Lesson 4 Population Dynamics of Forest Insects

Question 1

If a female Douglas-fir Tussock Moth lays 200 eggs in her cocoon and follows a life history pattern like that shown on Table 4.1; How many of the eggs would have to survive to adulthood to mimic the survival projection as seen on Table 4.1?

Answer 1

https://canvas.ubc.ca/courses/52107/pages/l4-dot-08-table-4-1-life-table-for-the-douglas-fir-tussock-moth?module_item_id=2674955

Surviving Individuals= Population - (population x Mortality%)

3.2= 200-(200*0.984)

Question 2

What percentage mortality does this number represent?

Answer 2

98.4%

Question 3

What are some of the major causes of mortality?

Answer 3

Predators and parasites pose a big threat. These include spiders, insects, and birds. As well bacteria and viruses. Another major cause of death is resource competition (food).

Question 4

would the population increase or decrease over time? Provide reasons why?

Answer 4

mortality quotient = ((fecundity)(sex ratio) -1)/ ((fecundity)(sex ratio))

fecundity = average number of eggs laid
sex ratio number for females to males

mortality quotient is the number of individuals needed to die to maintain population. if mortality rate

Question 5

How are populations of the Douglas-fir tussock moth monitored in B.C.?

Answer 5

on a yearly basis, pheromones traps are used to detect populations increases, egg surveys are conducted on ground to confirm.

https://www.for.gov.bc.ca/rsi/ForestHealth/PDF/DFTM_Strategy_Feb_2013.pdf

Question 6

What is the threshold level at which a forest manager will move towards making a control decision for a Douglas-fir tussock moth infestation?

Answer 6

When trap catches increase to the critical level that an outbreak is predicted within two years,
targeted ground surveys for egg masses should begin. Ground surveys should be conducted in
the vicinity of the high trap catches and all susceptible forest types adjacent to these traps.

Question 7

Differentiate density-dependent factors and density-independent factors in the context of insect population dynamics. Give examples for each.

Answer 7

Density dependent factors are directly correlated with the population density, where density independent factors are not affected by population dynamics.

Density dependent factor: as population increases Predators increase, parasites increase, and pathogens of dftm.

density independent factor: weather conditions outside the range of tolerance of an insect. This stressor could affect their survival or population growth.