W5, Biological control of insects, population dynamics of pests - INCOMPLETE Flashcards
Explain at least FOUR (4) desirable characteristics of a good natural enemy in biological control.
- Limited host range, preferably specific to the target pest
- = less time wasted searching for/attacking non-target organisms
- High searching capacity (able to locate pests at high and low densities)
- Synchronised life cycle with the target pest
- High reproductive capacity (high fecundity, short generation interval)
- Adaption to a variety of climate conditions
Using the formula below, how could you reduce the population of insect pests?
- Increase the number of predators
- Increase the birth rate of predators
Explain what ‘delayed density dependent responses’ are
Pest and predator populations fluctuate based on the density of each other.
The peak predator density occurs after the peak prey density.
Explain what is meant by ‘augmentation’ in relation to IPM
The periodic release of natural enemies for pest management.
In other words: the periodic use of biological controls for pest management.
Explain what is meant by ‘conservation biological control’ or ‘biological control conservation’.
Using practices that promote the survival and activity of natural enemies/predators.
- habitat manipulation
- provide resources (nectar, pollen, alternative hosts/prey, water, nesting sites, shelter, etc.)
- modification of existing practices
- reducing pesticide usage
- using more selective pesticides
- better timing of pesticide application
- avoidance of modifying cultural practices that disrupt natural enemy populations
What is it that makes exotic pests so problematic?
The absence of natural enemies that can control them.
Importing biological controls can be time consuming and expensive.
What is the difference between inoculative and inundative release strategies for predatory insects?
Inoculative release: For season-long control of a pest
Inundative release: Release of large numbers for immediate pest suppression.
How might you use biological controls to control weeds, and what strategy do weeds have to resist them?
Find an multiple insects with a stage that feeds on the weed (same strategy as with prickly pear and Cactoblastis cactorum in Aus - feeds inside the leaf lobes).
Attack by individual natural enemies will usually lead to a reduction in biomass, but not death. Usually, several species working together are usually required to achieve control.
Seed banks are plants’ way to try and avoid natural enemies, and can allow them to persist even when substantial mortality occurs at any one time.
Explain the main differences between biological control of weeds vs. insect pests. (8 mins)
Insects:
- might only need one natural enemy for effective control
Weeds:
- likely to require multiple natural enemies for effective control
- strategies for controlling weeds need to be effective over a longer time frame because the weed seed bank will replenish the problem year after year, unless it too is controlled (e.g. by not allowing weeds to contribute more seeds to the bank).
- forecasting models more useful for evaluating the life cycle of the enemy and when would best suit its introduction
How does biological control of/with microbes work?
- Direct parasitism/predation
- Competition for resources
- Antibiosis (production of antibiotics which inhibit the pathogen)
- Hypovirulence (reduced virulence)
- Induced resistance/systemic acquired resistance.
Describe the four main factors that influence the population dynamics of pests and discuss how each of these factors can be manipulated to manage pest populations
Weather (temperature, day length, relative humidity, rainfall, wind, variability, etc)
- Difficult to manipulate in field conditions, relatively easy to manipulate in controlled environments like greenhouses.
- Fungal and insect pests in particular have lifecycles that are very closely related to the environmental conditions, particuarly the interaction between temperature and moisture.
Natural enemies
- High [natural enemies] = low [pest], and vice-versa
- Can promote using Conservation Biological Control strategies (maintain current natural enemies)
- Can import natural enemies if none exist
- Can augment natural enemies with imported ones (inculative or inundative release)
Competition for resources
- The greater the competition for resources, the lower the pest population density is likely to be.
- Could introduce predators or competetors that don’t create damage that compete for the same resources as the pest, so even if they don’t directly ‘attack’ them to decrease their numbers, they still reduce their population density indirectly.
Food quality and availability
- The more food/nutrients available, and the better its quality, the higher the population density (i.e. pests can be promoted - develop faster, produce more offspring).
- This is difficult to control, as usually the food is the crop we want to grow, so we can’t reduce its availability, nor its quality.
- Resistant plants can reduce or prevent the growth, development, and/or reproduction of pests by producing toxins, for example
- N availability often limits populations of sucking insects.
Provide a definition or equation for calculating population density (hypothetically).
Population density = (Births + Immigration) - (Deaths + Emigration)
Explain how logarithmic plots of population density vs time can be used to interpret changing rates of population growth.
With a regular graph, it impossible to tell whether a population is growing at a constant (linear) rate or not. To do that, the population size needs to be converted to a log scale.
If you really want to understand population dynamics, you need to view the population density on a log scale; plain and simple.
True or False?
Many migrating insects use prevailing winds for migration.
True
True or False?
Feeding and reproductive functions are put on hold while migrating.
True
