Insect BiochemistryInsect Biochemistry- - PheromonesPheromones

Kuang-Hui LuKuang-Hui Lu

Department of EntomologyDepartment of EntomologyNational Chung Hsing UniversityNational Chung Hsing University

CONTENTSCONTENTSIntroductionClasses of semiochemicalsImportance of the olfactory sense in insectsThe active space conceptsPheromones classified according to behavior elicitedPheromone parsimonyChemical characteristics of pheromonesInsect receptors and the detection processInformation coding and processingGeographic and population differences and evolution of pheromone blendsHormonal control of pheromone synthesis and releaseBiosynthesis of pheromonesPractical applications of pheromones

Types of Communication Types of Communication

Introduction Introduction

Communication through exchange chemical signals is undoubtedly the oldest language known.– Semiochemical (Greek: semeon, a signal) are s

ignaling chemicals produced by an organism to send a message.

– Semiochemicals elicit changes in the behavior or physiology of the receiving organism.

Classes of Semiochemicals Classes of Semiochemicals

Semiochemicals are divided into two categories based on whether the use of the chemical is between members of the same or different species. (next slide)– Pheromones: mediate intraspecific interaction; i

nfluence the physiology or behavior of members of the same species

– Allelochemicals: mediate interspecific interaction; influence a different species

Pheromones Pheromones

Pheromones: Greek words, pherein, meaning to carry, and hormon, meaning to excite, by Karlson and Luscher (1959)

Pheromones are chemicals produced from exocrine glands, which are modified epidermal cells, and are secreted to the outside by one animal and have a specific effect on another individual of the same species.

Pheromones Pheromones

Pheromones were first called ectohormones because they were secreted by glands and had the physiological effects of a hormone.

Pheromones have been identified from more than 1600 species of insects in 90+ families from 9 order. (http://www.nysaes.cornell.edu/pheronet)

Parapheromones: analogs and mimics of the natural pheromones.

Pheromones Pheromones

Pheromones are typically active in extremely small concentrations, and usually as a mixture of compounds in a species-specific pheromone blend.

The individual components in the blends are often common to several species, with the precise proportions of the individual components conferring the species specificity.

It is not uncommon for geographic variants of a species to produce significantly different proportions of the pheromone components.

Pheromones Pheromones

Pheromones can be broadly subdivided according to their mode of influence. (next slide)– Releaser pheromone: stimulate an

immediate and reversible behavioral response that is mediated by the nervous system soon after the reversible perceives it.

– Primer pheromone: mediate a fundamental physiological change in the receiver that reprograms it for altered response, acting directly on the nervous system or some other physiological system.

Primer Pheromones Primer Pheromones

Primer pheromones alter the physiology of the receiver so that it displays a modified response pattern to future stimuli.

Primer pheromones are most often used by social insects for the regulation of colony activities.

In honeybee, the queen produces a multi-component pheromone from her mandibular glands to inhibit the ovarian development of workers and maintains them as nonreproductives.– The major compound of the queen mandibular

pheromone, 9-oxo-2-decenoic acid, acts on the endocrine system of workers to suppress their synthesis JH.

Primer Pheromones Primer Pheromones

– By regulating the levels of JH in workers, the queen mandibular pheromone also affects the ontogeny of worker polyethisms that affects the rate at which workers change their behavior as they age from inside activities of brood rearing to outside activities of foraging.

Low levels of JH maintain the workers in the nest.

Higher levels of JH trigger the onset of foraging behavior.

– If the queen is removed, levels of the queen mandibular pheromone decline within the colony and the worker soon became agitated and begin preparations for rearing a replacement queen.

AllelochemicalsAllelochemicals

Allelochemicals influence the behavior or physiology of members of a different species than that of the producer. (next slide)– Allomone: if the signal is adaptively favorable to the

emitter (producer) but not to the receiver. (defensive secretion) (next slide)

– Kairomone: if the signal is adaptively favorable to the receiver but not to the emitter. (next slide)

– Synomone: if both receiver and emitter benefit. (next slide)

AllomonesAllomones

AllomonesAllomones are chemical are chemical countermeasures that are used countermeasures that are used primarily for defense.primarily for defense.– Oral and anal dischargesOral and anal discharges– Toxic components in the hemolymph Toxic components in the hemolymph

made available reflex bleedingmade available reflex bleeding– Glandular dischargeGlandular discharge– Bites and stings that are supplemented Bites and stings that are supplemented

with poisonswith poisons

Fig. (A) A typical member of the termite soldier caste of coptotermes. (B) A specialized nasute of Nasutitermes.

The Production of Hot Benzoquinones by The Production of Hot Benzoquinones by the Bombardier Beetlethe Bombardier Beetle

KairomonesKairomones

Kairomones benefit the receiver rather than the emitter.– Kairomones may be hormones, pheromones, or a

llomones that are normally used by one organism but exploited by an illegitimate receiver.

– They may be normal products of metabolism of one species that another now uses to locate its host.

– e.g. the order of a prey vs. predators or parasites.

the order of a plant vs. phytophagous insects.

SynomonesSynomones

SynomonesSynomones are chemicals that are a are chemicals that are adaptive to both the sender and the redaptive to both the sender and the receiver.ceiver.– Floral scents that attract pollinators.Floral scents that attract pollinators.– e.g. hymenopterous parasites e.g. hymenopterous parasites TrichograTrichogra

mmamma are attracted to tomato plants whe are attracted to tomato plants where they may find suitable hosts to parasire they may find suitable hosts to parasitize.tize.

Is It Good or Bad?Is It Good or Bad?

VS.

The Plumose Antenna of The Plumose Antenna of a Male Gypsy Motha Male Gypsy Moth

Hair PencilsHair Pencils of of the Male Moth and Butterflythe Male Moth and Butterfly

Male Heliothis virescens.

Male giant danaine butterfly, Idea leuconoe.

The Active Space Concept The Active Space Concept

Active space – the physical space in which the concentration of a pheromone is sufficiently high to cause a behavioral effect in the receiving individual.

The active space influenced by – the sensitivity of the receiver,– the quantity of chemical produced and

released by the sender per unit time,– the volatility of the chemicals involved,– environmental factors such as wind velocity

and temperature.

Releaser Pheromones Releaser Pheromones

Pheromones are often described classified by the behavior elicited from the receiver, including– Sex pheromones– Aggregation pheromones– Alarm pheromones– Egg-laying pheromones– Brood-tending pheromones– Recruitment pheromones– Trail-following pheromones– Territory-marking pheromones– Many others

Sex Pheromones Sex Pheromones

Sex pheromones are chemicals produced by insects of one sex (either males or females) that elicit a behavioral response in members of the opposite sex.– Sex attractant: the perception of the pheromone

releases a long-range searching behavior.– Aphrodisiac: the pheromone release facilitates

closer-range courtship behavior or copulation.

Calling behavior: consists of a particular posture and the eversion of pheromone glands to allow the pheromone to evaporate.

Aggregation Pheromones Aggregation Pheromones

Aggregation pheromones bring many individuals of both sexes together.

They are produced mainly by coleopterans as a defense against predators and to overwhelm the resistance the resistance of a host tree.

The honeybee queen produces an aggregation pheromone from her mandibular glands that is responsible for the retinue of workers that attend to her, and also stabilizes the colony around the queen it swarms.

Alarm Pheromones Alarm Pheromones

Alarm pheromones are produced mostly by social insects to warn other colony members of danger and to recruit for colony defense.– Honeybee– Ants– Aphids and treehoppers

Trail Pheromones Trail Pheromones

Trail pheromones are found mostly in social insects, including the ants, termites, bees, and wasps.

When a workers locates a resource, she lays down a trail when returning to the colony that other workers can use to find the resource.

Epideictic Pheromones Epideictic Pheromones

Epideictic pheromones (spacing pheromones) maintain the densities of individuals attempting to exploit an exhaustible resource to numbers that are below its carrying capacity.– Female tephritid fruit flies– Female bark beetles

Funeral Pheromones Funeral Pheromones

Funeral pheromones are produced in dead ants that stimulate other live colony members to remove them to a pile outside the nest.

Pheromone Parsimony Pheromone Parsimony

Pheromone parsimony: the same pheromonal compound, sometimes synergized by additional compounds, can serve multiple functions, depending on ecological and behavior.The phenomenon is prevalent in social insects.For example the alarm pheromones that often serve, in proper context, as– Defensive allomones– Attractants– Trail pheromones– Antimicrobial agents– As releasers of several additional behavioral actions.

Chemical Characteristics of Chemical Characteristics of Pheromones Pheromones

Airborne pheromones– Low molecular weight, less than 200

e.g. acids, esters, alcohols, aldehydes, ketones, epoxides, lactones, hydrocarbons, terpenes, and sesquiterpenes, etc.

– High volatility

Contact pheromones– High molecular weight,

e.g. housefly sex pheromone - (Z)-9-tricosene (a hydrocarbon composed of 23 carbons)

Waterborne pheromones– e.g. in some crustaceans

Chemical Characteristics of Chemical Characteristics of Pheromones Pheromones

Pheromones often serve as species isolating mechanisms– Pheromone receptors on the opposite sex– Coding in pheromones

the ratio of each components

chirality in molecule - enantiomers

Insect Receoptors and the DetectInsect Receoptors and the Detection Process ion Process

Pheromones are generally detected by olfactory receptors located primarily on the antenna.

A sex pheromone receptor on the antenna typically consists of one or two nerve cells housed within a seta or fine “hair” on the antenna.

The Process of The Process of Semiochemical DetectionSemiochemical Detection

Adsorption of an odor molecule by sensory hairs on the antennaPenetration of the molecule through pores in the setal wallReceptor binding of the molecule and transport to the sensory nerve endingsMembrane alteration, probably opening of sodium channelsReceptor potential generation, a graded potential, followed by spikes in the axon hillock regionInactivation of the odor molecule and removal

Pheromone Binding ProteinsPheromone Binding Proteins

Sensillum liquor: lymph, extracellular fluid in sensory hairs (or setae) (next slide)

Pheromone binding proteins (PBPs)– the proteins that aid in transport of pheromone

through the sensillum liquor to contact with specific receptor proteins in the dendritic nerve endings

– a subset of a larger group of odorant binding proteins (OBPs)

Signal Transduction and Signal Transduction and Receptor ResponseReceptor Response

At the dendritic ending, the pheromone probably combines with a receptor protein in the dendritic membrane.

Some evidence suggests that IP3 might be a participant in pheromone response.

The electroantennogram (EAG) can be used effectively in pheromone identification. (next slide)

Signal Transduction and Signal Transduction and Receptor ResponseReceptor Response

Axons from sex pheromone receptor neurons located peripherally project into the antennal lobe of the deutocerebrum as labeled line (pheromone-specific neurons).

Most insects with pheromone receptors appear to have more than one type of receptor, each being sensitive to one or more of the blend components of the pheromone.

Pheromone Inactivation and Pheromone Inactivation and Clearing of the ReceptorClearing of the Receptor

Pheromones are attacked and destroy by enzyme (e.g. esterase)

The Structure of Odor PlumesThe Structure of Odor PlumesRelease of pheromone in females– Pulsed pheromone release (next slide)

Response in males to the pheromone– Detect– Process– Initiate flight commands – optomoter anemotaxis (upwind fli

ght) – Clear the sensory receptors rapidly in order to respond effe

ctively to the rapid changes that occur in a pheromone plume

Discontinuous pulsing of the pheromone in the plume is much more important to upwind flight than the concentration of pheromone in the plume.

Pheromone Signal ProcessingPheromone Signal Processing

Receptor neurons in the sensilla– through second messenger system of G-protein to op

en Na+, K+, and Ca2+ channels

Axons from olfactory receptors on the antennae pass through the antennal nerve and enter the large antennal lobe (AL) of the deutocerebrum.

Antennal lobe– Glomeruli (mechano- and taste-sensitive regions) : ax

ons from non-pheromone olfactory receptors– Macroglomerular complex (MGC): for axons from phe

romone receptors

Geographic and Population Differences Geographic and Population Differences and Evolution of Pheromone Blendsand Evolution of Pheromone Blends

Regional differences in response to a minor pheromonal component(s)– e.g. pine engraver, Ips pini

If sex pheromone blends evolve, then there must be concomitant evolution in both sexes.– the gland of producer– the receptors of the receiver

Hormonal Control of Hormonal Control of Pheromone ProductionPheromone Production

Pheromone synthesis is regulated hormonally by a neuropeptide from the subesophageal ganglion, the pheromone biosynthesis activating neuropeptide (PBAN) (next slide)

PBAN is produced in the subesophageal ganglion (SEG).

Juvenile hormone has been implicated in the controlled of pheromone biosynthesis in coleopterans. (next slide)

Mode of Action of PBANMode of Action of PBAN

In the redbanded leafroller, Argyrotaenia velutinana, PBAN regulates pheromone biosynthesis by increasing the supply of octadecanoyl and hexadecanoyl fatty acids needed for pheromone biosynthesis

PBAN regulates the Δ11 desaturase, which introduces a double bond into the pheromone precursor in some lepidopterans.

PBAN regulates enzyme activity for pheromone synthesis (next slide)

Pheromone SynthesisPheromone Synthesis

The synthesis of pheromones may occur throughout the adult insect’s life, but release of the synthesized pheromones generally occurs only during certain environmental and physiological circumstances.

Pheromones are generally produced by exocrine glands (modified epidermal cells).– Type I glands: formed by a simple epithelial layer or

lining an internal reservoir that temporarily stores the secretions.

– Type II glands: consist of both secretory and duct cells.

Fig. Sex pheromone synthesis from fatty acids in the cabbage looper, Trichoplusia ni.

Sex Pheromone ReleaseSex Pheromone Release

The release of sex pheromones by most moths occurs during the evening hours and is controlled both by an endogenous circadian rhythmicity and physiological factor such as mating status.

Practical Applications of Practical Applications of PheromonesPheromones

Monitoring insect emergence and population build-up.Direct control with pheromones– Mass trapping– Lure and kill– Mating disruption

Sensory fatigueFalse trail-followingCamouflage of natural pheromone plumePheromone antagonists and imbalanced blends

Chemical CommunicationChemical Communication

The Releaser and Primer Effects The Releaser and Primer Effects of Pheromonesof Pheromones

AllelochemicalsAllelochemicals

Basic Structure of Basic Structure of an Olfactory Receptoran Olfactory Receptor

A Typical Series of A Typical Series of Electroantennogram (EAG)Electroantennogram (EAG)

Fig. The EAD responses were made by the antenna of a male Idea aversata geometrid moth to the effluent from a gas chromatograph (GC).

Fig. The lower trace shows EAG (or EAD) responses by female antennal receptors to some of the volatiles released by “calling” Mediterranean fruit fly males.

A Circuit Diagram for Constructing a A Circuit Diagram for Constructing a Portable or Field EAG Measuring UnitPortable or Field EAG Measuring Unit

Fig. A schematic diagram to illustrate the structure of a pheromone plume in the air.

Structures of PBANStructures of PBAN

The PBAN belong to a class of peptides called pyrokinin

s

PBANs of those isolated thus far have 33 or 34 amino a

cid residues– Bombyx mori

Leu-Ser-Glu-Asp-Met-Pro-Ala-Thr-Pro-Ala-Asp-Gln-Glu-Met-Tyr-Gln-Pro-Asp-Pro-Glu-Gl

u-Met-Glu-Ser-Arg-Thr-Arg-Tyr-Phe-Ser-Pro-Arg-Leu-NH2

–Heliothis zeaLeu-Ser-Asp-Asp-Met-Pro-Ala-Thr-Pro-Ala-Asp-Gln-Glu-Met-Tyr-Arg-Gln-Asp-Pro-Glu-Gl

n-Ile-Asp-Asp-Ser-Arg-Thr-Lys-Tyr-Phe-Ser-Pro-Arg-Leu-NH2

All PBANs share a common C-terminal sequence of 5 a

mino acids

–Phe-X-Pro-Arg-Leu-NH2

Fig. Pheromone biosynthesis in bark beetles and its control by JH.

The Role of PBAN on The Role of PBAN on Sex Pheromone SynthesisSex Pheromone Synthesis