Insect Damage

1
Insect Damage
grasshopper
spider mites
potato beetle
aphids
2
Parasitoids

• This wasp is laying its egg inside an aphid
  where its young will develop. Parasitoid larvae
  develop on or inside a host, killing it as they
  mature. They emerge as adults and continue the
  cycle.

3
Predators

• A predator consumes many prey during its lifetime

Coccinellids
Chrysophids
Syrphids
4
Biological Control
5
Syrphid Aphid Ratios

• Temperature dependent aphid population growth
• Starvation of syrphids

6
N-isoclines for different growth rates of aphid
population
Number of Predators
Number of Prey
(Tenhumberg, Environ Entomol 1995)
7
How many predators do we need?

• Aphid density
• Aphid population growth rate
• Temperature
• Host plant (nutritional values)
• Predator species
• How much do they eat
• Temperature
• Nutritional value of aphid
• How quickly do the find and eat the prey

8
Temperature
Metopolophium dirhodum (Dean 1974)
9
Easy estimates

• Maximum number of aphids consumed during larval
  phase
• Episyrphus balteatus

10
Model System
Vicia faba
Hippodamia convergens (holometabolous)
Acyrthosiphon pisum (hemimetabolous)
11
Aphids

• 4,400 species of small insects
• 250 species are serious pests
• Aphids are divided up into 10 families all of
  which have been extant for 50 - 70 million years
• Superfamily Aphidoidea

Pemphigidae Anoeciidae Hormaphididae
Mindaridae Thelaxidae
Lachnidae Phloeomyzidae Greenideidae Aphididae
Drepanosiphidae
70 of species
12
Aphid Feeding

• Specialization
• Monophagous feeding only on 1 species of plant
• Polyphagous feed on hundreds of plant species
• How do they feed
• Passive feeding on sap of phloem vesselsThis
  sap being kept under high pressure, once a
  phloem vessel is punctured, it is forced into
  the food canal.
• Active feeding (sucking) from xylem vessels when
  thirsty
• Virus transmission

13
Plant Tissues

• Xylemconducts water and dissolved minerals from
  the roots to all the other parts of the plant.

• Phloem
• Sieve elements conducts the products of
  photosynthesis - sugars and amino acids - from
  the place where they are manufactured (a
  "source"), e.g., leaves, to the places ("sinks")
  where they are consumed or stored
• Companion cells move sugars and amino acids into
  and out of the sieve elements.

14
Honeydew

• Excretion of sticky substance known as
  "honeydew" which usually becomes black with sooty
  mold.Aphid honeydew is rich on carbohydrates
  (like melezitose), of which the aphids ingest an
  excess, being phloem-feeders.

• Some species of ants "farm" aphids, protecting
  them on the plant they eat, and eating the
  honeydew that the aphids secrete this is a
  mutualistic relationship.

15
Migration and Dispersal

• Most of the time aphids do not have wings, and in
  general they move very little, and life consists
  of feeding and giving birth.
• What stimulates movement
• death of the host plant
• danger
• end of season
• overpopulation
• Short distance dispersal 1.6 to 3.2 km per hour
• Long distance dispersal gt400 km in 9 hours
• Fly upwards to get above the planetary boundary
  layer (1000m above sea level) and are carried by
  the low level jet streams

Winged forms (alatae) appear
16
Reproduction

• Thelytokous parthenogenesisObligate
  parthenogenesis where females give birth only
  to female offspring
• Short generation time (about 10 days on average)
• Telescoping of generationsGrandaughters begin
  developing directly within the daughters which
  are themselves not yet born

17
Aphid Life Cycles

• Alteration of sexual and asexual generations
• Holocyclic
• Species that produce both sexual and asexual
  morphs
• Cyclical parthenogenesis Many generations of
  asexual (parthenogenetic) reproduction (all
  females), followed by single generation of sexual
  reproduction
• Anholocyclic
• Species that produce only asexual morphs
• Although many species are either holocyclic or
  anholocyclic, many other species possess both
  holocylic and anholocyclic populations
• Host plant alternation

18
Holocyclic Species

• Asexual and sexual morphs are produced at
  different times of the year.
• Males are present only in one part of the life
  cycle.

19
Anholocyclic Species

• No sexual males and females
• No direct descendants of the sexual morphs,
  namely the egg and the fundatrix.
• Often no primary host.

20
Host Alternation

• Autoecious single host plant
• Heteroecious alternating between host plants

Primary host Shrub or tree
Secondary host Herbaceous plant
21
Acyrthosiphon pisum

• Common name pea aphid
• Pink and green genotypes (polymorphism)
• Green morphs suffer higher rates of parasitism
  than red morphs
• Red morphs are more likely to be preyed on by
  predators than green morphs are
• Reproductive rates of both morphs are the same
• Aphid defensive behaviour of both morphs is the
  same.

22
A. pisum Life Cycle
23
Acyrthosiphon pisum

• Distribution
• Throughout the U.S. and Canada
• Host Plants
• Sweet peas, sweet clover, alfalfa, and some
  leguminous weeds.
• Vetch and crimson clover are important
  overwintering hosts

24
Plant Damage

• Extract sap from terminal leaves and stems
• Feed on pods causing them to curl, shrink, and
  partially fill.
• Feeding can result in deformation, wilting, or
  plant death
• Plants less than 15 cm (6 in) high are easily
  killed by a few aphids, whereas larger plants are
  only slightly damaged.
• Coated with shiny honeydew
• Virus transmission, e.g. pea enation mosaic and
  yellow bean mosaic viruses.

Heavy infestations of pea aphid have caused
chlorosis (yellowing) and wilting of plants in
this plot of susceptible alfalfa
Bean pod damage
25
Vicia faba
26
Lady Beetles(Coleoptera Coccinellidae)

• Over 450 species are found in North America. Some
  are native and some have been introduced from
  other countries.
• Food
• aphids
• mites, small insects, and insect eggs
• plants (Mexican bean beetle, Epilachna
  varivestis, squash beetle, Epilachna borealis)
• Low food availability
• pollen, nectar
• cannibalistic

27
Aposematism

• Warning colors
• Most predators associate bright colors
  (especially orange and black or yellow and black)
  with poison and other unpleasant properties.
• Toxin
• toxic to smaller predators, such as lizards and
  small birds
• Adults are able to reflex-bleed from their leg
  joints, releasing their oily yellow toxin with a
  strong repellent smell.

28
Adult Coccinellids

• Overwintering
• often in aggregations along hedgerows, beneath
  leaf litter, under rocks and bark, and in other
  protected places including buildings.
• Migration
• In spring, the adults disperse in search of prey
  and suitable egg laying sites.

29
Hippodamia convergens(1-2 generations / year)
30
Predation efficiency(H. convergens)

• Activity period late spring-early fall
• Consumption
• Cannibalism
• Fecundity (no. eggs) and fertility (fertile eggs)
• Migration
• Pesticide application

                                                                                                                               
31
References

• Dixon, A.F.G (1998) Aphid Ecology, Chapman and
  Hall, London, UK, pp.300
• Hodek, I. and A. Honek (1996) Ecology of
  Coccinellidae, Kluwer Academic Publishers, The
  Netherlands, Dordrecht, pp. 464

32
Lab overview

• Parameter estimation for aphid model
• Developmental time
• Survival
• Fecundity
• Testing predicted aphid population growth rate
• How much do predators eat?
• Maximum aphid consumption at different
  developmental stages

33
Aphid Experiments
Model
34
(No Transcript)
35
H. convergens

• Access food
• Larva gt 20 aphids/day
• Adults gt 50 aphids/day