the river bottom (e.g. caddisfly larvae). Insect Flight The capacity for flight is perhaps the single largest contributor to the evolutionary success of insects. Insects were the first flying organisms thus, flight was a great way to escape from predators! It is not clear from the fossil record how, exactly, wings arose. Insect wings are not segmented appendages like legs (or like the wings of birds) ). Paranotal flap hypothesis : Wings arose from flap-like extensions of the thoracic nota. The idea is that even small flaps (i.e. intermediate stages) would have been beneficial. Insects using flaps to glide could jump from trees and glide, land right-side up and running. Gill hypothesis: Wings evolved from expanded and modified gills. Many aquatic nymphs have flattened lobes on their thoracic and abdominal segments. They already have very thin cuticle and are infused with trachea (they are gills, after all). The tracheal branches in the gills look a lot like wing vein patterns. AND these gills can be flapped (think mayfly larva). The muscles are already there: flapping pulls water across body and facilitates gas exchange over gills. COURTSHIP PHEROMONES can be aphrodisiac chemicals, as seen in the queen butterfly (Nymphalidae: Danaus gilippus). The males have brushes coming off of their abdomen, and they dust a pheromone directly onto the antennae of the female, whilst both are in flight. Females can evaluate males based on the pheromone quality. An interested female alights, folds her wings, and allows copulation. Males need this alkaloid pheromonee for successful courtship. But, to get this alkaloid, must acquire the chemical precursor by feeding on special plantss as an adult. Semiochemicals chemical odors are important in both interspecific and intraspecific communication Pheromones a chemical used in communication between individuals of the same species. The presence of a specific Includes material from the intro. entomology course taughtt by Dr. Douglas Emlen and from Thee Insects, Authors: Gullan & Cranston.

pheromone results in a specific behavior or developmental change in the receiver.

They are synthesized in laboratories, usually to mimic sex pheromones, and commonly used as a pest-management technique.

pests. Methyl eugenol is a parapheromone that has been synthesized to attract male tephritid fruit flies.

These traps are used primarily to monitor pest populations, though in some organic agricultural operations enough of these traps may be placed

capitata, originated in sub-saharan Africa and is not knownn to be established in the United States.

and detection procedures so that the pest did not become established. It can feed on a lot of different fruits and vegetables.

As early as 1929, the Mediterranean fruit fly--ceratitis capitata--had made its mark in fruit orchards in Florida.

Since then, periodic infestations have occurred in Florida, California and Texas.

5 billion a year if it were to become established in the continental United States.

Because of its wide distribution over the world, its ability too tolerate cooler climates better than most other species of tropical fruit

4 pheromone results in a specific behavior or developmental change in the receiver. Allelochemicals acrosss species semiochemicals PARApheromones a synthetic chemical thatt mimics a pheromonee and can function as a male lure. They are synthesized in laboratories, usually to mimic sex pheromones, and commonly used as a pest-management technique. For example: A member of the Tephritidae family, the Mediterranean fruit fly, Ceratitis capitata, is one of the world's most destructive fruit pests. Methyl eugenol is a parapheromone that has been synthesized to attract male tephritid fruit flies. It smells like a sex pheromone produced by females. Males enter the trap and are killed with an insecticide. These traps are used primarily to monitor pest populations, though in some organic agricultural operations enough of these traps may be placed out to reduce the number of pests in a field. The Mediterranean fruit fly, C. capitata, originated in sub-saharan Africa and is not knownn to be established in the United States. When it has been detected in Florida and California, especially in recent years, each infestation necessitated intensive and massive eradication and detection procedures so that the pest did not become established. It can feed on a lot of different fruits and vegetables. In some areas of the world, all apples and pears have them. As early as 1929, the Mediterranean fruit fly--ceratitis capitata--had made its mark in fruit orchards in Florida. After apparently being eradicated, it was spotted again in Since then, periodic infestations have occurred in Florida, California and Texas. The medfly alone could generate agricultural losses of about $1.5 billion a year if it were to become established in the continental United States. Those losses would be the result of export sanctions, lost markets, treatment costs, reduced crop yields, deformities and prematuree fruit drop. Because of its wide distribution over the world, its ability too tolerate cooler climates better than most other species of tropical fruit flies, and its wide range of hosts, it is ranked first among economically important fruit fly species. Its larvae feed and develop on many deciduous, subtropical, and tropical fruits and some vegetables. Although it may be a major pest of citrus, often it is a moree serious pest of some deciduous fruits, such as peach, pear, and apple. The larvae feed upon the pulp of host fruits, sometimes tunneling throughh it and eventually reducing the whole to a juicy, inedible mass. In some of the Mediterranean countries, only the earlier varieties of citrus are grown, because the flies develop so rapidly that late season fruits are too heavily infested to be marketable. Some areas have had almost 100% Includes material from the intro. entomology course taughtt by Dr. Douglas Emlen and from Thee Insects, Authors: Gullan & Cranston.

5 infestation in stone fruits. Harvesting before complete maturity also is practiced in Mediterranean areas generally infested with this fruit fly. In this age of jet transportation, the "medfly" can be transported from one part of the world to some distant place in a matter of hours, which greatly complicates efforts to contain it within its present distribution. Once it is established, eradication efforts may be extremely difficult and expensive. In addition to reduction of crop yield, infested areas have the additional expense of control measures and costly sorting processes for both fresh and processed fruit and vegetables. Some countries maintain quarantines against the medfly, which could jeopardize some fresh fruit markets if it should become established in Florida. TYPES/USES OF PHEROMONES 1) Sex Pheromones come in two forms, a) Long-distance attraction pheromones. In most insect species females release long distance pheromones, and males use these pheromones to find females. b) Courtship pheromones. Once insects are in close range, males often release courtship pheromones in attempts to show off their quality and to persuade females to mate. 2) Aggregation Pheromones are used by insects to form aggregations. A pheromone is described as an aggregation pheromone if it causes conspecific insects of both sexes to crowd around the source of a pheromone. In social and sub social insects, this is often how insects find each other and stick together (though they may also use vision and/or vibrations). Bed bugs use aggregation pheromones to find each other and group together after feeding. 3) Spacing Pheromones. It is not always beneficial for insects to be around each other. For instance, a female insect who oviposits in a fruit may also lay down a spacing pheromone on the skin of the fruit. This spacing pheromone informs other females that the fruit has already been taken. 4) Train-marking Pheromones are commonly used by ants to provide a chemical trail for their kin to follow. Trail-marking pheromones are volatile and short-lived chemicals that evaporate within days unless reinforced. These pheromones are often needed in great quantity, so waste products are often used (abundant & cheap!). 5) Alarm Pheromones are chemicals released when a dangerous situation arises (often as defensive substances they may smell or taste bad to scare away a predator). They are volatile, non-persistent compounds that are readily dispersed throughout the aggregation. Other insects nearby may flee or attack an intruder when these pheromones are detected. The dual-use of these chemicals is a common example of semiochemical parsimony, because the same compound has multiple functions. Here, alarm pheromones can also be allelochemicals that drive away potential predators (often, allomones, see below). The California western pine beetle, Dendroctonus brevicomis (Coleoptera: Scolytinae), feeds upon ponderosa pine. Males and females release different chemicals (females exo-brevicomin; males frontalin), which serve as aggregation pheromones. The mixture of chemicals from males and females is a potent blend, really attracting other beetles. Aggregations are beneficial for the beetles, allowing them to work together to beat the defenses of the

overrun with beetles and dying, while others around them are fine Aggregating is useful for the

At a certain point, the density of the beetles can become too much, leading to severe competition.

more beetles from coming. The chemicals verbenone and ipsdienol deter further beetles.

pest control After oviposition, females of the Mediterranean fruit fly, Ceratitis capitata (Diptera:

Laboratory bioassays revealed a significant positive relationship between concentration of faeces and

Treatment of halves of coffee bushes with methanolic extracts containing 0.1, 1.

plots, probably due to the deterrent effect of host-marking pheromone on fly oviposition.

6 trees. Trees secrete resins (sticky sap with nasty chemicals such as terpenes and alcohols), but pine beetles can overwhelm them when in groups. Resin is known to be important in dissuading some insects, but this species of beetle has evolved a way to work together to beat the defenses. Because of the aggregation behavior of California western pine beetles, some trees in a field will be overrun with beetles and dying, while others around them are fine Aggregating is useful for the beetles, but only within limits. At a certain point, the density of the beetles can become too much, leading to severe competition. So, once the aggregation is at a sufficient level, these beetles use spacing pheromones to dissuade more beetles from coming. The chemicals verbenone and ipsdienol deter further beetles. Image to the right, only some trees are targeted by the beetles and die (red ones in the picture), while others nearby are fine. Other Examples of Spacing Pheromone Use: Because med flies use spacer pheromones they might be used in pest control After oviposition, females of the Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae), deposit a spacing pheromone on the fruit surface that deters oviposition by conspecifics. Laboratory bioassays revealed a significant positive relationship between concentration of faeces and the inhibition of oviposition responses by C. capitata. Treatment of halves of coffee bushes with methanolic extracts containing 0.1, 1.0 and 10mg faeces ml(-1) resulted in a significant reduction of infestation only at the highest concentrationn (P = 0.03) ). Treatment of blocks of coffee bushes with an extract of 10mg faeces ml(-1) resulted in an 84% reduction in infestation by C. capitata in sprayed plants and a 56% reduction in adjacent untreated coffee bushes surrounding treated plots, probably due to the deterrent effect of host-marking pheromone on fly oviposition. Faeces contain oviposition deterrent substances that effectively reduce fruit infestations by C. capitata, suggesting a clear potential for the use of this infochemical in integrated management programes targeted at this pest. Citation: Arredondoo 2006 African weaver ants Spacer pheromones of colony-specific odors may be usedd to ensure an even dispersal of colonies of conspecifics, as inn African weaver ants, Oecophylla longinoda (Hymenoptera: Formicidae). This is a highly aggressive species, and without this spacing pheromone, there would commonly be full-scale attacks against other colonies. Holldobler & Wilson (1977)) Includes material from the intro. entomology course taughtt by Dr. Douglas Emlen and from Thee Insects, Authors: Gullan & Cranston.

7 explained, we obtained evidence that workers of this exceptionally aggressive species use pheromones to advertise territories and deter invasion by alien workers. Communication chemicals are all considered semiochemicals. Semiochemicals include both pheromones AND allelochemicals. Semiochemicals Pheromones Allelochemicals If chemicals function between individuals of a different species they are allelochemicals. Allelochemicals that benefit the receiver but are disadvantageous to the producer are Kairomones Allomones benefit the producer by modifying the behavior of the receiver, although having a neutral effect on the receiver. Synomones benefit both the producer and the receiver. Semiochemical parsimony -- Some chemicals might do more than one thing, depending upon context. They might act in intraspecific communication, and also be a kairomone and a synomone at another time or place. Back to the California Western Pine Beetles. Damaged Ponderosa pines produce terpenes when damaged by the pine beetles. This kairomone acts as a synergist with aggregation pheromones that act to lure more beetles. Basically, the plant is accidentally saying I m injured! And that mixed with the smell of aggregating beetles is almost a sure thing for other beetles this is the place to go! In close range, terpenes are used in defense, and they do work well against many pests. In many situations, it is advantageous for pines to produce terpenes. However, in the case of the pine beetles, they communicate injury and susceptibility. The defenses of a single tree are no match for hundreds of pine beetles. Allomones are often repellent chemicals produced by insects to ward off attacks. They benefit the producer by keeping it safe. The recipient is presumably only marginally negatively affected, because it just smells the nasty chemicals and then leaves. For many other herbivore pests, pine terpenes act as allomones.

Every fall I find lepidopteran larvae eating my citrus trees in my yard. When I approach them, they swing their heads around, trying to look big.

The beetle family Lycidae has many distasteful and warning-colored members (aposematism) including species of Metriorrhynchus that are protected by alkylpyrazine allomones (they smell bad).

It pays other beetles, and moths, and flies, and wasps to mimic these beetles, because it will afford them some protection.

8 Every fall I find lepidopteran larvae eating my citrus trees in my yard. When I approach them, they swing their heads around, trying to look big. When I grab one, it inflates red osmeterium on its head, and releases a nasty odor. It can be surprising and cause many predators to flee. The beetle family Lycidae has many distasteful and warning-colored members (aposematism) including species of Metriorrhynchus that are protected by alkylpyrazine allomones (they smell bad). They are so effective at deterring predators that, in Australia, there are mimics of these beetles. It pays other beetles, and moths, and flies, and wasps to mimic these beetles, because it will afford them some protection. Some beetle species are similarly distasteful, and others have the warning chemical but appear to lack the distastefulness. We ll talk more about mimicry later in the semester. Another use of allomones occurs in certain orchids. The flowers actually produce similar odors to female sex pheromone of the wasp or bee species that they need as a pollinator. The color and shape of the flower and this pheromone fool the male wasp or bee to attempt to copulate with the flower. The flowers get pollinated a clear benefit to the plant. The cost to the male insect is wasted time and energy. And, back to the pines again To review, a few beetles find a tree that they find suitable, maybe it s one that is already a little weak had a rough winter, or not enough precipitation. The beetles then start releasing pheromones (females exo-brevicomin; males frontalin). These pheromones, along with terpenes from the trees, attract more beetles. So, the chemicals released from the beetles act as aggregation pheromones. The terpenes produced from the tree act to lure in more beetles they smell it and realize that the tree is damaged. So, these terpenes are Kairomones they act to benefit the receiver, receivers that will damage the tree. However, these same terpenes produced by the tree lure something else in. Parasitoids detect these terpenes, too. And, to them, the tree is saying I m injured, I m attacked and these terpenes are often correlated with the presence of bark beetles. So, if a parasitoid follows the terpene scent, it will likely find a lot of prey. These parasitoids are pteromalid hymenopterans that parasitize bark beetles. So, terpenes are also synomones. So, one chemical produced by a tree acts as a kairomone and a synomone at the same time. And, meanwhile, the bark beetles are using aggregation and spacing pheromones. There is a lot of

chemical communication going on there! A hiker looking up at a damaged tree might have no idea how complex the chemical communication is just above her or his head.

List the four ways insects achieve movement in the water. Where is the native range for the Mediterranean fruit fly? List four of the fruits that females will lay their eggs within.

9 chemical communication going on there! A hiker looking up at a damaged tree might have no idea how complex the chemical communication is just above her or his head. WEEK 3: INTERNAL ANATOMY AND PHYSIOLOGY STUDY GUIDE, PART II. Study Questions and Objectives Briefly describe the two hypotheses for how insect flight evolved. List the four ways insects achieve movement in the water. Where is the native range for the Mediterranean fruit fly? List four of the fruits that females will lay their eggs within. How much money will be lost if the Mediterranean fruit fly becomes established here in the USA? How are paraphermone traps used to help prevent the establishment of these flies? Explain the chemical communication going on when a ponderosa pine is attacked by western pine beetles (Dendroctonus brevicomis, Scolytinae). In your explanation, address aggregation pheromones, spacing pheromones, kairomones, and synomones. Provide two examples of the use of spacing pheromones and provide the full scientific names of both species (order, family, genus, and species in the correct format). Study Terms (be able to compare and contrast these, and all, study terms) Mechanoreception, chemoreception, photoreception, thermoreception Sensillum, chordotonal organs, Johnston s organ Tympanum, tympanal organs Semiochemicals, allelochemicals, Kairomones, allomones, synomones, Semiochemical parsimony Pheromones, two types of sex pheromones Trail-marking pheromones, alarm pheromones, Parapheromones, aggregation pheromone

28 3 Insects Slide 1 of 44

28 3 Insects Slide 1 of 44 1 of 44 Class Insecta contains more species than any other group of animals. 2 of 44 What Is an Insect? What Is an Insect? Insects have a body divided into three parts head, thorax, and abdomen. Three