Woets, J.

English

Name not available

Integrated control in vegetables under glass in the Netherlands

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26 
INTEGRATED CONTROL IN VEGETABLES UNDER GLASS 
IN THE NETHERLANDS 
by 
J. WOETS 
Proefstation voor de Groenten- en Fruitteelt onder Glas, 
Zuidweg 38, Naaldwijk, the Netherlands 
INTRODUCTION 
As Bravenboer (1970) stated 1970 was the first year Phytoseiulus pevsimilis 
controlled the red spider mite, Tetranychus urtiaae, on a large scale. It 
concerned 200 ha (500 acres) glasshouse cucumbers, i.e. nearly 25% of the Dutch 
acreage of cucumbers. More details about the production and introduction of the 
predator are given by Bravenboer (1970) and Hussey and Bravenboer (1970). 
In 1971 a severe outbreak of the greenhouse white fly, Trialeuvod.es vapovaviovum 
Westwood, occurred. All chemicals approved for the control of white fly are 
desastrous to the predator. Thus the producer of P.persimilis, Mr. Koppert, 
stopped his production. It happened that he had at his disposal a glasshouse 
of tomatoes with Enaavsia fovmosa. He utilized this parasite for introduction 
in eight commercial holdings (both tomatoes and cucumbers). 
In October 1971 he started the first planned production of E.fovmosa on tomatoes 
for introductions from December 1971 till April-1972. He provided the parasitic 
wasp for over 200 holdings (100 with cucumbers, 100 with tomatoes). Effective 
control of white fly was obtained on only 30 holdings (5 with cucumbers, 
25 with tomatoes; i.e. resp. 4 ha and 20 ha). 
For the introduction season December 1972 - May 1973 the production of Enaavsia 
fovmosa was started on tomatoes and later on he switched to cucumbers, primarily 
for phytosanitary reasons. Introduction was restricted to tomato holdings 
according to a scheme, developed at our station in the preceding years. Nearly 
all growers (over 150) obtained good results by Enaavsia introduction which 
was accompanied by Phytoseiulus for the control of red spider. It covered an 
acreage of about 120 ha (300 acres), i.e. 57, of the tomato-acreage in the 
Netherlands. Besides this, red spider control with P.pevsimilis was done on 
150 ha (375 acres) of cucumbers (i.e. 15% of the total cucumber acreage in the 
Netherlands) and in 10 holdings with sweet peppers. Roughly said the producer 
bred 30 millions of predators and 15 millions of parasites. 
This season Phytoseiulus—production was the first year round one. The predator 
was also applied on a limited scale in autumn crops. 
27 
THE INTRODUCTION SCHEME IN TOMATOES 
In 1971 and 1972 Enoavsia fovmosa was available on a more or less limited scale. 
There were limitations both on the quantities and on the moment of delivery. 
In these two years production and introduction schemes have been developed by 
Mr. Koppert and our station. 
On developing the introduction schedule the next considerations are of para-
mount importance: 
1. The grower does not like an arranged introduction of a pest 
2. It is doubtful whether population developments in practice are predictable 
3. Enoavsia fovmosa needs young larvae for host feeding and older stages 
for parasitizing 
4. Burnett (1960) states that in an interaction system of greenhouse white 
fly and Enaarsia fovmosa 
a. The numbers of host and parasite fluctuate with increasing amplitude 
b. The higher initial densities the higher the resulting amplitudes 
c. The fluctuations are smallest if the infestation period of both host 
and parasite is long. 
In practice the period of infestation starts when the first white fly adults 
are established. A long infestation period results from the length of the life 
time of the females. Besides some spread in the period of hatching from the 
pupae on the cotyledones or first leaves will occur. 
According to Burnett more parasite introductions are needed within the first 
generation of white fly. The best moment for the first introduction of Enoavsia 
as puparium in the scales of white fly is the moment when larvae (first and 
second stage) of white fly are present. When the wasps hatch from the intro-
duced scales, there are plenty of larvae available for host feeding (second 
stage). Repeated introductions are needed in the next generations (= months) 
of the white fly to prevent the increasing population fluctuations and to 
diminish the risk of damage to the crop. In our trials it appeared that four 
introductions during two generations of the white fly are sufficient for 
adequate control on tomatoes. We needed four till six wasps per plant, varying 
somewhat from year to year. 
Table 1 shows the data of populations in a glasshouse in our station (size 
670 m2, nearly 0.17 acres) in 1973. 
Table 1 Developments of the population of Tvialeuvodes vaporaviovum 
and its introduced parasite Enoavsia fovmosa in tomatoes at 
Naaldwijk on 14.XII.'72-20.VII.'73 
Days 
after 
planting 
5 
19 
40 
49 
53 
63 
77 
105 
117 
Average numb 
Eggs Larvae 
0.5 1.3 
1.0 9.7 
0 6.8 
1.0 11.2 
13.7 7.1 
6.4 19.4 
0 3.2 
ar of T.V. per plant 
Pupae 
0.8 
0.3 
0.2 
2.1 
0.5 
15.7 
18.9 
Adults 
0.3 
0.6 
0.8 
0.6 
0.5 
0.5 
0.1 
0.2 
Black 
pupae 
3.7 
0 
9.9 
24.9 
Introduced 
E.f. per 
plant 
0.6 
0.9 
1.7 
1.6 
Black/ 
white 
ratio 
1.8 
0.6 
1.4 
2.1 
3.1 
From this table it is clear that younger and older larvae were present on the 
plants when they were planted. So we decided to introduce immediately. The 
second introduction followed in a fortnight. The next (3rd and 4th) introductions 
were about one month later (day 40 and 49). In the beginning the introduced 
numbers were rather low, according to the tendency of the producer of the 
parasite to start with low numbers. In the second generation the numbers of 
28 
larvae of white fly were increasing, so we had to introduce more black scales 
with Enaarsia than in the first generation. 
The ratio of black and white pupae on the leaves gives a good indication for 
the degree of control. The grower can check this himself on the leaves on which 
most white flies have hatched and the first wasps are hatching. When the ratio 
is 1 or more in the second generation and the white fly numbers are rather low 
(translated by the grower as no honeydew on the leaves), controll will be good. 
Summarizing the trials 197! - 1973 it can be said that the first introduction 
of 1.5 or 2 scales per plant is realized when the first white fly larvae are 
present. This is repeated within a fortnight. New introductions follow after 
one month with lower numbers of scales (1 per plant) when parasitization is 
good, i.e. continuing increase of the portion of black scales. Parasitizing 
can be checked by the black/white ratio which should be at least 1. 
CONTROL IN TOMATOES IN PRACTICE 
Planting the young tomatoes (December - February), tying them up and twisting 
them in, are excellent occasions for the grower to detect the first white flies 
(adults). In most cases the first adults hatch from pupae on the cotyledones 
and lower leaves of the young plant. When the first spot with white fly is 
found the grower has to go through the whole glasshouse more thoroughly. 
After this he invites the producer of the parasite to check his tomato crop. 
Thus the producer fixes the day for the first introduction and the amount of 
Enaarsia to be used. When it is evident that there are only one or a few foci 
and no white flies are spread through the glasshouse, it can be decided to use 
a higher dose in the white fly patches and low doses in the rest of the glass-
house. This last point is important to avoid the development of unexpected spots. 
In this way the producer of natural enemies sells both enemies and guidance. 
It is included in the price of 16 cents per nr glasshouse area (£ 95,- per acre). 
There are three tomato plants on a square meter. Thus the 4-6 black scales 
per plant do cost 5 cents, included all guidance. 
The grower has to cut the cucumber leaves with scales he receives from the 
producer into pieces and distribute them through the glasshouse by putting the 
pieces on the leaves of the tomato plants. Thus he obtains a good spread of the 
parasites through the whole glasshouse. The producer will visit the grower 
regularly and fix the next introductions. In this way the results have been 
very good this year. 
Red spider control with P.persimilis also costs 16 cents/m . There are three 
plants on 1 m^ and a bean leaflet with + 8 predators is put on every second 
tomato plant when there are 6 - 8 patches of red spider per 1000 m^. Thus there 
is an average of 4 predators per plant, which costs 5 cents. Concluding it can 
roughly be said that the price per predator is 1.2 cents. 
Biological control of white fly requires a change in cultural practice. Taking 
off the older leaves of the tomato plant is common. It is important that the 
grower does not remove the puparia of Enaarsia in this way. So he has to check 
whether the wasps have already hatched from the black scales on the leaves the 
grower wants to take off. Generally speaking it is sufficient when the leaf 
picking is retarded a few days. 
Biological control of the white fly has consequences for other pests. It is 
evident that Phytoseiulus can control red spider and so the two major pests 
of tomatoes can be controlled biologically. Tomato leafminer can be a limiting 
factor, because all chemicals used against this insect are harmfull to the 
natural enemies. Thus the crop must be free from leaf miners before the intro-
duction of natural enemies can be started. When this pest is attacking the crop 
later on in the season (June), the population development is rather slow and can 
be retarded by consequent picking of mined leaves. Chemical control of leaf 
miners in summer has not been necessary with some growers and in the three years 
of trials at our station. 
29 
In July 1973 there was an outbreak of the tomato rust mite, Vesates lyaopersiai 
Massée, which caused severe damage in 30 holdings where biological control was 
practiced. The consequence of this new pest can not yet be predicted. 
CONTROL IN CUCUMBERS 
In comparison to tomatoes a cucumber crop is grown at higher temperatures 
allowing a quicker development of the parasite. So better results were expected 
with this crop. Nevertheless the results in tomato were much better, in 
1971/1972 25 out of 100 tomato growers had good control compared to only 5 out 
of 100 cucumber growers. Although there were problems concerning the date of 
introduction and the numbers to be used, there was no reason to ascribe the 
differences to the external factors in cucumber growing. Differences in host 
plants were therefore considered more closely. 
In the past it has been suggested by several authors that a high grade of 
pubescence and insufficient control are correlated, but others deny this. 
However, the leaf of tomato is more pubescent than that of cucumber. Criteria 
such as number of eggs laid on the host plant, the mortality of eggs, larvae 
and pupae, the length of development do have influence, and should be analysed. 
But some experiments carried out did not support the idea that the different 
results originated from this type of interactions between host plant and insect 
species. From observations on the behaviour of a single female wasp on a tomato 
leaf, it is clear that it walks rather quickly over the surface. After leaving 
a white fly scale it has no special trouble in finding another one. A wasp 
searching for scales on a cucumber leaf, however, looks like a mountaineer 
passing the high nerves as mountainchains. The stiff hairs are obstacles that 
cause a lot of trouble in going forward. The insect needs much more time to 
cover a certain distance on a cucumber leaf than on a leaf of a tomato plant. 
Owing to the rough surface there is more dust on a cucumber leaf and a wasp 
needs extra time for cleaning itself on cucumber. We hope it will be possible 
to express differences like these into a figure to obtain a better estimate of 
the numbers to be used on different crops. 
We do not advise biological control of white fly in cucumbers, but biological 
control of the red spider is certainly possible, as hydrocyanic acid is approved 
against white fly since 1972 and Phytoseiulus is relatively unsusceptible to it. 
Thus it is possible to combine Phytoseiulus with hydrocyanic acid if the 
chemical is applied only once in a fortnight. 
The price for Phytoseiulus is 16 cents/m2 glasshouse area, inclusive all the 
guidance the grower needs especially in the first year of biological control of 
red spider. The dosage is one bean leaflet with about 8 predators per plant. 
There are 1.5 plant per nr. Thus the price per predator is 2.5 cents for a 
cucumber crop. 
Two mildew fungicides ara available that do not harm the predator (curamil and 
"Imugan"). 
CONTROL IN SWEET PEPPERS 
This crop has two main pests: aphids and red spider. Since the approval of 
pirimicarb in 1972 it is possible to integrate this aphicide and Phytoseiulus 
which is introduced in the same way as in cucumbers (Bravenboer, 1970). 
This year about 20 growers carried out the integrated scheme. 
Since 1968 the broad mite Hemitarsonemus latus is a new pest in sweet pepper 
in glasshouses. Although it can disturb integrated control of the main pests, 
it needs not be a problem as it can be controlled by local application of 
dicofol (Kelthane). 
The use of specific chemicals (dicofol as an acaricide, pirimicarb as an 
aphicide) and Phytoseiulus as a predator have given a chance to Thrips tabaci 
as a pest in summer and autumn. The consequences of this new attack cannot yet 
be forecasted. 
30 
CONTROL IN EGG PLANTS 
In 1972 a provisional trial was carried out on integrated control in egg plants. 
Although the available quantities of Enaarsia were limited the results were 
encouraging. At the planting date (5.IV.1972) 2 to 3 white flies and several 
larvae per plant were present. Three and five black scales per plant were 
introduced on respectively 6 and 15.IV.'72. The percentage parasitism reached 
80 and more percent during the season. Despite of these results the white fly 
numbers increased and resulted in sticky fruits in July. 
In 1973 the crop was planted earlier and there was a sufficient supply of 
Enaarsia. We used this crop to check the general idea of the introduction 
schedule: 
1. More introductions per generation and 
2. introductions during more generations. 
As can be seen in table 2, the first introduction was rather high (4 scales 
per plant). Afterwards in the lesser infested glasshouse no.2 relatively low 
numbers of the parasite were introduced till the beginning of the third 
generation (day 47). 
In the more infested glasshouse no.1 we introduced the parasite four times 
in relatively high dosages and three times at low dosages as in glasshouse no.2. 
As can be seen there were no problems at all as to the control despite of the 
large numbers of larvae 45 - 60 days after planting. 
Table 2 Population developments of Trialeurodes vaporariorum and its introduced 
parasite Enaarsia formosa, in egg plants at Naaldwijk. Comparison of 
two glasshouses, 160 m^ each, 250 plants per glasshouse. 
Period: 1.II.*73 - 20.IX.'73 
Days 
after 
planting 
Glasshous 
1 
13 
20 
27 
34 
41 
47 
54 
61 
95 
174 
Average 
Larvae 
;e 1 
7.7 
9.5 
12.7 
17.7 
20.5 
28.0 
300 
300 
800 
number 
Pupae 
2.5 
1.4 
1.0 
1.6 
22.5 
4.2 
4.6 
11.4 
28.8 
5.3 
4.1 
of T.v. p 
Adults 
1.5 
0.5 
1.6 
1.5 
1.7 
1.7 
1.9 
2.4 
3.5 
er plant 
Black 
pupae 
9.0 
14.4 
15.3 
20.9 
57.0 
38.2 
37.1 
Introduced 
numbers of 
Enaarsia 
formosa 
4 
3 
3 
3 
1.3 
1.3 
2 
Black/ 
white 
ratio 
0.4 
3.4 
3.6 
1.8 
2.0 
7.2 
9.0 
Glasshouse 2 
1 
13 
20 
27 
34 
41 
47 
54 
61 
95 
174 
3.0 
2.9 
5.1 
10.0 
4.4 
32.7 
70 
60 
60 
0 
2.8 
0.5 
2.4 
2.5 
11.4 
16.2 
17.0 
38.0 
2.3 
6.2 
0.2 
0.3 
0.5 
0.5 
0.7 
1.0 
0.5 
1.7 
1.7 
1.4 
9.9 
14.7 
18.2 
28.0 
16.2 
57 
0.5 
0.9 
0.8 
1.0 
0.7 
7.0 
9.2 
31 
Phytoseiulus gave a good control of the red spider mite, although higher dosages 
were needed than in cucumbers (about two times higher). Pirimicarb was applied 
for the control of aphids. Thrips tabaai appeared in July but control measures 
were not necessary. 
TRENDS IN RESEARCH 
The chances are increasing that thrips will become a serious pest, as is known 
from cucumbers in England and from sweet peppers and egg plants in our country. 
The chemical control by drenching or spraying the soil has its limitations. 
Our research will be directed towards biological control, because we found 
a thrips feeding mite (Amblyseius aucumeri Oudemans) in a sweet pepper crop 
last year. But we have not yet been able to breed this predator. 
The second problem is the chemical control of white fly in cucumbers which 
limits the application of the predator Phytoseiulus. Apart from new introduction 
trials, we started to look for new parasites. More parasites are known from 
Western Europe but experiments to compare the efficiency of several species 
for the control of the greenhouse white fly have never been carried out. It 
would be of interest to have a parasite that is more efficient on cucumbers 
and at lower temperatures than Enaarsia formosa. 
In literature some data about Encarsia-species as parasite of T.vaporariorum 
are available (Butler, 1936; Ferrière, 1956; Speyer, 1927; Stuben, 1949; 
Trehan, 1940; Weber, 1930). 
Aleurodes proletella and A.lonicerae were found in natural habitats near our 
station. From both species, three parasites were bred: 
Enaarsia formosa fiahan, 
E. tricolor Förster and an 
Euderomphale species. 
Now we are trying to breed these parasites. 
REFERENCES 
Bravenboer, L. 1970. Some aspects of large scale introduction in practice of 
Phytoseiulus riegeli. 
Proc. O.I.L.B. Conference on Integrated control in glasshouses, Naaldwijk 
(the Neth.), 28-30. IX. 70 pp. 75-78. 
Burnett, T. 1960. Effects of initial densities and periods of infestation on 
the growth forms of a host parasite population. 
Can.J.Zool. 38: 1063-1077. 
Butler, CG. 1936. The occurrence of the chalcids Enaarsia partenopea Masi and 
E. tricolor Förster in England. 
Proc.R.ent.soc.Lond.(A) 11 (3-5): 79-80. 
Ferrière, Cl. 1965. Hymenoptera Aphelinidae, Paris. 
Hussey, N.W. and L. Bravenboer. 1971. Control of pests in glasshouse culture 
by the introduction of natural enemies. 
In: C.B. Huffaker (ed.) Biological control. Proc. AAAS. Symposium on 
biological control, Boston, Massch, 30-31-XII.69. pp 195-216. 
Speyer, E. 1927. An important parasite of the greenhouse white fly 
(Trialeurodes vaporariorum, Westwood). 
Bull.ent.Res. 17: 301-308. 
Stuben, M. 1949. Zur Biologie der Chalcidide Enaarsia tricolor. 
Biol.Zentrabi. 68: 413-429. 
Trehan, K.N. 1940. Studies on British white flies. 
Trans.R.ent.Soc.Lond. 90(22): 575-616. 
Weber, H. 1931. Lebensweise und Umweltbeziehungen von Trialeurodes vaporariorum, 
Westwood. 
Zeitschr.Morph.Oekol.Tiere 23: 575-753. 


An important parasite of the greenhouse white fly (Trialeurodes vaporariorum,

Control of pests in glasshouse culture by the introduction of natural enemies.

Effects of initial densities and periods of infestation on the growth forms of a host parasite population.

Hymenoptera Aphelinidae,

Lebensweise und Umweltbeziehungen von Trialeurodes vaporariorum,

Some aspects of large scale introduction in practice of Phytoseiulus riegeli.

The occurrence of the chalcids Enaarsia partenopea Masi and E. tricolor Förster in England.

Zur Biologie der Chalcidide Enaarsia tricolor.

Integrated control in vegetables under glass in the Netherlands

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