Lenteren, J.C., van

Roermund, H.J.W., van

Wageningen Yield 

SROPjWPRS Bull. XIII/5 (1990), 185-189 
SIMULATION OF THE POPULATION DYNAMICS OF THE GREENHOUSE 
WHITEFLY, TRIALEURODES VAPORARIORUM AND THE PARASITOID 
ENCARSIA FORMOSA 
Summary 
H.J.W. Van Roermund 1•2) and J.C. Van Lenteren 1) 
1 Department of Entomology, Wageningen Agricultural University, 
P.O. Box 8031, 6700 EH Wageningen, The Netherlands. 
2 Department of Theoretical Production Ecology, 
P.O.Box 430, 6700 AK Wageningen, The Netherlands 
185 
Biological control of greenhouse whitefly with the parasitoid Encarsia formosa has been very 
successful on vegetables since 1970. Much experimental research has been published on this 
pest insect and its parasitoid. These experimental results will be used in a simulation model 
of the population dynamics of the tritrophic system host plant-pest insect-parasitoid. The 
present paper summarizes experimental results published after 1983 and describes the 
development in modelling of this system. 
1. Introduction 
Research on greenhouse whitefly control with the parasitoid Encarsia formosa had 
already started circa 1920. Mter a lapse in interest following the second world war, biological 
control of this pest received more attention again circa 1970, due to problems of resistance 
and negative side-effects of chemical pesticides. At the moment, around 120 articles have been 
published on the pest insect, the parasitoid and/or their relationship as influenced by host 
plant and environmental factors. Data from these articles will be used to develop a simulation 
model of the population dynamics of the pest insect and its parasitoid, that includes the 
relationships between host plant, pest insect, parasitoid and the environment. The aim of this 
study is to increase the explanatory insight into a tritrophic system in order to improve 
biological control measures. 
2. Summary of new research data 
Hulspas-Jordaan and van Lenteren (1989) and Yano et aL (1989a, 1989b) developed 
a simulation model of the population dynamics of the greenhouse whitefly. A simplified, very 
user friendly version of the model was developed by van Giessen & Mollema (in prep). The 
main input for the model are autecological parameters, such as longevity, oviposition 
frequency, immature mortality, development duration from egg to adult and sex ratio. These 
parameters have been reviewed by, among others, van Lenteren and Hulspas-Jordaan (1983), 
Hulspas-Jordaan and van Lenteren (1989) and Yano et al. (1989b). A more complete review 
will be published containing autecological data from 1915-1989 of greenhouse whitefly and 
Encarsia fonnosa (mean, coefficient of variation, number of replicates, number of individuals 
per replicate) at different temperatures, host plants (variety) and host insect stages (van 
Roermund and van Lenteren, in prep). With this more complete data-set the above mentioned 
autecological parameters will be described as a function of temperature for each host plant 
(variety) or host insect stage separately. These functions will be the input for the simulation 
model. Most literature on autecological parameters was published in 1976-1983. New results, 
if different from information before 1983, are summarized in table 1 and will be discussed 
below. 
186 
Table 1. Summary of new research data if different from publications before 1983. Fecundity 
in eggs/female/lifetime, oviposition in eggs/female/day, immature mortality in%, 
development duration from egg to adult in day, temperature in degrees Celcius. 
Tv= Trialeurodes vaporariorum, Bt = Bemisia tabaci. 
T. vaporarionun 
Fecundit~ Oviposition Host T~mpera- Ref~r~n~~ 
~ 
52-83 4.2-4.6 Sweet pepper 23.4 10 
157 Gerbera 30.0 2 
2.4-6.8 Gerbera 15.0-30.0 2 
2.8-3.2 Sweet pepper 24.4 15 
1.7-7.8 Sweet pepper 20.0 6 
Long~vi~ 
8-18 Sweet pepper 23.4 10 
59-97 Eggplant 24 12 
22-60 Gerbera 15-30 2 
Mortali~ 
59.8 Tomato 22.9 10 
1.8-6.5 Tomato 15.0-25.0 1 
37-95 Sweet pepper 23 10,15 
4.2-20.2 Eggplant 24 12 
3.3-16.1 Gerbera 15-25 1 
50.5 Gerbera 30 2 
Duration 
27.4-26.6 Sweet pepper 22.9 10 
27.2-27.4 Sweet pepper 24.4 15 
29.1-32.4 Sweet pepper 20 6 
57.0-22.1 Gerbera 15-30 2 
E.fonnosa 
Fecundi~ Oviposition lliru Temp~ra- R~ferenc~ 
~ 9 
290 5.6 L1-P Tv/Bean 20 
Long~vi~ 9 
52 L1-P Tv/Bean 20 11 
18.7 L3L4 Bt/Bean 25 
Mortali~ 11 
10.2 L3L4 Bt/Bean 25 
Duration 11 
9.4-13.5 Ll-P Bt/Bean 25 
The oviposition frequency of greenhouse whitefly on sweet pepper published by van 
Lenteren et al (1989), Laska et al. (1986), and van Vianen et al. (1987) is higher than 
published earlier. This could be due to adaptation of the whitefly to the host plant. A 
difference has been found between Dutch and Hungarian whitefly strains (van Vianen et al., 
1987; van Lenteren et al., 1989). New results on tomato and eggplant are the same as those 
187 
published earlier. On gerbera results are comparable with tomato, except for at high 
temperatures where oviposition frequency is higher (Dorsman and van de Vrie, 1989). In 
general, the variation between individuals used in the same experiment is high: in 57 
experiments the average CV (coefficient of variation) is 54 % . 
The immature mortality varies quite a lot among different experiments and seems to 
be rather sensitive to the host plant variety (as shown for eggplant by Malausa, 1988) and it 
varies between whitefly strains (van Lenteren et al., 1989). On gerbera mortality was higher 
than on tomato, although in that experiment mortality on tomato was quite low (Dorsman and 
van de Vrie, 1987). Van Lenteren et al. (1989) found a much higher mortality on (another 
variety of) tomato. The CV between individuals is 19 % averaged over 6 experiments. 
The longevity of greenhouse whitefly on sweet pepper and eggplant is higher than 
published earlier (van Lenteren et al., 1989; Malausa et al., 1988). On tomato new results do 
not differ from previously published data. On gerbera the longevity seems to be higher than 
on tomato (Dorsman and van de Vrie, 1989). The CV between individuals is 50% averaged 
over 64 experiments. 
The developmental duration on sweet pepper is shorter than in earlier publications 
(Laska et al. 1986; van Vianen et al., 1987; van Lenteren et al.,1989). Again whitefly 
adaptation could be the cause. On tomato and eggplant it is the same as published earlier. 
New results were published for gerbera (Dorsman and van de Vrie, 1989). The CV between 
individuals is low: 7 % averaged over 26 experiments. 
New results for Encarsia fonnosa. The fecundity of Encarsia formosa as observed by van 
Lenteren (1987) is high compared with data in most other publications. The host stage 
parasitized seems to be important; fecundity and oviposition frequency are lower when second 
instead of third or fourth host instars are offered. The CV between individuals is 32 % 
averaged from 29 experiments. 
Also van Lenteren (1987) observed a high longevity. The longevity when emerged from 
T. vaporariornm seems to be the same as when Bemisia tabaci acts as host (Lopez Avila, 1988). 
In general, the longevity is higher without hosts, but with honeydew. The CV between 
individuals is 34 % averaged over 30 experiments. 
There are no new results on immature mortality on T. vaporariornm. It seems to be 
higher when Bemisia tabaci is offered (Lopez Avila, 1988). In general, mortality is influenced 
by the host stage; it is lowest in the second and third host instar. 
New results on developmental duration are not different. The developmental duration 
seems to be the same when Bemisia tabaci is used as host (Lopez Avila, 1988). Here also the 
host stage is important: the developmental duration is shortest on third and fourth instar 
nymphs. The CV between individuals is 8 % averaged over 68 experiments. 
3. Development of simulation model 
The simulation model developed by Hulspas-Jordaan and van Lenteren (1989) and 
Yano (1989a) is the basis for further development. The model for whitefly population 
dynamics has been rewritten in FORTRAN and structured into different submodels 
(subroutines). FORTRAN has been chosen because it is the most widely used computer 
language in mathematical and physical science; libraries with subroutines have been published 
and are available. This model will be extended by a model of Encarsia formosa population 
dynamics. These two (sub)models will be coupled by a functional response. As a start the 
functional response as measured experimentally can be taken (Fransen and van Montfoort, 
1987; Yano, 1989). Some parameters, like the searching efficiency and the handling time can 
be related to environmental factors (temperature) or internal state of the parasitoid (number 
of mature eggs in ovariole). It is also possible to make a separate model to simulate the 
functional response by integrating behavioural components at the individual level (e.g. walking 
188 
speed, host acceptance, oviposition, host feeding). Simulation results generated at different 
host densities but at constant environmental conditions will be used to derive a functional 
response. Thus these equations derived by simulation at the individual level will be input for 
the model at the population level. In this way a simulation model for population dynamics of 
pest insect and parasitoid at the leaf level can be developed. It will only be used to simulate 
population dynamics within one patch, in which the insect density can be assumed to be 
constant (one-patch model). 
To simulate the population dynamics at the canopy level, total canopy area will be 
divided into compartments. For every compartment, population dynamics will be calculated 
separately by using the first model as subroutine (multiple-patch model). If a vertical 
differentiation is desired, the canopy can be divided into leaf layers. If computation time 
appears to become too long, population density as simulated by the one-patch model can be 
used to fit a function (or table) which will be the input for the multiple-patch model. Insects 
can be divided among the compartments by a statistical distribution as measured 
experimentally. As this is unknown for the parasitoid, several distribution patterns can be 
assumed to study their effect. 
A next step in the development of the multiple-patch model is the simulation of the 
dispersion processes to explain the spatial development instead of describing it by a statistical 
distribution in order to increase the explanatory character of the model. The data of Noldus 
et al. ( 1986) can be used for whitefly but experiments need to be done on the dispersion of 
Encarsia adults. 
4. Aim of the modelling approach 
TI1e advantages of a simulation model approach to biological control is that it indicates 
shortages in knowledge, gives a better understanding of complex systems, enables distinction 
between important and less important factors influencing population dynamics, and allows 
predictions to be made. In our case it will be used to predict whether or not biological control 
will be feasible in a certain combination of host plant, pest insect, parasitoid and environment, 
and if not, to understand which factors are responsible for the failure. Additional possibilities 
are to extend the model with other natural enemies of whitefly, e.g. the fungus Aschersonia 
aleyrodis, or with other host insects, such as Bemisia tabaci. 
Acknowledgement 
The fjrst author is financially supported by the Netherlands Technology Foundation 
(ST\¥), and is coordinated by the Foundation for Biological Research (BION). 
5. References 
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vaporariornm on diffe.rent ge.rbera varieties. Bull. IOBC/WPRS 1987 /X/2: 46-51. 
DORSMAN, R. & VRJE, M. VAN DE, in prep. Population dynamics of the greenhouse whitefly on gerbera. 
FRANSEN, JJ. & MONTFORT, MAJ. VAN, 1987. Functional response ami host preference of Encarsiafonnosa 
Gahan (Hym., Aphelinidae), a parasitoid of greenhouse whitefly T. vaporariomm (Westwood) (Hom., Aleyrodidae). 
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Simulation of the population dynamics of the greenhouse whitefly, Trialeurodes vaporariorum and the parasitoid Encarsia formosa

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