biological control - universiti putra malaysia · · 2014-09-19defination of bc •centered on...
TRANSCRIPT
History
• Has a history of over 100 yrs.
• Track record of >5000 introduction against insect pests & >1000 against weeds
Concept and theories
• Natural control (NC)…has biocontrol component• Elements in Balance of nature• Population in equilibrium• Species diversity – in harmony within habitat.
• No one species continually increases OR decreases in relation to each other…
• Species niche concept… a given locality where a species is • more or less consistently abundant ; • others are less common ; • some species rarely encountered…
• cause varying niches !
Defination of BC
• centered on natural enemies (NE)• predators, parasitoids & pathogens ; • maintain density at a lower average.
• Present day workers… include• Host plant resistance • Autosterilisation• Modify environment • habitat manipulation• Genetic manipulation • GMOs and etc.
• Ecological basis… as opposed to technological.
Natural control
• A phase of natural control involving • importation• augmentation • conservation
• To regulate host population densities• To suppress pest number below economic injury• To modify environment favourable for Natural
Equilibrium• To modify environment, unsuitable for pest• To conduct mass release
• have insectary, intermittent inundative
• STRIVE to maintain for a long period…
– created at a stable environment (complex)
– achievable through population regulation
• equilibrium density (Smith, 1935)…
• steady state (Nicholson, 1933)…
• Discuss: GEP, ET, EIL, AT, Parasitoid/Predator introduction
• Stress levels in state of flux• the influence of rate of birth & death
• Have fluctuations• but consistent in population number year after year…
provided habitat not drastically disturbed.
• If population above GEP… natural regulating forces (biotic agents) will increase intensity (suppressive) with increase pest density… results in pest decline.
Category of natural regulating forces
• Density-independent mechanism…
– Forces operating independent of density of organism.
• Density-dependent mechanism…
– Forces influenced by density of organism.
• What are Density Independent forces? -• Forces that determine ecological areas or boundaries
of the pest.• Mainly meteorological & physical
• rain, wind, temperature, • genetic defects,• accidents, natural catastrophe• agriculture activities… ploughing, • host plant destruction, phytosanitation, etc.
• What about in an agroecosystem ?• Man-made, temporary ecosystem,• Heaven for pest… monocroping…food a plenty• Biotic-natural forces… low activity• Pesticides disrupt biotic forces…• remedy!… conservation, augmentation!
• What are Density Dependent forces? -
• Forces that regulate the pest number present or surviving in that ecological area.
• Mainly predation, parasitism, diseases,
• inadequate food,
• limited nesting, limited hiding places & shelters,
• When overcrowded… leads to…
• cannibalism, suicidal dispersal,
• displaced to be exposed to…• hostile climate,
• vulnerable to predation & parasitism.
• What if permanent displacement of GEP caused by disturbances (natural or otherwise) ?
• 1. Major changes in the environment• Draining of swamp land… decreases the
number of mosquitoes.
• Dam the river… kills the fireflies in Kuala Selangor.
• Extensive cocoa cultivation… increase number CPB & mosquito bugs.
• Extensive development of cities without well planned drainage infrastructures… will increase cases of dengue!
• 2. Transferring pest insects from native home into a new habitat where the natural enemies are absent or ineffective…
• a case of introduced (exotic) pest, like DBM !
• Oil palms in the early years were poor yielding, why? This is a case of transferring of plant into Malaysia without its natural pollinators ! … small Fruit Bunch.
• Present approach to population management
• Integrate Natural Enemies with other control measures… IPM
• Still not a guaranteed success… why ?• The key question is…
• can the Natural Enemies regulate pest population substantially, continuously for long periods (yrs)… not just immediate mortality in one yr., esp. in the case of predators, parasitoids & disease agents
• So IPM must be pest oriented…in monocrop.
• What about ICM ?… crop diversity helps.