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Advances in the physiology of Insects

Light Production Mechanism Sound Production MechanismThermoregulation

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LIGHT PRODUCTION IN INSECTS

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Insect having Intrinsic luminescence

Lampyridae (fireflies) Elateridae (click beetles) Phengodidae (railroad worms)

Coleoptera

Anurida granaria

Collembola

Fulgora lanternaria

Homoptera Diptera

Platyuridae Bolitophilidae

Coleoptera

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The light-producing organs • Collembolan: Onychiurus emits a general glow from the whole body• Hemiptera: Fulgora the light organ is in the head. The light organs are

generally derived from the fat body• Diptera: In glow worm fly Arachnocampa they are formed from the

enlarged distal ends of the Malpighian tubules.• Coleoptera:In male Photuris there is a pair of light organs in the ventral

region of each of the sixth and seventh abdominal segments. In the female the organs are smaller and often only occur in one segment.

• The larvae have a pair of small light organs in segment eight, but these are lost at metamorphosis when the adult structures form.

• Phengodidae:Larvae and females of railroad worms have 11 pairs of dorso-lateral light organs on the thorax and abdomen and another on the head.

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Mechanism of light production Light is produced in organelles called peroxisomes,

noted as centers for enzymatic oxidation reactions. A two-stage reaction occurs within these

peroxisomes. First, adenylation of substrate luciferin (which is

dependent on the presence of magnesium-ATP) occurs under the catalytic action of luciferase.

The subsequent oxygenation of luciferyl adenylate by molecular oxygen results in the emission of light and the production of oxyluciferin.

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Color of light produced

• Coleoptera: In Photinus and Lampyris the light produced is yellow-green in color(520–650 nm).

• Phrixothrix larval and adult female, thorax and abdomen produce green to orange light (530–590 nm). That on the head produces red light(580 nm to over 700 nm)

• Diptera: Arachnocampa produces blue-green

• Hemiptera: Fulgora produces white light.

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Control of light production

• Dorsal Unpaired Median (DUM) release octopamine. • DUM cells present in the last two abdominal ganglia

respectively, which release octopamine. • The axons from these cells divide to send symmetrical

branches to the lanterns on each side.• In most adult fireflies the axons terminate on the

tracheal end cells, • In larvae, where there are no end cells, they innervate

the photocytes directly.

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Role of Oxygen• In adult Photuris, light production appears to be regulated by the

availability of oxygen. • As the DUM neurons terminate on the tracheal end cells.• Neural activity causes a change in these cells, facilitating the flow of

oxygen to the photocytes.• This implies that the oxygen supply to the photocytes is closely

regulated. • It is believed that hydrogen peroxide plays a role in this regulation.• The peroxisome oxidases use oxygen arriving at open mitochondria

to create hydrogen peroxide that builds up explosively due to the shutdown of the catalase.

• This completes the oxidation reaction and triggers the flash.

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Role of nitric oxide (NO)• The precise temporal control of firefly flashing is understood to be

regulated by nitric oxide (NO). • NO synthase is localized near synaptic terminals within the firefly lantern.• Measurements indicate that externally added NO stimulates

bioluminescence production while the addition of NO scavengers inhibits light production.

• Furthermore, NO is known to control respiration by photocyte mitochondria reversibly.

• The proposed mechanism comprises neural stimulation resulting in the transient release of NO that diffuses into the periphery of adjacent photocytes.

• This inhibits mitochondrial respiration and permits oxygen to diffuse into the photocyte, which holds the bioluminescence reactants.

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A firefly's photic organ is functional throughout pupation and glows when the pupa is disturbed. Credit: ARMIN MOCZEK AND MATTHEW STANSBURY

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SOUND PRODUCTION IN INSECTS

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Sound-producing mechanisms in insects

A most recognised classification compiling five categories of sound producing mechanisms is as follows:

1) Vibration and Tremulation2) Percussion3) Stridulation4) Click Mechanisms5) Air Expulsion

Ewing (1989)

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1. Vibration and Tremulation

Sound emissions which result from:Vibrations Most usually oscillations of the abdomen Either dorso-ventrally or laterally, and/or by the wings. Tremulation Sound production transmitted through the legs to the

substrate on which the insect is walking or standing.

(Claridge, 2005)

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Vibration and Tremulation

Representative Orders

Diptera NeuropteraHemipteraPlecopteraHeteroptera Trichoptera

Major function(s)Mate findingSpecies-specific

recognitionMating inducement (Neuroptera)

(Capinera, 2008)

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2. Percussion

Striking of one body part against another or striking of the substrate with the tip of the abdomen.

(Claridge, 2005)

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2. Percussion

Representative Orders

Blattodea Lepidoptera Coleoptera OrthopteraHemiptera PlecopteraHeteroptera PsocopteraHymenoptera TrichopteraIsoptera

Major function(s)Mate findingSpecies-specific

recognitionMating inducement

(Blattodea)Queen stimulation

(Hymenoptera)Colony alarm

(Hymenoptera, Isoptera)(Capinera, 2008)

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3. Stridulation

Sounds produced by frictional mechanisms, involving the movements of two specialized insect body parts against each other in a regular patterned manner.

(Claridge, 2005)

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3. Stridulation

Representative Orders Blattodea OrthopteraHemiptera Plecoptera Heteroptera

Major function(s)Mate findingMating inducement

(Blattodea)Species-specific

recognitionDefensive and territorial

behaviour

(Capinera, 2008)

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4. Click Mechanisms

Unusual exhalatory sounds, often expelled via the tracheal spiracles.

(Claridge, 2005)

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3. Stridulation

Representative Orders BlattodeaLepidoptera

Major function(s) Mate finding Defensive and territorial

behaviour

(Capinera, 2008)

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5. Air ExpulsionThese sounds rely on the deformation of a modified

area of cuticle, generally by contraction and relaxation of special musculature within the insect body.

This movement results in a succession of clicks which may be repeated quickly in distinctive patterns.

(Claridge, 2005)

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5. Air Expulsion

Representative Orders BlattodeaLepidoptera

Major function(s) Mate finding Defensive and territorial

behaviour

(Capinera, 2008)

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THERMOREGULATION

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ThermoregulationBody temperature is the result of a balance between rate heat gain and heat loss. So two ways to regulated an elevated body temperature. Regulation of heat gain Regulation of heat lossLevels at which heat gain and heat loss occur Physiological mechanism: Regulation of heat production and heat

transfer within the body Behavioral mechanism: regulation of heat exchange between the

body and the external environment.A survey on 40 species of Lepidoptera showed that the preferred temperature fur butterflies to fly is 30-40 C. the flight temperautere for butterflies is very similar to many other insects.

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Physiological Mechanism

Regulation of heat gain :One mean of heat gain for thermoregulation is by metabolic generation of heat which is mainly produced by thoracic flight muscles during flight and preflight warm up. During preflight warm-up antagonistic muscles are activated simultaneously. That

makes little wing movement but produces heat. This phenomenon is present in majority of insect taxa including Lepidoptera Coleoptera and Diptera etc.

During flight heat is produced by rapid contraction of flight muscles. Different insects can increase their body temperature during flight ranging from 3-20 C.

Abdominal temperature is regulated by circulation of hemolymph. Thoracic temperature is regulated more precisely as compared to abdominal

temperature. Hemolymph flow in the wing veins also effect the heat transfer between thorax and

wings and contribute thoracic heating.

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Regulation of heat loss: At high temperatures heart beat is high and heat generated

through flight muscles is transferred to the hemolymph and then from thorax to the abdomen that is poorly insulated.

At low air temperatures heart beat is low and hemolymph flow is also slow that transfers small amount of heat to the abdomen. This provides a rather precise way of regulating heat loss and thoracic temperature.

Physiological Mechanism

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Behavioral thermoregulation

Microhabitat selectionBaskingDaily activity cycleEndothermy

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Microhabitat selection

Male crickets chose cracks in the ground at a temperature where the frequency and intensity of their calling songs were maximized.• Optimize attractive characteristics (e.g., chirp rate) of

calling songs to mates.Locust nymphs deprived of protein or carbohydrate and then fed a meal subsequently chose different temperatures.• Maximize the assimilation of the nutrient that

addresses their nutritional imbalance.

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Basking

Butterflies changed orientation of their wings to reflect solar radiation onto their thorax. • Attain body temperatures necessary for flight.Adult water striders submerged themselves underwater when water temperature was higher than ambient air temperature.• Increase the rate of gonad maturation and egg

production.

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Daily activity cycle

Flies at warm locations were mostly active in the evening.• Avoid exposure of eggs to high daytime

temperatures soon after oviposition.

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Endothermy

Moths beat and vibrated their wings pre-flight. • Warm up flight muscles to temperatures

necessary to initiate flight.Hornet workers beat their wings at the nest entrance when temperature increased.• Ventilate the nest to prevent it from

overheating.