VL 2 Flashcards
How many insects are there?
ca. 1’000’000 species are currently known, estimates from 2’000’000 to 30’000’000
Insects represent as much as 50% of all known species and 75% of known animals
What is the importance of insects?
Natural world (“the little things that run the world”)
Nutrient cycling
Plant Reproduction (pollination, seed disperal)
Community Structure / Population Dynamics (Phytophagy, seed feeding, parasitism, predation
food web
What is a pest?
Any living species whose activities, enhanced by numbers, causes economic losses to human possessions, directly threatens human health or is annoying
Name three types of pests
Aesthetic pests
Medical pests
Economic pests (Agricultural and forest)
Name examples of pests
Japanese Beetle
Stink Bug
European Corn Borer
Drosophila Suzuki
Asian Longhorn beetle
Wireworms
diseases caussed by pests:
Elephantiasis
Malaria
Bubonic plague
Population dynamics
Rate of increase (high reproductive potential)
Carrying capacity (population level that environment can sustain)
Natural enemies (presence or absence)
R-Strategist
“Ecological opportunists”
Organisms with high reproductive rate and low survival rates
Small bodies & short life cycles in order to produce large numbers of offspring quickly
Usually early colonizers of disturbed habitats, and have high dispersal ability
Thrive in ecosystems that are “unstable” or where food resources are short- lived
Populations go through huge fluctuations depending on the environment with large amounts of mortality followed by quick rebounds of population numbers.
K-strategists
Organisms with low rates of reproduction but high survival
Larger body size, longer lifespans
Found in stable, undisturbed environments (mature grasslands, climax forests)
More individuals reach sexual maturity and population levels stabilize near environmental carrying capacity
Environmental fluctuations do not cause major shifts in population levels.
Determinants of insect abundance
Effective environment
Elements in the ecosystem can also influence reproduction & survival
Factors such as weather, food quality/quantity and living space my help or inhibit population growth
Natural enemies can also inhibit population grwoth
r-Strategist vs. K-Strategists
“r” stands for “rate” (grwoth rate), r have a high r value and a low K value, they grow fast but most die
“K” stands for Kapazitätsgrenze (capacity limit) now called carrying capacity, K strategists have low r and high K. they grow slow but more survive
What are Insect population densities regulated by?
Perfectly density-dependent mortality factors
Imperfectly density-dependent mortality factors
density-independent mortality factors
Perfectly density-dependent mortality factors
A density-dependent factor that never fails to act on a population
Acts strongly to subtract numbers when the density is high and acts less strongly as density decreases.
Examples: Intraspecific competition between individuals for limited resources (usually food).
Imperfectly density-dependent mortality factors
Density-dependent factor that sometimes fails to limit numerical increase.
Examples: predators, parasites, pathogens
These factors can themselves be influenced by other environmental factors which sometimes leads to their
failures
Density-independent mortality factors
The impact of these factors do not vary across different insect densities.
Example: Weather (rainfall, temperature, humidity)
The strength of these effects is always the same with no influence from the density of the population
What are challenges in Agroecosystems?
Agroecosystems are either short lived or undergo frequent disruptions (environment unstable, abrupt changes in microclimate)
one or very few plant species, one species being dominant
plants are either non-native or have undergone intensive artificial selection for increased yield -> loss of ancestral anti-herbivore traits
uniform species with low or no genetic diversity leads to uniform phenological events
Agroecosystems frequently have added nutrients in form of fertilizers
What are abiotic and biotic factors that can affect insect populations abundance?
Birth rate
Immigration
Death rate
Emigration
Birth rate
two variables determine birth rate:
Fecundity - rate at which females produce gametes
- can be limited by nutritional & environmental factors
- total fecundity can be decreased by unfavorable conditions in the females environment
- certain varieties of resistant plants can limit the total fecundity of females feeding on them
fertility - the rate at which females produce fertilized eggs
- can be affected by nutritional and climate factors
- primarily influenced by mating success (sex ratio, population density, ability of males to locate females, life-expectancy of females)
- mating disruption techniques act on reducing the fertility of a pest species preventing males and females from meeting or by delaying those encounters until the females are too old
Death rate
main process by which individuals are lost for a population
survival curves
p. 42 - 44
Sources of mortality
Weak predctors
Aging - few insects die of old age, most will be killed by other factors before reachng this point
low vitality - some populations are gentically less resistant to adverse conditions and suffer higher mortality than more resistant populations
Accidents - Random abnormal events in the life of an insect that kills it. Example: Being eaten along with leaves by a browsing mammal herbivore.
Sources of mortality
strong predictors
Natural enemies:
All pest insects have predators, parasites, and pathogens that kill them.
The actions of natural enemies are density-dependent, which means their impact is related to the density of prey/hosts that are available to them.
Physiochemical Conditions:
Involves the physical and chemical conditions of the environment the insect lives in, mostly weather
variable winter and summer temperatures/humidity can have huge effects on mortality rates an insect population (even if the species is adapted for that environment)
Lack of shelter:
Many insects depend on shelter to avoid mortality due to weather or natural enemies.
Lack of shelter combined with another mortality factors can greatly increase the effect of that mortality factors
Direct effects of weather
Physiological damage
disrupted devekopment
reduced behaviour/activity
reduced resistance to biotic factors
indirect effects of weather
decrease in plant growth
Asynchronous phenology of plants and herbivores
can increase or reduce the effects of natural enemies
What favors Pest outbreaks?
Large scale monocultures
- changes the available food resources
Favorable environment (weather)
Indiscriminate use of pesticides
- changes the competitive situation
- reduces natural enemy populations
Quantitative damage
Destruction that results in lower yield or less marketable product than would occur in absence of the pest
loss of yield
lower plant (or animal tolerance to toher stress
disease transmission
annoyance of animals
invasion or destruction of structures and contents
Qualitative damage
destruction that affects the shape, size, appearance or nutritive composition of the product
loss of marketability
reduced nutritional content
disease transmission
aesthetic loss
annoyance of humans
Direct pests
injure part of the commodity we use
codling moth in apple fruit
Indirect pests
injure other parts of the commodity
aphid on an apple leaf
Example of direct and indirect pest
Rosy Apple Aphid
Severe curling of new foliage, later growth being twisted and deformed. Fruit may be blemished or stained.
Damage boundary
Injury level where damage can be measured
how much financial loss is the pest causing?
how much will it cost to control the pest?
p. 61
Economic injury level (EIL)
Economic injury level is the level of damage at which the loss caused by the pest equals in value the cost of available control measures (financial loss x control), break-even point
often we cannot measure the loss directly so we measure the number of individuals
Factors influencing the economic injury level
Cost of management
value of commodity
damage per unit injury, the crop response to injury
Economic Threshold (ET)
Economic threshold is the level of damage ata which we should begin to apply controls to prevent the pest population from reaching the EIL
We usually measure the ET in terms of numbers of individual pests
p. 66
