1. Insect Biochemistry - Pheromones
Kuang-Hui Lu
Department of Entomology
National Chung Hsing University

2. CONTENTS Introduction Classes of semiochemicals
Importance of the olfactory sense in insects
The active space concepts
Pheromones classified according to behavior elicited
Pheromone parsimony
Chemical characteristics of pheromones
Insect receptors and the detection process
Information coding and processing
Geographic and population differences and evolution of pheromone blends
Hormonal control of pheromone synthesis and release
Biosynthesis of pheromones
Practical applications of pheromones

3. Types of Communication

4. Introduction
Communication through exchange chemical signals is undoubtedly the oldest language known.
Semiochemical (Greek: semeon, a signal) are signaling chemicals produced by an organism to send a message.
Semiochemicals elicit changes in the behavior or physiology of the receiving organism.

5. 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; influence the physiology or behavior of members of the same species
Allelochemicals: mediate interspecific interaction; influence a different species

6. 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.

7. 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. (
Parapheromones: analogs and mimics of the natural pheromones.

8. 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.

9. 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.

10. 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.

11. 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.

12. Allelochemicals
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)

13. Allomones
Allomones are chemical countermeasures that are used primarily for defense.
Oral and anal discharges
Toxic components in the hemolymph made available reflex bleeding
Glandular discharge
Bites and stings that are supplemented with poisons

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

15. The Production of Hot Benzoquinones by the Bombardier Beetle

16. Kairomones Kairomones benefit the receiver rather than the emitter.
Kairomones may be hormones, pheromones, or allomones 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.

17. Synomones
Synomones are chemicals that are adaptive to both the sender and the receiver.
Floral scents that attract pollinators.
e.g. hymenopterous parasites Trichogramma are attracted to tomato plants where they may find suitable hosts to parasitize.

18. Is It Good or Bad?
VS.

19. The Plumose Antenna of a Male Gypsy Moth

20. Hair Pencils of the Male Moth and Butterfly
Male Heliothis virescens.
Male giant danaine butterfly, Idea leuconoe.

21. 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.

22. 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

23. 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.

24. 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.

25. 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

26. 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.

27. 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

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

29. 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.

30. Chemical Characteristics of 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

31. Chemical Characteristics of 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

32. Insect Receoptors and the Detection 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.

33. The Process of Semiochemical Detection
Adsorption of an odor molecule by sensory hairs on the antenna
Penetration of the molecule through pores in the setal wall
Receptor binding of the molecule and transport to the sensory nerve endings
Membrane alteration, probably opening of sodium channels
Receptor potential generation, a graded potential, followed by spikes in the axon hillock region
Inactivation of the odor molecule and removal

34. Pheromone 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)

35. Signal Transduction and Receptor 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)

36. Signal Transduction and Receptor 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.

37. Pheromone Inactivation and Clearing of the Receptor
Pheromones are attacked and destroy by enzyme (e.g. esterase)

38. The Structure of Odor Plumes
Release of pheromone in females
Pulsed pheromone release (next slide)
Response in males to the pheromone
Detect
Process
Initiate flight commands – optomoter anemotaxis (upwind flight)
Clear the sensory receptors rapidly in order to respond effectively 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.

39. Pheromone Signal Processing
Receptor neurons in the sensilla
through second messenger system of G-protein to open 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) : axons from non-pheromone olfactory receptors
Macroglomerular complex (MGC): for axons from pheromone receptors

40. Geographic and Population Differences and 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

41. Hormonal Control of Pheromone 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)

42. Mode 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)

43. Pheromone 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.

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

45. Sex 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.

46. Practical Applications of Pheromones
Monitoring insect emergence and population build-up.
Direct control with pheromones
Mass trapping
Lure and kill
Mating disruption
Sensory fatigue
False trail-following
Camouflage of natural pheromone plume
Pheromone antagonists and imbalanced blends

48. Chemical Communication

49. The Releaser and Primer Effects of Pheromones

50. Allelochemicals

51. Basic Structure of an Olfactory Receptor

52. A Typical Series of Electroantennogram (EAG)

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

54. 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.

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

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

57. Structures of PBAN
The PBAN belong to a class of peptides called pyrokinins
PBANs of those isolated thus far have 33 or 34 amino acid residues
Bombyx mori
Leu-Ser-Glu-Asp-Met-Pro-Ala-Thr-Pro-Ala-Asp-Gln-Glu-Met-Tyr-Gln-Pro-Asp-Pro-Glu-Glu-Met-Glu-Ser-Arg-Thr-Arg-Tyr-Phe-Ser-Pro-Arg-Leu-NH2
Heliothis zea
Leu-Ser-Asp-Asp-Met-Pro-Ala-Thr-Pro-Ala-Asp-Gln-Glu-Met-Tyr-Arg-Gln-Asp-Pro-Glu-Gln-Ile-Asp-Asp-Ser-Arg-Thr-Lys-Tyr-Phe-Ser-Pro-Arg-Leu-NH2
All PBANs share a common C-terminal sequence of 5 amino acids
Phe-X-Pro-Arg-Leu-NH2

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

59. The Role of PBAN on Sex Pheromone Synthesis