Ph. D. Scholar Department of Entomology Indira Gandhi Krishi Vishwavidyalaya Raipur (Chhattisgarh)

1. Conservation and Augmentation
of Natural Enemies.
Survivorship Analysis and
Ecological Manipulations
Prepared By
Aaliya Afroz
Ph. D. Scholar
Dept. of Entomology, IGKV, Raipur

2. Introduction
u Conservation means the avoidance of measures that destroy
natural enemies and the use of measure that increase their
longevity and reproduction of the attractiveness of an area to
natural enemies.
u If the natural enemies are properly conserved the need for other
control measures is greatly reduced.
An inverted flowerpot filled with straw to attract earwigs

3. Conservation of natural enemies
u Protection from Pesticides
u Resistant or Tolerant Natural Enemies
u Preservation of Inactive Stages
u Avoidance of Harmful Cultural Practices
u Maintenance of Diversity and Necessary Hosts
u Alternate Hosts
u Natural Foods (Nectar, Pollen, and Honeydew)
u Artificial Food Supplements

4. u Artificial Shelters
u Reduction of Undesirable Predators
u Control of Honeydew-Feeding Ants
u Favorable Temperatures
u Avoidance of Dust

5. Augmentation of Natural Enemies
u Augmentation includes all activities designed to increase
numbers or effect of existing natural enemies.
u These objectives may be achieved by releasing additional
numbers of a natural enemy into a system or modifying the
environment in such a way as to promote greater number
or effectiveness.
u These releases differ from introduction of imported natural
enemies in that these have to be repeated periodically.
u The periodic releases may be either Inoculative,
Inundative, Supplementary or Accretive release.

6. Survivorship analysis/ Prediction of Success of
released natural enemies for colonization
u The colonization of entomophagous and phytophagous natural
enemies largely remains a matter of empirical trial and error.
u Data from past efforts suggest that the probability of a newly
colonized entomophagous species becoming permanently
established averages one in three.
u Predictive data gathered at the point of origin of the natural enemy
may require a decade of labor intensive, costly effort.
u Nevertheless, in certain cases, such as in the biological control of
weeds and medically important arthropods, lengthy pre-introduction
studies are required to preclude the introduction of harmful
species.

7. FUNCTIONAL RESPONSE Model:
HOLLING'S DISK EQUATION
Introduction:
u In the type II functional response, the rate of prey consumption by a predator
rises as prey density increases, but eventually levels off at a plateau (or
asymptote) at which the rate of consumption remains constant regardless of
increases in prey density (see also TYPE I and TYPE III FUNCTIONAL RESPONSE).
u Holling's disk equation, named after experiments he performed in which a
blindfolded assistant picked up sandpaper disks from a table, describes the type
II functional response.
Importance:
A consumer's functional response to changes in food density is an important
component of population regulation. The type II response is the most common
type of functional response and is well documented in empirical studies.

8. Na number of prey items attacked
aí "attack rate" (searching efficiency)
N prey density
P predator density (usually one in experiments)
T total available searching time
Th handling time
Question: Why does the functional response reach a plateau? What variable determines the level of
the plateau?
Variables:

9. Methods:
u Holling's disk equation models the relationship between the number of
prey items eaten during a period of time and prey density.
u Na increases with the total time (T), prey density (N), and/or attack rate
(aí), but decreases as handling time (Th) increases. Handling time is
defined as the time spent pursuing, subduing, and consuming each prey
item plus the time spent preparing to search for the next prey item
(including effects of satiation).

10. Contd.
u Wiedenmann & OíNeil conducted laboratory experiments to measure
the functional response of the predatory stinkbug Podisus
maculiventris (Heteroptera) when exposed to six different densities of
larvae of the Mexican bean beetle (Epilachna varivestis).
u Although P. maculiventris exhibited a type II functional response,
predation rates measured in the laboratory differed noticeably from
those measured in the field.
u We can graph the observed number of Mexican bean beetles attacked
by P. maculiventris as a function of bean beetle density, and plot the
curve fitted using Holling's disk equation (T = 14 daylight hours;
parameter estimates are aí = 0.0952, and Th = 0.90).

11. Interpretation:
• Holling explained the type II functional response as follows.
• There is a specific amount of handling time (Th) associated with each prey item eaten or
attacked that is invariant to the density of the prey (N).
• Consequently, while prey items are easier to find as their density increases, handling time per
prey item is the same, and the maximum number of prey items eaten or attacked is
determined by the ratio of total available searching time to handling time (T/Th).
• In other words, at low prey densities (small N), a smaller proportion of a predatorís time is
spent handling prey, even if the predator attacks every prey item available. As prey density
increases and more prey are attacked, the proportion of time spent handling prey increases.
• This proportion reaches a maximum when all available
time is spent handling prey (T = Th); at this point, handling
time (Th), rather than prey availability, limits the number
of prey items that a predator can consume
(and consequently determines the level of the plateau).

12. Ecological Manipulations Techniques:
Vegetational
diversity

13. Refugia

15. Alternate food source Microclimate
Limited and Selective use of
pesticides

16. Semiochemical-based manipulation

18. Host plant resistance

19. s