PURPOSE: Population Dynamics, Management Strategies and Population Assessment.
  I.   The Logistic Equation as a basis for considering nematode management 
   a)  Consider a simple logistic description of a plant of genetic potential 
       size (Q), growth rate per unit size (a), and of current size (P):
                 then..... dP/dt=aP(Q-P)/Q
   b)  Consider a nematode population of current size (N), with growth rate (r),
       limited by carrying capacity of the root system (K):
                 then..... dN/dt=rN(K-N)/K 
   c)  The carrying capacity for the nematode at any point in time is 
       approximated by the size of the plant at that time:
                 K=P*s, where s is the number of nematodes that can be supported
                        per unit of plant size.
   d)  Besides being constrained by its genetic potential, the growth of the 
       plant is also constrained by the nematode population level in relation to
       its current carrying capacity; that is, the closer the nematode 
       population to the carrying capacity, the less functional the root system:
    e) The following general management strategies are suggested by this model,
       and are testable:
       (i) Reduction of the initial population - e.g. preplant pesticide, 
           non-host crop rotation, etc.
      (ii) Reduction of the rate of population increase - e.g. systemic 
           nematicide, horizontal resistance, biological antagonists, etc.
     (iii) Increase in carrying capacity of the plant, that is tolerance of the
           nematode damage - e.g. by improvement of water and nutrient status, 
           removal of other sources of stress, etc.
  II.  Life Table Parameters.
     The distributed-delay simulation model (POPSIM) is generalized for use
     with any nematode population. The model opens reads a soil temperature 
     weather data file and allows a crop to grow during a standard spring and 
     summer growing season. The nematode population will only grow and
     reproduce in the presence of the crop. The user is able to define the 
     number of individuals in each life stage on January 1, the developmental 
     time of each life stage, the standard deviation of this developmental time,
     the fecundity rate of females, and stage-specific survivorship for each 
     stage. The pathogenicity of the nematode, and hence the level of crop 
     damage can also be established.                                          
     For example, the simulation can be performed with parameter values
     reflective of r-selected attributes and K-selected attributes in separate 
     runs.  The probability of success of the organism in an annual 
     cropping system can be determined.
     A.   Determine sensitivity of the population dynamics and final densities 
          of the organism to length and variance of life-stage duration, to 
          stage- specific mortality levels, and to fecundity rates.  Use 
          reasonable estimates of life-stage duration for Meloidogyne 
          incognita, Xiphinema index, Paratrichodorus minor, and Mesocriconema xenoplax.  Some literature sources are provided and can be 
          researched in the nematology library.  Some paramater values will
          need to be estimated.  A useful approximation is derived
          from Shaffer (Env. Ent., 1984), who noted that the standard 
          deviation for development in 113 species of insects and mites could 
          be described by:
          S.D. = 0.209 X -0.73 where X - is the average development time.
   Lifetable estimates:       - Degree days
                  Egg/J1    J2        J3         J4        A       E/f/DD
   M. xenoplax    120       65         80        90       180        0.4
                 (25.0)   (15.0)      (16.0)   (20.0)    (60.0)
   M. incognita   160      120        300       100       500        0.8
                 (33.0)   (30.0)      (55.0)   (22.0)    (110.0)
   P. minor        68       50         45        88       100        0.7
                 (11.2)    (7.5)      (6.7)    (26.9)    (70.0)
   X. index       200      300        500       500       800        0.1
     7.   NEMAPLEX Exercise
          Main Menu:
            Select...Decision Support    
               Select...Management Strategy Simulator
                  Use the logistic-based simulation model to explore the effect 
                  of nematode management strategies,  and their costs, that:
                   a) reduce the initial population;                       
                   b) reduce the rate of population increase; and
                   c) change the tolerance (carrying capacity) of the host to
                      the nematode.                                         
                  Note the effect on the host, on the nematode population, and 
                  on the net crop value.
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             Select...Population Simulator
                   Use a range of initial densities for a single nematode 
                   species on a host to which it is moderately pathogenic.
                   Plot log final population (Pf) against log initial
                   population (Pi).
                   Repeat for a host on which it is highly pathogenic. 
                   Determine the maximum multiplication rate and equilibrium 
                   Determine the effect of host status on these parameters.
                   Determine the effect of management strategies that:
                   (i)     Reduction in survival of specific life stages;
                  (ii)     Reduction in fecundity;
                 (iii)     Change in life-stage duration;
                  (iv)     Change in life-stage variability.
                   Consider management tactics for achieving these changes.
               Select...Nematode Management
                  Review:  Principles of Nematode Management.
                           Tactics:  (Various tactics listed)     
                           Emerging Research Developments:  (Various topics
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            Select...Sampling Simulator
                  Do the sampling exercise and measure the population within
                  prescribed constraints.
           Return to Main Menu
               Select...Management of Nematodes.
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