Environmental Conditions (Temperature, Moisture, Wind)

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Environmental Conditions(Temperature, Moisture,
Wind)

• Peter B. McEvoy
• Oregon State University
• Corvallis

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Learning Objectives

1. Importance of temperature
2. Biogeographic patterns Arctic insects
3. Developmental rate in relation to temperature
4. Day-degree modeling
5. Survival and fecundity in relation to temperature
6. Temperature, species interactions, and population
   dynamics
7. Global climate change

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Biogeographic Perspective on Insect Life in
Extreme Environments Arctic Insects

• Studies by Downes and Danks
• Review by Strathdee and Bale 1998
• Cold is the single most important enemy of life
• F. Franks

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Arctic
Area where the average temperature for the
warmest month is below 10oC Arctic also defined
as region north of Arctic Circle, at latitude of
66o32N north of transition from boreal forest
zone to tundra, where growing season is typically
less than 600 day degrees above 0oC
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Retreating North Pole Ice CapEvidence of Global
Warming?
1979
Images compiled from satellite data show the
changes in the extent of the North Pole's summer
ice cap from 1979 to 2003.
2003
NY Times January 13, 2004
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Spitsbergen (Svalbard) 78oN lat
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Air temperatures, Spitsbergen (Svalbard), Norway
1969-1992
Longyearbyen, the capital of Spitsbergen
(Svalbard), is situated at 78 degrees north
latitude. Due to the influence of the Gulf
Stream, climatic conditions during the summer are
surprisingly good for the high Arctic. By
mid-June, temperatures are above zero, there is
little snow, and the sun does not set during the
24 hour cycle.
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Arctic Wooly Bear (Gynaephora groenlandica )
Some arctic insects are protected against winter
freezing by synthesizing trehalose, glycerol and
other so-called "cryoprotectants"
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Insect Life in the Arctic Nature of
environmental stress

1. Low temperatures, low heat budget
2. High winds
3. Low humidity and precipitation
4. Short growing season
5. Poor soils
6. Low primary production
7. Low predictability of adverse conditions

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Low heat budget in ArcticAssuming a
Developmental Threshold (DT) of 0OC
Location Lat Long Days/yr Day Degrees
Winnipeg, Manitoba 49.53o N 200 4900 DD 100
Coral Harbor, NW Territory 64.10o N, 83.15o W 95-100 950 19
High arctic lt250 lt5
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Low precipitation, low snow cover
Air Under Snow
Churchill, Manitoba 58.45oN 93.00oW -20o F (-29oC) for 6 wks -15 to -1 oC
Queen Elizabeth Islands, NW Terr 78-82oN -25oF (-32oC) for 2-4 mo -15 to -1 oC
Permafrost means no refuge from cold by burial in
soil
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Low primary production
Location Relative value
Temperate woodland 100
Well-developed tundra 20
High arctic 2
Expect low population levels of insects on
impoverished trophic base
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Faunal Characteristics

• Low species diversity
• Variation among insect orders (see handout)
• Lack of adaptive radiation
• Low Endemism
• Lack of Ecological Saturation
• Prolonged or indefinite life cycles
• Morphological/physiological adaptations
• Reduction

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Difference in success of insect orders(refer
to handout)
Diptera Chironomidae Midges (1/4 fauna) Sciaridae Dark-singed fungus gnats Mycetophilidae Fungus gnats Muscidae house fly, stable fly, face fly
Hymenoptera Ichneumonidae (parasitoid wasps) Tenthredinidae (sawflies)
Lepidoptera Rhopalocera (butterflies and skippers)
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Reasons for low diversity in the Arctic

• Low Colonization. Species has been unable to
  reach the region since the last glacial period
• Low Survival. Species is unable to survive in the
  arctic because of limited resources
• Limited Adaptation. Species has insufficient
  adaptation to the harsh environment
• Other barriers to colonization. After it
  arrives, small populations became extinct owing
  to stochastic fluctuations and inbreeding
  depression. Unless founding populations increase
  rapidly and expand their range to new habitat,
  they are unlikely to persist.
• Insufficient time to evolve necessary
  adaptations. Low temperatures ? slow development
  ? long generation times ?slow evolutionary rates.
• Slow succession rates and low environmental
  heterogeneity, many species become competitively
  excluded.

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Black Fly Life Cycle

• Clockwise from top
• Adult female eggs laid on emergent vegetation at
  surface of flowing water
• larvae attached to stream bottom, with labral
  brushes, usually called labral fans in this
  family, extended in feeding position
• pupae, each enclosed in its cocoon, attached to
  submerged vegetation
• adult, enclosed in air bubble, escaping to
  surface of water from submerged pupal skin.

Photo Ag Canada
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Syndrome of blackflies (Simuliidae)

• In southern blackflies
• Blood meal
• Eggs matured
• Oviposition flight
• Several gonotrophic cycles
• Mating in flight
• Males have enlarged ommatidia
• In tundra
• Female non-feeding as adult
• Eggs start to develop prior to adult emergence
• No mating flight
• Parthenogenesis
• Resorbtion of developing oocytes

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Summary on Blackflies

• Rigors of arctic life progressively strip black
  flies of all their characteristic features
• their dependence on the blood meal
• the biting mouthparts
• the habit of dispersal
• the maturation period before mating and egg
  laying
• the swarming flight
• the normal mating process
• the sense organs that mediate it
• ultimately the ability to fly and the sexual
  process itself

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Favorable Range
Movement
High temperatures death from enzyme
inactivation, metabolic imbalance,
dehydration Low temperatures death from ice
crystals within cells Intermediate temperatures
affect growth , development, behavior
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Extreme variation in insect body temperatures

• Extremely Cold. Adult form of flightless midge
  (Diamesa sp.) (Diptera, Chironomidae) walks on
  glacier ice even when its body temperature is
  chilled to -16oC. So sensitive to heat that
  perishes in the warmth of human hand
• Extremely Hot. Sphinx moths have insulating fur
  and thoracic T 46oC during flight over wide range
  in T ambient (hotter than human body temperature
  of 37oC)

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Temperature and organism interactions

• How does temperature mediate interactions among
  organisms at different trophic levels?
• Lab example
• Field example

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Temperature Effects on a Host Parasitoid-aphid-pla
nt InteractionMessenger, P. S. 1964. Ecol.
45119-131

• Parasitoid wasp Praon palitans (Braconidae)
• Aphid host Therioaphis maculata, spotted alfalfa
  aphid (Aphidae)
• Plant host Medicago sativa (Fabaceae)

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Low Temperatures Act As a Refuge for Aphid Prey

• Control success At 21oC, braconid checks
  increase of aphid
• Control failure At 12.5oC, braconid fails to
  check increase of aphid
• Why?
• Superparasitism reduced mobility ?adult
  crowding ?higher superparasitism
• Diapause increased incidence in parasite
  progeny
• Sex ratio reduced fertilization ?more males
  than females in parasite progeny

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Fall Webworm Life Cycle Hyphantria cunea
(Lepidoptera Arctiidae)
Carnivore
Herbivore
T
Plant
Price 1997 Insect Ecology
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Fall webworm
Adult
Larva

• Native to North America, introduced accidentally
  in Europe and Japan
• Univoltine, overwinters as a diapausing pupa
• Adults emerge June-July
• Larvae are polyphagous on broad-leaved deciduous
  trees

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Patterns in Population Dynamics

1. Oscillations in population density periodic and
   synchronized regionally
2. Climate limits distribution and abundance
   outbreaks associated with warm, dry summers
   distribution limit related to temperature
3. Resource limitation periodically depletes food
   supply, timing of development in relation to
   foliage quality important
4. Natural enemy limitation temperature affects
   host-parasitoid synchrony, parasitoid
   encapsulation

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Geographic Distribution in Relation to
Temperature for Fall WebwormClimate Envelope
Approach
Morris 1964
Temperate insect near northern limits of its
range, expect physical factors to be limiting
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Outbreaks of Fall Webworm are associated with
warmer-than-average summer temperaturesTemperatur
e fluctuations appear to be synchronized over
wide geographic area
Webworm outbreaks
Deviations in August and September Temperatures
Morris 1964
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Variation in Host QualityPupal mass and
developmental time vary among host plant species
in this polyphagous insect
Female pupal mass
 
Development time
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Phenology in Relation to TemperatureWhy do warm,
dry summers lead to outbreaks?
Warm Year Enough heat for adults? eggs-?
larvae?pupae
(gt10.5oC)
Cold Year Only enough heat for adults? eggs-?
larvae
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Temperature (16-32oC) and Humidity (50-100)
Interact in Their Effects on Egg Survival in Fall
Webworm
100 RH

• Parabolic relation between survival and
  temperature becomes flatter and lower as
  humidity decreases
• Humidity changes have a stronger effect on
  hatching (upper graph) than on embryogensis
  (lower graph)

70 RH
50 RH
Survival ()
10 16 21 27 32
38 oC
Morris and Fulton 1970
Temperature (oF and oC)
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Modeling Development as a function of temperature

• Developmental threshold temperature (t) - rear
  insect at various constant temperatures to obtain
  duration of development and its inverse,
  developmental velocity (V), for a range of
  temperatures (T)
• Heat requirement or thermal constant Ki for
  insect stage i
• Ki D(T-t) (1)
• Where D is number of days for development at
  ambient temperature T and threshold temperature t
• Solving V 100/D for D and substituting for D in
  (1)
• Ki 100 (T-t)/V (2)
• V/(T-t) given by slope b of the Velocity x
  temperature relationship so
• Ki 100/b (3)
• For line A for pupae (next slide), slope b
  0.262 so Kp 382oD where subscript p designates
  pupal stage

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Modeling Development as a function of temperature
B
A
Y 0.0144 X - 0.1514
Developmental Time (Days)
Developmental Velocity
Temperature oC

• From figure B
• Developmental Threshold - set Y 0 and solve for
  X 10.5 oC
• Thermal Constant 1/b 69.444 degree days
  required for stage development

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Pupal-development Rate in Fall Webworm As a
Function of Temperature
Daily environmental regime approximated as a sine
wave
Developmental rate curve approximately linear
After Diapause
Without Diapause
Optimum 80oF (27oC) Threshold 51oF (10.5oC)

1. After diapause
2. In lab without diapause

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Effects of Temperature and Humidity on Pupal Mass
in Fall Webworm Pupal Mass Rises-and-Falls With
Increasing Temperature From 55-95oF (13-35oC),
Increases As Humidity Increases From 40-100
100 70 40
Pupal mass of females often a good predictor of
fecundity
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Thermal Constants for each Stage
Radiant heat present in field absent in lab
increases temperature on leaves where eggs are
laid and in nests where larvae feed Net gain of
45oD during LI-LV due to radiant heat
Good agreement between observed and predicted for
continental and maritime populations
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Predictions closely match observations

R2 0 .96

• Observed and Predicted Thermal constants for fall
  webworm

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Survival and Fecundity decrease with Foliage Age

• Low quality, late foliage yields low survival
• Diet of larvae has effects on subsequent stages
  -pupa, adult, egg
• Recall cool weather slows development, forcing
  late instar larvae to feed on low quality foliage

Survival
Stage
An indirect effect of temperature acting via
variation in host quality
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Maternal Effects Survival and Fecundity of
Progeny decrease with decreasing Maternal Food
Quality
What mother ate
Diet of Mother
Decreasing maternal food quality
How well offspring perform
Performance of offspring depends on larval diet
of mother
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Heritable variation in Heat Requirements of Pupae
Offspring
Offspring-parent regression for logeKp yields a
slope of 0.60, where perfect correspondence would
yield a slope of 1
Parent

• Assortative mating helps conserve genetic
  variation in heat requirements (moths live only
  about 8 days)
• Selection regimes may differ in maritime vs.
  interior environments (yielding lower Kp in
  interior)

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Modern Themes Anticipated by This Classic Study
by Morris

• Role of density dependence and ressource
  limitation
• Role of genetic variation, selection, on
  population dynamics
• Importance of phenology and host-plant quality

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Conclusions

1. Temperature influences growth, development,
   behavior (e.g. movement), survival, reproduction
2. Temperature effects can be modified by variation
   in moisture
3. Temperature can act directly on the insect and
   indirectly via resource quality and natural
   enemies