Read Ch 12 Weed Biological control

Transcription

1 Read Ch 12 Weed Biological control 1. How do insects affect plants? (see pp#4) 2. How is weed biocontrol affected by components of the biotic community? 3. How do weed and insect biocontrol differ?

2 Feature #1: The role of plant-plant competition is unique Weed biocontrol agents act by changing the weed s competitiveness with other plants. In insect biological control, insect-insect competition among herbivorous insects is not important for insect biocontrol, which acts solely via antagonism imposed by introduced upper tropic level organisms.

3 Do not think of the plant-herbivore interaction in isolation. Galerucella pusilla cattail Purple loosestrife Herbivory s job is to reduce the invader s competitive advantage over native plants: plant-plant competition determines the outcome

4 How strong is cattail-loosestrife competition? How much herbivory will it take to restore the balance? Competition test

5 Feature #2:Impacts other than death are important to weed BC Weed biocontrol agents act in more ways that just killing plants outright. Other outcomes, might be slower growth, reduced seed set, reduced competitiveness, increased susceptibility to pathogens, shorter lifespans In insect biological control, nearly all impacts are the immediate death of the attacked stage. (In a few cases, reduced fecundity of attacked females is possible)

6 Weed biocontrol acts through many channels tissue galling seed destruction defoliation Increased susceptibility to pathogens reduced growth altered competitiveness

7 Feature #3:Reduction of reproduction is a frequent objective in weed biocontrol 1. some plants have long lived seed banks 2. some plants are very long lived (trees) 3. annuals have high annual seed set 4. many plants have vegetative reproduction from parts

8 How plants reproduce strongly influences approaches to reducing populations via suppression of reproduction Long lived plants Annuals, binenials-big seed banks Vegetative reproduction Waterhyacinth parts float and regrow Mature woody plants difficult to kill Seed banks maintain densities for years Indirect seed reduction by defoliation Purple loosestrife (Lythrum salicariae) in Ontario, Canada, in 1995, One year after first release of the leaf beetles. See the defoliation and lack of flowers Seed head flies eat seeds Direct destruction of seeds Green mat is S. molesta on lake in Australia 1995 Add photos of more species

9 Effects that act via thresholds example: seed bank reduction Urophora affinis Larinus minutus

10 Feature #4: Safety to nontarget plants has been a greater concern than impact on insects Platte thistle and R. conicus Ash whitefly and Encarsia inaron Damage to nontarget plants such as native thistles is likely to be noticed and objectionable Damage to nontarget insects, such as native whiteflies would be invisible to all but a tiny handful of specialists and impacts hard to measure

11 Feature #5: Time needed to conduct a weed biocontrol project is greater than an insect one Weed projects years Insect projects-2-10 years Weed biocontrol Insect biocontrol

12 Feature #6: Requires understanding of plant physiology and plant phylogenetics to assess impact and saftey, respectively Tribe Cardueae Phylogeney of family Asteraceae

13 Centaureinae Centaurea Cichorioideae Asteroideae Cardueae Carduinae Subfamily Tribe Subtribe Senecio vulgaris Senecio cineraria Helianthus annuus (1) Echinacea purpurea Hemizonia minthornii Eriophyllum stoechadifolium pupae (%) eggs (%) Gnaphalium californicum Liatris punctata Brickellia californica Aster chilensis Artemisia californica Veronieae Lactuceae Mutisieae Echinopsidinae Carlininae Stokesia laevis Stephanomeria cichoriacea Lactuca sativa (2) Agoseris grandiflora Trixis californica Gazania rigens Echinops exaltatus Xeranthemum cylindraceum Silybum marianum Saussurea americana Onopordum acanthium Cynara scolymus (3) Cirsium vulgare Ci. vinaceum Ci. occidentale Ci. loncholepis Ci. hydrophilum Ci. fontinale Ci. cymosum Ci. ciliolatum Ci. brevistylum Carduus pycnocephalus Crupina vulgaris Cnicus benedictus Carthamus tinctorius (4) Acroptilon repens Centaurea americana Ce. rothrockii? Ce. dealbata Ce. cineraria Ce. montana Ce. cyanus Ce. squarrosa Ce. x pratensis Native Commercial Target Ce. maculosa Ce. diffusa Ce. sulphurea Ce. melitensis Ce. calcitrapa Ce. solstitialis Percentage of trials

14 Centaureinae Centaurea Subtribe Carduus pycnocephalus Crupina vulgaris Cnicus benedictus safflower Carthamus tinctorius (4) Acroptilon repens pupae % eggs % Centaurea americana Ce. rothrockii Ce. dealbata Ce. cineraria Native Commercial Target? Ce. montana bach. Ce. button cyanus Ce. squarrosa Ce. x pratensis Ce. maculosa Ce. diffusa Ce. sulphurea Ce. melitensis Ce. calcitrapa YST Ce. solstitialis Percentage of trials

15 Feature #7:Complexes of agents are seen as necessary to a greater degree for weed biocontrol E. inaron Bangasternus orientalis Eustenopus villosus Larinus curtus Chaetorellia succinea Ash whitefly Yellow starthistle

16 soil fungus Life Cycle of Yellow Starthistle winter rainy season rosette fly rosette weevil fall seedling seedhead insects seeds in soil seed production seedling mite lacebug adult rosette flea beetle spring rust summer dry season

17 Feature # 8: Insect x pathogen interactions may be critical The impact of Cactoblastis cactorum on Opuntia is increased because caterpillar feeding opens pads to bacterial infections Pad fed on and diseased

18 Knapweed biocontrol success

19 Recovery of vegetation after knapweed biocontrol

20 CASE 1: Broad-leaved paperbark tree Melaleuca quinquenervia

21 The Everglades

22 Melaleuca Open marsh invasion in Florida Invasive stands of melaleuca Sawgrass marsh 22

23 Species displacement: little native lives here

24 Increased fire intensity

25 Soil accretion

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28 How much melaleuca is out there? (Source: South Florida Environmental Report 2007) ,000 ha 28

29 The Melaleuca weevil

30 The Melaleuca Psyllid

31 The Melaleuca Midge

32 Natural enemy impacts (tree level): defoliation crown thinning, dieback, mortality Thinned crown Weevil feeding Psyllid infestation Rust-fungus attack Lobate-lac insect infestation 32

33 Herbivory reduces stump regrowth: Replicated insect exclusion studies: 76% reduction in regrowth 80% mortality of cut stumps Rayamajhi et al. 20

34 Herbivory decreases reproduction Pratt et

35 Survival (%) Relative change in height Herbivory decreases recruitment Insect exclusion studies of seedling survival: b) a Density dependent Growth: shrinking! b c mortality: 40 to 80% Zero Low High Psyllid Density c) Zero weevil Low weevil High weevil Zero Low High Psyllid density

36 Melaleuca density (# of stems/ha) Melaleuca density and plant species richness 1.2e+5 1.0e+5 8.0e+4 6.0e+4 4.0e+4 2.0e Melaleuca density Number of plant species (mean) Years Pearson's Correlation coefficient = P value = N = Plant species richness (mean # of species) 36

37 Are native plants moving into the declining melaleuca? Number of plant species Total Native Exotic Uncertain Species' origin

38 1996- Florida (before natural enemy introduction) 38

39 2004-plants stressed by herbivore impact

40 2011 increased plant species diversity)

41 Transition is further speeded by manual removal of larger stems 41

42 Reduction of the size of infestation ,000 ha ,000 ha 90,000 ha (45% reduction infested area in FL in 15 years) 42

43 The Return of the Natives