Biological Control: A Natural Approach to Pest Management

biological control

1. Biological control
311 class
1

2. Definitions
Theterms“biologicalcontrol”anditsabbreviatedsynonym
“biocontrol”havebeenusedindifferentfieldsofbiology,most
notablyentomologyandplantpathology.Inentomology,ithas
beenusedtodescribetheuseoflivepredatoryinsects,
entomopathogenicnematodes,ormicrobialpathogensto
suppresspopulationsofdifferentpestinsects.Inplantpathology,
thetermappliestotheuseofmicrobialantagoniststosuppress
diseasesaswellastheuseofhostspecificpathogenstocontrol
weedpopulations.
Definitions
Theterms“biologicalcontrol”anditsabbreviatedsynonym
“biocontrol”havebeenusedindifferentfieldsofbiology,most
notablyentomologyandplantpathology.Inentomology,ithas
beenusedtodescribetheuseoflivepredatoryinsects,
entomopathogenicnematodes,ormicrobialpathogensto
suppresspopulationsofdifferentpestinsects.Inplantpathology,
thetermappliestotheuseofmicrobialantagoniststosuppress
diseasesaswellastheuseofhostspecificpathogenstocontrol
weedpopulations.
Inbothfields,theorganismthatsuppressesthepestor
pathogenisreferredtoasthebiologicalcontrolagent(BCA).
2

3. Morebroadly,thetermbiologicalcontrolalsohasbeenappliedto
theuseofthenaturalproductsextractedorfermentedfromvarious
sources.
Theseformulationsmaybeverysimplemixturesofnatural
ingredientswithspecificactivitiesorcomplexmixtureswithmultiple
effectsonthehostaswellasthetargetpestorpathogen.
And,whilesuchinputsmaymimictheactivitiesoflivingorganisms,
nonlivinginputsshouldmoreproperlybereferredtoasbio
pesticidesorbiofertilizers,dependingontheprimarybenefit
providedtothehostplant.
Morebroadly,thetermbiologicalcontrolalsohasbeenappliedto
theuseofthenaturalproductsextractedorfermentedfromvarious
sources.
Theseformulationsmaybeverysimplemixturesofnatural
ingredientswithspecificactivitiesorcomplexmixtureswithmultiple
effectsonthehostaswellasthetargetpestorpathogen.
And,whilesuchinputsmaymimictheactivitiesoflivingorganisms,
nonlivinginputsshouldmoreproperlybereferredtoasbio
pesticidesorbiofertilizers,dependingontheprimarybenefit
providedtothehostplant.
3

4. Types of interactions contributing to biological control
Throughouttheirlifecycle,plantsandpathogensinteractwitha
widevarietyoforganisms.Theseinteractionscansignificantly
affectplanthealthinvariousways.Inordertounderstandthe
mechanismsofbiologicalcontrol,itishelpfultoappreciatethe
differentwaysthatorganismsinteract.
4

5. Note,too,thatinordertointeract,organismsmusthavesome
formofdirectorindirectcontact.
Odum(1953)proposedthattheinteractionsoftwopopulations
bedefinedbytheoutcomesforeach.
Thetypesofinteractionswerereferredtoas:
mutualism
protocooperation
commensalism
neutralism
competition
amensalism
parasitism
predation.
Note,too,thatinordertointeract,organismsmusthavesome
formofdirectorindirectcontact.
Odum(1953)proposedthattheinteractionsoftwopopulations
bedefinedbytheoutcomesforeach.
Thetypesofinteractionswerereferredtoas:
mutualism
protocooperation
commensalism
neutralism
competition
amensalism
parasitism
predation.
5

6. Whiletheterminologywasdevelopedformacroecology,
examplesofallofthesetypesofinteractionscanbefoundinthe
naturalworldatboththemacroscopicandmicroscopiclevel.
And,becausethedevelopmentofplantdiseasesinvolvesboth
plantsandmicrobes,theinteractionsthatleadtobiologicalcontrol
takeplaceatmultiplelevelsofscale.
6

7. Neutralism
describesthebiologicalinteractionswhenthepopulation
densityofonespecieshasabsolutelynoeffectwhatsoeveron
theother.
7

8. 8

9. 9

10. 10

11. Related to biological control, an inability to
associate the population dynamics of
pathogen with that of another organism would
indicate neutralism.
11

12. Incontrast,
antagonismbetweenorganismsresultsinanegative
outcomeforoneorboth.
Competitionwithinand
betweenspeciesresultsindecreasedgrowth,activityand/or
fecundityoftheinteractingorganisms.
12

13. 13

14. 14

15. 15

16. 16

17. 17

18. 18

19. Biocontrolcanoccurwhennon-pathogenscompetewith
pathogensfornutrientsinandaroundthehostplant.
19

20. Mutualism
Mutualismisanassociation
betweentwoormorespecies
wherebothspeciesderive
benefit.Sometimes,itisan
obligatorylifelonginteraction
involvingclosephysicaland
biochemicalcontact,suchas
thosebetweenplantsand
mycorrhizalfungi.
.
Mutualism
Mutualismisanassociation
betweentwoormorespecies
wherebothspeciesderive
benefit.Sometimes,itisan
obligatorylifelonginteraction
involvingclosephysicaland
biochemicalcontact,suchas
thosebetweenplantsand
mycorrhizalfungi.
.
20

21. However,theyaregenerallyfacultativeandopportunistic.For
example,bacteriainthegenusRhizobiumcanreproduce
eitherinthesoilor,toamuchgreaterdegree,throughtheir
mutualisticassociationwithlegumeplants
21

22. These types of mutualism can
contributeto biologicalcontrol, by
fortifying the plant with improved
nutrition and/or by stimulatinghost
defenses.
22

23. Protocooperation:
Protocooperationisaformofmutualism,buttheorganisms
involveddonotdependexclusivelyoneachotherforsurvival.
ManyofthemicrobesisolatedandclassifiedasBCAscanbe
consideredfacultativemutualistsinvolvedinprotocooperation,
becausesurvivalrarelydependsonanyspecifichostanddisease
suppressionwillvarydependingontheprevailingenvironmental
conditions.
Protocooperation:
Protocooperationisaformofmutualism,buttheorganisms
involveddonotdependexclusivelyoneachotherforsurvival.
ManyofthemicrobesisolatedandclassifiedasBCAscanbe
consideredfacultativemutualistsinvolvedinprotocooperation,
becausesurvivalrarelydependsonanyspecifichostanddisease
suppressionwillvarydependingontheprevailingenvironmental
conditions.
23

24. 24

25. commensalism
isasymbioticinteractionbetweentwolivingorganisms,whereone
organismbenefitsandtheotherisneitherharmednorbenefited.
Mostplant-associatedmicrobesareassumedtobecommensalism
withregardstothehostplant,becausetheirpresence,individually
orintotal,rarelyresultsinovertlypositiveornegative
consequencestotheplant.
25

26. 26

27. 27

28. And, while their presence may present a variety
of challengesto an infecting pathogen, an
absence of measurable decrease in pathogen
infectionor diseaseseverity is indicative of
commensalinteractions.
28

29. Amensalism,associationbetweenorganismsoftwodifferent
speciesinwhichoneisinhibitedordestroyedandtheotheris
unaffected.Therearetwobasicmodes:competition,inwhicha
largerorstrongerorganismexcludesasmallerorweakeronefrom
livingspaceordeprivesitoffood,andantibiosis,inwhichone
organismisunaffectedbuttheotherisdamagedorkilledbya
chemicalsecretion.
29
Amensalism,associationbetweenorganismsoftwodifferent
speciesinwhichoneisinhibitedordestroyedandtheotheris
unaffected.Therearetwobasicmodes:competition,inwhicha
largerorstrongerorganismexcludesasmallerorweakeronefrom
livingspaceordeprivesitoffood,andantibiosis,inwhichone
organismisunaffectedbuttheotherisdamagedorkilledbya
chemicalsecretion.

30. Theclassicdemonstrationofantibiosisisthedestructiveeffectthat
thebreadmoldPenicilliumhasuponcertainbacteria;thesecretion,
knownaspenicillin,hasbecomeapotentmedicineincombating
bacterialinfections.Somehigherplantssecretesubstancesthat
inhibitthegrowthof—orkilloutright—nearbycompetingplants.An
exampleistheblackwalnut(Juglansnigra),whichsecretesjuglone,
asubstancethatdestroysmanyherbaceousplantswithinitsroot
zone.
30

31. 31

32. 32

33. Parasitism
isasymbiosisinwhichtwophylogeneticallyunrelatedorganisms
coexistoveraprolongedperiodoftime.Inthistypeofassociation,
oneorganism,usuallythephysicallysmallerofthetwo(calledthe
parasite)benefitsandtheother(calledthehost)isharmedto
somemeasurableextent.
33

34. 34

35. 35

36. 36

37. Theactivitiesofvarioushyperparasites,i.e.,thoseagentsthat
parasitizeplantpathogens,canresultinbiocontrol.
And,interestingly,hostinfectionandparasitismbyrelatively
avirulentpathogensmayleadtobiocontrolofmorevirulent
pathogensthroughthestimulationofhostdefensesystems.
37

38. Lastly,
predation
predationreferstothehuntingandkillingofoneorganismby
anotherforconsumptionandsustenance.Whilethetermpredator
typicallyrefertoanimalsthatfeedathighertrophiclevels.inthe
microscopicworld,ithasalsobeenappliedtotheactionsof
microbes,e.g.protists,andmesofauna,e.g.fungalfeeding
nematodesandmicroarthropods,thatconsumepathogenbiomass
forsustenance.
38
Lastly,
predation
predationreferstothehuntingandkillingofoneorganismby
anotherforconsumptionandsustenance.Whilethetermpredator
typicallyrefertoanimalsthatfeedathighertrophiclevels.inthe
microscopicworld,ithasalsobeenappliedtotheactionsof
microbes,e.g.protists,andmesofauna,e.g.fungalfeeding
nematodesandmicroarthropods,thatconsumepathogenbiomass
forsustenance.

39. 39

40. Biological control can result in varying degrees from all of these
typesof interactions, depending on the environmental context
within which they occur.
Significant biologicalcontrol, as defined above, most
generally arises from manipulatingmutualisms between
microbes and their plant hosts or from manipulating
antagonisms between microbesand pathogens.
40
Biological control can result in varying degrees from all of these
typesof interactions, depending on the environmental context
within which they occur.
Significant biologicalcontrol, as defined above, most
generally arises from manipulatingmutualisms between
microbes and their plant hosts or from manipulating
antagonisms between microbesand pathogens.