#Steinernema feltiae$ appliqué à l'aide de pulvérisateurs hydrauliques à la dose de 780 000 nématodes/m2 sur des fuchsias cultivés en serre provoque une diminution de 92 % du nombre des #Bradysia paupera$ adultes provenant du compost. Les nématodes se répartissent correctement dans le compost et ont persisté pendant les 64 jours qu'a duré l'expérience. (Résumé d'auteur

Gouge, D.H.

Hague, N.G.M.

Name not available

Glasshouse control of fungus gnats, Bradysia paupera, on fuschsias by Steinernema feltiae

Horizon / Pleins textes

Fundam. appl. Nemawl., 1995,18 (1), 77-80
Glasshouse control of fungus gnats, Bradysia paupera,
on fuchsias by Steinernema feltiae
Dawn H. GOUGE and Nigel G. M. HAGUE
Depa-rtment of Agriculture, University of Reading,
Earley Gate, P. O. Box 236, Reading, RG6 2A T, UK.
Accepted for publication 22 March 1994.
Summary - In glasshouse grown fuchsias, SleinernemafelLiae applied by hydraulic sprayer at 780 000 nematodes/ml resulted in a
decrease of92 % in the numbers of Bradysia paupera adults emerging from the compost. The nematodes were weU distributed in the
poned compost and they persisted in the compost over the 64 day experimental period.
Résumé - Contrôle par Steinernema feltiae du moucheron Bradysia paupera surfuchsias cultivés en serre - Steinerne-
ma felliae appliqué à j'aide de pulvérisateurs hydrauliques à la dose de 780 000 nématodes/ml sur des fuchsias cultivés en serre
provoque une diminution de 92 % du nombre des Bradysia paupera adultes provenant du compost. Les nématodes se répartissent
correctement dans le compost et ont persisté pendant les 64 jours qu'a duré l'expérience.
Key-words : Entomopathogenic nematodes, Steinernema felliae, sciarids, Bradysia paupera, glasshouses.
Sciarid flies commonly infest glasshouse ornamentals
where they rapidly increase to levels when serious dam-
age may occur. The larvae feed on organic matter, fungi
or algae (Freeman, 1983) also on the roots of cuttings
and smali plants, tunnelling into their stems (Binns,
1973). Sciarid larvae can damage mature plants and are
vectors of bacterial and fungal pathogens (Leath &
Newton, 1969).
Sleinernemafelliae (Steinernematidae), a rhabditid ne-
matode occurring throughout Europe, is mutualisticaliy
associated with a bacterium Xenorhabdus sp. The nema-
todes have an infective third stage juvenile (I}) which
can enter the insect host through the mouth, anus or
spiracles (Georgis & Hague, 1981; Mracek el al., 1988).
IJs are able to survive for long periods in soil at low
densities (Kaya, 1991) and are best suited to cryptic
environments where insecticides are more difficult to
apply. IJs are attracted to excretory products, probably
COz, of the host larvae (Gaugler el al.) 1980), and after
entering the insect host, IJs invade the haemocoel where
Xenorhabdus is released from an cesophageal vesicle
causing septicemia and death to the insect host (Poinar
& Thomas, 1966). The nematodes feed on the septi-
cemie tissue, reproduce and leave the host as a new
generation of IJs when the food reserves in the insect
cadaver are depleted. In sciarids S. felliae undergoes
only one generation compared to three or more in Galle-
ria mellonella (Gouge, unpubl.).
The use of insecticides to control sciarids, particularly
in mushroom houses, has resulted in widespread resist-
ance in these insects (White, 1981). Successful control
of sciarids with S. feltiae has been demonstrated by sev-
eral authors, e.g. against Lycoriella mali in the USA
ISSN 1164-5571195/01 S 4.00/ © Gauthier-Villars - ORSTOM
(Nickie & Cantelio, 1991) and against L. auripila in the
OK (Richardson & Grewal, 1991).
The present paper describes experiments in a glass-
house growing fuchsias where S. felliae was applied to
control Bradysia paupera (Tuomikoski), one of the most
common sciarids in OK glasshouses. The distribution
and persistence of S. felliae in the potted compost was
also investigated.
Materials and methods
The experiment was conducted in a commercial
glasshouse growing potted fuchsias where there was a
natural infestation of Bradysia paupera.
The S. felliae used in this experiment was isolated
from woodland soil on the Reading University campus,
cultured on Galferia mellonella (the greater wax moth),
and then formulated by Biosys where it was produced in
a fermenter and sent back to the UK in alginate gel
preparation (Biosys, isola te 244). The commercial for-
mulation was applied to fuchsias cv. Snow Cap, grown
individualiy in plastic plant pots (8 cm deep, 8 cm diam-
eter) at a rate of 780 000 nematodes/ml using a Brink-
man hydraulic sprayer, the nematode suspension being
flood-irrigated onto the benches of fuchsias. Samples of
nematodes were visuaily examined before and after pas-
sage through the sprayer to estimate the effect on nema-
tode viability.
There were 720 pots per bench, four benches were
treated with nematodes and four untreated benches re-
ceived water only. The peat based potting medium was
Fisons M2 (+ Phycote 3 kg ml), pH 4.5, and ail pots
were top watered daily, the temperature in the glass-
house being maintained at 20-24 oc.
77
D. H. Gouge & N. G. M. Hague
DAYS AFTER APPLICATION
DAYS AFTER APPLICATION
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Fig. 2. The mean number of adult Bradysia paupera per pal
caughl on sticky lraps hung inside cages, lrealed (.) and unlrealed
(.Â.). (Verlicallines are standard errors; four replicales).
application (Table 1), with a small increase by day 64.
Small numbers of infecrive juveniles were detected in
the untreated pots, indicating that sciarid adults, infect-
Fig. 1. The mean number of adult Bradysia paupera caughl on
slicky lraps hung above lhe crop for 64 days, lrealed (.) and
unlrealed (.Â.). (Verticallines are sr.andard errors; lhree replicales
covering 36 ml per lrap).
Results
By visual assessmem under the binocular microscope
there was no effect on viability of passing S. feltiae
through a hydraulic sprayer, 95 % of the nematodes
being viable 24 h after application. There was a signif-
icam decrease (73 %) in the number of flies caught (Fig.
1) using sticky traps suspended over the crop for assess-
ment, but it was also noted that there was a decrease in
flies caught on the untreated pots. Caging pots after
treatrnem resulted in a decrease of 93 % in flies emerg-
ing by day 64 compared to a 53 % decrease in the un-
treated pots (Fig. 2).
On the day of application, nematodes were found in
the top 4 cm of the pot (Fig. 3). With time, nematodes
became distributed throughout the pots. After 29 days
there was no significam difference in the numbers in
each section of the pots. There was an overall decline in
the number of nematodes sampled up to 43 days after
ESTIMATION OF SCIARID POPULATION
The experiment was sampled immediately after treat-
mem and then at 7, 28, 42 and 62 days after the applica-
tion of the nematodes. Two methods of estimating the
sciarid population were used on each sampling date:
(1) Four pots were taken at random, one from each
of the treated and one from each of the untreated
benches, and caged under muslin in the laboratory. The
emerging adults were caught over a period of two weeks
on sticky traps hung inside the cages and counted.
(2) Three sticky traps were hung above each glass-
house bench and the number of adult sciarids caught
were counted; sticky traps were replaced on each sam-
pling date. Results were expressed as the number of
sciarid adults caught on traps hung to coyer an area of
approximately 240 plants (ca 36 m 2).
DISTRIBUTION OF NEMATODES IN POTS
On the day of application and at 8,29,43 and 64 days
after treatment, samples were taken as follows. Three
pots were taken at random from each bench and the
compost in each pot divided into four equal 2 cm sec-
tions from top to bottom of the pot. Each section was
placed in a 500 ml plastic container and baited with
three G. mellonella larvae. After 5 days the G. mellonella
larvae were removed, dissected in 1/4 strength Ringers
solution and the number of developed IJs counted.
Three more G. melZonella larvae were then added to each
sample and the process repeated, baiting being contin-
ued until no more IJs emered G. melZonella larvae (Fan &
Hominick, 1991). This exhaustive baiting technique
was used to estimate the number of infective nematodes
in the compost.
Gouge (unpubl.) has shown that sciarid adults which
crawl on the compost can be infected by S. feltiae, there-
fore the untreated compost was sampled for nematodes
with Galleria at the end of the experimem.
78 Fundam. appl. Nemawl.
Control offungus gnaLS by Steinernema feltiae
Discussion
Table 1. The mean and sw.ndard error of the nwnbers of IJs ofS.
feltiae recovered by exhaustive baiting with Galleria meUonellafor
64 days.
ed when crawling on treated pots, had moved over to
untreated pots, where nematodes were transferred to the
compost when the sciarid adults died.
only one generation of S. felliae occurs in sciarids due to
the small size of the host. Sciarid flies continuously enter
the glasshouse, lay eggs on the compost, so the nema-
todes are suppJied with new hosts, hence the sciarid
cadaver can yield reasonable numbers of IJs (Gouge,
unpubl.). Nematode numbers in compost declined untiJ
day 43 and then increased, indicating that nematodes
are being recycled as reported by Grewal and Richard-
son (1993).
In these experiments fly populations fell by 40-50 %
in the untreated pots. With the exception of the un-
treated pots, the whole of the glasshouse had been treat-
ed with nematodes. Gouge (unpubl.) has shown that
adult sciarids can be infected with nematodes and a low
population of nematodes was detected in the untreated
pots: this effect combined with the use of sticky traps
probably reduced the overall population of sciarids in
the glasshouse leading to an overall reduction in sciarid
population.
Sticky traps are used to evaluate sciarid populations
(Lindquist & Piatkowski, 1993) and also to control
sciarids directly by trapping. Caging pots resulted in an
estimate of 92 % control, compared to 73 % using sticky
traps : caging pots eliminates contamination by flies and
hence is likely to give a more accurate estimate of con-
trol.
Fungus gnats have been controlled satisfactorily in
Scandinavian countries with the S. felliae isolate, Biosys
27 (Georgis, pers. comm.). Most of the published data
on sciarid control is on mushrooms, where LycO'Ilella
species have been controlled by S. felliae in the UK
(Richardson & Grewal, 1991) and the USA (Nickie &
Cantello, 1991). The results presented here indicate that
another sciarid, B. paupeTa, can be controlled to a level
satisfactory to the grower.
Sciarids are pests of protected crops either close to
consumption (mushroom) or where application of pes-
ticides might be considered undesirable (house plants).
Entomopathogenic nematodes are increasingly the pre-
ferred choice for growers who favour biological control.
Acknowledgements
The authors wish ta thank Biosys, Palo Alto, California, for
financial support for this research and supply of formulated
nematodes.
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6443
701 ± 51
672 ± 70
582 ± 128
369 ± 137
536 ± 60
29
Mean 9 SE of numbers
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DAYS AFTER APPLICATION
o
8
29
43
64
Days after nematode
application
800
IX
W
a..
if! 500WI-
..Jif!
-0Za..
W:2 400>0~U
Wo T>W 300-~GO
:fa..
ZLl.. 200
-0
~:2
IX U 100WN
o:l
:2
~
Z
Fig. 3. The mean number of IJs ofSteinernema feltiae extTQcted
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Fundam. appl. Nematol.


Glasshouse control of fungus gnats, Bradysia paupera, on fuschsias by Steinernema feltiae

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