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Thermoregulation. Peter B. McEvoy Insect Ecology Ent 420/520. Classifying Thermal Relationships. Homeotherm. Body Temperature Tb. Poikilotherm. Ambient Temperature Ta. Homeothermy in Ectotherms Hyles lineata (Lepidoptera: Sphingidae). Occurs in Mojave desert of SW USA

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Peter B. McEvoy

Insect Ecology

Ent 420/520

classifying thermal relationships
Classifying Thermal Relationships


Body Temperature Tb


Ambient Temperature Ta

homeothermy in ectotherms hyles lineata lepidoptera sphingidae
Homeothermy in EctothermsHyles lineata (Lepidoptera: Sphingidae)
  • Occurs in Mojave desert of SW USA
  • Polyphagous on desert annuals
  • Abundant in April and May, dormant rest of year
  • Population size varies drastically yr to yr
  • Caterpillars regulate Tb through position and postural changes
caterpillars maintain body temperatures above ambient
Caterpillars Maintain Body Temperatures Above Ambient

Tb = Ta

Tb – Ta is greater for low T than for high

how do caterpillars maintain steady t b above t a



How Do Caterpillars Maintain Steady Tb Above Ta?
  • By exploiting thermal heterogeneity of it microhabitat through position and postural changes
    • As Ta increase mid-day, spend less time on ground and more on plant (can feed either on ground or plant)
    • On warm days, as temperature increases, spends more time in vertical position on stem
shifts in location and posture with changing t on hot and cold days
Shifts in Location and Posture With Changing T on Hot and Cold Days

 Location

 Posture






% on ground decreases, % vertical increases, with increasing T




apache cicada sonoran desert dicerooproctoa apache
Apache cicada Sonoran desert Dicerooproctoa apache
  • Among the loudest insects on record
  • Sings when TA 40oC in shade
  • Keeps cool by evaporative cooling from fluid shed from dorsal pores
  • Extravagant water loss for desert insect made possible by xylem feeding
stilts and parasols tenebrionidae of the namib desert
Stilts and ParasolsTenebrionidae of the Namib Desert

The head-standing beetle (Onymacris unguicularis) creeps to the crest of a dune when fog is present, faces into the wind and stretches its back legs so that its body tilts forward, head down. As fog precipitates onto its body and runs down into its mouth the beetle drinks (Armstrong 1990).

morphology and thermoregulation
Morphology and Thermoregulation
  • Insulation – air sacs, scales, setae
  • Color – dark wing undersides
  • Stilts add Parasols – ground dwelling beetles on host sands of Namib Desert
  • Countercurrent and Alternating-Current Heat Exchanges
environmental uncertainty and evolution of physiological adaptations in colias butterflies
Environmental Uncertainty and Evolution of Physiological Adaptations in Colias Butterflies
  • Variation in melanin on the underside of the hind wing, seasonal polyphenism
  • Allows insect to absorb solar energy and warm more quickly to 35-38oC required for flight
  • Intraspecific and interspecific variation
orange sulphur colias eurytheme



Orange Sulphur (Colias eurytheme)

adjusting phenotype to environmental regime
Adjusting Phenotype to Environmental Regime
  • If cues to thermal regime, two factors contribute to uncertainty
    • Noise in the signal
    • Magnitude (or strength) of the signal
  • If cues to photoperiod
    • Signal noise free
    • Free to respond to lack of accuracy with which signal predicts temperature
seasonal variation in hindwing underside coloration in colias eurytheme in relation to photoperiod
Seasonal Variation in hindwing Underside Coloration in Colias eurytheme in relation to photoperiod

Short day, low reflectance, high melanin

Long day, high reflectance, low melanin

predicting thermal regimes from photoperiod cycles
Predicting Thermal Regimes From Photoperiod Cycles

Thermoperiod and photoperiod out of phase

Slope (signal strength) and scatter (precision in prediction)

warming up by shivering
Warming Up by Shivering
  • Who does it?Found among large, active flyers across the insects
    • dragonflies (Odonata)
    • moths and butterflies (Lepidoptera)
    • katydids (Orthoptera)
    • cicadas (Clypeorrhyncha or Homoptera)
    • flies (Diptera)
    • beetles (Coleoptera)
    • wasps and bees (Hymenoptera)
  • How do they do it?Involves disengaging flight muscles form wings and synchronous contractions of muscles that normally alternate in flight
  • Who does it best?Honey bees and bumble bees represent the zenith of shivering response among any host-blooded animal (invertebrate and vertebrate)
countercurrent and alternating current
Countercurrent and Alternating Current
  • Countercurrent flow recovers heat from thorax by passing cold, incoming flow from abdomen by the warm, outgoing flow from the thorax
  • Alternating current removes heat from thorax by alternating warm outgoing and cool incoming flow
high artic bumblebee bombus polaris
High artic bumblebeeBombus polaris

By incubating brood with abdomen, queen can produce a batch of workers in ~2 weeks

  • Insect performance depends on temperature
  • Thermoregulation allows some insects a measure of independence from variation in the thermal environment
  • Biochemical, physiological, behavioral, morphological mechanisms involved
  • Consequences from individuals to populations and communities